The Catalyst Review March 2020 - 9

SPECIAL FEATURE
Evonik. These operate at a temperature of up to 50 °C and 17 bar pressure. There are five of these membrane separation lines
operating in parallel in the plant, each with a capacity of 1,250 m3 per hour. The streams from the five membrane separation units
are then combined and purified further using liquefaction and cryogenic separation to remove acetaldehyde, residual nitrogen,
oxygen, methane and water. The output is 7,000 tons of food-grade CO2, with a base cost of production of €25 per ton ($27.33). The
benefit of this as a revenue stream is that it brings the overall cost of the biogas supplied for heating to match that of natural gas
(Esposito et al. 2019). Therefore, CCP have the propensity to be feasible at small scale and not only that but to boost the profitability
of the existing business at an emitting plant.
Milk Production/Food Grade CO2
German industrial gases specialist company Messer, in conjunction with its ASCO subsidiary, has installed many CRUs globally.
Interestingly, three of its largest plants are in China, capturing a total of 300,000 tons of CO2 per year. In Switzerland, it has installed a
CRU at Hochdorf Swiss Nutrition in Hulgen. In this process, flue gas from the plant's steam boiler is collected, cooled and scrubbed to
remove the sulphur compounds and other higher-level contaminants. The precleaned gas is then sent to an absorber tower, where
it flows counter current through the company's proprietary ASCOSORB solvent which absorbs the CO2. The company states that the
formulation of the solvent and the process have been optimized to save 30% of the energy compared with conventional processes
(Messer 2015).
Figure 3. ASCO CO2 by-product recovery systems.

Source: ASCO 2016.

The laden ASCOSORB solution is heated to desorb the CO2 which is then compressed to a pressure of 18 bar. The compressed gas
stream is then further washed, to give a CO2 purity of >99.9%. The gas is dried over an activated desiccant bed at -40 °C, polished
over a carbon filter and condensed in a refrigeration system which can work at 18 bar and -24 °C. The output liquid CO2 flows under
gravity to a final liquid purification unit to give a product with >99.998% food grade purity. From there it is pumped for storage into
tanks and can be transferred into cylinders, fed to a dry ice unit. At the Hochdorf facility it is reutilized on-site for inert gas packaging
of milk powder. Any surplus is sold to end customers locally in Switzerland providing a dual saving for the plant owners (ASCO 2016).
Bioethanol Plant/Power-To-Gas
Ethanol plants are significant emitters of CO2. It arises both from the fermentation chemistry and from process heaters in the plant.
The by-product emissions are at a high concentration (98-99%) and are therefore preferential sources of CO2 for use in industrial
operations. These are also "good emitters" for use in applications where CO2 is further converted into a chemical or fuel. An example
is the UNIPER Store-and-Go Power-To-Gas facility at Falkenhagen which utilizes biogenic CO2 from the nearby Crop Energy bioethanol
plant in Zeitz. The Crop Energy plant is one of the largest in Europe, with an annual capacity of 400,000 m³ per annum of bioethanol.
It has been producing liquefied CO2 in the amount of 100,000 tons per year since 2010. This has been supplied for carbonic acid in
the food industry, as well as in anti-freeze agents and for dry ice production. The CO2 liquefaction plant was built with Tyczka Energie
GmbH, Geretsried through the two companies' equally-held JV company-CT Biocarbonic GmbH, Zeitz (Crop Energies 2019).
Power-To-Gas (PTG) is a much newer technology growing in popularity which converts green hydrogen obtained from water
electrolysis and waste CO2 into substitute natural gas (SNG). There are several demonstration plants in place in Europe. The UNIPER
Store-and-Go Power-To-Gas facility at Falkenhagen in Germany utilizes a Hydrogenics electrolyser as well as the Thyssenkrupp
Industrial Solutions (TKIS) new catalytic methanation process for conversion of CO2 to methane. The SNG product is injected into
the gas grid for district heating. This type of project is very significant for catalyst demand because it introduces more catalysts into
the production of natural gas compared with the conventional process. The Hydrogenics proton exchange membrane electrolyser
(PEMEL) also uses a precious metal electrocatalyst and the TKIS methanation process utilizes a solid heterogeneous catalyst as well as
a polishing catalyst (Schirrmeister 2019).
The Catalyst Review

March 2020

The Catalyst Review March 2020

Table of Contents for the Digital Edition of The Catalyst Review March 2020