EFFECT OF WATER ACTIVITY ON TRANSESTERIFICATION KINETIC PARAMETERS OF COCONUT OIL WITH ETHANOL

ABSTRACT

This work is focused on determining quantitatively how water, even in its smallest amount, affects transesterification kinetic parameters of coconut oil with ethanl; with the view of assessing whether it is preferable to use anhydrous ethanol with high price or ethanol containing a certain amount of water in biodiesel production process. Physicochemical properties of the coconut oil were also determined. The coconut oil produced was yellow and had the following values for viscosity, 21.24 ± 0.22mm2/s, relative density, 0.92 ± 0.001, flash point, 1900C, cloud point, +27, pour point, +25, refractive index, 1.45 ± 0.001 and moisture content, 0.1%.The average acid, iodine, peroxide and saponification values of the coconut oil were 0.523 ± 0.03 mgKOHg-1, 9.33 ± 0.04 mgIodineg-1, 0.00 meq/1000g and 270.26 ± 0.05 mgKOHg-1 respectively.The crude coconut oil was transesterified using serially diluted anhydrous ethanol with water activity 0.002, 0.022, 0.042, 0.062 and 0.102. NaOH was used at constant reaction conditions.The ethyl ester produced (biodisel) was light yellow with the following values for viscosity 2.66 ± 0.22mm2/s, relative density, 0.86 ± 0.001, flash point, 1420C, cloud point, +5, pour point, -3, refractive index 1.43pr ± 0.001 and moisture content 1.7%. The average acid, iodine, peroxide, cetane number and saponification values of the biodiesel produced were 0.094 ± 0.002 mgKOHg-1, 1.53 ± 0.28 mgIodine g1, 0.160 ± 0.001 meq/1000g, 70.81 and 222.99 ± 0.10 mgKOH g-1 and 70.81 respectively. During kinetic study, it was observed that the sample with the least water activity (0.002) generated higher biodiesel yield than others. The reaction rates for biodiesel samples with water activities of 0.002, 0.022, 0.042, 0.062 and 0.102 were 0.0978, 0.0786, 0.0498, 0.0276 and 0.0054 (mg/g/m) respectively. The function of ethyl ester concentration with time when determined showed a first order reaction.The reaction rate decreased as water activity increased while the over – all reaction rate constant  K was found to be 2.4 × 10-2. The presence of water in the reacting mixture had a negative effect on the transesterification reaction progress and this effect has been quantitatively presented. The reaction kinetics gave a better understating of the techno-economic process, in other to avoid waste of reactants during biodiesel production process and maximize profit.