Ammonia production catalysts used

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

Presently, the Fe-based ammonia synthesis catalysts used in industry are produced by traditional molten method, and are also known as fused iron catalysts. The advantages of molten method include simple processes, easy operation, low cost and excellent performance of product. Even though there are some differences in the chemical composition and catalytic performance of various types of fused iron catalysts, their manufacture process is mainly the same as follow. 12... 

Oxidation of sulfur dioxide in aqueous solution, as in clouds, can be catalyzed synergistically by iron and manganese (225). Ammonia can be used to scmb sulfur dioxide from gas streams in the presence of air. The product is largely ammonium sulfate formed by oxidation in the absence of any catalyst (226). The oxidation of SO2 catalyzed by nitrogen oxides was important in the eady processes for manufacture of sulfuric acid (qv). Sulfur dioxide reacts with chlorine or bromine forming sulfuryl chloride or bromide [507-16 ]. 

The catalyst temperature is about 1100°C. Precious metal catalysts (90% Pt/10% Rh in gauze form) are normally used in the commercial processes. The converters are similar to the ammonia oxidation converters used in the production of nitric acid (qv) although the latter operate at somewhat lower temperatures. The feed gases to the converter are thoroughly premixed. The optimum operating mixture of feed gas is above the upper flammabiUty limit and caution must be exercised to keep the mixture from entering the explosive range. 

Ethylamines. Mono-, di-, and triethylamines, produced by catalytic reaction of ethanol with ammonia (330), are a significant outlet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, siUca, or sihca—alumina. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethylamine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give W-ethylpiperidine [766-09-6] (332). 

Fischer Tropsch technology is best exemplified by the SASOL projects in South Africa. After coal is gasified to a synthesis gas mixture, it is purified in a rectisol unit. The purified gas mixture is reacted in a synthol unit over an iron-based catalyst. The main products are gasoline, diesel fuel, and jet fuels. By-products are ethylene, propylene, alpha olefins, sulfur, phenol, and ammonia which are used for the production of downstream chemicals. 

Nitric Add by the Oxidation of Ammonia. Here, the catalytic oxidation of ammonia under press using a Pt catalyst maintained at a temp of 900—1000° is the process used. The reaction press is the rate determining step, being directly proportional to the product nitric acid concn (Refs 6, 22, 26, 30, 34, 36, 37 41). 

Alicyclic amines are used as pesticides, plasticizers, explosives, inhibitors of metal corrosion and sweetening agents as well as having uses in the pharmaceuticals industry. Aniline hydrogenation has been studied in the literature with the main reaction products cyclohexylamine, dicyclohexylamine, A-phenylcyclohexylamine, diphenylamine, ammonia, benzene, cyclohexane, cyclohexanol and cyclohexanone [1-9], The products formed depend on the catalyst used, reaction temperature, solvent and whether the reaction is performed in gas or liquid phase. For example high temperature, gas-phase aniline hydrogenation over Rh/Al203 produced cyclohexylamine and dicyclohexylamine as the main products [1],... 

For more expensive enzymes the continuous use of enzymes made possible by their iimnobihsation can result in considerable savings. By comparison typical chemical catalysts represent a smaller proportion of the total manufacturing costs. Thus the catalysts used in ammonia, cyclohexane and styrene manufacture have been estimated to cost approximately only 0.7, 0.6 and 0.6% of the total production costs respectively. Thus biocatalysts are still in general comparatively expensive compared with chemical catalysts. 

It is well known that sugars react with aqueous ammonia to produce heterocyclic compounds in low yield. The products of the reaction of the mono- and di-saccharides with concentrated, aqueous solutions of ammonia are dependent on three factors (I) the length of time during which the reaction proceeds, (2) the temperature of the reaction, and (3) the catalyst used. This matter has been briefly but comprehensively reviewed.1 The present article is more detailed it covers the literature to the end of July 1970, and has been prepared for the use of chemists who may not be specialists in the carbohydrate field, as well as of those who are. 

The above are equilibrium reactions, and their successful exploitation requires that they be carried out under conditions in which the equilibrium favors the product. Specifically, this requires that the adsorbed species in Reactions (D)-(I) not be held so tightly on the catalyst surfaces as to inhibit the reaction. On the other hand, strong interaction between adsorbate and catalyst is important to break the bonds in the reactant species. Optimization involves finding a compromise between scission and residence time on the surface. Although we are especially interested in metal surfaces, those constituents known as promoters in catalyst mixtures are also important. It is known, for example, that the potassium in the catalyst used for the ammonia synthesis shifts Equilibrium (F) to the right and also increases the rate of Reaction (D) by lowering its activation energy from 12.5 kJ mole to about zero. 

Lower aliphatic amines are widely used as intermediates for the synthesis of herbicides, insecticides and drugs or can be applied as rubber accelerators, corrosion inhibitors, surface active agents etc. [l]. The most widespread method for the preparation of lower aliphatic amines involves the reaction of ammonia with an alcohol or a carbonyl compound in the presence of hydrogen. The most common catalysts used for reductive amination of alcohols, aldehydes and ketones contain nickel, platinum, palladium or copper as active component [ I — 3 ]. One of the most important issues in the reductive amination is the selectivity control as the product distribution, i.e. the ratio of primary to secondary or tertiary amines, is strongly affected by thermodynamics. 

Methanators are usually used in the ammonia production line to guard the catalyst of the ammonia converters from the ill effect of carbon monoxide and carbon dioxide. This section includes precise models for different types of methanators using the dusty gas model with reliable kinetic expression and the results are compared with those of the simplified models (A) and (B). 

As catalysis proceeds at the surface, a catalyst should preferably consist of small particles with a high fraction of surface atoms. This is often achieved by dispersing particles on porous supports such as silica, alumina, titania or carbon (see Fig. 1.2). Unsupported catalysts are also in use examples of these include the iron catalysts for ammonia synthesis and CO hydrogenation (the Fischer-Tropsch synthesis), or the mixed metal oxide catalysts used in the production of acrylonitrile from propylene and ammonia. 

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