Transesterification of trimethylolpropane and rapeseed oil methyl ester to environmentally acceptable lubricants

Abstract

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).

Lubricants from renewable energy sources – a review

“…Some examples of esterification and transesterification products are: trimethylolpropane (TMP) esters derivatives of TMP and rapeseed oil methyl ester (51) or jatropha methyl ester (JME) (52). They possess cold stability, friction and wear characteristics, and resistivity against oxidation at elevated temperatures.…”

Green waxes, adhesives and lubricants

“…Transesterification (Anand et al 1998;Bírová et al 2002;Hörner 2006) is one of the common ways to chemically break the molecules of the raw vegetable oils into their methyl or ethyl esters with glycerol as a by-product. Transesterification reactions of the partially hydrogenated and cyclized ester vegetable oils are important because these reactions yield monoesters of vegetable oils with better thermal stability and lower freezing points than the vegetable oils as such (Uosukainen et al 1998;Bokade & Yadav 2007). The glycerol obtained as a by-product commands as much market value or more than the monohydric alcohols used for transesterification.…”

Lubrication properties of trimethylolpropane esters based on palm oil and palm kernel oils

“…However, to function as a lubricant, their inherent characteristics of inadequate oxidation stability, poor low temperature properties, and hydrolytic stability are impediments that must be overcome. To eliminate these negative properties, one approach is to convert the oils to natural synthetic esters through various structural modifications [4][5][6]. The new ester may have better pour point (PP), thermal and oxidative stability properties but could also exhibit negative traits such as inferior viscosity, viscosity index (VI), and biodegradability.…”