Iron oxide process high pressure operation

Absorption trains of early ammonia oxidation processes to nitric acid were constructed of chemical stoneware or acid-proof brick, which restricted acid production to near ambient atmospheric pressure because of the low strength of the structural materials. The discovery that Duriron (silicon-iron) or high chrome stainless steels could tolerate these corrosive conditions well allowed the adoption of pressure absorption. This measure markedly decreased the size of the absorbers required and reduced nitrogen oxide stack losses. Pressure operation was easiest to achieve by compression of the feed gases at the front end of the process. In this way improved acid production is obtained at comparable capital costs per unit of product by operation at atmospheric pressure. 

Process "simulation. This technique is applied to equipment that is easily fouled and for which spare parallel units are provided. The fouled equipment s isolated, drained of process fluid, and filled with the cleaning solution the process operation is then simulated, thereby cleaning the equipment. An example of this route is the removal of iron oxide and copper deposits from high-pressure steam generators, using ammoniated ethylenediaminetetraace-tic acid (EDTA) solution. 

This is an endothermic reaction in which a volume increase accompanies dehydrogenation. The reaction is therefore favoured by operation at reduced pressure. In one process steam is passed through the dehydrogenating equipment with the ethyl benzene in order to reduce the partial pressure of the latter rather than by carrying out a high temperature reaction under partial vacuum. By the use of selected catalysts such as magnesium oxide and iron oxide a conversion of 35-40% per pass with ultimate yields of 90-92% may be obtained. 

Veba-Combi Cracking Also called VCC. A Bergius-Pier high-pressure thermal hydrotreating process. The catalyst is usually a promoted iron oxide, operated in a slurry, but an added catalyst may not be necessary. 

Subsequently, patents covering the conversion of synthesis gas to complex mixtures of organic oxygen compoimds, including methanol, were issued to BASF during 1913. This followed work by Mittasch and Schneider. Full-scale production of methanol was not attempted, however, imtil 1923. By that time high-pressure equipment had been in operation for several years in the new ammonia process. The methanol process was developed by Piers and the plant, built at Leima, used mixed zinc oxide-chromic oxide catalyst. The use of metallic iron for the internal parts of the reactor was avoided to prevent the formation of the volatile iron penlacarbonyl. The would have decomposed on the surface of the catalyst, to deposit finely divided iron metal, which in turn would have promoted the exothermic formation of methane. 

Thus, Figure 4.4 shows a pressure vessel filter, operating in upflow mode, and developed for the removal of dissolved iron from water supplies. The filter medium takes the form of a bed of catalysed manganese dioxide in grannlar form, approximately 1 m deep. This medium has the ability to cause dissolved iron to react with the oxygen present in the water to form insoluble iron oxides, which will precipitate and be retained by the bed. Cleaning is then undertaken by a high velocity backwash process which fluidizes the bed medium and removes the precipitated iron. 

In the second step, H2 and CO2 are produced by water-gas shift (WGS) reaction (12.20) and this process occurs in two stages consisting of high temperature shift (HTS) and low pressure shift (LTS) reactors. TTie HTS is loaded with high temperature catalyst, generally chromium-promoted iron oxide which operates at 350-400°C, whereas the LTS is loaded with low-temperature catalyst of copper-promoted zinc oxide, which operates at 200°C (Ledjeff-Hey et al, 2000). 

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