Sulfur removal temperature effects

It is well established that sulfur compounds even in low parts per million concentrations in fuel gas are detrimental to MCFCs. The principal sulfur compound that has an adverse effect on cell performance is H2S. A nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Chemisorption on Ni surfaces occurs, which can block active electrochemical sites. The tolerance of MCFCs to sulfur compounds is strongly dependent on temperature, pressure, gas composition, cell components, and system operation (i.e., recycle, venting, and gas cleanup). Nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Moreover, oxidation of H2S in a combustion reaction, when recycling system is used, causes subsequent reaction with carbonate ions in the electrolyte [1]. Some researchers have tried to overcome this problem with additional device such as sulfur removal reactor. If the anode itself has a high tolerance to sulfur, the additional device is not required, hence, cutting the capital cost for MCFC plant. To enhance the anode performance on sulfur tolerance, ceria coating on anode is proposed. The main reason is that ceria can react with H2S [2,3] to protect Ni anode. 

A process innovation was introduced by Valentine [61], who added an SOx sorbent for mitigating the inhibiting effects of the formed oxysulfides. This process was developed for sulfur removal from extra heavy oils, bitumens, and its emulsions, such as the trade mark Orimulsion. Any active biocatalyst may be used in this process carried out at temperatures close to 50°C. The main features disclosed in patents protecting the use of R. rhodochrous-bas d biocatalysts, in desulfurization reactions are summarized in Table 12. 

The objective of the present work is to evaluate the effect of a wide range of process or reaction variables— reaction temperature, hydrogen partial pressure, catalyst loading, and reaction time—on hydrodesulfurization and hydrogenation of filtered liquid product (coal-derived liquid) obtained from the coal dissolution stage in the presence of a commercial presulfided Co-Mo-Al catalyst. The selectivity for desulfurization over hydrogenation (Se) is used to rate the effectiveness of the above mentioned process variables. Se is defined as the fraction of sulfur removal per unit (g) of hydrogen consumed, that is,... 

Typical dryer exhaust emissions are sulfur compounds such as hydrogen sulfide, carbon disulfide, carbonyl sulfide, and methyl and n-propyl mercaptans. In addition to ammonia, the only amine present is trimethyl amine. Since the emissions from the dryers contain considerable moisture at temperature of about 95°C, necessary means should be provided to remove most of this moisture and to cool the air before further odor treatment. Also, there may be dust particles in the cyclone exhanst that shonld be removed before effective odor measnres can be applied. This is normally... 

Based on the work of Attar (60), who has reported the distribution of sulfur functional groups in the Lower Freeport coal, Joshi and Shah (61) have Investigated the overall kinetics of organic sulfur removal for the Lower Freeport coal in the temperature range of 130-190 0, oxygen partial pressure of 0.32-1,36 MPa and batch times up to 3600 seconds. The effect of pH of the medium on organic sulfur removal was also studied. 

Figure 2 shows some experimental results about the effect of both reaction temperatures and LHSV on SRGO hydrodesulfurization using upflow and downflow systems. It can be clearly seen the differences in sulfur removal between these two systems, specially at low temperature and high space velocity. 

Li and King [32] also reported on COS formation above ZnO. Experiments were performed on a dry base at concentrations of 25 ppmv H2S, at temperatures of 150-250°C and at high space velocities of 75 000h h The sum of CO and CO2 always amounted to 21%, whereas CO was varied between 0 and 12%. Their experiments showed that CO has a negative effect on the sulfur removal capacity, which was attributed to COS formation over ZnS. COS measurements were not performed. Equihbrium calculations for a mixture of 3% CO, 13% CO2, 32% H2, and 23% steam (balanced He as inert gas) led to a concentration of 234 ppmv COS via formation from CO and 7 ppmv COS via formation from CO2. A coupling effect by the WGS reaction was neglected as ZnO does not catalyze this reaction. 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

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