Vanadium catalysts process

In order to control the concentration of lower dibasic acid by-products in the system, a portion of the mother liquor stream is diverted to a purge treatment process. Following removal of nitric acid by distillation (Fig. 3, K), copper and vanadium catalyst are recovered by ion-exchange treatment (Fig. 

Citric acid is used to chelate vanadium catalyst in a process for removing hydrogen sulfide from natural and refinery gas and forming elemental sulfur, a valuable product (133). 

The contact process which replaced the chamber process reacts the products using a platinum or a vanadium catalyst. 

Stretford A process for removing hydrogen sulfide and organic sulfur compounds from coal gas and general refinery streams by air oxidation to elementary sulfur, using a cyclic process involving an aqueous solution of a vanadium catalyst and anthraquinone disulfonic acid. Developed in the late 1950s by the North West Gas Board (later British Gas) and the Clayton Aniline Company, in Stretford, near Manchester. It is the principle process used today, with over 150 plants licensed in Western countries and at least 100 in China. 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

The chief advantages of the contact process are the high purity of the product and the fact that the product is a concentrated acid. Disadvantages are the high cost of the catalysts and the fact that if sulfides are used as raw materials, costly purification of the sulfur dioxide is necessary, because impurities such as arsenic trioxide and selenium dioxide poison the catalyst (i.e., render the catalyst inactive). Platinum catalysts are particularly sensitive to these impurities, while vanadium catalysts are claimed to be free from this disadvantage. 

Alkanes also undergo carboxylation with CO, as shown in Scheme 2. Carboxylation of alkanes to carboxylic acids is one of the interesting and important functionalization processes. The first example of carboxylation of alkanes was performed on cyclohexane using a Pd(0Ac)2/K2S208/TFA catalyst system [2]. This carboxylation reaction was extended to gaseous alkanes, for example methane, ethane, and propane. Thus, acetic acid (AcOH) was synthesized from methane and CO in the presence of a Pd catalyst but with a low conversion yield [3]. Recently, the acetic acid synthesis was much improved by using vanadium catalysts such as VO(acac)2 and afforded AcOH almost quantitatively [4],... 

Aside from oxidative dimerizations [175-186] vanadium catalysts are able to induce C-C and C-0 bond cleavages. Momose and coworkers developed a catalytic system to fragment a-hydroxy ketones 101 to diesters or ketoesters 102 (Fig. 31) [190]. Using 1 mol% of EtOVOCl2 as a catalyst and oxygen as the terminal oxidant, 55-87% of 102 was obtained. The reaction mechanism is not known, but the reaction is inhibited by 2,6-di-tert-butylcresol (BHT) pointing to the involvement of a radical process. 

Another court (8) discounted a second chemist s contribution because it did not include the whole essence of the invention. The invention concerned a vanadium catalyst and carrier used in the process for making sulfuric acid. The first set of inventors came up with the idea of using an alkali in vanadic acid solution and fine carriers in which the particle size was no more than 60 microns. The particle size of the carrier was important. Another chemist told them to use kieselguhr as... 

As part of the early work to find alloys ofplatinum with higher reactivity for oxygen reduction than platinum alone, International Fuel Cells (now UTC Fuel Cells, LLC.) developed some platinum-refractory-metal binary-alloy electrocatalysts. The preferred alloy was a platinum-vanadium combination that had higher specific activity than platinum alone.25 The mechanism for this catalytic enhancement was not understood, and posttest analyses26 at Los Alamos National Laboratory showed that for this binary-alloy, the vanadium component was rapidly leached out, leaving behind only the platinum. The fuel- cell also manifested this catalyst degradation as a loss of performance with time. In this instance, as the vanadium was lost from the alloy, so the performance of the catalyst reverted to that of the platinum catalyst in the absence of vanadium. This process occurs fairly rapidly in terms of the fuel-cell lifetime, i.e., within 1-2000 hours. Such a performance loss means that this Pt-V alloy combination may not be important commercially but it does pose the question, why does the electrocatalytic enhancement for oxygen reduction occur ... 

In order to control the concentration of lower dibasic acid by-products in the system, a portion of the mother liquor stream is diverted to a purge treatment process. Following removal of nitric acid by distillation (Fig. 3, K), copper and vanadium catalyst are recovered by ion-exchange treatment (Fig. 3, N). This area of the process has received considerable attention in recent years as companies strive to improve efficiency and reduce waste. Patents have appeared describing addition of S02 to improve ion-exchange recovery of vanadium (111), improved separation of glutaiic and succinic acids by dehydration and distillation of anhydrides (112), formation of imides (113), improved nitric acid removal prior to dibasic acid recovery (114), and other claims (115). 

The model of Schiott and Jorgensen [98] shows that the proximity of vanadium atoms in a dimer present on the (200) plane of (VOjaPaOy and ti -superoxo or r -peroxo species chemisorbed on coordinatively unsaturated vanadium site are required for the selective oxidation of hydrocarbons. In fact, such activated molecular oxygen species are responsible for the activity and selectivity of vanadium catalysts in homogeneous oxidations [99-101]. Such oxidations are one-electron processes and involve free radicals. Although Schiott and Jorgensen [98] did not provide the complete mechanism of n-butane oxidation to maleic anhydride on vanadyl dimers, their model indicated that the superoxo species and one-electron, free radical processes may be involved in such oxidation. 

This paper focuses on the metal deposition process during hydrodemetallisation (HDM) of vanadyl-tetraphenylporphyrin (VO-TPP) under industrial conditions. In catalyst pellets of a wide pore, low loaded molybdenum on silica, the vanadium deposition process was determined with EPMA and HREM. The effect of quinoline and HjS on the vanadium deposition profile is studied and an attempt is made to simulate the deposition profiles based on intrinsic reaction kinetics and percolation concepts. 

Three different long duration vanadium deposition experiments, I, II and III, have been carried out. Experiment I was a test under reference conditions. Experiment II was carried out to determine the influence of quinoline on the vanadium deposition process. Experiment III was carried out to determine the effect of a low HjS partial pressure on the vanadium deposition profiles. Each experiment was split into two parts A and B. Experiment A is the first part of the vanadium deposition experiment. At the end of experiment A, the reactor was removed fi om the microflow equipment and catalyst pellets fi om every tray were collected and analysed. After this short stop, the reactor was mounted again in the microflow equipment, the catalyst sulfided and the experiment B started. Details on the reaction conditions of the three experiments are summarized in Table 2. 

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