Activated magnesia process

The Active Magnesia Process (24) can be viewed as the gas phase equivalent of the Wellman-Lord (to be discussed below) in that it serves primarily to concentrate the SO2 values in the combustion effluent to a suitable concentration for feed to an oxidative process yielding sulphuric acid. The absorption temperature, however, is quite low compared with typical combustion effluent temperatures. 

As discussed in Section 4.3.1 the presence of alkali results in a significant decrease in the activity reflected by a lower pre-exponential factor. This is not the case with active magnesia, which shows the promoting effect of enhanced steam adsorption (although smaller than that for alkali promotion), but without the loss of activity [380] [381]. As a result, a Ni/MgO catalyst is able to process liquid hydrocarbon feedstocks, even kerosene and diesel if properly desulphurised [405] [427]. The method of preparation of the Ni/MgO catalyst is critical to achieving the promoter effect [381] [415] as illustrated in Figure 5.24. 

It has been ten years since Amoco announced the UltraCat process O) for SOx control in FCC units. In those ten years, as well as in the years previous to the announcement, much work was done to develop catalysts that would control SOx emissions. The evidence is the 80 or more U.S. patents that have issued in that time to Amoco and others. One of the first patents issued was to Amoco in 1974 ( ) for the addition of magnesia and other group IIA oxides to cracking catalyst. This paper reviews the SOx catalyst developments and emphasizes the work done at Amoco to identify the active materials, explain the deactivation mechanism and, finally, to make a side-by-side comparison of various catalytic systems that are being pursued commercially today. 

Many of the catalysts for the hydrodesulfurization process are produced by combining (Table 5-5) a transition metal (or its salt) with a solid support. The metal constituent is the active catalyst. The most commonly used materials for supports are alumina, silica, silica-alumina, kieselguhr, magnesia (and other metal oxides), as well as the zeolites. The support can be manufactured in a variety of shapes or may even be crushed to particles of the desired size. The metal constituent can then be added by contact of the support with an aqueous solution of the metal salt. The whole is then subjected to further treatment that will dictate the final form of the metal on the support (i.e., the metal oxide, the metal sulfide, or even the metal itself). 

Several different types and sizes of catalyst have been employed in commercial catalytic cracking processes. The commercial catalysts have been composed predominantly of either silica and alumina, or silica and magnesia. Other compositions have been investigated in the laboratory although some, such as silica-zirconia, alumina-boria, and alumina activated with various fluorides, have high activities, none has yet proved sufficiently attractive to warrant displacing the presently used catalysts. 

Porter and Schoonmaker (1 ) obtained an appearance potential curve near threshold for KOH which extrapolates to 7.8 eV at zero ion current. They presented evidence which Indicated that a large fraction of KOH was formed by dissociative ionization of the dimer, in a later study, these same workers (2) rejected their earlier results, since it was found that the presence of magnesia in their cell had reduced the activity of the hydroxide. Qusarov and Gorokhov (3) in a similar mass spectrometric study of the evaporation products of KOH have shown that KOH is formed primarily from direct ionization of the hydroxide. Very recently, Gorokhov et al. (4) reported the appearance potential of KOH from KOH as 7.5 0.2 eV. We adopt this result as A H for the process e + KOH(g) KOH (g) + 2e", since it is consistent with the expected mode of ionization. This value leads to AjH (K0H, g, 0 K) = 118 10 kcal mol" when used in conjunction with A H (K0H, g, 0 K) = -54.6 3.0 kcal mol" ( ). 

Step for determining the activity of the product as related to its end use. The process of extraction of magnesia from seawater may invoive reaction ofiime siurry with MgCl2 and MgS04 dissolved in seawater to form Mg(OH)2 that is further calcined as in the Premier Periclase process [4] or thermal decomposition of a concentrated MgCl2 brine in a special reactor as in the Dead Sea Periclase (DSP) process, also known as the Aman Process [6]. 

Over two hundred dry or wet processes have been proposed for the removal of SO2 gases. Limestone and dolomite find extensive use in many of the desulfurization processes. Activated soda is considered as an attractive and more reactive alternate to limestone. In addition to calcium and sodium based processes, ammonia based, magnesia based, organic based scrubbing systems and catalytic processes have also been proposed for SQ2 removal. Calcium based dry processes have found wide application especially in fluidized bed combustors and in... 

The common catalysts lose most of their activity at the following temperatures Super Filtrol natural, 1400°F silica-alumina synthetic, 2000 F silica-magnesia, 1400°F and silica-boria, 1400°F. However, in practice, regeneration temperatures are kept below 1000 to 1100 or 1150°F except bauxite which may be regenerated at even 1300°F without appreciable loss in activity. All catalysts lose some activity upon long use. The decline is. particularly noticeable with natural catalyst processing sour stocks and even the excellent catalyst cases of the Houdry process allow some decline in activity over a period of a... 

We have previously studied the role played by the support (silica, alumina, magnesia and titania, both anatase and rutile) on the surface properties of vanadia (ref. 6-9), concluding that the interaction between the support and the supported phase, and hence their activity in the above mentioned processes, greatly depends on the difference in their basicities. The aim of the present paper is to insight in this study, analyzing the role played by a usual dopant (sodium) on the properties of alumina- and titania- supported vanadia, using two different methods to incorporate vanadia on the surface of the support, i.e., standard impregnation methods and mechanical mixture of the oxides, as we have observed (ref. 7 and 9) that some of the properties of the final... 

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