Hanifa Taher

A Review of Enzymatic Transesterification of Microalgal Oil-Based Biodiesel Using Supercritical Technology

Biodiesel is considered a promising replacement to petroleum-derived diesel. Using oils extracted from agricultural crops competes with their use as food and cannot realistically satisfy the global demand of diesel-fuel requirements. On the other hand, microalgae, which have a much higher oil yield per hectare, compared to oil crops, appear to be a source that has the potential to completely replace fossil diesel. Microalgae oil extraction is a major step in the overall biodiesel production process. Recently, supercritical carbon dioxide (SC-CO2) has been proposed to replace conventional solvent extraction techniques because it is nontoxic, nonhazardous, chemically stable, and inexpensive. It uses environmentally acceptable solvent, which can easily be separated from the products. In addition, the use of SC-CO2 as a reaction media has also been proposed to eliminate the inhibition limitations that encounter biodiesel production reaction using immobilized enzyme as a catalyst. Furthermore, using SC-CO2 allows easy separation of the product. In this paper, conventional biodiesel production with first generation feedstock, using chemical catalysts and solvent-extraction, is compared to new technologies with an emphasis on using microalgae, immobilized lipase, and SC-CO2 as an extraction solvent and reaction media.

RF Microalgal lipid content characterization

Most conventional techniques for the determination of microalgae lipid content are time consuming and in most cases are indirect and require excessive sample preparations. This work presents a new technique that utilizes radio frequency (RF) for rapid lipid quantification, without the need for sample preparation. Tests showed that a shift in the resonance frequency of a RF open-ended coaxial resonator and a gradual increase in its resonance magnitude may occur as the lipids content of microalgae cells increases. These response parameters can be then calibrated against actual cellular lipid contents and used for rapid determination of the cellular lipids. The average duration of lipid quantification using the proposed technique was of about 1 minute, which is significantly less than all other conventional techniques, and was achieved without the need for any time consuming treatment steps.

Enzymatic production of biodiesel from waste oil in ionic liquid medium

ABSTRACT In biodiesel production, catalyzed by immobilized lipase, a solvent is needed to reduce the inhibition effects caused by excessive use of short-chain alcohols and deposited glycerol. Volatile and toxic organic chemicals are commonly used to achieve this by enhancing the solubility of the alcohols and glycerol. In this work, non-volatile ionic liquids (ILs) are proposed as alternative solvents, which are safer and easier to recycle. Several ILs were tested and their effectiveness was compared to that of the conventional solvents, n-hexane and tert-butanol. Hydrophobic ILs showed much more promising results and much higher biodiesel production yields compared to hydrophilic ILs. A set of experiments was designed using full factorial (33) experimental design to statistically evaluate the results. The effects of reaction temperature, methanol-to-oil molar ratio and enzyme loading were considered. Response surface methodology (RSM) was then used to optimize process variables. The highest yields of 72 and 48% were achieved after 14 hrs of reaction at 50°C, 6:1 molar ratio and 40% enzyme loading in [bmim][PF6] and [bmim][NTf2], respectively. Regression models were developed to predict the optimal production yields and found to be adequate and statistically acceptable.

High Concentration Phenol Removal Using Freshwater Microalgae

The ability of three freshwater microalgae strains, namely Chlorella sp. , Pseudochlorococcum sp . and Chlamydomonas sp. to grow in water containing different concentrations of phenol has been tested. The effectiveness of the selected strains to utilize the phenol as a carbon source and reduce its concentration has also been assessed. The phenol removal efficiency and cells growth rates were evaluated at different initial phenol concentrations, in the range of 100-450 ppm. It was found that growing, under a reduced illumination condition, increased the inhibition onset concentration, enhanced the phenol removal and allowed the strains to tolerate higher phenol concentrations reaching 450 ppm. In the tested range of the phenol concentrations, Chlamydomonas sp . has shown to have the highest specific growth rate of 0.59 day -1 , whereas Pseudochlorococcum sp showed the highest phenol removal rate of 166 ppm day -1 . Three kinetics models that incorporate substrate inhibition were tested to describe the growth, which show almost identical fittings.

Improving the reusability of an immobilized lipase-ionic liquid system for biodiesel production

ABSTRACT Commercial applications of enzymatic biodiesel production have been hindered by the enzymes high cost and poor reusability. Ionic liquids (ILs) have been proposed as alternatives to organic solvents conventionally used in enzymatic biodiesel production. In this work, the reusability of an enzyme-IL system was tested at different methanol-to-oil molar ratios for four consecutive cycles, of 60 and 120 min each. Extracting biodiesel alone by n-hexane resulted in a sharp drop in the overall activity due to the accumulation of the by-product, glycerol. Extracting glycerol by 1-butanol enhanced the stability and allowed the enzyme-IL to be used successfully for four cycles. This study also shows the effect of methanol inhibition on the enzyme stability. The results of this work provide important information for the success of using enzyme-IL systems for biodiesel production, which is essential for the process to be economic.

Emerging Green Technologies for Biodiesel Production

The current global energy demand is met by burning the non-renewable fossil fuels. As the demand is escalating, resources and reserves are diminishing. In addition, the environment is threatened by the continuous emission of greenhouse gases; mainly CO2, which is worrying. Therefore, searching for alternatives is inevitable. Biodiesel received a considerable attention to potentially replace petroleum-based fuels. It can be produced from oil-rich feedstocks through several methods using different technologies, including transesterification. Although alkali catalyzed biodiesel process is commercially viable, several challenges were raised. In this chapter, an overview of the current status of biodiesel production approaches is discussed and the emerging technologies are highlighted. The chapter rewards the attention of using green processes, where the effectiveness of using; microalgae biomass as a green feedstock (compared to conventional crop-based seeds), lipases as green catalysts (compared to conventional chemical catalysts), and green and tunable solvents, such as neoteric solvents and supercritical fluids (compared to conventional volatile organic solvents) are addressed.

Monitoring of microalgae lipid accumulation system overview

Various methods have been proposed to monitor and determine microalgae lipid content accumulation, but they are indirect, time consuming, require sample preparations, and costly treatment steps. In this work, a novel electrical based technique, utilizing the impedance measurements to quantify the microalgae lipid accumulations. The lipid content estimation is an important element in the development of continuous non-invasive monitoring systems. The proposed technique correlates the lipid content to the change property in the measured impedance phase. A capacitor is used to host the microalgae suspension and is probed to the Gamry impedance analyzer tool, which records the impedance phase change versus frequency variations for various lipid accumulation. The relationship between lipid content and phase measurements is used to predict the unknown lipid content for microalgae.

Effectiveness of Enzymatic Biodiesel Production from Microalga Oil in Supercritical Carbon Dioxide

Biodiesel production from microalgae lipids showed to be the promise approach for alternative fuels. However, this is not yet commercialized. In the present study, the efficient production of biodiesel from Nannochlorpsis sp. grown locally was confirmed. Novozyme®435 and supercritical carbon dioxide were used as reaction catalyst and reaction medium, respectively, and the results were compared to lamb fat. In addition, the microalgae biomass production was studied extensively. It was found that Nannochlorpsis sp. can accumulate lipids by nitrogen starvation reaching 29 % with 21.06 mg L-1d-1 lipid productivity when grown in nitrogen sufficient medium. The enzymatic production in supercritical carbon dioxide was efficient with 55 % ester yield higher than lamb meat fat.