Document Type

Dissertation - University Access Only

Award Date

2010

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

Abstract

Biodiesel is a renewable fuel alternative being developed, as its similarities to petroleum diesel allow for distribution by available infrastructure and direct use in diesel engines. Biodiesel is comprised of monoalkyl esters of long chain fatty acids derived from vegetable oils and animal fats. The majority of commercial operations utilize transesterification catalysis to result in the fuel alternative and glycerol by-product. Though the final product is environmentally benign, current production is not ecologically sound on large-scales due to necessary washing of the caustic mixture and separation of by-products. The objective of this research was to develop a recyclable heterogeneous catalyst for biodiesel synthesis capable of reacting recycled oils and waste grease feedstock and whose optimal catalytic conditions are environmentally benign on an industrial scale. Synthesis of a titanium niobate multiphase crystal was optimized for application in biodiesel processing. Optimal catalyst synthesis ratio for biodiesel application was I :2: I, TiO2:K2CO3:NbO5. In the synthesis procedure, impregnation of K2CO3 serves as a promoter for titanium support on which niobium oxide is deposited. Catalyst is calcined at 500°C for three hours to achieve optimal crystal form. Catalyst character was studied by XRD and BET analysis, confirming under synthesis conditions a robust, amorphous crystal results. Multiphase crystal form is maintained through multiple recyclings of catalyst. Optimal calcining conditions reduce operation energy input and result in an effective catalyst for biodiesel application. Biodiesel processing variables were optimized for the titanium niobate multiphase crystal catalyst including, catalyst activation/reactivation conditions, reactant ratios, reaction temperature, and internal stir rate. Transesterification of soybean oil with methanol achieved 99% conversion in 5 minutes. Reaction was in an open system under reflux with an internal temperature of 67°C and stir rate at 300 rpm. Molar ratio of methanol:oil was 3: l using 7.4 wt.% catalyst. Restaurant grease resulted in equal conversion in one hour under pressure of 2.72 atm and temperature of 105°C. In an open system, the waste grease required 15 hours to reach similar conversion. Recycling the catalyst with potassium salt regenerated surface active sites and maintained catalyst efficiency up to 21 times, with no decrease expected in continued use. Quantitative analysis of transesterification was by 1 H NMR. Optimized time of reaction and reaction conditions are a significant improvement over current industrial processing systems and practical for large-scale implementation. The quality of biodiesel is determined by the level of free and bonded glycerol byproduct. Elevated glycerol concentration leads to injector fouling and excessive carbon deposits. To date, the standardized analytical method utilizes GC, however cost and availability to manufacturers limits this technique for strict quality control. A bench-top method was developed to extract glycerol by-product by normal-phase SPE column. In the optimized method, glycerol is concentrated and reacted with anthrone reagent for quantitative analysis by developed spectrophotometric method against a standard curve. The method developed has a detection range comparable to that of the established ASTM D6584 GC technique and published HPLC method. With limited instrumentation and instruction necessary, the method would be favorable for adoption by biodiesel manufacturers.

Library of Congress Subject Headings

Biodiesel fuels

Heterogeneous catalysis

Glycerin

Renewable energy sources

Format

application/pdf

Number of Pages

205

Publisher

South Dakota State University

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