Acetic Acid Plant Design

Definition of The Project A Methane to Acetic acid plant is to be set up at Brammanbaria in Bangladesh having a capacity of 300 ton 99% Acetic Acid per day, corresponding to 109500 ton of 99%Acetic Acid per year, and an intermediate capacity of 450 ton of 91.5% Methanol per day corresponding to ton of 16500 tons 91.5% of Methanol per year including all offsites, auxiliaries, utilities and supporting facilities using Industrial Grade Methane (96.48% CH4) fromTitas Gas Field as raw material.

Product & Raw material Specifications Acetic Acid, CH3COOH:

Acetic acid,systematically named ethanoic acid,is an organic compound.It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid has a distinctive sour taste and pungent smell. Liquid acetic acid is a hydrophilicprotic solvent, similar to ethanol and water. It dissolves not only polar compounds such as inorganic salts and sugars, but also non-polar compounds such as oils and elements such as sulfur and iodine. It readily mixes with other polar and non-polar solvents such as water, chloroform, and hexane. With higher alkanes (starting with octane), acetic acid is not completely miscible anymore, and its miscibility continues to decline with longer n-alkanes. This dissolving property and miscibility of acetic acid makes it a widely used industrial chemical, for example, as a solvent in the production of dimethyl terephthalate.Although it is classified as a weak acid, concentrated acetic acid is corrosive and can attack the skin. Table 1.1:Properties of CH3COOH: Molecular formula Molar mass Appearance Odor Density Melting point Boiling point Solubility in water log P Acidity (pKa) Basicity (pKb) Refractive index (nD) Viscosity Dipole moment Specific heat capacity (C)

CH3COOH

60.05 g·mol−1 Colourless liquid Pungent/Vinegar-like 1.049 g cm−3 16 °C; 61 °F; 289 K 118 °C; 244 °F; 391 K Miscible -0.322 4.76 9.198 (basicity of acetate ion) 1.371 1.22 mPa s 1.74 D 123.1 J K−1 mol−1

Std molar entropy (So298) Std enthalpy of formation (ΔfHo298) Std enthalpy of combustion (ΔcHo298)

158.0 J K−1 mol−1 -483.88--483.16 kJ mol−1 -875.50--874.82 kJ mol−1

Methanol, CH3OH: Methanol, also known as methyl alcohol,wood alcohol, wood naphtha or wood spirits. It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a pleasant smell . It is highly toxic and unfit for consumption. At room temperature, it is a polar liquid, and is used as an antifreeze, solvent, fuel, and as a denaturant for ethanol.

Table 1.2: Properties of Methanol Molecular formula Molar mass Appearance Density Melting point Boiling point log P Vapor pressure Acidity (pKa) Refractive index (nD) Viscosity Dipole moment Flash point Autoignition temperature Explosive limits

CH3OH 32.04 g·mol−1 Colorless liquid 0.7918 g·cm−3 0.7925 g·cm−3 @20°C −97.6 °C (−143.7 °F; 175.6 K) 64.7 °C (148.5 °F; 337.8 K) -0.69 13.02 kPa (at 20 °C) 15.5[3] 1.33141[4] 0.545 mPa×s (at 25°C) [5] 1.69 D 11 to 12 °C (52 to 54 °F; 284 to 285 K) 385 °C (725 °F; 658 K) 6%-36%

Availability of Raw Materials: 

CH4: Bought from Titas Gas Field, Brammanbaria



H2O (cooling, treated, DM water, etc.): Available in Bangladesh.

Raw material specification Natural Gas from Titas Gas Fiel

Process Selection Methane to Methanol conversion process

Catalytic Conversion Features:    



Conversion of methane to methanol with an economic yield of 10% In most experiments with solid catalysts, selectivities to methanol fell rapidly as methane conversions exceeded 59% complete oxidation of methane to carbon dioxide (ΔH = -877 kJ/mol) is highly favored over partial oxidation of methane to methanol (ΔH = -200 kJ/mol) A noticeable progress, however, has been made in the field of molecular catalysis by Periana et al., who demonstrated the selective conversion of methane to methanol at temperatures around 473 K over platinum bipyrimidine complexes. According to their experiment, 81% selectivity to methyl bisulfate, a methanol derivative, was reached at methane conversion of 90% in concentrated sulfuric acid Although these results are promising, commercial applications are hampered by difficult separation and recycling of the molecular catalyst.

Thermal Cracking 

 

Methane is converted to methanol by partial oxidation to hydrogen gas and carbon monoxide (synthesis gas or syngas) at high temperatures normally several hundred degrees celsius Syngas is then catalytically converted to methanol over a copper or platinum surface, also at a couple hundred degrees Celsius It is only around five or ten percent efficient due to accidental total oxidation to carbon dioxide and water.

Photo-Catalytic Conversion 

Ultraviolet light breaks water into a hydrogen and hydroxyl free radical, which are highly reactive. When a hydroxyl radical reacts with a methane molecule, a hydrogen is displaced and methanol is produced.

   

With the use of tungsten oxide or a similar semiconductor, photons of lower energy than ultraviolet (down to blue) can be used. Using Of WO₃ as photo-catalyst visible laser light can be used in room temperature It is highly energy inefficient (only 2-3% efficiency) The process is not out in commercial production yet

Biological conversion 

     

Conversion combines both methane and ammonia streams using methane-oxidizing bacteria and ammonia-oxidizing bacteria, in both wild type and genetically modified forms Can convert heterogeneous methane feedstocks, unlike existing commercial process Does not require a pure source of methane It does not require expensive chemical catalysts Cleanup and dehumidification processes not required Widely applicable to digester gas, landfill gas, peatbogs, marshes, and wastewater treatment facilities Conversion process is time consuming

ICI process     

Catalyst: Copper-Zinc oxide catalyst Temperature: 200-30000C Pressure: 5-10 MPa Activity of this catalyst is more sensitive to impurities (poisoning) Reduced manufacturing costs.

Methanol to Acetic acid Cativa Process         

Process developer: BP chemicals Catalyst: Iridium/iodide catalyst Improved catalyst stability Allowing operation at low water concentrations High reaction rates Reduced formation of liquid by-products Improved yield on carbon monoxide Temperature: Pressure:

Monsanto process      

Process developer: Monsanto Temperature: 150-2000C Pressure: 30-60 bar Catalyst: rhodium/iodide catalyst Selectivity: 99% To prevent rhodium loss the reactor composition is maintained within limits on water, methyl acetate, methyl iodide and rhodium concentrations High H2O concentrations to prevent catalyst precipitation and maintain high reaction rates



BASF process    

Catalyst: cobalt /iodide catalyst Temperature: 2500C Pressure: 680 bar Selectivity: 90% (based upon methanol)