Market and Competitive Analysis

13 inert gas, such as water or nitrogen, may prevent excess oxidation of propylene by enhancing the desorption of acrylic and acetic acids from the catalyst surface. Kinetics Propane partial oxidation to acrylic acid over vanadium pyrophosphate VPO catalysts, heteropolyacids, and multi-component oxidic catalysts has been studied in great depth. Only recently has a catalyst system been developed that is active and selective enough to substitute for the existing industrial process. 9 This is due to the difficulty in maintaining high reaction temperatures so the reaction rate will be high while preventing total oxidation reactions. A thorough review of mixed metal oxide catalyst literature was performed and the results are summarized in Table 3.1. 10 The conversions listed are based on propane and the yield and selectivities are based on acrylic acid. Table 3.1: Mixed metal-oxide Catalysts for Propane Oxidation to Acrylic Acid Catalyst Feed Temp o C Conversion Yield Selectivity Mo 1 V 0.3 Nb 0.05 Sb 0.15 Te 0.06 O x PropaneO 2 H 2 ON 2 380 21 12 54 Mo 1 V 0.3 Nb 0.05 Sb 0.09 Te 0.09 O x PropaneO 2 H 2 ON 2 380 19 12 60 Mo 1 V 0.3 Sb 0.16 Nb 0.05 O x Propaneair H 2 O 380 50 16 32 Mo 1 V 0.3 Sb 0.25 Nb 0.11 O x PropaneO 2 H 2 ON 2 400 21 12 61 Mo 1 V 0.3 Te 0.23 Nb 0.125 O x PropaneairH 2 O 400 80 48 60 Mo 1 V 0.3 Te 0.23 Nb 0.12 O x PropaneairH 2 O 390 71 42 59 Mo 1 V 0.3 Te 0.23 Nb 0.12 O x PropaneO 2 H 2 OHe 350 23 14 61 According to experimental data, the most effective catalysts to date are Mo-V-Te-Nb-O catalysts. The proposed process design uses the Mo 1 V 0.3 Te 0.23 Nb 0.125 O x catalyst. 9 Hatano, M. Kayo, A. 1991. U.S. Patent No. 5,049,692. 10 Lin, M. 2001. Selective oxidation of propane to acrylic acid with molecular oxygen. Applied Catalysis A: General, 207, 1-16. 14 Separation After acrylic acid is produced, it must be separated from the reactants oxygen, nitrogen, and propane and the by-products of the reaction acetic acid, water, and propylene. While a simple flash drum will be able to separate the reactants from acrylic acid, the final product separation from acetic acid and water is difficult due to three separate azeotropes as seen in Figure 3.2: In order to determine the most economic and efficient method of separation, three different processes were evaluated and the results compared. The first proposed method of separation, displayed in Figure B.2 located in Appendix B, page 133, involved the use of a liquid-liquid extraction process to allow better separation of organic components from water. The product stream from the reactor was fed to a flash drum and a distillation column, which separated and recycled the gaseous components. The bottoms product was separated in an eight- tray column into a pure acrylic acid stream. The distillate contained water, acetic acid, and residual acrylic acid and was fed into a decanter. The decanter was operated with n-propyl Figure 3.2: Azeotrope Diagram for Acetic AcidWaterAcrylic Acid. The diagram was produced using Aspen, based on the NRTL-RK model.