DEVELOPMENT OF AN INTEGRATED CATALYTIC METHANOL REFORMER ETSU F/02/00060/REP Contractor C J B Developments Ltd Prepared by R A J Dams S C Moore P Hayter M Verhaak The work described in this report was carried out under contract as part of the New and Renewable Energy Programme, managed bythe Energy Technology Support Unit (ETSU) on behalf of the Department of Trade and Industry. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of ETSU or the Department of Trade and Industry. First published 1996 CONTENTS 1. EXECUTIVE SUMMARY 1 2. BACKGROUND 2 3. OBJECTIVES 4 4. CATALYST DEVELOPMENT 4 5. BENCH-SCALE REFORMER CONSTRUCTION AND OPERATION 6 6. EVALUATION OF RESULTS 10 7. CONCLUSIONS 10 8. RECOMMENDATIONS 11 Figure 1 Figure 2 Table 1 1. EXECUTIVE SUMMARY As part of a successful collaboration with Vickers Shipbuilding and Engineering Limited (VSEL), CJB Developments Limited (CJBD) developed a methanol reformer to supply hydrogen-rich gas for a Solid Polymer Fuel Cell (SPFC) power system with an output of 10kW. The methanol reformer used a packed bed pelleted proprietary catalyst. The endothermic heat of reaction was supplied by combusting the fuel cell off-gases. Although the reformer performed successfully in terms of the objectives of the breadboard power system, it was clear that for an on-board fuel cell vehicle application the start-up time and response to transient changes in load was not adequate. Consequently, CJBD investigated different forms of construction of reformer and as a result formed a collaboration with ECN of the Netherlands and VSEL to develop, in the longer term, an all metal methanol reformer using metal substrates coated with both reforming and combustion catalysts. ECN’s Applied Catalysis department had previous experience in this area. This report describes the development and evaluation of a bench-scale methanol reformer system, incorporating novel catalysts. In this project ECN developed methanol reforming catalysts and ways of applying them to metal substrates. These catalysts and coating techniques were used to produce a series of aluminium tubes which CJBD evaluated on a specifically designed test rig. After initial problems with their coating techniques, ECN produced a set of tubes which demonstrated a performance similar to that achieved by CJBD with pelleted catalyst. As these tubes were not optimised, there is scope for further improvement. In 1995, CJBD and ECN, as part of an expanded team, applied successfully for funding from the JOULE and DTI Advanced Fuel Cell Programmes to develop a compact methanol reformer and gas clean-up system for a mobile SPFC vehicle. The work undertaken during this project was a significant factor in the success of the joint application. 1 2. BACKGROUND In 1990, CJB Developments Limited (CJBD) and Vickers Shipbuilding and Engineering (VSEL) developed, built and tested a 10kW breadboard Solid Polymer Fuel Cell (SPFC) power system using methanol as a source of hydrogen-rich fuel. This was a generic demonstrator which showed that such a system could be assembled and operated successfully. CJBD’s contribution to this programme was the development of the methanol reformer and gas clean-up system. Methanol was chosen as the fuel source because of its high energy density and because it can easily be reformed to hydrogen at low temperatures. Furthermore, methanol can be manufactured from coal, natural gas and other feedstocks including bio-mass. It also has some advantages over other fuels in term of fuel storage and distribution. The method of storing methanol on a vehicle is simple and comparable to conventional vehicles. In addition, a fuel cell vehicle using methanol would be able to attain a similar range as an internal combustion engine vehicle and drivers are comfortable with a liquid fuel. Steam reforming was chosen because methanol is easily processed in this manner to form a hydrogen-rich mixture. The typical hydrogen content of the reformed gas is 75% with the balance being 24.8% carbon dioxide and 0.2% carbon monoxide. The process is a catalytic endothermic reaction which occurs at about 225°C. The endothermic heat is provided by burning the fuel cell off-gases. At the start of this work, other technologies such as partial oxidation, autothermal reforming and pyrolysis were less well developed and had a number of potential system problems. Partial oxidation requires air introduction (a potential parasitic loss), produces a reformed gas diluted with nitrogen (typical hydrogen content is 45%) and contains higher levels of carbon monoxide (requires a shift reactor prior to final carbon monoxide removal). Additionally, partial oxidation is an exothermic reaction at a higher temperature than steam reforming and hence produces heat which has to be used within the complete fuel cell system. Autothermal reforming, which is a combination of partial oxidation and steam reforming resulting in a thermally neutral situation, was in the early stage of development and operates at temperature of about 500°C using natural gas. Pyrolysis 2 was considered to require too high an operating temperature (800°C /1000°C). Both autothermal reforming and pyrolysis would appear to have more difficult start-up problems because of high operating temperatures. The methanol reformer developed by CJBD was a packed bed device using a commercially available steam reforming catalyst. The reformer performed satisfactorily for the purposes of the breadboard demonstration. However, it was clear that the speed of response to transients and time to start from cold would not meet the requirements for a reformer to be used on-board an SPFC driven vehicle. To overcome these problems, the use of catalysts coated onto metal substrates was considered to be the best step forward. An organisation with experience of coating techniques and catalyst development was sought. Contact was made with the Applied Catalysis department of ECN in the Netherlands. It was agreed that ECN would lead a group, with CJBD and VSEL as partners, to develop a compact, responsive, methanol reformer for use on board a fuel cell driven vehicle. ECN was to develop an improved methanol reforming catalyst (lower operating temperature, lower carbon monoxide levels in exit gases) and a combustion catalyst for burning fuel cell off­ gases. These catalysts were to be applied to metal substrates which would be used to construct an all metal reformer. The enhanced heat transfer characteristics were expected to improve the start-up time and transient response. CJBD was to test this reformer and VSEL was to undertake system modelling. This work programme formed the basis of an unsuccessful submission to the JOULE II programme. However, in order to gain an understanding of the potential for the development of such a reformer, the UK DTI Advanced Fuel Cell Programme and the Netherlands government agreed to fund a preliminary investigation. The aim was to focus on the key development issues, concentrating on developing and evaluating an improved methanol reforming catalyst and its application to a metal substrate. In addition, the project was seen as a step to building a suitable collaboration that would be capable of taking forward the technology in any future phase. 3 3. OBJECTIVES The objectives of the programme were: • To develop and evaluate stable and highly active copper based catalysts to produce reformate with low levels of carbon monoxide and apply these catalysts to metal substrates. • To test and evaluate these catalytic metal substrates to determine their suitability as the basis of an integrated catalytic methanol steam reformer for the production of a hydrogen-rich fuel for SPFCs in transport applications. • To evaluate different design options for a reformer using catalytically coated metal substrates and assess the likely future cost of volume production of the reformer. The development and evaluation of the copper based catalysts and support systems was carried out by ECN. The construction of a bench scale reformer and evaluation of the catalyst coated substrates was carried out by CJBD. The use of metal substrates was designed to improve the heat characteristics and temperature profiles in the reformer. Improving these characteristics is believed to lead to improved performances (reduced start-up time and faster dynamic response), reduced costs and a compact construction. ECN supplied the metal substrates inside a tube which was installed in the bench- scale reformer test rig built by CJBD. 4. CATALYST DEVELOPMENT ECN has developed a copper based catalyst for methanol steam reforming. Several promoted and unpromoted copper-on-alumina catalysts were prepared by wet impregnation of a gamma alumina support with the objective of improving the activity and selectivity of the copper with respect to the desired reactions. Impregnations were carried out with solutions containing either copper nitrate, the promoter precursor salt(s) or a combination using a one-step procedure. In most preparations the promoters were added to the support by co-impregnation with copper nitrate. After impregnation, the heated powders were homogenised and air dried at 80°C for 15 hours. After drying, the catalyst precursors were calcined in air at 4 different temperatures to form a metal oxide and release nitrogen dioxide. The concentration of copper nitrate in the impregnating solution was adjusted to obtain the desired metal loading. The gas-phase reformation of methanol to carbon dioxide (CO2) , carbon monoxide (CO) and hydrogen (H2) was studied in a fully automated micro-flow apparatus, operating at atmospheric pressure. Prior to the catalytic experiments, the precursors were dried in situ at 100°C for 30 minutes in a flowing hydrogen-nitrogen (N2) mixture (25% hydrogen). Following the drying step, reduction was performed by raising the reactor temperature to 250°C at a rate of 1°C/min and maintaining this temperature for 4 hours. After reduction, the catalyst sample was cooled to 150°C in flowing nitrogen.