[PCCMNL]

I am no chemical engineer or have a chemical profession just exploring the possibility at present of the process of extracting raw feedgas CO2 from the biogas and have tested the impurities.

The results are as follows:
CO2 Purity = 99.60%
Total Hydrocarbon ppm v/v as CH4 = 2750ppm
Methane' = 1700 ppm
Hydrogen Sulfide = greater than 10,000 ppm

-I may need a Hydrogen Sulfide Scrubber for this application installed before the raw feed gas CO2
enters the CO2 purification/recovery (plant) to achieve desired results(?).
-The hydrogen sulfide after passing the H2S scrubber should be at least 20 ppm.
-The raw feed gas CO2 is about 1.5 psi with 20,000 kilos output per day.
-The source of biogas is from the alcohol distillery and the raw material is molasses.

1.)I understand the NaOH may scrub the CO2 but this may cost a lot considering the 10,000ppm of H2S in the system  are there any other alternatives besides NaOH and bacteria Catalysts?

2.) Could anyone point me at the right direction of the most cost efficient alternative solution to remove H2S from the CO2 stream?

Your response would be highly appreciated thanks

[pankajshah]

You may use very dilute solution of Calcium Nitrate & maintain pH at 8+. This will precipitate Calcium sulfide which may be converted to calcium sulphate by presence of Nitric acid.The dilution will prevent deposition of gypsum all over.

[eugenedakin]

Hello PCCMNL,

You may want to laboratory pilot testing of various amines (see the webpage - http://en.wikipedia.org/wiki/Gas_sweetening)

Amines can selectively, and reversibly react with H₂S, and may also react with some of the CO₂.

This is just an option that you may want to consider.

Sincerely,

Eugene

[mbeychok]

PCMNL:

Your compositions are not correct. 10,000 ppm by volume of Hydrogen Sulfide = 1 % by volume and 2,750 ppm by volume of Hydrocarbons = 0.275 % by volume. Therefore, your Carbon Dioxide purity of 99.6 % is either incorrect or your Hydrogen Sulfide and Hydrocarbon values are incorrect.

[marcuswilly]

There are no real cost effective methods at this concentration.
In the oil and gas industry the most common and effective method is to use a triazine compound
It is non reversible , readily available and reasonably easy to administer.

Standard triazine will get 0.2 - 0.3 liters /ppm/MMscf of gas if administered on a continuous basis, and 0.4-0.5 in a batch process

Contact me if you require any additional information

Marc