A comparative study on predictions of vapour liquid equilibrium of Ethylene Oxide & Water Using Simulator

In process simulation, reliable and accurate property estimation methods play an important role in the solution of various simulation problems where convergence is often traced to failures in the reliable predictions of physical and thermodynamic properties. Convergence and reliability of the simulation is heavily dependent on the fluid package selected. Predictions of phase equilibrium using various thermodynamic models provide an idea about which model will be able to represent the entire process in better way. Paper presents a review on various simulation studies done for Ethylene oxide and Water system to highlight the fact that thermodynamic models were used with little knowledge or by intuitions. A comparative study is presented for the proper selection of fluid packages by determining vapour liquid equilibrium data for Eo-Water systems (Ethylene oxide and Water). The comparison was done with the help of making a model of experimental VLE data simulated VLE data (by various thermodynamic models). Keyword: UNISIM, VLE, Ethylene oxide simulation Introduction: Ethylene Oxide was first reported in 1859 as being prepared from the reaction of potassium hydroxide on ethylene chlorohydrins. But nowadays it is mainly prepared by direct oxidation of ethylene with oxygen on silver based catalyst. In its final product stream along with ethylene oxide many other impurities like formaldehyde, acetaldehyde, unconverted ethylene, water and other inert gases are also present. So its purification consist of many stages which includes stripping zone, scrubbing zone, phase separator, an ethylene oxide purification zone and their interconnections. In its scrubbing step ethylene oxide is scrubbed from other impurities with help of excess of water which needs to be removed so it can be reused for scrubbing purpose as well as to get pure ethylene oxide. For commercial purpose like its use in epoxy paints, as surfactants demands highly pure ethylene oxide having purity of more than 99.5%. Ethylene Oxide is widely used petrochemical compound derived from ethylene. Ethylene Oxide can be manufactured mainly by two processes which include: 1) Direct oxidation of Ethylene with Oxygen and 2) Production from ethylene Chlorohydrins. But now it is produced mainly by direct oxidation process. Molecular Weight of Ethylene Oxide is 44.05 kg/kmole. The boiling point of ethylene oxide at atmospheric conditions is 10 o C. In process simulation, reliable and accurate property estimation methods play an important role in the solution of various simulation problems where convergence is often traced to failures in the reliable predictions of physical and thermodynamic properties. The purpose of this study is to compare different thermodynamic models available for the simulation of process using UNISIM and select the best model for the simulation of Ethylene oxide & Water system. 5,6, 7 . Selection of Fluid Package The appropriate selection of thermodynamic models has a strong influence on calculations. The appropriate selection of thermodynamic models has a strong influence on VLE and LLE calculations. This reason makes this comparison of model using VLE, especially important. Fluid package selection can do mainly in two ways. One is in which it can be selected by using the selection chart or decision tree available from literature and second is it can done by cross verifying VLE data International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) www.ijset.com, Volume No.1, Issue No.3, pg:-47-49 01 July 2012 48 obtained from simulator with that of the data available in literature which is very accurate method and gives surety of the results of process simulation with that particular property package. Various thermodynamic packages used for the simulation of EO-Water system. The presence of polar and non-electrolyte compounds makes necessary the use of the nonrandom two liquids (NRTL) model or Universal Quasi Chemical (UNIQUAC) model, WILSON which gives binary coefficients of our desired compound which in turn gives physical and chemical properties of our compound (Ethylene Oxide & water). Next we collected VLE data of Ethylene Oxide and water from literature with different temperature & Pressure condition. After that we generated VLE data using UNISIM at the same temperature pressure condition as that collected from literature and calculated deviation of UNISIM from that of literature. The table shows the comparison of VLE data of UNISIM with that of literature and also shows the deviation of both the data 11 . Table 1: VLE Data comparison for EO-Water at 1 atm Pressure for NRTL Mole Fraction A(C) B C(C) D(C) % Deviation 0.951 11.5 1 11.52 10.42 9.548611 0.953 11.7 0.9 10.37069 11.99 15.61425 0.91 11.8 0.8 12.26858 12.71 3.598005 0.89 11.9 0.7 12.94321 12.85 0.720115 0.875 12 0.6 12.97478 12.85 0.961742 0.615 13.2 0.5 13.51375 12.85 4.911664 0.56 13.7 0.4 14.42966 12.85 10.94734 0.432 14.3 0.3 14.88937 13.61 8.592481 0.274 15 0.2 16.36442 16.4 0.217447 0.232 15.1 0.1 28.06781 26.72 4.801991 Table 2 : VLE Data Comparison for EO-Water at 1 atm Pressure for Wilson Mole Fraction A( C) B C(C) D(C) % Deviation 0.951 11.5 1 11.52 10.42 9.548611 0.953 11.7 0.9 10.37069 11.52 11.08225 0.91 11.8 0.8 12.26858 12.01 2.107628 0.89 11.9 0.7 12.94321 12.34 4.660406 0.875 12 0.6 12.97478 12.68 2.271976 0.615 13.2 0.5 13.51375 13.16 2.617704 0.56 13.7 0.4 14.42966 13.95 3.324152 0.432 14.3 0.3 14.88937 15.43 3.631008 0.274 15 0.2 16.36442 18.66 14.0279 0.232 15.1 0.1 28.06781 27.8 0.954168 Table 3: VLE Data Comparison for EO-Water at 1 atm Pressure for UNIQUAC Mole A(C) B C(C) D(C) % Fracti on Deviation 0.951 11.5 1 11.52 10.42 9.548611 0.953 11.7 0.9 10.37069 11.78 13.58931 0.91 11.8 0.8 12.26858 12.35 0.663679 0.89 11.9 0.7 12.94321 12.578 2.821604 0.875 12 0.6 12.97478 12.69 2.194904 0.615 13.2 0.5 13.51375 12.87 4.763667 0.56 13.7 0.4 14.42966 13.33 7.620857 0.432 14.3 0.3 14.88937 14.55 2.279251 0.274 15 0.2 16.36442 17.72 8.28373 0.232 15.1 0.1 28.06781 27.3 2.735568 Table Error! No text of specified style in document.-4: Comparison of Average Deviation at 1 atm Pressure NRTL WILSON UNIQUAC TOTAL DEVIATION 59.91364466 54.22580201 54.50118156 AVG DEVIATION 4.992803721 4.171215539 4.192398582 Table 5: VLE Data Comparison for EO-Water at 5 0 C Temperature for NRTL MOLE FRACTIO N A(mm Hg) B(mm Hg) DEVIATIO N 0.0253 111.1 144.2368616 29.82615804 0.0408 171.1 216.8428325 26.73456018 0.0562 215.7 246.9203059 14.47394805 0.0727 266 317.2010856 19.24852843 0.1231 405.4 428.6602517 5.737605246 0.154 544.5 472.1638293 13.28487984 0.2299 584.9 533.9689119 8.707657392 Table 6: VLE Data Comparison for EO-Water at 5 0 C Temperature for WILSON MOLE FRACT ION A(m m Hg) B(mm Hg) DEVIATION 0.0253 111.1 122.7850975 10.51763948 0.0408 171.1 179.189736 4.728074809 0.0562 215.7 209.1171971 3.051832574 0.0727 266 269.9471996 1.483909626 0.1231 405.4 366.1801135 9.674367663 0.154 544.5 406.9084629 25.26933648 0.2299 584.9 472.0888231 19.28725883 Table 7: VLE Data Comparison for EO-Water at 5 0 C Temperature for UNIQUAC MOLE FRACTI ON A(m m Hg) B(mm Hg) DEVIATIO N 0.0253 111.1 115.434493 3.901433815 0.0408 171.1 171.0140637 0.0502258 0.0562 215.7 201.2415495 6.703036871 0.0727 266 264.4717493 0.57453033 0.1231 405.4 368.655317 9.063809312 0.154 544.5 413.7340242 24.01578987 0.2299 584.9 485.5149272 16.99180591 Table 8: Comparison of Average Deviation at 5 0 C Temperature NRTL WILSON UNIQUAC TOTAL 118.0133372 74.01241946 61.30063191 International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) www.ijset.com, Volume No.1, Issue No.3, pg:-47-49 01 July 2012 49 DEVIATION AVG DEVIATION 16.85904817 10.57320278 8.75723313 Table 9: VLE Data comparison for EO-Water at 20 0 C Temperature for NRTL MOLE FRACT ION A(mm Hg) B(mm Hg) DEVIATIO N 0.0253 190.4 231.3190229 21.49108 0.0408 291.8 337.6777696 15.72233 0.0562 371.1 394.6824574 6.354745 0.0727 471.7 511.3920553 8.414682 0.1231 670.2 696.6572909 3.947671 Table 10: VLE Data comparison for EOWater at 20 0 C Temperature for WILSON MOLE FRACT ION A(m m Hg) B(mm Hg) DEVIATIO N 0.0253 190.4 220.0680977 15.58198 0.0408 291.8 318.7762151 9.244762 0.0562 371.1 371.1305206 0.008224 0.0727 471.7 473.0639033 0.289146 0.1231 670.2 647.228226 3.4276 Table 11: VLE Data comparison for EOWater at 20 0 C Temperature for UNIQUAC MOLE FRACTI ON A(m m Hg) B(mm Hg) DEVIATI ON 0.0253 190.4 211.0673575 10.8547 0.0408 291.8 309.9254873 6.211613 0.0562 371.1 363.6299038 2.01296 0.0727 471.7 475.6891192 0.84569 0.1231 670.2 660.2792993 1.48026 Table 12: Comparison of Average Deviation at 20 0 C Temperature NRTL WILSON UNIQUAC TOTAL DEVIATION 55.93051 28.55172 21.40523 AVG DEVIATION 11.1861 5.710343 4.281046 Note: Where, A=Literature value B= HYSYS value Table shows individual deviation and overall deviation of NRTL, WILSON & UNIQUAC. Similarly VLE data were compared at other temperature and pressure condition and was found that average deviation of all three fluid packages were nearly same.