Esterification reactions, zeolite membrane

Recently [43] Gao et al. applied a zeolite-fiOlled polyvinyl alcohol (PVA) membrane in esterification and acetalization reactions. Zeolites NaA, KA and CaA as well as NaX were loaded into PVA up to 27 wt% and the composites tested in selective water removal during reaction. A pervaporation cell with a membrane area of 22.9 cm was coimected to a collection system kept at a vacuum of 0.1 mm Hg. A sulfonated resin was used as Bronsted acid catalyst in the esterification mixture (120 ml). Figure 28 shows the progress of the esterification of salicylic acid and methanol at 60°C. The reaction is accelerated considerably as a result of the water removal. 

Esterification/ alkylation, deNOx reaction, hydrogenation, and Zeolite molecular sieve membrane It is found that zeolite membranes, disk, and coating show high performance or potential as catalysts compared with conventional catalysts [160]... 

Tanaka K, Yoshikawa R, Ying C, Kita H, and Okamoto K. Application of zeolite membranes to esterification reactions. Catal Today 2001 67 121-125. 

Jafar JJ, Budd PM, and Hughes R. Enhancement of esterification reaction yield using zeolite-A vapour permeation membrane. J Membr 50 2002 199 117-123. 

A membrane reactor using a H-ZSM5 membrane was used by Bernal et al. [3.42] to carry out the esterification reaction of acetic acid with ethanol. An equimolar etha-nol/acetic acid liquid mixture was fed in the membrane interior, while He gas was used as an inert sweep on the shell-side. In this particular application the membrane, itself, provides the catalysis for the reaction. NaA and T-type zeolite membranes have been utilized for esterification reactions in a PVMR and in a vapor permeation membrane reactor (VPMR) by Tanaka et al [3.43, 3.44]. Both membranes are hydrophilic and show good separation characteristics towards a number of alcohols. The NaA membrane was used to study the oleic/acid esterification in a vapor permeation membrane reactor (VPMR) at 383... 

K. The reaction is carried out in a batch reactor in the presence of /7-toluenesulfonic acid as a catalyst, and the water and ethanol vapors circulate through the NaA membrane, which removes the water vapor. The VPMR was shown to reach complete conversion. The NaA, which is unstable in the presence of acids, performed stably under such conditions. The T-zeolite membrane is more stable under acidic conditions, and was used for the study of the esterification of acetic acid with ethanol at 343 K in a PVMR with the membrane being in direct contact with the reaction medium. 

Among the publications related to this subject, Jafar et al. [268] used a tubular NaA zeolite membrane prepared on a carbon-zirconia support in the vapor space of an esterification reactor to remove the product, water, formed in the reaction of lactic acid with ethanol catalyzed by p-toluenesulfonic acid. This protected the sensitive zeolite A membrane from acid attack and still allowed high permeation fluxes responsible for the enhanced yields of ethyl lactate. The same group [269] applied a... 

Li X, Kita H, Zhu H, Zhang Z, Tanaka K. Synthesis of longterm acid-stable zeolite membranes and their potential application to esterification reactions. J Membr Sci 2009 339(1-2) 224-223. 

Peters et al. (2005a-d) developed a continuous composite catalytic PV man-brane. Composite catalytic membranes were prepared by applying a zeolite coating on top of a ceramic hf silica membrane. The performance of the composite catalytic membrane was examined in the esterification reaction between acetic acid and butanol (esterification coupling). In the PV-assisted esterification reaction, the catalytic membrane was able to couple catalytic activity and water removal. 

Most of the research pertained on membrane reactors is carried out on gas phase reactions i using ceramic, metal or zeolite membranes. However, the concept can be used as well for liquid phase reactions. A verj specific class of reactions are the condensation or polycondensation reaction in which water is one of the products. Water is easily be removed by pervaporation (see section Vl.4.3 ) and therefore pervaporation can be applied if the reaction temperature is not too high. As example we will use here an esterification reaction [89,90]. This reaction may be carried out in a batch reactor coupled with a pervaporation unit in which water is removed constantly (see figure VI - 76). 

Using a hydrophilic zeolite membrane such as LTA and zeolite T to remove the water from the reaction system by sweep gas or vacuum (pervaporation), the esterification reaction would drive toward the product side with the result of enhanced yields. Beneficial aspects of PVMRs also include low energy consumption and the possibility of carrying out esterification at a selected temperature. 

One of them employs membrane-based separation processes connected to the esterification reaction. In this respect, vapor permeation and pervaporation process have been tested and dn-ee different layouts have been reported for ethyl lactate production. In one of them, membrane module is located outside the reactor unit and the retenate is recirculated to the reactor." " In another scheme, the membrane module is placed inside the reactor, but the membrane does not participate in the reaction directly and simply acts as a filter," " and in the third configuration, membrane itself participates in die reaction catalysis (catalytic membrane reactor)." Different hydrophilic membranes, such as polymeric, ceramic, zeolites and organic-inorganic hybrid membranes were tested. ... 

NaA/polyelectrolyte multilayer-pervaporation membrane showing a greater stability under acidic conditions in comparison with a pure zeolite A membrane and maintaining a high selectivity for water over alcohols. For the same purpose, Kita et al. [181-183] proposed a zeolite T membrane, prepared by ex situ crystallization, for the per-vaporation-aided or vapor-permeation-aided esterification of acetic acid with ethanol. This membrane has a higher acid resistance and can be directly immersed in the liquid-phase reaction mixture. The conversions achieved exceed the equilibrium limit and reached to almost 100% after a stabilization period of 8 h. 

Gao, Yue, and Li (1996) studied the same reaction using a zeolite A-PVA composite membrane (at temperatures ranging from 20 to 50 °C). In this work, together with the pervaporation-aided catalytic esterification of acetic acid with ethanol, the reaction between salicylic acid with methanol was also treated. Among other results, it showed that the continuous removal of water from the system displaced the equilibrium limit (79%), making possible a 95% conversion, when using PVA, PVA -I- KA, and PVA -I- CaA membranes for 20.0, 11.3, and 10.0 h, respectively. 

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