Analysis of contaminants in biogas

Biogas produced in Anaerobic Digestion-plants or landfill sites is primarily composed of methane and carbon dioxide with smaller amounts of hydrogen sulphide and ammonia. Trace amounts of hydrogen, nitrogen, carbon monoxide, saturated and halogenated carbohydrates, sulphur gases and siloxanes are occasionally present in the biogas. Usually the mixed gas is saturated with water vapour and may contain dust particles.
The presence of contaminants in biogas for vehicles can harm the gas distributing system or the gas utilities or cause unwanted exhaust products. High quality is thus required in order to avoid performance disturbances.
As example, actual requirements in Sweden:
 Sum carbon dioxide, oxygen, nitrogen less than 5 %-vol
 Oxygen less than 1 %-vol
 Total sulphur less than 23 mg/ Nm3
 Ammonia less than 20 mg/ Nm3
SP provides in addition to the main components, methane, carbon dioxide etc. analyses of contaminants in biogas or any other gases via sampling in a gas-tight bag or by enrichment onto an adsorbent. The analyses are performed by gas chromatography (GC) together with a FID (flame ionisation detector) and MS (mass spectrometry) as well as ICP-MS (inductively coupled plasma - mass spectrometry). We can assist with the sampling directly at the facility or send equipment to perform the sampling if required.
With access to many different instruments of analyses, we can offer extensive gas analyses, all after requirement.
Siloxanes
During combustion, siloxanes are converted to silicon dioxide - SiO2 (a white ash). Silicon dioxide accumulates on the heated surfaces in combustion equipment, especially in the cylinders, on the valve etc. Silicon dioxide is a solid compound and will remain in the engine and cause considerable damage.
Halogenated hydrocarbons
They cause corrosion in engines, in the combustion chamber, at spark plugs, valves, cylinder heads, etc.
Sulphur gases
Biogas and, especially, landfill gas can contain a variety of sulphur compounds, such as sulphides, disulphides and thiols. The sulphur-containing compounds may be oxidized to corrosive sulphates and sulphites in the presence of water. Sulphur gases are also known to be responsive for unpleasant odours already at very low concentrations. Moreover they are a well known poison for some fuelcells.
Example of analyses we can offer

Analysis Compounds of interest Quantification limits
Siloxanes

The organic silicon compounds in biogas are in the form of linear and cyclic methyl siloxanes:
Silanol, trimethyl
Tetramethyldisiloxane, L2
Octamethyltrisiloxane, L3
Decamethyltetrasiloxane, L4
Dodecamethylpentasiloxane, L5
Hexamethylcyclotrisiloxane, D3
Octamethylcyclotetrasiloxane, D4
Decamethylcyclopentasiloxane, D5
Dodecamethylcyclohexasiloxane, D6

50 ppb
Halogenated
hydrocarbons
Method in development  50 ppb 
Sulfur gases
Hydrogen sulfide
Methyl mercaptan
Sulfides
Tetrahydrothiophene

1ppm-vol

1ppm-vol

50 ppb-vol

50 ppb-vol

Ammonia

 

Amines

Ammonia, NH3

 

Method in development 

2 ppm-vol

Related Information

Business Areas

RISE Bioscience and Materials

Contact Persons

Karine Arrhenius

Phone: +46 10 516 57 28

Haleh Bohlén

Phone: +46 10 516 57 99

RISE Research Institutes of Sweden, Phone 010-516 50 00, E-mail info@ri.se

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