Production and treatment of rapessed oil methyl esters AS alternative fuels for diesel engines

Rapeseed oil methyl esters are important alternative diesel fuels based on renewable sources. A discountinuous plant production of methyl esters (ME) is described using two-stage low-temperature transesterification of cold pressed rapeseed oil with methanol at temperatures up to 70°C. The total methanol:acyls molar ratio is 4:3 with an optimum distribution of methanol between the two stages. NaOH 4% in methanol is used as the catalyst. The final treatment of ME with phosphoric acid and ammonia provides for an exchange of ashy soap forms in ME for ashless forms, thus rendering ME non-corrosive.

Key words: rapeseed oil methyl esters; alternative diesel fuels; diesel fuel substitutes; biofuels

Running title: Rapessed Oil Methyl Esters

* To whom all correspondence should be addressed

In looking for new energy sources, attention is naturally being focused on biomass as a reliable and continuously renewable resource able to saturate the needs of the society for energies (Ruiz-Altisent, 1994).

In particular, the following alternatives are being considered with respect to the substitution of classical liquid fuels:

- vegetable oils and their derivatives, in particular methyl esters,

- alcohols (ethanol, methanol) and ethers (methyl-t-butyl ether, ethyl-t-butyl ether).

Curently, there is a number of serious reasons for using biofuels as alternative fuels:

- expected growth of prices of fossile liquid fuels in the near future, related to the gradual exhaustion of crude oil sources in the next 80 - 100 years;

- overproduction of agricultural products, in particular in developed countries, and the offer to use surplus land to produce products for technical uses. Similarly, devastated land excluded from food production may also be used for this purpose;

- environmental protection. Compared to traditional fuels, the contents of hamrful emissions in exhaust gases are markedly reduced. Biofuels are non-toxic and fully biologically degradable. Their sulfur content is negligible and they provide a better safety of handling. Burning of fossile fuels releases carbon dioxide which accumultes in the atmosphere and represents a potential source of drastic changes of Earth´s climate, although experts differ in their opinions concerning the influence of this compound on the greenhouse effect.

Vegetable oils can be obtained from a number of plants, being mainly present in seeds or fruits. In Europe, the most important seems to be sunflower, but mainly rapeseed oil. The rape (Brassica napus) yields high crops reaching to approx. 3 t/hectar, it grows well at higher altitudes as well as in submountainous areas. It can be grown at the same piece of land in four-year intervals without compromising its yields, the seed contains approx. 42 w% oil. It is a preferred agricultural intermediate since it does not exhaust the soil. The orientation to the variety 00 with negligible contents of antinutritional factors (erucic acid and glucosinolates) allows to use the cake as a valuable component of fodder mixtures.