High-Pressure Converters

One of the first steps taken in Ludwigshafen in 1910 was to build two experimental converters appreciably larger than Haber s laboratory model (fig. 5.2). Then Mannes-mann produced the contact tubes 2.5 m long with a 15 cm inside diameter and wall thickness about 30 mm for the first technical trials (fig. 5.3). They were heated electrically from the outside, filled with the catalyst, and housed in reinforced concrete chambers. Both tubes burst after about eighty hours of operation under high pressure.  

The converter s precautionary placement in a concrete container prevented any wider damage, but that was a small consolation. Examination of the burst tubes revealed that their structure had totally changed their inner part had totally lost its elasticity, it contained countless line fractnres, and it had become hard and brittle, very much like cast iron. Once the undamaged perimeter metal became too thin, the tubes gave in to the internal pressure. 

Haber s experiments had not provided even an inkling of snch a severe problem, and its cause was not obvions hydrogen should have been harmless to the metal, and tests showed no bnildnp of embrittling iron nitride. There were no precedents to consult at that time the only technique involving high pressures was Linde s liqnefaction of air, which was done in an apparatus made of soldered copper, a metal unsuitable for use in temperatures of up to 600 °C. Owing to its mechanical strength, carbon steel was the only practical choice to be used for the ammonia converter.  

Mannesmann contact tube used in first technical trials in 1910. 

Immediate laboratory investigations showed that at high pressure and high temperature all carbon steels will be invariably weakened by hydrogen and will fail in just a matter of hours or days. ° Obvious solutions did not work all the suitable 

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Just as high pressures convert Si02 in one of its forms containing Si04 tetrahedra into stishovite which contains Si06 octahedra, so some silicates, e.g., the feldspar KAlSi308, at 120 kbar and 900° can be transformed into a form containing SiOe octahedra, and these are then metastable at normal temperature and pressure. 

BASF high pressure converter for ammonia synthesis, with (inset) Carl Bosch (above) and Fritz Haber (below). Photos courtesy BASF (converter and Haber), and Deutsches Museum, Munich (Bosch). Reproduced from the cover of Chemistry Industry, 2 August 1993, with permission. 

The steam is led to a mist eliminator which recycles sulfuric acid to the high pressure converter to improve further the concentration of the acid. 

Selective oxidation of NH3 to NO is the key step in the production of nitric acid. Since the beginning of the last century this process has been based on the use of Pt-based gauzes through which reactants are selectively converted at very short contact times (a few ms). Despite several improvements, including the adoption of Pt-Rh and Pt-Pd-Rh alloys with reduced metal volatility and the use of better gauzes downstream that are made of Pd alloy for metal recovery, Pt losses stiU remain a major problem, especially in medium and high pressure converters operating at about... 

The second system, as shown on Figure 4, also uses liquid nitrogen as the cooling medium. However, this system is considerably less complicated and lighter in weight than the high pressure converter described above. 

Question by J. H. Beckman, Linde Company In view of the much greater refrigeration efficiency of the liquid feed system, why is the weight and space saving so small as compared with the high pressure converter system ... 

Answer by author As stated in this paper, the duration time for the liquid transfer system was longer than the duration stated for the high pressure converter system. If the duration times had been equal, the difference in weight and size would have been more pronounced. 

As already noted, Bosch s conviction was decisive in persuading the company s leadership to proceed with the commercialization of the process. He was the only expert who knew the capabilities of the steel industry, and he believed that a sizable high-pressure converter could be built he also believed that cheaper catalysts could be found, and that raw materials could be supplied in requisite amounts and purities. Bosch s inventiveness was decisive in removing a critical obstacle to further progress when the walls of experimental steel converters began failing after only short periods of operation. 

The jet pump relies on the same hydraulic power being delivered sub-surface as to the hydraulic reciprocating pump, but there the similarity ends. The high-pressure power fluid is accelerated through a nozzle, after whioh it is mixed with the well stream. The velocity of the well stream is thereby increased and this acquired kinetic energy is converted to pressure in an expander. The pressure is then sufficient to deliver the fluids to surface. The jet pump has no moving parts and can be made very compact. 

With short periods of irradiation (with high-pressure mercury lamps) under oxygen in chloroform containing methylene blue as a sensitizer, variously substituted 2-arylthiazoles are converted in the corresponding 2-aryloxazoles (823). 

Urea is produced from liquid NH and gaseous CO2 at high, pressure and temperature both reactants are obtained from an ammonia-synthesis plant. The latter is a by-product stream, vented from the CO2 removal section of the ammonia-synthesis plant. The two feed components are deUvered to the high pressure urea reactor, usually at a mol ratio >2.5 1. Depending on the feed mol ratio, more or less carbamate is converted to urea and water per pass through the reactor. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

An independent development of a high pressure polymerization technology has led to the use of molten polymer as a medium for catalytic ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization at a high pressure (see Olefin polymers, low density polyethylene) have been converted to accommodate catalytic polymerization, both stirred-tank and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C (57,83,84). CdF Chimie uses a three-zone high pressure autoclave at zone temperatures of 215, 250, and 260°C (85). Residence times in all these reactors are short, typically less than one minute. 

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