Patent Publication Number: US-2013245131-A1

Title: Hydrogenation of Mixed Oxygenate Stream to Produce Alcohol

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to processes for producing alcohol and, in particular, to processes for hydrogenating a mixed oxygenate stream in the presence of a catalyst comprising platinum, tin and cobalt to produce ethanol. In one embodiment, the mixed oxygenate stream is derived from synthesis gas. 
     BACKGROUND OF THE INVENTION 
     Ethanol for industrial use is conventionally produced from organic feed stocks, such as petroleum oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from organic feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in organic feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose materials, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use. 
     Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acids, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. These impurities limit the production and recovery of ethanol from such reaction mixtures. For example, during hydrogenation, esters are produced that together with ethanol and/or water form azeotropes, which are difficult to separate. In addition, when conversion is incomplete, acid remains in the crude ethanol product, which must be removed to recover ethanol. 
     EP02060553 describes a process for converting hydrocarbons to ethanol involving converting the hydrocarbons to ethanoic acid and hydrogenating the ethanoic acid to ethanol. The stream from the hydrogenation reactor is separated to obtain an ethanol stream and a stream of acetic acid and ethyl acetate, which is recycled to the hydrogenation reactor. 
     U.S. Pat. No. 7,842,844 describes a process for the conversion of hydrocarbons to C 2  oxygenates, and uses a conventional catalyst to hydrogenate the C 2  oxygenate feed. 
     The need remains for improved processes for recovering ethanol from a crude product obtained by hydrogenating various feed sources with high selectivity to ethanol. 
     SUMMARY OF THE INVENTION 
     In a first embodiment, the present invention is directed to a process for producing ethanol, comprising the steps of: converting a syngas stream comprising hydrogen and carbon monoxide in a first reactor in the presence of a first catalyst to form a mixed oxygenate stream comprising acetic acid and ethyl acetate; feeding the mixed oxygenate stream and hydrogen to a second reactor; and reacting the mixed oxygenate stream with hydrogen in the presence of a second catalyst comprising platinum, tin and cobalt on a support to form a crude ethanol product stream, wherein the second catalyst is capable of reducing the mixed oxygenate stream to ethanol. The first reactor is at a temperature from 200° C. to 350° C. and the second reactor is at a temperature from 125° C. to 350° C. The second catalyst comprises a support from 25 to 99 wt. % and a support modifier. The mixed oxygenate feed comprises from 1 to 40 wt. % acetic acid, from 1 to 40 wt. % ethyl acetate, acetaldehyde and ethanol. Selectivity to ethanol is at least 60%. At least a portion of the hydrogen from the syngas stream is separated and fed to the second reactor. The crude ethanol product obtained by this process comprises from 25 to 65 wt. % ethanol and from 10 to 26 wt. % water. 
     In a second embodiment, the present invention is directed to a process for producing ethanol, comprising the steps of: providing a mixed oxygenate stream comprising 1 to 40 wt. % acetic acid and 1 to 40 wt. % ethyl acetate; and reacting the mixed oxygenate stream and hydrogen in the presence of a second catalyst comprising platinum, tin and cobalt on a support to form a crude ethanol product stream, wherein the second catalyst is capable of reducing the mixed oxygenate stream to ethanol. 
     In a third embodiment, the present invention is directed to a process for producing ethanol, comprising the steps of: converting a syngas stream comprising hydrogen and carbon monoxide in a first reactor in the presence of a first catalyst to form a mixed oxygenate and methanol stream, wherein the mixed oxygenate are selected from the group consisting of acetic acid, ethyl acetate and mixtures thereof; feeding the mixed oxygenate and methanol stream to carbonylation unit to form a crude carbonylation product comprising acetic acid; reacting the crude carbonylation product with hydrogen in the presence of a second catalyst comprising platinum, tin and cobalt on a support to form a crude ethanol product stream, and recovering ethanol from the crude ethanol product stream. The first catalyst comprises copper and zinc. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, wherein like numerals designate similar parts. 
         FIGS. 1A and 1B  are general flow schemes for producing ethanol from a carbon source in accordance with one embodiment of the present invention. 
         FIG. 2  is a schematic diagram of a hydrogenation process in accordance with one embodiment of the present invention. 
         FIG. 3  is a schematic diagram of another hydrogenation process in accordance with another embodiment of the present invention. 
         FIG. 4  is a schematic diagram of yet another hydrogenation process in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to processes for producing ethanol from a mixed oxygenate stream by using a catalyst comprising platinum, tin and cobalt that both hydrogenates the mixed oxygenate stream. The mixed oxygenate stream preferably comprises acetic acid and ethyl acetate, and may also comprise acetaldehyde. In some embodiment, the mixed oxygenate stream may also comprise ethanol. However, because the mixed oxygenate stream will be converted to ethanol it is not necessary for the mixed oxygenate stream to contain any ethanol. By using a catalyst that is capable of converting both acetic acid and ethyl acetate to ethanol, ethanol selectivities may be improved. 
     The embodiments of the present invention may also be integrated with methods for producing syngas as shown in  FIGS. 1A ,  1 B and  1 C. The mixed oxygenate stream may be produced from syngas, which primarily comprises hydrogen, carbon monoxide and carbon dioxide. The syngas may be formed by partial oxidation reforming or steam reforming, and the carbon monoxide may be separated from syngas. Similarly, hydrogen that is used in the step of hydrogenating the mixed oxygenate stream to form the crude ethanol product may be separated from syngas. The syngas, in turn, may be derived from a variety of carbon sources. The carbon source, for example, may be selected from the group consisting of natural gas, oil, petroleum, coal, biomass, and combinations thereof. Syngas or hydrogen may also be obtained from bio-derived methane gas, such as bio-derived methane gas produced by landfills or agricultural waste. As shown in  FIG. 1B , methanol from the syngas may be reacted to form acetic acid, which may be combined with the mixed oxygenate stream prior to or in a second reactor. Additionally, carbon monoxide separated from syngas may be used to form acetic acid. 
     In one embodiment, to produce the mixed oxygenate stream, syngas is fed to a first reactor in the presence of a first catalyst. Syngas may have a molar ratio of hydrogen to from 20:1 to 0.1:1, e.g., from 5:1 to 1:1, or from 2.5:1 to 1.5:1. In some embodiments, the molar ratio of hydrogen to carbon monoxide is 2:1. 
     The first reactor may be operated at a temperature from 200° C. to 350° C., e.g., from 300° C. to 350° C. or from 300° C. to 325° C. The first reactor may comprise a catalyst comprising rhodium. The rhodium may present from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. % or from 0.1 to 5 wt. %. In some embodiments, rhodium is present at 1 wt. %. 
     For purposes of the present invention, the term “conversion” in the first reactor refers to the amount of syngas in the feed that is converted to a compound other than hydrogen or carbon monoxide. Conversion is expressed as a percentage based on carbon monoxide and hydrogen in the feed. The conversion of syngas may be at least 60%, e.g., at least 70%, at least 80%, at least 90%, or at least 95%. 
     The mixed oxygenate stream produced from syngas is primarily comprised of acetic acid, ethyl acetate, and acetaldehyde. Acetic acid may be present from 1 to 40 wt. %, e.g., from 5-30 wt. %, from 5 to 20 wt. %. Ethyl acetate may be present from 1 to 40 wt. %, e.g., from 5 to 30 wt. %, from 5 to 20 wt. %. In one embodiment, the mixed oxygenate stream may comprise more acetic acid than ethyl acetate based on weight. Acetaldehyde may be present from 1 to 40 wt. %, e.g., from 5 to 30 wt. %, from 5 to 20 wt. %. Other oxygenates, including acids, esters, ketones, and aldehydes may also be present in the mixed oxygenate stream. In some embodiments, the mixed oxygenate stream may also comprise ethanol in an amount from 0 to 40 wt. %, e.g., from 0 to 30 wt. %, from 0 to 20 wt. %. 
     In some embodiments, the mixed oxygenate stream is fed to a second reactor comprising a second catalyst. The hydrogenation of the mixed oxygenate stream to form ethanol is preferably conducted in the presence of a hydrogenation catalyst. In some embodiments, the hydrogenation catalyst is capable of converting acetic acid, and ethyl acetate. Suitable hydrogenation catalysts include catalysts comprising platinum, tin, and cobalt. 
     Some embodiments of the process of hydrogenating the mixed oxygenate stream to form ethanol may include a variety of configurations using a fixed bed reactor or a fluidized bed reactor. In many embodiments of the present invention, an “adiabatic” reactor can be used; that is, there is little or no need for internal plumbing through the reaction zone to add or remove heat. In other embodiments, a radial flow reactor or reactors may be employed, or a series of reactors may be employed with or without heat exchange, quenching, or introduction of additional feed material. Alternatively, a shell and tube reactor provided with a heat transfer medium may be used. In many cases, the reaction zone may be housed in a single vessel or in a series of vessels with heat exchangers therebetween. 
     In some embodiments, the catalyst is employed in a fixed bed reactor, e.g., in the shape of a pipe or tube, where the reactants, typically in the vapor form, are passed over or through the catalyst. Other reactors, such as fluid or ebullient bed reactors, can be employed. In some instances, the hydrogenation catalysts may be used in conjunction with an inert material to regulate the pressure drop of the reactant stream through the catalyst bed and the contact time of the reactant compounds with the catalyst particles. 
     The hydrogenation reaction may be carried out in either the liquid phase or vapor phase. Preferably, the reaction is carried out in the vapor phase under the following conditions. The reaction temperature may range from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to 300° C., or from 250° C. to 300° C. The pressure may range from 10 kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2100 kPa. The reactants may be fed to the reactor at a gas hourly space velocity (GHSV) of greater than 500 hr −1 , e.g., greater than 1000 hr −1 , greater than 2500 hr −1  or even greater than 5000 hr −1 . In terms of ranges the GHSV may range from 50 hr −1  to 50,000 hr −1 , e.g., from 500 hr −1  to 30,000 hr −1 , from 1000 hr −1  to 10,000 hr − , or from 1000 hr −1  to 6500 hr −1 . 
     The hydrogenation optionally is carried out at a pressure just sufficient to overcome the pressure drop across the catalytic bed at the GHSV selected, although there is no bar to the use of higher pressures, it being understood that considerable pressure drop through the reactor bed may be experienced at high space velocities, e.g., 5000 hr −1  or 6,500 hr −1 . 
     Although the reaction consumes two moles of hydrogen per mole of acetic acid to produce one mole of ethanol, the actual molar ratio of hydrogen to acetic acid in the feed stream may vary from about 100:1 to 1:100, e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 8:1. Most preferably, the molar ratio of hydrogen to acetic acid is greater than 2:1, e.g., greater than 4:1 or greater than 8:1. 
     Contact or residence time can also vary widely, depending upon such variables as amount of acetic acid, catalyst, reactor, temperature, and pressure. Typical contact times range from a fraction of a second to more than several hours when a catalyst system other than a fixed bed is used, with preferred contact times, at least for vapor phase reactions, of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 30 seconds. 
     In particular, the hydrogenation of acetic acid may achieve favorable conversion of the mixed oxygenate stream and favorable selectivity and productivity to ethanol. For purposes of the present invention, the term “conversion” in the second reactor refers to the amount of the mixed oxygenate stream that is converted. For purposes of conversion calculations, the mixed oxygenate stream excludes ethanol. Conversion is expressed as a percentage based on acetic acid, acetaldehyde and ethyl acetate in the feed. The conversion may be at least 60%, e.g., at least 70%, at least 80%, at least 90%, or at least 95%. 
     Although catalysts that have high conversions are desirable, especially mixed oxygenate stream conversions that are at least 80% or at least 90%, in some embodiments a low mixed oxygenate stream conversion may be acceptable at high selectivity for ethanol. It is, of course, well understood that in many cases, it is possible to compensate for low mixed oxygenate stream conversion by appropriate recycle streams or use of larger reactors, but it is more difficult to compensate for poor selectivity. 
     Selectivity in the second reactor is expressed as a mole percent based on conversion of components in the mixed oxygenate stream to ethanol. The total amount of the conversion of each component in the mixed oxygenate stream, other than ethanol, if present, to ethanol may be referred to as total selectivity. In some embodiments, the amount of ethanol in the mixed oxygenate stream is minimized. In other embodiments, ethanol may not be present in the mixed oxygenate stream. In some embodiments, the selectivity of mixed oxygenate stream to ethanol is at least 60%, e.g., at least 70%, at least 80%, at least 90% or at least 95%. 
     Preferred embodiments of the hydrogenation process also have low selectivity to undesirable products, such as methane, ethane, and carbon dioxide. The selectivity to these undesirable products preferably is less than 4%, e.g., less than 2% or less than 1%. More preferably, these undesirable products are present in undetectable amounts. Formation of alkanes may be low, and ideally less than 2%, less than 1%, or less than 0.5% of mixed oxygenate stream passed over the catalyst is converted to alkanes, which have little value other than as fuel. 
     The term “productivity,” as used herein, refers to the grams of a specified product, e.g., ethanol, formed during the hydrogenation based on the kilograms of catalyst used per hour. A productivity of at least 100 grams of ethanol per kilogram of catalyst per hour, e.g., at least 400 grams of ethanol per kilogram of catalyst per hour or at least 600 grams of ethanol per kilogram of catalyst per hour, is preferred. In terms of ranges, the productivity preferably is from 100 to 3,000 grams of ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500 grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000 grams of ethanol per kilogram of catalyst per hour. 
     In certain embodiments where the catalyst includes two or more metals, e.g., a first metal and a second metal, the first metal is present in the catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt. %, or from 0.1 to 3 wt. %. The second metal preferably is present in an amount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %. For catalysts comprising two or more metals, the two or more metals may be alloyed with one another or may comprise a non-alloyed metal solution or mixture. 
     The preferred metal ratios may vary depending on the metals used in the catalyst. In some exemplary embodiments, the mole ratio of the first metal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4, from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1. 
     The catalyst may also comprise a third metal selected from any of the metals listed above in connection with the first or second metal, so long as the third metal is different from the first and second metals. In preferred aspects, the third metal is selected from the group consisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin, and rhenium. More preferably, the third metal is selected from cobalt, palladium, and ruthenium. The third metal, when present, may be present in the catalyst in an amount from 0.05 to 20 wt. %, e.g. from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %. 
     In addition to one or more metals, in some embodiments of the present invention the catalysts further comprise a support or a modified support. As used herein, the term “modified support” refers to a support that includes a support material and a support modifier, which adjusts the acidity of the support material. 
     The total weight of the support or modified support, based on the total weight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from 78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments, the support material is present in an amount from 25 wt. % to 99 wt. %, e.g., from 30 wt. % to 98 wt. % or from 35 wt. % to 95 wt. %. In preferred embodiments that utilize a modified support, the support modifier is present in an amount from 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %, or from 1 to 8 wt. %, based on the total weight of the catalyst. The metals of the catalysts may be dispersed throughout the support, layered throughout the support, coated on the outer surface of the support (i.e., egg shell), or decorated on the surface of the support. 
     As will be appreciated by those of ordinary skill in the art, support materials are selected such that the catalyst system is suitably active, selective and robust under the process conditions employed for the formation of ethanol. 
     Suitable support materials may include, for example, stable metal oxide-based supports or ceramic-based supports. Preferred supports include silicaceous supports, such as silica, silica gel, silica/alumina, a Group IIA silicate such as calcium metasilicate, pyrogenic silica, high purity silica, and mixtures thereof. Other supports may include, but are not limited to, iron oxide, alumina, titania, zirconia, magnesium oxide, carbon, graphite, high surface area graphitized carbon, activated carbons, and mixtures thereof. 
     As indicated, the catalyst support may be modified with a support modifier. In some embodiments, the support modifier may be an acidic modifier that increases the acidity of the catalyst. Suitable acidic support modifiers may be selected from the group consisting of: oxides of Group IVB metals, oxides of Group VB metals, oxides of Group VIB metals, oxides of Group VIIB metals, oxides of Group VIIIB metals, aluminum oxides, and mixtures thereof. Acidic support modifiers include those selected from the group consisting of TiO 2 , ZrO 2 , Nb 2 O 5 , Ta 2 O 5 , Al 2 O 3 , B 2 O 3 , P 2 O 5 , and Sb 2 O 3 . Preferred acidic support modifiers include those selected from the group consisting of TiO 2 , ZrO 2 , Nb 2 O 5 , Ta 2 O 5 , and Al 2 O 3 . The acidic modifier may also include selected from the group consisting of WO 3 , MoO 3 , Fe 2 O 3 , Cr 2 O 3 , V 2 O 5 , MnO 2 , CuO, Co 2 O 3 , and Bi 2 O 3 . 
     In another embodiment, the support modifier may be a basic modifier that has a low volatility or no volatility. Such basic modifiers, for example, may be selected from the group consisting of: (i) alkaline earth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metal metasilicates, (iv) alkali metal metasilicates, (v) Group IIB metal oxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. In addition to oxides and metasilicates, other types of modifiers including nitrates, nitrites, acetates, and lactates may be used. Preferably, the support modifier is selected from the group consisting of oxides and metasilicates of any of sodium, potassium, magnesium, calcium, scandium, yttrium, and zinc, as well as mixtures of any of the foregoing. More preferably, the basic support modifier is a calcium silicate, and even more preferably calcium metasilicate (CaSiO 3 . The calcium metasilicate may be crystalline or amorphous. 
     A preferred silica support material is SS61138 High Surface Area (HSA) Silica Catalyst Carrier from Saint Gobain N or Pro. The Saint-Gobain N or Pro SS61138 silica exhibits the following properties: contains approximately 95 wt. % high surface area silica; surface area of about 250 m 2 /g; median pore diameter of about 12 nm; average pore volume of about 1.0 cm 3 /g as measured by mercury intrusion porosimetry and a packing density of about 0.352 g/cm 3  (22 lb/ft 3 ). 
     A preferred silica/alumina support material is KA-160 silica spheres from Sud Chemie having a nominal diameter of about 5 mm, a density of about 0.562 g/ml, an absorptivity of about 0.583 g H 2 O/g support, a surface area of about 160 to 175 m 2 /g, and a pore volume of about 0.68 ml/g. 
     The catalyst compositions suitable for use with the present invention preferably are formed through metal impregnation of the modified support, although other processes such as chemical vapor deposition may also be employed. Such impregnation techniques are described in U.S. Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197985 referred to above, the entireties of which are incorporated herein by reference. 
     Operating under the conditions of the present invention may result in ethanol production on the order of at least 0.1 tons of ethanol per hour, e.g., at least 1 ton of ethanol per hour, at least 5 tons of ethanol per hour, or at least 10 tons of ethanol per hour. Larger scale industrial production of ethanol, depending on the scale, generally should be at least 1 ton of ethanol per hour, e.g., at least 15 tons of ethanol per hour or at least 30 tons of ethanol per hour. In terms of ranges, for large scale industrial production of ethanol, the process of the present invention may produce from 0.1 to 160 tons of ethanol per hour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80 tons of ethanol per hour. Ethanol production from fermentation, due the economies of scale, typically does not permit the single facility ethanol production that may be achievable by employing embodiments of the present invention. 
     In various embodiments of the present invention, the crude ethanol product produced by the hydrogenation process, before any subsequent processing, such as purification and separation, will typically comprise acetic acid, ethanol and water. Exemplary compositional ranges for the crude ethanol product are provided in Table 1. The “others” identified in Table 1 may include, for example, esters, ethers, aldehydes, ketones, alkanes, and carbon dioxide. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 CRUDE ETHANOL PRODUCT COMPOSITIONS 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Conc. 
                 Conc. 
                 Conc. 
                 Conc. 
               
               
                 Component 
                 (wt. %) 
                 (wt. %) 
                 (wt. %) 
                 (wt. %) 
               
               
                   
               
               
                 Ethanol 
                 5 to 72 
                 15 to 72  
                 15 to 70 
                 25 to 65 
               
               
                 Acetic Acid 
                 0 to 90 
                 0 to 50 
                  0 to 35 
                  0 to 15 
               
               
                 Water 
                 5 to 40 
                 5 to 30 
                 10 to 30 
                 10 to 26 
               
               
                 Ethyl Acetate 
                 0 to 30 
                 0 to 20 
                  1 to 12 
                  3 to 10 
               
               
                 Acetaldehyde 
                 0 to 10 
                 0 to 3  
                 0.1 to 3   
                 0.2 to 2   
               
               
                 Others 
                 0.1 to 10   
                 0.1 to 6   
                 0.1 to 4   
                 — 
               
               
                   
               
            
           
         
       
     
     In one embodiment, the crude ethanol product comprises acetic acid in an amount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. % or less than 5 wt. %. In terms of ranges, the acetic acid concentration of Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2 wt. % to 15 wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt. %. In embodiments having lower amounts of acetic acid, the conversion of acetic acid is preferably greater than 75%, e.g., greater than 85% or greater than 90%. In addition, the selectivity to ethanol may also be preferably high, and is preferably greater than 75%, e.g., greater than 85% or greater than 90%. 
     In some embodiments, the mixed oxygenate stream may be separated prior to entering the second reactor. This separation may be used to remove any unreacted syngas from the mixed oxygenate stream. 
     In recovering ethanol, the processes of the present invention use two or more distillation columns. In one embodiment, a first distillation column is used to separate the feed stream into a residue stream comprising acetic acid and a distillate stream comprising ethanol, ethyl acetate, water. The distillate may be further separated in an extractive column and the ethanol subsequently recovered from the remaining water. There may be at least one liquid recycle stream that comprises ethyl acetate from this separation. 
     In another embodiment, a first distillation column is used to separate the feed stream into a residue stream comprising water and acetic acid from the crude ethanol product and a distillate stream comprising ethanol, acetaldehyde and ethyl acetate. The residue may comprise a substantial portion of the water. In one embodiment, 30 to 90% of the water in the crude ethanol product is removed in the residue, e.g., from 40 to 88% of the water or from 50 to 84% of the water. Water may also be removed from the distillate to form an ethanol mixture stream, preferably comprising less than 10 wt. % water, less than 6 wt. % water or less than 4 wt. % water. In terms of ranges the ethanol mixture stream comprises from 0.001 to 10 wt. % water, e.g., from 0.01 to 6 wt. % water or from 0.1 to 4 wt. % water. Water may be removed, for example, using an adsorption unit, membrane, molecular sieves, extractive column distillation, or a combination thereof. Suitable adsorption units include pressure swing adsorption (PSA) units and thermal swing adsorption (TSA) units. The adsorption units may comprise molecular sieves, such as aluminosilicate compounds. Product ethanol is then recovered from the ethanol mixture stream. There may be at least one liquid recycle stream that comprises ethyl acetate that is also recovered from the ethanol mixture stream. 
     In another embodiment, a first distillation column is used to separate the feed stream into a residue stream comprising ethanol, ethyl acetate, water and acetic acid from the crude ethanol product and a distillate stream comprising acetaldehyde, ethanol and ethyl acetate. The distillate may be at least one liquid recycle stream. The residue stream, for example, may comprise at least 50% of the ethanol from the crude ethanol product, and more preferably at least 70%. In terms of ranges, the residue stream may comprise from 50% to 97.5% of the ethanol from the crude ethanol product, and more preferably from 70% to 97.5%. The amount of ethanol from the crude ethanol recovered in the residue may be greater than 97.5%, e.g. up to 99.9%. The residue may also comprise a substantial portion of the water and acetic acid from the crude ethanol product. The residue stream comprising ethanol, ethyl acetate, water, and acetic acid may be further separated to recover ethanol. Because these compounds may not be in equilibrium, additional ethyl acetate may be produced through esterification of ethanol and acetic acid. In one preferred embodiment, the water and acetic acid may be removed as another residue stream in a separate distillation column. 
     Mixed Oxygenate and Methanol Stream 
     In an alternative embodiment of this invention, acetic acid is produced from a mixed oxygenate and methanol stream. As shown in  FIG. 1C , syngas may be fed to a reactor to be converted to a mixed oxygenate and methanol stream. The mixed oxygenates may comprise acetic acid, acetaldehyde, ethyl acetate, and mixtures thereof. Thus the stream may comprise methanol and at least one compound selected from the group consisting of acetic acid, acetaldehyde, ethyl acetate, and mixtures thereof. The mixed oxygenate and methanol stream may then be carbonylated to form acetic acid, which may then be hydrogenated in the presence of a catalyst to form an ethanol product. In addition, other acids may be formed with the acetic acid. As discussed above, carbon monoxide from the syngas may be used in the carbonylation reaction to form acetic acid. In some embodiments, the catalyst used to form the mixed oxygenate and methanol stream comprises copper and zinc. The hydrogenation of acetic acid and recovery of ethanol remains the same as is described herein. 
     When the catalyst comprises copper and zinc and or oxides thereof, the molar ratio of copper to zinc is from 0.5:1 to 20:1, e.g., from 0.7:1 to 15:1, from 0.8:1 to 5:1 or from 1.5:1 to 2.5:1. 
     The reactor may be operated at a temperature from 150° C. to 450° C., e.g., from 175° C. to 350° C., from 200° C. to 325° C., or from 260° C. to 300° C. The reactor may be operated at a pressure from 0.1 to 150,000 kPa, e.g., from 1000 to 100,000 kPa, or from 5000 to 75,000 kPa. The reactor may have a gas hourly space velocities from 50 hr −1  to 50,000 hr −1 , e.g. from. 250 hr −1  to 25,000 hr −1 , or from about 500 hr −1  to about 10,000 hr −1 . 
     Additional Acetic Acid for Mixed Oxygenate Stream 
     In addition to feeding the mixed oxygenate stream to the second reactor, in some embodiments an additional source of acetic acid is fed to the reactor. This source may be an acetic acid stream that is capable of enriching the mixed oxygenate stream and increasing the concentration of acetic acid if desired. The acetic acid may be derived from any suitable source including natural gas, petroleum, coal, biomass, and so forth. As examples, acetic acid may be produced via methanol carbonylation, acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, and anaerobic fermentation. Methanol carbonylation processes suitable for production of acetic acid are described in U.S. Pat. Nos. 7,208,624; 7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976; 5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosures of which are incorporated herein by reference. Optionally, the production of ethanol may be integrated with such methanol carbonylation processes. 
     In another embodiment, the acetic acid used in the hydrogenation step may be formed from the fermentation of biomass. The fermentation process preferably utilizes an acetogenic process or a homoacetogenic microorganism to ferment sugars to acetic acid producing little, if any, carbon dioxide as a by-product. The carbon efficiency for the fermentation process preferably is greater than 70%, greater than 80% or greater than 90% as compared to conventional yeast processing, which typically has a carbon efficiency of about 67%. Optionally, the microorganism employed in the fermentation process is of a genus selected from the group consisting of  Clostridium, Lactobacillus, Moorella, Thermoanaerobacter, Propionibacterium, Propionispera, Anaerobiospirillum , and  Bacteriodes , and in particular, species selected from the group consisting of  Clostridium formicoaceticum, Clostridium butyricum, Moorella thermoacetica, Thermoanaerobacter kivui, Lactobacillus delbrukii, Propionibacterium acidipropionici, Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodes amylophilus  and  Bacteriodes ruminicola . Optionally in this process, all or a portion of the unfermented residue from the biomass, e.g., lignans, may be gasified to form hydrogen that may be used in the hydrogenation step of the present invention. Exemplary fermentation processes for forming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180; 6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and 7,888,082, the entireties of which are incorporated herein by reference. See also US Publ. Nos. 2008/0193989 and 2009/0281354, the entireties of which are incorporated herein by reference. 
     Examples of biomass include, but are not limited to, agricultural wastes, forest products, grasses, and other cellulosic material, timber harvesting residues, softwood chips, hardwood chips, tree branches, tree stumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover, wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus, animal manure, municipal garbage, municipal sewage, commercial waste, grape pumice, almond shells, pecan shells, coconut shells, coffee grounds, grass pellets, hay pellets, wood pellets, cardboard, paper, plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety of which is incorporated herein by reference. Another biomass source is black liquor, a thick, dark liquid that is a byproduct of the Kraft process for transforming wood into pulp, which is then dried to make paper. Black liquor is an aqueous solution of lignin residues, hemicellulose, and inorganic chemicals. 
     U.S. Pat. No. RE 35,377, also incorporated herein by reference, provides a method for the production of methanol by converting carbonaceous materials such as oil, coal, natural gas and biomass materials. The process includes hydrogasification of solid and/or liquid carbonaceous materials to obtain a process gas which is steam pyrolized with additional natural gas to form synthesis gas. The syngas is converted to methanol which may be carbonylated to acetic acid. The method likewise produces hydrogen which may be used in connection with this invention as noted above. U.S. Pat. No. 5,821,111, which discloses a process for converting waste biomass through gasification into synthesis gas, and U.S. Pat. No. 6,685,754, which discloses a method for the production of a hydrogen-containing gas composition, such as a synthesis gas including hydrogen and carbon monoxide, are incorporated herein by reference in their entireties. 
     The acetic acid fed to the hydrogenation reaction may also comprise other carboxylic acids and anhydrides, as well as acetaldehyde and acetone. Generally ethyl acetate may be recovered from the liquid recycle streams when recovering ethanol. Preferably, a suitable acetic acid feed stream comprises one or more of the compounds selected from the group consisting of acetic acid, acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof. These other compounds may also be hydrogenated in the processes of the present invention. In some embodiments, the presence of carboxylic acids, such as propanoic acid or its anhydride, may be beneficial in producing propanol. Water may also be present in the acetic acid feed. 
     Alternatively, acetic acid in vapor form may be taken directly as crude product from the flash vessel of a methanol carbonylation unit of the class described in U.S. Pat. No. 6,657,078, the entirety of which is incorporated herein by reference. The crude vapor product, for example, may be fed directly to the ethanol synthesis reaction zones of the present invention without the need for condensing the acetic acid and light ends or removing water, saving overall processing costs. 
     Ethanol Separation 
     Ethanol produced by the second reactor may be recovered using several different techniques. In  FIG. 2 , the separation of the crude ethanol product uses four columns. In  FIG. 3 , the crude ethanol product is separated in two columns with an intervening water separation. In  FIG. 4 , the separation of the crude ethanol product uses three columns. Other separation systems may also be used with embodiments of the present invention. 
     Hydrogenation system  100  includes a reaction zone  101  and separation zone  102 . Hydrogen, mixed oxygenate stream and acetic acid via lines  104 ,  116  and  105 , respectively, are fed to vaporizer  106  to create a vapor feed stream in line  107  that is directed to reactor  108 . Liquid recycle stream  113  from reaction zone  102  may also be fed to vaporizer  106 . Hydrogen feed line  105  may be preheated to a temperature from 30° C. to 150° C., e.g., from 50° C. to 125° C. or from 60° C. to 115° C. Hydrogen feed line  105  may be fed at a pressure from 1300 kPa to 3100 kPa, e.g., from 1500 kPa to 2800 kPa, or 1700 kPa to 2600 kPa. Mixed oxygenate stream in line  116  may be produced from syngas or other sources, as described above. Acetic acid in line  105  comprises fresh acetic acid. In one embodiment, lines  104 ,  116  and  105  may be combined and jointly fed to vaporizer  106 . The temperature of the vapor feed stream in line  107  is preferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Any feed that is not vaporized is removed from vaporizer  106  in blowdown stream  115  and may be recycled or discarded thereto. The mass ratio of feed stream in line  107  to blowdown stream  115  may be from 6:1 to 500:1, e.g., from 10:1 to 500:1, from 20:1 to 500:1 or from 50:1 to 500:1. In addition, although vapor feed stream in line  107  is shown as being directed to the top of reactor  108 , line  107  may be directed to the side, upper portion, or bottom of reactor  108 . 
     Reactor  108  contains the catalyst that is used in the hydrogenation of the carboxylic acid, preferably acetic acid. In one embodiment, one or more guard beds (not shown) may be used upstream of the reactor, optionally upstream of first vaporizer  106  and second vaporizer  113 , to protect the catalyst from poisons or undesirable impurities contained in the feed or return/recycle streams. Such guard beds may be employed in the vapor or liquid streams. Suitable guard bed materials may include, for example, carbon, silica, alumina, ceramic, or resins. In one aspect, the guard bed media is functionalized, e.g., silver functionalized, to trap particular species such as sulfur or halogens. During the hydrogenation process, a crude ethanol product stream is withdrawn, preferably continuously, from reactor  108  via line  109 . 
     The crude ethanol product stream in line  109  may be condensed and fed to a separator  110 , which, in turn, provides a vapor stream  111  and a liquid stream  112 . In some embodiments, separator  110  may comprise a flasher or a knockout pot. The separator  110  may operate at a temperature of from 20° C. to 250° C., e.g., from 30° C. to 225° C. or from 60° C. to 200° C. The pressure of separator  110  may be from 50 kPa to 2000 kPa, e.g., from 75 kPa to 1500 kPa or from 100 kPa to 1000 kPa. Optionally, the crude ethanol product in line  109  may pass through one or more membranes to separate hydrogen and/or other non-condensable gases. 
     The vapor stream  111  exiting separator  110  may comprise hydrogen and hydrocarbons, and may be purged and/or returned to reaction zone  101 . When returned to reaction zone  101 , vapor stream  110  is combined with the hydrogen feed  104  and co-fed to vaporizer  106 . In some embodiments, the returned vapor stream  111  may be compressed before being combined with hydrogen feed  104 . 
     In  FIG. 2 , the liquid stream  112  from separator  110  is withdrawn and introduced in the lower part of first column  120 , e.g., lower half or lower third. First column  120  is also referred to as an “acid separation column.” In one embodiment, the contents of liquid stream  112  are substantially similar to the crude ethanol product obtained from the reactor, except that the composition has been depleted of hydrogen, carbon dioxide, methane and/or ethane, which are removed by separator  110 . Accordingly, liquid stream  112  may also be referred to as a crude ethanol product. Exemplary components of liquid stream  112  are provided in Table 2. It should be understood that liquid stream  112  may contain other components, not listed in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 COLUMN FEED COMPOSITION 
               
               
                 (Liquid Stream 112) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Ethanol 
                 5 to 70 
                 10 to 70 
                 15 to 65 
               
               
                 Acetic Acid 
                 &lt;90  
                  0 to 50 
                  0 to 35 
               
               
                 Water 
                 5 to 30 
                  5 to 28 
                 10 to 26 
               
               
                 Ethyl Acetate 
                 &lt;30  
                 0.001 to 20   
                  1 to 12 
               
               
                 Acetaldehyde 
                 &lt;10  
                 0.001 to 3    
                 0.1 to 3   
               
               
                 Acetals 
                 0.01 to 10   
                 0.01 to 6   
                 0.01 to 5   
               
               
                 Acetone 
                 &lt;5 
                 0.0005 to 0.05  
                 0.001 to 0.03  
               
               
                 Other Esters 
                 &lt;5 
                 &lt;0.005 
                 &lt;0.001 
               
               
                 Other Ethers 
                 &lt;5 
                 &lt;0.005 
                 &lt;0.001 
               
               
                 Other Alcohols 
                 &lt;5 
                 &lt;0.005 
                 &lt;0.001 
               
               
                   
               
            
           
         
       
     
     The amounts indicated as less than (&lt;) in the tables throughout the present specification are preferably not present and if present may be present in trace amounts or in amounts greater than 0.0001 wt. %. 
     The “other esters” in Table 2 may include, but are not limited to, ethyl propionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butyl acetate or mixtures thereof. The “other ethers” in Table 2 may include, but are not limited to, diethyl ether, methyl ethyl ether, isobutyl ethyl ether or mixtures thereof. The “other alcohols” in Table 2 may include, but are not limited to, methanol, isopropanol, n-propanol, n-butanol, 2-butanol or mixtures thereof. In one embodiment, the liquid stream  112  may comprise propanol, e.g., isopropanol and/or n-propanol, in an amount from 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03 wt. %. In should be understood that these other components may be carried through in any of the distillate or residue streams described herein and will not be further described herein, unless indicated otherwise. 
     Optionally, crude ethanol product in line  109  or in liquid stream  112  may be further fed to an esterification reactor, hydrogenolysis reactor, or combination thereof. An esterification reactor may be used to consume residual acetic acid present in the crude ethanol product to further reduce the amount of acetic acid that would otherwise need to be removed. Hydrogenolysis may be used to convert ethyl acetate in the crude ethanol product to ethanol. 
     In the embodiment shown in  FIG. 2 , line  112  is introduced in the lower part of first column  120 , e.g., lower half or lower third. In first column  120 , unreacted acetic acid, a portion of the water, and other heavy components, if present, are removed from the composition in line  121  and are withdrawn, preferably continuously, as residue. Some or all of the residue may be returned and/or recycled back to reaction zone  101  via line  121 . Recycling the acetic acid in line  121  to the vaporizer  106  may reduce the amount of heavies that need to be purged from vaporizer  106 . Optionally, at least a portion of residue in line  121  may be purged from the system. Reducing the amount of heavies to be purged may improve efficiencies of the process while reducing byproducts. 
     First column  120  also forms an overhead distillate, which is withdrawn in line  122 , and which may be condensed and refluxed, for example, at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1. 
     When column  120  is operated under standard atmospheric pressure, the temperature of the residue exiting in line  121  preferably is from 95° C. to 120° C., e.g., from 110° C. to 117° C. or from 111° C. to 115° C. The temperature of the distillate exiting in line  122  preferably is from 70° C. to 110° C., e.g., from 75° C. to 95° C. or from 80° C. to 90° C. Column  120  preferably operates at ambient pressure. In other embodiments, the pressure of first column  120  may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components of the distillate and residue compositions for first column  120  are provided in Table 3 below. It should also be understood that the distillate and residue may also contain other components, not listed, such as components in the feed. For convenience, the distillate and residue of the first column may also be referred to as the “first distillate” or “first residue.” The distillates or residues of the other columns may also be referred to with similar numeric modifiers (second, third, etc.) in order to distinguish them from one another, but such modifiers should not be construed as requiring any particular separation order. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 ACID COLUMN 120 (FIG. 2) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Distillate 
                   
                   
                   
               
               
                 Ethanol 
                 20 to 75 
                 30 to 70 
                 40 to 65 
               
               
                 Water 
                 10 to 40 
                 15 to 35 
                 20 to 35 
               
               
                 Acetic Acid 
                  &lt;2 
                 0.001 to 0.5  
                 0.01 to 0.2  
               
               
                 Ethyl Acetate 
                 &lt;60 
                 5.0 to 40  
                 10 to 30 
               
               
                 Acetaldehyde 
                 &lt;10 
                 0.001 to 5    
                 0.01 to 4   
               
               
                 Acetals 
                 0.01 to 10   
                 0.05 to 6   
                 0.1 to 5   
               
               
                 Acetone 
                    &lt;0.05 
                 0.001 to 0.03  
                  0.01 to 0.025 
               
               
                 Residue 
               
               
                 Acetic Acid 
                  60 to 100 
                 70 to 95 
                 85 to 92 
               
               
                 Water 
                 &lt;30 
                  1 to 20 
                  1 to 15 
               
               
                 Ethanol 
                  &lt;1 
                 &lt;0.9 
                 &lt;0.07 
               
               
                   
               
            
           
         
       
     
     As shown in Table 3, without being bound by theory, it has surprisingly and unexpectedly been discovered that when any amount of acetal is detected in the feed that is introduced to the acid separation column  120 , the acetal appears to decompose in the column such that less or even no detectable amounts are present in the distillate and/or residue. 
     The distillate in line  122  preferably comprises ethanol, ethyl acetate, and water, along with other impurities, which may be difficult to separate due to the formation of binary and tertiary azeotropes. To further separate distillate, line  122  is introduced to the second column  123 , also referred to as the “light ends column,” preferably in the middle part of column  123 , e.g., middle half or middle third. Preferably the second column  123  is an extractive distillation column. In such embodiments, an extraction agent, such as water, may be added to second column  123 . If the extraction agent comprises water, it may be obtained from an external source or from an internal return/recycle line from one or more of the other columns. 
     The molar ratio of the water in the extraction agent to the ethanol in the feed to the second column is preferably at least 0.5:1, e.g., at least 1:1 or at least 3:1. In terms of ranges, preferred molar ratios may range from 0.5:1 to 8:1, e.g., from 1:1 to 7:1 or from 2:1 to 6.5:1. Higher molar ratios may be used but with diminishing returns in terms of the additional ethyl acetate in the second distillate and decreased ethanol concentrations in the second column distillate. 
     In one embodiment, an additional extraction agent, such as water from an external source, dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethylene glycol-1,5-pentanediol; propylene glycol-tetraethylene glycol-polyethylene glycol; glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane, N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, an alkylated thiopene, dodecane, tridecane, tetradecane and chlorinated paraffins, may be added to second column  123 . Some suitable extraction agents include those described in U.S. Pat. Nos. 4,379,028, 4,569,726, 5,993,610 and 6,375,807, the entire contents and disclosure of which are hereby incorporated by reference. 
     In the embodiments of the present invention, without the use of an extractive agent, a larger portion of the ethanol would carry over into the second distillate in line  127 . By using an extractive agent in second column  123 , the separation of ethanol into the second residue in line  126  is facilitated thus increasing the yield of the overall ethanol product in the second residue in line  126 . 
     Second column  123  may be a tray or packed column. In one embodiment, second column  123  is a tray column having from 5 to 70 trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although the temperature and pressure of second column  123  may vary, when at atmospheric pressure the temperature of the second residue exiting in line  126  preferably is from 60° C. to 90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C. The temperature of the second distillate exiting in line  127  from second column  123  preferably is from 50° C. to 90° C., e.g., from 60° C. to 80° C. or from 60° C. to 70° C. Column  123  may operate at atmospheric pressure. In other embodiments, the pressure of second column  123  may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components for the distillate and residue compositions for second column  123  are provided in Table 4 below. It should be understood that the distillate and residue may also contain other components, not listed, such as components in the feed. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 SECOND COLUMN 123 (FIG. 2) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Distillate 
                   
                   
                   
               
               
                 Ethyl Acetate 
                 10 to 99 
                 25 to 95 
                 50 to 93 
               
               
                 Acetaldehyde 
                 &lt;25 
                 0.5 to 15  
                 1 to 8 
               
               
                 Water 
                 &lt;25 
                 0.5 to 20  
                  4 to 16 
               
               
                 Ethanol 
                 &lt;30 
                 0.001 to 15   
                 0.01 to 5   
               
               
                 Acetal 
                 0.01 to 20   
                  1 to 20 
                  5 to 20 
               
               
                 Residue 
               
               
                 Water 
                 30 to 90 
                 40 to 85 
                 50 to 85 
               
               
                 Ethanol 
                 10 to 75 
                 15 to 60 
                 20 to 50 
               
               
                 Ethyl Acetate 
                  &lt;3 
                 0.001 to 2    
                 0.001 to 0.5  
               
               
                 Acetic Acid 
                   &lt;0.5 
                 0.001 to 0.3  
                 0.001 to 0.2  
               
               
                   
               
            
           
         
       
     
     In preferred embodiments, the recycling of the third residue promotes the separation of ethyl acetate from the residue of the second column  123 . For example, the weight ratio of ethyl acetate in the second residue to second distillate preferably is less than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1. In embodiments that use an extractive distillation column with water as an extraction agent as the second column  123 , the weight ratio of ethyl acetate in the second residue to ethyl acetate in the second distillate approaches zero. Second residue may comprise, for example, from 30% to 99.5% of the water and from 85 to 100% of the acetic acid from line  122 . The second distillate in line  127  comprises ethyl acetate and additionally comprises water, ethanol, and/or acetaldehyde. Second distillate  127  is preferably substantially free of acetic acid. At least a portion of second distillate  127  is combined with line  132  discussed below and fed to vaporizer  113 . 
     The weight ratio of ethanol in the second residue to second distillate preferably is at least 3:1, e.g., at least 6:1, at least 8:1, at least 10:1 or at least 15:1. All or a portion of the third residue is recycled to the second column. In one embodiment, all of the third residue may be recycled until process  100  reaches a steady state and then a portion of the third residue is recycled with the remaining portion being purged from the system  100 . The composition of the second residue will tend to have lower amounts of ethanol than when the third residue is not recycled. As the third residue is recycled, the composition of the second residue, as provided in Table 4, comprises less than 30 wt. % of ethanol, e.g., less than 20 wt. % or less than 15 wt. %. The majority of the second residue preferably comprises water. Notwithstanding this effect, the extractive distillation step advantageously also reduces the amount of ethyl acetate that is sent to the third column, which is highly beneficial in ultimately forming a highly pure ethanol product. 
     As shown, the second residue from second column  123 , which comprises ethanol and water, is fed via line  126  to third column  128 , also referred to as the “product column.” More preferably, the second residue in line  126  is introduced in the lower part of third column  128 , e.g., lower half or lower third. Third column  128  recovers ethanol, which preferably is substantially pure with respect to organic impurities and other than the azeotropic water content, as the distillate in line  129 . The distillate of third column  128  preferably is refluxed as shown in  FIG. 2 , for example, at a reflux ratio of from 1:10 to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to 2:1. The third residue in line  130 , which comprises primarily water, preferably is returned to the second column  123  as an extraction agent as described above. In one embodiment (not shown), a first portion of the third residue in line  124  is recycled to the second column and a second portion is purged and removed from the system. In one embodiment, once the process reaches steady state, the second portion of water to be purged is substantially similar to the amount water formed in the hydrogenation of acetic acid. In one embodiment, a portion of the third residue may be used to hydrolyze any other stream, such as one or more streams comprising ethyl acetate. 
     Third column  128  is preferably a tray column as described above and operates at atmospheric pressure or optionally at pressures above or below atmospheric pressure. The temperature of the third distillate exiting in line  129  preferably is from 50° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature of the third residue in line  124  preferably is from 15° C. to 100° C., e.g., from 30° C. to 90° C. or from 50° C. to 80° C. Exemplary components of the distillate and residue compositions for third column  128  are provided in Table 5 below. It should be understood that the distillate and residue may also contain other components, not listed, such as components in the feed. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 THIRD COLUMN 128 (FIG. 2) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Distillate 
                   
                   
                   
               
               
                 Ethanol 
                 75 to 96 
                  80 to 96 
                  85 to 96 
               
               
                 Water 
                 &lt;12 
                  1 to 9 
                  3 to 8 
               
               
                 Acetic Acid 
                 &lt;12 
                 0.0001 to 0.1  
                 0.005 to 0.05 
               
               
                 Ethyl Acetate 
                 &lt;12 
                 0.0001 to 0.05 
                  0.005 to 0.025 
               
               
                 Acetaldehyde 
                 &lt;12 
                 0.0001 to 0.1  
                 0.005 to 0.05 
               
               
                 Acetal 
                 &lt;12 
                 0.0001 to 0.05 
                 0.005 to 0.01 
               
               
                 Residue 
               
               
                 Water 
                  75 to 100 
                   80 to 100 
                  90 to 100 
               
               
                 Ethanol 
                   &lt;0.8 
                 0.001 to 0.5 
                 0.005 to 0.05 
               
               
                 Ethyl Acetate 
                  &lt;1 
                 0.001 to 0.5 
                 0.005 to 0.2  
               
               
                 Acetic Acid 
                  &lt;2 
                 0.001 to 0.5 
                 0.005 to 0.2  
               
               
                   
               
            
           
         
       
     
     In one embodiment, the third residue in line  130  is withdrawn from third column  128  at a temperature higher than the operating temperature of the second column  123 . 
     Any of the compounds that are carried through the distillation process from the feed or crude reaction product generally remain in the third distillate in amounts of less 0.01 wt. %, based on the total weight of the third distillate composition, e.g., less than 0.05 wt. % or less than 0.02 wt. %. In one embodiment, one or more side streams may remove impurities from any of the columns in the system  100 . Preferably at least one side stream is used to remove impurities from the third column  128 . The impurities may be purged and/or retained within the system  100 . 
     The third distillate in line  129  may be further purified to form an anhydrous ethanol product stream, i.e., “finished anhydrous ethanol,” using one or more additional separation systems, such as, for example, distillation columns, adsorption units, membranes, or molecular sieves. Suitable adsorption units include pressure swing adsorption units and thermal swing adsorption unit. 
     Returning to second column  123 , the second distillate preferably is refluxed as shown in  FIG. 2 , optionally at a reflux ratio of 1:10 to 10:1, e.g., from 1:5 to 5:1 or from 1:3 to 3:1. As explained above, at least a portion of second distillate in line  127  may be purged or a portion may be recycled to the reaction zone as the liquid recycle stream and fed to second vaporizer  113 . In one embodiment, at least a portion of second distillate in line  127  is further processed in fourth column  131 , also referred to as the “acetaldehyde removal column.” In fourth column  131 , the second distillate is separated into a fourth distillate, which comprises acetaldehyde, in line  132  and a fourth residue, which comprises ethyl acetate, in line  133 . The fourth distillate preferably is refluxed at a reflux ratio of from 1:20 to 20:1, e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and at least a portion of the fourth distillate is returned to vaporizer  113 . Additionally, at least a portion of fourth distillate in line  132  may be purged. Without being bound by theory, since acetaldehyde may be reacted, e.g., by hydrogenation, to form ethanol, the recycling of a stream that contains acetaldehyde to the reaction zone increases the yield of ethanol and decreases byproduct and waste generation. In another embodiment, the acetaldehyde may be collected and utilized, with or without further purification, to make useful products including but not limited to n-butanol, 1,3-butanediol, and/or crotonaldehyde and derivatives. 
     The fourth residue of fourth column  131  may be purged via line  133 . The fourth residue primarily comprises ethyl acetate and ethanol, which may be suitable for use as a solvent mixture or in the production of esters. In one preferred embodiment, the acetaldehyde is removed from the second distillate in optional fourth column  131  such that no detectable amount of acetaldehyde is present in the residue of column  131 . 
     Fourth column  131  is a tray column as described above and may operate above atmospheric pressure. In one embodiment, the pressure is from 120 kPa to 5,000 kPa, e.g., from 200 kPa to 4,500 kPa, or from 400 kPa to 3,000 kPa. In a preferred embodiment the fourth column  131  may operate at a pressure that is higher than the pressure of the other columns. 
     The temperature of the fourth distillate exiting in line  132  preferably is from 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature of the residue in line  133  preferably is from 70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 110° C. Exemplary components of the distillate and residue compositions for optional fourth column  131  are provided in Table 6 below. It should be understood that the distillate and residue may also contain other components, not listed, such as components in the feed. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 FOURTH COLUMN 131 (FIG. 2) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Distillate 
                   
                   
                   
               
               
                 Acetaldehyde 
                 2 to 80 
                    2 to 50 
                   5 to 40 
               
               
                 Ethyl Acetate 
                 &lt;90 
                   30 to 80 
                   40 to 75 
               
               
                 Ethanol 
                 &lt;30 
                 0.001 to 25 
                 0.01 to 20 
               
               
                 Water 
                 &lt;25 
                 0.001 to 20 
                 0.01 to 15 
               
               
                 Residue 
               
               
                 Ethyl Acetate 
                 40 to 100 
                    50 to 100 
                  60 to 100 
               
               
                 Ethanol 
                 &lt;40 
                 0.001 to 30 
                 0.01 to 15  
               
               
                 Water 
                 &lt;25 
                 0.001 to 20 
                  2 to 15 
               
               
                 Acetaldehyde 
                  &lt;1 
                  0.001 to 0.5 
                 Not detectable 
               
               
                 Acetal 
                  &lt;3 
                 0.0001 to 2   
                  0.001 to 0.01 
               
               
                   
               
            
           
         
       
     
     In one embodiment, a portion of the third residue in line  124  is recycled to second column  123 . In one embodiment, recycling the third residue further reduces the aldehyde components in the second residue and concentrates these aldehyde components in second distillate in line  127  and thereby sent to optional fourth column  131 , wherein the aldehydes may be more easily separated. The third distillate in line  129  may have lower concentrations of aldehydes and esters due to the recycling of third residue in line  124 . 
       FIG. 3  illustrates another exemplary separation system. The reaction zone  101  of  FIG. 3  is similar to  FIG. 2  and produces a liquid stream  112 , e.g., crude ethanol product, for further separation. In one preferred embodiment, the reaction zone  101  of  FIG. 3  operates at above 80% acetic acid conversion, e.g., above 90% conversion or above 99% conversion. Thus, the acetic acid concentration in the liquid stream  112  may be low. 
     Liquid stream  112  is introduced in the middle or lower portion of a first column  150 , also referred to as acid-water column. For purposes of convenience, the columns in each exemplary separation process, may be referred as the first, second, third, etc., columns, but it is understood that first column  150  in  FIG. 3  operates differently than the first column  120  of  FIG. 2 . In one embodiment, no entrainers are added to first column  150 . In  FIG. 3 , first column  150 , water and unreacted acetic acid, along with any other heavy components, if present, are removed from liquid stream  112  and are withdrawn, preferably continuously, as a first residue in line  151 . Preferably, a substantial portion of the water in the crude ethanol product that is fed to first column  150  may be removed in the first residue, for example, up to about 75% or to about 90% of the water from the crude ethanol product. First column  150  also forms a first distillate, which is withdrawn in line  152 . 
     When column  150  is operated under about 170 kPa, the temperature of the residue exiting in line  151  preferably is from 90° C. to 130° C., e.g., from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of the distillate exiting in line  152  preferably is from 60° C. to 90° C., e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In some embodiments, the pressure of first column  150  may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. 
     The first distillate in line  152  comprises water, in addition to ethanol and other organics. The concentration of water in the first distillate in line  152  preferably is less than 20 wt. %, e.g., from 1 wt. % to 19 wt. % or from 5 wt. % to 15 wt. %. A portion of first distillate in line  153  may be condensed and refluxed, for example, at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1. It is understood that reflux ratios may vary with the number of stages, feed locations, column efficiency and/or feed composition. Operating with a reflux ratio of greater than 3:1 may be less preferred because more energy may be required to operate the first column  150 . The condensed portion of the first distillate may also be fed to a second column  154 . 
     The remaining portion of the first distillate in  152  is fed to a water separation unit  156 . Water separation unit  156  may be an adsorption unit, membrane, molecular sieves, extractive column distillation, or a combination thereof. A membrane or an array of membranes may also be employed to separate water from the distillate. The membrane or array of membranes may be selected from any suitable membrane that is capable of removing a permeate water stream from a stream that also comprises ethanol and ethyl acetate. 
     In one embodiment, water separator  156  is a pressure swing adsorption (PSA) unit. The PSA unit is optionally operated at a temperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressure of from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit may comprise two to five beds. Water separator  156  may remove at least 95% of the water from the portion of first distillate in line  152 , and more preferably from 99% to 99.99% of the water from the first distillate, in a water stream  157 . All or a portion of water stream  157  may be returned to column  150  in line  158 , where the water preferably is ultimately recovered from column  150  in the first residue in line  151 . Additionally or alternatively, all or a portion of water stream  157  may be purged via line  159 . The remaining portion of first distillate exits the water separator  156  as ethanol mixture stream  160 . Ethanol mixture stream  160  may have a low concentration of water of less than 10 wt. %, e.g., less than 6 wt. % or less than 2 wt. %. Exemplary components of ethanol mixture stream  160  and first residue in line  151  are provided in Table 7 below. It should also be understood that these streams may also contain other components, not listed, such as components derived from the feed. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 FIRST COLUMN 150 WITH PSA (FIG. 3) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Ethanol Mixture 
                   
                   
                   
               
               
                 Stream 
               
               
                 Ethanol 
                 20 to 95 
                 30 to 95 
                 40 to 95 
               
               
                 Water 
                 &lt;10 
                 0.01 to 6   
                 0.1 to 2   
               
               
                 Acetic Acid 
                  &lt;2 
                 0.001 to 0.5  
                 0.01 to 0.2  
               
               
                 Ethyl Acetate 
                 &lt;60 
                  1 to 55 
                  5 to 55 
               
               
                 Acetaldehyde 
                 &lt;10 
                 0.001 to 5    
                 0.01 to 4   
               
               
                 Acetal 
                   &lt;0.1 
                 &lt;0.1 
                 &lt;0.05 
               
               
                 Acetone 
                    &lt;0.05 
                 0.001 to 0.03  
                  0.01 to 0.025 
               
               
                 Residue 
               
               
                 Acetic Acid 
                 &lt;90 
                  1 to 50 
                  2 to 35 
               
               
                 Water 
                  30 to 100 
                 45 to 95 
                 60 to 90 
               
               
                 Ethanol 
                  &lt;1 
                 &lt;0.9 
                 &lt;0.3  
               
               
                   
               
            
           
         
       
     
     Preferably, ethanol mixture stream  160  is not returned or refluxed to first column  150 . The condensed portion of the first distillate in line  153  may be combined with ethanol mixture stream  160  to control the water concentration fed to the second column  154 . For example, in some embodiments the first distillate may be split into equal portions, while in other embodiments, all of the first distillate may be condensed or all of the first distillate may be processed in the water separation unit. In  FIG. 3 , the condensed portion in line  153  and ethanol mixture stream  160  are co-fed to second column  154 . In other embodiments, the condensed portion in line  153  and ethanol mixture stream  160  may be separately fed to second column  154 . The combined distillate and ethanol mixture has a total water concentration of greater than 0.5 wt. %, e.g., greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, the total water concentration of the combined distillate and ethanol mixture may be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10 wt. %. 
     The second column  154  in  FIG. 3 , also referred to as the “light ends column,” removes ethyl acetate and acetaldehyde from the first distillate in line  153  and/or ethanol mixture stream  160 . Ethyl acetate and acetaldehyde are removed as a second distillate in line  161  and ethanol is removed as the second residue in line  162 . Second column  108  may be a tray column or packed column. In one embodiment, second column  154  is a tray column having from 5 to 70 trays, e.g., from 15 to 50 trays or from 20 to 45 trays. 
     Second column  154  operates at a pressure ranging from 0.1 kPa to 510 kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa. Although the temperature of second column  154  may vary, when at about 20 kPa to 70 kPa, the temperature of the second residue exiting in line  162  preferably is from 30° C. to 75° C., e.g., from 35° C. to 70° C. or from 40° C. to 65° C. The temperature of the second distillate exiting in line  161  preferably is from 20° C. to 55° C., e.g., from 25° C. to 50° C. or from 30° C. to 45° C. 
     The total concentration of water fed to second column  154  preferably is less than 10 wt. %, as discussed above. When first distillate in line  153  and/or ethanol mixture stream comprises minor amounts of water, e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may be fed to the second column  154  as an extractive agent in the upper portion of the column. A sufficient amount of water is preferably added via the extractive agent such that the total concentration of water fed to second column  154  is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %, based on the total weight of all components fed to second column  154 . If the extractive agent comprises water, the water may be obtained from an external source or from an internal return/recycle line from one or more of the other columns or water separators. 
     Suitable extractive agents may also include, for example, dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethylene glycol-1,5-pentanediol; propylene glycol-tetraethylene glycol-polyethylene glycol; glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane, N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, an alkylated thiopene, dodecane, tridecane, tetradecane, chlorinated paraffins, or a combination thereof. When extractive agents are used, a suitable recovery system, such as a further distillation column, may be used to recycle the extractive agent. 
     Exemplary components for the second distillate and second residue compositions for the second column  154  are provided in Table 8, below. It should be understood that the distillate and residue may also contain other components, not listed in Table 8. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 SECOND COLUMN 154 (FIG. 3) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
               
               
                 Second Distillate 
                   
                   
                   
               
               
                 Ethyl Acetate 
                 5 to 90 
                 10 to 80 
                 15 to 75 
               
               
                 Acetaldehyde 
                 &lt;60 
                  1 to 40 
                  1 to 35 
               
               
                 Ethanol 
                 &lt;45 
                 0.001 to 40   
                 0.01 to 35   
               
               
                 Water 
                 &lt;20 
                 0.01 to 10   
                 0.1 to 5   
               
               
                 Second Residue 
               
               
                 Ethanol 
                  80 to 99.5 
                 85 to 97 
                 90 to 95 
               
               
                 Water 
                 &lt;20 
                 0.001 to 15   
                 0.01 to 10   
               
               
                 Ethyl Acetate 
                  &lt;1 
                 0.001 to 2    
                 0.001 to 0.5  
               
               
                 Acetic Acid 
                   &lt;0.5 
                 &lt;0.01 
                 0.001 to 0.01  
               
               
                 Acetal 
                    &lt;0.05 
                 &lt;0.03 
                 &lt;0.01 
               
               
                   
               
            
           
         
       
     
     The second residue in  FIG. 3  comprises one or more impurities selected from the group consisting of ethyl acetate, acetic acid, and acetaldehyde. The second residue may comprise at least 100 wppm of these impurities, e.g., at least 250 wppm or at least 500 wppm. In some embodiments, the second residue may contain substantially no ethyl acetate or acetaldehyde. 
     The second distillate in line  161 , which comprises ethyl acetate and/or acetaldehyde, preferably is refluxed as shown in  FIG. 3 , for example, at a reflux ratio of from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3 to 3:1. In one aspect, second distillate  161  or a portion thereof is returned to second vaporizer  113 . Additionally, at least a portion of second distillate  161  may be purged. 
       FIG. 4  illustrates another exemplary separation system. The reaction zone  101  of  FIG. 4  is similar to  FIG. 2  and produces a liquid stream  112 , e.g., crude ethanol product, for further separation. In one preferred embodiment, the reaction zone  101  of  FIG. 4  operates at above 80% acetic acid conversion, e.g., above 90% conversion or above 99% conversion. Thus, the acetic acid concentration in the liquid stream  112  may be low. 
     In the exemplary embodiment shown in  FIG. 4 , liquid stream  112  is introduced in the lower part of first column  170 , e.g., lower half or middle third. In one embodiment, no entrainers are added to first column  170 . In first column  170 , a weight majority of the ethanol, water, acetic acid, and other heavy components, if present, are removed from liquid stream  112  and are withdrawn, preferably continuously, as residue in line  171 . First column  170  also forms an overhead distillate, which is withdrawn in line  172 , and which may be condensed and refluxed, for example, at a ratio of from 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 1:5 to 5:1. The overhead distillate in stream  172  preferably comprises a weight majority of the ethyl acetate from liquid stream  112 . 
     When column  170  is operated under about 170 kPa, the temperature of the residue exiting in line  171  preferably is from 70° C. to 155° C., e.g., from 90° C. to 130° C. or from 100° C. to 110° C. The base of column  170  may be maintained at a relatively low temperature by withdrawing a residue stream comprising ethanol, water, and acetic acid, thereby providing an energy efficiency advantage. The temperature of the distillate exiting in line  172  from column  170  preferably at 170 kPa is from 75° C. to 100° C., e.g., from 75° C. to 83° C. or from 81° C. to 84° C. In some embodiments, the pressure of first column  170  may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components of the distillate and residue compositions for first column  170  are provided in Table 9 below. It should also be understood that the distillate and residue may also contain other components, not listed in Table 9. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 FIRST COLUMN 170 (FIG. 4) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Distillate 
                   
                   
                   
               
               
                 Ethyl Acetate 
                 10 to 85 
                 15 to 80 
                 20 to 75 
               
               
                 Acetaldehyde 
                 0.1 to 70  
                 0.2 to 65  
                 0.5 to 65  
               
               
                 Diethyl Acetal 
                 0.01 to 10   
                 0.01 to 6   
                 0.01 to 5   
               
               
                 Acetone 
                    &lt;0.05 
                 0.001 to 0.03  
                  0.01 to 0.025 
               
               
                 Ethanol 
                 &lt;25 
                 0.001 to 20   
                 0.01 to 15   
               
               
                 Water 
                 0.1 to 20  
                  1 to 15 
                  2 to 10 
               
               
                 Acetic Acid 
                  &lt;2 
                 &lt;0.1 
                 &lt;0.05 
               
               
                 Residue 
               
               
                 Acetic Acid 
                 0.01 to 35   
                 0.1 to 30  
                 0.2 to 25  
               
               
                 Water 
                  5 to 40 
                 10 to 35 
                 15 to 30 
               
               
                 Ethanol 
                 10 to 75 
                 15 to 70 
                 20 to 65 
               
               
                   
               
            
           
         
       
     
     In another embodiment of the present invention, column  170  may be operated at a temperature where most of the water, ethanol, and acetic acid are removed from the residue stream and only a small amount of ethanol and water is collected in the distillate stream due to the formation of binary and tertiary azeotropes. The weight ratio of water in the residue in line  171  to water in the distillate in line  172  may be greater than 1:1, e.g., greater than 2:1. The weight ratio of ethanol in the residue to ethanol in the distillate may be greater than 1:1, e.g., greater than 2:1 
     The amount of acetic acid in the first residue may vary depending primarily on the conversion in reactor  108 . In one embodiment, when the conversion is high, e.g., greater than 90%, the amount of acetic acid in the first residue may be less than 10 wt. %, e.g., less than 5 wt. % or less than 2 wt. %. In other embodiments, when the conversion is lower, e.g., less than 90%, the amount of acetic acid in the first residue may be greater than 10 wt. %. 
     The distillate preferably is substantially free of acetic acid, e.g., comprising less than 1000 ppm, less than 500 ppm or less than 100 ppm acetic acid. The distillate may be purged from the system or recycled in whole or part to reactor  108 . In some embodiments, the distillate may be further separated, e.g., in a distillation column (not shown), into an acetaldehyde stream and an ethyl acetate stream. Either of these streams may be returned to the reactor  108  or separated from system  100  as a separate product. 
     Some species, such as acetals, may decompose in first column  170  such that very low amounts, or even no detectable amounts, of acetals remain in the distillate or residue. 
     To recover ethanol, the residue in line  171  may be further separated in a second column  173 , also referred to as an “acid separation column.” An acid separation column may be used when the acetic acid concentration in the first residue is greater than 1 wt. %, e.g., greater than 5 wt. %. The first residue in line  171  is introduced to second column  173  preferably in the top part of column  173 , e.g., top half or top third. Second column  173  yields a second residue in line  174  comprising acetic acid and water, and a second distillate in line  175  comprising ethanol. Second column  173  may be a tray column or packed column. In one embodiment, second column  173  is a tray column having from 5 to 150 trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although the temperature and pressure of second column  173  may vary, when at atmospheric pressure the temperature of the second residue exiting in line  174  preferably is from 95° C. to 130° C., e.g., from 100° C. to 125° C. or from 110° C. to 120° C. The temperature of the second distillate exiting in line  175  preferably is from 60° C. to 100° C., e.g., from 75° C. to 100° C. or from 80° C. to 100° C. The pressure of second column  173  may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components for the distillate and residue compositions for second column  173  are provided in Table 10 below. It should be understood that the distillate and residue may also contain other components, not listed in Table 10. 
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 SECOND COLUMN 173 (FIG. 4) 
               
            
           
           
               
               
               
               
            
               
                   
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Second Distillate 
                   
                   
                   
               
               
                 Ethanol 
                  70 to 99.9 
                    75 to 98 
                 80 to 95 
               
               
                 Ethyl Acetate 
                 &lt;10  
                 0.001 to 5 
                 0.01 to 3   
               
               
                 Acetaldehyde 
                 &lt;5 
                 0.001 to 1 
                 0.005 to 0.5  
               
               
                 Acetal 
                 0.01 to 10  
                  0.01 to 6 
                 0.01 to 5   
               
               
                 Water 
                 0.1 to 30 
                   1 to 25 
                  5 to 20 
               
               
                 Second Residue 
               
               
                 Acetic Acid 
                 0.1 to 45 
                   0.2 to 40 
                 0.5 to 35  
               
               
                 Water 
                   45 to 100 
                    55 to 99.8 
                   65 to 99.5 
               
               
                 Ethyl Acetate 
                 &lt;2 
                 &lt;1 
                 &lt;0.5 
               
               
                 Ethanol 
                 &lt;5 
                 0.001 to 5 
                 &lt;2   
               
               
                   
               
            
           
         
       
     
     The weight ratio of ethanol in the second distillate in line  175  to ethanol in the second residue in line  174  preferably is at least 35:1. In one embodiment, the weight ratio of water in the second residue  174  to water in the second distillate  175  is greater than 2:1, e.g., greater than 4:1 or greater than 6:1. In addition, the weight ratio of acetic acid in the second residue  174  to acetic acid in the second distillate  175  preferably is greater than 10:1, e.g., greater than 15:1 or greater than 20:1. Preferably, the second distillate in line  175  is substantially free of acetic acid and may only contain, if any, trace amounts of acetic acid. 
     As shown, the second distillate in line  175  is fed to a third column  176 , e.g., ethanol product column, for separating the second distillate into a third distillate (ethyl acetate distillate) in line  178  and a third residue (ethanol residue) in line  177 . Second distillate in line  175  may be introduced into the lower part of column  176 , e.g., lower half or lower third. Third distillate  178  is preferably refluxed, for example, at a reflux ratio greater than 2:1, e.g., greater than 5:1 or greater than 10:1. At least a portion of the third distillate is returned to second vaporizer  113 . Additionally, at least a portion of third distillate  178  may be purged. Third column  176  is preferably a tray column as described herein and preferably operates at atmospheric pressure. The temperature of the third residue exiting from third column  176  preferably is from 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature of the third distillate exiting from third column  176  preferably is from 70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 105° C., when the column is operated at atmospheric pressure. 
     The remaining water from the second distillate in line  175  may be removed in further embodiments of the present invention. Depending on the water concentration, the ethanol product may be derived from the second distillate in line  175  or the third residue in line  177  Some applications, such as industrial ethanol applications, may tolerate water in the ethanol product, while other applications, such as fuel applications, may require an anhydrous ethanol. The amount of water in the distillate of line  175  or the residue of line  177  may be closer to the azeotropic amount of water, e.g., at least 4 wt. %, preferably less than 20 wt. %, e.g., less than 12 wt. % or less than 7.5 wt. %. Water may be removed from the second distillate in line  175  or the third residue in line  177  using several different separation techniques as described herein. Particularly preferred techniques include the use of distillation column, membranes, adsorption units, and combinations thereof. 
     Some of the residues withdrawn from the separation zone  102  comprise acetic acid and water. Depending on the amount of water and acetic acid contained in the residue of first column, e.g.,  120  in  FIG. 2 ,  150  in  FIG. 3 , or residue of second column  173  in  FIG. 4 , the residue may be treated in one or more of the following processes. The following are exemplary processes for further treating the residue and it should be understood that any of the following may be used regardless of acetic acid concentration. When the residue comprises a majority of acetic acid, e.g., greater than 70 wt. %, the residue may be recycled to the reactor without any separation of the water. In one embodiment, the residue may be separated into an acetic acid stream and a water stream when the residue comprises a majority of acetic acid, e.g., greater than 50 wt. %. Acetic acid may also be recovered in some embodiments from the residue having a lower acetic acid concentration. The residue may be separated into the acetic acid and water streams by a distillation column or one or more membranes. If a membrane or an array of membranes is employed to separate the acetic acid from the water, the membrane or array of membranes may be selected from any suitable acid resistant membrane that is capable of removing a permeate water stream. The resulting acetic acid stream optionally is returned to the reactor  108 . The resulting water stream may be used as an extractive agent or to hydrolyze an ester-containing stream in a hydrolysis unit. 
     In other embodiments, for example, where the residue comprises less than 50 wt. % acetic acid, possible options include one or more of: (i) returning a portion of the residue to reactor  108 , (ii) neutralizing the acetic acid, (iii) reacting the acetic acid with an alcohol, or (iv) disposing of the residue in a waste water treatment facility. It also may be possible to separate a residue comprising less than 50 wt. % acetic acid using a weak acid recovery distillation column to which a solvent (optionally acting as an azeotroping agent) may be added. Exemplary solvents that may be suitable for this purpose include ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, vinyl acetate, diisopropyl ether, carbon disulfide, tetrahydrofuran, isopropanol, ethanol, and C 3 -C 12  alkanes. When neutralizing the acetic acid, it is preferred that the residue comprises less than 10 wt. % acetic acid. Acetic acid may be neutralized with any suitable alkali or alkaline earth metal base, such as sodium hydroxide or potassium hydroxide. When reacting acetic acid with an alcohol, it is preferred that the residue comprises less than 50 wt. % acetic acid. The alcohol may be any suitable alcohol, such as methanol, ethanol, propanol, butanol, or mixtures thereof. The reaction forms an ester that may be integrated with other systems, such as carbonylation production or an ester production process. Preferably, the alcohol comprises ethanol and the resulting ester comprises ethyl acetate. Optionally, the resulting ester may be fed to the hydrogenation reactor. 
     In some embodiments, when the residue comprises very minor amounts of acetic acid, e.g., less than 5 wt. % or less than 1 wt. %, the residue may be neutralized and/or diluted before being disposed of to a waste water treatment facility. The organic content, e.g., acetic acid content, of the residue beneficially may be suitable to feed microorganisms used in a waste water treatment facility. 
     The columns shown in  FIGS. 2 to 4  may comprise any distillation column capable of performing the desired separation and/or purification. Each column preferably comprises a tray column having from 1 to 150 trays, e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays. The trays may be sieve trays, fixed valve trays, movable valve trays, or any other suitable design known in the art. In other embodiments, a packed column may be used. For packed columns, structured packing or random packing may be employed. The trays or packing may be arranged in one continuous column or they may be arranged in one or more columns, preferably two or more columns such that the vapor from the first section enters the second section while the liquid from the second section enters the first section, etc. 
     The associated condensers and liquid separation vessels that may be employed with each of the distillation columns may be of any conventional design and are simplified in the figures. Heat may be supplied to the base of each column or to a circulating bottom stream through a heat exchanger or reboiler. Other types of reboilers, such as internal reboilers, may also be used. The heat that is provided to the reboilers may be derived from any heat generated during the process that is integrated with the reboilers or from an external source such as another heat generating chemical process or a boiler. Although one reactor and one flasher are shown in the figures, additional reactors, flashers, condensers, heating elements, and other components may be used in various embodiments of the present invention. As will be recognized by those skilled in the art, various condensers, pumps, compressors, reboilers, drums, valves, connectors, separation vessels, etc., normally employed in carrying out chemical processes may also be combined and employed in the processes of the present invention. 
     The temperatures and pressures employed in the columns may vary. As a practical matter, pressures from 10 kPa to 3000 kPa will generally be employed in these zones although in some embodiments subatmospheric pressures or superatmospheric pressures may be employed. Temperatures within the various zones will normally range between the boiling points of the composition removed as the distillate and the composition removed as the residue. As will be recognized by those skilled in the art, the temperature at a given location in an operating distillation column is dependent on the composition of the material at that location and the pressure of column. In addition, feed rates may vary depending on the size of the production process and, if described, may be generically referred to in terms of feed weight ratios. 
     The ethanol product produced by the process of the present invention may be an industrial grade ethanol comprising from 75 to 96 wt. % ethanol, e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on the total weight of the ethanol product. Exemplary finished ethanol compositional ranges are provided below in Table 11. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 FINISHED ETHANOL COMPOSITIONS 
               
            
           
           
               
               
               
               
            
               
                 Component 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
                 Conc. (wt. %) 
               
               
                   
               
               
                 Ethanol 
                 75 to 96 
                 80 to 96 
                 85 to 96 
               
               
                 Water 
                 &lt;12 
                 1 to 9 
                 3 to 8 
               
               
                 Acetic Acid 
                 &lt;1 
                 &lt;0.1 
                 &lt;0.01 
               
               
                 Ethyl Acetate 
                 &lt;2 
                 &lt;0.5 
                 &lt;0.05 
               
               
                 Acetal 
                 &lt;0.05 
                 &lt;0.01 
                 &lt;0.005 
               
               
                 Acetone 
                 &lt;0.05 
                 &lt;0.01 
                 &lt;0.005 
               
               
                 Isopropanol 
                 &lt;0.5 
                 &lt;0.1 
                 &lt;0.05 
               
               
                 n-propanol 
                 &lt;0.5 
                 &lt;0.1 
                 &lt;0.05 
               
               
                   
               
            
           
         
       
     
     The finished ethanol composition of the present invention preferably contains very low amounts, e.g., less than 0.5 wt. %, of other alcohols, such as methanol, butanol, isobutanol, isoamyl alcohol and other C 4 -C 20  alcohols. In one embodiment, the amount of isopropanol in the finished ethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000 wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment, the finished ethanol composition is substantially free of acetaldehyde, optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5 wppm or less than 1 wppm. 
     In some embodiments, when further water separation is used, the ethanol product may be withdrawn as a stream from the water separation unit as discussed above. In such embodiments, the ethanol concentration of the ethanol product may be higher than indicated in Table 11, and preferably is greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greater than 99.5 wt. %. The ethanol product in this aspect preferably comprises less than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %. 
     The finished ethanol composition produced by the embodiments of the present invention may be used in a variety of applications including applications as fuels, solvents, chemical feedstocks, pharmaceutical products, cleansers, sanitizers, hydrogenation transport or consumption. In fuel applications, the finished ethanol composition may be blended with gasoline for motor vehicles such as automobiles, boats and small piston engine aircraft. In non-fuel applications, the finished ethanol composition may be used as a solvent for toiletry and cosmetic preparations, detergents, disinfectants, coatings, inks, and pharmaceuticals. The finished ethanol composition may also be used as a processing solvent in manufacturing processes for medicinal products, food preparations, dyes, photochemicals and latex processing. 
     The finished ethanol composition may also be used as a chemical feedstock to make other chemicals such as vinegar, ethyl acrylate, ethyl acetate, ethylene, glycol ethers, ethylamines, aldehydes, and higher alcohols, especially butanol. In the production of ethyl acetate, the finished ethanol composition may be esterified with acetic acid. In another application, the finished ethanol composition may be dehydrated to produce ethylene. Any known dehydration catalyst can be employed to dehydrate ethanol, such as those described in copending U.S. Pub. Nos. 2010/0030002 and 2010/0030001, the entireties of which is incorporated herein by reference. A zeolite catalyst, for example, may be employed as the dehydration catalyst. Preferably, the zeolite has a pore diameter of at least about 0.6 nm, and preferred zeolites include dehydration catalysts selected from the group consisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite X is described, for example, in U.S. Pat. No. 2,882,244 and zeolite Yin U.S. Pat. No. 3,130,007, the entireties of which are hereby incorporated herein by reference. 
     While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed herein in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited herein and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.