(600am) Rapid Screening of Heterogeneous Catalysts for Biodiesel Production Via Triglyceride Transesterification
AIChE Annual Meeting
Wednesday, November 19, 2014 - 6:00pm to 8:00pm
Triglyceride transesterification is an important reaction in productions of fatty acid alkyl esters (biodiesel) used as an alternative to petro-diesel fuel. Conventional biodiesel process occurs mainly by homogenous catalysis which adds to the cost of the operation as a result of extra costs of downstream purifications. Therefore, heterogeneously catalysed biodiesel process has the potential to reduce the cost of production. In this study, heterogeneous catalysts were screened both in batch and continuous mode for their activity, reusability and water tolerance in catalysis of triglycerides (rapeseed oil and triacetin) transesterification with methanol. The catalysts investigated were a strontium zirconate-based solid and amberlyst resins functionalised with sulphonic acid (AmberlystTM 70) and quaternary ammonium hydroxide (AmberlystTMA26 OH) groups. These catalysts were screened either suspended or in packed bed using a mesoscale oscillatory baffled reactor (integral baffles) as a multiphase mixing reactor. The mesoscale oscillatory baffled reactor also allowed for the investigations of the process parameters in batch and continuous mode using small quantity of reagents which reduces the amount of waste generated. Effects of operating conditions, such as catalyst types and loadings, feed molar ratios (6:1 – 30:1), water content in the range of 0 – 2.5% (v/v), mixing intensity and temperatures (40 – 60°C) were investigated.
The results clearly indicated that methyl esters yield from the rapeseed oil and triacetin transesterification increased with temperature, catalyst loading and methanol molar ratio, e.g. after 2h reaction time with 3wt% strontium-zirconate-based catalyst, the fatty acid methyl esters (FAME) yield increased from 86.3% at 40°C to 91.7% at 60°C at a 12:1 methanol to rapeseed oil molar ratio, and from 85.6% at 6:1 molar ratio to 96.8% at 24:1 molar ratio. However, the FAME yield decreased significantly with water content: it was 92% at 0% (v/v) water but only 12% at 2% (v/v) water after 2h reaction time. Substantial loss in activity of the strontium zirconate-based catalyst was observed as it leached into the methanol phase, for instance the FAME yield after 2h reaction time decreased from 96.8% for fresh catalyst to 0.3% after 2 cycles at 60°C and 24:1 molar ratio. The AmberlystTM 70 and AmberlystTM A26 OH resin catalysts were active in catalysing rapeseed oil and triacetin transesterification with methanol. But lower conversions were obtained for the rapeseed oil, e.g. the FAME yields after 60min reaction time at 60°C were < 1% for AmberlystTM 70 and ~7% for AmberlystTM A26 OH compared to ~99% for the triacetin reaction. The amberlyst resin catalysts were further screened continuously in dynamic and multi-steady states using methanolysis of triacetin. There was consistency in the triacetin conversions at various residence times for the dynamic and multi-steady state screening, indicating that there was no catalyst leaching or deactivation. This was a demonstration of the catalytic stability and reusability of the AmberlystTM 70 and AmberlystTM A26 OH resins for triacetin transesterification. The AmberlystTM A26 OH resin had substantially higher catalytic activity for triacetin transesterification, even at lower methanol molar ratio (6:1), as >98% triacetin conversion was achieved after 20min reaction time and 60°C compared to 83% for the AmberlystTM 70 at 30:1 methanol molar ratio. Presence of water in the methanol feed (2.5% (v/v)) resulted in lower triacetin conversion for the AmberlystTM 70, but the catalyst recovered its activity after the feed line was switched to anhydrous methanol. However, this was not the case for the AmberlystTM A26 OH which lost its activity when methanol that contained water was used. Finally, this study shows that heterogeneously catalysed biodiesel processes based on the AmberlystTM 70 and AmberlystTMA26 OH resins could be developed. The dynamic and multi-steady states screening techniques allows for rapid means of assessing various solid catalysts.