Demonstration of unmixed steam reforming of vegetable oil.

Unmixed steam reforming is an emerging concept for enhancing the steam reforming process. It encompasses the concepts of unmixed combustion, regenerative sorption assisted steam reforming, and is potentially auto-thermal. It can be operated on a smaller scale to conventional steam reforming at lower pressures and has potential benefits for stationary decentralised hydrogen production. The production of hydrogen from vegetable oils represents a realistic renewable source. This paper describes the design and operation of a bench scale unmixed steam reforming reactor which provided preliminary results for methane and sunflower oil. The selected catalysts and adsorbents tested include a steam reforming catalyst and a Spanish dolomite, previously identified as being suitable for this process. Operating conditions such as variation of steam:fuel ratio, and reactor temperature are studied. Process variables initially developed for methane provided bench mark conditions for sunflower oil. Selectivity to carbon and oxygen containing products are calculated together with selectivity to hydrogen. During the methane feed step, the main dry gas product is hydrogen, accompanied by CO2, un-reacted methane, and negligible CO. The influence of steam has a marked effect on hydrogen selectivity. A much-improved selectivity to H2 product is achieved when introducing steam in the feed indicating that the steam reforming reaction is active. The presence of steam also effects the formation of carbon, which was produced using both methane and sunflower oil. For methane and sunflower oil reforming on the catalyst alone, a hydrogen yield of between 50-60% can be achieved. The rate of NiO reduction and Ni oxidation are important factors for this process as is the total conversion. The rate of NiO reduction is slower than the rate of Ni oxidation and a conversion of around 40% is achieved. When operating with an adsorbent present at a Ni:Ca ratio of 4:1, the production of hydrogen increases significantly. The extent of CO2 adsorption is sensitive to the bed temperature. At a bed temperature of 600oC the dry gaseous products contained over 85 vol% hydrogen.