Electrothermal Swing Adsorption Research Articles

Regeneration of beaded activated carbon saturated with volatile organic compounds by a novel electrothermal swing adsorption system

A commercially available beaded activated carbon (KBAC) was selected for combination with a novel electrothermal swing system in examining the Joule heating effects on the physical and chemical properties of activated carbon and its adsorption regenerability at various regeneration temperatures (120, 140, and 160 °C) after saturation by toluene (TOL) and methylethylketone (MEK). The specific surface area (1278 m2 g− 1) and micropore volume (0.48 cm3 g− 1) for KBAC after one adsorption/desorption cycle were slightly reduced, while KBAC micropore surface area (1158 m2 g− 1) and micropore volume decreased significantly after six adsorption/desorption cycles. It can be inferred that the pores of KBAC, especially micropores, are blocked by heel buildup caused mainly by formation of cracked TOL and MEK coke generated by cyclic Joule heating. The desorption efficiencies of TOL-KBAC and MEK-KBAC (KBAC saturated with TOL and MEK, respectively) evaluated per the gravimetric method ranged from 55 to 80 and 85–90%, respectively, and both showed great correlation between regeneration temperature and desorption efficiency. Notably, the desorption efficiencies calculated from the integral method based on breakthrough curves were 8 and 16% lower than those directly obtained by the gravitational method for TOL-KBAC and MEK-KBAC, respectively. The larger difference in desorption efficiency evaluated by the two methods for MEK-KBAC is likely caused by the decomposition of MEK into CO or CO2, which was less prominent in TOL-KBAC. In the cyclic adsorption/desorption tests, the adsorption capacities of both TOL-KBAC and MEK-KBAC decreased after the 6-cycle electrothermal swing regeneration, such that TOL-KBAC adsorption capacity significantly reduced to around 50%, while that of MEK-KBAC retained around 70% of their respective original adsorption capacities. As aforementioned, heel buildup blocks the pores and leads to decreasing adsorption, especially for TOL.

Pore-scale study on heat and mass transfer of electrothermal swing adsorption process into X-ray tomography reconstructed activated carbon fibre felt

Activated carbon fibre (ACF) absorbent is a promising material for capturing volatile organic compounds from gas streams. Electrothermal swing adsorption (ESA) technology was proposed to achieve the regeneration of adsorption-saturated ACF materials. A numerical study on the adsorption and electrothermal desorption processes in ACF felt at the pore scale was conducted. A 3D pore-scale lattice Boltzmann model was used to describe the momentum/heat/mass transfers coupled with the adsorption/desorption effect. Using this model, a numerical simulation was performed to investigate the heat and mass behaviours of ESA in the pore structure of ACF felt, which was reconstructed using X-ray micro-tomography technology. The simulation results reveal the effects of key operation parameters on the process properties of ESA in the adsorption step and the electrothermal regeneration step. Moreover, the pore-scale study illustrates the influence of carrier gas velocity on the distribution homogeneity of the adsorbate concentration and desorption temperature.

Feasibility of regenerative adsorption of a hydrofluorocarbon (HFC-134a) using activated carbon fiber studied by the gaseous flow method

The adsorption and desorption behavior of the refrigerant HFC-134a on pitch-based activated carbon fibers (ACFs) with various Brunauer–Emmett–Teller surface areas was investigated by the flow method. Fixed-bed adsorption experiments performed at 20, 5, –15, –20, and −25 °C showed that the use of lower temperatures resulted in an increase in the adsorption capacity of the ACF. In particular, the complete adsorption time was dramatically increased at −25 °C. Crucially, even after five cycles of adsorption at –20 °C and desorption at 30 °C of HFC-134a in a electrothermal swing adsorption apparatus, significant decreases in the adsorption capability were not observed. The desorption of HFC-134a from saturated ACF was carried out using electric power directly applied to the ACF itself. The electric heating increased the ACF temperature, causing desorption within several minutes. The results of this study show that the regenerative adsorption of HFC-134a by ACF coupled with electric power is possible.

Isobutane adsorption with carrier gas recirculation at different relative humidities using activated carbon fiber cloth and electrothermal regeneration

An improved gas recovery system (GRS) using activated-carbon fiber-cloth (ACFC), electrothermal swing adsorption (ESA), and carrier gas recirculation was shown to capture and recover >99% isobutane while reducing N2, H2O, and energy consumption. ACFC-15 was selected as the adsorbent after a trade-off of adsorption capacity and cost. Carrier gas recirculation was used for the first time to conserve N2 and H2O at relative humidity (RH) up to 80% while recovering volatile organic compound (VOC) (i.e., isobutane). When RH is 24% and 77%, overall energy (EOverall) consumed with recirculation decreases by 2.5% and 26% compared to without recirculation, respectively. Recommendations are provided to reduce the gap of energy consumption of the GRS with recirculation based on idealized and experimental conditions. Unique contributions and importance of this work are demonstrating that carrier gas recovery and reuse can be used to better conserve N2, H2O, and energy; analyzing specific energy consumption values; and proposing improvements of such a system to let the GRS with recirculation operate closer to idealized conditions.

Monitoring and Control of an Adsorption System Using Electrical Properties of the Adsorbent for Organic Compound Abatement.

Adsorption systems typically need gas and temperature sensors to monitor their adsorption/regeneration cycles to separate gases from gas streams. Activated carbon fiber cloth (ACFC)-electrothermal swing adsorption (ESA) is an adsorption system that has the potential to be controlled with the electrical properties of the adsorbent and is studied here to monitor and control the adsorption/regeneration cycles without the use of gas and temperature sensors and to predict breakthrough before it occurs. The ACFC's electrical resistance was characterized on the basis of the amount of adsorbed organic gas/vapor and the adsorbent temperature. These relationships were then used to develop control logic to monitor and control ESA cycles on the basis of measured resistance and applied power values. Continuous sets of adsorption and regeneration cycles were performed sequentially entirely on the basis of remote electrical measurements and achieved ≥95% capture efficiency at inlet concentrations of 2000 and 4000 ppmv for isobutane, acetone, and toluene in dry and elevated relative humidity gas streams, demonstrating a novel cyclic ESA system that does not require gas or temperature sensors. This contribution is important because it reduces the cost and simplifies the system, predicts breakthrough before its occurrence, and reduces emissions to the atmosphere.

Environmental and Economic Assessment of Electrothermal Swing Adsorption of Air Emissions from Sheet-Foam Production Compared to Conventional Abatement Techniques.

A life-cycle assessment (LCA) and cost analysis are presented comparing the environmental and economic impacts of using regenerative thermal oxidizer (RTO), granular activated carbon (GAC), and activated carbon fiber cloth (ACFC) systems to treat gaseous emissions from sheet-foam production. The ACFC system has the lowest operational energy consumption (i.e., 19.2, 8.7, and 3.4 TJ/year at a full-scale facility for RTO, GAC, and ACFC systems, respectively). The GAC system has the smallest environmental impacts across most impact categories for the use of electricity from select states in the United States that produce sheet foam. Monte Carlo simulations indicate the GAC and ACFC systems perform similarly (within one standard deviation) for seven of nine environmental impact categories considered and have lower impacts than the RTO for every category for the use of natural gas to produce electricity. The GAC and ACFC systems recover adequate isobutane to pay for themselves through chemical-consumption offsets, whereas the net present value of the RTO is $4.1 M (20 years, $0.001/m(3) treated). The adsorption systems are more environmentally and economically competitive than the RTO due to recovered isobutane for the production process and are recommended for resource recovery from (and treatment of) sheet-foam-production exhaust gas. Research targets for these adsorption systems should focus on increasing adsorptive capacity and saturation of GAC systems and decreasing electricity and N2 consumption of ACFC systems.

Performance of an Electrothermal Swing Adsorption System with Postdesorption Liquefaction for Organic Gas Capture and Recovery

The use of adsorption on activated carbon fiber cloth (ACFC) followed by electrothermal swing adsorption (ESA) and postdesorption pressure and temperature control allows organic gases with boiling points below 0 °C to be captured from air streams and recovered as liquids. This technology has the potential to be a more sustainable abatement technique when compared to thermal oxidation. In this paper, we determine the process performance and energy requirements of a gas recovery system (GRS) using ACFC-ESA for three adsorbates with relative pressures between 8.3 × 10(-5) and 3.4 × 10(-3) and boiling points as low as -26.3 °C. The GRS is able to capture > 99% of the organic gas from the feed air stream, which is comparable to destruction efficiencies for thermal oxidizers. The energy used per liquid mole recovered ranges from 920 to 52,000 kJ/mol and is a function of relative pressure of the adsorbate in the feed gas. Quantifying the performance of the bench-scale gas recovery system in terms of its ability to remove organic gases from the adsorption stream and the energy required to liquefy the recovered organic gases is a critical step in developing new technologies to allow manufacturing to occur in a more sustainable manner. To our knowledge, this is the first time an ACFC-ESA system has been used to capture, recover, and liquefy organic compounds with vapor pressures as low as 8.3 × 10(-5) and the first time such a system has been analyzed for process performance and energy consumption.

Temperature Control during Regeneration of Activated Carbon Fiber Cloth with Resistance-Feedback

Electrothermal swing adsorption (ESA) of organic compounds from gas streams with activated carbon fiber cloth (ACFC) reduces emissions to the atmosphere and recovers feedstock for reuse. Local temperature measurement (e.g., with a thermocouple) is typically used to monitor/control adsorbent regeneration cycles. Remote electrical resistance measurement is evaluated here as an alternative to local temperature measurement. ACFC resistance that was modeled based on its physical properties was within 10.5% of the measured resistance values during electrothermal heating. Resistance control was developed based on this measured relationship and used to control temperature to within 2.3% of regeneration set-point temperatures. Isobutane-laden adsorbent was then heated with resistance control. After 2 min of heating, the temperature of the adsorbent with isobutane was 13% less than the adsorbent without isobutane. This difference decreased to 2.1% after 9 min of heating, showing desorption of isobutane. An ACFC cartridge was also heated to 175 °C for 900 cycles with its resistance and adsorption capacity values remaining within 3% and 2%, respectively. This new method to control regeneration power application based on rapid sensing of the adsorbent's resistance removes the need for direct-contact temperature sensors providing a simple, cost-efficient, and long-term regeneration technique for ESA systems.

Capture and Recovery of Methyl Ethyl Ketone with Electrothermal-Swing Adsorption Systems

The amount of organic vapors that are emitted to the atmosphere can be reduced with the use of electrothermal-swing adsorption (ESA) with activated carbon fiber cloth (ACFC). This paper describes a pilot-scale ESA system that was scaled up based on two ESA bench-scale systems. Each ESA system consists of two vessels with four ACFC cartridges. The bench-scale and pilot-scale systems were tested with adsorption and desorption cycles using gas streams containing 73–10,000 ppmv and from 170–940 ppmv methyl ethyl ketone, respectively. Total flow rate ranged from 5 sL/min to 140 sL/min for the bench unit and 1,700 sL/min for the pilot unit. Scale-up procedure of an ESA system from the bench-scale to the pilot-scale is presented for the first time. Scale-up was based on throughput ratio, length of unused bed, adsorption capacity, pressure drop, superficial gas velocity in the ACFC, organic vapor removal efficiency, duration of the adsorption cycle, duration of the regeneration cycle, liquid recovery efficiency, electrical power/energy applied to the ACFC cartridges, and temperature of the ACFC cartridges.

Control of Electrothermal Heating during Regeneration of Activated Carbon Fiber Cloth

Electrothermal swing adsorption (ESA) of organic gases generated by industrial processes can reduce atmospheric emissions and allow for reuse of recovered product. Desorption energy efficiency can be improved through control of adsorbent heating, allowing for cost-effective separation and concentration of these gases for reuse. ESA experiments with an air stream containing 2000 ppm(v) isobutane and activated carbon fiber cloth (ACFC) were performed to evaluate regeneration energy consumption. Control logic based on temperature feedback achieved select temperature and power profiles during regeneration cycles while maintaining the ACFC's mean regeneration temperature (200 °C). Energy requirements for regeneration were independent of differences in temperature/power oscillations (1186-1237 kJ/mol of isobutane). ACFC was also heated to a ramped set-point, and the average absolute error between the actual and set-point temperatures was small (0.73%), demonstrating stable control as set-point temperatures vary, which is necessary for practical applications (e.g., higher temperatures for higher boiling point gases). Additional logic that increased the maximum power application at lower ACFC temperatures resulted in a 36% decrease in energy consumption. Implementing such control logic improves energy efficiency for separating and concentrating organic gases for post-desorption liquefaction of the organic gas for reuse.

Capture and Recovery of Isobutane by Electrothermal Swing Adsorption with Post-Desorption Liquefaction

A bench-scale capture and recovery system to convert a low concentration organic gas to a liquid is described here. Adsorption of isobutane onto activated carbon fiber cloth (ACFC) followed by electrothermal desorption and subsequent liquefaction is demonstrated. Experimental conditions to condense desorbed isobutane were determined based on Dalton's law and Antoine's equation. Breakthrough curves for a gas stream containing 2000 ppm(v) isobutane in air adsorbing onto ACFC-15 demonstrate an adsorption capacity of 0.094 ± 0.017 g of isobutane/g of ACFC with >98% capture efficiency. The system described here utilizes two adsorbers, which operate cyclically to allow for continuous treatment of the isobutane. Adsorption followed by electrothermal desorption provided a concentration ratio of 240, which facilitates condensation of the isobutane after compression and cooling and is an order of magnitude greater than what has been previously demonstrated.

CO 2 capture by electrothermal swing adsorption with activated carbon fibre materials

This paper presents progress made in CO 2 capture by electrothermal swing adsorption (ESA) with activated carbon fibre materials. The current barrier in CO 2 capture and storage is the high cost of CO 2 separation and capture. CO 2 capture by electrothermal swing adsorption can potentially be more energy-effective than conventional temperature swing adsorption (TSA) and pressure swing adsorption (PSA), thus reduces CO 2 capture cost. Activated carbon fibre materials have been utilised as the adsorbents due to their demonstrated capabilities for CO 2 capture and their good electrical conductivity. This paper reviews the major results in the literature in the development of activated carbon fibre materials and the process of ESA. It also suggests future research directions in CO 2 capture by electrothermal swing adsorption.

Desorption of CO 2 from activated carbon fibre–phenolic resin composite by electrothermal effect

CO 2 capture by electrothermal swing adsorption is considered superior over conventional adsorption approaches: temperature swing adsorption and pressure swing adsorption. In this work, the effects of electricity, preheating and flow rate were studied. An increase in energy input by electricity has been found able to improve desorption performance more significantly than an increase in current level. However, higher current level is recommended because it can minimise energy loss while passing electricity. Higher flow rate can also be beneficial due to the improved desorption rate and reduced desorption time. However, there is a drop in CO 2 concentration in the effluent gas. When desorption takes place at a high current level, preheating is not required as it extends desorption duration with no obvious improvement in desorption rate. CO 2 capture by electrothermal swing adsorption has also been tested with different concentrations of CO 2. It is found that electrothermal swing adsorption can be more energy efficient while dealing with higher concentration CO 2.

Concomitant Adsorption and Desorption of Organic Vapor in Dry and Humid Air Streams using Microwave and Direct Electrothermal Swing Adsorption

Industrial gas streams can contain highly variable organic vapor concentrations that need to be processed before they are emitted to the atmosphere. Fluctuations in organic vapor concentrations make it more difficult to operate a biofilter when compared to a constant vapor concentration. Hence, there is a need to stabilize the concentration of rapidly fluctuating gas streams for optimum operation of biofilters. This paper describes new concomitant adsorption desorption (CAD) systems used with variable organic vapor concentration gas streams to provide the same gas stream, but at a user-selected constant vapor concentration that can then be more readily processed by a secondary air pollution control device such as a biofilter. The systems adsorb organic vapor from gas streams and simultaneously heat the adsorbent using microwave or direct electrothermal energy to desorb the organic vapor at a user-selected set-point concentration. Both systems depicted a high degree of concentration stabilization with a mean relative deviation between set-point and stabilized concentration of 0.3-0.4%. The direct electrothermal CAD system was also evaluated to treat a humid gas stream (relative humidity = 85%) that contained a variable organic vapor concentration. The high humidity did not interfere with CAD operation as water vapor did not adsorb but penetrated through the adsorbent These results are important because they demonstrate the ability of CAD to effectively dampen concentration fluctuation in gas streams.

Steady-State and Dynamic Desorption of Organic Vapor from Activated Carbon with Electrothermal Swing Adsorption

A new method to achieve steady-state and dynamic-tracking desorption of organic compounds from activated carbon was developed and tested with a bench-scale system. Activated carbon fiber cloth (ACFC) was used to adsorb methyl ethyl ketone (MEK) from air streams. Direct electrothermal heating was then used to desorb the vapor to generate select vapor concentrations at 500 ppmv and 5000 ppmv in air. Dynamic-tracking desorption was also achieved with carefully controlled yet variable vapor concentrations between 250 ppmv and 5000 ppmv, while also allowing the flow rate of the carrier gas to change by 100%. These results were also compared to conditions when recovering MEK as a liquid, and using microwaves as the source of energy to regenerate the adsorbent to provide MEK as a vapor or a liquid.

Adsorption and electrothermal desorption of organic vapors using activated carbon adsorbents with novel morphologies

Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal–swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal–swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.

Electrothermal swing adsorption of toluene on an activated carbon monolith: Experiments and parametric theoretical study

The purpose of the present work is to investigate electrothermal swing adsorption (ESA) process with an activated carbon monolith as adsorbent. Experiments are performed with toluene as VOC. Several parameters are investigated both experimentally and through a mathematical model. It is shown that the monolith, as a carbon material, behaves as a semi-conductor. Its resistivity decreases as temperature and amount adsorbed increase. This leads to different types of evolution of dissipated electrical power during desorption at constant current intensity. The concentration of the desorbed VOC as a function of time has the shape of a peak followed by a tail. This shape is interpreted as a dispersive wave in the sense of the equilibrium theory of adsorption columns. The performance of the process is strongly dependent on the operating conditions. The maximal (that is initial) concentration increases almost linearly with current intensity and purge gas flow rate, and increases also with preheating duration. The purge gas flow rate has mainly an effect of dilution. The efficiency of desorption (% VOC desorbed) is almost constant in average with different preheating times. It increases with current intensity and gas purge flow rate.