| Oil deodorizer distillate (ODD) is a byproduct in the refining of oil. It contains free fatty acids (FFAs), triglycerides, tocopherols(VE), sterols, hydrocarbons and other unsaponifiables. ODD is natural source of phytosterols and tocopherols. But FFAs and triglycerides, which are about70%content in ODD were discarded. FFAs and triglycerides can be transformed to fatty acid methyl ester (FAME) which has many industrial usages. There are very few reports on FAME production using ODD as material. Traditional methods for producing FAME were usually mechanical stirring and it has such disadvantages as high catalyst content, long-time reaction and high energy consumption. Thus, there is a need to develop sustainable intensification technology for FAME production from non-edible oil sources with an objective of reducing the cost of processing. Using soybean oil deodorizer distillate (SODD) as material, the ultrasound intensification method for FAME production was studied systematically and the main contents are summarized as following:(1) The chemical and physical properties of the SODD were analyzed. Water, acid value, saponification value, free fatty acid, triglycerides, VE and phytosterols contents were analyzed and results showed that FAME production using SODD as material needs two-step method:firstly the acid value was decreased by using acid catalyst which was also called pre-esterification, then using alkali as catalyst and catalyze the esterification of triglycerides.(2) Using acid value (AV) as target, the pre-esterification process was studied and optimized by single factor method and response surface methodology. Using Box-Behnken design, fixed catalyst content1.5%, agitation speed200rpm, the data were handled by statistica8.0software. The values of regression coefficients were computed, predicted response could be expressed by the following polynomial model according to coded values:Y=0.69750Xi-2.60625xi2-2.10500X2-0.57875X22+0.70750X3-2.52125X32+0.03500X1X2+0.1600XiX3+0.82500X2X3, R2=0.99219.(In the equation, Y is acid value, X1is methanol to fatty acid molar ratio, X2is reaction time and X3is reaction temperature) Results indicated that the experiment design and analysis method was reliable. The optimal process SODD pre-esterification process was:methanol to triglycerides molar ratio12:1, reaction time120min, reaction temperature60℃, and the predicted AV was8.083, the results of experiments was8.114which was close to the predicted value. After extracted two times by ethanol, the AV could be under2mg KOH/g. The kinetics was studied. Mathematic model, rate constants was got and results indicated that the presume that the reaction was first order reaction was reasonable. The activation energy was24.6593kJ-mol"1which indicating that the esterification was easy going.(3) Four enhancing methods including mechanical stirring (MS), probe ultrasonic irradiation (PUI), flat plate ultrasonic irradiation (FPUI), flat plate ultrasonic irradiation with mechanical stirring (UIMS) were studied. The effects of methanol to triglycerides ratio, catalyst content, reaction time and energy consumption were studied. Results indicated that enhancing methods including ultrasound needs less methanol to triglycerides ratio, less catalyst content and less time to reach equilibrium. The energy consumption of ultrasound was lower and PUI was the optimum method.(4) The kinetics of MS and28kHz PUI were studied. The mathematic model, rate constants, reaction order and the activation energy were got. Results showed that MS and PUI were both pseudo-second reaction order, under the same condition, the rate constants of PUI method was about50%higher than that of MS method. The activation energy of PUI was26.034kJ-mol"1and it was about15%lower than that of MS which was29.981kJ·mol-1.These results indicated that the esterification reaction was easier for PUI than for MS.(5) Different ultrasound mode including single frequency, composite working two frequency and alternating working two-frequency, static and counter-current were applied to enhance SODD transesterification. Results showed that in the single frequency experiment, the FAME yield increased with the increase of frequency. Compared with two frequency ultrasound, FAME yields were low for single frequency ultrasound. For two frequency ultrasound, FAME yields were higher for composite working mode than alternating working mode. So20kHz/28kH composite working mode was the best method.(6)The process of20kHz/28kH composite working mode was studied and the optimal conditions were:methanol to triglycerides molar ratio was8:1, catalyst content1.4%, initial reaction temperature25℃, pulsed working on-time4s, off-time2s, water content of material lower than0.4%, AV of material lower than2mgKOH·g-1and the counter current flow rate200mL/min. Under these conditions, the FAME yield was96.6%. Compared with28kHz single frequency, the FAME yield of20kHz/28kH composite working mode was about22.6%higher, this means two-frequency composite working mode could increase FAME yield significantly. Results of VE determination showed that the recovery of MS and counter-current ultrasound was78%,75%, respectively. This means the difference of the two methods was not significant.(7)Results showed that20kHz/28kHz composite working mode was pseudo-second reaction order, the activation energy was18.122kJ·mol-1, under the same condition, the rate constants of PUE method was about33.81～43.55%higher than that of static single frequency method. These results indicated that the esterification reaction was easier for20kHz/28kHz composite working mode than for static single frequency method.(8)Effects of ultrasound treatments on material, catalyst and in the process were compared with MS method. Results showed that the main mechanic for ultrasound enhancing effect was its vigorous stirring effect and cavitation effect. Ultrasound could produce·OH, methoxy group, and the heat effect of ultrasound has some enhancing effect on transesterification, but it was not the main effect.(9) The rectification of FAME was studied. The optimal condition for hargil decoloration was content10%, temperature35℃and40min, the recovery of FAME was about81%. The physico-chemical property study results showed that the FAME got in this experiment could meet the standard. |
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