Vapor–Liquid Equilibria for the Ternary System Methanol + Dimethyl Carbonate + Dimethyl Oxalate and Constituent Binary Systems at Different Temperatures

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Vapor–liquid equilibria for the ternary system methanol + dimethyl carbonate + dimethyl oxalate and constituent binary systems at different temperatures

Xin-Bin Ma∗, Xin-Gang Liu, Zhen-Hua Li, Gen-Hui Xu

Key Laboratory for Green Chemical Technology, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China

Received 30 December 2003; accepted 29 April 2004 Available online 24 June 2004

Abstract

Isothermal vapor–liquid equilibrium data are measured for the ternary system methanol + dimethyl carbonate (DMC) + dimethyl oxalate (DMO) and constituent binary systems at different temperatures. The activity coefﬁcients were found to be thermodynamically consistent and were correlated by the Wilson, NRTL and UNIQUAC equations. The correlated parameters of the constituent binary systems were used to calculate the phase behavior of the ternary mixture, which showed satisfactory agreement with the experiments. © 2004 Elsevier B.V. All rights reserved.

Keywords: Vapor–liquid equilibria; Wilson; NRTL; UNIQUAC; Dimethyl carbonate

1. Introduction were obtained. Based on these results, the VLE data of the ternary system methanol + DMC + DMO was predicted Dimethyl carbonate (DMC) is an important intermediate and compared with experimental data. for further chemical production. It can replace the toxic dimethyl sulﬁde and phosgene as methylating agent or carbonylating agent. A new process for the synthesis of 2. Experimental DMC by oxidative carbonylation of methanol has attracted much attention in the past years [1,2]. The products contain 2.1. Materials methanol, DMC and dimethyl oxalate (DMO). In order to get the mixture separated by distillation, vapor–liquid Methanol and dimethyl oxalate were obtained from the equilibrium data are needed for process design. Some in- Tianjin Third Chemical Reagent Factory in China and DMC vestigations have been carried out for the constituent binary was supplied by Acros Organics. The purities and Antoine systems [3–9], but the VLE data of this ternary system constants are listed in Table 1 together with literature values are rarely reported. In this paper, a device which uses a [10,11]. The Antoine equation is: headspace sampler and gas chromatograph was used to B measure the VLE data of the following three binary sys- Ps = A − log i C + T (1) tems: methanol + DMC, methanol + DMO, DMC + DMO. The Wilson, NRTL and UNIQUAC equations were used 2.2. Apparatus and procedure to correlate the experimental data and satisfactory results Isothermal VLE data have been measured by using a ∗ Corresponding author. Tel.: +86 22 27406498; headspace gas chromatograph (HSGC) comprised by a fax: +86 22 27890905. headspace sampler (HP19395A) and a gas chromatograph E-mail address: [email protected] (X.-B. Ma). (Shimadzu 8A) for all the binary and ternary systems. The

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Table 1 Purities and Antoine constants of pure components Chemicals Purity (wt.%) Boiling point (K) Antoine constants Temperature range (K) ABC

Methanol [10] 99.6 338.15 7.1973 1575.0 −34.29 257–364 DMC [10] 99.2 363.25 6.4337 1413.0 −44.25 333–443 DMO [11] 99.6 436.65 6.6995 1776.0 −58.15 328–443 s Note: the Antoine constants of DMO were correlated by the data in reference [11] and the maximum relative error of Pi is 0.2%.

HSGC system has an electro-pneumatic sampling system results are listed in Tables 5–7. The correlated results were and a precision thermostat with accuracy of ±0.1 K. A used to predict the VLE data of these binary systems and packed column (OV-101, length 2 m, outer diameter 3 mm satisfying results were obtained as proved by the maximum and thickness 0.5 mm) and a FID were used for GC analysis. relative error (εmax)ofyi listed in Tables 5–7. The molar By HSGC method, only equilibrated vapor phase is auto- volumes used are listed in Table 8. matically analyzed with the help of the electro-pneumatic y − y sampling-system, while the liquid phase compositions are 1,exp 1,cal εmax = max × 100% calculated from the feed compositions using thermodynamic y1,exp i relations and the mass balance. All the mixture samples (ca. 4 ml) were prepared in a glass vial equilibrium cell (22 ml) after precise weight mea- Table 2 surement by a digital electronic balance with an accuracy of Experimental vapor–liquid equilibrium data of methanol (1) + dimethyl −4 ±1×10 g. Then the sample was put into the sample holder carbonate (2) system at different temperatures and heated to certain temperature for about 1 h to make sure 343.15 Ka 348.15 Kb 353.15 Kc 358.15 Kd that the vapor–liquid equilibrium has been achieved. The vapor was sampled automatically and injected to the GC to x1 y1 x1 y1 x1 y1 x1 y1 analyze the composition until the reproducible results were 0.0593 0.3285 0.0521 0.3110 0.0535 0.3070 0.0574 0.3485 obtained. 0.1306 0.4901 0.1119 0.4715 0.1055 0.4622 0.1035 0.4584 The VLE data of the binary system methanol (1)–benzene 0.2660 0.6234 0.2205 0.5952 0.2140 0.5933 0.2358 0.6031 0.3842 0.6831 0.4168 0.6899 0.3146 0.6579 0.4128 0.6864 (2) was measured by this device and compared with the 0.4708 0.7125 0.4945 0.7121 0.4057 0.6931 0.5062 0.7121 literature data. It was found that the maximum deviation of 0.6256 0.7524 0.6012 0.7338 0.5564 0.7290 0.6247 0.7475 yi was 1.5%, which proved the reliability of this device. 0.7178 0.7832 0.7119 0.7839 0.7181 0.7935 0.7284 0.7969 0.8214 0.8349 0.8269 0.8375 0.8128 0.8365 0.8213 0.8420 0.9037 0.8864 0.8847 0.8755 0.9041 0.8905 0.8786 0.8815 0.9397 0.9215 0.9645 0.9486 0.9754 0.9635 0.9695 0.9598 3. Results and discussion a D = 1.84%. b = 3.1. VLE data of binary systems D 0.98%. c D = 1.51%. d D = 1.03%. The HSGC system was used to measure the VLE data of following binary systems and the results are listed in Table 3 Tables 2–4. Experimental vapor–liquid equilibrium data of methanol (1) + dimethyl oxalate (2) system at different temperatures (1) Methanol + DMC at 343.15, 348.15, 353.15, and a b c 358.15 K. 353.15 K 363.15 K 373.15 K

(2) Methanol + DMO at 353.15, 363.15, and 373.15 K. x1 y1 x1 y1 x1 y1 + (3) DMC DMO at 373.15, 393.15, and 413.15 K. 0.8407 0.9901 0.9141 0.9925 0.7746 0.9836 At low pressure, the vapor phase can be considered as 0.7137 0.9830 0.8497 0.9880 0.6611 0.9766 0.5972 0.9779 0.7541 0.9821 0.5688 0.9724 ideal gas and the equilibrium equation is: 0.5026 0.9739 0.6758 0.9796 0.4698 0.9655 s 0.4525 0.9711 0.5695 0.9760 0.3917 0.9600 Pyi = γixiPi (2) 0.3925 0.9667 0.4737 0.9724 0.3024 0.9495 The thermodynamic consistency of the experimental VLE 0.2654 0.9511 0.3632 0.9675 0.2175 0.9343 0.2151 0.9421 0.2305 0.9525 0.1737 0.9202 data has been checked by means of the Herington method 0.1106 0.8976 0.0945 0.9085 0.1250 0.8936 and the criteria was D ≤ 2%. The value of D is given in a = Tables 2–4. The activity coefﬁcients were correlated by the D 0.65%. b D = 1.83%. Wilson, NRTL and UNIQUAC equations and the correlation c D = 1.94%. 中国科技论文在线 http://www.paper.edu.cn

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Table 4 Table 7 + Experimental vapor–liquid equilibrium data of DMC (1) + DMO (2) at Correlation results for dimethyl carbonate (1) dimethyl oxalate (2) different temperatures Model Parameters εmax (%) 373.15 Ka 393.15 Kb 413.15 Kc A12 A21 α12 (J mol−1) (J mol−1) x1 y1 x1 y1 x1 y1 Temperature (373.15 K) 0.8478 0.9732 0.8039 0.9549 0.8264 0.9562 Wilson 1888.412 1278.524 – 0.6124 0.7727 0.9643 0.7330 0.9431 0.6941 0.9257 NRTL 1712.458 999.614 0.2 0.7570 0.6787 0.9530 0.6710 0.9331 0.5964 0.9039 UNIQUAC 112.208 843.140 – 0.6672 0.5401 0.9330 0.5240 0.9106 0.5001 0.8856 0.4433 0.9173 0.4502 0.8992 0.4029 0.8585 Temperature (393.15 K) 0.3415 0.8910 0.3549 0.8809 0.2900 0.8190 Wilson 2551.057 1838.209 – 0.4078 0.2477 0.8559 0.2719 0.8549 0.2006 0.7675 NRTL 2785.616 1101.406 0.2 0.3769 0.1354 0.7674 0.1915 0.8129 0.1064 0.6456 UNIQUAC 278.893 982.059 – 0.3769 0.0421 0.5291 0.1374 0.7635 0.0548 0.4909 Temperature (413.15 K) a D = 1.00%. Wilson 3056.799 446.286 – 1.2337 b D = 1.52%. NRTL 655.940 2594.080 0.2 1.0655 c D = 1.26%. UNIQUAC −455.219 1657.668 – 1.0938

Table 5 Correlation results for methanol (1) + dimethyl carbonate (2) Table 8 Model Parameters εmax (%) The molar volumes at different temperatures

−1 −1 3 A12 (J mol ) A21 (J mol ) α12 Material T (K) Density Vi (cm /mol) (kg/m3) Temperature (363.15 K) Wilson 3894.411 823.216 – 0.6327 Methanol [11] 343.153 749.4 42.75 NRTL 2641.108 1429.444 0.2 1.2712 348.15 743.4 43.10 UNIQUAC 267.826 1080.191 – 1.7979 353.15 737.4 43.45 358.15 731.2 43.82 Temperature (368.15 K) 363.15 724.9 44.20 Wilson 4418.351 479.581 – 1.0791 373.15 712.0 45.00 NRTL 1895.505 2233.461 0.2 0.8638 383.15 698.7 45.86 − UNIQUAC 1.447 1441.868 – 1.1230 393.15 684.7 46.79 Temperature (373.15 K) DMC [12] 290.15 1065.0 84.51 Wilson 4158.183 855.094 – 2.2186 NRTL 2472.456 1716.249 0.2 2.0910 DMO [11] 353.15 1131.0 104.41 UNIQUAC 171.953 1248.138 – 2.2619 363.15 1119.0 105.53 373.15 1107.0 106.68 Temperature (378.15 K) 393.15 1082.0 109.14 Wilson 4974.627 22.702 – 1.8368 413.15 1056.0 111.83 NRTL 968.881 3202.295 0.2 2.2155 UNIQUAC −335.347 1912.787 – 2.8984

Since it is hard to measure the pressure directly Table 6 by this device and no measured pressure is provided, Correlation results for methanol (1) + dimethyl oxalate (2) we calculated the pressure using the Wilson equa- ε Model Parameters max (%) tion. −1 −1 A12 (J mol ) A21 (J mol ) α12 The results were used to construct Figs. 1–3. Temperature (353.15 K) Wilson 3779.086 −494.685 – 0.3596 3.2. VLE data of ternary system NRTL 2305.324 691.873 0.2 0.3507 UNIQUAC −604.266 3195.268 – 0.3540 The experimental VLE data of methanol (1) + DMC Temperature (363.15 K) (2) + DMO (3) at different temperatures are listed in Wilson 4663.108 766.729 – 0.1980 Table 9 and the absolute errors y1 of predictions with NRTL 3199.371 1386.304 0.2 0.1927 the Wilson, NRTL and UNIQUAC model are listed in − UNIQUAC 319.999 3807.487 – 0.1978 Table 10. It can be seen that the predicted results by the Temperature (373.15 K) Wilson equation are better than the results from the NRTL − Wilson 4308.046 741.183 – 0.1028 and UNIQUAC equations. The experimental VLE data NRTL 1776.805 1439.805 0.2 0.0844 + + UNIQUAC −738.387 3639.676 – 0.0731 of methanol (1) DMC (2) DMO (3) are shown in Figs. 4–6. 中国科技论文在线 http://www.paper.edu.cn

54 X.-B. Ma et al. / Fluid Phase Equilibria 221 (2004) 51–56

Fig. 1. Isothermal VLE for the methanol–DMC system at different temperatures.

Fig. 2. Isothermal VLE for the methanol–DMO system at different temperatures.

Table 9 Experimental vapor–liquid equilibrium data of methanol (1) + DMC (2) + DMO (3) at different temperatures 353.15 K 363.15 K 373.15 K

x1 x2 y1 y2 x1 x2 y1 y2 x1 x2 y1 y2 0.0841 0.8001 0.3730 0.5903 0.0985 0.6685 0.4484 0.4984 0.0598 0.7207 0.4314 0.4937 0.1155 0.7565 0.4760 0.4900 0.1517 0.6098 0.5989 0.3868 0.0880 0.6911 0.5039 0.4611 0.2197 0.6498 0.5803 0.4066 0.2870 0.5086 0.6598 0.3211 0.1656 0.6009 0.4442 0.3718 0.3476 0.5333 0.6460 0.3268 0.3994 0.3836 0.7033 0.2870 0.2654 0.5280 0.6598 0.3285 0.4299 0.4505 0.7007 0.2808 0.4918 0.3093 0.7204 0.2534 0.4034 0.3882 0.6993 0.2888 0.5119 0.3691 0.7330 0.2531 0.5797 0.2261 0.7700 0.2203 0.4917 0.2962 0.7115 0.2646 0.5746 0.2969 0.7591 0.2101 0.6355 0.1516 0.8103 0.1311 0.5861 0.2224 0.7629 0.2329 0.6854 0.1939 0.8150 0.1792 0.7263 0.0722 0.8633 0.1254 0.6547 0.1394 0.8161 0.1754 0.7447 0.1289 0.8647 0.1105 ––––0.7155 0.0740 0.8954 0.0938 0.8295 0.0585 0.9195 0.0493 ––––0.7889 0.0317 0.9168 0.0597 中国科技论文在线 http://www.paper.edu.cn

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Fig. 3. Isothermal VLE for the DMC–DMO system at different temperatures.

Table 10 The absolute errors of correlated yi and experimental yi 353.5 K 363.5 K 373.5 K

y1 y2 y3 y1 y2 y3 y1 y2 y3 Wilson Mean 0.0194 0.0180 0.0057 0.1000 0.0155 0.0111 0.0138 0.0245 0.0324 Maximum 0.0536 0.0578 0.0088 0.0177 0.0456 0.0557 0.0613 0.0660 0.0623 Minimum 0.0063 0.0024 0.0014 0.0025 0.0056 0.0001 0.0022 0.0013 0.0052 NRTL Mean 0.0155 0.0140 0.0058 0.0163 0.0184 0.0107 0.0232 0.0306 0.0312 Maximum 0.0465 0.0504 0.0085 0.0320 0.0373 0.0547 0.0680 0.0926 0.0612 Minimum 0.0043 0.0003 0.0013 0.0029 0.0062 0.0003 0.0019 0.0022 0.0040 UNIQUAC Mean 0.0199 0.0168 0.0069 0.0334 0.0271 0.0244 0.0381 0.0390 0.0487 Maximum 0.0655 0.0524 0.0131 0.0461 0.0598 0.0686 0.0933 0.1234 0.0840 Minimum 0.0005 0.0024 0.0029 0.0122 0.0040 0.0136 0.0109 0.0017 0.0185

Fig. 4. Isothermal VLE for the ternary system of methanol (1) + DMC Fig. 5. Isothermal VLE for the ternary system of methanol (1) + DMC (2) + DMO (3) at 353.13 K. (2) + DMO (3) at 363.13 K. 中国科技论文在线 http://www.paper.edu.cn

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Acknowledgements

We appreciate the ﬁnancial support from National Science Foundation Committee (No.: 20276050).

References

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Greek letters ␣12 non-randomness parameters in the NRTL equation ε relative error (%) γi activity coefﬁcient of component i