Abstract:
The presently disclosed subject matter is a new technology, related to a simulated moving bed membrane reactor. This novel technology includes a reactor with two different separation techniques: i) chromatography (simulated moving bed—SMB); ii) selective permeable membrane (namely, pervaporation and permeation, among others) into a single device, allowing a significant increase in the unity productivity and considerable reduction of solvent consumption and consequently lowers downstream costs associated to the following separation units, for the same product purity and reactants conversion criteria. It has its main applications in the chemical industry, particularly, in the continuous production of oxygenated compounds as esters, acetals, ethers, carbonates, among others.

Description:
[0001]    This application is a U.S. national phase filing under 35 U.S.C. §371 of PCT Application No. PCT/IB2010/051510, filed Apr. 7, 2010, and claims priority to Portuguese patent application no. 104496 filed on Apr. 8, 2009, under U.S.C. §119, the entireties of which are hereby incorporated by reference herein. 
     
    
     FIELD 
       [0002]    The presently disclosed subject matter is a new hybrid technology, the simulated moving bed membrane reactor. The technology shown here integrates a reactor with two different separation techniques: i) chromatography (simulated moving bed—SMB); ii) selective permeable membrane (namely, pervaporation and permeation, among others) into a single device. 
       SUMMARY 
       [0003]    The simulated moving bed reactor (SMBR) consists of a set of interconnected columns packed with a solid (or a mixture of a solid catalyst and an adsorbent) that catalyzes the reaction and separates the reaction products by selective adsorption of one of the products. The technology shown here integrates the SMBR with the membrane reactor by the use of selective permeable membranes incorporated into the columns of the SMBR, enhancing its global performance, since additionally to the products separation by selective adsorption there is, also, the selective membrane removal of one of the products. 
         [0004]    The presently disclosed subject matter allows the intensification of a process that involves equilibrium limited reactions where more than one product is formed and their simultaneous separation (by adsorption and membranes), leading to conversions higher than the equilibrium ones, until complete conversion. This process is, therefore, appropriate for application to the continuous production and at industrial scale of oxygenated compounds, as esters and acetals. 
       BACKGROUND 
       [0005]    Reaction and separation in a chemical process are seen, traditionally, as separated steps. This paradigm is still the current thought in the chemical industry. However, the combination of these steps (reaction/separation) in a single device has gain a considerable interest in the investigation and in the chemical industry, mainly for equilibrium limited reactions, since the continuous removal of at least one reaction product shifts the equilibrium in order to increase conversion and reduce by-product formation. 
         [0006]    The term multifunctional reactor is often used to embrace reactive separations technology, which main advantages are: reduction of energy requirements, decrease of solvents consumption, lower capital investments, higher yields in the formation of the product and improvement in the selectivity, in the case of competitive reactions. Typical examples of equilibrium limited reactions include: 
         [0000]      Esterification: R′—COOH+HO—R═R′COOR+H 2 O
 
         [0000]      Acetalization: R′—CHO+2 HO—R═R′CH—(OR) 2 +H 2 O
 
         [0000]      Ketalization: R′R″CO+2 HO—R═R′R″C(OR) 2 +H 2 O
 
         [0007]    In the state of the technique, the custom multifunctional reactors used for that type of reactions are: reactive distillations, membrane reactors and chromatographic reactors. Regarding to reactive distillation (RD) the best example is the methyl acetate production developed and patented by the company Eastman Kodak Company (Agreda and Partin, 1984). This technology allowed reducing five times the capital investment and the energy consumption when compared with the traditional process (reaction followed by separation by distillation). However, there are some disadvantages in the use of reactive distillation for systems that exhibit azeotropes formation and/or when the boiling points of the products are similar. 
         [0008]    Membrane reactors are widely used in several chemical applications. Typical examples are the pervaporation and permeation reactors, where the catalyst is in a fixed (Zhu et al., 1996; Lafarga and Varma, 2000) or fluidized bed (Alonso et al., 2001; Lee et al., 2006). Several times, processes where the reactor and membrane are housed in separate units in series or parallel are also regarded as membrane reactors (Datta and Tsai, 1998; Tsotsis et al., 2007). Chromatographic reactors include fixed bed (FBR) (Silva and Rodrigues, 2002; Gyani and Mahajani, 2008), pressure swing adsorption (PSAR) (Harale et al., 2008) and simulated moving bed reactors (SMBR) (Kawase et al., 1996; Rodrigues and Silva, 2005; Silva and Rodrigues, 2005; Pereira et al., 2008). However, from all the mentioned chromatographic reactors, the most common for process intensification for the production of oxygenated products is the SMBR. The SMBR is well-known equipment (Broughton and Gerhold, 1961), that consists of a set of interconnected columns packed with an acid solid or a mixture of solids (catalysts and adsorbents). Typically, are introduced into the unit two inlet streams and are obtained two outlet streams, as shown in  FIG. 1 . One of the inlet streams is the desorbent (Dsb) that is normally one of the reactants (A) and that is used to regenerate the solid (or mixture of solids) in the first zone. The reactants (A and B) are introduced in the feed stream (F). The products formed are removed from the reactor in two different streams, one comprising the less retained product and the desorbent (raffinate—R), and other stream comprising the most retained product and the desorbent (extract—X). All the inlet/outlet streams are fed/removed from the system through ports positioned between the columns; these ports are periodically shifted in the direction of the liquid flow in order to simulate the counter-current motion between the solid(s) and the liquid. The reactor is equipped with a plurality of inlet and outlet ports, and a rotary valve or a plurality of valves arranged in manner such that any feed stream may be introduced to any column and any outlet or effluent stream may be withdraw from any column. The position of the inlet/outlet streams defines the different zones existing in the SMBR system, each one accomplishing a certain function and containing a variable number of columns. In  FIG. 1 , the zone I is comprised between the desorbent stream port (Dsb) and the extract stream port (X); the zone II is comprised between the extract stream port (X) and the feed stream port (F); the zone III is comprised between the feed stream port (F) and the raffinate stream port (R); and the zone IV is comprised between the raffinate stream port (R) and the recycle stream port (Rec). The reactants (A and B) introduced in the feed stream (F) are converted within zones II and III. In these zones, the separation of the products formed (C and D) is carried out; the less retained product (C) is removed from the raffinate port and the most retained one (D) is removed from the extract port. As the products are removed from the reaction zone as they are formed, the equilibrium is shifted towards products formation. As these products are continuously removed, the reaction proceeds till the complete consumption of the limiting reactant (B), achieving conversion values above the thermodynamic equilibrium, being possible to achieve complete conversion (100%). In the zone I, the regeneration of the solid saturated with product D is performed using a desorbent (reactant A) and in zone IV the desorbent is regenerated since it can contain some product C. The successful design of SMBR involves the right choice of the operation conditions, mainly the switching time period and flow rates in each zone of the unit. The appropriate choice of those parameters will ensure the regeneration of acid solid (or mixture of solids) containing adsorbed water, in zone I; the regeneration of the desorbent contaminated with the less retained product in zone IV; and the complete conversion of reactants and the separation of the formed products in zones II and III. The flowrates for each zone are given by the following expressions: Q I =Q Rec +Q Dsb ; Q II =Q I −Q X ; Q III =Q II +Q F ; Q IV =Q III −Q R =Q Rec . The switching time, t*, is the time necessary to shift all ports from a position P′ to a position P. This process of shifting the ports could be made synchronously or asynchronously. 
         [0009]    The SMBR has several advantages, as the ones already mentioned for the reactive separations; however, it has also some disadvantages, as for example, the difficulty in removing the more adsorbed species, which implies high desorbent consumption. Besides, in several applications, the feed is a mixture of reactants with one of the products (as for example, in esterifications where the carboxylic acids are aqueous solutions of the acid, being that water is a by-product obtained in the esterification reaction), which will influence the performance of the unit resulting in low reactants conversion and products purity, low unit productivity and high eluent/desorbent consumption, mainly when the product in the feed is the more retained one. In order to overcome these issues, it is the aim of the presently disclosed subject matter to provide a novel technology to perform, simultaneously, reaction and separation into a single device, minimizing the desorbent consumption, increasing the productivity, the reactants conversion and the products purity. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0010]      FIG. 1 . SMBR unit, where a reaction of type A+B         C+D is considered and where the product D is the most adsorbed and C is the less adsorbed one, in which Dsb is the desorbent, R is the raffinate, X is the extract, F is the feed and (13) is the liquid direction and ports shift. 
           [0011]      FIG. 2 . Membrane reactor where a reaction of type A+B         C+D is considered and where the membrane is selective to product D, in which P is the permeate, F is the feed, Rt is the retentate and M is the membrane. 
           [0012]      FIG. 3 . PermSMBR unit used to produce a product C, from a mixture of reactants, A and B, and a by-product D removed by adsorption, as well as, by selective permeable membranes, in which Dsb is the desorbent, R is the raffinate, X is the extract, F is the feed and (13) is the liquid direction and ports shift. 
           [0013]      FIG. 4 . PermSMBR unit with 4 zones: two inlet ports for the feed and the desorbent stream; and two outlet ports for the raffinate and extract streams, in which Dsb is the desorbent, R is the raffinate, X is the extract, F is the feed, P is the permeate and Rec is the recycle stream. 
           [0014]      FIG. 5 . PermSMBR unit with 3 zones: two inlet ports for the feed and the desorbent streams; and one outlet port for the raffinate stream, in which Dsb is the desorbent, R is the raffinate, F is the feed, P is the permeate and Rec is the recycle stream. 
           [0015]      FIG. 6 . PermSMBR unit with 3 zones: two inlet ports for the feed and the desorbent streams; and one outlet port for the extract stream, in which Dsb is the desorbent, X is the extract, F is the feed, P is the permeate and Rec is the recycle stream. 
           [0016]      FIG. 7 . PermSMBR unit with 5 zones: three inlet ports for two feed streams and one desorbent stream; and two outlet ports for the raffinate and extract streams, in which Dsb is the desorbent, R is the raffinate, X is the extract, F1 and F2 are the feed streams, P is the permeate and Rec is the recycle stream. 
           [0017]      FIG. 8 . PermSMBR unit with 6 zones: three inlet ports for two feed streams and one desorbent stream; and three outlet ports for two raffinate streams and one extract stream, in which Dsb is the desorbent, R1 and R2 are the raffinate streams, X is the extract, F1 and F2 are the feed streams, P is the permeate and Rec is the recycle stream. 
           [0018]      FIG. 9 . Bypass to perform the regeneration/activation step of the catalyst/adsorbent and/or of the membranes in zone I of the PermSMBR unit, in which Dsb is the desorbent, Rg is the regeneration step, X is the extract and P is the permeate. 
           [0019]      FIG. 10 . Internal concentration profiles at the middle of the switching time at cyclic steady state for the ethyl lactate production in a PermSMBR unit. 
           [0020]      FIG. 11 . Internal concentration profiles at the middle of the switching time at cyclic steady state for the 1,1-dietoxiethane production in a PermSMBR unit. 
       
    
    
     GENERAL DESCRIPTION 
       [0021]    In the presently disclosed subject matter, a new hybrid technology is proposed, the simulated moving bed membrane reactor (PermSMBR), which integrates in a single equipment one reaction step with two different separation techniques: chromatography (SMB) and selective permeable membrane (pervaporation or permeation). The PermSMBR technology is particularly suitable for the intensification of processes that involve an equilibrium reaction and where more than one product is formed and where the feed is also comprised by one of the products, since they are removed from the reaction zone by adsorption and membranes processes, leading to higher conversions than the equilibrium ones, till almost complete conversion. 
         [0022]    This process is, therefore, appropriate for application to the continuous production at industrial scale of oxygenated compounds, as esters and acetals, since besides increasing the productivity (by increasing the conversion), increases also the purity and leads to a significant reduction of the desorbent consumption. 
         [0023]    In this disclosed subject matter, the SMBR unit is integrated with the membrane reactor using selective permeable membranes inside the columns of the SMBR, called the simulated moving bed membrane reactor (PermSMBR). The columns are packed with a solid, that should be simultaneously catalyst and selective adsorbent, could be acidic ion exchange resins, zeolites (Y, mordenites, ZSM, ferrierites), alumina silicates (mortmorillonites and bentonites) or hydrotalcites. Examples of acid resins are: Dowex 50 (Dow Chemical), Amberlite IR 120, Amberlyst A15 and A36 (Rohm &amp; Haas), Lewatit (Bayer). Alternatively, it is possible to use a mixture of acid solids as catalyst and as selective adsorbent. The membranes must be selective to one of the products and can be classified regarding to the material (polymeric, ceramics, glass, metals and liquids), to the structure (symmetric, asymmetric, microporous, homogeneous) and to the process (microfiltration, ultrafiltration, nanofiltration, inverse osmosis, electrodyalisis, vapour permeation and pervaporation). For application in reactions for the synthesis of organic products will be particularly interesting:
   the pervaporation membranes:
       zeolite type A, T or Y membranes (Mitsui Engineering &amp; Shipbuilding ltd., Japan);   hydrophilic membranes, as for example, the Pervap 1000 (Sulzer Chemtech, German);   PVA membranes, as for example, the Pervap 2201 and 2216 (Sulzer Chemtech, German) and the GFT-1005 (Deutsche Carbone AG);   silica membranes, commercialized as Pervap SMS (Sulzer chemtech) or supplied by the Pervatech company (The Netherlands).   
       the vapour permeation membranes-zeolite type A or T membranes, and carbon molecular sieves (CMS).   
 
         [0030]    Typically, in the permSMBR unit are introduced two inlet streams and are obtained three outlet streams, dividing the reactor in 4 zones ( FIG. 4 ), similarly to the traditional SMBR ( FIG. 1 ). One of the inlet streams is the desorbent (Dsb) that is used to regenerate the solid saturated with the most adsorbed specie; and a feed that contains the reactants (F), and that can also contain the products. The products formed are removed from the reactor in three different streams, one rich in the less adsorbed product (raffinate—R), other rich in the most strongly adsorbed product (extract—X) and other that comprises, mainly, the product for which the membranes are selective, (total permeate—P), which combines all the permeate streams removed from each column. All the inlet/outlet streams, with exception of the permeate streams, are fed/removed from the system through ports positioned between the columns; these ports are periodically shifted (switching time, t*) in the direction of the liquid flow in order to simulate the counter-current motion between the solid(s) and the liquid. The shift of the ports can be made asynchronously. The reactor is equipped with a plurality of inlet and outlet ports, and a rotary valve or a plurality of valves arranged in manner such that any feed stream may be introduced to any column and any outlet or effluent stream may be withdraw from any column; and it is also equipped with vacuum in order to remove the permeate of each column. This (vacuum) can be performed in all the columns or just on the selected ones. Similarly to the SMBR, the position of the inlet/outlet streams defines different zones existing in the PermSMBR unit, each one accomplishing a certain function and containing a variable number of columns. In  FIG. 4 , the zone 1 is comprised between the desorbent (Dsb) and extract nodes (X), the zone 2 is comprised between the extract (X) and feed node (F); the zone 3 is comprised between the feed (F) and raffinate node (R), and the zone 4 is comprised between the raffinate (R) and desorbent node. In zone 1, the adsorbent is regenerated by desorption of the more strongly adsorbed product from the solid using a desorbent; in zones 2 and 3, reactive zones, the products are separated as they are being formed. These products are continuously removed from the unit by adsorption and also through the selective membranes and, therefore, the reaction will proceed beyond the thermodynamic equilibrium, being possible to obtain 100% of reactants conversion. In zone IV, before being recycled to zone I, the desorbent is regenerated by adsorption of the less adsorbed product (C). 
         [0031]    The PermSMBR can have different configurations depending on the number of streams fed/removed from the unit. The total number of streams, with exception of the permeate streams, corresponds to the total number of zones. For example, the PermSMBR unit can be simplified to a unit of three zones: eliminating the extract stream (X), when the membrane is selective to the more adsorbed product ( FIG. 5 ); or eliminating the raffinate stream (R), when the membrane is selective to the less retained product ( FIG. 6 ). 
         [0032]    If necessary, the PermSMBR unit can also be more complex, having five or more zones. For example, the schematic diagram of the process represented in  FIG. 7  is similar to the one described for the  FIG. 4 , but it has 5 zones since an additional feed stream (F 2 ) is introduced to the system. In this case, the regeneration of the solid and the desorbent is accomplished in zones 1 and 5, respectively; and the complete conversion of reactants and separation of the products formed occurs in zone 2, 3 and 4. The feed F2 can comprise the same reactants as the ones in feed F1, but in different proportions, or other reactants in order to obtain the desired product. In the case where 3 products are formed, it will be necessary to have other extra stream designed as R2 in  FIG. 8 . Additionally, if it is observed a decrease in the PermSMBR unit performance (decrease of products purity, reduction of reactants conversion and/or loss of productivity, among others) due to problems related to deactivation/poisoning of the catalyst/adsorbent and/or of the membranes, the PermSMBR unit can be operated in order to correct those problems, making a bypass to each one of the columns during a cycle to perform the necessary treatments (treatments with acids, solvents, replacement of the solid and/or of the membrane, thermal treatments, . . . ). For example, if the desorbent is more expensive than the more adsorbed product, the treatment should be applied to the last column of zone I ( FIG. 9 ), since this column is still saturated with the most adsorbed product, avoiding the unnecessary consumption of desorbent if other column of the same zone was selected. This procedure can also be performed in other zones in the most appropriate column. Other ways of correction along time can be performed to the operational variables of the PermSMBR unit, similarly to the procedure described in literature for the SMB unit (Sá Gomes et al., 2007). 
       DETAILED DESCRIPTION 
       [0033]    The presently disclosed subject matter, the PermSMBR unit, can be applied in a variety of different types of reactions, mainly, in equilibrium limited reactions, as for example, esterifications, acetalizations, and Ketalizations. The examples below show the application of the PermSMBR unit for the ethyl lactate production through the esterification reaction between ethanol and lactic acid; and for the acetaldehyde diethylacetal (or 1,1-dietoxiethane) production from ethanol and acetaldehyde. Both reactions have water has a by-product, as can be seen in the reactions described above. 
       EXAMPLES 
     Example 1 
       [0034]    In this example, the PermSMBR unit is applied for the ethyl lactate (EL) production. The Ethyl lactate is a green solvent, biodegradable, non toxic and FDA approved. Its synthesis comprises a reversible reaction between ethanol and lactic acid having water as by-product. The equilibrium conversion of this reaction at 50° C. and for an initial molar ratio between ethanol and lactic acid of 2 is about 66%. The acidic ion exchange resin Amberlyst 15-wet (Rohm &amp; Haas, France) was used as catalyst and selective adsorbent to water. The feed was a commercial lactic acid solution (85%) in water (15%) and the desorbent was ethanol p.a. (99.5%). 
         [0035]    The PermSMBR unit considered consisted in 12 columns packed with the Amberlyst 15-wet (average diameter of 342.5 μm), where each column had 13 commercial hydrophilic tubular membranes selective to water (Pervatech B V, The Netherlands) in order to dehydrate the reaction medium; the length, the porosity and the bulk density were of 23 cm, 0.424 and 390 kg/m 3 , respectively. The water and ethanol membrane permeabilities were of 1.3×10 −1  mol dm 2  min 1  bar 1  and 6.0×10 −4  mol dm −2  min −1  bar −1 , respectively (Sommer and Melin, 2005). The flowrates were Q Dsb =58.0 mL/min; Q Rec =27.0 mL/min; Q F =9.6 mL/min and Q X =37.0 mL/min. The switching time was set at 2.1 minutes and the adopted configuration was of 3 columns in zone I, 3 columns in zone II, 4 columns in zone III and 2 columns in zone IV. The internal concentration profiles at the middle of the switching time at cyclic steady state are shown in  FIG. 10 . The lactic acid conversion obtained was of 99.34% and it was observed the products separation: the ethyl lactate is removed in the raffinate stream (99.19% purity, without desorbent) and the water is collected in the extract stream (99.98% purity, without desorbent). Additionally, the water was also removed by the permeate streams in all twelve columns. The PermSMBR parameters were chosen in order to compare its performance to the one of the SMBR, since this technology will be the most competitive regarding to the PermSMBR. The same mass of catalyst and effective area was considered. 
         [0036]    In order to show the PermSMBR unit enhancement when compared with the SMBR unit with the same mass of Amberlyst 15-wet it is presented, in Table 1, the results of a first optimization obtained for the ethyl lactate production in each one of the technologies. The switching time, desorbent and recycle flowrate were kept equal to 2.1 min, 58.0 mL/min and 27.0 mL/min, respectively; while the extract, raffinate and feed flowrates were changed in order to optimize the performance of each unit. As can be observed, the ethyl lactate synthesis in the PermSMBR unit is enhanced in about 42% and the desorbent consumption is decreased in 25%, which will reduce the costs associated to the desorbent recovery in the following separation steps. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 SMBR 
                 PermSMBR 
                 Improvement 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 EL Productivity 
                 18.06 
                 25.68 
                 42.22% 
               
               
                 (KgL −1  day −1 ) 
                   
                   
                   
               
               
                 Desorbent consumption 
                 4.75 
                 3.57 
                 24.74% 
               
               
                 (Lkg −1 ) 
               
               
                   
               
             
          
         
       
     
       Example 2 
       [0037]    This example is related to the acetaldehyde diethylacetal (or 1,1-dietoxiethane) synthesis in the PermSMBR unit. This product can be used as green additive for fuel since it decreases the particles emissions. The diethylacetal is formed through the reversible reaction between acetaldehyde and ethanol having water as by-product (Rodrigues and Silva, 2005). For this reaction, at room temperature and for a 2.2 initial molar ration of ethanol/acetaldehyde, the equilibrium conversion is of 55%. The acidic ion exchange resin Amberlyst 15-wet (Rohm &amp; Haas, France) was used as catalyst and selective adsorbent to water. It were considered 12 columns packed with the Amberlyst 15-wet (average diameter of 342.5 μm), where each column had 13 commercial tubular membranes selective to water (Pervatech B V, The Netherlands); the length, the porosity and the bulk density were of 25.5 cm, 0.424 and 390 kg/m 3 , respectively. The water and ethanol membrane permeabilities were of 1.3×10  −1  mol dm −2  min −1  bar −1  and 6.0×10 −4  mol dm −2  min −1  bar −1 , respectively (Sommer and Melin, 2005); and, due to the similarity in terms of size and chemical composition between the acetaldehyde and ethanol, the permeance of this species was considered equal to the one of the ethanol. However, as the acetaldehyde has a high vapour pressure, the vacuum was not performed on the columns where the reaction occurs, in order to avoid the loss of this reactant. Additionally, since the membrane has a high selectivity and permeability to water, it was possible to eliminate the extract stream, removing the water only through the permeate streams. 
         [0038]    The feed was a mixture of ethanol (30%) /acetaldehyde (70%) and the desorbent was ethanol (99.5%). The flowrates were Q Dsb =19.0 ml/min; Q F =10.0 ml/min; Q X =0.0 ml/min and Q Rcc =19.0 ml/min. The switching time was set at 4.2 minutes and the configuration adopted was of 6 columns in zone I, 3 columns in zone II and 3 columns in zone III. The pervaporation step was activated just in the first 4 columns of zone I and in all the columns of zone III, since the acetaldehyde is very volatile, having high vapour pressure and, consequently, a high driving force for the membrane flux. The internal concentration profiles at the middle of the switching time after the cyclic steady state be achieved are shown in  FIG. 11 . It was observed, that the acetaldehyde conversion was of 99.93%, the diethylacetal was obtained in the raffinate stream with 99.78% purity (without desorbent), the diethylacetal productivity was of 22.51 KgL −1 day −1  and the desorbent consumption was of 0.57 Lkg 1 . A SMBR unit to have the same purity and diethylacetal productivity as the PermSMBR, would have to operate in the following conditions: Q Dsb =35.0 mL/min; Q Rec =19.0 mL/min; Q F =10.0 mL/min and Q X =16.0 mL/min and switching time of 3.8 minutes. It were considered 12 columns, with 2.6 cm of diameter, length of 23 cm and porosity of 0.4, which corresponds to the same mass of Amberlyst 15-wet used in the PermSMBR unit. The adopted configuration was of 3 columns per zone. As can be seen in Table 2, using the PermSMBR unit the desorbent consumption is reduced in 67%, and, moreover, it is necessary to separate the ethanol just from one stream, the raffinate stream, reducing the energetic costs, as well as, the initial investment (one separation unit less). 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 SMBR 
                 PermSMBR 
                 Improvement 
               
               
                   
               
             
             
               
                 Desorbent consumption 
                 1.74 
                 0.57 
                 67.2% 
               
               
                 (Lkg −1 ) 
               
               
                   
               
             
          
         
       
     
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       [0000]    
       
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