Abstract:
A process for the production of oxygenated C 2  hydrocarbons from cellulose is disclosed. The input cellulose waste is gasified using steam in the absence of air and the primary gaseous products of carbon monoxide and hydrogen are subjected to heat, pressure, and catalysts to form methyl alcohol. Carbon monoxide is added to the methyl alcohol and further subjected to heat, pressure and catalysts to form acetic acid. The acetic acid is purified using a distillation tower, and removed for sale. Output production is increased by adding further carbon monoxide and hydrogen from burners used to heat the gasifiers. Further carbon monoxide and hydrogen are also produced by steam gasification of the carbon residue to promote a water/gas shift. These gases are fed into the gas stream produced by the gasification of cellulose, and provide more feedstock for the reactions. The three input gas streams arising from: 1) the steam gasification of cellulose; 2) the water/gas shift in the carbon reactor; and 3) the sub-stoichiometic oxygen burning of input burner gas to heat both retorts, maximize the output chemical production while reducing the consumption of energy needed for processing the cellulose and the carbon.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION  
       [0001]    This patent application relates to U.S. Provisional Patent Application Ser. No. 60/1187,166 filed on Mar. 6, 2000 entitled Process for Producing Oxygenated C 2  Products from Biomass 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a process for converting biomass or cellulose material and in particular to converting wood waste of various types into liquid hydrocarbons and in particularly acetic acid.  
         BACKGROUND OF THE INVENTION  
         [0003]    Our civilization has been burdened with the products of modern living since the industrial revolution began. It has resulted in the defilement of the environment, and even natural product residues have contributed to the problems we now face.  
           [0004]    For example, there has been over the years an accumulation of piles of wood waste from logging operations and the production of laminates, plywoods, furniture, dimensional lumber for buildings, and pallets. The pulp and paper industry can only utilize specific parts of a tree and therefore leaves considerable residue that to date has little use.  
           [0005]    In addition to “clean” wood residues, there are many other types of wood residues which contain, or are coated with, paints, varnishes and chemicals: for example, demolished buildings or used and discarded wood from any source. These are more toxic to the environment because their on-board chemicals leach into the ground on which they sit.  
           [0006]    The wood industry is very busy trying to find ways to utilize wood waste. A common alternate to landfill disposal is burning. Recently the industry has been focussing on using the heat from combusting wood waste to generate synthesis gas (syngas). Syngas is used to generate steam which is used to produce electrical power. But there is a disadvantage seldom emphasized, i.e. the large quantities of carbon dioxide produced and emitted into the atmosphere.  
           [0007]    In addition, secondary industries have arisen to utilize wood waste, and these are the producers of particleboards, fiberboards, waferboards and extruded products. Other processes make animal bedding, animal litter, landscaping mulches, compost or ground covers. Some waste goes to erosion control.  
           [0008]    Only a small percentage of wood waste is processed by the chemical industry. Some is used to produce methanol. Others utilize bacterial fermentation as a means of modifying wood residues into usable chemicals. These processes are relatively inefficient with only the by-products of bacterial metabolism recovered. Enzymatic degradation of organic matter is a newer method to decompose the wood, but the economic viability of the process may be less than rewarding.  
           [0009]    Accordingly, there exists a real need to utilize the cellulose waste to economically produce useful chemicals. Cellulose lends itself to reforming into the raw materials for plastics. Plastics are currently made using raw materials derived from petrochemical sources. In fact, we have relied heavily on the petrochemical industry to supply these raw materials. An efficient process to provide substantial volumes of these materials would have immediate positive impact on the world petrochemical industry. If indeed these materials could be produced at a lower cost, then not only would natural petroleum reserves be extended, but the economies of the plastic industry would shift in favour of the consumer.  
           [0010]    A product with an extremely large world market such as acetic acid, would therefore be dramatically more lucrative than, for example, methanol since it is a raw material for the plastics industry. Additionally, chemical production with minimal greenhouse gas emissions would not only be economically more desirable, but environmentally more desirable. If wood waste is used to make raw materials for plastics, then the environment would be cleaned up and the world petroleum reserves would last longer.  
         SUMMARY OF THE INVENTION  
         [0011]    A process for the production of oxygenated C 2  products from cellulose is disclosed. The cellulose is steam-gasified in the absence of air and the products consisting primarily of carbon monoxide and hydrogen are subjected to heats pressure, and catalysts to form methyl alcohol. The methyl alcohol is mixed with carbon monoxide and subjected to heat, pressure and catalysts to form oxygenated C 2  product.  
           [0012]    Additional carbon monoxide and hydrogen are generated from the burners using natural gas, under starved oxygen conditions, to provide heat for the gasifiers and additional feedstock for the conversion process. These gases are added to the gases emerging from the gasification of the cellulose.  
           [0013]    The carbon monoxide and hydrogen gases needed to make methyl alcohol and oxygenated C 2  products are, firstly separated in molecular sieves, secondly metered into the pressure vessels in the correct ratios to form the products. Small amounts of mixed hydrocarbon gases (CxHy) are also removed by the molecular sieves, and sent back to the burners to supplement the heating gas.  
           [0014]    In a further enhancement of the process, carbon particles are filtered from the gas stream after steam gasification of the cellulose, and heated with steam in the presence of a catalyst, to form carbon monoxide and hydrogen. These gases are sent to the molecular sieves to be separated, and used subsequently in the pressure vessels to add to the products formed.  
           [0015]    The final product liquid is run through an oil/water separator to remove water, then sent to a distillation tower where it is purified and removed from the system for sale. Any extraneous hydrocarbons which emerge from the distillation process, most of which form in the first pressure vessel, are sent back to the initial reactor to be re-processed with new cellulose input.  
           [0016]    A process for the production of oxygenated C 2  hydrocarbons from cellulose is disclosed. The input cellulose waste is gasified using steam in the absence of air and the primary gaseous products of carbon monoxide and hydrogen are subjected to heat, pressure, and catalysts to form methyl alcohol. Carbon monoxide is added to the methyl alcohol and further subjected to heat, pressure and catalysts to form acetic acid. The acetic acid is purified using a distillation tower, and removed for sale.  
           [0017]    Output production is increased by adding further carbon monoxide and hydrogen from burners used to heat the gasifiers. Further carbon monoxide and hydrogen are also produced by steam gasification of the carbon residue to promote a water/gas shift. These gases are fed into the gas stream produced by the gasification of cellulose, and provide more feedstock for the reactions.  
           [0018]    The three input gas streams arising from: 1) the steam gasification of cellulose; 2) the water/gas shift in the carbon reactor; and 3) the sub-stoichiometic oxygen burning of input burner gas to heat both retorts, maximize the output chemical production while reducing the consumption of energy needed for processing the cellulose and the carbon.  
           [0019]    Further features of the invention will be described or will become apparent in the course of the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The invention will now be described by way of example only, with reference to the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1 is a schematic diagram of the equipment and process flow of the process for producing acetic acid of the present invention;  
         [0022]    [0022]FIG. 2 is a flow diagram of materials and their progression through the process for producing acetic acid of the present invention;  
         [0023]    [0023]FIG. 3 is a flow diagram of the heat recovery loop portion of the process of the present invention;  
         [0024]    [0024]FIG. 4 is a schematic diagram of an alternate embodiment the equipment and process flow of the process for producing acetic acid of the present invention;  
         [0025]    [0025]FIG. 5 is a flow diagram of the biomass volatization loop portion of the process of the present invention;  
         [0026]    [0026]FIG. 6 is a flow diagram of carbon volatization loop portion of the process of the present invention;  
         [0027]    [0027]FIG. 7 is a flow diagram of the indirect heating loop portion of the process of the present invention;  
         [0028]    [0028]FIG. 8 is a flow diagram of the process of the present invention wherein methanol is produced;  
         [0029]    [0029]FIG. 9 is a flow diagram of the process of the present invention wherein formaldehyde is produced; and  
         [0030]    [0030]FIG. 10 is a flow diagram of the process of the present invention wherein urea-formaldehyde is produced. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    Referring to FIG. 1, the process for producing acetic acid from celluose waste is shown generally at  10 . It will be appreciated by those skilled in the art that the process disclosed herein is disclosed in terms of ideal conditions as the conditions in the system fluctuate the gases and liquids that are produced will vary.  
         [0032]    Cellulose material or wood waste  11  is fed into a first retort  12  and heat is applied to gasify the molecules. Typically the temperature of the material is raised to between 650 and 900° C. and preferably it is raised to 675° C. First retort  12  is a closed vessel whereby air is excluded and the pressure is kept at sufficient slight sub-atmospheric pressure to maximize the gasification. One alternative is that the first retort  12  is heat with a fluid bed type system. Preferably the pressure is maintained between 14.5 and 12 psi. Steam is infused into first retort  12  and the amount is optimized the formation of H 2 O, CO and H 2  to minimize the formation of CH 4  and CO 2 . The gas stream thus generated is largely carbon monoxide (CO) and hydrogen (H 2 ) with very small amounts of other hydrocarbons (CxHy) and some carbon dioxide (CO 2 ). The gas stream carries with it particulate including fly ash and carbon. The gas stream is cleaned to remove the particulate. One option shown herein is to send the gas through a series of two cyclones  14 , in which the particulate is removed and sent to a second retort  16 , described in more detail below. Alternatively the gas could be cleaned with electrostatic precipitators or bag houses.  
         [0033]    The cleaned gas stream enters a molecular sieve  18  to remove the larger hydrocarbons (CxHy) ( 19 ) from the CO and H 2 . These CxHy are directed into first burner  20  or second burner  22  to supplement the heating gases therein. The other gases emerging from molecular sieve  18  enter a second sieve  24 , which separates the carbon monoxide (CO) from the hydrogen (H 2 ). The H 2  is sent through a hydrogen metering valve  26  and enters a first pressure vessel  28 . The CO is sent through a carbon monoxide metering valve  30 . The gases are metered such that the quantity of gases are generally in a ratio 2:1 of H 2  to CO.  
         [0034]    In first pressure vessel  28  the gases are heated to temperatures typically between 200-300° C. at pressures between 50 -150 atmospheres in the presence of catalysts to achieve maximum conversion of the carbon monoxide and hydrogen mixture into methanol. To date, the most efficient catalysts have been shown to be Cu—ZnO—Al 2 O 3 , a copper zinc oxide on an aluminium base. In the first pressure vessel  28  methanol forms, plus minor amounts of other hydrocarbons, higher alcohols, ethers, ketones and esters. These hydrocarbons are in gaseous form and are sent to a first cooler  32  where the hydrocarbons are condensed and are then sent to a second pressure vessel  34 .  
         [0035]    In second pressure vessel  34  the condensates are blended with CO from molecular second sieve  24 . Preferably methanol and CO are combined in a ratio of 1:1. The material in second pressure vessel  34  are typically heated to 150-200° C. at pressures of between 33-65 atmospheres with a catalyst. Catalyst such as a combination of rhodium, phosphine and iodine (in the form of HI, MeI or I 2 ) are used to produce acetic acid. These conditions are selected to maximize the reaction of the methyl alcohol to form acetic acid. The resulting products are in gaseous form, and include the acetic acid plus the other hydrocarbons previously referred to that were formed in first pressure vessel  28 . The gas stream is sent to second cooler  36  where the hydrocarbon liquids condense specifically acetic acid. It will be appreciated by those skilled in the art that the predominant liquid will be acetic acid but other liquid hydrocarbons may also be present.  
         [0036]    The liquids are sent to an oil/water separator  38  where the hydrocarbons are separated from any water. The water is recycled back into the system. The remaining liquids are sent to a distillation tower  40 , and acetic acid  42  is removed. The other hydrocarbons  44  are not separated from each other, but are sent to the feed  11  and are fed into first retort  12  to be reprocessed.  
         [0037]    First retort  12  is a fluid bed system that is indirectly heated using hot gases from first  20 . Typically the material is heated to between 650° C. and 900° C. and preferably 675° C. The burner is supplied with oxygen which is derived from a third molecular sieve  46  and utilizes methane (or natural gas). The burner is operated with volumes of oxygen to provide starved (sub-stoichiometic) conditions to produce as much carbon monoxide (CO) and hydrogen (H 2 ) and as little carbon dioxide (CO 2 ) as possible. The hot gases are used to heat the retort then are sent to a first heat recovery boiler  48  which heats water to make steam to feed into first retort  12  to supply limited oxygen to the cellulose material. As discussed earlier, this minimizes the production of CO 2 . The gases that emerge from the first heat recovery boiler  48  are sent to second heat recovery boiler  50 .  
         [0038]    The carbon and fly ash removed by the cyclones  14  are fed into second retort  16 . Steam is supplied to the retort  16  by second heat recovery boiler  50  and the gases therein are heated to temperatures sufficient, typically between 400-500° C. at typically 3-15 atmospheres, to cause a water/gas shift to occur and form a maximum amount of carbon monoxide (CO) and hydrogen (H 2 ). This gas is commonly referred to as Synthesis gas. The gases are then fed into a pressure equalizer  52  prior to entering second molecular sieve  24 . The gas streams emerging from molecular sieve  24  are joined by gases from molecular sieve  18  and first and second heat recovery boilers  48  and  50 .  
         [0039]    Second retort  16  is indirectly heated using hot gases from second burner  22 . The second burner  22  utilizes methane (or natural gas) plus CxHy from first molecular sieve  18  and is supplied with sufficient oxygen from second molecular sieve  24  to produce sub-stoichiometic (starved) oxygen conditions to produce carbon monoxide (CO) and hydrogen (H 2 ). These hot gases are used to indirectly heat the retort then are sent to the second heat recovery boiler  50  which heats water to make steam. The spent gases from this loop are then sent to second molecular sieve  24  where they are separated.  
         [0040]    Referring to FIGS. 2 and 3, the above process is shown in a flow diagram form.  
         [0041]    An alternate process is shown in FIG. 4 wherein only those portions that are different will be provide with different reference numbers and described herein. In this embodiment the second molecular sieve is not used, allowing CO and H 2  into the first pressure vessel  28  without being metered. The gases, mostly CO and H 2 , from the water/gas shift in second retort  16  are fed direction into the second pressure vessel  34 . Extraneous H 2  not consumed in the reaction to form acetic acid in second pressure vessel  28  is send back to first pressure vessel  28  to be used in the formation of methanol. A chiller  54  cools the gases emerging from the first molecular sieve  18  and water is condensed out and is sent back to first heat recovery boiler  48 . Exhaust gases from the partial combustion of heating gases from second heat recovery boiler  16  are sent to join the gas stream emerging from the first molecular sieve  18 .  
         [0042]    It will be appreciated that the above description related to embodiments by way of example only. Many variations on the invention will be obvious to those skilled in the art and such obvious variations are within the scope of the invention as described herein whether or not expressly described.  
         [0043]    Chemistry  
         [0044]    In theory, cellulose breaks down under steam gasification to yield carbon monoxide and hydrogen gases.  
         [0045]    The balanced equation for the reaction is:  
               C   6          H   10          O   5         (   cellulose   )       +   Heat     →         5      CO     +     5        H   2       +   C       (       carbon                 monoxide     +   hydrogen   +   carbon     )                             
 
         [0046]    Under ideal conditions, this breakdown is complete, and no other products are formed. However, if the input contains other organic or inorganic molecules, the breakdown will result in other compounds. Wood, by it&#39;s nature, does contain other molecules.  
         [0047]    The “real world” equation, therefore is:  
         C 6 H 10 O 5 +CxHy→5CO+5H 2 +CxHy+C  
         [0048]    Other reactions in the process are:  
         CH 4 +½O 2 →CO+2H 2    
         C+H 2 O→CO+H 2    
         [0049]    The above description relates to one possible use of the process. However, the general principles shown herein could be used to produce other hydrocarbons. For example the catalysts could be changed and some further gases introduced to produce such formaldehyde or urea-formaldehyde. Alternatively the process could be optimized to produce methanol. It will be appreciated that minor variations could be used to produce a wide variety of liquid hydrocarbons and all such variations are considered within the scope of this invention. Hereafter a general process will be discussed with some specific alternatives.  
         [0050]    Referring to FIGS. 5, 6 and  7  there are a number of methods to provide the required gases. All of the systems are designed to turn cellulosic material into salable hydrocarbon liquids. Accordingly the main source of gaseous inputs is shown in FIG. 5 wherein the biomass waste is volatized. In addition carbon waste which is a bi-product of the biomass process can be used to create needed input gases and that process is shown in FIG. 6. In addition gases from the indirect heating loop can also be used as input gases and that process is shown in FIG. 7.  
         [0051]    Referring to FIG. 5 a flow diagram showing the volatization of the biomass is shown generally at  70 . The Cellulosic materials are pretreated by chipping to a size which is maximum two inches in diameter, then dried to extract moisture until the material contains less than 10% moisture content. The materials is fed by a continuous feed mechanism into the heating vessel (retort) and heat is applied to raise the temperature of the material to between 650 and 900° C., preferably to 675° C. The feed injection is done in a manner which excludes air from ingressing. Steam is infused continuously into the retort in a quantity calculated to optimize the cracking of the material into the fragments of CO and H 2  and minimize the formation of CO 2  and larger hydrocarbon molecules.  
         [0052]    The gas stream thus formed by the cracking of the cellulosic materials are drawn out of the retort, which is kept at slightly less then atmospheric pressure. The hot gas stream is passed through mechanical separators such as cyclones, electrostatic precipitators or a bag house to remove carbon and any other particulate matter which has been formed in the cracking process. The cleaned gases are then processed further, as described.  
         [0053]    Referring to FIG. 6 is the carbon volatization loop is shown generally at  80 . Carbon particulate material which is removed from the mechanical precipitators in the cellulosic cracking process described are collected and sent to a second indirectly heated retort. Steam is supplied to the retort by a second heat recovery boiler and the gases therein are heated to temperatures sufficient, typically between 400-500° C. at typically 3-15 atmospheres, to cause a water/gas shift to occur and form a maximum amount of carbon monoxide (CO) and hydrogen (H 2 ). This gas is commonly referred to as Synthesis gas (syngas). The gases are then fed into a pressure equalizer prior to entering second molecular sieve.  
         [0054]    Referring to FIG. 7 shows the indirect heating loop generally at  90 . The burner for the first heated retort, used to crack the cellulosic materials, is supplied with oxygen which is derived from a molecular sieve and utilizes methane (or natural gas). The burner is operated with volumes of oxygen to provide starved (sub-stoichiometic) conditions to produce as much carbon monoxide (CO) and hydrogen (H 2 ) and as little carbon dioxide (CO 2 ) as possible. The hot gases are used to indirectly heat the retort then are sent to a first heat recovery boiler which heats water to make steam to feed into first retort to supply limited oxygen to the cellulose material. As discussed earlier, this minimizes the production of CO 2 . The gases that emerge from the first heat recovery boiler are sent to second heat recovery boiler.  
         [0055]    The second retort used to process the carbon particulates removed from the mechanical separators is indirectly heated using hot gases from a second burner. The second burner utilizes methane (or natural gas) plus CxHy from first molecular sieve and is supplied with sufficient oxygen from second molecular sieve to produce sub-stoichiometic (starved) oxygen conditions to produce carbon monoxide (CO) and hydrogen (H 2 ). These hot gases are used to indirectly heat the retort then are sent to the second heat recovery boiler which heats water to make steam. The spent gases from this loop are then sent to join the gases emerging from the mechanical separator  
         [0056]    Referring to FIG. 8 a first variation of the process is shown generally at  100  wherein the gas produced is methanol. A representative aliquot of the cleaned gas stream  102  is measured on its way to the pressure vessel. A calculated volume of the gas stream is diverted into a molecular sieve to separate  104  the CO  106  from the H 2    108  according to the amount of H 2  needed in the correct ratio to CO in the pressure vessel to form methanol  110 . The H 2  is sent to the pressure vessel, and the CO  106  is reacted with water  112  to form CO 2    114  and H 2 116 . The H 2  is sent to the pressure vessel to complete the requirement for methanol  110  formation. The CO 2  is vented to the atmosphere, or collected for resale.  
         [0057]    The gas mix in the vessel are subjected to pressure of 50-100 atmospheres at 220-250° C. The catalyst  118  is selected from copper based, zinc oxide with another oxide such as alumina or chromia, or others shown to be more effective.  
         [0058]    Referring to FIG. 9 a second variation of the process is shown generally at  200  wherein the gas produced is formaldehyde. A representative aliquot of the cleaned gas stream is measured on its way to the pressure vessel. A calculated volume of the gas stream  202  is diverted into a molecular sieve to separate  204  the CO  206  from the H 2    208 , according to the amount of H 2  needed in the correct ratio to CO in the pressure vessel to form methanol  210 . The H 2  is sent to the pressure vessel, and the CO is reacted with water  212  to form CO 2    214  and H 2    216 . The H 2  is sent to the pressure vessel in the presence of a catalyst  218  to complete the requirement for methanol formation. The CO 2  is vented to the atmosphere, or collected for resale.  
         [0059]    The methanol formed is sent to a second reactor in vapor form, in which a stationary bed silver catalyst  220  is used, and heat of 700° C. is applied. A small amount of air is allowed into the vessel to promote the reaction, and formaldehyde  222  is formed. A small amount of H 2    224  gas remains which is sent back and utilized in the methanol reaction vessel. It should be noted that the a volume of the gas stream  202  only needs to be diverted in the start up phase because thereafter H 2    222  can be used.  
         [0060]    Referring to FIG. 10 a third variation of the process is shown generally at  300  wherein the gas produced is urea-formaldehyde. A representative aliquot of the cleaned gas stream  302  is measured on its way to the pressure vessel. A calculated volume of the gas stream is diverted into a molecular sieve to separate  304  the CO  306  from the H 2    308 , according to the amount of H 2  needed in the correct ratio to CO in the pressure vessel to form methanol  310 . The H 2  is sent to the pressure vessel, and the CO is reacted with water  312  to form CO 2    314  and H 2    316 . The H 2  is sent to the pressure vessel to complete in the presence of a catalyst  318  the requirement for methanol  310  formation. The CO 2  is sent to the third reaction vessel to be used in the urea-formaldehyde formation.  
         [0061]    The methanol  310  formed is sent to a second reactor in vapor form, in which a silver catalyst  320  is used and heat of 700° C. is applied. Atmospheric nitrogen  322  is fed into the vessel, and ammonia (NH 4 )  324  and formaldehyde  326  are formed. Water  328  is added to dissolve the formaldehyde  326 , leaving the ammonia  324  in vapor form. The NH 4    324  is sent to a third reactor to which the CO 2    314  from the steps above is added. Urea  330  then forms, which is sent to a fourth reactor together with the formaldehyde  326  and water  328 . The mixture of formaldehyde  326  and urea  330  react to form urea-formaldehyde  332  and H 2    334 , The reaction is catalysed  336  by a slightly alkaline reactant which is selected on the basis of selectivity. The H 2    334  is sent back to the methanol vessel if needed for more methanol formation, or if there is excess, fed into the primary burner  338  to supply heat to the initial cellulosic materials gasification step.  
         [0062]    It will be appreciated that the above description related to the invention by way of example only. Many variations on the invention will be obvious to those skilled in the art and such obvious variations are within the scope of the invention as described herein whether or not expressly described.