Even more important for industrial applications is that polyethylene glycol dimethyl ethers also are very good absorbents for gases like H2S (hydrogen sulfide), CO2 (carbon dioxide), COS (carbonyl sulfide, carbon oxysulfide), R-SH (organic mercaptans).
Gases like natural gas (methane) or synthesis gas (syngas, hydrogen and CO / CO2) may contain significant concentrations of these compounds. These byproducts are toxic and would poison downstream catalysts used for syngas processing. Hence, they have to be removed.
A well-established Acid Gas Removal (AGR) process - the Selexol® process -uses Genosorb 1753 (a polyethylene glycol dimethyl ether) as absorption liquid. Sulfur-containing compounds, such as hydrogen sulfide, mercaptans, COS and also CO2 are absorbed by the glycol diether, whereas there is only very little co-absorption of methane and other aliphatic hydrocarbons. After desulphurization, the cleaned syngas is used to produce ammonia (NH3) or is used in IGCC processes to generate electrical power and hydrogen for chemical processes or refinery uses.
The document "Process Screening Analysis of Alternative Gas Treating and Sulfur Removal for Gasification" by SFA Pacific Engineering & Economic Consultants was prepared for the US Department of Energy. It reviews commercial gas treating and sulfur recovery processes that are also suitable for IGCC processes. The section about acid gas removal using physical solvents states:
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"The Selexol process solvent is a mixture of dimethyl ethers of polyethylene glycol, and has the formulation CH3O(CH2CH2O)nCH3 where n is between 3 and 9. There are other process suppliers using the same solvent as the Selexol process. For example Clariant GmbH of Germany offers a family of dialkyl ethers of polyethylene glycol. The Clariant solvents, under the Genosorb name, include dimethly ether- as well as dibutyl ether- of polyethylene glycols. The first mentioned Clariant solvent is the same as that used in the Selexol process."
The first mentioned Clariant solvent is Genosorb 1753.
This process is not to be confused with amine scrubbing processes (scrubbing liquids like MDEA, aMDEA etc.) which are based on chemical absorption. The physical absorption based on glycol diethers is more economical in many cases, especially when the feed gas has a high initial pressure and deep sulfur removal (down to 10 ppmv) is required.
Another quite recent application uses Genosorb 1753 to remove H2S and CO2 from bio gas in order to obtain natural gas that meets pipeline specification. The biogas resulting from fermentation of organic material contains considerable amounts of hydrogen disulfide and carbon dioxide which have to be removed befor the gas can be passed to the public gas grid. Typical commercial installations for biogas treatment comprise gas streams of 250-800 Nm3/h that are treated with Genosorb 1753.
On industrial scale the Acid Gas Removal (Selexol®) process is used to treat gas streams from 250 Nm3/h (biogas scrubbing) up to 800.000 Nm3/h (IGCC process) in over 60 plants worldwide. This demonstrates the flexibility of this process and the stability and versatility of Genosorb 1753. |