ABSORPTION FLUIDS FOR GAS TREATMENT
Polyethylene glycol dialkyl ethers have proved successful for scrubbing waste air and waste gas streams containing a variety of organic substances and acid gases. Clariant has developed the Genosorb® range of absorption liquids as tailor-made solutions for many specific waste gas problems.
Genosorb® absorption liquids have a low vapor pressure and low viscosity. A waste gas stream containing VOCs and/or acid gases is passed through a packed tower. The removal of VOCs and/or acid gases is achieved through the direct contact between the upward gas and the downward Genosorb® absorption liquid. This rich Genosorb® solution is then passed downward through a packed stripping tower.
The VOCs and/or acid gases are removed from Genosorb® by stripping with steam or air, typically at temperatures between 70°C and 130°C, or even at low temperatures by pressure change. The resulting lean Genosorb® solution is then passed back to the absorber column.
A very important industrial application for Genosorb® 1753 is the removal of acid gases from natural gas and synthesis gas. This is the so-called Selexol® process. Polyglycol dimethyl ethers (Polyglycol DME) are selective solvents for hydrogen disulfide, mercaptans, COS and carbon dioxide. Hydrocarbons and inert gases like hydrogen and carbon monoxide are not absorbed.
In many industrial applications this process has proven successful for the sweetening of natural gas, desulphurization and CO2 removal from synthesis gas (e.g. IGCC processes H2 production for NH3-plants, Synthetic Natural Gas production) or bulk CO2 removal.
Several commercial gas processing units with gas streams from 250 Nm3/h to 600 000 Nm3/h are using Genosorb® 1753 as scrubbing liquid.
The physical absorption based on glycol diethers is more economical than chemical absorptions based on organic amines, especially if deep sulfur removal is required and if the gas has a high initial pressure. A very similar process is used to remove CO2 and / or H2S from biogas. Natural gas meeting pipeline specifications is obtained.
Typical commercial Genosorb® installations for biogas treatment comprise gas streams of around 250-2 000 Nm3/h. In the same manner landfill gas can be upgraded with Genosorb® 1753.
Another important application for glycol diether based absorption liquids is the Solinox® process. The Solinox® process was developed by Linde AG with Genosorb® 1900 as absorption liquid.
In this process, Genosorb® 1900 absorbs large amounts of SO2 from flue gases. The product contains a proprietary stabilizer that protects Genosorb® against harmful effects of SO2 and SO3.
The sulfur dioxide resulting from the Solinox® process has a very high purity and can be converted to sulfuric acid or sold as food grade quality.
Several commercial units are operating globally. The following table shows data of a Solinox® plant based in Europe:
- Air flow: 225 000 m³/h
- SO2/SO3 inlet concentration: 20 000 mg/m³
- SO2 in cleaned gas: max. 200 mg/m³
- Sulfuric acid production: approx. 40 t/day
- Sulfur dioxide emissions are reduced by 99.9%
The products Genosorb® 300 and Genosorb® 1843 were designed for scrubbing of VOCs such as alcohols, ketones, chlorinated and fluorinated hydrocarbons, aromatics, hydrocarbons etc.
They have proved successful in around 50 installations for VOC abatement around the world. Unlike incineration or adsorption, the Genosorb® process allows recycling of valuable organic compounds from waste gases.
Genosorb® 1843 is a polyglycol dibutyl ether and is used to physically absorb non-polar compounds such as aromatics and hydrocarbons. Genosorb® 1843 does not mix with water. It contains a stabilizer and tolerates acidic components in the gas stream.
Genosorb® 300 is a polyglycol dimethyl ether and physically absorbs polar VOCs like alcohols, aldehydes etc. It is completely miscible with water. It contains a stabilizer and tolerates acidic components in the gas stream.
Genosorb® 1753 - used in the Selexol® process - effectively removes hydrogen sulfide (H2S), carbon dioxide (CO2) as well as other trace compounds from biogas to obtain natural gas (methane) that meets pipeline specifications.
The biogas resulting from fermentation of organic material contains considerable amounts of hydrogen sulfide and carbon dioxide which have to be removed before the gas can be passed to the public gas grid.
Typical commercial installations for biogas treatment comprise gas streams of 250-2 000 Nm³/h that are treated with Genosorb® 1753.
Advances of upgrading technology with Genosorb® 1753
- Excellent selectivity
- Low energy consumption for absorbent regeneration
- Very low methane slip
- Biogas upgrading and gas drying in one step