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Ind. Eng. Chem. Res. 2001, 40, 2402-2408
Parameters of Epoxidation of Cyclohexene by tert-Butyl Hydroperoxide Grzegorz Lewandowski* and Eugeniusz Milchert Department of Organic Technology, Technical University of Szczecin, Pulaskiego 10, PL-70-322 Szczecin, Poland
The process of epoxidation of cyclohexene by tert-butyl hydroperoxide in the presence of Mo(CO)6 as the catalyst has been investigated by applying statistical methods of experimental design. The influence of essential process parameters on the hydroperoxide conversion, the selectivity of transformation to the epoxy compound with regard to the hydroperoxide consumed, the cyclohexene conversion, and the selectivity of transformation to the epoxy compound with regard ˆ 4, respectively) have been described by to the cyclohexene consumed (response functions Y ˆ 1-Y regression equations in the form of polynomials of second order. The analysis of the obtained regression equations and the technological parameters allows the optimum ranges of the reaction parameters for cyclohexene epoxidation with tert-butyl hydroperoxide to be established as follows: reaction time, 2.4-5 h; temperature, 90-120 °C; and molar ratio of alkene to tertbutyl hydroperoxide, (2.1-4.4):1. Introduction The synthesis of epoxides (oxiranes) by the use of tertbutyl hydroperoxide (TBHP) proceeds according to the following reaction scheme:
synthesis of new polymers, copolymers, and solvents. Another very interesting application is the preparation of cyclohexanol and pyrocatechins.6 Experimental Section
2(H3C)3C-H + 1.5O2 f (H3C)3C-OOH + (H3C)3C-OH (1)
The process is characterized by small amounts of wastewater and a lack of corrodible agents. The profitability of epoxidation with hydroperoxides depends on the possible utilization of coproducts, namely, tert-butyl alcohol in the case of TBHP and 1-phenylethanol in the case of R-(hydroperoxy)-ethylbenzene (HPEB). Until now, there have been functioning installations of propene epoxidation with TBHP and HPEB on the industrial scale of production.1 These methods provide considerable economic and ecological benefits when compared to the traditional chlorohydrin method of making epoxides.2 Syntheses of new epoxides are usually carried out by methods using hydroperoxide. In this work, through the application of statistical experimental design methods, the most advantageous technological parameters and the influence of changes in these parameters on cyclohexene (CH) epoxidation with TBHP to 1,2-epoxycyclohexane (ECH) have been defined. Such results concerning CH epoxidation3-5 have not previously been presented. ECH is of great technical importance as it is applied in the modification of epoxy resin properties and the * Author to whom correspondence should be addressed. E-mail:
[email protected].
Raw Materials. The raw materials used in the experiments were TBHP (98.5 wt %), which was prepared in the laboratory of Department of Organic Technology, Technical University of Szczecin CH (>98 wt %), from Loba (Germany) and molybdenum hexacarbonyl, Mo(CO)6, which was acquired pure from Merck (Germany). Method of Measurement. All experiments were carried out according to the same procedure. Accurately weighed amounts of CH, TBHP, and the catalyst Mo(CO)6 were placed in a stainless steel 7-cm3 autoclave. The autoclave was then shaken for a defined period of time in a temperature-controlled bath. After the reaction was completed, the autoclave was quickly cooled to ambient temperature. The product was analyzed, and a mass balance was performed. For each experiment, the following parameters were calculated: the degree of conversion of TBHP (Y1), the selectivity of transformation to ECH in relation to TBHP consumed (Y2), the degree of conversion of CH (Y3), and the selectivity of transformation to ECH with regard to CH consumed (Y4). Analytical Method. The concentration of TBHP was determined by an iodometric method.7 The concentrations of CH and ECH were determined by gas chromatography. Analyses were performed on a Chrom 5 apparatus equipped with a flame-ionization detector (FID), using a stainless steel column (3 m long and 4 mm in diameter) filled with 15 wt % LAC17R770 (neopentyl glycol sebacate) on Chromosorb G DMCS AW (80/100 mesh), with a column temperature of 150 °C, a sample chamber temperature of 160 °C, and a detector temperature of 170 °C. The flow rates of the gases were: nitrogen, 30 cm3/min; air, 300 cm3/min; and
10.1021/ie0006662 CCC: $20.00 © 2001 American Chemical Society Published on Web 04/27/2001
Ind. Eng. Chem. Res., Vol. 40, No. 11, 2001 2403
of a polynomial of second order
Table 1. Levels of the Examined Factors factor value in natural form factor value in coded form
time
temperature
CH/TBHP molar ratio
xi
X1 (h)
X2 (°C)
X3 (mol/mol)
2.75 4.09 1.41 5.00 0.50
75.0 101.7 48.2 30.0 120.0
3.50 4.99 2.01 6.00 1.00
basic higher lower star higher star lower
0 +1 -1 +1.6818 -1.6818
Table 2. Design Matrix and Experimental Results expt no.
X1 (h)
X2 (°C)
X3 (mol/mol)
Y1
Y2 (mol %)
Y3
Y4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1.41 4.09 1.41 4.09 1.41 4.09 1.41 4.09 0.50 5.00 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75
48.2 48.2 101.7 101.7 48.2 48.2 101.7 101.7 75.0 75.0 30.0 120.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0
2.01 2.01 2.01 2.01 4.99 4.99 4.99 4.99 3.50 3.50 3.50 3.50 6.00 1.00 3.50 3.50 3.50 3.50 3.50 3.50
35.6 50.1 80.9 90.3 30.1 46.2 73.8 85.1 50.6 70.3 35.7 90.1 75.2 73.1 84.0 89.1 87.2 90.5 86.1 87.2
68.1 38.7 25.7 23.1 76.0 68.1 64.5 57.7 60.1 38.8 70.2 30.9 24.2 56.8 42.7 50.1 42.7 46.3 45.4 47.3
18.6 25.8 52.9 60.1 7.0 15.1 30.1 35.7 21.3 45.1 10.9 45.9 70.2 23.2 38.1 39.3 37.1 33.1 34.2 36.3
64.7 37.3 19.5 17.2 65.5 41.8 31.7 27.6 40.8 17.3 65.7 17.3 25.9 29.8 26.9 32.5 28.7 36.2 32.7 32.5
hydrogen, 30 cm3/min. The calculations were performed by the internal standard method using 1,4-dioxane. Results and Discussion Preliminary investigations have shown that the epoxidation of CH with TBHP is influenced in different ways by numerous parameters. Therefore, statistical experimental design methods were applied to determine the optimum parameters for ECH synthesis.8,9 On the basis of results of the preliminary experiments, it was found that the course of the process is significantly influenced by the following parameters: reaction time (X1), temperature (X2), and CH-to-TBHP molar ratio (X3). Of no great importance for CH epoxidation was the influence of the molar ratio of the catalyst Mo(CO)6 to TBHP; thus, this variable was excluded as an essential parameter. Subsequent experiments were carried out with a Mo(CO)6-to-TBHP ratio of 2 × 10-4 mol/mol. To find the optimum conditions, the investigations were carried out according to rotatable-uniform design. The parameters defined in the preliminary investigations (independent factors) of CH epoxidation and the ranges of their changes in natural (Xi) and coded forms (xi) on the levels resulting from the design matrix are presented in Table 1. The TBHP conversion (Y1), selectivity of transformation to ECH in relation to TBHP consumed (Y2), CH conversion (Y3), and selectivity of transformation to ECH with regard to CH consumed (Y4) were chosen as the response functions characterizing the CH epoxidation process. The design matrix and experimental results for Y1-Y4 are shown in Table 2. Based on the results of experiments for each response function, the approximating functions were calculated by applying the CADEX computer program10 in the form
k
Y ˆ ) b0 +
∑ i)1
k
bixi +
∑ i
