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Biodiesel - A Sustainable, Cleaner Burning Alternative Fuel to Crude-Oil Derived Diesel

Biodiesel is a sustainable, cleaner burning alternative fuel to crude-oil derived diesel. Researchers at the Department of Chemical Engineering, Cambridge University have developed a continuous pilot process, consisting of a reactor and various downstream separation steps, to produce biodiesel of a saleable quality. The process uses the novel Oscillatory Flow Reactor [OFR], an intensified plug flow reactor ideally suited to relatively long, two-phase reactions, such as the biodiesel reaction.

Operation of the new 30 litre/hour pilot plant started in October 2004 and following a number of minor modifications, an experimental programme has now started. The first objective is to look at the effect of residence time on conversion and product quality whilst at the same time investigating the performance of the separation/purification train. The feedstock for all the initial trials has been new commercial cooking oil, largely rapeseed oil.

The initial work has been carried out at a reactor temperature of 60oC and a pressure of 1 barg. The methanol ratio has been the literature standard of 0.2 litres per litre of feed oil with a catalyst concentration equivalent (as sodium methoxide) to 3g of NaOH per litre of oil.

The number of runs to date has been dictated largely by the time needed to carry out the analysis, a typical one day run produces about 30 samples which can take over a week to analyse in full.

Results so far are encouraging with conversions (as measured by the remaining tri-glyceride content) of almost 99% with residence times of 30 minutes and 99.5% at 40 minutes. Separation/purification has also worked well with methanol contents below 0.5% and flash points greater than 150oC. Final glycerol content has generally been below 0.02%. The density is 880 kg/m3 and the viscosity at 40oC is 4.2 mPas. The product is thus very close to meeting EU Specification EN14241.

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