Cleaning CO₂ for valorisation

• Drivers

Until recently, most CO₂ used by European industry originated from ammonia production for fertiliser. However, the recent rise in oil and gas prices has led to a drastic drop in European ammonia production. Therefore, new sources of CO₂ are being sought to improve availability. In North America, CO₂ consumption is mainly driven by organic growth of Enhanced Oil Recovery (EOR) and the food and beverage industry.

The EU Green Deal, the EPA Net Zero Initiative and similar legislation around the world encourage the decarbonisation of industry and greening of CO₂ production. Incentives may include tax breaks and subsidies, while carbon trading certificates are also applicable under certain circumstances.

In addition, the growing awareness of climate change is influencing buyers’ decisions in all markets. Biogenic sources of CO₂ such as biogas are particularly sought after as they offer negative emissions, making them more sustainable and cost-effective. 

• Markets

Each market has different requirements for CO₂ purity.

For food grade applications, the gas must meet stringent standards. For other markets, specifications are set by end users. In non-food applications, the main reason to purify CO₂ is generally to avoid poisoning downstream catalysts and prevent corrosion of piping and instruments.

Established markets:

- Food and beverage, currently the largest market. CO₂ is used for carbonation and as dry ice for food preservation. For food grade CO₂, purity must be high. In the EU, EIGA Document 70/17 stipulates the following limits: total S 0.1 µmol/mol = 0.1 ppm, total volatile hydrocarbons 50 µmol/mol = 50 ppm.

Already, this market is struggling to find CO_2. Further roadblocks are the need for certification and traceability, and religious requirements e.g. CO₂ produced from halal sources.

- Food production. Food grade CO₂ is used for: inert atmosphere for packaging e.g. for ham and cheese; stunning methods in slaughterhouses; and fruit preservation in warehouses.

- Industry: welding, water treatment, surface cleaning, electronics etc.

- Chemical production and novel chemicals: e.g. replacing oil with CO₂ for PU production for green mattresses; producing sodium bicarbonate; as solvent/ inert atmosphere etc.

- Oil & gas industry: enhanced oil recovery.

- Greenhouses, to speed up vegetable growth.

Emerging markets:

- Sustainable fuels and Power to X (PtX). Methanol and higher molecular weight hydrocarbons are made from CO₂ and hydrogen via processes such as direct hydrogenation, Fischer-Tropsch synthesis or methanol to olefins (MTO). It is used for sustainable aviation fuel (SAF) and other synthetic fuels or chemicals. This market is likely to grow substantially in the coming years as countries strive to reach their EU Green Deal targets. 

As shown in above examples, the impurities of an off-gas depend on its origin, while the intended end use determines the level of cleaning required. 

These impurities may include:

• Large volumes of H₂O, O₂, N₂, H₂, Ar.
• Particulates/ dust, which need to be mechanically separated.
• Traces of components that may be catalyst poisons or toxic for downstream process microorganisms or even human consumption:

- Acidic components such as H₂S, SO₂, SO₃, HCl, HF, COS, CS₂, CH₃SH, HCN, NO, NO₂/NO₃, and Cl₂.

- Basic components such as NH₃ and Amines.

- Combustible components such as CO, CH₄, organics.

- Biological organic components such as yeasts and fungi.

- Metallic components such as mercury (Hg), heavy metals (Ni, Cr, etc.), and alkaline and earth alkaline metals (Na, K, Ca, Ba), which occur as aerosols rather than particulate matter.

- Volatile Organic Components such as aromatic hydrocarbons, olefins, aldehydes/ organic acids, dioxins/ furans, oils/ greases etc. 

Once the CO₂ has been separated, the CO₂ stream may contain residual water plus traces of impurities as listed above. Therefore, in many cases it will have to be cleaned.

Activated carbon filtration is a proven technology, commonly used to clean or polish CO₂. It offers the following key benefits:

• Removal of VOCs, acid and basic components, mercury, halogen components, organics, sulphur and odours.  
• Highly useful as a polishing step after other technology, reducing the last traces of components to below detectable levels.
• Potential to clean both  air/ gas  and  water/ liquid  flows.
• Straightforward to install and use.
• Handling of varying flow rates, making it suitable for batch or intermittent processes.
• Circular process, producing waste that may be reactivated for further use, boosting sustainability.

Activated carbon filtration has the following limitations:

• It can be uneconomical for very large flows, e.g. from heavy industry.
• It cannot separate out permanent gases, methane, ethane, or particulates. 

DESOTEC supplies mobile sustainable solutions using activated carbon to companies in a range of industrial sectors, in Europe and North America.

Our modular filter fleet allows for flow rates from a few hundred cubic meters per hour (m³/ h) up to 55 000 m³/ h in gas phase, and 2 m³/ h to 50 m³/h in liquid phase. By placing filters in parallel, higher flows are also treatable.

We offer a range of carbon grades to treat and capture different components. For acidic/ basic impurities such as ammonia, amines, HCl, HCN, H₂S, etc and metals like mercury, impregnated carbon is used.

Sustainable filtration waste handling is key to our circular service. All filtration waste is transported in closed filters away from customers’ sites and taken to our state-of-the-art facilities. Components adsorbed onto the carbon are desorbed and broken down in DESOTEC’s furnaces, or valorised. In most cases, the active carbon is reactivated for reuse, driving down customers’ costs, improving sustainability and lowering our and your CO₂ footprint.