Gas Purification: Cryogenic Condensation with Liquid Nitrogen

In the fields of emissions control and environmental sustainability, Volatile Organic Compounds (VOCs) are becoming an increasingly more important issue. Companies often struggle to find the right balance between investment, operating cost, and system reliability.?Cryogenic Condensation?is an interesting and proven solution for process emission streams containing VOCs usually at high concentration (≥ 0,5 %v).

This technology is able to achieve VOC?outlet concentration levels of few ppm?– which is in compliance with the more restrictive local regulations – while also creating a sustainable option to?recover and reuse VOCs.?By contrast to thermal oxidation, there is no risk of the formation of dangerous toxins like dioxins, secondary pollutants, or greenhouse gases, because the process strictly relies on phase changes (solid?liquid, liquid?gas).

The principle of the technology is based on decreasing the vapor pressure to a low temperature and consequently condensing and/or freezing the VOCs by cooling the stream with liquid nitrogen or another cryogenic fluid.

Liquid nitrogen is generally used as a cooling source for pollutant condensation. Since it is circulated in a dedicated circuit and it’s never in contact with the effluent, the nitrogen is not contaminated and can easily be reused in gaseous form inside the factory network.

Below a summary of previous Linkedin posts and relative papers related:

One of the most applied application of cryogenic condensation is the abatement of Dichloromethane (DCM).

Dichloromethane’s volatility and ability to dissolve a wide range of organic compounds makes it a useful solvent for many chemical processes. In the food industry, it is used to decaffeinate coffee and tea as well as to prepare extracts of hops and other flavourings. Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for polyurethane foams. In this interesting patent Masetto et al. (https://lnkd.in/e2re9Ed) published an optimized cryogenic condensation configuration than can copes with the abatement of several?VOCs including DCM.

Tetrahydrofuran (THF) is another pollutant that can be easily treated using cryogenic condensation. THF is an organic compound with the formula (CH2)4O. It is a colorless, water-miscible organic liquid with low viscosity. Being polar and having a wide liquid range, it is a versatile solvent. In the image below is reported an example of its application: hydrodecyanation of a benzyl cyanides with NaH in THF under reflux conditions for cycloalkylarenes production.

Also pollutant that polimerize easily like acrylonitrile, styrene, butadiene, etc.. can be treated with this technology.

At room temperature, acrylonitrile is a volatile, flammable ??, colourless liquid with a weakly pungent odour. It is a polar molecule because of the presence of the cyano (CN) group and soluble in water (75.1 g/l at 25 °C). The vapours are explosive ?? and cyanide gas being produced spontaneous polymerization?during storage and transport.

Several applications can be found also in the silicum organic compounds applications when the stream is concentrated and with relatively low flowrate (e.g. 1-25 %wt and 100-1000 Nm3/h). For instance, Tetramethylsilane (TMS), Si(CH3)4, is one of the simplest volatile silicon compounds (VOSiCs), representing an emerging solvent and industrial chemical. The atmospheric chemistry of silicon compounds remains relatively unstudied. Importantly, we do not know if the Si heteroatom alters the classical reaction processes expected for oxygenated hydrocarbons nor do we know the ultimate atmospheric fate of the Si atoms.

The cryogenic condensation technique can be applied and customized also on specific process like the spray drying technology. Spray drying is a method for producing a dry powder directly from a solution or slurry. In a continuous process, the liquid feed-stock is dispersed as a mist of fine droplets into a stream of hot drying gas, all within a cylindrical drying chamber. In aqueous processes, the drying gas is typically air. For solutions composed of flammable solvents such as ethanol and acetone, the inert drying gas is nitrogen and the system operated in a closed cycle. Because the kinetics of drying are so rapid, materials are dried in a fraction of a second which helps to make the process viable for thermal sensitive materials such as foods, extracts and biologics.

This review by R. Wisniewski (https://lnkd.in/dqWBmfP) investigates spray drying principles of convection, radiation and mixed convection-radiation and their relations with design and performance. The condensation in the water and solvent based configuration is further analysed.

With the continuous improvement of VOC emission standards and the limitation of the refrigeration temperature, for some applications the traditional condensation process for VOC recovery needs to be combined with other methods such as adsorption and membrane separation to meet the existing standards.

For instance, the membrane?VOC pre-concentration step can be interesting in order to increase the VOC content of the condensation unit and possibly improve the energy efficiency of the overall operation. In the study of Belaissaoui et al.(https://lnkd.in/dSGefBz), a comparison in terms of the energy efficiency (overall electrical energy needed per kg of recovered VOC) is carried out between:

?? Standalone condensation

?? Hybrid process based on membrane + condensation

Another combination can be the scenario when there are soluble VOCs but with a load too high, then the condensation can be a first step before the absorption/scrubber section:

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Dr. Matteo Compagnoni is a Business Development Manager focusing on Gas & Liquid purification and treatment technologies.

Ph.D. in Industrial Chemistry at University of Milan (Italy), Master degree in Industrial Chemistry and Management and Bachelor degree in Environmental Chemistry. Publications on International Journals: https://www.researchgate.net/profile/Matteo-Compagnoni-2