Chemical Engineering Journal 138 (2008) 200–206 Monitoring biodiesel production (transesterification) using in situ viscometer Naoko Ellis ∗ , Feng Guan, Tim Chen, Conrad Poon Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, Canada Received 29 August 2006; received in revised form 11 June 2007; accepted 29 June 2007 Abstract Biodiesel, an alternative diesel fuel made from renewable sources, is produced by the transesterification of oil or fat with alcohol. In order to monitor the progress of this reaction, in situ viscosity measurements were taken using an acoustic wave solid state viscometer. This novel concept is reported from the proof-of-concept stage to a pilot plant installation. The viscometer was able to monitor the reaction until the end-point was reached, and could therefore be adapted in the future for process control in a batch transesterification reactor for biodiesel production. © 2007 Elsevier B.V. All rights reserved. Keywords: Biodiesel; In situ viscosity measurement; Transesterification; Process monitor 1. Introduction Biodiesel is becoming well-known as an environmentally friendly fuel due to its non-toxic and biodegradable charac- teristics. It has reduced engine emissions of sulphur oxides, particulate matter and hydrocarbons and, in terms of the car- bon cycle, it is a carbon neutral fuel [1]. Furthermore, biodiesel can be produced from renewable resources, such as vegetable oil, animal fats and waste cooking oil. In Europe and North America, the demand for biodiesel has steadily increased along with gov- ernment subsidies to promote renewable and alternative fuels. In May 2006 the Federal Government of Canada set a target of 5% biofuel content in Canada by 2010. Currently, petroleum fuel still dominates the market due to its favourable economics. The average price per gallon of diesel in the USA in June 2006 was $2.98. B20 (20% biodiesel plus 80% diesel) was $2.92, and B100 (100% biodiesel) was $3.76 [2]. However, the dedication of lab- oratory and industrial investigators to increase the efficiency of biodiesel production will result in a greater availability of biodiesel; and prices will, therefore, become increasingly com- petitive. Thus, the use of biodiesel may soon supplement or possibly replace diesel oil in some applications such as marine engines and domestic heating. ∗ Corresponding author. Tel.: +1 604 822 1243; fax: +1 604 822 6003. E-mail address: nellis@chml.ubc.ca (N. Ellis). Biodiesel is produced by converting triglycerides to alkyl esters. This reaction step has the largest effect on the quality and quantity of the final product. An unsuccessful reaction step for the alkali catalyzed transesterification reaction is most likely caused by a high water or free fatty acid contents and results in a partial or incomplete conversion of the triglycerides, thus adding complexity to the purification step. It is therefore advantageous to be able to monitor the transesterification reaction until the end-point. Conversion and quality analyses of biodiesel are commonly done by chromatographic methods [3,4]. These methods are suitable for laboratory scale analysis, providing detailed compo- sition of the products. However, some of the draw backs are high cost, extensive sample preparation and no real time indication. Size exclusion chromatography (SEC) and Fourier- transformed infrared spectroscopy (FTIR) were used to monitor reaction yields in a study by Zagonel et al. [5]. This allowed the direct monitoring of conversion rates inside the transesterifica- tion vessel, though no details were given on how this was done. Knothe [6] monitored the transesterification of model com- pounds using NIR spectroscopy with a fibre optic probe. One of the challenges in this method was that the peaks of interest were not resolved from others such as that of methanol. In the acid catalyzed transesterification reaction, alcohol-to-oil ratio can be as high as 30:1 [7] in order to drive the equilibrium shift toward the product side. Monitoring such a reaction would be difficult due to the broad peaks presented by the alcohol. In a subse- quent study, Knothe [8] used NIR to quantitatively monitor the 1385-8947/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2007.06.034