Ion-exchange resins as heterogeneous catalysts in biodiesel production from triolein and canola oil
Date
2012-08-14
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Degree Level
Masters
Abstract
Biodiesel is an alternative to petroleum diesel produced from renewable sources. A heterogeneous solid acid catalyst is required to circumvent the issues associated with the continued use of homogeneous catalysts in the production of biodiesel. Ion-exchange resins can be used as catalysts in transesterification. The objective of this research was to identify an ion-exchange resin as an effective heterogeneous catalyst for the production of biodiesel.
Commercial ion-exchange resins from various sources were tested in the transesterification of oils to fatty acid methyl esters (biodiesel). Triolein was used as a model oil feedstock for catalyst screening and statistical optimization of the operating conditions. Amberlyst 15 was the most active ion-exchange resin tested during catalyst screening. Optimized reactor variables were 200˚C, 13 wt% catalyst loading and 1:24 oil to alcohol molar ratio. Conversion of triolein to products at 2 hours was 97 mol%. The acid value of the products was 56 mg KOH/g sample. Water was added to the reactants up to 2 wt% to determine if a hydrolysis reaction was responsible for this increase in acid value and to determine whether water would have a hindering effect on transesterification. Water addition did not have a measurable effect on the reaction products up to 1 wt%. At 2 wt%, conversion to products decreased slightly. Free fatty acid addition up to 15 wt% to simulate low quality feedstock had a negligible impact on conversion to products. From the water and acid value testing it was determined that the catalyst was performing the hydrolysis, esterification and transesterification reactions. In longevity experiments, the catalyst was reused once without an impact on conversion to products. Use of canola oil from green seed as a low cost and low quality feedstock demonstrated similar reaction results compared to results using triolein as feedstock.
The reaction kinetics of Amberlyst 15 in transesterification were studied at temperatures lower than the optimal temperature to minimize the effects of the hydrolysis and esterification side reactions. Alcohol to oil molar ratio was increased in order to increase conversion to products at the lower temperatures. In the kinetic study, the temperatures examined were 100˚C, 110˚C and 120˚C. Additional reaction parameters were: catalyst loading of 13 wt%, 1:77 oil to alcohol molar ratio, 600 RPM stirring speed and 50 grams of canola oil. This experiment demonstrated a conversion to products of 79 mol% after 72 hours. The rate constants of the three reversible reactions were calculated using a MATLab program to simulate transesterification reaction kinetics. Reaction rate constants for the forward reactions at 120˚C for TG to DG, DG to MG and MG to GL were 0.08, 0.22 and 6.5 L/mol/day, respectively. The activation energy for the rate limiting step (TG to DG) was 120 kJ/mol. Diffusion and internal mass transfer limitations were neglected during the kinetic study due to the results from experiments with a crushed catalyst, the large pore size of Amberlyst 15, the rate of agitation and the high activation energy calculated from experimental results.
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Keywords
biodiesel, transesterification, ion-exchange resins, triolein, statistical optimization
Citation
Degree
Master of Science (M.Sc.)
Department
Chemical Engineering
Program
Chemical Engineering