Consumption, catalysts

H-acid, l-hydroxy-3,6,8-ttisulfonic acid, which is one of the most important letter acids, is prepared as naphthalene is sulfonated with sulfuric acid to ttisulfonic acid. The product is then nitrated and neutralized with lime to produce the calcium salt of l-nitronaphthalene-3,6,8-ttisulfonic acid, which is then reduced to T-acid (Koch acid) with Fe and HCl modem processes use continuous catalytical hydrogenation with Ni catalyst. Hydrogenation has been performed in aqueous medium in the presence of Raney nickel or Raney Ni—Fe catalyst with a low catalyst consumption and better yield (51). Fusion of the T-acid with sodium hydroxide and neutralization with sulfuric acid yields H-acid. Azo dyes such as Direct Blue 15 [2429-74-5] (17) and Acid... 

Acid modifiers have been used to a limited extent to reduce acid consumption in the H2SO4 alkylation process (27). Increased catalyst costs will encourage the further development and appHcation of such acid modification techniques in the future. In addition, the development of new technology, such as two-step alkylation, may be accelerated based on the incentive to reduce catalyst consumption and increase product octane (28). 

Improved feedstock pretreatment is important to minimize catalyst consumption and reduce subsequent spent-catalyst handling requirements. Selective hydrogenation of dienes can be used to reduce acid consumption, both in HF and H2SO4 alkylation (29). More effective adsorptive treating systems have been appHed to remove oxygen-containing contaminants that are frequently introduced in upstream processing steps. 

Fig. 1. Bulk polymerization of diethylene glycol bis(aHylcarbonate) at 45°C with initial addition of 3.0% diisopropyl percarbonate. Rates of polymerization as measured by density and catalyst consumption decrease with time at a given temperature (14).

The Heck reaction and other related transformations for selective C-C couplings are receiving a great deal of attention among synthetic chemists, due to their versatility for fine chemical synthesis. However, these reactions suffer in many cases from the instability of the Pd-catalysts used, resulting in high catalyst consumption and difficult processing. 

Despite all the advantages of this process, one main limitation is the continuous catalyst carry-over by the products, with the need to deactivate it and to dispose of wastes. One way to optimize catalyst consumption and waste disposal was to operate the reaction in a biphasic system. The first difficulty was to choose a good solvent. N,N -Dialkylimidazolium chloroaluminate ionic liquids proved to be the best candidates. These can easily be prepared on an industrial scale, are liquid at the reaction temperature, and are very poorly miscible with the products. They play the roles both of the catalyst solvent and of the co-catalyst, and their Lewis acidities can be adjusted to obtain the best performances. The solubility of butene in these solvents is high enough to stabilize the active nickel species (Table 5.3-3), the nickel... 

Typical conditions in a process using H2SO4 as the catalyst are 5-10 °C, 2-5 bar, iso-butane olefin ratios of 10, and a residence time in the reactor of 20-30 min. The catalyst consumption rate is high (about 100 kg of acid per ton of alkylate prod-... 

A feasible hydrogenation process was developed for the production of 4,6-diamino resorcinol from 4,6-bisphenylazo resorcinol. In the final process 0.8% catalyst (SQ-6, 10% Pd/C) was nsed in five snbseqnent reactions, this means that the specific catalyst consumption was less than 1 500 with respect to the substrate. The yield of the raw product (diamino resorcinol.2HC1) was quantitative, but its aniline content was 3-6 %, after purification the yield was 74-76%, the purity >99%. Even the color of the product was white. The aniline conld be recycled with more than 80% yield. The key to the improved results is that the hydrogenation was performed in the absence of HCl. After the reaction, the product was treated with HCl under hydrogen, and this procedure improved catalyst life. 

As work began on the process, it quickly became apparent that the extraordinary catalyst properties required for the process were not then available, and even with a superior catalyst, consumption would undoubtedly be severe. Figure 3 shows how Ramsbottom Carbon and nickel plus vanadium vary in the same reduced crude oils. All levels are very high far beyond anything normally encountered in a gas oil feedstock. 

Reaction engineering helps in characterization and application of chemical and biological catalysts. Both types of catalyst can be retained in membrane reactors, resulting in a significant reduction of the product-specific catalyst consumption. The application of membrane reactors allows the use of non-immobilized biocatalysts with high volumetric productivities. Biocatalysts can also be immobilized in the aqueous phase of an aqueous-organic two-phase system. Here the choice of the enzyme-solvent combination and the process parameters are crucial for a successful application. 

Temperature is an important variable in the alkylation process. When alkylating isobutane with butenes, a reaction temperature of 40° to 50° F. produces the highest quality alkylate with the lowest catalyst consumption. Commercial operation has been... 

The catalyst consumption for sulfuric acid alkylation is expressed in terms of pounds of fresh acid depleted per barrel of alkylate produced. When alkylating isobutane with butenes at 50° F. and maintaining an isobutane-olefin ratio of 5 to 1, the acid consumption will average 35 to 40 pounds per barrel when charging 98% acid and discarding 88% acid in a batchwise operation. 

Although the preceding discussion of the sulfuric and hydrofluoric acid processes has been confined to butene alkylation, isobutane has also been alkylated commercially with other olefins. Ethylene, propylene, pentenes, and dimers of butenes have been used for this purpose. It is also possible to use these olefins for the alkylation of isopentane. Such an operation, however, has not achieved commercial acceptance because it produces an inferior alkylate with a high catalyst consumption, and because isopentane is a satisfactory aviation gasoline component in its own right. 

Because propylene is highly volatile and must be marketed as fuel gas rather than as gasoline, it is low in cost and would appear to be a desirable alkylation feed stock. Balanced against its low cost, however, are the increased catalyst consumption and decreased product quality encountered in its alkylation. Consequently, its inclusion in alkylation feed is usually limited to minor quantities by the alkylate quality required for the maximum production of aviation gasolines. 

Pentene alkylation also has the disadvantages of increased catalyst consumption and decreased alkylate quality. A further disadvantage is that pentenes are a satisfactory motor gasoline blending stock and are thus a more expensive alkylation charge stock. For these reasons, commercial alkylation of pentenes is not extensively practiced. 

Butenes can also be alkylated in the form of various polymers, such as the by-product diisobutene polymers from butadiene plants. In this operation, each octene molecule appears to react as two individual butene molecules, and the high alkylate quality and low catalyst consumption characteristic of butene alkylation are obtained. For the most part, polymers have been alkylated only as supplemental feed stocks from external sources in periods of high aviation gasoline demand. 

One of the major items contributing to the high processing cost is the cost of the catalyst consumed. This is particularly true for propylene alkylation, where the catalyst cost is about 2.5 to 3.0 cents per gallon of alkylate produced. Several courses that research might follow in order to reduce catalyst consumption would be the development of a more efficient reactor, a more efficient catalyst, or an additive which would retard catalyst degeneration. 

In contrast, the alcohols of low molecular weight give poor, yields and a mixture of products. This can be explained by the intermediate aldehydes water solubility, which favors enolization and hydration in the acidic medium, leading to catalyst consumption and a distribution of products. 

Catalyst consumption is a major aspect of the hydrodesulfurization process and costs of the process increase markedly with the high-metal feedstocks. The ease with which the catalyst can be replaced depends, to a large extent, on the bed type, and with the high-metal feedstocks it is inevitable that frequent catalyst replacement will occur. From the data available (Table 5-7) (Nelson, 1976), attempts have been made to produce a correlation (Figure 5-10) (Nelson, 1976)... 

Table 5-7 Catalyst Consumption During the Desulfurization of Various Feedstocks... 

Figure 5-10 Catalyst consumption for metal-containing feedstocks. 

These benefits, coupled with possible savings in catalyst consumption, unwanted by-product production, and hydrogen costs suggest that two-stage processing may be attractive in individual cases. 

Contamination by heavy metals (V, Ni). To maintain the metal content on catalyst constant, usually a large increase in catalyst consumption (from an average of 0.15 lb/bbl up to and above 0.5 lb/bbl) is required. Alternatively special metal resistant catalyst can be applied in order to minimize catalyst consumption. Arbitrarily a metals content (Ni + V) of above 1500 ppm on catalyst is sometimes considered to be a metals contaminated resid operation. 

For catalytic application where a transition metal catalyst is dissolved in the ionic liquid or the ionic liquid itself acts as the catalyst two additional aspects are of interest. Firstly, the special solubility properties of the ionic liquid enables a biphasic reaction mode in many cases. Exploitation of the miscibility gap between the ionic catalyst phase and the products allows, in this case, the catalyst to be isolated effectively from the product and reused many times. Secondly, the non-volatile nature of ionic liquids enables a more effective product isolation by distillation. Again, the possibility arises to reuse the isolated ionic catalyst phase. In both cases, the total reactivity of the applied catalysts is increased and catalyst consumption relative to the generated product is reduced. For example, all these advantages have been convincingly demonstrated for the transition metal catalysed hydroformylation [17]. 

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