Esterification reactions, zeolite membrane reactors

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... 

PV is a promising option to enhance the conversion of reversible condensation reactions in which water is formed as a by-product. Peters et al. (2005) prepared composite catalytic membranes by a dip-coating technique. Composite catalytic membranes have been prepared by applying a zeolite coating on top of ceramic hf silica membranes. In the PV-assisted esterification reaction, the catalytic manbrane was able to couple catalytic activity and water removal. A reactor evaluation proved that the outlet conversion of the catalytic PV-assisted esterification reaction exceeded the conversion of a conventional inert PV membrane reactor, with the same loading of catalyst dispersed in the bulk liquid. Further, the performance of the zeolite-coated PV membranes can be increased by optimization of the catalytic layer thickness or by an increase in catalytic activity. 

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). 

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. ... 

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