Refine catalysts

Beside the above-mentioned catalysts used for the production processes of ammonia, hydrogen, urea and other important inorganic chemicals, some other catalysts might be used during some accessorial processes. They are N2 production catalysts, CO selective oxidation catalysts, sulfur recovery catalysts, CO2 dehydrogenation catalysts, molecular sieve desiccants and de-poison catalysts such as desulfurization, dechlorination, and dearsenization, etc. 

N2 can be generated via ammonia combustion. The combustion of ammonia in air over catalyst produces N2 and H2O. The above generated N2 along with the original N2 in air is used as an inert gas, while the generated H2O is removed by cooling. The reactions of combustion and decomposition of ammonia in the primary burning furnace filled with N2 production catalysts are as follows  

A series of side reactions may occur. However, the final products have only N2 and H2O under the designed temperatures and ratios of air to NH3. The ammonia combustion method has high production capacity, low investment, low energy consumption, simple operation and high purity of N2 in comparison with air separation method. 

With the presence of H2, the selective oxidation of CO to CO2 competes with the oxidation reaction of H2 to H2O. Both reactions possess high eqmlibrimn constants, which can reach up to below 200°C. This side reaction caimot be 

The Claus method is based on reaction that H2S is combusted into SO2 with a mole ratio (H2S/SO2) of 2 1 in the presence of limited amount of air. The resulted gas mixture is then transformed into elemental sulfur on AI2O3 catalyst. Meanwhile, the organic sulfur compounds are hydrolyzed on the Claus catalyst. The basic reactions are as follows  

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These compounds can be malodorous as in the case of quinoline, or they can have a plecisant odor as does indole. They decompose on heating to give organic bases or ammonia that reduce the acidity of refining catalysts in conversion units such as reformers or crackers, and initiate gum formation in distillates (kerosene, gas oil). 

A few industrial catalysts have simple compositions, but the typical catalyst is a complex composite made up of several components, illustrated schematically in Figure 9 by a catalyst for ethylene oxidation. Often it consists largely of a porous support or carrier, with the catalyticaHy active components dispersed on the support surface. For example, petroleum refining catalysts used for reforming of naphtha have about 1 wt% Pt and Re on the surface of a transition alumina such as y-Al203 that has a surface area of several hundred square meters per gram. The expensive metal is dispersed as minute particles or clusters so that a large fraction of the atoms are exposed at the surface and accessible to reactants (see Catalysts, supported). 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

Hydrodenitrogenation (HDN) is an important process in petroleum refining. It removes nitrogen from oil distillates, so that less NOx pollutes the air when oil is burned and poisoning of the subsequent refining catalysts is reduced when the oil is processed further. Although HDN has been studied intensively and different reaction mechanisms, catalytic active sites, and functions of the catalytic components have been proposed, there are stiU many questions to be answered in order to better mderstand the reaction and the catalyst (1-4). 

Corma, A., Diaz-Cabanas, M.J., Martinez-Triguero, J., Rey, F., and Rius,. (2002) A large-cavity zeolite with wide pore windows and potential as an oil refining catalyst. Nature, 418, 514-517. 

Nitrogen is a severe refining catalyst poison. Crude oils containing >0.25 wt% nitrogen are difficult to refine. 

The metal content can range from only a few parts per million to >1000 ppm. Trace elements such as iron, sodium, nickel, vanadium, lead, and arsenic can corrode metallic parts and damage heating equipment. Low levels of nickel, vanadium, and copper are known to deactivate refining catalysts. 

A variety of non-hydrocarbon species is found in crude oil. These compounds are found in all molecular weight ranges of crude oil components, but seem to concentrate in the heavier distillate and residual oil fractions. The effect of these materials on processing equipment, refining catalysts, and finished product quality can be dramatic. Corrosion, catalyst poisoning, and fuel stability problems can all be due to the effect of these nonhydrocarbon species. 

The nitrogen-containing porphyrin ring species can be found in most asphaltic crude oils. The porphyrin ring usually holds a metal ion such as nickel or vanadium. These metals are known as powerful poisons for refining catalysts. 

Refining Catalyst Most catalysts used in the refining industry are solid heterogeneous catalysts. The chemical reactions they enhance would not proceed at all, or would do so quite slowly, in the absence of the catalyst. Reactions of this nature are believed to occur due to a dramatic disruption of the existing chemical bonds of an absorbed molecule. Molecules or molecule fragments may enter into reactions much different from those which occur in uncatalyzed reactions. 

Hoffman. H.J.L.. Refining Catalyst Market." Hydrocarbon Prrxessing. 37 iFcbruary [991). 

Food Beverage Sealants Refining Catalysts Silica Products Construction Products... 

The topological approach provides guidelines for optimizing the cluster size achieving maximum selectivity and resistance to coke formation It offers a tool for refined catalyst development, provided the kinetic equations are available. 

A. Corma, M. Diaz-Cabanas, J. Martinez-Triguero, F. Rey, and J. Rius, A Large-cavity Zeolite with Wide Pore Windows and Potential as an Oil Refining Catalyst. Nature (London) 2002, 418, 514-517. 

Elemental analysis of petroleum shows that the major constituents are carbon and hydrogen with smaller amounts of sulfur (0.1-8% w/w), nitrogen (0.1-1.0% w/w), and oxygen (0.1-3% w/w), and trace elements such as vanadium, nickel, iron, and copper present at the part per milHon (ppm) level. Of the non-hydrocarbon (heteroelements) elements, sulfur is the most abundant and often considered the most important by refiners. However, nitrogen and the trace metals also have deleterious effects on refinery catalysts and should not be discounted because of relative abundance. Process units with, for example, a capacity of 50,000 bbl/day that are in operation continuously can soon reflect the presence of the trace elements. The effect of oxygen, which also has an effect on refining catalysts, has received somewhat less study than the other heteroelements but remains equally important in refining. 

Most refining catalysts consist of two active phases a metallic phase and an acid phase, Fig. 10. 

More recent developments include the refined catalyst 123 with extra bulk and an extra chiral centre. This catalyses reactions between functionalised dienes such as 120 and acyclic enones such as 121. The very high yields, ees, and endo exo selectivity of the product 122 compensate for the 20% catalyst loading. It is very difficult to get high ees in Diels-Alder reactions with acyclic ketones and you will see in the next section why this catalyst is successful.27... 

Development or modification of refining catalysts and processes to make them less sensitive to contamination by the nitrogen present 1n raw shale oil. 

The uses of lanthanide compounds are diverse and are expanding due to modern technological advances. In 2000, the principal applications for the rare earths were glass polishing and ceramics, 39% automotive catalytic converters, 22% permanent magnets, 16% petroleum refining catalysts,... 

In 1999, the world market for catalysts (including precious metals) reached 9 G with 24 % for refining, 23 % polymers, 24 % chemicals and 29 % enviromnent. Table 9 gives the refining catalyst market in tons and by application for 1999 and 2005 (2). 

Zeolites are important refining catalysts for two reasons. The first, and most important, is the presence of strong acid sites. Two types of acid sites are present in zeolites. The first are Brpnsted acid sites, shown in Figure 10.6. These are protons that act as charge-compensating cations for framework aluminum. The second are Lewis acid sites, which are less well defined than Brpnsted sites and involve extra-framework aluminum species formed by removing framework aluminum (often due to steam). Both of these are extremely active catalytic centers, which can activate relatively inert substrates such as normal alkanes. 

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