Rabitah Zakaria

Biodiesel production by in situ transesterification.

Biodiesel is conventionally produced by transesterification of vegetable oils using an alcohol (usually methanol) and a catalyst (usually hydroxides or methoxides of sodium or potassium). The process usually uses pre-extracted oil as the raw material, which is usually produced by pressing the oil-bearing seeds, often followed by solvent extraction to extract any remaining oil. Alternatively, biodiesel can be produced via ‘in situ transesterification’ or ‘reactive extraction’. In this process, oil-bearing seeds are ground, then reacted directly with the alcohol and catalyst, thereby eliminating the need for pre-extracted oil, and its associated capital and intensive running cost production methods. Various parameters play important roles in determining the conversion, reaction rate and quality of the biodiesel in in situ transesterification. These include: catalyst type, seed moisture content, agitation intensity, molar ratio of alcohol to oil, reaction temperature, catalyst concentration, seed fragment particle size and alcohol type. This article gives an overview of in situ transesterification, the parameters that have a significant effect on this process and the advantages and disadvantages of this process.

Degradation of enriched biodiesel under different storage conditions

ABSTRACT Although the commercial prospects for biodiesel have grown, some concern remains with respect to its resistance to oxidative degradation during storage. The presence of double bonds in the molecule induces a high level of reactivity with oxygen when it makes direct contact with air. Consequently, biodiesel storage over extended periods can lead to increased degradation of fuel properties, which can compromise fuel quality. This work used enriched biodiesel samples prepared by enriching palm oil methyl ester (PME) with methyl oleate (MO) at specified volumetric proportions (% v/v) PME80/MO20, PME70/MO30, PME60/MO40, and PME50/MO50 to determine the effects of long storage under two different conditions. The samples were stored either unexposed to air and daylight or exposed to air and daylight for 200 days. At regular intervals, the following physicochemical properties of the samples were measured: kinematic viscosity (KV), acid value (AV), higher heating value (HHV), and peroxide value (PV). Samples showed small differences under unexposed condition for KV, AV, HHV, and PV; however, samples showed significantly large differences under exposed condition. Biodiesel exposed to air and daylight tended to degrade at a faster rate than biodiesel under unexposed condition. The measured parameters of tested samples were not affected under unexposed condition but were affected under exposed condition.

Direct utilization of kitchen waste for bioethanol production by separate hydrolysis and fermentation (SHF) using locally isolated yeast

ABSTRACT Kitchen wastes containing high amounts of carbohydrates have potential as low-cost substrates for fermentable sugar production. In this study, enzymatic saccharification of kitchen waste was carried out. Response surface methodology (RSM) was applied to optimize the enzymatic saccharification conditions of kitchen waste. This paper presents analysis of RSM in a predictive model of the combined effects of independent variables (pH, temperature, glucoamylase activity, kitchen waste loading, and hydrolysis time) as the most significant parameters for fermentable sugar production and degree of saccharification. A 100 mL of kitchen waste was hydrolyzed in 250 mL of shake flasks. Quadratic RSM predicted maximum fermentable sugar production of 62.79 g/L and degree of saccharification (59.90%) at the following optimal conditions: pH 5, temperature 60°C, glucoamylase activity of 85 U/mL, and utilized 60 g/L of kitchen waste as a substrate at 10 h hydrolysis time. The verification experiments successfully produced 62.71 ± 0.7 g/L of fermentable sugar with 54.93 ± 0.4% degree of saccharification within 10 h of incubation, indicating that the developed model was successfully used to predict fermentable sugar production at more than 90% accuracy. The sugars produced after hydrolysis of kitchen waste were mainly attributed to monosaccharide: glucose (80%) and fructose (20%). The fermentable sugars obtained were subsequently used as carbon source for bioethanol production by locally isolated yeasts: Saccharomyces cerevisiae, Candida parasilosis, and Lanchancea fermentati. The yeasts were successfully consumed as sugars hydrolysate, and produced the highest ethanol yield ranging from 0.45 to 0.5 g/g and productivity between 0.44 g L–1 h–1 and 0.47 g L–1 h–1 after 24-h incubation, which was equivalent to 82.06–98.19% of conversion based on theoretical yield.