Seed Grant: Construction of a Fixed Bed Reactor for Continuous Production of Biodiesel

Low-cost, high capacity processes for the conversion of biomass into fuels and chemicals are essential for expanding the utilization of carbon neutral processes, reducing dependency on fossil fuel resources, and increasing rural income. The production of biodiesel from vegetable oil represents a well established means of producing liquid fuels from biomass, and one which is growing rapidly in importance. Commercially, biodiesel is produced from vegetable oils, including soybean, rapeseed, and sunflower oil, as well as animal fats. These oils and fats are typically composed of CWC20 fatty acid triglycerides (constituting -90-95% of the oil by weight). In order to produce a fuel that is suitable for use in diesel engines, the triglycerides are converted to the respective fatty acid esters and glycerol by base-catalyzed transesterification with short chain alcohols (generally methanol). Transesterification can be catalyzed by both acids and bases. Industrially, homogeneous base catalysts are used, including sodium or potassium hydroxides or alkoxides. However, removal of the base after reaction is problematical, since the current practice of aqueous quenching with acid results in some degree of saponification (i.e., hydrolysis of the ester and formation of the corresponding metal carboxylate), as well as the formation of emulsions which render recovery of the fatty acid esters difficult [1]. Further, an alkaline waste water stream is generated. In order to circumvent these problems, the use of heterogeneous catalysts has been explored. This approach eliminates the need for an aqueous quench and largely eliminates the formation of metal salts, thereby simplifying downstream separation steps; consequently, biodiesel production can be more readily performed as a continuous process. Against this background, a wide variety of solid bases have been examined as potential transesterification catalysts. Examples include alkaline earth oxides [2-4], K- and Li-promoted oxides [5,6], zeolites [4], anion exchange resins [2] and calcined hydrotalcites [7,8]. However, in general the activity of these catalysts is rather low, while concerns also exist with respect to catalyst durability. During the course of an on-going GOEP-funded project ("Development of Heterogeneous Catalysts for Improved Biodiesel Production"), we have discovered a heterogeneous catalyst that is highly active for the production of biodiesel from soybean oil. The catalyst consists of the calcined form of a layered double hydroxide of the type [AbLi(OH)6](C03)os8mH20, and, according to our data, appears to be the most active heterogeneous catalyst reported to date for the transesterification of soybean oil with methanol. Catalyst recycling studies show that the catalyst maintains a high level of activity over several cycles, although analyses indicate that a small amount of lithium is leached from the catalyst.