# From crude oil and natural gas to the C1-C4 building blocks: C1 chemistry: synthesis gas, methanol, ammonia and coal

Source page: https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p4/

[Understanding Chemicals](https://www.materialinsights.org/learn/chemicals/) / [Module 5: From crude oil and natural gas to the C1-C4 building blocks](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/) Part 4 of 5

## C1 chemistry: synthesis gas, methanol, ammonia and coal

Methane cannot be cracked into olefins the way ethane can. Its value comes instead from synthesis gas, a mixture of carbon monoxide and hydrogen, from which ammonia and methanol are made. The same gas can be made from coal, which is how China built a coal-based chemical industry. This part traces those routes and what they cost in energy and carbon.

### 4.1 Steam reforming turns methane into synthesis gas, and the mix is tuned to the product

Synthesis gas (syngas) is a mixture of carbon monoxide and hydrogen. Different uses need different ratios, Wittcoff explains. Methanol and Fischer-Tropsch synthesis need CO:H2 of 1:2. Hydroformylation needs 1:1. Ammonia needs N2:H2 of 1:3 and no CO at all.

The dominant route is steam reforming of methane. First the gas is desulphurised over zinc oxide at 360-400 C to below 2 ppm sulphur, because sulphur poisons the nickel catalyst. It is then mixed with 2.5-3.5 moles of steam per mole of methane. The mixture passes through catalyst-filled tubes at about 800 C and 35 bar: CH4 + H2O → CO + 3H2. The reaction absorbs about 227 kJ per mole. The heat comes from burners outside the tubes, so the reformer is a large furnace. About 7% of the methane passes through unchanged. Shreve (1984) gives a reformer range of 760-980 C. His typical product contains about 75% hydrogen, 8% CO and 15% CO2.

The water-gas shift then adjusts the mix: CO + H2O → CO2 + H2. It releases a little heat and is favoured at lower temperature, so it runs at about 315-370 C over iron oxide. For ammonia, air is added in a second reformer to supply nitrogen. CO is shifted to CO2, and the CO2 is scrubbed out with an amine solution. For a CO-rich gas, CO2 can be added to push the shift backwards.

Partial oxidation is the alternative. The feed is burned with about 35% of the oxygen needed for full combustion, at 1300-1400 C and 60-80 bar. It accepts heavy oils and needs no desulphurisation, but it needs a costly oxygen plant.

Data Synthesis gas requirements and routes

| Use | Gas needed | Typical source and adjustment |
|---|---|---|
| Ammonia | N2:H2 = 1:3, no CO | Steam reforming, air in secondary reformer, shift, CO2 removal |
| Methanol | CO:H2 = 1:2 (H2 in slight excess) | Steam reforming; purge surplus H2 or add CO2 |
| Hydroformylation (oxo) | CO:H2 = 1:1 | Add CO2 at shift stage to move equilibrium towards CO |
| Fischer-Tropsch | CO:H2 = 1:2 | Coal gasification (Sasol) or gas reforming |
| Pure hydrogen | H2 only | Reforming plus full shift, CO2 removal and methanation |

 Source: Wittcoff (2004), Ch 10 section 10.4, pdf pp. 379-383  Worked example

#### Why methane gives too much hydrogen for methanol

Reforming gives 3 H2 per CO, but methanol (CO + 2H2 → CH3OH) needs only 2. Wittcoff lists two fixes. The surplus hydrogen can be purged and burned as reformer fuel. Or CO2 from an outside source, such as an ammonia plant, can be added to use up the excess: CO2 + 3H2 → CH3OH + H2O. Naphtha reforming, by contrast, gives a gas close to the right ratio.

- Wittcoff (2004), Ch 10 sections 10.4-10.4.5 · pdf pp. 379-384
- Shreve (1984), Ch 7 Industrial Gases (hydrogen) · pdf pp. 125-127

### 4.2 Methanol: a low-pressure copper catalyst, a big recycle loop and giant plants

Methanol is made by CO + 2H2 → CH3OH over a catalyst. The reaction gives off heat and the gas shrinks from three moles to one. So the equilibrium favours methanol at low temperature and high pressure. Shreve's table shows the effect. At 300 C, one-pass equilibrium conversion rises from 8% to 62% as pressure is raised sixfold, from 500 to 3,000 in the table's units.

The industry history is a story of catalysts allowing gentler conditions. BASF's original process used zinc-chromium oxide at 320-380 C and 340 bar. In 1972 ICI introduced a low-pressure process using copper-zinc on alumina at 240-260 C and 50-100 bar. Shreve describes a Lurgi low-pressure plant at 5-8 MPa and 250-260 C. The copper catalyst is more active and selective, giving purer methanol, but it needs syngas almost free of sulphur and chlorine. Lower pressure saves a great deal of compression energy and allows centrifugal compressors. Because conversion per pass is limited, unreacted gas is recycled many times. A small purge removes inert gases. Crude methanol is distilled in two columns. The main by-product is dimethyl ether.

The economics are dominated by the front end. Shreve states that making the syngas accounts for nearly 75% of the final cost of methanol. That is why licensors developed "megamethanol" plants of 5,000-10,000 t a day. Wittcoff explains these as a way to use cheap stranded gas at remote sites and still ship the product to distant markets.

Uses: the IEA (2018) says about 40% of methanol becomes formaldehyde. Wittcoff puts formaldehyde at about 35% excluding MTBE, followed by acetic acid.

Process flowchart Steam methane reforming to methanol (low-pressure process) Inputs **Natural gas**about 0.71 t methane per t methanol, feed plus fuel (Brennan, indicative) **Steam**2.5-3.5 mol per mol methane **CO2 (optional)**added to use surplus hydrogen Process steps 1 **Desulphurisation**

zinc oxide bed, 360-400 C, sulphur to below 2 ppm to protect nickel and copper catalysts
 2 **Steam reformer (fired tubular furnace)**

nickel catalyst, about 800 C, 35 bar; CH4 + H2O → CO + 3H2, +227 kJ/mol; about 7% methane slip
 3 **Heat recovery**

hot gas raises steam that drives compressors
 4 **Syngas compression**

to 5-10 MPa for the low-pressure loop
 5 **Methanol converter**

Cu-Zn on alumina, 240-260 C, 50-100 bar; CO + 2H2 → CH3OH; exothermic, limited conversion per pass
 6 **Condenser and separator**

crude methanol condensed; unreacted gas recycled; small purge to reformer fuel
 7 **Distillation (two columns)**

removes low- and high-boiling impurities such as dimethyl ether and water
 Outputs **Methanol**1 t **Purge gas (H2-rich)**burned as reformer fuel **Flue gas CO2**from reformer burners

Syngas preparation is nearly 75% of methanol cost (Shreve). Plants of 5,000-10,000 t/day were being developed for stranded gas (Wittcoff).
 Source: Wittcoff (2004), Ch 10; Shreve (1984), Ch 38; Brennan (2020), Table 4.2, Wittcoff pdf pp. 380, 388-389; Shreve pdf pp. 781-782; Brennan pdf p. 106  Worked example

#### Worked example: how much gas per tonne of methanol

Stoichiometry first: one CH4 (16 g) gives one CO, which gives one CH3OH (32 g). So feedstock alone is 16/32 = 0.5 t methane per t methanol. Brennan (2020) gives an indicative consumption of 0.71 t methane per t methanol. The difference, 0.21 t or about 30% of the total, is gas burned to heat the reformer and drive the plant. Kent (2012) likewise notes that syngas units consume 30% or more of the methane's energy.

- Wittcoff (2004), Ch 10 section 10.5.2 · pdf pp. 388-389
- Shreve (1984), Ch 38 Petrochemicals (methanol) · pdf pp. 781-782
- Brennan (2020), Ch 4, Table 4.2 · pdf p. 106
- Kent (2012), Ch 20 Natural Gas · pdf p. 829
- IEA (2018), Ch 1 · pdf p. 24

### 4.3 Ammonia, formaldehyde and acetic acid: what syngas and methanol become

Wittcoff calls ammonia by far the most important chemical made from syngas. It consumes about 5% of the world's natural gas, against about 1% for methanol. In the Haber-Bosch process, N2 + 3H2 react over promoted iron oxide at about 450 C and 250 bar. Only about 10% converts per pass, so most of the gas is recycled. Early plants ran at 1,000 bar with reciprocating compressors. Modern plants accept lower pressure because centrifugal compressors driven by waste-heat steam are cheaper and need less maintenance. That switch let plant size grow from about 200 t a day in 1960 to 1,500-1,850 t a day in the early 2000s. Ammonia links back to carbon chemistry too. Its process CO2 is fed to the urea plant next door: 2NH3 + CO2 → urea + water. The IEA (2018) says more than half of ammonia becomes urea and about 80% of ammonia use is agricultural.

Formaldehyde is methanol's largest outlet. In the main route, methanol vapour and air pass over a silver catalyst at about 700 C and near atmospheric pressure. Partly it is dehydrogenated and partly oxidised, so the heat roughly balances. Molar yields are 83-92%. A second route uses iron-molybdenum oxide at 300-400 C. The product is sold mostly as a 37% water solution. It goes into urea-formaldehyde resins for particle board, phenolic resins and polyacetal plastics.

Acetic acid shows how a catalyst can reshape an industry. In the Monsanto process, methanol and CO combine (CH3OH + CO → CH3COOH) over an iodide-promoted rhodium catalyst at about 200 C. Selectivity is over 99%. BP's Cativa process uses iridium at lower water content, cutting energy and capital. By the early 2000s about 88% of US acetic acid came this way.

Value chain What synthesis gas becomes

- **Synthesis gas (CO + H2, or N2 + H2)**

  - **Ammonia** Haber-Bosch, iron catalyst, about 450 C, 250 bar, about 10% per pass

    - **Urea** uses ammonia plant CO2; more than half of ammonia
    - **Nitric acid, ammonium nitrate, ammonium phosphates** fertilisers
    - **Acrylonitrile, caprolactam, HCN, amines** chemical uses

  - **Methanol** Cu-Zn catalyst, 240-260 C, 50-100 bar

    - **Formaldehyde** about 35-40% of methanol; resins, polyacetals, MDI
    - **Acetic acid** methanol + CO over rhodium or iridium; then vinyl acetate (over 60%)
    - **MTBE** methanol + isobutene
    - **Methanol-to-olefins** ethylene and propylene; commercial in China
    - **Methylamines, methyl methacrylate, solvents** smaller uses

  - **Hydrogen** about 60% of all hydrogen goes to ammonia; refineries second
  - **Fischer-Tropsch liquids and oxo alcohols** fuels, waxes, alpha-olefins; aldehydes from olefins + CO + H2

 Source: Wittcoff (2004), Ch 10, pdf pp. 383-393  In the data

#### A cost sheet for acetic acid

Brennan's illustrative cost sheet is for a 40,000 t a year methanol carbonylation plant with $100 million of fixed capital. It uses 0.54 t methanol and 0.52 t carbon monoxide per tonne of acid, each at $300 a tonne. Raw materials therefore cost $162 + $156 = $318 per tonne of acid, plus 0.12 MWh of electricity at $14.40. His separate table of indicative consumptions gives 0.53 t methanol and 0.47 t CO.

- Wittcoff (2004), Ch 10 sections 10.4.5-10.5.2.2 · pdf pp. 383-393
- IEA (2018), Ch 1 · pdf pp. 16, 24
- Brennan (2020), Ch 4, Tables 4.2 and 4.7 · pdf pp. 106, 126

### 4.4 Coal can replace gas through gasification, and China does so at scale

Coal was the chemical industry's first raw material. Heating coal to about 1,000 C without air in a coke oven gives, by weight, about 80% coke, 12% coke oven gas, 3% tar and 1% light oil. The light oil is mostly benzene, toluene and xylenes. Wittcoff notes that coal tar supply is tied to steel's need for coke, so it cannot grow to replace petrochemicals.

The larger route is gasification. Coal reacts with steam and oxygen to give syngas (C + H2O → CO + H2), and the syngas is then used exactly as gas-based syngas would be. The hard part is handling solids. Gasifiers use moving beds (Lurgi), fluid beds (Winkler) or entrained flow (Texaco, Shell, Koppers-Totzek). Their product gases range from H2/CO of about 0.5 to 1.7. The IEA (2018) adds that coal-based ammonia equipment costs more than twice as much as gas-based. Even the best coal plants use about twice the process energy of gas plants.

China makes these routes pay because it has abundant cheap coal and little gas rich in ethane. The IEA (2018) gives China 20% of world HVC capacity, 33% of ammonia and 55% of methanol, with coal dominant for both ammonia and methanol. About 20% of Chinese methanol uses coke oven gas. Methanol-to-olefins (MTO) is commercial only in China. Those plants sit inland near the coal, while naphtha crackers sit on the coast beside refineries. Before the 2014 oil price slump, Chinese MTO undercut the cheapest naphtha cracker by nearly $300 per tonne of HVC. By 2017 that discount had almost vanished. Kent (2012) records how unstable coal-to-liquids policy was. In 2008 China's planners required approval for all coal-to-liquids projects except two run by Shenhua.

Data Light olefins from steam cracking versus methanol (t per t ethylene + propylene)

|  | Naphtha cracker (light naphtha) | Ethane cracker | MTO (SAPO-34) | MTP (zeolite) |
|---|---|---|---|---|
| Catalyst | None | None | SAPO-34 | Zeolite |
| Temperature, C | 850-860 | 880-900 | 350-500 | 420-490 |
| Feedstock | 1.9 | 1.2 | 3.0 methanol | 3.1 methanol |
| Light products | 0.39 | 0.20 | 0.07 | 0.02 |
| C4+ | 0.51 | 0 | 0.23 | 0.37 |
| Water | 0 | 0 | 1.7 | 1.75 |

Methanol loses its oxygen as water: 56% of MTO reactor output is water. Wittcoff says MTO pays only with very cheap gas (or, per the IEA, cheap coal).
 Source: Wittcoff (2004), Ch 10, Table 10.4, pdf p. 398  Case

#### Sasol and the Fischer-Tropsch route

South Africa built coal-based Fischer-Tropsch plants as insurance against an oil boycott. Syngas over an iron catalyst grows carbon chains of every length, from methane to hard wax. At Sasol's 325 C fluid bed, about 40% is gasoline-range and 12% propylene. The products did not match the country's fuel needs, leaving too little diesel. Sasol later "mined" the streams for alpha-olefins such as hexene-1 and octene-1, becoming a major supplier.

- Wittcoff (2004), Ch 12 Chemicals from Coal · pdf pp. 425-434
- Wittcoff (2004), Ch 10 section 10.5.2.5 · pdf pp. 397-398
- IEA (2018), Ch 2 · pdf pp. 31, 33, 40-41, 44, 46
- Kent (2012), Ch 19 Coal Technology · pdf pp. 777-778, 806-807

### See it in the table
[H₂O Water](https://www.materialinsights.org/commodities/water/)[Gas Natural gas](https://www.materialinsights.org/energy/natural_gas/)[Cu Copper](https://www.materialinsights.org/commodities/copper/)[Zn Zinc](https://www.materialinsights.org/commodities/zinc/)[Ni Nickel](https://www.materialinsights.org/commodities/nickel/)[St Steel](https://www.materialinsights.org/commodities/steel/)[Cr Chromium](https://www.materialinsights.org/commodities/chromium/)[Mo Molybdenum](https://www.materialinsights.org/commodities/molybdenum/)[Ag Silver](https://www.materialinsights.org/commodities/silver/)[Rh Rhodium](https://www.materialinsights.org/commodities/rhodium/)[Cl2 Chlorine](https://www.materialinsights.org/chemicals/chlorine/)[H2 Hydrogen](https://www.materialinsights.org/chemicals/hydrogen/)[O2 Oxygen](https://www.materialinsights.org/chemicals/oxygen/)[NH3 Ammonia](https://www.materialinsights.org/chemicals/ammonia/)

### Check your understanding

Steam reforming of methane is run at about 800 C in externally fired tubes. Why so hot?
 Wittcoff gives a heat of reaction of +227 kJ/mol at 800 C. Shreve notes that because moles increase, the reaction is favoured by high temperature and low pressure. The shift reaction, by contrast, prefers lower temperature.

Brennan gives 0.71 t of methane per tonne of methanol. Stoichiometry needs 0.5 t. What explains most of the gap?
 Feedstock alone is 16/32 = 0.5 t/t. The remaining 0.21 t is fuel, roughly 30% of the total, consistent with Kent's note that syngas units consume 30% or more of the methane's energy.

Why can China profitably make methanol and olefins from coal when most of the world uses gas or naphtha?
 The IEA notes that coal equipment costs more than twice as much as gas equipment for ammonia, and that coal routes use about twice the process energy. Cheap Chinese coal and a lack of ethane-rich gas still make coal the lower-cost route there.

[← Part 3: Propylene, the C4 stream and the aromatics](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p3/)[Mark read · Part 5: The economics: feedstock, scale, integration and carbon →](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p5/)

## Other sections

- [Module overview](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/index.md)
- [The raw materials: crude oil, natural gas and the refinery](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p1/index.md)
- [Steam cracking: the engine of the petrochemical industry](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p2/index.md)
- [Propylene, the C4 stream and the aromatics](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p3/index.md)
- [The economics: feedstock, scale, integration and carbon](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/p5/index.md)
- [Key terms, quiz and sources](https://www.materialinsights.org/learn/chemicals/oil-gas-to-building-blocks/review/index.md)