Vacuum-temperature swing adsorption

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Category: Carbon capture (mature) Subcategory: Physical adsorption Combustion type: Post

DESCRIPTION

Vacuum temperature swing adsorption (VTSA) is a cyclic adsorption and desorption process that allows continuous separation of gas streams. It utilizes a combination of temperature and vacuum to enhance the adsorption and desorption cycles of CO₂ on a solid sorbent. A VTSA process may consist of several columns, steps, and different cycle times to achieve a certain performance. A basic VTSA configuration has two beds and comprises four steps, namely adsorption, evacuation, desorption, and cooling. Each VTSA system uses specialised adsorbent materials such as zeolites, molecular sieves, activated carbon, etc. This technology is suitable for both point source capture (PSC) and direct air capture (DAC).¹

Feed gas is sent to the adsorber (adsorption) operating at atmospheric pressure. The CO₂ adheres to the adsorbent while the other gas components pass through. The existing free gas is evacuated from the column using an evacuation pump. In the third step, the CO₂ is desorbed in a countercurrent mode by applying a vacuum, followed by heat supply either through indirect heating using a working fluid (hot water) or direct heating using an electric supply.¹ The application of vacuum allows for low-quality heat (waste heat) utilization, reducing the energy consumption. Similarly, a cooling step may be required either indirectly through working fluid (cooling water) or directly cooling using purge gas. The column is then pressurized with the feed gas for the next adsorption cycle.

Vacuum-Temperature Swing Adsorption Process

TECHNICAL ASPECTS (all % are volume-based)

Point sources:

Pulp & paper, biomass, oil & gas, steam-methane reforming, lime, steel, cement, petrochemicals.²

Direct air capture – all values in parentheses below belong to DAC.³

CO₂ concentration range: 10%-20%^2,4 (400 ppm³)

CO₂ capture efficiency: > 90%² (70%⁵)

CO₂ purity: > 95%² (98.5 - 99.9%³)

Min. feed gas pressure: 1.1 bar⁴ (fan to overcome pressure drop3)

Max. feed gas temperature: 50 °C⁴ (40 – 50 °C⁶)

Typical scale: Small to Large (same for DAC⁷)

Primary energy source: Heat (direct or indirect by working fluid) and electricity for the vacuum pump.

Impurity tolerance: SOx = 1.5 ppm⁸; PM = 0.2 mg/m³ (assuming same as TSA). None required for DAC.

FUNCTION IN CCU VALUE CHAIN

Capture CO₂ from flue gases (or) directly from air.
Adsorbents such as zeolites are highly affected by the presence of water in feed gas, requiring an upstream dehydration step in PSC.⁹ No such dehydration step is used in DAC.
Highly affected by flue gas impurities in PSC, such as SOx and NOx, requiring appropriate pre-treatment steps.⁹ No such pre-treatment steps are used in DAC.

LIMITATIONS

Adsorbent material may degrade over time due to thermal cycling and exposure to impurities in the flue gas, reducing overall capture efficiency.
Maintaining a vacuum system adds complexity to the operation. The vacuum pumps and associated equipment require regular maintenance and can be a source of operational issues.

ENERGY

Electricity is used by the blower at the upstream to be needed to overcome the pressure drop in the column in PSC.
Electricity is consumed by the fans to direct the air to the DAC contactor and also by the control systems.³
Electricity is consumed by the evacuation and vacuum pump to remove free gas and desorb CO₂, respectively, in both PSC and DAC.
Either low-grade/waste heat or electricity is used to complete CO₂ desorption in both PSC and DAC.

CONSUMABLES

Hot water could be used as a working fluid during CO₂ desorption, but it can be reused.
Cooling water may be required to cool the feed gas after the blower and cool the desorbed CO₂ after the vacuum pump.
No chemicals/solvents are used.

Energy and Consumables
Parameter	PSC	DAC
Electricity (kWh/tCO₂)	90 ^{10 a} 81 ^b	200 – 300 ^{3 c} 150 – 260 ^{3 d}
Heat (GJ/tCO₂)	2.9 ^{10 a} 5.0 ^b	5.4 – 7.2 ^{3 c} 4.2 – 5.1 ^{3 d}
Cooling water makeup (t/tCO₂)	-NA- 12.8 ^b	0.1 ⁷
Adsorbent (t/tCO₂)	-NA- 0.0015 ^b	0.003 ⁷
^a 13X adsorbent; feed pressure 1.5 bar; vacuum pressure 0.1 bar; 15% CO₂ in dry gas; cycle time 4000 s; CO₂ purity 97%. ^b VITO study; indirect heating using hot water at 90 °C; NGCC plant - 4% CO₂; 360,000 tCO₂/yr; adsorbent working capacity – 0.06 gCO₂/g-sorbent; CO₂ purity – 70%; CO₂ capture efficiency – 75%. ^c Climeworks: amine-based adsorbent; indirect heat at 100 °C; Pvac – 0.2 bar; full cycle – 4 to 6 hrs.³ ^d Global Thermostat: amino polymer adsorbent; direct steam at 85-95 °C; Pvac – 0.5-0.9 bar; full cycle – 0.5 hrs.³

COSTS

CO₂ capture costs of PSC

CAPEX: 8.5 €/tCO₂*

Main CAPEX: adsorption columns and vacuum pump

OPEX: 77.5 €/tCO₂*

Main OPEX: cooling water, electricity, and adsorbent

CO₂ capture cost: 90 €/tCO₂* (71% adsorbent cost)

Depends on adsorbent price, scale, CO₂ concentration, and purity requirements.

* VITO study; indirect heating using hot water; free waste heat at 90 °C; NGCC plant – 4% CO₂; capture capacity – 360,000 tCO₂/yr; CO₂ purity – 70%; CO₂ capture efficiency – 75%; WACC – 4.6%; lifetime – 25 yrs; 2022 euros; electricity – 80 €/MWh; sorbent – 40 €/kg; adsorbent working capacity – 0.06 gCO₂/g-sorbent; cooling water – 0.3 €/m³; fixed OPEX – 5% of CAPEX; operating hours – 8000 hr/yr.

CO₂ capture cost of DAC

€800 in 2023, €400-€700 by 2030 and €100-€300 by 2050 per tonne CO₂ estimated by Climeworks.⁷

(no financial assumptions are provided)

€220 per tonne CO₂ in 2020

Capacity – 360,000 tCO₂/yr; lifetime – 20 yrs; electricity – 250 kWh/tCO₂ at 103 €/MWh; heat – 1750 kWh/tCO₂ at 51 €/MWh by heat pump.

Depends on scale, specific energy consumption, and energy prices.

CO₂ avoidance cost: Not available.

ENVIRONMENTAL

CO₂ footprint:

PSC - 273 kgCO₂eq/tCO₂ captured ¹¹

(assumed same as TSA; Estimate includes footprint (scope 1-3) for CO₂ capture plant, compression, and conditioning.

DAC - 15-45 kgCO₂eq/tCO₂ captured ¹²

(Net footprint = Capture CO₂ from air – CO₂ footprint from energy consumption)

Spatial footprint:

PSC - 74,420 m² (305x244) for 1.6 MtCO₂/yr ⁴

(assumed same as TSA, additional footprint required for main and evacuation vacuum pumps)

DAC – 220 acres for 1 MtCO₂/yr ⁷

Environmental issues: Disposal or recycling of spent adsorbents.^7,13

ENGINEERING

Maturity:

PSC - Pilot (TRL 7)¹⁴

A pilot plant tested for a waste combustion plant.

DAC - Demonstration (TRL 7-8)⁷

Demonstration plants have been developed.

Retrofittability: Feasible

Heat and electricity are the main energy sources; phased implementation due to modular nature; handles flue gas impurities depending upon the adsorbent used.

Challenges due to large spatial footprint requirement.

Scalability: High²

Well-suited for capturing CO₂ at a wide capture rate range due to its modular nature.²

Process type: Solid stationary adsorbent-based without chemical reactions.

Deployment model: Centralized only.

Each column with adsorbent undergoes cyclical CO₂ adsorption and desorption.

Technology flexibility: Hybridization with other capture technologies is feasible. It can be used to increase CO₂ concentration.

MAIN TECHNOLOGY PROVIDERS

PSC

KCC system by Kawasaki, Japan (direct regeneration by steam at 60°C and 0.2 bar)
CSAR by SINTEF and Caox, Norway. (uses heat and vacuum pumps)
VeloxoTherm™ by Svante Inc, Canada. (same as TSA but with a vacuum; CALF-20 MOF; 8-25% CO₂ concentration in flue gas)

DAC

Direct Air Capture by Climeworks, Switzerland.
Direct Air Capture by Global Thermostat, USA.
Direct Air Capture by Skytree, The Netherlands.
Direct Air Capture by Kawasaki, Japan.
Metal Organic Frameworks for DAC by Mosaic Materials, USA.
More DAC companies here.¹⁵

CONTACT INFO

Mohammed Khan (mohammednazeer.khan@vito.be)

Miet Van Dael (miet.vandael@vito.be)

ACKNOWLEDGEMENT

This infosheet was prepared as part of the MAP-IT CCU project funded by VLAIO (grant no. HBC.2023.0544).

REFERENCES

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12. Deutz S, Bardow A. Life-cycle assessment of an industrial direct air capture process based on temperature–vacuum swing adsorption. Nat Energy. 2021;6(2):203-213.

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14. Tveten SG. New technology makes carbon capture easier - SINTEF. Norwegian SciTech News. November 6, 2024

15. Faber G. Direct Air Capture: Definition and Company Analysis.; 2025.

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Infosheet on Vacuum-Temperature Swing Adsorption