Houdry process regeneration

Dehydrogenation of /i-Butane. Dehydrogenation of / -butane [106-97-8] via the Houdry process is carried out under partial vacuum, 35—75 kPa (5—11 psi), at about 535—650°C with a fixed-bed catalyst. The catalyst consists of aluminum oxide and chromium oxide as the principal components. The reaction is endothermic and the cycle life of the catalyst is about 10 minutes because of coke buildup. Several parallel reactors are needed in the plant to allow for continuous operation with catalyst regeneration. Thermodynamics limits the conversion to about 30—40% and the ultimate yield is 60—65 wt % (233). 

Heat is removed from the regenerator by means of the circulating catalyst, supplemented by water-cooled tubes. This technique eliminates the need for the complex and expensive temperature-control system used in the Houdry process (the closely spaced, perforated inlet and outlet pipes, and the circulating molten-salt system). 

Operations in both the reactor and regenerator are continuous, so there is no need for the complicated system of valves, control mechanisms, and safety devices required in the Houdry process. 

Entrained catalyst is removed from the product off-gas by means of cyclones. The catalyst circulates continuously from the reactor to the regenerator and vice versa by means of transfer lines. Coke deposited on the catalyst is burnt off in the regenerator however, because the amount of coke is relatively small, additional fuel must be burnt in the regenerator to satisfy the thermal requirements of the endothermic dehydrogenation reaction. However, while this approach is similar to that in the Houdry process, FED does not have a catalyst reduction step with hydrogen before proceeding to the dehydrogenation cycle lack of this step is believed to be somewhat detrimental to the overall performance of the process. 

Initially, in spite of its complexity, the Houdry process hardware worked satisfactorily. However, the steam cooling tubes were subjected to severe conditions so that after about two years corrosion was sufficiently severe to allow water to contact the catalyst. The steam reacted with the catalyst during regeneration, resulting in severe declines in activity. To overcome this problem, the water/steam fluid was replaced with molten salt to cool the tubes in the case and to act as an intermediate heat transfer agent from the case to the steam generators. This invention has been credited to Socony-Vacuum (27). 

A serious disadvantage of Houdry s process was the semi-continuous, cyclic nature of the operation. The complexity and limitations of the Houdry process were apparent to engineers of the day and a race was on for a simpler, more elegant solution. The next step in this evolutionary process was to move the catalyst between vessels in place of the complex piping and control schemes to used to alternate between oil contact, steam stripping, and combustion air regeneration phases. 

Obviously, the large amount of heat contained in the hot flue gases (1000 to 1200°F) from the regeneration operation must be recovered by heat exchange or the use of waste-heat boilers. In addition, the Houdry process employs these gases to drive the air turbine. 

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... 

The Catofin process, which was formerly the property of Air Products (Houdry Division), uses a proprietary chromium catalyst in a fixed-bed reactor operating under vacuum. There are actually multiple reactors operating in cycHc fashion. In sequence, these reactors process feed for about nine minutes and are then regenerated for nine minutes. The chromium catalyst is reduced from Cr to Cr during the regeneration cycle. 

Butadiene and Isoprene. Butane may be transformed directly to 1,3-buta-diene on chromia-alumina (Houdry Catadiene process).144-146 172 The most significant condition is operation under subatmospheric pressure (0.1-0.4 atm), which provides an improved yield of 1,3-butadiene. Operating at about 600°C, the process produces a mixture of butenes and 1,3-butadiene. After the removal of the latter, the remaining butane-butenes mixture is mixed with fresh butane and recycled. Extensive coke formation requires regeneration of the catalyst after a few minutes of operation. 1,3-Butadiene yields up to 63% are obtained at a conversion level of 30 40%. 

Clays are a family of crystalline aluminosilicate solids that interact with a variety of organic compounds (Theng, 1974). Acid treatment develops acidic sites by removing aluminum from the structure and often enhances the reactivity of the clay with specific families of organic compounds. The acid sites also catalyze the formation of coke, and Houdry developed a moving bed process that continuously removed the coked beads from the reactor for regeneration by oxidation with air (McEvoy, 1996). 

Houdry fixed-bed catalytic cracking a cyclic regenerable process for cracking of distillates. 

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