Preliminary Process Synthesis Propane to Acrylic Acid design plant proses

15 acetate, an extraction solvent recommended by U.S. Patent Number 5,315,037. 11 The decanter succeeded in separating the mixture into a water stream containing 97 by mass water and the balance organic components and an organic stream. Through a series of two more distillation columns a majority of the solvent which can be recycled, and 96 of the total acrylic acid were recovered. Ultimately, this method of separation was not selected because the additional costs associated with the decanter and the solvent feed of n-propyl acetate did not result in better acrylic acid separation. The second method of separation proposed was an extractive distillation process performed in a distillation column, which eliminated the use of a decanter but still required an entrainer. 12 An Aspen diagram of the separation process can be seen in Figure B.3 located in Appendix B, page 134. The extractive agent is introduced near the top of the column and its presence alters the relative volatility of the compounds to allow a greater degree of separation. After a separation using different entrainers based on suggestions from U.S. Patent 5,154,800 12 was designed in Aspen, dimethylsulfoxide was selected as the optimal extractive agent. As with the decanter process, this method of separation was not selected because it did not result in higher acrylic acid separation despite the added cost of solvent and keeping the number of distillation towers four used the same. The final separation process evaluated was a network of four distillation towers which maneuvered around the azeotropes within the system. This processes proved to be better than the other two alternatives based on cost, optimal separation of acrylic acid and final stream purity. This separation scheme is discussed later on in detail. 11 Sakamoto, K., Tanaka, H., Ueoka, M., Akazawa, Y., Baba, M. 1994. U.S. Patent No. 5,315,037. 12 Berg, L. 1992. U.S. Patent No. 5,154,800. 16

3.4 Assembly of Database

Input Costs The input cost for water, including pressurized steam, was taken from Aspen Economic Analyzer. Current pricing from Aspen is based on 2010 dollars, so a multiplying factor of 1.0447 CE 20122010 = 575.4550.8 was used. Input costs for liquid propane and compressed oxygen were specified in the problem statement found in Appendix A, page 130. Aspen Simulation Specifications In this project, Aspen Plus v7.3 was used. All simulations should be run in this version of Aspen to avoid compatibility issues. In order to accurately model the three azeotropes in the process, the non-random two-liquid NRTL activity coefficient model, along with the Redlich- Kwong RK equation of state model, was used in all simulations. RStoic was used over a PFR model reactor, as conversion, selectivities, and yield data was more easily available and more complete than kinetic models which are needed for PFR models in Aspen. RStoic was used to model the conversion information taken from patented processes, and to model the heat rise in the reactor with given conversion data. MComp was used to model the two compressor blocks in the system. The compressors were designed to have the lowest possible outlet pressure conditions such that pressure conditions into the Flash block were as specified without doing extra work. Heat exchangers, including the reactor, were designed outside of Aspen. Design specifications were used to optimize conditions in the system. Design specifications were used to change reflux ratio and distillate-to-feed ratio in each tower to ensure the purity of acrylic acid. Tower trays and feed location were optimized by plotting tray temperatures and tray concentrations to eliminating dead zones. A design specification for the oxygen inlet flow rate was used such that propane exiting the reactor was in extreme excess of oxygen so that further oxidation is limited. 17 Section 4 Process Flow Diagram Material Balance 18

4.1 Overall Process Outline

Figure 4.1: Overall Process Diagram. This shows the overall process, which is made up of three sections: the mixing section, the reactor section, and the separation section. 19 Table 4.1: Overall Process Stream Summary. This table provides temperature, pressure, vapor fraction, and component flow rates for all streams in the process flowsheet. Stream S‐ AIR O2 PRODUCT PROPANE PURGE S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ Temperature °F 225 75 75 100 75 85 ‐ 6 230 406 24 230 228 740 780 280 85 82 85 85 Pressure psia 54 14.6959 500 75 150 25 60 55 54 60 55 54 49 45 40 35 30 25 25 Vapor Fraction 1 1 1 1 1 1 1 0.2 1 1 1 1 1 0.92 0.92 1 1 Total Flow lbhr 554490 12636 23839 25314 23616 17149 23839 23839 12636 23616 23616 620230 620230 620230 620230 620230 620230 571630 554490 Component Flows lbhr Propane 153820 23616 4757 23616 23616 180250 180250 162230 162230 162230 162230 158570 153820 Oxygen 2427 2943 23839 75 23839 23839 2943 29212 29212 2505 2505 2505 2505 2502 2427 Propylene 19146 592 19451 19451 20119 20119 20119 20119 19739 19146 Acrylic Acid 1791 25286 55 1901 1901 28548 28548 28548 28548 1846 1791 Water 5713 25 177 7547 7547 22309 22309 22309 22309 5890 5713 Nitrogen 313410 9693 9693 9693 323240 323240 323240 323240 323240 323240 323110 313410 Acetic Acid 379 2.5 12 537 537 1393 1393 1393 1393 390 379 Carbon Dioxide 57798 1788 58094 58094 59894 59894 59894 59894 59585 57798 Dowtherm Stream S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ S‐ WASTE Temperature °F 225 85 86 86 400 418 318 317 295 307 374 371 415 100 298 287 265 264 236 Pressure psia 59 25 150 130 125 98 95 90 70 73 68 68 68 63 65 67 65 60 25 Vapor Fraction 1 1 1 1 1 1 1 1 1 1 0.3 Total Flow lbhr 554490 48596 48596 48596 48596 23846 24750 24750 19472 5278 5278 1469 25314 25314 3809 13819 5653 5653 17628 Component Flows lbhr Propane 153820 3651 3651 3651 3651 3651 3651 3651 834 2817 2817 834 Oxygen 2427 3 3 3 3 3 3 3 3 3 Propylene 19146 380 380 380 380 380 380 380 75 305 305 75 Acrylic Acid 1791 26702 26702 26702 26702 23844 2858 2858 1024 1834 1834 1443 25286 25286 392 913 110 110 1305 Water 5713 16419 16419 16419 16419 16419 16419 13036 3383 3383 25 25 25 3358 11202 1834 1834 14560 Nitrogen 313410 130 130 130 130 130 130 130 130 130 Acetic Acid 379 1003 1003 1003 1003 1 1001 1001 941 60 60 1 3 3 59 783 158 158 842 Carbon Dioxide 57798 308 308 308 308 308 308 308 12 296 296 12 Dowtherm Stream DOWTHERM‐1 DOWTHERM‐2 DOWTHERM‐3 DOWTHERM‐4 DOWTHERM‐5 DOWTHERM‐6 Temperature °F 198 738 458 299 203 198 Pressure psia 40 35 30 25 20 15 Vapor Fraction Total Flow lbhr 385000 385000 385000 385000 385000 385000 Component Flows lbhr Dowtherm 385000 385000 385000 385000 385000 385000