Carbon dioxide removal from biogas

[MABELTD]

I've been searching the posts here and I think this question may be a little below most of you.
I've cobbled together a homemade biogas generator and I'm wanting to improve the quality of the biogas by removing some of the CO2 (or all of it if I can) which will leave me with a higher calorific value gas (as the remaining gas is predominantly Methane) and possibly something which I could even burn in my standard gas boiler?

I know CO2 will dissolve in water, and I also know that if I add heat to the water it will liberate some of the CO2 dissolved (/reacted)

The questions are

How much heat do I need to input to liberate the CO2?
What temperature do I need to achieve, I'll be using waste gas from a condensing boiler so probably about 60 C is my limit?
What by-products will I produce either with or without releasing the CO2? (so I'll know what materials I can use)
Is it all worth the effort of should I just constantly replenish the water supply? (again by-products above will tell me if I can re-use the waste water for irrigation, or if I'll cause any problems by dumping it in the sewer, albeit as a constant low flow).
Would water saturated with CO2 actually be beneficial in the greenhouse (i.e. tomatoes not day after tomorrow)

I hope this isn't too simple for you guys out there, Chemistry is about twenty five years old for me!
Regards
Paul

 

[uby]

it sounds like you want to 'getter' the CO2. a 'getter' is any compound which can selectively react with a species and sequester it.

for CO2, any carbonate-forming oxide would do the trick. for example, barium oxide will react rapidly with CO2 to form barium carbonate. a newly discovered reaction is getting some buzz involving the reaction of lithium nitride (Li3N) with CO2 at elevated temperatures to form lithium oxide, lithium cyanamide and carbon nitride.

 

[MABELTD]

it sounds like you want to 'getter' the CO2. a 'getter' is any compound which can selectively react with a species and sequester it.

for CO2, any carbonate-forming oxide would do the trick. for example, barium oxide will react rapidly with CO2 to form barium carbonate. a newly discovered reaction is getting some buzz involving the reaction of lithium nitride (Li3N) with CO2 at elevated temperatures to form lithium oxide, lithium cyanamide and carbon nitride.

Thanks uby,
Are these reactions easily reversible? i.e. can I use nature to regenerate a 'getter'?
More importantly are the reagents cheap??
The reactions will be taking place at room temperature, I'm trying to remove CO2 from biogas, before I burn it.
Thanks again.

 

[henlus]

Search google for "co2 water scrubber for biogas". It is a tank with some parking materials (plastic balls). Compressed biogas at 1000kpa comes from the bottom to mix with compressed water (1200kpa) coming from the top. Co2 dissolve in the water and purified biogas is gotten from the top of the tank. To remove Co2 and recycle the water, you pump the water to a stripping system where you use air to strip out CO2 from the water at low pressure.

 

[LudusRex]

I can provide some insight into the process of carbon dioxide removal from biogas. First, it is important to understand that biogas is a mixture of gases produced by the breakdown of organic matter in the absence of oxygen. This process, known as anaerobic digestion, produces a mixture of methane, carbon dioxide, and small amounts of other gases.

One method of removing carbon dioxide from biogas is through a process called scrubbing. This involves passing the biogas through a liquid, usually water, which absorbs the carbon dioxide. The amount of heat required to liberate the CO2 from the water will depend on the concentration of CO2 in the biogas. Generally, the higher the concentration of CO2, the more heat will be needed to remove it. However, with a homemade biogas generator, it may be difficult to accurately determine the concentration of CO2 in the biogas.

The temperature needed to achieve for CO2 liberation will also depend on the concentration of CO2. The higher the concentration, the lower the temperature needed. In general, a temperature of around 60 degrees Celsius should be sufficient for removing CO2 from biogas.

The by-products produced during the scrubbing process will depend on the type of liquid used. Water saturated with CO2 will produce carbonic acid, which can be beneficial for plants in small amounts. However, it is important to monitor the pH of the water and not use too much as it can be harmful to plants.

In terms of whether it is worth the effort to remove CO2 from biogas, it depends on the specific situation and goals of the individual. Removing CO2 will increase the calorific value of the gas, making it more useful for burning in a gas boiler. However, it may require additional equipment and maintenance. Constantly replenishing the water supply may be a simpler option, but it is important to consider the impact of the by-products produced.

In summary, removing carbon dioxide from biogas can be achieved through scrubbing with water. The specific requirements for heat and temperature will depend on the concentration of CO2 in the biogas. The by-products produced should also be considered when deciding whether it is worth the effort to remove CO2. It is always important to carefully monitor and adjust the process to ensure safe and efficient removal of CO2 from biogas.