transesterification. Thus, these reaction parameters were selected for the first pretreatment.
For the second pretreatment reaction, the experiments were performed with 10% sulfuric acid and 30:1 methanol molar ratio, and the FFA level was decreased to 1.37%. It seemed that the FFA level was not reached to less than 1%. Therefore, greater amount of sulfuric acid and methanol molar ratio were used. The reaction conditions of the next second pretreatment were the methanol molar ratios of 40:1 and sulfuric acid amount of 15% for 1 h at 60 C. The FFA level was reduced to 0.81% after this reaction. This value is enough to continue the process with transesterification reaction. Therefore, these reaction parameters were selected for the second pretreatment reaction.
The pretreatment reaction parameters determined in the laboratory experiments were used in the pilot scale biodiesel production. The ingredient amounts used in the pretreatment reactions for the chicken fat were given in Table 4a. After the first pretreatment reaction in the biodiesel pilot plant, the acid value of the chicken fat was reduced from 52.3 to 3.3 mg KOH g1 on average. This value is close to values obtained in the laboratory experiments but there is a little difference between the acid value of the laboratory experiments and pilot scale pretreatments. The reason of this situation was probably effective and more homogenous mixing in the main reaction tank of the biodiesel pilot plant for the first pretreatment reaction. In the pretreatment reactions, there were oil loss about 10% and 8% of the chicken fat during the alcohol-catalyst-water removing and drying process for the first and second pretreatment reactions, respectively. The pretreated chicken fat was subjected to the second pretreatment reaction. The esterification process was repeated for two times for the chicken fat. After the second pretreatment reactions, the acid value of the chicken fat was reduced to 1.94 mg KOH g1 on average.
The pretreatment results for chicken fat were given in Table 4b. As seen in the table, the viscosity, density and water content of the chicken fat were reduced by pretreatment reaction while the heat of combustion of the chicken fat was slightly increased. According to results, the fuel properties of the pretreated oils obtained after two experiments were very close to each other. In this study, the sulfur content of chicken fat was 135 ppm and the reason of high sulfur content is probably the sulfur-containing compounds such as protein (He et al., 2009). After the first pretreatment reactions in the biodiesel pilot plant, the sulfur content of chicken fat was increased and measured approximately as 700 ppm on average. This situation indicates that the alcohol–water–acid catalyst removing process after pretreatment is very important to get low sulfur content pretreated chicken fat. However, the second pretreatment results showed that there was no significant change in the sulfur content values after the first and second pretreatments. Probably, some amount of sulfur cannot be separated with the alcohol–water–acid catalyst phase and still it is included in the ester-initial triglyceride phase. As will be stated in the next section, the sulfur content of the pretreated chicken fat was decreased to lower values by transesterification reaction