Industrial ammonia synthesis

Obviously, the most effective approach for increasing the synthetic quotient per pass is increasing the catalyst s activity at low temperatures. It is necessary for ammonia synthesis industry to develop the catalysts with higher activities at lower temperatures and pressures. Correspondingly new process and reactors should be developed based on these novel catalysts. ... 

In order to investigate the catalytic activity of Ru catalysts, and compare with iron catalyst, we choose the representative iron catalyst A301 with wiistite as precursor as the reference sample. A301 has the highest activity among all of the iron-based catalysts for ammonia synthesis and now it has been widely used in ammonia synthesis industry. In order to get the reliable and comparable data of the evaluation of catalytic activity, the experiment was conducted under the same conditions and four samples were filled in four reactor contained in one shell. The results were shown in Table 6.41 and Figs. 6.56-6.58. 

Recently, the ammonia synthesis was called as the setting sun industry and someone also lamented the foreground obscuration of the chemistry of nitrogen fixation, in particular, in the research area of organometallic biochemical nitrogen fixation. However, ammonia is a fundamental building block for modern society and is essential for ammonia synthesis industry which drives the innovation and development of ammonia synthesis catalyst forward. 

This is a continuous process. In addition to questions about the elementary steps of the reaction and the importance of the real structure and subnitrides for the catalyst efficiency, as well as the wide-open question about new catalyst materials, there are also new challenges for new applications. The ammonia synthesis industry still requires higher efficient catalyst. 

Table 10.11 lists the raw materials for hydrogen production in ammonia synthesis, joint production process and use of ammonia. As an energy industry, it appears that the ammonia synthesis industry has following characteristics. 

The fused iron catalyst is one of the most successful and most fully studied catalysts in the world. But the discussion on the inbeing of the ammonia synthesis reaction has not ended. There are a lot of questions still needing to be answered on the structure of the catalysts and the formation mechanism of ammonia molecules. Although the relative importance of research on catalytic ammonia synthesis has decreased and now it is not the focus of research on catalysis due to the development of the fields on petrochemistry, biochemistry, macromolecule and environmental catalysis etc, the development of ammonia synthesis industry and the progress of the catalytic technology will never stop. 

At present, the whole world has paid more and more attention to the energy problems and the strict limit of CO2 emission. This makes the ammonia synthesis industry face a great new challenge. 

Fortunately, since 1960s, the author has discerned the development of ammonia synthesis industry in China, and has joined in the research of Fes04-based, Fes04-cobalt-based, Fei xO-based and ruthenium-based catalysts. The author and his co-workers have first invented a novel generation of Fei-xO-based catalysts which is more active than the best magnetite-based catalysts in the world, and have developed successfully a series of new catalysts such as AllO-2, A301 and ZA-5 etc that are widely used in industry. 

This book is of important reference value to researchers, engineers and graduate students who undertake catalysis research and industrial applications. It is believed that the publication of this book will promote the development and industrial applications of ammonia synthesis catalysts and is beneficial for energy saving of the ammonia synthesis industry. 

Promoters. Many industrial catalysts contain promoters, commonly chemical promoters. A chemical promoter is used in a small amount and influences the surface chemistry. Alkali metals are often used as chemical promoters, for example, in ammonia synthesis catalysts, ethylene oxide catalysts, and Fischer-Tropsch catalysts (55). They may be used in as Httie as parts per million quantities. The mechanisms of their action are usually not well understood. In contrast, seldom-used textural promoters, also called stmctural promoters, are used in massive amounts and affect the physical properties of the catalyst. These are used in ammonia synthesis catalysts. 

The industrial catalysts for ammonia synthesis consist of far more than the catalyticaHy active iron (74). There are textural promoters, alumina and calcium oxide, that minimise sintering of the iron and a chemical promoter, potassium (about 1 wt % of the catalyst), and possibly present as K2O the potassium is beheved to be present on the iron surface and to donate electrons to the iron, increasing its activity for the dissociative adsorption of N2. The primary iron particles are about 30 nm in size, and the surface area is about 15 m /g. These catalysts last for years. 

Since theoretical calcination of effectiveness is based on a hardly realistic model of a system of equal-sized cylindrical pores and a shalq assumption for the tortuosity factor, in some industrially important cases the effectiveness has been measured directly. For ammonia synthesis by Dyson and Simon (Ind. Eng. Chem. Fundam., 7, 605 [1968]) and for SO9 oxidation by Kadlec et aJ. Coll. Czech. Chem. Commun., 33, 2388, 2526 [1968]). 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

This book briefly reviews ammonia synthesis, its importance in the chemical process industry, and safety precautions. This case study is integrated into several chapters in the text. See the Introduction for further details. 

The production of ammonia is of historical interest because it represents the first important application of thermodynamics to an industrial process. Considering the synthesis reaction of ammonia from its elements, the calculated reaction heat (AH) and free energy change (AG) at room temperature are approximately -46 and -16.5 KJ/mol, respectively. Although the calculated equilibrium constant = 3.6 X 108 at room temperature is substantially high, no reaction occurs under these conditions, and the rate is practically zero. The ammonia synthesis reaction could be represented as follows ... 

C.G. Yiokari, G.E. Pitselis, D.G. Polydoros, A.D. Katsaounis, and C.G. Vayenas, High pressure electrochemical promotion of ammonia synthesis over an industrial iron catalyst, /. Phys. Chem. 104, 10600-10602 (2000). 

As an indispensable source of fertilizer, the Haber process is one of the most important reactions in industrial chemistry. Nevertheless, even under optimal conditions the yield of the ammonia synthesis in industrial reactors is only about 13%. This Is because the Haber process does not go to completion the net rate of producing ammonia reaches zero when substantial amounts of N2 and H2 are still present. At balance, the concentrations no longer change even though some of each starting material is still present. This balance point represents dynamic chemical equilibrium. 

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