(374e) Catalyst-Free Biodiesel Reactions and Post Treatment Using Commercial Polymeric Resins as Opposed to Centrifugation in Facilitating Glycerine Separation

Typical biodiesel processes utilize either acidic catalyst solutions during an esterification reaction, or basic catalyst solutions during transesterification reactions. These reaction pathways result in high reaction conversions, have been successfully implemented in industry, and well studied in academia. There are, however, several challenges to these reactions such as corrosivity of the dilute acidic catalysts and the high cost of process construction material. Additionally, after reaction, both acidic and basic catalysts require extensive neutralization methods that can be costly and create an unsafe working environment. In order to alleviate these concerns, a number of alternative biodiesel processes are being developed including some that use solid catalysts and catalyst-free supercritical alcohol reactions. To take advantage of the catalyst-free alternative process, the current study tested the feasibility of making biodiesel with oil and methanol at supercritical conditions. The biodiesel reactions were conducted using refined soybean oil that consisted mainly of triglycerides at 250 to 325oC and 8000 psi using a 1-liter high-pressure batch reactor. A series of multiple experiments were performed at 6 to 80 molar ratios of methanol to oil. Results from experiments at 300oC and 8000 psi with increasing molar ratios were analyzed using a GCMS and a GC with an FID. The presence of methyl esters in GCMS results suggested that a transesterification reaction occurred during the supercritical methanol and oil reaction. Supplemental analysis using a GC-FID implied that triglycerides were converted into digylceride, monoglyceride, and glycerine byproduct. Based on these results, an optimum % conversion was attained at 27 molar ratios resulting in about 97% conversion. Additional experiments are underway to assess the effect of temperature, reaction kinetics, residence times, and other alcohols on the conversion rate.

During a transesterification reaction, glycerine is formed as a byproduct. A standard reaction using a basic catalyst and methanol at 6 molar ratio, typically results in three distinct phases, which include methanol at the top, FAME (crude biodiesel) in the center, and glycerine at the bottom. However, in the current study under supercritical methanol conditions only two phases (FAME and methanol) were noticed after placing the final product into a separatory funnel and allowing it to settle for up to 24 hours. Based on this observation, it can be speculated that the glycerine phase was distributed between the two phases. To ensure that the glycerine phase was removed from the FAME phase, post treatment techniques were undertaken using a centrifuge at 6000 rpm for 15 minutes or a polymeric resin Amberlite BD10dry at 10% and 25% loading. Under these conditions, Amberlite BD10dry was more effective than centrifugation in reducing free glycerine from crude biodiesel.