Heterogeneous transesterification

Heterogeneous Transesterification and Esterf cation Catalysts 333 MeOH HaSOj... 

Esterfip-H A process for converting vegetable oils to methyl esters for use as diesel fuel ( biodiesel ). A heterogeneous transesterification catalyst is used. Developed by IFP and Sofiproteol, France licensed by Axens. Proposed for operation in Sete, France, in 2006, and by Perstorp Oxo in Stenungsund, Sweden, in 2007. 

Alba-Rubio, A. C., Santamaria-Gonzalez, J., Merida-Robles, J. M., Moreno-Tost, R., Martm-Alonso, D., Jimenez-Lopez, A., and Maireles-Torres, P. Heterogeneous transesterification processes by using CaO supported on zinc oxide as basic catalysts. Catal Today 149,281-287 (2010). 

Biodiesel from Transesterification of Cottonseed Oil by Heterogeneous catalysis... 

Generally, the above transesterification reactions are catalyzed by strong acids or alkalis [1, 2]. In the homogeneous catalytic process by acids or alkalis, neutralization is required of the product. This post-treatment produces waste water, and increases equipment investment and production cost. Recently, more attention has been paid to the heterogeneous catalysis process [3] for an easier production process and to reduce pollution of the environment. 

The activities of the heterogeneous catalysts toward transesterification were measured. 

In this communication a study of the catalytic behavior of the immobilized Rhizomucor miehei lipase in the transesterification reaction to biodiesel production has been reported. The main drawbacks associated to the current biodiesel production by basic homogeneous catalysis could be overcome by using immobilized lipases. Immobilization by adsorption and entrapment have been used as methods to prepare the heterogeneous biocatalyst. Zeolites and related materials have been used as inorganic lipase supports. To promote the enzyme adsorption, the surface of the supports have been functionalized by synthesis procedures or by post-treatments. While, the enzyme entrapping procedure has been carried out by sol-gel method in order to obtain the biocatalyst protected by a mesoporous matrix and to reduce its leaching after several catalytic uses. 

In biomass transesterification it is necessary to develop (basic) catalysts with high conversion efficiency operating under heterogeneous conditions, which avoid the presence of catalyst residues in the final product and allow a cleaner product with concurrent savings of catalyst, as well as simpler separation of the reacted materials from the reactants, e.g., integration of catalysts and membrane in a new advanced reactor design. 

A 50% functionalization evokes the interesting question, bearing in mind facile transesterification, of how the fluoroalkyl chains will be distributed over the molecules and how they will be distributed on one particular molecule This question has been examined in detail for dendrimers of the poly(propyleneimine) type functionalized with stearic acid [33]. It was proven that the compositional heterogeneity (distribution of degree of substitution) is random, but the positional heterogeneity (spatial distribution of the substituents over the dendrimer molecule) is not random. However, due to flexibility, no particular effect of the spatial distribution can be observed. Unlike the dendrimers, we expect the hyperbranched polyesteramides to be stiffer, so that spatial distribution could lead to interesting effects if the molecule were composed of a functionalized side and a non-func-tionalized side (Fig. 28), as shown possible for dendrimers via a convergent synthesis [34]. 

In this chapter, we report just a few selected examples of heterogeneous catalytic systems for the esterification of fatty acids and for the simultaneous esterification and transesterification of acidic oils and fats, and we discuss the use of selective hydrogenation as a tool for the production of high-quality biodiesel from non-edible raw materials. 

The use of heterogeneous basic catalysts for the transesterification of triglycerides has long been considered the main tool to reduce processing costs in the production of biodiesel, as it would lead to simplified operations and eliminate waste streams. 

Catalysis by Solid Acids. Two aspects are considered here. The first aspect is concerned with transesterification reactions catalyzed by solid acids. Unfortunately, little research dealing with this subject has been reported in the literature. The second aspect deals with esterification reactions of carboxylic acids (or FFAs). This second part addresses an important characteristic of inexpensive TG feedstocks, i.e., high FFA content. Ideally, an active solid catalyst should be able to carry out transesterification and esterification simultaneously, thus eliminating pretreatment steps. It is likely that heterogeneous catalysts that perform well in esterification should also be good candidates for transesterification since the mechanisms for both reactions are quite similar. 

Transesterification Reactions. The heterogeneous acid-catalyzed transesterification of TGs has not been investigated as much as its counterpart, the base-catalyzed reaction. Various solids are available with sufficient acid strength to be effective catalysts for the named reaction. Among the solid acids available are functionalized polymers, such as the acid forms of some resins, as well as inorganic materials, such as zeolites, modified oxides, clays, and others. Some of these solids have already been found to be effective in transesterification reactions of simple esters and (3-ketoesters. 

An important issue concerning the use of heterogeneous catalysts for biodiesel synthesis is the lack of systematic research exploring the principles of solid catalyst activity for transesterification of TGs and esterification of FFAs with alcohols. For instance, the question about the true catalytic nature of some solid bases, called heterogeneous, remains unanswered. For example, the most active heterogeneous catalysts reported to date is Ba(OH)2. However, due to its... 

Because of the difficulty encountered in acetylation of the complexed alcohol, it was of interest to see if the ester complex behaves in a normal fashion. Refluxing (HaO) [Cr(AcO-A)2] in methanol or ethanol caused methyl or ethyl acetate to be formed, while refluxing in ethyl propionate formed ethyl acetate. When the potassium salt was used in place of the oxonium salt no transesterification was observed this could be due to the necessity of acid catalysis or a difference in solubility in these essentially heterogeneous systems. The oxonium salt, (H30) [Cr(AcO-A)2], appears to have typical ester reactivity. 

The reactants and inorganic catalysts used in kinetic studies of heterogeneous catalytic esterifications (transesterifications) are summarised in Table 20. As can be seen, no systematic comparative study with more than one catalyst (with the exception of paper [406]) has been performed by any one worker. The greatest attention was paid to silica gel [407— 411]. The reactants were usually low molecular weight acids and alcohols a typical pair of reactants is acetic acid—ethanol. Only in one study [126] was the structure of the reactants systematically varied in order to establish the effect on the reactivity. 

In most homogeneously catalysed esterifications, the protonated species is considered to be formed from the acid (or from the ester in transesterification) [397,398,467]. Starting with this view, Bochner et al. [449] assumed a mechanism for heterogeneous esterification [see eqn. 

Very often, the transesterification reaction implies the need for an alkylene or CC (e.g., EC or PC) and an alcohol in the presence of either a homogeneous or heterogeneous acidic or basic catalyst [268], to co-produce dialkyl carbonate and the alkane diol or glycol (Equation 7.30). 

When Mg-Al-C03 hydrotalcite was tested for the synthesis of DMC via transesterification, this heterogeneous basic catalyst showed good activity for the process [287]. Cu-KF/MgSiO was also reported to be capable of catalyzing such a process [84]. 

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