Pressure swing adsorption/membrane hybrid processes for hydrogen purification with a high recovery

Innovative metal oxides (CaO, SrO, MgO) impregnated waste-derived activated carbon for biohydrogen purification

In this work, a series of innovative metal oxide impregnated waste-derived activated carbons (MO/AC) was synthesized and used to purify the simulated biohydrogen based on the concept of CO₂ removal from the gas stream. Effects of metal oxide types (CaO, SrO and MgO) and contents of the best metal oxides on the morphology and the CO₂ adsorption capacity from the biohydrogen were investigated. It was found that both metal oxide types and contents played an important role on the adsorbent textural property and surface chemistry as well as the CO₂ adsorption capacity. Among all synthesized adsorbent, the MgO-impregnated AC with 12 wt.% MgO (12MgO/AC) exhibited the highest CO₂ adsorption capacity of around 94.02 mg/g. With this successive adsorbent, the biohydrogen with the H₂ purity higher than 90 mol% can be achieved from the gas stream with 50 mol% CO₂ for the first 2 min of adsorption period in a fixed bed reactor. The mechanism of CO₂ adsorption occurred via a combined process of the physisorption and chemisorption. Besides, the 12MgO/AC exhibited a high recyclability after several repetitive adsorption/desorption cycles.

Separation and purification of syngas-derived hydrogen: A comparative evaluation of membrane- and cryogenic-assisted approaches

Hydrogen (H₂) separation and purification is challenging because of the high purity and recovery requirements in particular applications, as well as the critical properties of H₂ and its associated components. Unlike pressure swing adsorption, cryogenic- and membrane-based technologies are currently employed for H₂ separation. Membrane-assisted (case-I) and cryogenic-assisted (case-II) separation and purification of H₂ were evaluated in this study in terms of the energy, exergy, and economic aspects of the processes. In case-I and case-II, H₂ was first produced from synthesis gas via the water-gas shift reaction and was then separated from other components using membrane and cryogenic systems, respectively. Additionally, an organic Rankine cycle was integrated with the water-gas shift reactors to recover the waste heat. A well-known commercial process simulation software, Aspen Hysys® v11, was employed to simulate both processes. Energy analysis revealed that case-I has a lower energy consumption (0.50 kWh/kg) than case-II (2.01 kWh/kg). However, low H₂ purity and recovery rates are the main limitations of case-I. In terms of exergy, the H₂ separation section in case-I exhibited a higher efficiency (28.4%) than case-II (14.7%). Furthermore, the economic evaluation showed that case-I was more expensive ($17.7 M) than case-II ($10.2 M) because of the high cost of the compressors required. In conclusion, this study could assist industry practitioners and academic researchers in selecting optimal H₂ separation and purification technologies for improving the overall H₂ economy.

Review of the Pressure Swing Adsorption Process for the Production of Biofuels and Medical Oxygen: Separation and Purification Technology

The production of biofuels has had a great impact on climate change and the reduction of the use of fossil fuels. There are different technologies used for the separation and production of biofuels, which allow having compounds such as ethanol, methane, oxygen, and hydrogen, one of these promising technologies is the Pressure Swing Adsorption process (PSA). The objectives of this article focus on the production and purification of compounds that achieve purities of 99.5% bioethanol, 94.85% biohydrogen, 95.00% medical oxygen, and 99.99% biomethane through the PSA process; also, a significant review is contemplated to identify the different natural and synthetic adsorbents that have greater adsorption capacity, the different configurations in which a PSA operates are studied and identified, and the different mathematical models that describe the dynamic behavior of all the variables are established that interact in this PSA process, parametric studies are carried out in order to identify the variables that have the greatest effect on the purity obtained. The results obtained in this review allow facilitating the calculation of parameters, the optimization of the process, the automatic control to manipulate certain variables and to achieve the rejection of disturbances to have a recovery and production of biofuels with a high degree of purity.

Design and Economic Evaluation of a Hybrid Membrane Separation Process from Multiple Refinery Gases Using a Graphic Synthesis Method

Petrochemical tail gases have various components and many separation methods, thus there are many possible design schemes, making it difficult to determine the optimal scheme. In this work, a graphic synthesis method was used to design a hybrid multi-input refinery gas separation process consisting of membranes, pressure swing adsorption (PSA), shallow condensation (SC), and distillation units for the production of valuable products which include H2, C2, LPG, and C5+. Ten refinery gases with different compositions were visualized and represented with vector couples in a triangular coordinate system. Firstly, according to the characteristics of the refinery gases, the feeds located in the same region of the triangular coordinate system were merged to simplify the number of input streams, then ten original input streams were combined into two mixed streams. Secondly, the optimal separation sequence was determined by using the unit selection rules of a graphic synthesis method. Thirdly, the process was simulated in UniSim Design and the process parameters were determined by sensitivity analysis. Finally, economic assessments were carried out, which led to an annual gross product profit of USD 38.62 × 106 and a payback period of less than 4 months.

Hydrogen Recovery from Coke Oven Gas. Comparative Analysis of Technical Alternatives

The recovery of energy and valuable compounds from exhaust gases in the iron and steel industry deserves special attention due to the large power consumption and CO₂ emissions of the sector. In this sense, the hydrogen content of coke oven gas (COG) has positioned it as a promising source toward a hydrogen-based economy which could lead to economic and environmental benefits in the iron and steel industry. COG is presently used for heating purposes in coke batteries or furnaces, while in high production rate periods, surplus COG is burnt in flares and discharged into the atmosphere. Thus, the recovery of the valuable compounds of surplus COG, with a special focus on hydrogen, will increase the efficiency in the iron and steel industry compared to the conventional thermal use of COG. Different routes have been explored for the recovery of hydrogen from COG so far: i) separation/purification processes with pressure swing adsorption or membrane technology, ii) conversion routes that provide additional hydrogen from the chemical transformation of the methane contained in COG, and iii) direct use of COG as fuel for internal combustion engines or gas turbines with the aim of power generation. In this study, the strengths and bottlenecks of the main hydrogen recovery routes from COG are reviewed and discussed.

Hydrogen production technologies - Membrane based separation, storage and challenges

The production of hydrogen, its separation, and storage for use as a primary source of energy is an important component of the green energy economy of the world. Hydrogen is a potential non-carbon-based energy source, which is gradually replacing the dependency on fossil fuels. It is anticipated that as the alternative fuel since hydrogen can be produced from green and clean sources. The evolution of hydrogen from renewable and non-renewable sources by various technologies has now gained tremendous research and industrial interest. The most appropriate methods for hydrogen generation involve the direct conversion of solar energy, exploitation of solar and wind energy for the electrolysis of water, besides conversion of fuel and biomass. To produce cleaner hydrogen and its separation from the chemical impurities is crucial and several methods including photobiological, photoelectrochemical, electrochemical, photocatalytic, thermochemical, thermolysis, and steam gasification have been used. The diverse types of membranes along with the pressure gas swing adsorption technique is another technique used to separate hydrogen, but the storage of hydrogen in an inexpensive, safe, compact, and environmentally friendly manner is one of the major concerns contributing to the country's economy. Apart from the countless advantages, storage and handling of hydrogen is a serious concern. Owing to its high inflammability, enough safety measures should be adopted during its production and storage as a fuel. It is necessary to provide information regarding the production technologies, storage, and separation methods of hydrogen and the present review addresses these issues.

A Novel Process of H2/CO2 Membrane Separation of Shifted Syngas Coupled with Gasoil Hydrogenation

A novel process of membrane separation for H2/CO2 of shifted syngas coupled with gasoil hydrogenation (NMGH) is proposed. First, a new process, with two-stage CO2-selective and one-stage H2-selective membranes, was developed to substitute the conventional PSA separation devices to remove CO2 and purify H2 in coal gasification refineries to reduce energy consumption and investment costs. Then, the process was coupled with gasoil hydrogenation and the recycled H2 produced by the hydrogenation reactor could be further purified by the H2-selective membrane, which increased the H2 concentration of the hydrogenation reactor inlet by about 11 mol.% compared with the conventional direct recycling process, and the total system pressure was reduced by about 2470 kPa. At the same time, this additional membrane separation and purification prevented the accumulation of CO/CO2 in the recycled H2, which ensured the activity of the catalyst in the reactor and the long-term stable operation of the devices. Further, parameters such as compressor power, PI (polyimide)/PEO (polyethylene oxide) membrane area, pressure ratio on both sides of the membrane, and purity of make-up H2 were optimized by sensitivity analysis. The results showed that, compared with the conventional method, the NMGH process simplified operations, significantly reduced the total investment cost by $17.74 million, and lowered the total annual costs by $1.50 million/year.

Membrane-based separation technologies: from polymeric materials to novel process: an outlook from China

During the past two decades, research on membrane and membrane-based separation process has developed rapidly in water treatment, gas separation, biomedicine, biotechnology, chemical manufacturing and separation process integration. In China, remarkable progresses on membrane preparation, process development and industrial application have been made with the burgeoning of the domestic economy. This review highlights the recent development of advanced membranes in China, such as smart membranes for molecular-recognizable separation, ion exchange membrane for chemical productions, antifouling membrane for liquid separation, high-performance gas separation membranes and the high-efficiency hybrid membrane separation process design, etc. Additionally, the applications of advanced membranes, relevant devices and process design strategy in chemical engineering related fields are discussed in detail. Finally, perspectives on the future research directions, key challenges and issues in membrane separation are concluded.

Highly selective CO removal by sorption enhanced Boudouard reaction for hydrogen production

Development of an effective technology for the purification of a hydrogen rich stream to achieve a CO concentration below 10 ppm, suitable for low temperature fuel cell applications.

Optimal Design of a Two-Stage Membrane System for Hydrogen Separation in Refining Processes

This paper fits into the process system engineering field by addressing the optimization of a two-stage membrane system for H2 separation in refinery processes. To this end, a nonlinear mathematical programming (NLP) model is developed to simultaneously optimize the size of each membrane stage (membrane area, heat transfer area, and installed power for compressors and vacuum pumps) and operating conditions (flow rates, pressures, temperatures, and compositions) to achieve desired target levels of H2 product purity and H2 recovery at a minimum total annual cost. Optimal configuration and process design are obtained from a model which embeds different operating modes and process configurations. For instance, the following candidate ways to create the driving force across the membrane are embedded: (a) compression of both feed and/or permeate streams, or (b) vacuum application in permeate streams, or (c) a combination of (a) and (b). In addition, the potential selection of an expansion turbine to recover energy from the retentate stream (energy recovery system) is also embedded. For a H2 product purity of 0.90 and H2 recovery of 90%, a minimum total annual cost of 1.764 M$·year−1 was obtained for treating 100 kmol·h−1 with 0.18, 0.16, 0.62, and 0.04 mole fraction of H2, CO, N2, CO2, respectively. The optimal solution selected a combination of compression and vacuum to create the driving force and removed the expansion turbine. Afterwards, this optimal solution was compared in terms of costs, process-unit sizes, and operating conditions to the following two sub-optimal solutions: (i) no vacuum in permeate stream is applied, and (ii) the expansion turbine is included into the process. The comparison showed that the latter (ii) has the highest total annual cost (TAC) value, which is around 7% higher than the former (i) and 24% higher than the found optimal solution. Finally, a sensitivity analysis to investigate the influence of the desired H2 product purity and H2 recovery is presented. Opposite cost-based trade-offs between total membrane area and total electric power were observed with the variations of these two model parameters. This paper contributes a valuable decision-support tool in the process system engineering field for designing, simulating, and optimizing membrane-based systems for H2 separation in a particular industrial case; and the presented optimization results provide useful guidelines to assist in selecting the optimal configuration and operating mode.