Study On Preparation Of Lignite-supported Sorbent Through High-pressure Impregnation For Gas Desulfurization At Mid-temperature

Mid-temperature desulfurization is a key step for coal gasification as the source of the coal conversion technology. Sorbent preparation, the active component and carrier selection is the key factor in mid-temperature desulfurization technology. Among other preparation methods of desulfurization sorbent, impregnation method with high utilization of the active ingredient and easy to operate was widely used in the preparation and study of the fine sorbent. High-pressure impregnation to some extent could improve the pore structure of the carrier and distribute the active ingredient in the carrier uniformly. Semi-coke as a cheap and conventional sorbent carrier has better applicability in high-pressure impregnation hydrothermal synthesis for preparation of desulfurization sorbent.Lignite reserves in china account for13%of the total coal resources. Lignite with characteristics such as good chemical reaction, easily weathering in the air, not easily to store and transport causes limited utilization of lignite resources. Porosity and specific surface area of lignite is much larger than other kind of coal, which leads to the lignite with high absorbency. Active component could be supported on lignite surface by impregnation method by use of good absorbency of lignite, which will be of great significance for both preparation of sorbent for purifying coal gas and utilization of lignite resource.The high-pressure impregnation method is used to prepare sorbent using lignite as support for removing H2S from hot coal gas in this study. The effects of different impregnation methods, metal active component, precursor solution concentration, impregnation time and impregnation pressure during sorbent preparation on the removal of H2S in simulated coal-derived gas were investigated. The characterization results from XRD, atomic absorption and so on were correlated the loading amounts of metal oxide, crystal form, disperse of metal oxide and pore structure with desulfurization activity of sorbent to explore the effects of the operation parameters in high-pressure impregnation preparation on the activity of sorbent desulfurization. In addition, the preferred sorbent was studied three vulcanization/regeneration cycles performance and further modification.The main conclusions are summarized as follows:1. Effects of the active component precursor and preparation method on properties of vulcanizing properties1) The desulfurization activity of sorbent prepared by Zn(NO3)2as an active ingredient precursor was higher than that of Fe(NO3)3, Cu(NO3)2, Mn(NO3)2precursor solution prepared sorbent.2) Sulfidation behavior of sorbents prepared by activated carbon and lignite as carrier respectively using16wt%Zn (NO3)2as the precursor solution was compared. Desulfurization activity of sorbent using activated carbon as carrier is much higher than lignite as carrier, which implied the pore structure and the loading of active component are important factors influencing the sorbent desulfurization activity.3) Desulfurization activity of sorbent prepared by high-pressure impregnation is far better than sorbents prepared by static impregnation, bubbling impregnation and ultrasound-assisted impregnation. The high-pressure impregnation is optimal method. Specific surface area and pore volume of sorbents prepared under20atm impregnation pressure compared with that of raw lignite increased by45%and60%respectively, which implied impregnation pressure could improve the pore structure of the carrier to some extent.4) The release content of reducing gases H2and CO during pyrolysis of lignite is little, which didn’t influence the generating of active component of metal oxide.2. Effects of impregnation conditions and regeneration of the sorbent1) Impregnation pressure has a great influence on the specific surface area and pore structure of the sorbent. The sorbent obtained under the impregnation pressure of20atm with the best specific surface area and pore structure had highest desulfurization activity. The loading of active ingredient increased with the increasing of the impregnation solution concentration; the greater the amount of the loading of active ingredient, the higher desulfurization accuracy and the sulfur capacity were. The sorbent obtained at an impregnating solution concentration of36wt%had the maximum utilization of the active ingredient. The loading of active ingredient increased gradually when impregnation time increased from3h to7h, but specific surface area and pore volume of the sorbent prepared on the condition of7h impregnation time reduced significantly compared with the sorbent prepared on the condition of5h impregnation time. Active ingredient of zinc nitrate precursor, impregnation pressure of20atm, immersion time of5h and impregnation solution concentration of36wt%are optimum conditions for preparing sorbent.2) Three vulcanization/regeneration cycles test of sorbent HP20Zn36h5was carried out. Zinc content in the sorbent reduced by5.3%after each regeneration, which implied active ingredient could loss in the regeneration process. The desulfurization activity of the regenerated sorbent was slightly lower than fresh sorbent; the sorbent after three regeneration still had a good desulfurization capacity with the breakthrough time of43h and sulfur capacity of7.22gS/100g sorbent.3) The addition of copper and manganese component can effectively promote the dispersion of zinc oxide on lignite support and improve the utilization of active component zinc. There is a new phase ZnMnO3, which improved desulfurization activity of the sorbent, especially the improvement for desulfurization precision.