Experiments were conducted to study the absorption reaction of hydrogen sulphide with zinc oxide forming zinc sulphide and water. The reaction is of commercial importance for the removal of hydrogen sulphide from reactor feed streams and from natural gas. Most of the experiments were performed on a commercial ICI zinc oxide-based absorbent prepared by calcination of basic zinc carbonate but a number of experiments were also performed on samples of basic zinc carbonate or of zinc oxide prepared by different treatments. The reactions were carried out in a shallow bed flow reactor containing 0.2-0.6g of absorbent at a pressure just above atmospheric and at temperatures in the range 0 to 45<SUP>0</SUP>C. Feed gases containing 0.06-0.7% v/v hydrogen sulphide and 0-0.5% v/v water in nitrogen were used. On-line gaseuos analysis was performed using a Thermal Conductivity Detector with complementary information provided by sulphur analysis and electron microprobe analysis of the discharged partially sulphided absorbent. The specific reaction rate was observed to be very high initially but to decline to a much slower pseudo-steady state (pss) rate. The pattern of this decline was found to be a function of particle size, with larger particles exhibiting slower, diffusion-limited rates in the initial period but higher pss rates than smaller particles. This latter result was attributed to an enhanced water concentration in the centre of larger particles. Microprobe analysis indicated uniform sulphiding at about 20% absorbent conversion whereas at low conversions an outer sulphided shell surrounds a central unreacted core. The conversion of the absorbent at pss (in the range 9-23%) was observed to increase with increasing partial pressures of water and of hydrogen sulphide in the feed. A marked dependence of the pss rate upon water partial pressure and a decrease in the rate with increasing temperature were observed and interpreted as indicative of an autocatalytic reaction. The role of water in facilitating solid rearrangement is consistent with the results of interrupted experiments which showed enhanced water adsorption and reaction rate after isolation. The pss rate was found to be insensitive to hydrogen sulphide concentration in the range studied. There appears to be an optimal calcination temperature of the absorbent precursor although this may not correspond with the temperature yielding maximal specific surface area. The effects of some impurities in the commercial absorbent were also investigated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653731 |
| Date | January 1990 |
| Creators | Lawrie, Catriona H. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11041 |
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