| dc.description.abstract | Biodiesel is one of the fuels that many countries develop because it’s renewable and eco-friendly. Biodiesel is used to substitute petroleum fuel especially diesel fuel. However, biodiesel still have disadvantages, that is the biodiesel’s cloud point and pour point is higher than petroleum based diesel fuel. This disadvantage becomes a problem on biodiesel utilization especially in subtropical countries. This problem can be solved by addition of chemicals to prevent agglomeration of crystals that are formed in biodiesel in low temperature. Increasing production of biodiesel cause increasing biodiesel by products as well, one of the biodiesel by products is glycerol. Glycerol has characteristic as anti -freezing (cryoprotectant) but it can’t be added directly to fuel because of polarity difference, decomposition, and polymerization can rise consequential engine problems at high temparatures. Glycerol must be modified to derivatives that are compatible with diesel and biodiesel prior to be added to the fuel. The most obvious derivative of glycerol has an analogy in gasoline reformulation (oxygenated gasoline). Etherification of glycerol with isobutylene produce branched ether that can be mixed with biodiesel to make a fuel with lower viscosity and cloud point value below 0°C. Beside of using isobutylene, etherification of glycerol also can be done with tert -butyl alcohol (TBA). The commonly used catalyst in etherification of glycerol is commercial strong acid ion-exchange catalyst, such as Amberlist. In this research, the possibility to replace expensive Amberlist with local bentonite was evaluated. Natural bentonite was activated by hydrochloric acid (HCl) prior to use as catalyst. The effect and optimization of reaction time, temperature and concentration of catalyst to the concentration of produced GTBE was studied. Experimental design that used is central composite design, it is one kind of the Response Surface Methodology (RSM). Lower level for reaction time is 6 hours, temperature is 60C, and concentration of catalyst is 2.5%. Higher level for reaction time is 10 hours, temperature is 80C, and concentration of catalyst is 7.5%. The result showed that reaction time doesn’t have signification influence to concentration of GTBE in confidence interval 95 %. Whereas , temperature and concentration of catalyst have signification influence s to concentration of GTBE in confidence interval 95 %. The result from analysis with software Design Expert 7.1.6 (free trial) shows that the relationship between reaction time (X 1), temperature (X2), and concentration of catalyst (X3) generate saddle point model. From optimization t est, the sqrt GTBE’s value is predicted 613.10 with reaction time is 4.9 hours, temperature is 66.2C and concentration of catalyst is 9 .7 %. Verification of that prediction of optimum condition resulted in sqrt GTBE’s value of 980. 86. This result showed that the model couldn’t predict the optimum condition of GTBE reaction, since the optimum point was out of the range. Optimum concentration of GTBE was predicted when reaction time below 6 hours, temperature above 60°C, and concentration of catalyst above 7 .5 %. The GTBE effectiveness test to reduce biodiesel’s cloud point and pour point was done by mixing GTBE in biodiesel with volume ratio 1:10. The result from this test showed that biodiesel which has been mixed with GTBE has cloud point and pour point 3C lower than biodiesel alone. GTBE that has been produced is still less effective to reduce biodiesel’s cloud point and pour point because GTBE that has been formed mainly is mono-tert-butyl ether that has less soluble in biodiesel. | en |
