Sour shift

S. S. Hla, G. J. Duffy, L. D. Morpeth, A. Cousins, D. G. Roberts, J. H. Edwards, Investigation into the performance of a Co-Mo based sour shift catalyst using simulated coal-derived syngases, Int. J. Hydrogen Energy 36 (2011) 6638 645. 

It may be advantageous to carry out the WGS reaction on the raw S5mgas from gasification of coal and heavy hydrocarbons by a so-called sour shift catalyst. This allows removal of CO2 and H2S in the same wash system (see Section 1.5.3). It requires a catalyst that is sulphur-tolerant and capable of working at low H2O/C ratios. The conventional iron-based HTS catalyst can operate in the presence of sulphur, but it requires addition of significant amounts of steam to eliminate the problem of the carbide formation reaction. This problem is solved by using a molybdenum sulphide-based catalyst [168] [232]. The catalyst is promoted and is based on alumina support. It requires the presence of... 

However, it has been demonstrated on sulphide catalysts [236] [467], which are related to sour shift catalysts (refer to Section 1.5.2). 

Sterigmatocystin carbon Soured Shift, c/p.p.m. Reference compound Carbon Shift, 5Jp.p.m. 

Another commercial trail of MIP-CGP for processing intermediate-based sour residual feed has been put on stream in SINOPEC Cangzhon Company in 2005. Table 5.6 shows the commercial comparison of CGP-2 and CGP-1. After shifting to CGP-2 the propylene yield increased by 1.15%, and the light ends yield increased by 0.57%. The snlfnr content of gasoline was decreased from 840 to 580 J,g/g. The olehn content, RON and MON of gasoline remained essentially constant. 

The shift from carbon monoxide to carbon dioxide generally occurs in two steps - first a High Temperature Shift Conversion and then a Low Temperature shift conversion. In some cases the two steps may be combined in one isothermal or adiabatic step called Medium Temperature Shift Conversion. When the feed gas to the CO conversion is not desulfurized, the CO conversion is called Sour Gas Shift and a special type of sulfur-resistant catalyst is used166. 

Obviously, the end-of-pipe measures can fix tbe problem temporarily, but not remove tbe cause. Sometimes tbe problem is shifted or masked into another one. For this reason, an end-of-pipe solution should be examined from a plantwide viewpoint and beyond. For example, sour-gas scrubbing by chemical absorption may cut air pollution locally, but involves tbe pollution created by the manufacture of chemicals elsewhere. In this case, physical processes or using green (recyclable) solvents are more suitable. The best way is tbe reduction of acid components by changing the chemistry, such as for example using a more selective catalyst. 

FeS also catalyzes the shift reaction, but its activity is only half that of Fe,04 [592]-[594], In principle the catalyst can tolerate up to 500 or 1000 ppm H2S, but with a considerable loss of mechanical strength, which is additionally affected by other contaminants in the gas, such as soot and traces of formic acid. For this reason the so-called dirty shift catalyst is used in this case, which was originally introduced by BASF [639]. This cobalt-molybdenum-alumina catalyst [603], [630], [640]-[644] is present under reaction conditions in sulfidized form and requires for its performance a sulfur content in the gas in excess of 1 g S/m3. Reaction temperatures are between 230 and 500 °C. COS is not hydrolyzed on dirty shift catalysts, but may be removed in the subsequent sour-gas removal stage using the Rectisol process. Separate hydrolysis on alumina based catalysts is possible at temperatures below 200 °C [603],... 

Rebalancing of new and existing refinery process capacity to regard shale oil as a primary feed rather than a contaminant - analogous to shifting from a sweet crude refinery to a sour crude refinery - with a corresponding shift of product slate (consistent with overall market demand) to best exploit the different optimum product mixes from shale oil and petroleum. 

A consumer usually knows what to expect in the flavor of a food and downgrades it when the flavor is unbalanced or in some manner is not representative. If, for example, the characteristics of rawness, such as earthy, starchy, bitter, and sour, are of relatively high intensity in a cooked vegetable, the vegetable will have more negative than positive flavor features. A most important means of shifting emphasis to the positive side is to add salt, along with such flavorful materials as butter and pepper and, as these present studies indicated, possibly a sweet substance. 

The commercial Co-Mo catalysts operate in the temperature range 250-350 °C and at pressures from atm to 40 bar. The typical process conditions for a Texaco partial oxidation process that generate syngas from heavy oil which use sour Co-Mo WGS catalyst are shown in Table 4.3. Three Co-Mo catalysts beds are used. The syngas from partial oxidation reactor contains 0.25% of H2S. The inlet CO concentration of 46% is reduced to 1% at the exit of third bed. However, the Co-Mo catalyst converts H2S and CO into COS. Hence, COS hydrolysis has to be performed after the water-gas shift reaction. However, if we... 

B. Liu, Q. Zong, P. P. Edwards, F. Zou, X. Du, Z. Jiang, T. Xiao, H. AlMegren, Effect of titania addition on the performance of C0M0/AI2O3 sour water gas shift catalysts under lean steam to gas ratio conditions, Ind. Eng. Chem. Res. 51 (2012) 11674-11680. 

A distinction is normally made between clean gas conversion where the CO shift conversion unit is preceded by a gas purification stage to remove the major part of the sulfur components and any higher hydrocarbons that may be present in the gas, and sour gas conversion which accepts the untreated coal gas as a feed. A special type of the latter is what has been termed raw gas conversion, where considerable quantities of high boiling hydrocarbons are not eliminated from the raw gas but are left to pass the CO shift conversion stage. 

The process diagram shown here is used for such gas condensates whose sour gas content is as least as high as their ammonia content. The NH3/CO2/H2O system exhibits different boiling properties at different pressures. The so-called maximum temperature azeotrope lines, which are defined so that the CO2/NH3 ratios are the same in both phases when the liquid and gas phases are in equilibrium, are shifted in the direction of higher ammonia mixes as pressures are increased. 

The above concentration limits refer to cold sour gases and cold combustion air. If the gases are preheated, the limits will be shifted downward. The limit for using the Claus process is an H2S concentration around 5 %. Leaner gases can be treated only if the reaction is supported by burning additional sulfur. Nor can gases be treated in Claus units if they contain major proportions of hydrocarbons or ammonia. Such gases can only be incinerated and the SO2 then absorbed or reduced by suitable processes (Sect. 5.3.2). 

Modern WGS catalysts can be divided into four classes, namely, HTS, LTS, sour gas shift, and precious-metal-containing catalysts. Iron oxide or iron-chromium mixed oxides promote the WGS in the 350-450 °C range and are modified by MgO or ZnO for good sulfur resistance and mechanical strength. The second type of WGS catalysts are mixed copper-zinc oxides which promote WGS in... 

Chemical Stability Since all inhibitors contain functional groups (carboxylic acids, amines, Schiffs bases, phosphates, phosphonates, sulfur derivatives, and many more), they are pH sensitive, and therefore, their activity varies over actually fairly narrow pH ranges. For example, it has been shown that certain amines in sour systems lose activity if the pH of the environment shifts from 4 to 7 [S], while in CO2 systems the reverse has been observed [9]. 

Depending on the operating conditions, three different types of WGS processes are applied [232] [303] [391]. High-temperature shift (300— 500°C) over a robust catalyst is used for primary conversion. Medium temperature shift (200—330 C) is used for special purposes. Low-temperature shift (185—250 C) is used to achieve maximum conversion. Sour gas shift (350 C) is used to operate under high sulphur eonditions and low H2/CO (raw coal gas, etc)... 

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