Reactive Adsorptive Desulfurization Based On Metal Hydroxide Adsorbents

Considering the urgent demand of removing trace sulfur compounds for the environment protection,we aim to explore reactive metal hydroxide-based adsorbents in this work for the ultra-deep desulfurization of trace secondary heavy mercaptan from hydrorefined gasoline and the removal of trace H₂S.This work belongs to the field of separation,material engineering and reaction engineering,which is of great significance for the scientific research and pratical application.To overcome the bottleneck of low adsorption desulfurization efficientcy of secondary heavy mercaptan from hydrorefined gasoline,reactive supported hydroxide adsorbent Z-sorb with high adsorption capacity and selectivity was developed in this work.A pronounced adsorption capacity（25.7 mg-S/g-ads.）and selectivity（206.1）of C₇H₁₆S over Z-sorb were achieved,which were much higher than that of other competitive components,such as aromatic hydrocarbon,thiophene,olefin and additives,etc.The high selectivity of Z-sorb can be attributed to the strong interaction（-44.6 k J/mol）between adsorbate and adsorbent.The adsorption sites of Z-sorb were identified as supported Zn（OH）₂ domains.Characterization results indicated that C₇H₁₆S replaced the surface hydroxyl groups of Z-sorb through deprotonation process and be adsorbed on Z-sorb with the form of Zn-SR.A novel catalytic reactive regeneration approach was proposed to tackle the trade-off between adsorption selectivity and regenerability.Compared to the low regeneration efficiency by solvent washing（35%）in multiple cycles of selective adsorption,the oxidative treatment demonstrates dramatically enhanced regenerability.Experiments and DFT results indicated that the strongly adsorbed heptanethiol was readily converted to disulfide over Zn（OH）₂ domains in presence of trace H₂O₂ under ambient conditions,which helps completely recover reactivity of Z-sorb.Because of its good de-mercaptan performance and efficacious regeneration,the cyclic process of selective adsorption-reactive regeneration shows great potential to balance the contradiction between adsorption selectivity and regenerability for industrial adsorptive de-mercaptan.In order to further improve the reactivity of Zn-domains in metal hydroxide-based adsorbents,Zn layered hydroxide salts（Zn LHS）adsorbents with high dispersion of Zn bronzes were developed and investigated for the reactive adsorptive desulfurization of mercaptan from gasoline.Intercalated anions have great influence on the de-mercaptan performance of Zn LHS adsorbent,and Zn LHS adsorbent intercalated with acetate anions（Zn-Ac^-）presents outstanding mercaptan adsorption capacity（336 mg-S/g-ads）and selectivity（286.1）.Compared to the supported Z-sorb adsorbent reported in Chapter 2,the saturated adsorption capacity per mass and per metal site of Zn-Ac-adsorbent were increased by 13 times and 4 times（1.37 mol-S/mol-Zn）,respectively.The appropriate interlyar distances pillared by the intercalated anions inhibit the stacking of metal hydroxide layers and make the active Zn²⁺sites more accessible by C₇H₁₆S.Characterization results implied that the C₇H₁₆S was mainly intercalated on Zn-Ac^-adsorbent by chemical adsorption,while small fraction of C₇H₁₆S was captured as free species.Interestingly,the adsorption rate of C₇H₁₆S over Zn-Ac^-adsorbent can be greatly improved by the introduction of steam to the surface of materials or expanding the layer spacing.As expected,catalytic reactive regeneration reported in Chapter 3 can fully recover the de-mercaptan capacity of spent Zn-Ac^-adsorbent.In the last Chapter,the idea of reactive adsorptive desulfurization of mercaptan using metal hydroxide-based adsorbent was extened to the adsorptive removal of trace H₂S in enclosed space.Nanostructured Cu Co-layer double hydroxide（LDH）hollow polyhedron adsorbent was developed for the trace amount of H₂S elimination.Further study showed that Cu Co4 LDH adsorbent exhibited suporior H₂S removal performance,whose saturated adsorption capacity was up to 187 mg/g-ads..Besides,the selectivity toward H₂S/CO₂ reached to 375781,much higher than most ionic liquids and MOF materials reported in the literature.Charaterization like FTIR,XRD and XPS revealed that the active adsorption sites of Cu Co4 LDH adsorbent mainly comes from the Cu（OH）₂/Cu（OH）host layer.H₂S was dissociated to HS^-and S^2-with the aid of hydroxyl groups from LDH layer,and then was captured by Cu²⁺/Cu⁺sites to form Cu₂S and Cu S.Given these,we conclude that the chemisorption of H₂S by Cu²⁺/Cu⁺leads to the selective removal of H₂S on the developed Cu-based material.It should be mentioned that high humidity is not beneficial to the desulfurization performance of Cu Co4 LDH adsorbent activity.