Graded catalyst deposition

The results of the analysis of spent catalyst samples collected at different reactor positions are exhibited in Figure 8.6. Vanadium tends to deposit in greater proportion at the top of the reactor, whereas carbon is accumulated preferably at the bottom. The descending-type vanadium deposit profile clearly indicates that the front-end of the catalytic bed is catching more metals. This is the reason why commercial reactors use graded catalyst systems, the front-end catalyst being more tolerant to metal deposition in order to protect downstream catalysts designed to accomplish other... 

Supported Nickel Catalyst is typically used in the manufacture of edible oils. It is prepared from a Nickel salt deposited onto an inert carrier consisting of various types of acceptable silicas, aluminas, or combinations thereof. The Nickel salt-carrier complex is not catalytically active and is converted to Supported Nickel Catalyst in a stream of hydrogen at elevated temperatures. After activation, Supported Nickel Catalyst also is pyrophoric and must be protected from air, typically by suspending it in a food-grade stearine. It usually is supplied as droplets or flakes. 

The active constituent of the catalyst is an oxide of tungsten prepared by partial reduction of WO - Unsupported WOj was found to have activity but better specific activity is obtained by depositing the oxide on a support. A number of grades of alumina and silica were tested. Gamma alumina was found to react with WOj at 400°C to a considerable extent to form aluminium tungstate. This was identified by XPS and tests on AljfWO ) showed it to be inactive as a catalyst for the isomerization reaction. 

Catalyst with 12% Mo loading was deposited on silica support via precipitation of metal sulphide from a homogenous solution containing calculated amount of ammonium molybdate ((NH4)Mo7024.4H20), urea, thioacetamide and nitric acid. Reaction was carried out in a water bath shaker kept at 90 C for 3 hours. The slurry was then filtered and the precipitate was dried in oven at 120 C for 14 hours. All chemicals were obtained from Aldrich as AnalaR grade and ultra-pure water was used to prepare the solutions... 

Two C0/S1O2 catalysts, one supported on silica gel (Grace Davison Grade 654) and the other supported on fumed silica (Cab-O-sil M-5) were prepared by a non-aqueous (acetone) evaporative deposition. The cobalt metal loading was 11 wt. % for both catalysts. Details of the preparation method are discussed elsewhere [22, 23]. 

Miller [48] attempted to catalyze TFE to HFP and OFCB by providing a high surface area for TFE to react using nuclear grade graphite as the catalyst. No catalytic action was observed other than some carbon deposits on the walls of the nickel tube. 

Examination of Table 3.4 shows that the deposition of Bis(triphenylsilyl) chromate into porous silica/alumina support increased catalyst activity by at least a factor of 500. The FI/MI ratio of 86-137 indicates that the molecular weight distribution of polyethylene prepared with this catalyst is relatively very broad compared to the Phillips catalyst, which may provide significant product advantages in certain applications over a similar grade of polyethylene prepared with the Phillips catalyst. 

During desulfurization, the process streams are not very corrosive, so carbon steel or low-grade alloys are used in the construction of reformers. Because the feed is very clean to protect the catalyst, there will be very little fouling of these units. The deposits that will be present will be cyclic naphtha, which is the second type of refinery coke. These deposits require an oxidizing solution (such as chromic acid or permanganate). There may also be iron sulfides, if the upstream processes are not properly operating. 

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