To: Dr. M. Timko From: B. Drury, W. Gao, N. Thompson, E. Towle Subject: Separation Process for the Reutilization of Acetone and Methanol Waste Introduction This company currently disposes of a waste stream of 60% acetone and 40% methanol, as a mixture at this composition does not have commercial use. However, this is a wasteful practice, as the waste could be separated into two relatively pure streams of 28% acetone in methanol for use in processing and 95% acetone for use in cleaning. It was initially believed that this would be impractical to separate these components as the mixture forms an azeotrope of 78% acetone at 101.3 kPa. However, this report endeavors to present practical options for separating this waste in a cost efficient manner, reducing the environmental impact of this company and potentially adding revenue if these streams are sold for use by other companies in processing and cleaning. Methodology The methods we considered were a pressure swing distillation system with two distillation columns and a single high pressure distillation column. The pressure swing distillation system was designed with the premise that shift of about 10% acetone in the azeotrope would be sufficient to distill relatively pure streams of each component. The design was optimized for cost, where cost is dependent on pressure and number of stages. The Wilson Model was used to approximate the fugacity coefficient of this mixture, using the parameters calculated at the azeotrope 78% at 101.3 kPa. The high pressure system was designed to have an azeotrope outside of the range of 28% to 95% acetone. The pressure was chosen such that the azeotrope would be at 28% acetone, allowing 28% acetone and 95% acetone to be isolated. Once again, the Wilson model was used to approximate fugacity coefficients, using the parameters mentioned above. As the pressure was over 300 kPa it was not assumed that gases in this system would behave ideally. MathCad and Excel were used for calculations and graphing.
Results and Discussion Wilson Model This data was calculated using data from the azeotrope at 78% and 101.3 kPa. It was calculated that the Wilson parameters, a12/R and a21/R are 388.129 and 68.111 respectively, as can be seen in Appendix 5. These yield calculated values that are able to predict the given data near the azeotrope, from approximately 60% to 100%. However, as the composition strays from this range the Wilson Model becomes less effective at predicting the system. This is demonstrated in Appendices 6-7. While these differences may have an impact on the number of stages needed in the ultimate calculations, it was not deemed to be significant as the azeotrope is the most important data to have modeled precisely. Pressure Swing Distillation The pressure swing distillation system uses first a column of 101.3 kPa which has 11 stages. A feed of 60% acetone at 150 kgmol/hour is fed into this column at the 8th stage, which produces a stream of 71.64 kgmol/hr of 28% acetone. A reflux ratio of 0.97 was used here, which is 1.4 times the minimum of 0.692. This column also produces a stream at the azeotropic composition of 78% acetone at 129.6 kgmol/hr, which is fed into a second column at 250 kPa . The feed is 1fed in at stage 13 of 22 total stages, where a reflux ratio of 0.8925 was used, which is 1.4 times the minimum of 0.6375. This produces a 78.36 kgmol/hr stream of 95% acetone, and a stream of azeotropic composition that is 52% acetone that is then recycled back at 51.24 kgmol/hr to be combined with the feed before it enters the first column. These flows can be seen in Appendix 10, and their calculations can be found in Appendix 9. The stages were designed by the steps shown in Appendix 11. This system will cost $112,500, as can be seen in Appendix 12. High Pressure Distillation A column of 14 stages was designed to operate at 1267 kPa, where there is an azeotrope of 28% acetone. A feed of 60% acetone at 150 kgmol/hr is fed in at stage 8 and then processed to yield a stream of 28% at 78.36 kgmol/hr and a second stream of 95% acetone at 71.64 kgmol/hr. A reflux ratio of 0.9625 was used here, which is 1.4 times the minimum of 0.6875. The process flow diagram and calculations associated with its design can be found in Appendix 16 and Appendix 15 respectively. This column would cost $68,680 and the pump would cost $4,479, resulting in a total cost of $73,159, as can be seen in Appendix 17.
1 Upon discussion with our group members we decided upon a pressure of 2.5 bar for the second distillation column. We believe that, although this shifts the azeotrope 26% instead of the suggested 10%, that this decrease in amount of recycle and number of stages would create a more energy efficient system.
Health and Safety As with all chemicals it is imperative to prevent the chemicals from interacting with workers, mechanical systems, and the environment in ways deemed unsafe by governmental organizations and common sense. Acetone and methanol are no exception and thus the appropriate preventative measures should be taken. Neither should be allowed to come into contact with workers skin, eyes, and other sources of entrance into the body. While acetone is relatively non-reactive, precautions should be taken against the interaction of methanol and various oxidizers, salts, metals, plastics, rubbers, and coatings, all of which are further specified in the MSDS found in the Works Cited. With regards to environmental exposure, neither chemical should be released into the environment and both chemicals should be disposed of safely following the proper procedures specified by the region, state, and federal laws and regulations. Conclusion and Recommendations Based on our calculations and research, we can conclude the best option for the separation of acetone and methanol in the waste stream is a High Pressure Distillation Column which eliminates the difficulties associated with the azeotrope by reducing it to 28%. This is evidenced by its lower cost of $73,160 on comparison to the Pressure Swing Distillation System, which would cost $112,500, making it $39,340 cheaper to utilize the High Pressure Column. Adjustments to the pressure would be unlikely to change this conclusion, as these costs are largely influenced by the difference in stage numbers for these two options. Especially at this high pressure, it is always important to take the necessary precautions concerning this mixture of acetone and methanol.
Appendices Appendix 1: Given VLE Data for Acetone and Methanol at 101.325 kPa
Appendix 2: X-Y Plot of VLE Data for Acetone and Methanol at 101.325 kPa
Appendix 3: T-x,y Plot of VLE Data for Acetone and Methanol at 101.325 kPa
Appendix 4: T-x Plot of VLE Data for Acetone and Methanol at 101.325 kPa
This graph was used to find the azeotropic temperature.
Appendix 5: X-Y Wilson Parameter Calculations for Azeotrope of 78% at 101.325 kPa
Appendix 6: X-Y Wilson Model Comparison to Given Data at 101.325 kPa
Appendix 7: X-Y Wilson Model Comparison to Given Data at 101.325 kPa
Appendix 8: Calculations of azeotropic point when P=2.5 bar
Appendix 9: Pressure Swing Flow Rate Calculations Finding B 2 F = 150 kgmol/hr z = 0.6 xB12 = 0.95 xB11 = 0.28 F = B1 + B2 B1 = F - B2 Fz = B1xB11 + B2xB12 Fz = (F - B2)xB11 + B2xB12 B2 = (Fz - FxB11)/(xB12 -xB11) B2 = 78.36 kgmol/hr Finding B 1 B1 = F - B2 B1 = 71.64 kgmol/hr Finding D 2 xD11 = 0.78 xD12 = 0.52 D1 = D2 + B2 D1xD11 = D2xD12 + B2xB12 (D2 + B2)xD11 = D2xD12 + B2xB12 D2 = (B2xB12 - B2xD11)/(xD12 - xD11) D2 = 51.24 kgmol/hr Finding D 1 D1 = D2 + B2 D1 = 129.6 kgmol/hr Finding F 1 F1 = F + D2 F1 = 201.24 kgmol/hr Finding x F11 F1xF11 = Fz + D2xD12 xF11 = (Fz + D2xD12)/F1 xF11 = 0.58
Appendix 10: Pressure-Swing Distillation Design
Appendix 11. Pressure Swing Distillation Stages
Appendix 12. Total cost of two column distillation and pumps
Appendix 13: Calculations of High Pressure Distillation Column
Appendix 14. High Pressure Distillation X-Y Graph with Stages
Appendix 15: High Pressure Column Flow Rate Calculations F = 150 kgmol/hr xD1 = 0.95 xB1 = 0.28 Finding D F = D + B B = F - D Fz = DxD1 + BxB1 Fz = DxD1 + (F - D)xB1 D = (Fz - FxB1)/(xD1 - xB1) D = 71.64 kgmol/hr Finding B B = F - D B = 78.36 kgmol/hr Finding L 1 /V 1 Determined from graph: L1/V1min = 0.675 L1/V1 = 1.4L1/V1min L1/V1 = 0.9625 Finding V 1 L1 = V1 - D L1/V1 = 1 - D/V1 V1 = D/(1 - L1/V1) V1 = 1910.4 kgmol/hr Finding L 1 L1 = 0.9625V1 L1 = 1838.76 kgmol/hr Finding V 2 Determined from graph: L2/V2 = 1.03 L2 = V2 + B L2/V2 = 1 + B/V2 V2 = B/(L2/V2 - 1) V2 = 2612 kgmol/hr Finding L 2 L2 = 1.03V2 L2 = 2690.36 kgmol/hr
Appendix 16: High Pressure Column Design
Appendix 17. Total cost of high pressure distillation column and pump
Works Cited "Material Safety Data Sheet Acetone MSDS." Msds.php . Science Lab.com, 21 May 2013. Web.
21 Feb. 2016. . "Material Safety Data Sheet Methyl Alcohol MSDS." Msds.php . Science Lab.com, 21 May
2013. Web. 21 Feb. 2016. .