Investigating the Use of Ion Exchange Resins for Processing Biodiesel Feedstocks

Ion exchange resins, commonly used in water treatment, demonstrate promise for the production of biodiesel from biomass feedstocks. The goal of this presented PhD research is to investigate novel uses of ion exchange resins for processing biodiesel feedstocks. Specifically, this research explored using ion exchange resins to remove free fatty acids (FFA) from soybean and waste cooking oils, catalyze transesterification of soybean oil, and catalyze in-situ conversion of dried algal biomass to biodiesel and other recoverable organics.

The effect of temperature, moisture content, mixing rate, and resin drying on deacidification of soybean oil with 5% oleic acid feedstock was explored using Dowex Monosphere MR-450 UPW within a batch reactor. The resins were observed to remove up to 83 +/- 1.3% of FFA from soybean oil with less than 5% moisture content while operated at a 20% resin loading at 50 degrees C while mixing at 550 rpm. Once operation characteristics impacting deacidification were evaluated, a series of experiments were carried out to demonstrate the use of mixed bed resin to remove FFA from waste cooking oils. An investigation of wash solutions capable of regenerating the resins was also carried out. Using methanol to regenerate the resins resulted in more than 40% FFA removal over three regeneration cycles, highlighting the utility of resin regeneration as a cost saving measure.

Transesterification of soybean oil on Amberlyst A26-OH, a basic ion exchange resin, in the presence of excess methanol was carried out to determine the mechanism of the reaction occurring on the surface. A batch reactor approach was used and reactions were carried out with and without FFA present in the soybean oil feed stock at a 20% resin loading at 50 degrees C while mixing at 550 rpm. When FFA was present in the feedstock and methanol is present in excess, the rate constant for methanol consumption increased. Based upon model fitting, the rate constant of methanol consumption was determined to be 2.08 x 10^-7 /sec with FFA absent and 5.39 x 10^-4/sec when FFA is present when the Eley-Rideal model was used to fit the data.

In-situ conversion of dried algal biomass to biodiesel and other recoverable organics was investigated using a batch reaction system with 1 gram of algae. The system was operated with 40:60 methanol:hexane as the solvent system operated at 50 degrees C while mixing at 550 rpm over a range of catalyst loadings. The highest observed ester yield, approximately 60% yield (37 mg_ester/g_algae), was observed when air dried algae was reacted with a 20% resin. An evaluation of the reaction products showed a mixture of esters, phytol, alcohols, and ketones; highlighting the complexity of the reactions occurring during in-situ biomass conversion.