Date of Award

6-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Dr. Sulaiman Al-Zuhair

Second Advisor

Muftah El-Naas

Third Advisor

Dr. Mohammed Hamdan

Abstract

Lipids were extracted from microalgae using supercritical carbon dioxide (SC-CO2), and used for enzymatic biodiesel production in SC-CO2. The growth of several fresh water and marine strains was tested under aeration with different CO2 enrichments. The highest growth found was for Chlorella sp. grown at 27 oC, 1 % CO2 enrichment and 460 mM NaCl concentration, at which carbon fixation rate was 1.7 g L-1 d-1. The highest enhancement of lipids content by nitrogen starvation was found with Scenedesmus sp., but with a lower growth rate. Two step cultivation of Scenedesmus sp. was carried out in a 5 L internally-illuminated photobioreactor, to combine high growth rate with high lipids content.

SC-CO2 extraction of lipids from lyophilized microalgae at 50 °C, 350 bar and a flow rate of 2.69 g min−1 was found to be more effective than conventional extraction techniques. The effects of extraction conditions, namely 200–500 bar; 35–65 °C and CO2 flow rate of 1.38–4.02 g min−1, on extraction yield were investigated. The optimum yield was found to be 7.4 at 53 °C and 500 bar after 1 h. The possibility of extracting lipids directly from wet cells, avoiding the drying step, was studied. Lytic enzymes were efficient in disrupting the cell walls and enhancing the extraction. Lipids extraction yield from wet cells was found to be 12.5% using SC-CO2 compared to 16.6 % using n-hexane.

Enzymatic production of biodiesel from extracted lipids in a SC-CO2 medium was studied in a batch reactor. The effect of enzyme loading (15-50 % wt), temperature (35-55 oC) and methanol to lipid (M:L) molar ratio (3-15:1) ii

Were investigated. A reaction yield of 82 % was obtained at 50 oC, 200 bar, 35% enzyme loading, and 9:1 M:L molar ratio after 4 h. The extraction and reaction processes were combined in a continuous integrated process, and the best M: L ratio was found to be 10:1, and the enzyme was reused for 6 cycles retaining 78 % of its original activity. The enzyme washed with tert-butanol at the end of the sixth cycle and was success fully reused for 24 cycles retaining 70% of its activity

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