Sulfur breakthrough

The scheme of the methanation demonstration units is presented in Figure 2. Synthesis gas is heated in heater El and is then mixed with recycle gas. Zinc oxide reactor D1 serves as an emergency catchpot for sulfur breakthrough from the purification plant. The total feed is heated... 

These tests demonstrated that the Lurgi Rectisol process provides an extremely pure synthesis gas which can be charged directly to the metha-nation plant without problems of sulfur poisoning of the nickel catalyst. However, in order to cope with a sudden sulfur breakthrough from Rectisol as a result of maloperation, a commercial methanation plant should be operated with a ZnO emergency catchpot on line. 

Sulfur Breakthrough , U. S. Department of Transportation, Federal Highway Administration, February, 1980. 

Prior to H2S introduction to the reactor, the bypass was filled with H2S by flowing fresh H2S through the U-lube for a half hour. Then a pulse of M2 was carried to the reactor by switching and flowing the feed gas thtough bypass for a half hour. During the H2S pulses, H2S concentration in the effluent stream was monitored and no sulfur breakthrough was detected except fcM 0.5-1 ppm H2S within the first five minutes. This was probably due to sulfur adsorption on the metal surfaces in the system for this reason sulfur content in the used catalysts was analyzed. 

The authors [141] proposed a multistep desulfurization process with two adsorption beds so that the species not adsorbed in the first bed could be trapped in the second one. The first bed is based on molecular sieves the second one contains activated carbons that are able to remove aU the S-compounds present in the biogas. Tests that have been performed on the SOFC power generation system at the Turbocare site in Turin [171]. A two component arrangement of 130 kg zeolite-X followed by 90 kg activated carbon provided an acceptable solution for large-scale SOFC unit. After 4 months of operation no sulfur breakthrough was observed. 

D. R. McAlister and co-woikets,F Mcp or Breakthrough in Sulfuric Fcid, AIChE National Meeting, New Odeans, La., Apr. 1986. 

Since cbiral sulfur ylides racemize rapidly, they are generally prepared in situ from chiral sulfides and halides. The first example of asymmetric epoxidation was reported in 1989, using camphor-derived chiral sulfonium ylides with moderate yields and ee (< 41%) Since then, much effort has been made in tbe asymmetric epoxidation using sucb a strategy without a significant breakthrough. In one example, the reaction between benzaldehyde and benzyl bromide in the presence of one equivalent of camphor-derived sulfide 47 furnished epoxide 48 in high diastereoselectivity (trans cis = 96 4) with moderate enantioselectivity in the case of the trans isomer (56% ee). ... 

The space velocity was varied from 2539 to 9130 scf/hr ft3 catalyst. Carbon monoxide and ethane were at equilibrium conversion at all space velocities however, some carbon dioxide breakthrough was noticed at the higher space velocities. A bed of activated carbon and zinc oxide at 149 °C reduced the sulfur content of the feed gas from about 2 ppm to less than 0.1 ppm in order to avoid catalyst deactivation by sulfur poisoning. Subsequent tests have indicated that the catalyst is equally effective for feed gases containing up to 1 mole % benzene and 0.5 ppm sulfur (5). These are the maximum concentrations of impurities that can be present in methanation section feed gases. 

Adequate control of the chemistry in the front end furnace can significantly effect the lifetime and efficiency of the downstream catalyst beds in a sulfur plant. Inadequate removal of Ce+ hydrocarbons from the acid gas feed can result in catalyst fouling by polymeric materials formed under furnace conditions. Toluenes, ethylbenzenes and xylenes have been shown to be particularly troublesome in this regard. Oxygen breakthrough into the catalyst beds can also shorten the effective lifetime of the Alumina catalyst by sulfation i.e. 

The breakthrough came in 1839 while Goodyear was exhibiting his most recent samples at a general store in Woburn, Massachusetts. When he accidentally dropped a piece on a hot stove, it burned, but the uncharred part was transformed into a smooth, firm material that was not affected by high or low temperature. The additive in the sample was sulfur, but it took Goodyear several months to determine the right combination of heat, pressure, and sulfur to produce a stable compound. He found that the best material was produced when the compound was steam-heated under pressure at 120°C (248°F) for four to six hours. Its first commercial use was as elastic thread in men s shirts. 

The application of the model of Wise et al. (195, 233) to determining deactivation rate constants encounters rather serious experimental limitations in that at low poison concentrations and space velocities, the breakthrough curves are very slow to appear, and the accurate measurement of sulfur concentrations in the ppm or ppb range is difficult. If activity decline of the catalyst for the reaction of interest could be related to the loss of sites by poisoning, a more direct measurement of deactivation rate would be realized. Bartholomew and co-workers (113, 140, 161) extended this model by expressing the rate of deactivation in terms of normalized activity a ... 

Deactivation parameters obtained by plotting ln[(l — a) a)] versus time are listed in Table XIX for a number of nickel and nickel bimetallic catalysts. The fact that these plots were generally linear confirms that these data are fitted well by this deactivation model. These data, which include initial site densities for sulfur adsorption, deactivation rate constants, and breakthrough times for poisoning by 1-ppm H2S at a space velocity of 3000 hr-1 provide meaningful comparisons of sulfur resistance and catalyst life for both unsupported and supported catalysts. Table XIX shows that the... 

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