Ammonia manufacture catalysts

A ruthenium-based catalyst is used but low yields resulting from unexpected side reactions are stiU a problem. Refinement of alternative route ammonia manufacture and advances in genetic engineering, allowing a wider range of plant life to fix nitrogen in situ should provide assurance for long term world food needs. 

Research in catalysts for ammonia manufacture is stiU going on, and though the use of supported metals such as mthenium may be two to three times as active as promoted iron oxide, catalysts 50—100 times more active than promoted iron oxide are required to affect process economics significantly. 

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. 

This diagram shows the stages in the Haher-Bosch process for manufacturing ammonia. The catalyst is a mixture of MgO, AI2O3, and Si02, with embedded iron crystals. 

Stoltze P (1995), Structure and surface chemistry of industrial ammonia synthesis catalysts , p. 21, Kinetics of ammonia synthesis and decomposition in Ammonia Catalysis and Manufacture (Ed.) Nielsen A, Springer-Verlag. 

Purification of Feedstock. The feedstock is first desulfurized or purified. This is a very crucial step in ammonia manufacture. It is required in order to maintain the life of the catalyst. 

Catalysts have often been referred to, but few details have been given. For heterogeneous reactions of the above type, catalysts are mostly manufactured as the metal oxide on a ceramic support and reduced in situ to their active state. (The iron oxide ammonia synthesis catalyst is a major exception, in that it has no support but is simply the oxide with some promoters.) The shape of typical catalysts varies from lumps to pellets to granules, and in addition to being firm... 

In 1951, A102 catalyst, the first ammonia synthesis catalyst in China, was developed and manufactured by Nanjing Chemical Industry Corporation. A106 and A109 catalysts were developed in 1956 and 1967, respectively, and were widely used in industry, but their activity were low and running temperatures were high. 

FeO has three chemical characteristics, i.e., oxidative, non-stoichiometry and meta-stability. They must be taken seriously during the manufacture, reduction and application of Fei xO based ammonia synthesis catalyst. As shown in the researches on iron catalyst during the past century, the iron oxides precursor of the catalysts is Fe304 all along, so it has been studied intensively, while that of FeO is not. Hence, here is a detailed introduction to FeO. 

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... 

During the manufacture of the catalyst, small amounts of impurities such as silicon, titanium, sulfur, phosphorus and chlorine can be inevitably introduced into the system. These impurities are catalyst poisons. Hence, the total content of impurities in catalysts should be limited in an allowable range, e.g. the content of sulfur must be less than 0.01%, phosphorus less than 0.04%, and chlorine less than (5 — 10) x 10 in the ammonia synthesis catalyst according to Chinese standard. 

A section of the iron-oxygen phase diagram is shown in Fig. 2.7. The dashed line represents a typical path for the manufacture and activation of an ammonia synthesis catalyst. All effects due to the promoter are omitted. 

Although ammonia synthesis catalyst is normally supplied in the oxidized form, it may also be reduced and stabilized by the manufacturer and supplied as pre-reduced catalyst. The stabilization consists of a controlled partial re-oxidation to allow handling of the catalyst and charging to the converter. Stabilized prereduced catalyst is usually less than 10% oxidized. 

In the early days of ammonia manufacture, the average lifetime of the ammonia synthesis catalyst was limited to a few years, while today, lifetimes in excess of 10 years are common. This dramatic increase arises from a number of improvements. Most noteworthy are the introduction of centrifugal compressors and the application of lubrication oils with low sulfur content as outlined by Nielsen. Another significant improvement is the incorporation of a secondary ammonia condensation system, in which the make-up gas together with the recirculating gas is washed in liquid ammonia before entering the ammonia synthesis converter (see Fig. 8.1). 

Processes available for license are described in Chapter 7, Ammonia Synthesis Commercial Practice. The following catalyst manufacturers are listed as supplying steam reforming and/or ammonia synthesis catalysts ... 

Ammonia manufacture from lower hydrocarbons, carbon monoxide, steam, and nitrogen in the presence of a ruthenium catalyst. (Shokubai Kasei Kogyo). JP 55047219 A (1980). 

Method of manufacture of an ammonia synthesis catalyst containing iron, alumina, potassium, etc., promoters, with two stages of fusion. E. Dworak, A. Golebiowski, and K. Stolecki (Instytut Nawozow Sztucznych). PL 131490 (1985). 

These books in the series will deal with particular techniques used in the study of catalysts and catalysis these will cover the scientific basis of the technique, details of its practical applications, and examples of its usefulness. The volumes concerned with an industrial process or a class of catalysts will provide information on the fundamental science of the topic, the use of the process or catalysts, and engineering aspects. For example, the inaugural volume. Principles of Catalyst Development, looks at the science behind the manufacture of heterogeneous catalysts and provides practical information on their characterization and their industrial uses. Similarly, an upcoming volume on ammonia synthesis will extend from the surface science of single iron crystals to the design of reactors for the special duty of ammonia manufacture. It is hoped that this approach will give a series of books that will be of value to both academic and industrial workers. 

---