반응표면법을 이용한 대두유로부터 바이오디젤 생산의 최적화

Theories and Application of Chem. Eng., 2002, vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

이 세진, 김 의용*, 유 정우

서울시립대학교 화학공학과*, 신한에너지**

Optimization of Biodiesel Product Condition from soybean oil

using Response Surface Method

Se-Jin Lee,  Eui-Yong Kim, Jeong-Woo Yoo

．Department of Chemical Engineering, University of Seoul, Korea,

** Neo Energy Korea

Introduction

The high energy demand in the industrialized world, as much in the domestic sector, as in transport and industry, its increase, and the derived problems of the widespread use of fossil fuels, make increasingly necessary the development of renewable energy sources of limitless duration and smaller environmental impact than the traditional ones[1].

Biodiesel obtained from energy crops produces favorable effects on the environment, such as a d crease in acid rain and in the greenhouse effect caused by combustion. Due to these factors and to its biodegradability, the production of biodiesel is considered an advantage to that of fossil fuels. In addition to this, it also shows a decrease in the emission of CO2, SOx, non-toxic, has lower emission profiles compared and unburned hydrocarbons during the combustion process[2].

The transesterification reaction can be represented as(Fig. 1):

Biodiesel is synthesized from direct. Transesterification of vegetable oils with methyl alcohol can be carried out using homogeneous catalysts. The use of homogeneous catalysts requires conditioning and purification steps for the reaction products (methyl ester and glycerol) to separate the catalysts at the end of the reaction. Glycerol is obtained as a by-product of the transesterification reaction, and once separated from the reaction mixture, it has a number of applications in the pharmaceutical, cosmetics, food and plastics industries[3]. The most widely used vegetable oils for the production of biodiesel are rapeseed, sunflower and soybean oils. From an environmental point of view biodiesel shows clear advantages over conventional fuels.

The present work is chosen optimum values for the variable affecting the biodiesel product to process will be determined by application of the response surface methodology.

Experimental

1. Meterials

Methanol and hydroxides were obtained from Samchun(Co.), and the soybean oil from

Neo Energy Korea was used in this work as a vegetable oil. In addition, various methyl esters such as palmitic, stearic, oleic, linoleic and linolenic acids were purchased from Sigma-Aldrich(Co.) as a standard.

2. Experimental Design

The produce parameter were optimized using response surface methodology. The central composite design was employed by three quantitative variables( temperature, reaction time, agitation rate), which made of fractional matrices of 23 plus 1 factorial point, 1 axial(star) point , and 5 center points leading to a total of 15 experiments. The second degree regression equation and optimum values were determined using SAS system software 8.0(SAS institute inc.).

3. Methods

The transesterification experiments were performed in high-pressure reactor using 100g of soybean oil. Catalyst were 1g ( 1% by weight of oil) of potassium hydroxide. The catalyst was first dissolved in 10g of methanol which represented a 200% excess of the stoichiometric amount the transesterification. It was necessary to heat the methanol slightly with stirring to completely dissolve the catalyst. The methanol and dissolved catalyst were than added to the oil and stirring was begun.

4. Fatty acid Composition

After methyl esterification, fatty acid are analyzed by gas chromatography(GC). The GC analyses were performed using a Young-Lin 600D, equipped with a capillary column of HP-5(Crosslinked 5% PH ME Siloxane, 30m×0.25□×0.25□), injection temperature 280℃, detector temperature 300℃. The GC oven was kept at 160℃ for 1min, heated at 5℃/min up to 300℃, where it was kept for 15min. The detector was a flame ionization detector (FID), and the carrier gas Nitrogen (4ml/min).

Results and discussion

The optimization of the variables affecting the synthesis of methyl esterification from soybean oil was carried out following the design of response surface methodology, ordinally developed by Box and Wilson[4]. The response was soybean oil conversion methyl esters after reaction. The factors chosen were temperature, reaction time, and agitation rate. Atmospheric pressure was used for all the tests, since preliminary experiments indicated  that the reaction proceeds very rapidly even at low pressure. The use of higher pressures would largely increase the cost of the process both in terms of equipment and energy.

The experimental matrix and the results of the central composite design are shown in Table 2. The methyl esterification conversion varied markedly with the conditions tested in a range of 43∼98%. when ANOVA analysis reflects the significance of model with a confidence to greater than 99%(P〈 0.01), the F-value and P-value were 21.99 and 0.0017 (Table 3). The coefficient of variation is low, 4.70, indicating a better precision and reliability for the experiments carried out. The coefficient of determination (R2) of the model was calculated to be 0.98.

The response surface equation obtained is as follows;

Conversion= 90.79+ 13.54X1+ 4.56X2+ 5.94X3- 7.54X12- 6.04X22- 2.66X32- 0.39X1X2                    -4.56X1X3- 0.33X2X3

where, X1= temperature, X2= agitation rate, X3= reaction time

The second-order model can be plotted as a three-dimensional surface representing the response(conversion) as a function of the two factors for the experimental range considered. The reaction time course profile of biodiesel product under the optimized condition is shown Fig 2 and Fig 3. According to these results, optimal condition for biodiesel production was 63.85℃, 90.4rpm, and 61.6min.

References

Mittelbach, M., Enzelsberger, H.: Transesterification of heated rapeseed oil for extending diesel fuel. JAOCS, 76, 545-550(1999).

Mittelbach, M., Tritthart, P.: Diesel fuel derived from vegetable oils, Ⅲ. Emission tect using methyl esters of used frying oils. JAOCS, 65 (7), 1187-1187 (1988).

Sonntag, N. O. V.: Glycerolysis of fats and methyl esters-status, review and critique. JAOCS, 59(10), 795A-802A(1982).

Box, J., Wilson, W.: Central composite design. J. R. Stat. Soc, X111(1), 1-35(1951).

Fig 1. Transesterification of triglycerides with alcohol.

그림 2. The effect of reaction temperature. (Reaction conditions : agitation rare 174rpm)

그림 3. The effect of reaction agitation rate.

(Reaction conditions : temperature 63.80℃)

Table 1. Design Matrix for Experimental Design

Run	temperature	agitation of rate	reaction time	catalyst	conversion
1	60	125	50	1.25	78.2
2	93.64	125	50	1.25	88.6
3	40	50	20	0.5	56.5
4	60	125	50	1.25	77.9
5	80	50	20	2	70.8
6	80	50	80	2	83.8
7	40	200	20	2	61.2
8	26.36	125	50	1.25	49.5
9	40	50	80	0.5	59.6
10	60	125	50	1.25	78.6
11	60	125	50	1.25	79.3
12	40	200	80	2	73.6
13	60	125	50	0	0
14	60	125	3	1.25	27.1
15	80	200	80	0.5	95.6
16	60	125	50	2.5	78.6
17	60	251	50	1.25	92.8
18	60	0	50	1.25	7.45
19	80	200	20	0.5	85.1
20	60	125	100	1.25	84.6
21	60	125	50	1.25	79.3

Table 2. Analysis of variance (ANOVA) for the full regression.

Source	Sum of squares	Degrees of freedom	Mean square	F-value	P-value
Model	2953.33	9	328.15	21.99	0.0017
Error	74.60	5	14.92
Total	3027.93	14

R2 = 0.98,  C.V.= 4.70