The reaction rate in stoichiometric mixtures of nitrogen and hydrogen or deuterium has been measured on two different doubly promoted iron catalysts, between 218 and 302 °C, ⅓ and 1 atm and over a 300-fold range of efficiencies. The kinetic data as well as the isotope effect indicate that the rate-determining step is the chemisorption of nitrogen on a surface mainly covered with NH radicals. The presence on the surface of NH radicals instead of nitrogen atoms opens new perspectives on the kinetics and mechanism of ammonia synthesis.

Kinetics and mechanism of the ammonia synthesis

The article contains sections titled: 

1.	Introduction	
2.	Historical Development	
3.	Thermodynamic Data	
4.	Ammonia Synthesis Reaction	
4.1.	General Aspects	
4.2.	Catalyst Surface and Reaction Mechanism	
4.3.	Kinetics	
5.	Catalysts	
5.1.	Classical Iron Catalysts	
5.1.1.	Composition	
5.1.2.	Particle Size and Shape	
5.1.3.	Catalyst-Precursor Manufacture	
5.1.4.	Catalyst Reduction	
5.1.5.	Catalyst Poisons	
5.2.	Other Catalysts	
5.2.1.	General Aspects	
5.2.2.	Metals with Catalytic Potential	
5.2.3.	Commercial Ruthenium Catalysts	
6.	Process Steps of Ammonia Production	
6.1.	Synthesis Gas Production	
6.1.1.	Feedstock Pretreatment and Raw Gas Production	
6.1.2.	Carbon Monoxide Shift Conversion	
6.1.3.	Gas Purification	
6.2.	Compression	
6.3.	Ammonia Synthesis	
6.3.1.	Synthesis Loop Configurations	
6.3.2.	Formation of Ammonia in the Converter	
6.3.3.	Waste-Heat Utilization and Cooling	
6.3.4.	Ammonia Recovery from the Ammonia Synthesis Loop	
6.3.5.	Inert-Gas and Purge-Gas Management	
6.3.6.	Influence of Pressure and Other Variables of the Synthesis Loop	
6.3.7.	Example of an Industrial Synthesis Loop

Ammonia, 2. Production Processes

In diesem Beitrag wird versucht, die katalytische Aktivitat von Ammoniakkatalysatoren verschiedener Zusammensetzung in Zusammenhang zu bringen mit ihrer inneren Oberflache, ihrem Porengefuge und ihrer Fahigkeit, Kohlenmonoxyd und Kohlendioxyd zu chemisorbieren. Die Wirkungsweise der Aktivatoren Al2O3, CaO, K2O und SiO2 wir diskutiert.

Zur Funktion der Aktivatoren im technischen Ammoniak‐Katalysator

Effect of pH on the aqueous phase ozonation of various organic compounds was investigated. The reaction was accelerated in alkaline media due to the formation of active hydroxyl radical by an interaction of ozone with hydroxide ion. However, in a strongly alkaline media (pH < 11.9), hydroxyl radical dissociated into less reactive oxygen ion and the efficiency of ozonation decreased. By means of the theory of gas absorption accompanied by chemical reaction, it was found that the rate of the decomposition of ozone in the presence of about 300 ppm of 1-butanol was 5-80 times larger than that catalyzed only by hydroxide ion in the pH range of 11-13. Efficiency of ozonation showed that an optimum range of pH for the removal of total organic carbon was 9-10.



On a etudie l'effet du pH sur l'ozonisation, en phase aqueuse, de divers composes organiques. Il se produit une acceleration de la reaction dans les milieux alcalins, par suite de la formation d'un radical hydroxyle actif qui resulte de l'interaction de l'ozone avec l'ion hydroxyde. Toutefois, dans les milieux fortement alcalins (pH < 11.9), le radical hydroxyle est dissocie en un ion oxygene moins reactif et l'efficacite de l'ozonisation decroi't. On a constate, au moyen de la theorie de l'adsorption des gaz avec reaction chimique, que la decomposition de l'ozone, en presence d'environ 300 ppm de 1-butanol, etait 5 a 80 fois plus elevee que dans le cas de la decomposition catalysee par l'ion hydroxyde seul pour des pH compris entre 11 et 13. Les resultats sur l'efficacite de l'ozonisation montrent que la gamme optimale de pH pour eliminer tout le carbone organique varie entre 9 et 10.

Ozonation of organic compounds in alkaline aqueous media

The effect of intraparticle temperature distribution on the catalytic effectiveness factor is derived, and its magnitude is estimated using an approximate solution. These calculations show that for the several cases examined the term containing the effect of temperature is less than 10% of that due to the concentration effect.

The effect of intraparticle temperature distribution on the catalytic effectiveness factor of a porous catalyst

As one of the rate expressions of high pressure ammonia synthesis in which industrial iron catalyst is employed, Temkin's Eqs. (1) and (2) are well known, but neither of them satisfy the data published by other investigators. This has been pointed out by Emmett, Uchida, Comings and others.The authors propose here some rate expressions, Eqs. (10) and (11) which they have obtained after examining all the data available. Eq. (10) is correspondent to the case where the rate-determining step is the dissociated adsorption of nitrogen molecule and the active site of catalyst is partly covered with atomic nitrogen, viz., in the Langmuir type adsorption.Eq. (10) is for the data of doubly or triply promoted catalyst (Cf. Fig. 1), while Eqs. (14) and (15) are for the singly promoted (by Al2O3) catalyst. Eq. (10) is found to be of great practical use, because the constant Ka remains constant, regardless of the variety of temperature and the kinds of catalysts employed.

The Rate Expression of High Pressure Ammonia Synthesis in Which Industrial Iron Catalyst is Employed.

For the fixed-bed reactors such as adiabatic multistage reactors, autothermic reactors and externally cooled reactors, the authors studied on the process optimum condition. which means the condition where the necessary amount of catalyst in VR/F is minimized when the conversion is specified.Considering the reaction whose rate at a given composition of the reaction mixture have maximum at a temperature, as in the ammonia synthesis and the catalytic oxidation in sulphur dioxide, the authors extended Konoki's treatment for the adiabatic multistage reactor3, 4) in whose operation maximum temperature is fixed, into the more general form, Eq. (18) through Eq. (21). These results were sucessfully applied to the sulphur dioxide convertor of adiabatic 3-stage.For the autothermic process with two flow paths (Fig. 5), the authors using the simpler design equation (30) instead of Eq.(24), proposed a graphical method of solution based on Picard's method.10) By this method we can easily determine optimum Γ and T10 As an example the authors showed the result of trial and error for the determination of T and T10 for the autothermic ammonia synthesis process. The basic equations (32) for the externally cooled reactor can be also reduced to the simpler form, Eq. (35), and so the same method above described will be employed.

Process Optimum Condition for Gas-Solid Catalytic Reaction Process in Fixed-Bed

It is well known that, in the high temperature region, the diffusional resistances within the boundary film and that within the pores of catalyst pellet have an important effect on the overall effective reaction rate. In reactor design, it is essential to analyze the experimental data and to distinguish the effect of diffusion from the chemical reaction rate so as to predict the over-all effective reaction rate for the given industrial conditions.Previously, Kubota and Shindo5) presented a method for calculating effectiveness factor of the porous catalyst, which is applicable to any reaction but which involves considerable complicated computations.In this paper, the authors present a new method for calculating effectiveness factor, based on the approximation of reaction rate to a kind of first-order reaction as expressed by Eq. (6) or (7). When this method was applied to ammonia synthesis, whose rate was expressed by Eq. (13) and which was far from the first-order reaction, the value of Ef' obtained was found to be a very good approximation to the value of Ef obtained by the previous method (Fig. 2).Other proposals the authors make in this paper are (i) a general analytical procedure for predicting the effective reaction rate by taking into account the diffusional resistances within the boundary film and that within pores of catalyst pellet, and (ii) two other methods for estimating the chemical reaction rate from the experimental data, by taking into account the above-mentioned diffusional resistances. Of these two methods, the first one is applicable when veA (pAG) can be obtained from the reaction, viz. when the reaction is carried on in a differential reactor, and the second one is applicable when veA (pAG) cannot be obtained directly from the experiment, viz., when the reaction is carried on in an integral reactor. When the latter was applied to the ammonia synthesis data, obtained by one of the authors4), great difference was found in the range of above 475°C or so, between the apparent values of reaction rate constant and their corrected values given according to this procedure.

On the Over-all Effective Reaction Rate of Gas-Solid Catalytic Reaction Process

Expression of Deactivation caused on Catalyst Fouling

The method of Calculating effectiveness factor of the porous catalyst, which factor depends upon the diffusibility of reactants or products insid catalyst as well as on the pure chemical reaction, had formerly been developed to the first order reaction or to a few other cases. Whereupon the authors have tried and succeeded in extending its application to the cases in general in which chemical reaction rates are given and equations are presented as a function of constitution. As an example, the calculation method for ammonia synthesis is illustrated.

https://www.jstage.jst.go.jp/article/kakoronbunshu1953/20/1/20_1_11/_pdf

Masuo Shindo

Papers

The Rate Expression of High Pressure Ammonia Synthesis in Which Industrial Iron Catalyst is Employed.

Process Optimum Condition for Gas-Solid Catalytic Reaction Process in Fixed-Bed

On the Over-all Effective Reaction Rate of Gas-Solid Catalytic Reaction Process

Expression of Deactivation caused on Catalyst Fouling

On the Method of Calculating Effectiveness Factor of the Porous Catalyst in Any Reaction