Synthesis Gas and its Derivatives (Part - 1) | Chemical Technology - Chemical Engineering PDF Download
Synthesis Gas and Its Derivatives: Hydrogen, Co, Methanol, Formaldehyde, Metanol to Olefin Technology
Methane and synthesis gas are important petrochemical feedstock for manufacture of a large number of chemicals, which are used directly or as intermediates, many of these products are number of which are finding use in plastic, synthetic fiber, rubber, pharmaceutical and other industries. ‘Synthesis gas’ is commonly used to describe two basic gas mixtures - synthesis gas containing CO, hydrogen and synthesis gas containing hydrogen and nitrogen for the production of ammonia. Major requirements of synthesis gas in world scale petrochemical are given in Table M-VII 4.1.
Some of the emerging technologies in utilization of synthesis gas and methane for the production of petrochemicals, are Fischer-Tropsch synthesis, oxidative coupling of methane with chlorine to yield ethane and ethylene, methanol to olefin technology (MTO). Fischer-Tropsch synthesis is being studied in great detail world over and it is promising to be a future technology for manufacture of olefins from synthesis gas. CO that can be separated from synthesis gas either by cryogenic or by pressure swing adsorption is a promising feedstock for production of a variety of products. Product profile of methane, synthesis gas and CO based building blocks are given in Figure M-VII 4.1.
Table M-VII 4.1: Synthesis Gas Requirements for Major World Scale Petrochemicals
Product | Required H2 : CO | Typical world-scale capacity, TPA | Syn. gas required, Nm3/hr. |
Methanol | 2:1 | 1,60,000-12,75,000 | 48,000-1,90,000 |
Acetic acid | 0:1 | 2,75,000-5,45,000 | 18,000-36,000 |
Acetic anhydride | 0:1 | 90,000 | 3500 |
Oxo alcohol | 2:1 | 1,15,000-2,75,000 | 12,000-25,000 |
Phosgene | 0:1 | 4,800-1,60,000 | 3,500-12,000 |
Formic acid | 0:1 | 45,000 | 3,500 |
Methyl formate | 0:1 | 9,000 | 600 |
Propionic acid | 0:1 | 45,000-68,000 | 2,400-3,500 |
Methyl methacrylate | 1:1 | 45,000 | 4,700 |
1,4-Butandiol | 2:1 | 45,000 | 4,700 |
Figure M-VII 4.1: Methane, Synthesis Gas and CO Building Blocks
Synthesis Gas
Methane and synthesis gas are important petrochemical feedstock for the manufacture of a large number of chemicals, which are used directly or as intermediates, a number of which are finding use in plastic, synthetic fiber, rubber, pharmaceutical and other industries. ‘Synthesis gas’ is commonly used to describe two basic gas mixtures - synthesis gas containing CO, hydrogen and synthesis gas containing hydrogen and nitrogen for the production of ammonia.
Petrochemical derivatives based on synthesis gas and carbon monoxide have experienced steady growth due to large scale utilization of methanol and development of a carbonylation process for acetic acid and Oxo synthesis process for detergents, plasticizers, and alcohols. Recent market studies show that there will be a dramatic increase in demand of CO and syngas derivatives . Methanol is the largest consumer of synthesis gas. The reformed gas is to meet certain requirements with regard to its composition. It is characterized by the stoichiometric conversion factor, which differs from case to case
Raw Materials for Synthesis Gas
Various raw materials for synthesis gas production are natural gas, refinery gases, naphtha, fuel oil/residual heavy hydrocarbons and coal. Although coal was earlier used for production of synthesis gas, it has now been replaced by petroleum fractions and natural gas. Petrocoke is the emerging source for Synthesis gas. Coal is again getting importance alone are with combination of petroleum coke. Various Routes for Synthesis gas and Ammonia and Methanol manufacture is shown in Figure M-VII 4.2. Reactions in the manufacture of synthesis gas by Steam reforming and Partial oxidation in Table M-VII 4.2
Process Technology
Various synthesis gas production technologies are steam methane reforming, naphtha reforming, auto-thermal reforming, oxygen secondary reforming, and partial oxidation of heavy hydrocarbons, petroleum coke and coal.
Various steps involved in synthesis gas production through steam reforming are:
- Desulphurization of gas
- Steam reforming and compression
- Separation of CO2
Various available synthesis gas generation schemes are:
- Conventional steam reforming
- Partial oxidation
- Combined reforming
- Parallel reforming
- Gas heated reforming
Figure M-VII 4.2: Various Routes for Synthesis gas and Ammonia and
Methanol manufacture
Table M-VII 4.2: Reactions in the manufacture of synthesis gas by Steam reforming and Partial oxidation
Process steps | Reaction | Process Condition |
Desulphurisat |
|
|
ion: 1st Stage | C2H5SH +H2— H2S + C2H6 | Al-Co-Mo |
First Stage | C6H5SH + H2—— H2S + C6H6 | Al-Ni-Mo |
| C4H4SH + 3H2— H2S + C4H9 | Catalyst |
2nd Stage | CS2 +4H2— 2H2S + CH4 COS + H2— H2S + CO | 350-400oC |
CH3SC2H5 + H2— H2S + CH4 + C2H4 | Zinc oxide | |
Second Stage | H2S + ZnO—ZnS + H2O | absorbent 200-500 0C |
Steam reforming two stages | CnHm+1/4(4n-m)H2O—1/8(4n+m)CH4 + 1/8(4n-m)CO2 CH4 + H2O — CO + 3H2 CO + H2O — CO2 + H2 | Nickel catalyst 800 oC Endothermic reaction |
Partial Oxidation |
| Exothermic reaction |
Product | Uses |
DMT/ Polyethylene terephthalate | Polyester fiber and film, Adhesives, Wire coating, Textile sizing, Herbicides |
Methyl methacrylate (MMA) | Cast sheet, surface coating, molding resins, oil additives |
MTBE | Oxygenate |
Mono methanolamine | Naphthyl-n-methyl carbamate, monoethyl hydrazine, Monomethylamine nitrate |
Dimethylamine | Dimethyl acetamide, Dimethyl formamide, Dimethyl hydrazine, 2,4- Dichlorophenoxyacetic salt |
Methyl acetate | Paint remover |
Dimethylaniline | Solvent, Flavoring, Dyes, Fragrance |
Aceticacid | Vinyl acetate, Acetic anhydride, Chloro acetic acid, Ethyl acetate, Butyl acetate, Isopropyl acetate, Acetyl chloride, Acetanilide |
Formaldehyde | Phenolic resins, Pentaerythritol, Trioxane, 1,4-butanediol, Formaldehyde, sulphoxylate, Tetraoxane, Resorcinol resin |
Methylhalides | Quaternary amines, Methyl cellulose, Butyl rubber, Tri-methanol propene |
Table M-VII 4.4: Profile of Methanol production and Consumption Pattern in India Capacity for Methanol in India
Units | Location | Capacity (Tpa) | Share (%) |
Gujarat Narmada Valley Fertilisers Ltd. | Gujarat | 238100 | 51.11 |
Deepak Fertilisers& Petrochemicals Ltd. | Maharashtra | 100000 | 21.46 |
Rashtriya Chemicals & Fertilisers Ltd. | Maharashtra | 72600 | 15.58 |
Assam Petrochemicals Ltd. | Assam | 33000 | 7.11 |
National Fertilisers Ltd. | Punjab | 22110 | 4.74 |
Total |
| 465810 | 100.00 |
Units | Production | Sales | ||
2009-10 | 2010-11 | 2009-10 | 2010-11 | |
Gujarat Narmada Valley Fertilisers Ltd. | 187079 | 202544 | 111511 | 126059 |
Deepak Fertilisers& Petrochemicals Ltd. | 65647 | 81888 | 65703 | 81708 |
Rashtriya Chemicals &Fertilisers Ltd. | 44103 | 68700 | 19746 | 41264 |
Assam Petrochemicals Ltd. | 33759 | 30000 | 15040 | 15000 |
National Fertilisers Ltd. | 2669 | 516 | 131 | 44 |
Total | 333257 | 383648 | 212131 | 264075 |
Table M-VII 4.6: Methanol Consumption Pattern and Growth
Users | Share (%) | Growth Rate (%) |
Formaldehyde | 48 | 7 |
Pharmaceuticals | 21 | 8.5 |
Oxygenates | 9 | - |
Acetic Acid | 5 | 4 |
Alkyl Amines | 4 | 9 |
Dimethyl Sulphate | 3 | 8 |
Agrochemicals | 3 | 5 |
Chloromethanes | 4 | 8 |
Solvents/Others | 3 | 8 |
Total | 100 | 6 |
Methanol Process Technology
From the early 1800s until 1920s, the distillation of wood to make wood alcohol was the source of Methanol. The most common industrially favored method for the production of methanol was first developed by BASF in 1923 in Germany from synthesis gas utilising high pressure process using zinc-chromic oxide catalyst. However, due to high capital and compression energy costs compounded by poor catalyst activity, high-pressure process was rendered obsolete when ICI in the year 1966 introduced a low-pressure version of the process at 5-10 MPa and 210-270oC, with a new copper-zinc oxide based catalyst of high selectivity and stability.
Process steps involved in the production of methanol are:
- Production of synthesis gas using steam reforming or partial oxidation
- Synthesis of methanol
- High-pressure process (25 – 30 MPa)
- Medium pressure (10-25 MPa) process
- Low-pressure process (5-10 MPa)
Figure M-VII 4.3 illustrate the production of methanol from steam reforming of natural gas and naphtha.
Figure M-VII 4.3: Methanol from steam reforming of Natural gas and Naphtha
The major reactions take place during methanol synthesis converter can be described by following equilibrium reactions:
The first two reactions are exothermic and proceed with reduction in volume. In order to achieve a maximum yield of methanol and a maximum conversion of synthesis gas, the process must be effected at low temperature and high pressure.
After cooling to ambient temperature, the synthesis gas is compressed to 5.0-10.0 MPa and is added to the synthesis loop which comprises of following items – circulator, converters, heat exchanger, heat recovery exchanger, cooler, and separator. The catalyst used in methanol synthesis must be very selective towards the methanol reaction, i.e. give a reaction rate for methanol production which is faster than that of competing
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