Pure hydrogen from pyrolysis oil using the steam-iron process

Abstract

The novelty of using pyrolysis oil in the steam-iron process to produce pure hydrogen is introduced. In this process, products of pyrolysis oil gasification are used to reduce iron oxides which are subsequently oxidized with steam, resulting in pure hydrogen. Two process alternatives are considered: (i) a once-through concept in which cheap iron oxide (in our case sintered pellets of natural iron ore, Fe 2O 3) is used in one cycle, before further processing in a blast furnace, and (ii) a continuous system, in which specially developed iron oxides (in our case an ammonia catalyst) are cycled between a reduction and oxidation reactor. By injecting pyrolysis oil in a fluidized bed filled with Fe 3O 4 at 800 °C, it has been shown that CO and H 2 as well as coke by the gasification reactions contribute to the reduction. Experiments including a complete redox cycle with the ammonia catalyst have shown that a hydrogen production in the oxidation of 0.84 N m 3/kg dry pyrolysis oil (LHV H 2/LHV oil = 0.4) can be obtained when the conversion of iron oxides are low (∼1.0%). The gas produced in the reduction step under these conditions contains 38% of the heating value of the input and has an LHV of 7.8 MJ/N m 3 gas product. Deactivation of the iron oxides has been observed by a decreasing reduction rate in subsequent redox cycles. BET and SEM analysis showed a decrease in surface area, which could partly explain the observed deactivation.