Carbon dioxide (CO2)

Apsley Farms supplies high-grade, sustainably produced carbon dioxide that is used within the UK food industry.

Carbon dioxide is indispensable for the food industry, where it is used for:

  • Putting the ‘fizz’ into soft drinks and beers
  • Increasing shelf life for food products
  • Keeping food fresh in transport

We manufacture CO2 through low energy, sustainable processes. These have a fraction of the carbon footprint of traditional manufacture — yes, making commercial carbon dioxide releases more carbon dioxide, through the huge energy demands of production.

To find out more about the sustainability of the process, please visit our sustainability page.

The CO2 production process

All of our CO2 is recovered from our biodigesters, where it is produced through anaerobic digestion.

In essence, anaerobic digestion involves the breakdown of plant or other biodegradable material by bacteria. It is a process seen throughout nature, fuelling the energy needs of countless bacterial species, and it happens on every farm, compost heap and landfill site throughout the world.

Our biodigesters harness anaerobic digestion to sustainably produce four useful products: biogas, carbon dioxide, mulch and liquid plant food.

The ‘raw’ biogas produced by our digesters is mainly composed of methane and CO2, though it has many impurities which must be removed.

What’s in our gas?

The composition of the raw gas produced by our biodigesters is:

Compounds Biogas Natural gas Unit
Methane 45 – 70 mol %
Carbon dioxide 30 – 45 ≤ 2 mol %
Hydrogen sulfide ≤ 2000 ≤ 5 mg/m3 (STP)
Ammonia ≤ 1000 0 mg/m3 (STP)
Oxygen ≤ 2 ≤ 0.5 mol %
Nitrogen ≤ 8 ≤ 5 mol %
Water 37 at 1 bar ≤ 8 at 40 bar °C
Combustion heat 6.7 – 8.4 10.7-12.8 kWh/m3(STP)
Wobbe index 6.9 – 9.5 13.3 – 15.7 kWh/m3(STP)

The aim of the process is to remove most of the impurities from biogas to obtain biogas with a concentration of over 97% methane. Pure methane has a calorific value of 9100 kcal/m3 (15,5°C, 1 atm).

Dutch manufacturer DMT has developed a membrane system that upgrades the biogas, separating the carbon dioxide from the methane. Because the CO2 and CH4 molecules are different sizes, the membrane system acts like a sieve, allowing them to be separated.

This separation system has massive advantages compared to traditional methods of removing CO2. Its low cost, high energy efficiency, easy operation, modular construction and flexibility all add up to a more efficient and sustainable approach.

  • The CO2 from the membrane is 98.7% pure – pretty good, but not a high enough standard for the food industry. We start the cleaning process by compressing the gas up to 17 bars. For comparison, pressure inside the tyres of passenger cars is typically 2 – 2.2 bar.
  • The CO2 is ‘dried’, turned into liquid, re-boiled and turned back into liquid again. Each process helps to remove further impurities. moving gases that can be condensed into liquid.
  • Liquid CO2 at -43 degrees is passed into our storage tanks, with a total capacity of 150 m3.
  • The final stage is to check the quality of the CO2 Once certified, the CO2 is collected and distributed.

Our CO2 output

All of the energy needed for the manufacture of CO2 is supplied by our own biodigestion process. This means that we are unaffected by fluctuations in energy prices and were able to keep supplying the UK during the commercial CO2 shortages in 2021.

Currently, our daily production is around 32 tons of CO2. With a purity of 99.99%, this is suitable for any use within the food industry.

To enquire about our commercial CO2, or discuss any aspect of our process, please get in touch.