Low-pressure transesterification

New Method of Low-Pressure Transesterification. The modified process has the following aims ... 

Ecological Aspects of the New Low-Pressure Transesterification Process with Pre-Esterific on. In the earlier process, refined oil was used. The waste streams produced in the oil refining process are completely avoided by use of preesterification. Moreover, the waste fatty add produced in the low-pressure transesterification process can be reutilized. 

With the aim of proposing simple environmentally benign procedures, simultaneous transesterification and transglycosylation reactions were carried out with -butyl ( -butyl ot-D-mannopyranosiduronate) 4 in fatty alcohols (octyl, decyl, dodecyl, tetradecyl, hexadecyl alcohols) without any additional solvent, at 65°C, in the presence of MSA and at low pressure (2-5 mbar) in order to eliminate the butanol formed in the reaction. The main products are the -alkyl ( -alkyl ot-D-mannopyranosiduronates) 6 which are the thermodynamically and kineticaUy products. A minor compound was defined as the -alkyl o-mannofuranurono-... 

The transesterification reaction is typically carried out in a CSTR by continuously feeding a paste of premixed DMT/diol into a diol-ester prefllled reactor operating between 160 and 240 °C. Typically DMT/diol molar ratios of 1 2 to 1 2.2 are used for PET and 1 1.1 to 1 1.5 for PBT. The reaction for PET is catalyzed by a metal acetate. Zinc acetate is commonly used, but antimony, barium, calcium, and magnesium acetates may also be used. For PBT titanium orthoesters, such as tetra-butyl titanate, are employed as catalysts. The CSTR operates at low pressures, 0.1 to... 

Molecular distillation process represents a type of vaporization at low pressure and low temperature. The transesterification can also be used as pre-step in molecular distillation process, like centrifuge distillatory. Batistella and Maciel studied the extraction in palm oil with 2,400 ppm of carotenoids applying a centrifugal distillator and a falling film distillator. The first process obtained a decomposition of 12 % at 155 °C and 25 % at 175 °C. The centrifugal distillator results in loss of 13 % at 190 °C and 14 % at 210 °C [83]. 

During the transesterification, oligomerization is possible. The oligomer content does not increase before BD is removed from the reaction medium. Transesterification, similar to PET and PBT homopolymer synthesis, is carried out in excess of glycol, and the conversion is most often 80-90%. Thus, the reactions are carried out in the low pressure melt polycondensation stage [143-147] and in the post-polycondensation process [112,148-151]. 

Esters. Neopentyl glycol diesters are usually Hquids or low melting soflds. Polyesters of neopentyl glycol, and in particular unsaturated polyesters, are prepared by reaction with polybasic acids at atmospheric pressure. High molecular weight linear polyesters (qv) are prepared by the reaction of neopentyl glycol and the ester (usually the methyl ester) of a dibasic acid through transesterification (37—38). The reaction is usually performed at elevated temperatures, in vacuo, in the presence of a metallic catalyst. 

Higher molecular primary unbranched or low-branched alcohols are used not only for the synthesis of nonionic but also of anionic surfactants, like fatty alcohol sulfates or ether sulfates. These alcohols are produced by catalytic high-pressure hydrogenation of the methyl esters of fatty acids, obtained by a transesterification reaction of fats or fatty oils with methanol or by different procedures, like hydroformylation or the Alfol process, starting from petroleum chemical raw materials. 

Compared with the fatty alcohol sulfates, which are also oleochemically produced anionic surfactants, the ester sulfonates have the advantage that their raw materials are on a low and therefore cost-effective level of fat refinement. The ester sulfonates are produced directly from the fatty acid esters by sulfona-tion, whereas the fatty alcohols, which are the source materials of the fatty alcohol sulfates, have to be formed by the catalytic high-pressure hydrogenation of fatty acids esters [9]. The fatty acid esters are obtained directly from the fats and oils by transesterification of the triglycerides with alcohols [10]. 

Alkyl esters often show low reactivity for lipase-catalyzed transesterifications with alcohols. Therefore, it is difficult to obtain high molecular weight polyesters by lipase-catalyzed polycondensation of dialkyl esters with glycols. The molecular weight greatly improved by polymerization under vacuum to remove the formed alcohols, leading to a shift of equilibrium toward the product polymer the polyester with molecular weight of 2 x 10" was obtained by the lipase MM-catalyzed polymerization of sebacic acid and 1,4-butanediol in diphenyl ether or veratrole under reduced pressure. ... 

A wide variety of monomers, such as (3,5-dibromophenyl)boronic acid, 3,5-bis(trimethylsiloxy)benzoyl chloride, 3,5-diacetoxybenzoic acid, and 2,2-dimethylol propionic acid have been used for the synthesis of hyperbranched polymers. A selection of these polymers are described in Sect. 3. The majority of the polymers are synthesized via step-wise polymerizations where A B monomers are bulk-polymerized in the presence of a suitable catalyst, typically an acid or a transesterification reagent. To accomphsh a satisfactory conversion, the low molecular weight condensation product formed during the reaction has to be removed. This is most often achieved by a flow of argon or by reducing the pressure in the reaction flask. The resulting polymer is usually used without any purification or, in some cases, after precipitation of the dissolved reaction mixture into a non-solvent. 

The above acid-catalyzed polycondensations were carried out at more than 100 °C, whereas Takasu et al. reported room temperature polyesterification with scandium trifluoromethanesulfonate [Sc(OTf)3] or scandium trifluo-romethanesulfoimide [Sc(NTf2)3] [27,28]. Thus, the direct polycondensation of methylsuccinic acid and 1,4-butanediol proceeded in bulk under reduced pressure (0.3-30 mmHg) using 1.4 mol % of Sc(OTf)3 at 35 °C for 96 h to afford poly(butylene methylsuccinate) with Mn of 12400 (Scheme 5). When HfCl4-(THF)2 was used in this room temperature polymerization instead of Sc(OTf)3, only low molecular weight polyester (Mn = 1100) was afforded. The scandium catalysts did not promote transesterification ethanol selectively reacted with acetic acid even in the presence of equimolar methyl acetate. 

We conclude that a commercial immobilized lipase from C. antarctica (Novozym 435) was stable in SCC02 for all experimental conditions investigated. Based on the results obtained here and comparison of them with the results obtained by other investigators, it can be concluded that the magnitude of pressure, temperature, decompression rate, and exposure time needed to inactivate the enzyme strongly depends on the nature and the source of enzyme and, primarily, whether the enzyme is in its native or immobilized form. For the purpose of using this enzyme to catalyze the transesterification reaction of vegetable oils in order to produce esters, the results obtained herein are relevant, because the immobilized lipase can be used with low activity loss at typical conditions of temperature and pressure employed in many biotransformations of raw materials. 

The transesterification reaction can be catalyzed by enzymes, the most common being the lipase. The reaction takes place at normal pressure and temperatures 50 to 55 °C with low energy consumption. The yield of methanolysis depends on several factors as temperature, pH, type of micro-organism producing the enzyme, the use of cosolvents, etc. However, low yields in methyl esters and very long reaction times make the enzymatic processes not competitive enough at this time [9, 11, 17]. 

The inline measurement of the water vapour pressure makes it possible to monitor its progress in the course of the reaction. The water vapour pressure does not stay constant but slowly decreases until a very low value is reached. In the absence of the enzyme however no such decrease was detected (Figure 6). We believe that the enzymatically catalyzed hydrolysis of isopropenyl acetate is responsible for this decrease in water content. The hydrolysis occurs as a parallel reaction to the transesterification of isopropenyl acetate to menthyl acetate. It is not yet clear how significant the contribution of this parallel reaction to the overall decrease in (transesterification)reactivity is. If we assume that the rate constants for the hydrolytic reaction are of the same order of magnitude as those for the transesterification such a parallel reaction would lead to a significant decrease in the rate of transesterification as the water activity rises. At low water activities the hydrolytic reaction might be responsible for the observed decrease in reactivity. Very likely however the accumulation of water around the enzyme... 

As ILs are nonvolatile, products can also be isolated be means of distillation. Alternatively, a reduced pressure can be applied to remove volatile products such as water or low alcohols, driving the reaction toward product formation. The latter technique was demonstrated by Itoh and co-workers, who continuously removed methanol from the transesterification of a methyl ester in [BMIM][PF ] [15]. The reaction was catalyzed by the B-lipase from Candida antarctica (CaLB). Itoh s group also most recently identified [BMMIM)[BF4] (BMMIM = l,2-dimethyl-3-butyl-imidazoHum) to be an excellent solvent for setting up a lipase-recycling system using vinyl acetate as the acyl donor [16]. The lipase was used 10 times here without loss of reactivity and enantioselectivity. 

The PTT is aromatic polyester prepared by the melt polycondensation of 1,3-propanediol (1,3-PDO) with either TPA or dimethyl terephthalate (DMT). The PTT is synthesized by the transesterification of propanediol with dimethylene terephthalate or by the esterification of propane diol with TPA. The reaction is carried out in the presence of hot catalyst like titanimn butoxide (Ti(OBu) ) and dibutyl tin oxide (DBTO) at a temperature of 260°C. The important by-products of this reaction include acrolien and allyl alcohol (Chuah, 2001). Direct esterification of propane diol and TPA is considered as the least economic and industrial method. The reaction is carried out in the presence of a heel imder a pressure of 70-150 kPa at a temperature of 260°C. The heel is usually referred to the added PTT oligomers which act as a reaction mediiun and increase the solubility of TPA (Chuah, 2001). Recent studies by different groups show that the selection of the catalyst plays a major role on the reaction rate and PTT properties. Commonly used catalysts like titanium (Doerr et al., 1994), tin (Kurian and Liang, 2001 Fritz et al., 1969) and antimony (Karayannidis et al., 2003 Fitz et al., 2000) compounds have their own limitations. Titanimn-based catalysts are active but the PTT is discolored, antimony-based catalysts are toxic and only active in polycondensation while tin-based compounds have lower catalytic activity. Karayannidis and co-workers (2003) reported the use of stannous oetoate ([CHj(CH2)3CH(C2Hj)COO]jSn) as the catalyst for PTT synthesis but its catalytic activity is poor, resulting in a low molecular weight PTT which was confirmed... 

---