# Refining and reforming: Science and limits

Why distillation burns five times the energy physics demands

Source page: https://www.materialinsights.org/energy/e_refining/science/

What this tab covers What physically happens in the conversion, step by step, the science behind it, and the hard limits that physics sets on how well it can ever work.

Refineries separate crude oil by boiling point and then rebuild its molecules into fuels; reformers and gasifiers break natural gas or coal into hydrogen and carbon monoxide (syngas). These are chemical-to-chemical conversions that keep most of the feed's energy but consume a slice of it as process heat.

#### The conversion, step by step
**Fired heater and distillation**
Chemical (crude oil) → Separated fractions: gases, naphtha, kerosene, diesel, gas oil, residue · Atmospheric distillation uses about 109 thousand Btu per barrel, about 5 times its theoretical minimum of 22 (calculated ratio); a US refinery yields about 19 to 20 gallons of gasoline per 42-gallon barrel^[1](https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil.php)^[2](https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil-the-refining-process.php)^[6](https://www.energy.gov/sites/default/files/2013/11/f4/bandwidth.pdf)**Cracking**
Heavy gas oil and residue → Lighter gasoline and diesel molecules · Fluid catalytic cracking: about 183 thousand Btu per barrel of feed^[2](https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil-the-refining-process.php)^[6](https://www.energy.gov/sites/default/files/2013/11/f4/bandwidth.pdf)**Reforming, alkylation, hydrotreating**
Naphtha and light gases → High-octane gasoline, low-sulphur fuels · Catalytic reforming: about 264 thousand Btu per barrel of feed^[2](https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil-the-refining-process.php)^[6](https://www.energy.gov/sites/default/files/2013/11/f4/bandwidth.pdf)**Whole refinery**
Crude oil → Finished fuels · About 606 MJ of energy used per barrel, roughly 10% of the crude's energy content (calculated, taking crude as about 6.1 GJ per barrel)^[5](https://eao.stanford.edu/publications/journal-articles/carbon-intensity-global-crude-oil-refining-and-mitigation-potential)**Steam methane reforming (SMR)**
Chemical (natural gas) plus steam → Chemical (hydrogen) · About 75% (higher heating value basis) for a large plant without carbon capture^[9](https://www.netl.doe.gov/projects/files/ComparisonofCommercialStateofArtFossilBasedHydrogenProductionTechnologies_041222.pdf)**Coal gasification**
Chemical (coal) plus oxygen and steam → Syngas, then hydrogen or liquid fuels · About 65% (HHV) to hydrogen^[9](https://www.netl.doe.gov/projects/files/ComparisonofCommercialStateofArtFossilBasedHydrogenProductionTechnologies_041222.pdf)

#### The science

Crude is a mix of thousands of hydrocarbons. Heating it to vapour in a column lets each fraction condense at its own height: light ones rise, heavy ones stay low. A vacuum column handles the heaviest part without overheating it. Because markets want more gasoline and diesel than crude naturally contains, catalysts crack big molecules (fluid catalytic cracking, or hydrocracking with added hydrogen), reforming reshapes naphtha into high-octane ring molecules, and alkylation joins small gas molecules into gasoline. A US refinery turns a 42-gallon barrel into about 19 to 20 gallons of gasoline, 11 to 13 of distillate (mainly diesel) and 3 to 5 of jet fuel. In SMR, methane and steam react over a nickel catalyst (CH4 + H2O to CO + 3H2, strongly endothermic, heat supplied by burning gas outside the tubes), then a water-gas shift (CO + H2O to CO2 + H2) adds more hydrogen and a pressure swing adsorption unit purifies it. Gasification partially burns coal with oxygen to make syngas, which can be shifted to hydrogen or turned into liquid fuels by Fischer-Tropsch synthesis.

#### Limits set by science

| Limit | Value | Why it exists | Best today |
|---|---|---|---|
| **Minimum separation and reaction energy** | Theoretical minimum: 22 (atmospheric distillation), 40 (FCC), 79 (reforming) thousand Btu per barrel, against actual 109, 183 and 264^[6](https://www.energy.gov/sites/default/files/2013/11/f4/bandwidth.pdf) | Separating and rearranging molecules has a thermodynamic floor, but today's units use 2 to 5 times that because of heat-exchange temperature gaps and losses (calculated ratios). | DOE judged practical minimums imply 23 to 54% savings by unit, around 30% plant-wide, with overlaps. |
| **SMR energy ceiling** | Close to 100% (HHV) if the reaction heat were supplied and recovered perfectly (calculated from standard enthalpies: CH4 + 2H2O(liquid) to CO2 + 4H2 needs about 253 kJ, about 0.28 mol of extra methane burned)^[9](https://www.netl.doe.gov/projects/files/ComparisonofCommercialStateofArtFossilBasedHydrogenProductionTechnologies_041222.pdf) | Hydrogen carries more energy than the methane it came from, because the steam's hydrogen also ends up in the product; the extra comes from heat. | 75.4% HHV without capture, 68.4% with 96% CO2 capture. |
| **Carbon chemistry** | At least 5.5 kg CO2 per kg H2 from the feed carbon alone (calculated: 44 g CO2 per 8 g H2)^[10](https://www.iea.org/reports/global-hydrogen-review-2024/ghg-emissions-of-hydrogen-and-its-derivatives) | Every carbon atom in methane leaves as CO2; more comes from burning gas for heat and from upstream supply. | Unabated gas hydrogen: 10 to 12 kg CO2-eq per kg H2; coal: 22 to 26. |
| **Coal-to-liquids yield** | Ningxia plant: 4 Mt a year of products from about 24.5 Mt of coal for the whole complex, a mass yield of about 16%; energy yield roughly 35 to 40% (calculated, assuming about 20 GJ/t coal and 44 GJ/t products)^[13](https://www.sustainable-carbon.org/blogs/visiting-the-worlds-biggest-single-coal-to-liquid-project-in-yinchuan-china/) | Coal is hydrogen-poor, so making liquid fuels means adding hydrogen from water via the shift reaction and rejecting carbon as CO2. | The plant also uses 6.1 t of water per tonne of oil. |

#### Sources

1. [Oil and petroleum products explained: Refining crude oil](https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil.php) US Energy Information Administration, 2025
2. [Refining crude oil: the refining process](https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil-the-refining-process.php) US Energy Information Administration, 2025
3. [Carbon intensity of global crude oil refining and mitigation potential (Jing et al.), Nature Climate Change](https://eao.stanford.edu/publications/journal-articles/carbon-intensity-global-crude-oil-refining-and-mitigation-potential) Stanford University / Nature, 2020
4. [Energy Bandwidth for Petroleum Refining Processes](https://www.energy.gov/sites/default/files/2013/11/f4/bandwidth.pdf) US Department of Energy (Energetics Inc.), 2006
5. [Comparison of Commercial, State-of-the-Art, Fossil-Based Hydrogen Production Technologies](https://www.netl.doe.gov/projects/files/ComparisonofCommercialStateofArtFossilBasedHydrogenProductionTechnologies_041222.pdf) National Energy Technology Laboratory, US DOE, 2022
6. [Global Hydrogen Review 2024: GHG emissions of hydrogen and its derivatives](https://www.iea.org/reports/global-hydrogen-review-2024/ghg-emissions-of-hydrogen-and-its-derivatives) International Energy Agency, 2024
7. [Visiting the world's biggest single coal-to-liquid project in Yinchuan, China](https://www.sustainable-carbon.org/blogs/visiting-the-worlds-biggest-single-coal-to-liquid-project-in-yinchuan-china/) IEA Clean Coal Centre (sustainable-carbon.org), 2017

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_refining/index.md)
- [Overview](https://www.materialinsights.org/energy/e_refining/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_refining/correlation/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_refining/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_refining/economics/index.md)
- [Engineering methods](https://www.materialinsights.org/energy/e_refining/methods/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_refining/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_refining/links/index.md)