Two-bed Pressure Swing Adsorption Process Research Articles

A Robust Metal-Organic Framework with Scalable Synthesis and Optimal Adsorption and Desorption for Energy-Efficient Ethylene Purification.

Adsorptive separation is an energy-efficient alternative, but its advancement has been hindered by the challenge of industrially potential adsorbents development. Herein, a novel ultra-microporous metal-organic framework ZU-901 is designed that satisfies the basic criteria raised by ethylene/ethane (C2 H4 /C2 H6 ) pressure swing adsorption (PSA). ZU-901 exhibits an "S" shaped C2 H4 curve with high sorbent selection parameter (65) and could be mildly regenerated. Through green aqueous-phase synthesis, ZU-901 is easily scalable with 99 % yield, and it is stable in water, acid, basic solutions and cycling breakthrough experiments. Polymer-grade C2 H4 (99.51 %) could be obtained via a simulating two-bed PSA process, and the corresponding energy consumption is only 1/10 of that of simulating cryogenic distillation. Our work has demonstrated the great potential of pore engineering in designing porous materials with desired adsorption and desorption behavior to implement an efficient PSA process.

Parallel and series multi-bed pressure swing adsorption processes for H2 recovery from a lean hydrogen mixture

The demand for clean energy sources has made H2 recovery from various lean hydrogen mixtures increasingly attractive. In this study, parallel and series pressure swing adsorption (PSA) processes were investigated experimentally and theoretically, and > 99% pure H2 was produced from a lean hydrogen mixture (H2:CO:N2:CO2 = 19.9:0.1:44.6:35.4 mol%) at 10 bar. A mathematical model for a PSA process using activated carbon and zeolite 13X was simultaneously validated with results from breakthrough experiments and a parallel two-bed PSA process. The parallel two-bed PSA process using a layered bed (lower bed: activated carbon, upper bed: zeolite 13X) experimentally produced H2 with a purity of 94.6–98.3% and a recovery of 33.5–63.2%; CO was not detected in the H2 product. In the parallel four-bed PSA process, the H2 recovery was drastically increased to 77.3% due to an additional pressure equalization step, but the increase in H2 purity was minute. The series PSA process, which was divided into the bulk separator and the purifier, was theoretically studied under various operating conditions. The series three- and four-bed PSA processes could produce H2 with over > 99% purity and a recovery of 62.478% and 82.643%, respectively, due to the additional pressure equalization step and the utilization of blowdown gas. The parallel four-bed PSA process showed the highest H2 productivity (33.58 molH2 kgads−1 day−1), while the series four-bed PSA process achieved an H2 productivity of 23.96 molH2 kgads−1 day−1 with > 99% H2 purity.

Modelling and simulation of two-bed PSA process for separating H2 from methane steam reforming

Abstract Methane steam reforming is the main hydrogen production method in the industry. The product of methane steam reforming contains H2, CH4, CO and CO2 and is then purified by pressure swing adsorption (PSA) technology. In this study, a layered two-bed PSA process was designed theoretically to purify H2 from methane steam reforming off gas. The effects of adsorption pressure, adsorption time and purge-to-feed ratio (P/F ratio) on process performance were investigated to design a PSA process with more than 99.95% purity and 80% recovery. Since the feed composition of the PSA process changes with the upstream process, the effect of the feed composition on the process performance was discussed as well. The result showed that the increase of CH4 concentration, which was the weakest adsorbate, would have a negative impact on product purity.

Layered two- and four-bed PSA processes for H2 recovery from coal gas

Huge amounts of global warming gas emissions have prompted interest in the recovery of H2 from off-gases in the iron and steel industries. Pressure swing adsorption (PSA) processes with layered beds packed with zeolite 5A and activated carbon were applied for H2 recovery from coal gas with relatively low H2 concentrations (H2/CO2/CH4/CO/N2; 38/50/1/1/10 vol.%). Breakthrough curves in the layered bed showed behavior results between the zeolite 5A bed and the activated carbon bed. The bed with the higher zeolite ratio produced H2 of higher purity in the PSA operation, but recovery loss became more significant with its increasing ratio. The variation of purity and recovery by operating variables were more significant in the two-bed PSA process than they were in the four-bed PSA process. The purity in the two-bed PSA varied asymptotically according to P/F ratio in the range of 0.1–0.3, while purity variation in the four-bed PSA process was almost linear. The zeolite layer in the two-bed PSA process worked as a separator of N2, while that in the four-bed PSA process worked as a purifier of N2. The four-bed PSA process could produce H2 with a purity of 96–99.5% and a recovery of 71–85% with N2 as the major impurity. The dynamics of the breakthrough and H2 PSA processes were studied using a non-isothermal dynamic model.

Kinetic Separation of Landfill Gas by a Two-Bed Pressure Swing Adsorption Process Packed with Carbon Molecular Sieve: Nonisothermal Operation

To produce pipeline-quality methane with a high level of adsorbent productivity from landfill gas, the pressure swing adsorption (PSA) process with carbon molecular sieve (CMS) was investigated experimentally and theoretically by using CO2/CH4 feed (50/50 vol %). Due to the high throughput as well as the high heat of adsorption of the faster diffusing component (CO2), the isothermal assumption was no longer valid and energy balance equations were inevitable for accurate prediction. Owing to the strong concentration dependency of sorption rate, the adsorption dynamics of the CMS bed in the PSA process were predicted by using a modified LDF model with concentration-dependent diffusivity. The nonisothermal and nonadiabatic model successfully predicted the performance of the CMS PSA process, which was operated by the Skarstrom cycle with cocurrent equalization. The purity was significantly affected by the changes in the adsorption pressure and adsorption step time, while the change in the recovery due to these operating variables was relatively small. The purge-to-feed ratio played a key role in improving the productivity based on the production of 90+% CH4 from the CH4/CO2 mixture.

Performance of a Two-Bed Pressure Swing Adsorption Process with Incomplete Pressure Equalization

Incomplete pressure equalization (PE) is practiced in a commercial oxygen concentrator for medical use by adopting simultaneous PE and feed-pressurization for pressurizing an adsorption bed. In such a cycle configuration, extent of equalization during PE affects process performance. In order to assess the effect, performance of pressure swing adsorption (PSA) process with incomplete PE was determined by both simulations and experiments. In simulations, an equilibrium model was used with the assumptions of multicomponent Langmuir isotherms, isothermal operation, and no pressure drop through a bed. The required parameters for simulations were measured in separate experiments. PSA experiments were performed for a two-bed cycle with PE. Two kinds of pressurization, feed and product, were examined. Effects of purge amount and extent of equalization on process performance were assessed in view of productivity and light-component recovery. From the obtained results performance contours were constructed. 95 oxygen mole percent production from air with zeolite 13× was considered as a case study. In both pressurizations, an optimal specific purge and an extent of equalization for the productivity and recovery were observed, but with a different level of equalization. For a maximum productivity feed-pressurization favored incomplete PE, while a maximum recovery occurred at complete PE for both pressurizations. The simulations depicted well existence of optimum conditions, though they showed quantitative disagreement with experiments.

Separation of Hydrogen Mixtures by a Two-Bed Pressure Swing Adsorption Process Using Zeolite 5A

A study on a two-bed six-step pressure swing adsorption (PSA) process using zeolite 5A was performed experimentally and theoretically for bulk separation of H2/CO and H2/CH4 systems (70/30 vol %) as major components in coke oven gas. When the pressure is cycled between 1 and 11 atm at ambient temperatures, 70% H2 in the feed could be concentrated to 99.99% in the product with a recovery of 75.87% in the H2/CO mixture and 80.38% in the H2/CH4 mixture. The effects of adsorption pressure, P/F ratio, adsorption/purge step time, and pressure equalization step time were investigated experimentally. If the product end of an adsorption bed was not contaminated during the adsorption and depressurizing pressure equalization steps, elongation of both the adsorption and purge steps gave good adsorbent productivity and recovery without any decrease in purity. Certain elongations of step time in the pressure equalization step resulted in a better performance of a PSA process. When the H2 mole fraction of effluent stream during the pressure equalization step was not high, the initial H2 purity of the adsorption step was not good because of the contamination of the product end section. These results were analyzed by a mathematical model incorporating heat and momentum balances.

Combined reaction and separation in pressure swing processes

Theoretical studies of a novel reactor which combines pressure swing adsorption (PSA) and chemical reaction are presented; such a reactor is referred to as a pressure swing reactor, or PSR. The design is based on a conventional two-bed PSA process, in which many of the usual cycle configurations for operation are possible, e.g. simple and purge cycles. Each bed contains a mixture of an active catalyst for reaction, and a selective adsorbent for the adsorption of one or more of the reaction species. Theoretical calculations predict that such a process may lead to greater conversions than conventional steady flow reactors, and thus allow a lower temperature of operation for a desired conversion. Furthermore, for equilibrium reactions of the general form aA ⇌ bB + cC, and especially when an adsorbent can be chosen such that the adsorption equilibrium constants are in the sequence H B > [ H A , H C ], possible improvements over equilibrium conversions are indicated. In this work, theoretical investigations have concentrated on three types of reversible reaction schemes; isomerisation, dissociation/disproportionation, and dehydrogenation; potential advantages of a PSR have been illustrated for these. As a test case, experimental investigations have concentrated on the dehydrogenation reaction of methylcyclohexane to toluene, for which a Pt Al 2O 3 catalyst was found to have suitable activity at temperatures as low as 450 K. Pulse chromatography experiments have been carried out to scan the high temperature (400 K to 700 K) adsorption properties of methylcyclohexane, toluene and hydrogen on some commercial adsorbents; clay-based adsorbents were found to be particularly suitable for this case, yielding the desired sequence of adsorption strengths.