Хемосорбція гідроген сульфіду модифікованими природними сорбентами

Summary

Stepova K.V. Chemisorption of hydrogen sulfide by modified natural sorbents. - Manuscript.

Thesis for Cand. Tech. Sci. degree by specialization 05.17.08 - Processes and Equipment for Chemical Technology. - Lviv National Polytechnic University, Lviv, 2010.

Dissertation is dedicated to theoretical and experimental research of hydrogen sulfide chemisorption by natural clay minerals modified by heavy metals' (salts of iron(III) and copper(II)) wastes.

For the first time the possibility of production of effective sorbents on the basis of clay minerals modified by heavy metals wastes was substantiated and proved. Method of solventless metals (hydro-)xoforms (Fe³⁺ and Cu²⁺) dispersion on the surface of carbonate-containing clay mineral was improved and optimal bentonite - modifier ratios was found.. As a result new sorbents for hydrogen sulphide capture from exhaust gases of industrial plants were produced.

Carbonate destruction and hydroxides' deposition on the bentonite surface were proved due to quantitative (atomic absorption spectroscopy) and structural (XRD, FTIR, SEM) analysis of original and modified bentonite. Influence of thermal treatment up to 1100^oC on sorbents structure was analyzed by means of thermogravimetric and differential thermogravimetric analysis. Due to porosity investigations it was found out that chemical treatment of natural clay by acid salts of Fe (III) and Cu (II) results in an increase of the BET surface area and pore volume.

Influence of different modifiers on the properties of synthesized clay sorbent was determined.

Regularities of H₂S chemisorption by solid sorbents were studied and the mechanism of sorption in gas-solid system was proposed. Basic constants and coefficients for defining of chemical adsorption velocity and duration were determined. The model of chemisorption of hydrogen sulfide by sorbents based on Fe- and Cu-modified clay mineral was presented. Model of the process is supposed to consist of three stages. First stage is limited by external diffusion of hydrogen sulfide to the sorbent's surface, second stage is limited by rate of reaction between hydrogen sulfide and iron (copper) hydroxide deposited on the surface of the grain and it can be described by the rate equation. Third stage of adsorption is carrying out within the internal diffusion region and mathematically it can be described by Fick's second law in a spherical coordinate system with the boundary conditions of the third kind. Cu-modified sample shows higher rate on all stages than the Fe-modified one.

For the first time basic sorption properties of synthesized materials at dynamic conditions from the model gas flows were determined. Breakthrough capacities and maximum sorption capacities of sorbents and original bentonite were determined and compared. Fe-modified sample shows the enhanced capacity in comparison of unmodified and copper-modified samples. Though, the time before H₂S appears on the outlet of adsorption column for Fe-modified clay is less than for Cu-modified sample but the breakthrough capacity of the former sample is much higher.

Dependence of sorption capacity of sorbents on H₂S concentration in the gas flow was studied. H₂S concentration in the gas flow doesn't affect sorption capacity of Cu-modified clay, whereas the reducing of concentration of H₂S in the gas flow results in increase of sorption capacity of Fe-modified sample.

Optimal granulometric composition of sorbents was chosen.

Dependence of sorption capacity of Fe-bentonite on quantity of sorption-regeneration cycles was identified. The adsorption capability of the iron-containing sample steadily decreased after every adsorption-regeneration cycle and adsorbent total saturation with sulfur was reached when sulfur content came up to 34%.

Flow diagram of new sorbents application was presented. Optimal parameters for its realization were proposed. Prospective economic effect from new materials application in production plant was calculated.

Keywords: chemisorption, natural sorbents, hydrogen sulfide, heavy metals.

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