High Temperature gas-solid reactions have been commercially limited to applications like coal combustions, lime production, iron smelting where solids act as raw materials. There are hardly any processes where gas-solid reactions are the core reason for the process to exist. For this purpose, the particles need to be regenerable, i.e. they should be able to undergo multiple reaction/regeneration reactions without loss in activity. However, at high temperatures, the particles rapidly lose activity with reaction cycling and hence have to be replaced increasing the process costs making the processes unviable.
The work described in this Thesis starts with understanding key issues that would allow the metal oxide particles to be regenerable over numerous reaction/regeneration cycles. It was found that around 400-700°C, the particle pore structure plays a crucial role. At temperatures above 800°C, sintering leads to complete collapse of the pore structure and other properties like oxygen ion diffusivity becomes important to ensure complete recyclability.
Given the understanding obtained regarding causes for recyclability, further work describes process development for particles that are regenerable at low and high temperatures. Studies were carried out to control the pore structure present in SiC for hot desulfurization of syngas. Subsequent sorbent development led to a Fe2O3-SiC that could remove more than 95% of the sulfur and was regenerable for multiple reaction/regeneration cycles. Two other processes were developed that can convert coal or coal derived syngas into hydrogen with high efficiencies at much lower cost than competing technologies. These processes were based on cyclic reduction and oxidation of metal oxide by the hydrocarbon fuel and steam respectively. Both particle and process development was carried out. The first process named Syngas Redox (SGR) process converts coal gasification derived syngas to hydrogen with an efficiency of 75%. The second process, Chemical Looping Reforming, converts coal to hydrogen at an efficiency of 81-90%. A number of developmental issues like ash handling, role of sulfur, contacting pattern, reactor designs, etc. have been discussed. Finally the design of a bench scale reactor is described that can be used to demonstrate and develop the processes discussed. Experiments conducted demonstrated the feasibility of the reaction schemes involved.