Optimization of biodiesel production from castor oil by response surface methodology

This work investigated the possibility of using response surface methodology based on a four factor five level central composite design to optimize biodiesel production from castor oil. The reaction variables were oil: ethanol ratio, lipozyme concentration, time and temperature. The properties of the biodiesel produced were assessed. The linear coefficient of lipozyme 2 concentration (B), temperature (D), the quadratic coefficient of lipozyme concentration (B ), time 2 2 (C ), temperature (D ), the interaction of oil/ethanol ratio and lipozyme concentration (A*B), the interaction of lipozyme concentration and time (B*C) had significant effect on the biodiesel yield (p<0.05).The other variableswere not significant (p>0.05).The specific gravity was (0.91), refractive index (1.41 + 0.01), viscosity (14.1), cetane number (53.9), calorific value (38.0+ o o 0.10), flash point (150 C), cloud point (7 C) iodine value (101 + 0.53), acid value (0.57 + 0.01), and saponification value (180+0.25). Maximum yield was found to be 93.0% under the conditions of oil: ethanol ratio of (1:7.14), lipozyme concentration (40 U), time (165 min) and temperature o 50 C.The properties of the biodiesel produced were largely in conformity with ASTM D6751 standards.


Introduction
threats to food security when used as feedstock in fuel The rapid depletion of world's petroleum industry (Koh and Mohd, 2011). reserves and increased ecological concerns have Several parameters, such as the type of prompted the demand of environment friendly catalyst, alcohol/ oil molar ratio, temperature, purity renewable energy resources (Ashish et al., 2010). The of the reactants and free fatty acid content have a development of alternative energy source to extend greater influence on the transesterification reaction the fossil fuels has received a large interest in the last (Giovanilton et al., 2011). few decades due to an increasing concern to protect This study's main objective was to develop an the environment and conserve the nonrenewable approach for better understanding the relationships natural energy resources (Vicente et al., 1998).
between the variables (factors) and the response A number of processes such as chemical, ethyl ester formation to obtain the optimum enzymatic and supercritical alcohol treatment have conditionsthat will improve the biodiesel yieldusing been employed for biodiesel production (Warabi et al., response surface methodology (RSM).

2004). Transesterification reaction consists of reversible reactions between alcohol and
Materials and methods triacylglycerol present in oil or fats to produce three Collection of castor seed moles of fatty acid alkyl esters and glycerol as a co- The castor seeds were collected from Sabonproduct (Abdullahi et al., 2009). The use of non-edible Gari Market Kaduna State Nigeria and were ground oils such as karanja, polanga, jatropha, and castor oil into powdered form by using a simple grinder have attracted great attention as they do not pose machine.

Oil extraction
Characterization of the biodiesel produced The castor oil was extracted using soxhlet The fatty acid ethyl ester was characterized for specific gravity using specific gravity bottle, extractor. About 500 ml of n-hexane was poured in a viscosity was determined using viscometer (NDJ-5A) round bottom flask and 100 g of ground castor seed model, refractive index using Abbe's refractometer packed in a filter paper was placed in the thimble (Model AR-001). The cetane number of the produced according to AOAC (2000) with modification. b i o d i e s e l w a s d e t e r m i n e d a c c o r d i n g t o Krisnangkura(1989). Calorific value was measured Transesterification reaction according to the method of Gerpen (2005), Flash Transesterification reaction was carried out in point was determined according to ASTM D 93 screw-capped vials placed inside a reciprocal shaker.
(2000). The cloud points was determined according to The initial reaction mixture consisted of castor oil: ASTM D2500 (2000). Acid value, iodine and ethanol molar ratio of 1:7.14 lipozyme (40 U) saponification number were determined by titrimetric immobilized from Mucormiehei and was stirred at 200 method according to AOAC (2000). rpm along with the respective controls according to Kumari et al. (2009) Results The highest biodiesel yield of 93.0% and Design of Experiments 75.53% was obtained for experimental and predicted Central composite design integrated in responses respectively in run 18. The lowest response response surface methodology (RSM) provided in the of 5.0 % was recorded at run 23 with the predicted Design-Expert 7.1.4 (Stat-Ease, Inc) was employed to being 10.78% (Table).    Figure 1 shows the 3D plot for the interaction levels of lipozymeconcentration the biodiesel yield did of oil: ethanol ratio and lipozyme concentration on not increase. However at optimum lipozyme biodiesel yield. The lower and higher levels of concentration, a maximum biodiesel yield was lipozyme did not result in higher yield of biodiesel, but obtained, but the yield decreased with increase and maximum biodiesel yield was obtained at optimum decrease in temperature. Figure 1 (f) shows the 3D lipozyme concentration. Figure 1 (b) shows that the plot for the interaction of incubation time and biodiesel yield increased with increase in oil: ethanol temperature on biodiesel yield. ratio. The yield decreased with increase in the Table 3 shows some fuel properties of incubation time. Figure 1 (c) shows the 3D plot for the biodiesel produced. The specific gravity was 0.91 and interaction of oil: ethanol ratio and temperature. The refractive index was 1.41 + 0.01. The biodiesel had yield increased with the increase in oil: ethanol ratio. the viscosity of 14.1, the calorific value of 38.0 + 0.10 Figure 1 (d) shows that at lower and higher levels of mJ/ kg and cetane number of 53.9. The flash point 0 0 lipozyme concentration the biodiesel yield did not and cloud point were 150 C and 7 C respectively. The increase. However at optimum lipozyme iodine value was 101.0 + 0.53 gI2/100?g, acid value concentration, a maximum biodiesel yield was was 0.57 + 0.01 mg KOH/g and saponification value obtained. Figure 1(e) shows that at lower and higher was 180 + 0.25 mg KOH/g respectively.   Table 3. Physicochemical properties of castor oil seed biodiesel

Discussion
The high viscosity of the fuel reduces the In each of the three dimensional plots, the atomization but this issue can be handled with the use interaction effect of the two parameters was plotted of blends with petro-diesel (Deep et al., 2017). while the third and fourth parameters were fixed at The result shows the less likelihood of the the medium values. The decrease in biodiesel yield biodiesel produced to ignite accidentally and could be at higher oil ethanol ratio could be due to separation safely handled for storage owing to its high flash point. problem resulting from excessive ethanol, or in The low cloud point helps in keeping the biodiesel in activation of the enzyme by ethanol (Molla and liquid condition which makes transportation easier. The Nigus, 2014).The decrease in biodiesel yield at high lower calorific value could be attributed to the presence lipozyme concentration and oil ethanol ratio could of chemically bound oxygen in the fatty acid chains be that, in the presence of a high amount of lipase (Srivastava and Prasad, 2000). Aldo et al. (2003) -1 because the enzyme active site cannot be exposed reported the calorific value of 30.4 mJkg in castor oil to the substrates and many molecules of the biodiesel.The molecular weight, fatty acid chain length, enzyme aggregate together and thus results in low degree of unsaturation and degree of conjugation biodiesel yield (Liou et al., 1998). The elliptical determine the refractive index of biodiesel nature of the 3D plots shows the significance of the (Sadrolhossein et al.,2011). interactions of variables on biodiesel yield (Samukawa et al., 2000). Bello and Makanju (2011) Conclusion used ethanol; oil molar ratio of 6 to 1 and obtained The analysis of variance for the quadratic model the biodiesel yield of 92% after 3 hours of stirring revealed that lipozyme concentration, oil methanol from castor oil. ratio, temperature and incubation time are the The analysis of variance for the quadratic significant factors in biodiesel production from castor model revealed that lipozyme concentration, oil. The properties of the biodiesel produced were temperature, incubation time with their quadratic largely in conformity with ASTM D6751standards coefficients were the significant factors in biodiesel production. The value of the regression coefficient