Rhizopus arrhizus ile Atık Yemeklik Yağdan Biyodizel Üretiminin Kesikli Sistemde İncelenmesi ve Optimizasyonu

Abstract

In this thesis study, the production of biodiesel by transesterification reaction from waste cooking oil and methanol was investigated in a batch system using dried R. arrhizus fungus, cultivated in different conditions, containing intracellular lipase enzyme directly as a catalyst. Also the parameters affecting the reaction were researched. In the first stage of study, R. arrhizus cultivated in the growth medium prepared from the waste orange peel at 30 oC and 120 rpm was determined having the maximum intracellular lipase activity compared to the intracellular lipase activities obtained from R. arrhizus grown in the nutrient media prepared from the glucose and the molasses. The effect of the initial concentration of total reducing sugar (TRS) of waste orange peel in the range of 9-21 g/L on microbial growth rate, yield and intracellular and extracellular lipase hydrolysis activities were investigated. While the maximum microbial growth was found as 3,83 g dried m.o./L in the growth medium prepared from 70 g/L waste orange peel containing 21,0 g/L TRS, the maximum intracellular lipase hydrolysis activity was obtained as 0,40 U/mg in the growth medium prepared from 50 g/L waste orange peel containing 15,0 g/L TRS. Olive oil or waste cooking oil (WCO) was added in the range of 5-40 g/L to the growth medium prepared from 50 g/L waste orange peel as an inducer to increase the intracellular lipase hydrolysis activity of the microorganism. The effects of additive oil concentrations on the microbial growth and intracellular lipase hydrolysis activity were examined. It was observed that the addition of WCO much more increased both microbial growth and intracellular lipase hydrolysis activity compared to olive oil addition. When 10 g/L WCO was added to the growth medium, intracellular lipase hydrolysis activity reached to 0,52 U/mg, increasing 30% compared to the activity obtained in the growth medium containing no WCO. The growth medium prepared from 50 g/L waste orange peel with 10 g/L WCO was used to grow the R. arrhizus fungus having the highest intracellular lipase hydrolysis activity to be used in biodiesel production studies. In the second part, the biodiesel production studies were performed in a batch system, and the parameters of methanol/waste oil molar ratio, shaking rate, temperature and amount of biocatalyst, which directly affect the conversion of WCO to biodiesel were investigated. By using Design-Expert Programme with ANOVA, the conversion values of WCO to biodiesel by weight obtained by L9 test system with 4 parameters and 3 level designed and studied according to Taguchi method were analyzed. A second order quadratic polynomial equation which describes the experimental system perfectly and gives the simultaneous effects of all parameters studied on conversion was found. The effects of selected parameters on the conversion of WCO to biodiesel were also evaluated statistically and three dimensional surface curves were also obtained. In order to determine the most suitable operating parameters, optimization was done by using the numerical optimization function taking place in the same programme and the highest conversion of WCO to biodiesel was obtained as 22,3% at the operating conditions including 4:1 methanol/waste oil molar ratio, 177 rpm shaking rate, 33 oC temperature and 1,3 g catalyst amount. The kinetic modeling of the transesterification reaction was performed by taking into consideration the experiments meeting the optimization conditions most closely in the nine experiments designed according to the Taguchi method. The reaction rate constants were obtained as 0,0079 ve 0,0149 (mol/L)-2sa-1 at 25 and 35 oC, respectively. Activation energy and frequency factor were found as 48,42 kJ/mol and 2,43x106 (mol/L)-2sa-1, respectively.