Enhancement of Desulfurization Capacity with Cu-Based Macro-Porous Sorbents for Hydrogen Production by Gasification of Petroleum Cokes  
[PERSON]  
1 [PERSON] Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA;  
petroleum coke contains various impurities, including sulfur compounds, chlorides, nitrogen compounds, such as ammonia, and heavy metals. Among these impurities, gaseous sulfur compounds, such as H\({}_{2}\)S and COS are emitted. COS can be converted to hydrogen sulfide in the catalytic hydrolysis process. It is removed selectively using wet amine process and iron chelate process. High purity hydrogen can be produced by processes where purified syngas passes through the water gas shift (WGS) reaction and the pressure swing adsorption (PSA) separation process. A large amount of carbon monoxide in synthesis gas is converted to hydrogen by the water gas shift reaction. The hydrogen and carbon dioxide generated are separated in the PSA process to produce high-purity hydrogen. Importantly, when trace amounts of sulfur compounds are present in the synthesis gas, they deactivate the catalyst (generally CuO/ZnO/Al\({}_{2}\)O\({}_{3}\) catalysts) for the water gas shift reaction due to the sulfidation of active sites. Because of the deactivation issue, a desulfurization process is a critical and essential step to produce hydrogen gas from petroleum coke. Various types of sorbents including activated carbon, metal oxides, zeolite, composite oxides, metal-organic frameworks, etc. have been extensively studied [6; 7; 8]. Different types of absorbent have different strength and weakness. For example, metal oxides have shown high reactivity and high sulfur capacity; however, metal oxides need to be regenerated at high temperature and it triggers aggregations deactivating the absorbents [9; 10; 11; 12]. Compared to the other metal oxides absorbents, Cu-based sorbents have been proposed to have higher desulfurization performance than ZnO, Fe\({}_{2}\)O\({}_{3}\), MnO\({}_{2}\), and CaO at a low temperature (\(<\)400 \({}^{\circ}\)C) owing to their thermodynamic equilibrium [8; 13]. Recently, studies on desulfurization sorbents with high sulfur capacity for the removal of low concentration sulfur compounds using mesoporous materials and MOFs as supports as Cu-based desulfurization sorbents have been reported. Absorbents with a high surface area are required to remove low concentrations of sulfur compounds effectively. Hence, mesoporous materials with high surface areas have been evaluated as support materials [12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. Although Cu-based sorbents with a support improve the surface area and show good desulfurization performance, they generally have high gas diffusion resistance reducing the desulfurization capacity. Gas-phase molecules containing sulfur adsorb on the outer surface, but unreacted active sites can remain inside the absorbent due to the high gas diffusion resistance. This study developed a macro-porous alumina support to enhance gas diffusion to resolve the above mentioned issue of gas diffusion resistance. CuO absorbents were supported on commercial \(\gamma\) alumina and macro-porous alumina prepared by an impregnation method. In particular, macro-porous alumina has been synthesized with nano-sized colloidal particles (template) by the suspension polymerization of a polymer, such as poly-methyl-meta-acrylate (PMMA) and polystyrene (PS). The colloidal particles used as a template are mixed with an alumina precursor solution. The moisture is then removed by vacuum evaporation. The particles can be prepared on the macro-porous alumina by oxidatively decomposing the polymer by heat treatment. In previous studies, macro-porous materials were synthesized using polymer beads as templates for catalyst materials, such as silica, titania, and alumina [22; 23; 24; 25]. With these \(\gamma\)-alumina and macro-porous alumina supports, pellet and powder types of Cu-based absorbents were prepared.