Regeneration Characteristics and Kinetics of Ni/ZnO–SiO2–Al2O3 Adsorbent for Reactive Adsorption Desulfurization

Adaptable strategy for reactivation and recycling of spent S-Zorb adsorbents at the laboratory and pilot scale

The spent S-Zorb adsorbents containing Ni and Zn elements are hazardous wastes. It would generate significant economic and environmental benefits to reactivate and recycle these solid wastes through a reactivation strategy. Furthermore, adaptability investigation of this strategy is also indispensable before its industrial application. Herein, the spent S-Zorb adsorbents (Spent-TJ/MM/QD) from different plants were reactivated at laboratory and pilot scale in 3 m3 reactor via an acid-base coupling reactivation strategy. The spent adsorbents exhibit distinct phase compositions and microstructures of active components. Formation of ZnSi2O4 and ZnS is the primary reason for abandonment of the Spent-TJ (Spent-MM) and Spent-QD, respectively. The nickel species also exhibit different aggregation extent. Fortunately, the inert zinc and nickel species are respectively converted into ZnO and NiO during the reactivation process. Higher surface area (1.7-4.0 times that of the spent adsorbents) and more acid sites are generated over the reactivated adsorbents. Besides, all the reactivated adsorbents possess similar phase compositions and microstructures. Both the adsorbents reactivated at pilot and laboratory scale exhibit comparable desulfurization activity to fresh ones. The sulfur content of the gasoline desulfurized by the reactivated adsorbents is below 10 μg g-1, meeting the Euro V legislations. All the results indicate the excellent adaptability and commercial potential of the reactivation strategy. The possible mechanism for the excellent adaptability of the reactivation method was proposed.

Reactive Adsorption Desulfurization Coupling Olefin Conversion in Fluid Catalytic Cracking Gasoline Upgrading Process

Reactive adsorption desulfurization experiments were carried out on fluid catalytic cracking gasoline over a Ni/ZnO adsorbent in a fixed bed reactor. Results demonstrated that desulfurization is accompanied by hydrogen transfer, while isomerization and aromatization reactions are rare. Reactive adsorption desulfurization coupling olefin conversion was attempted by mixing a catalyst consisting Zn-ZSM-5 with an adsorbent at a certain proportion. The process reduced the loss of octane number and sustained ultradeep desulfurization ability simultaneously. An Fe-modified Ni/ZnO adsorbent was developed, which possessed better olefin retention ability than the Ni/ZnO adsorbent. The Ni-Fe/ZnO adsorbent mixed catalyst exhibited better olefin conversion performance and lower octane number loss than that of the Ni/ZnO adsorbent mixed catalyst because more olefins were retained for isomerization and aromatization reaction on the catalyst. The proportion of the catalyst added and the operating conditions of the process were optimized, ultralow sulfur gasoline was produced, and loss of octane number was low under optimal operating conditions. The amount of octane number lost was reduced by 85% compared with conventional reactive adsorption desulfurization. In addition, the process exhibited excellent desulfurization and olefin conversion performance in multiple regeneration cycles, demonstrating the feasibility of continuous processing.

Investigation on the Cause of the SO2 Generation during Hot Gas Desulfurization (HGD) Process

In the integrated gasification combined cycle (IGCC) process, the sulfur compounds present in coal are converted to hydrogen sulfide (H2S) when the coal is gasified. Due to its harmful effects on sorbent/solvent and environmental regulations, H2S needs to be removed from the product gas stream. To simulate the H2S removal process, desulfurization was carried out using a dry sorbent as a fluidizing material within a bubbling, high-temperature fluidized bed reactor. The ZnO-based sorbent showed not only an excellent capacity of H2S removal but also long-term stability. However, unexpected SO2 gas at a concentration of several hundred ppm was detected during the desulfurization reaction. Thus, we determined that there is an unknown source that supplies oxygen to ZnS, and identified the oxygen supplier through three possibilities: oxygen by reactant (fresh sorbent, ZnO), byproduct (ZnSO4), and product (H2O). From the experiment results, we found that the H2O produced from the reaction reacts with ZnS, resulting in SO2 gas being generated during desulfurization. The unknown oxygen source during desulfurization was deduced to be oxygen from H2O produced during desulfurization. That is, the oxygen from produced H2O reacts with ZnS, leading to SO2 generation at high temperature.

Density functional theory study of thiophene desulfurization and conversion of desulfurization products on the Ni(111) surface and Ni55 cluster: implication for the mechanism of reactive adsorption desulfurization over Ni/ZnO catalysts

Density functional theory calculations were performed to study thiophene desulfurization and conversion of desulfurization products on the Ni(111) surface and Ni₅₅ cluster.

Fabrication of magnetically responsive HKUST-1/Fe3O4 composites by dry gel conversion for deep desulfurization and denitrogenation

Selective adsorption by use of metal-organic frameworks (MOFs) is an effective method for purification of hydrocarbon fuels. In consideration that the adsorption processes proceed in liquid phases, separation and recycling of adsorbents should be greatly facilitated if MOFs were endowed with magnetism. In the present study, we reported for the first time a dry gel conversion (DGC) strategy to fabricate magnetically responsive MOFs as adsorbents for deep desulfurization and denitrogenation. The solvent is separated from the solid materials in the DGC strategy, and vapor is generated at elevated temperatures to induce the growth of MOFs around magnetic Fe₃O₄ nanoparticles. This strategy can greatly simplify the complicated procedures of the well-known layer-by-layer method and avoid the blockage of pores confronted by introducing magnetic Fe₃O₄ nanoparticles to the pores of MOFs. Our results show that the adsorbents are capable of efficiently removing aromatic sulfur and nitrogen compounds from model fuels, for example removing 0.62mmolg^-1S and 0.89mmolg^-1N of thiophene and indole, respectively. In addition, the adsorbents are facile to separate from liquid phases by use of an external field. After 6 cycles, the adsorbents still show a good adsorption capacity that is comparable to the fresh one.