High-Pressure Catalytic Synthesis

The reaction proceeded in an iron tube under a pressure of 20.3 MPa inside a nickel heating coil was used to raise the temperature of gases to a desired level, and there was a thick-walled tube of transparent quartz—which was drawn on one side into a fine capillary—that continued to a point outside of the furnace, as the converter was called at that time (fig. 4.6). The catalyst was placed just in front of the tube s narrowed outlet so the gases, once they passed over the catalyst, would leave the oven rapidly. Their immediate cooling allowed the maintenance of the equilibrium according to the catalyst s temperature, which was measured with a thermoelement. 

A new apparatus also needed an improved circulation system so that the synthesized ammonia could be separated from the flowing gas at a constant high pressure. 

Haber s experimental laboratory apparatus for ammonia synthesis (1909). 

This setup was outlined in Haber s first patent concerning ammonia synthesis— No. 235421, valid since October 13,1908, and issued on June 8,1911, later widely described as the circulation patent—and its principle is still used in every ammonia plant today. A twelve-line patent claim summed up the invention  

Process for synthetic production of ammonia from its elements, whereby an appropriate mixture of nitrogen and hydrogen is continuously subjected to both the production of ammonia under the influence of heated catalysts, and continuous removal of the resulting ammonia, characterized by constant pressure and the transfer of process heat from the ammonia-containing reaction gases to the incoming ammonia-free gas mixture.  

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Derivation (1) By high-pressure catalytic synthesis from carbon monoxide and hydrogen (2) partial oxidation of natural gas hydrocarbons (3) several processes for making methanol by gasification of wood, peat, and lignite have been developed but have not yet proved out commercially (4) from methane with molybdenum catalyst (experimental). 

The synthesis which forms the basis of production at Hoffmaim-La Roche (Fig. 5) proceeds via the pyrimidinenitrile [698-29-3] (26) made from malononittile, trimethylorthoformate, ammonia, and acetonitrile (42,43). High pressure catalytic reduction of the nitrile furnishes diamine (16). The overall sequence is short, highly efficient, and generates almost no waste. However, malononittile is a relatively expensive and ha2ardous three-carbon source. 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

In this representation the FeCl2 which takes part in the first step of the reaction is not a tme catalyst, but is continuously formed from HQ. and iron. This is a highly exothermic process with a heat of reaction of 546 kj /mol (130 kcal/mol) for the combined charging and reaction steps (50). Despite the complexity of the Bnchamp process, yields of 90—98% are often obtained. One of the major advantages of the Bnchamp process over catalytic hydrogenation is that it can be mn at atmospheric pressure. This eliminates the need for expensive high pressure equipment and makes it practical for use in small batch operations. The Bnchamp process can also be used in the laboratory for the synthesis of amines when catalytic hydrogenation caimot be used (51). 

F. Haber s catalytic synthesis of NH3 developed in collaboration with C. Bosch into a large-scale industrial process by 1913. (Hater was awarded the 1918 Nobel Prize in Chemistry for the synthesis of ammonia from its elements Bosch shared the 1931 Nobel Prize for contributions to the invention and development of chemical high-pressure methods , the Hater synthesis of NH3 being the first high-pressure industrial process.)... 

The scheme of commercial methane synthesis includes a multistage reaction system and recycle of product gas. Adiabatic reactors connected with waste heat boilers are used to remove the heat in the form of high pressure steam. In designing the pilot plants, major emphasis was placed on the design of the catalytic reactor system. Thermodynamic parameters (composition of feed gas, temperature, temperature rise, pressure, etc.) as well as hydrodynamic parameters (bed depth, linear velocity, catalyst pellet size, etc.) are identical to those in a commercial methana-tion plant. This permits direct upscaling of test results to commercial size reactors because radial gradients are not present in an adiabatic shift reactor. 

The synthesis of aromatic amines is an active and important area of research.2 Many methods are available in the literature for the synthesis of these compounds. Though some of these are widely used, still they have limitations based on safety or handling considerations. For example, catalytic hydrogenation3 of nitro or azido compounds in the presence of metals such as palladium on carbon or Raney nickel require stringent precautions because of their flammable nature in the presence of air. In addition, these methods require compressed hydrogen gas and a vacuum pump to create high pressure within the reaction flask. To overcome these difficulties, several new methods have been reported in the... 

Higher molecular primary unbranched or low-branched alcohols are used not only for the synthesis of nonionic but also of anionic surfactants, like fatty alcohol sulfates or ether sulfates. These alcohols are produced by catalytic high-pressure hydrogenation of the methyl esters of fatty acids, obtained by a transesterification reaction of fats or fatty oils with methanol or by different procedures, like hydroformylation or the Alfol process, starting from petroleum chemical raw materials. 

The catalytic synthesis of ammonia from its elements via the Haber-Bosch process is of major industrial importance. The high pressure synthesis is catalyzed by Fe promoted with K20, CaO and A1203. 

FIGURE 9.14 One of the high-pressure vessels used for the catalytic synthesis of ammonia. The vessel must be able to withstand internal pressures of greater than 250 atm. 

The development of ammonia synthesis represents a landmark in chemical engineering, as it was the start of large-scale, continuous high-pressure operation in flow reactors, and in catalysis, because the numerous tests of Mittasch provided a systematic overview of the catalytic activity of many substances. 

The studies of ammonia synthesis over Fe and Re and the hydrodesulfurization of thiophene over Mo, described above, illustrate the importance and success of our approach of studying catalysis over single crystal samples at high pressures. The use of surfaces having a variety of orientations allows the study of reactions that are surface structure sensitive 6Uid provides insight into the nature of the catalytic site. Here we have shown that the ammonia synthesis... 

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