Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

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Chemical Engineering : Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

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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

 

 

Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

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 CO

Various available synthesis gas generation schemes are:

  • Conventional steam reforming
  • Partial oxidation
  • Combined reforming
  • Parallel reforming
  • Gas heated reforming 

Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

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

Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

Exothermic reaction

 
 
Methanol 
 
Methanol was first obtained by Robert Boylein in the year 1661 through rectification of crude wood vinegar over milk of lime and was named adiaphorous spiritusliglorum. The term methyl was introduced in chemistry in 1835. Methanol is one of the largest volume chemicals produced in the world. Methanol consumption can be separated into three end use categories – chemical feedstock, methyl fuels, and miscellaneous uses. About 71% of the current global consumption of methanol is in the production of formaldehyde, acetic acid, methyl methacrylate, and dimethyl terephthalate. The global methanol industry has experienced very fundamental and structural changes and has settled down considerably.  
 
Demand changes in key methanol derivatives may adversely affect future demand in case of methanol. Product profile of methanol is given in Table M-VII 4.3. Globally the demand is expected to grow exponentially, not only caused by growing internal market of traditional applications but accelerated by new applications such as directing blending with gasoline, methanol to olefins (e.g. propylene) and dimethyl ether . Global demand for methanol will reach 122.6 million tones by 2020. Global methanol demand was 26.6 million tons and 44.9 million tones in 2000 and 2010 respectively . Present capacity of methanol in India is 4.65 lakh tones. Capacity for methanol and trends in production of methanol is given in Table M-VII 4.4, Table M-VII 4.5 and Table M-VII 4.6.
 
Table M-VII 4.3: Product Profile of Methanol

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

Table M-VII 4.5: Unit-wise Production and Sales of Methanol 

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.  

Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

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:

Synthesis Gas and its Derivatives (Part - 1) Chemical Engineering Notes | EduRev

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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