Biodegradable trimethylolpropane [2-ethyl-2-(hydroxymethyl)-1,3-propanediol] esters of rapeseed oil fatty acids were synthesized by transesterification with rapeseed oil methyl ester both by enzymatic and chemical means, both in bench and pilot scales. Nearly complete conversions were obtained with both techniques. A reduced pressure of about 2 to 5 kPa, to remove the methanol formed during transesterification, was critical for a high product yield. The quantity of added water was also critical in the biocatalysis. Candida rugosa lipase was used as biocatalyst and an alkaline catalyst in chemical transesterifications. In biocatalysis the maximum total conversion to trimethylolpropane esters of up to 98% was obtained at 42°C, 5.3 kPa, and 15% added water. The maximum conversion of about 70% to the tri-ester was obtained at the slightly higher temperature of 47°C. The reaction time was longer in the biocatalysis, but considerably higher temperatures were required in chemical synthesis. In the chemical synthesis tri-ester yields increased when the temperature was first held at 85 to 110°C for 2.5 h and subsequently increased to up to 120°C for 8 h. The trimethylolpropane esters obtained were tested as biodegradable hydraulic fluids and compared to commercially available hydraulic oils. The hydraulic fluids based on trimethylolpropane esters of rapeseed oil had good cold stability, friction and wear characteristics, and resistance against oxidation at elevated temperatures. JAOCS 75, 1557-1563 (1998) . FIG. 3. Effect of the type of carrier on the total conversion of trimethylolpropane to trimethylolpropane esters (C. rugosa lipase 40%, w/w; added water 15%, 47°C, 5.3 kPa, 42 h). For abbreviation see Figure 1. FIG. 4. Typical time courses of transesterification between trimethylol-propane and rapeseed oil methyl ester, catalyzed by (a) C. rugosa lipase immobilized in Duolite ES 561 (47°C, 5.3 kPa, biocatalyst 40%, w/w; water 15% of substrates) and (b) immobilized R. miehei lipase Lipozyme IM 20 (58°C, 5.3 kPa, biocatalyst 40%, w/w, no added water); ◆ trimethylolpropane tri-ester; ■ ■ trimethylolpropane di-ester; ▲ ▲ trimethylolpropane mono-ester; × rapeseed oil methyl ester; • • unknown).
Lipase biocatatysis was investigated as a tool for the production of butyl oleate and rapeseed oil 2-ethy]-I -hexy[ ester by esterification and transesterification, respectively. We screened 25 commercially available [ipases and found that butyl oleate was produced at high yields from oleic acid and 1butanol by [ipases from Candida rugosa, Chromobacterium viscosum, Rhizomucor miehei, and Pseudomonas fluorescens. The initial water content of the system, lipase quantity, and the molar ratio of t-butanol to oleic acid were important factors in influencing the ester yield. In general, no ester was formed without the addition of water. The exception was Ch. viscosum lipase, which yielded 98% of ester in 12 h with t-butanol excess without additional water. The addition of 3.2% water increased the initial rate of reaction. With an oleic acid excess and only 0.3% lipase, C. rugosa and R. miehei lipases yielded 94 and 100% esters with initiaf water contents of 3.2 and 14%, respectively. Lipase-catatyzed alcoholysis of [ow-erucic acid rapeseed oil and 2-ethyl-I -hexanol without additional organic solvent also was studied in stirred batch reactors. In this case, C. rugosa lipase was the best biocatalyst with an optimal 2-ethyl-1 -hexanol to rapeseed oil molar ratio of 2.8, a minimum of 1.0% added water, and 37°C. An increase in temperature up to 55°C increased the rate of reaction but did not affect the final ester yield. The enzyme was inactivated at 60°C. Under optimal conditions, the ester yield increased from 88% in 7 h to nearly complete conversion in 1 h when the lipase content was increased from 0.3 to 14.6%. In a 2-kg small pilot scale, up to 90% conversion (97% of theoretical) was obtained in 8 h at 37°C with 3.4% lipase in the presence of Amberlite XAD-7 resin with 3% added water.
Lipase-catalyzed transesterification (alcoholysis) of lowerucic acid rapeseed oil and 2-ethyl-l-hexanol without an additional organic solvent was studied in stirred batch reactors. Of a number of commercially available enzymes investigated, the best results were obtained with a Candida rugosa Upase. The optimal transesterification conditions were an oil/alcohol molar ratio of 1:2.8, a minimum of 1.0% (w/w) added water, and with a temperature of 37-55~ Under the optimal conditions, a nearly complete conversion was obtained in one hour with 14.6% (w/w) lipase, whereas 0.3% (w/w) lipase required 10 h for similar results. The enzyme was inactivated at 60~ KEY WORDS: Alcoholysis, biocatalysis, enzyme, 2-ethyl-l-hexanol, 2-ethyl-l-hexyl ester, lipase, rapeseed oil, transesterification.
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