The Production of Acetic Acid via Carbonylation of Methanol - Coursework Example

The Production of Acetic Acid via Carbonylation of Methanol In presenting the method of producing acetic acid through continuous reaction of methanol with carbon monoxide under the catalytic action of Rhodium, the paper would investigate on the patented invention of Hidetaka Kojima and Hiroyuki Miura. The proposed schematic process includes addition of iodide salt, methyl iodide, methyl acetate, and water in facilitating the Rhodium catalyst so that the invention meets the principal objective of generating high-quality acetic acid wherein the designed reaction is capable of lowering the synthesis of undesired by-products while rate of reaction is maintained. Introduction Acetic acid (CH3COOH), being one of the simplest known carboxylic acids, is an organic compound often produced in liquid form which possesses a hydrophilic property as a protic solvent. It is found to be slightly corrosive in metals such as Mg, Fe, and Zn whereupon reaction evolves H2 gas along with the formation of salts (acetates). The industrial production of acetic acid is carried out either via synthetic means or through bacterial fermentation and among a number of methods, carbonylation of methanol is widely known in acetic acid production. By this method, methanol is made to react with carbon monoxide which proceeds under the general stoichiometric equation: CH3OH + CO ---- CH3COOH Basically, when metal carbonyl is used to catalyze the reaction involving iodomethane as an intermediate, the three-step process is given by CH3OH + HI → CH3I + H2O CH3I + CO → CH3COI CH3COI + H2O → CH3COOH + HI Other than the common approach of methanol carbonylation, acetic acid may be formed as well through acetaldehyde oxidation, anaerobic fermentation, ethylene oxidation, and oxidative fermentation. Method Basic Process I. Fresh methanol (2) (injected to the stream of reactor recycling line) and carbon monoxide (1) enter the reactor which releases gaseous purging flow (4) upon reaction which yields liquid product mixture (5). II. Liquid product proceeds to the evaporator / flasher (6) from which are recovered the bottom flow (7) that is processed back into the reactor and the overhead (8) that enters distillation column which separates the acetic acid formed from low-boiling components. III. Distillates (10) of the distillation column are further sent to the unit (11) for removing carbonyl impurities (20) and are recycled back to the reactor. IV. The high-boiling components leaving the distillation column flow into the acetic-acid distillation column which splits into three – the generated crude acetic acid (15), the remaining low-boiling components (16), and the rest of the high-boiling components with boiling point higher than that of acetic acid (17). V. Crude acetic acid moves into a treatment tank filled with a cation exchange resin (18) after which the desired acetic acid product (19) is collected. (Note: Unit 6 (evaporator) is optional and is not necessary in the modified version of these steps in Figure 2). During Purification -- The model scheme proposed by inventors H. Kojima and H. Miura may be designed with a purification system that works as follows: Separation of the reaction mixture into volatile components (acetic acid, water, methyl acetate, and methyl iodide) and low-volatile components (Rhodium catalyst and iodide salt) takes place by distillation; Volatile components are further distilled to set the high-boiling component (acetic acid) apart from the low-boiling components which consist of water, methyl acetate, and methyl iodide. On the other hand, the low-volatile components are designated to the reactor to be reprocessed; Removal of carbonyl impurities from the low-boiling components recovered in (II) follows in order to yield residual components which also undergo recycling within the reactor; Another stage of distillation is required to accumulate acetic acid from the mixture with high-boiling components then the acid is treated in an exchange resin containing a silver or mercury-exchanged cation bed. Figure 1: Process Flow Diagram for the Production of Acetic Acid via Carbonylation of Methanol (with Evaporator) Figure 2: Another Version (without Evaporator) Catalyst / Concentrations Used Invention Settings Preferred: Rhodium catalyst in the form of Rh-complex in the reaction mixture like RhI3, [Rh(CO)2I2]- and rhodium carbonyl complexes (ranging between 200 and 3000 ppm); Methyl Acetate ≥ 2% (by weight); Iodide Salt (to stabilize the Rh-catalyst) preferrably metal iodides as LiI which can be 0.07 to 2.5 M in concentration; Water content ≤ 15% (by weight) in the reaction mixture With production rate of 11 mol/L*hr, acetaldehyde by-products ≤ 500 ppm for optimum yield of acetic acid Pressure and Temperature Carbonylation is basically reported to have been conducted in a reaction where the partial pressure of gaseous carbon monoxide in the reactor is 1.05 MPa in value or higher. Monsanto Company, an acetic acid plant founded in the city of Texas, operates at CO pressure of approximately 7500 psi (≈ 151.71 MPa). The company, nevertheless, claims that the use of Rh-catalyst can function independent of CO pressure conditions which apparently can go as low as in the range within 200 to 1800 psi (about 1.38 MPa – 12.41 MPa). According to inventors H. Kojima and H. Miura, “A typical reaction temperature of carbonylation according to the present invention is about 150°C to about 250°C, preferably about 180°C to about 220°C, and more preferably about 182°C to about 195°C.” Through the experimental studies carried out by Alamjit D. Singh and Norman W. Krase, on the synthesis of acetic acid from methanol and carbon monoxide, it is found that inaccurate estimates of thermal properties of acetic acid and other components render it unlikely for thermodynamic computations to bear the intended accuracy. However, Singh and Krase have managed to determine that the carbonylation reaction to produce acetic acid is an exothermic reaction which requires around 20,000 to 30,000 calories of heat energy occurring at temperatures from 300°C up to 500°C. STREAMS (CONTENT DESCRIPTION) (1)  carbon monoxide (2)  fresh methanol (5)  liquid reaction mixture (CH3COOH, H2O, C3H6O2, CH3I, Rh-catalyst, and I-salt) (7)  bottom flow (H2O, C3H6O2, CH3I, Rh-catalyst, and I-salt) (8)  overhead (CH3COOH, H2O, C3H6O2, CH3I, Rh-catalyst, and I-salt) (10)  distillate/overhead (with Rh-catalyst & I-salt) (13)  high-boiling component acetic acid (with H2O, C3H6O2, and CH3I) (15)  crude acetic acid (12)  recycled Rh-catalyst and I-salt combined with CH4O (2) back into the reactor References Hidetaka, Kojima et al. (Mar 2010). “Methods for Producing Acetic Acid.” Retrieved from http://www.google.com/patents?id=gTjVAAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false on October 21, 2012. Roth, James F. The Production of Acetic Acid -- Rhodium Catalysed Carbonylation of Methanol. Platinum Metals Rev. Monsanto Co., St. Louis, Missouri. Singh, A.D. and Krase, N.W. “Synthesis of Acetic Acid from Methanol and Carbon Monoxide.” ACS Publications. Retrieved from http://pubs.acs.org/doi/pdf/10.1021/ie50308a015 on October 21, 2012. Read More