Methanol Production

Introduction

First discovered by famous English chemist Sir Robert Boyle, for most of its history, methanol was produced by the distillation of wood. Today, methanol is manufactured from syngas derived from hydrocarbons like natural gas, oil, or coal. As of 2011, methanol production exceeded 40 million tons per year. Almost 70% of that production is used as a feedstock for other petrochemicals such as formaldehyde, methyl tert-butyl ether (MTBE), dimethyl ether, and methyl methacrylate.

Nearly all plants today utilize the low-pressure method. In this method, the syngas reacts with itself in the presence of a metal catalyst. Most reactors have pressures ranging from 5-10Mpa and temperatures ranging from 200-300 ℃. After exiting the reactor, the gas is partially condensed. The vapor phase is recycled to the reactor, and the liquid phase is sent to a flash tank. Once flashed, the crude methanol is sent to a column where components with a boiling point below methanol are removed. After this separation, the methanol is sent to a final distillation column where the methanol is distilled from the water.

Crucial to this process is the reaction’s stoichiometry number, also known as S. This number is defined as

Typically, the process is most efficient when this ratio is equal to 2. When this ratio exceeds 2, this indicates a hydrogen excess. Excessive hydrogen will cause the reactor to be less selective towards methanol—lowering overall yields. Values below 2 cause larger amounts of hydrogen to accumulate in the recycle loop. Increasing the hydrogen to carbon ratio also tends to cause more reactants to be lost in the plant’s vent stream.

Because syngas typically needs to have its stoichiometry number adjusted by adding additional CO₂, monitoring both the reactants and methanol product is crucial to providing feedback for CO₂ adjustments. The dual measurement both helps to confirm readings but also aids in troubleshooting (IE ratio imbalance vs passivated catalyst).

Applied Analytics offers superior monitoring solutions with our OMA-InGaAs-300, MCP-200, and APG-710 series products to help producers provide first-in-class measurements for methanol, carbon dioxide, carbon monoxide, and hydrogen. The continuous analysis combined with low maintenance makes it an easy choice for any producer looking to optimize their stoichiometry number.

Further Reading