(490a) Integration Options of Electrochemical Hydrogen Pumping | AIChE

(490a) Integration Options of Electrochemical Hydrogen Pumping


Seferlis, P. - Presenter, Aristotle University of Thessaloniki
Papadopoulos, A., Center for Research and Technology-Hellas
Bampaou, M., AUTH
Hydrogen is a key component in the chemical, petrochemical and biomass industry, in processes such as hydrocracking, catalytic reforming and hydrodeoxygenation. A variety of renewable and fossil-based hydrogen production technologies exist with the costs mainly depending on the hydrogen source [1]. Pressurized hydrogen production costs make up for a considerable portion of the overall operation expenditures [2] and therefore, increasing hydrogen pressurization and recirculation effectiveness is crucial for process economics. An electrochemical hydrogen compressor (EHC) is a promising technology that combines hydrogen separation and purification within a compact piece of equipment. It is a device similar to a proton exchange membrane fuel cell (PEMFC) and involves no moving parts. A membrane acts as an electrolyte for proton exchange and is positioned between two catalyst containing electrodes (usually with Pt as catalyst [3]), which in turn are positioned between two porous gas diffusion layers [4]. The electrochemical compression is an one-stage, isothermal process that requires about half of the adiabatic power needed for fixed compression ratio, at constant temperature [5].

During the last years, multiple projects have been funded, aiming at the commercialization of this application. In the USA, Analytic Power Corp. [6] and Fuel Cell Energy [7] are some of the corporations involved in such projects. In Europe, Hydrogen Efficiency Technologies (HyET, the Netherlands) demonstrated hydrogen electrochemical compression up to 1000 bar using a single-stage compressor [8]. Lower power requirements, simplicity of the system and hydrogen purification are the major advantages that triggered research into this application.

Electrochemical hydrogen compressors are mainly classified based on the operating temperature: low-temperature EHC refers to electrochemical pumping conducted at 50 - 80 oC using Nafion® membranes as electrolytes, whereas high-temperature EHC (conducted at >100 oC) uses polybenzimidazole (PBI) membranes. Several losses and irreversibilities have to be taken into account, irrespective of the operating temperature before integrating an EHC into existing process flowsheets. Losses associated with the proton resistance of the membrane (Ohmic losses), as well as activation losses that refer to the energy associated with the activation of the anode and cathode reactions, have to be taken into consideration. In addition, due to the anode and cathode pressure difference, molecular hydrogen flows back from the cathode to the anode department, which results in lower actual compressed hydrogen. The selection of the temperature range presents several characteristics and operation modes, which are different at each EHC type. For example, operating at low temperatures render the anode catalyst susceptible to CO and other impurities, whereas at higher temperatures the catalyst tolerance increases drastically. In addition, Nafion® membranes require hydration in order to reduce the losses associated with proton conductivity across the membrane, which is mainly conducted by humidifying the inlet gaseous mixture. This hydration requirement needs proper management in order to prevent drying of the anode or liquid water accumulation at the cathode department. On the other hand, high-temperature operation requires no hydration, whereas at normal conditions, water exists only in gaseous phase. However, higher outlet pressures are reported for low-temperature EHC, making them suitable for high pressure refinery and biorefinery applications. Figures 1-4 present some example results of operation characteristics of the low-temperature EHC operation.

In this work, EHC process integration options are explored, based on process modelling accounting for all important phenomena and losses in such systems, including water management for the low-temperature EHC. The proposed model enables the investigation of a broad range of operating parameters and conditions, while it can also be easily integrated in flowsheets representing wider process systems. In addition, case studies are conducted that investigate the combination of electrochemically compressing (either low- or high-temperature) up to a certain intermediate pressure and then mechanically compressing H2 to the required, higher pressure.


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