Cocatalysts commercial process

Various ways of overcoming the PTA oxidation problem have been incorporated into commercial processes. The predominant solution is the use of high concentrations of manganese and cobalt ions (2,248—254), optionally with various cocatalysts (204,255,256), in the presence of an organic or inorganic bromide promoter in acetic acid solvent. Operational temperatures are rather high (ca 200°C). A lesser but significant alternative involves isolation of intermediate PTA, conversion to methyl/)-toluate, and recycle to the reactor. The ester is oxidized to monomethyl terephthalate, which is subsequentiy converted to DMT and purified by distillation (248,257—264). 

Molecular weight is regulated to some degree by control of the chain transfer with monomer and with the cocatalyst, plus internal hydride transfer. However, hydrogen is added in the commercial processes to terminate the reaction because many systems tend to form longer chains beyond the acceptable balance between desired processing conditions and chain size. 

There are substantial differences between the mechanisms of polymerization with single site catalysts and the closely related Ziegler-Natta catalysts (37-42). Most notably, the active centers of single site catalysts are believed to be cationic. Currently, cocatalysts are used in all commercial processes using single site catalysts, but this may change in the not-too-distant future (see p. 76). 

The commercial processes for methanol carbonylation discussed above all employ homogeneous rhodium complex or iridium complex catalysts that require an iodide cocatalyst. The highly corrosive nature of acidic iodide-containing solutions and the costly product separation steps mean that catalytic process that avoid these problems are potentially attractive,... 

The catalyst and metal alkyl cocatalyst can be brought into contact in a number of ways, depending on the commercial process. In a slurry or solution polymerization process, it is most convenient to simply feed a solution of the cocatalyst directly into the reactor, where it comes in contact with the catalyst in dilute solution and in the presence of ethylene and any comonomer. This procedure allows for continuous adjustment of the cocatalyst concentration for control of polymer properties. 

This method of control has been used in commercial polymer manufacture for almost two decades by our company and its licensees, to produce polymers with densities as low as 0.918 g/mL. In this commercial process, some highly susceptible Cr(II) sites are thought to react with cocatalyst, perhaps breaking Si-O-Cr linkages to generate the mono-attached (bare) species. Most of the olefin produced is 1-hexene. 

The Japanese company Maruzen Oil Co. [50] and Catalytica Associates Co. [51] use ferric sulfate as oxidant (cocatalyst) [52] (also compare [2]) Catalytica claims a commercial process in existing Wacker two-stage plants. 

Other THF polymerization processes that have been disclosed in papers and patents, but which do not appear to be in commercial use in the 1990s, include catalysis by boron trifluoride complexes in combination with other cocatalysts (241—245), modified montmorrillonite clay (246—248) or modified metal oxide composites (249), rare-earth catalysts (250), triflate salts (164), and sulfuric acid or Aiming sulfuric acid with cocatalysts (237,251—255). 

Complexation of the initiator and/or modification with cocatalysts or activators affords greater polymerization activity (11). Many of the patented processes for commercially available polymers such as poly(MVE) employ BE etherate (12), although vinyl ethers can be polymerized with a variety of acidic compounds, even those unable to initiate other cationic polymerizations of less reactive monomers such as isobutene. Examples are protonic acids (13), Ziegler-Natta catalysts (14), and actinic radiation (15,16). 

The gas-phase process, successfully commercialized independently by Bayer and USI,417 involves passing a mixture of ethylene, acetic acid and oxygen over a supported palladium catalyst contained in a multitubular reactor at 150 °C and about 5-10 atm pressure. The overall yield in vinyl acetate is about 92%, and the major by-product is C02. The catalyst consists of a palladium salt (e.g. Na2PdCl4) deposited on silica (or alumina) in the presence of a cocatalyst (e.g. HAuC14), reduced and impregnated with potassium acetate before use.384,418 The lifetime of the catalyst is about 2... 

In all of the above processes, the organoaluminum compounds serve as cocatalysts that activate a transition metal for the desired organic transformations. There are several important processes that do not involve transition metals and in which the organoaluminum reagents acts as a catalyst or stoichiometric reagent. The two most important of these are the formation of fatty alcohols and terminal alkenes from ethylene. These capitalize on the Aufbau reaction for formation of alkyl chains that can reach to C200, but the commercially important alkyls are those from C14 to C20 Oxidation of the aluminum alkyl followed by acidic hydrolysis yields predominately C14 to C20 alcohols and alumina (equation 36). The alcohols are converted to... 

In this case, the aluminum alkyl is functioning as a cocatalyst, sometimes also called an "activator." Titanium alkyls, believed to be active centers for polymerization, are created through transfer of an alkyl from aluminum to titanium, known as "alkylation." Molar ratios of cocatalyst to transition metal (Al/Ti) are typically 30 for commercial polyethylene processes using Ziegler-Natta catalysts (lower ratios are used for polypropylene). The vast majority of aluminum alkyls sold into the polyethylene industry today is for use as cocatalysts. With TEAL, the most widely used cocatalyst, alkylation proceeds as in eq 4.8 ... 

In some commercial operations, the catalyst is made in a batch process by impregnating a metal alkyl cocatalyst onto the Cr/silica in a fixed ratio. This method is not ideal for the control of in situ branching, however, because there is no way to adjust the degree of branching once the catalyst... 

Commercially, Dow appears to have implemented activation by well-defined cocatalyst for its Insite solution-phase metallocene process. Aside from historical priority, one reason for the persistent use of MAO is that the perfluorinated boron compounds are difficult to prepare, thus raising their expense. (One of the intermediates, (CeFslLi, must be handled at very low temperatme to prevent violent decomposition.) Another is that, unlike the MAO systems, catalysts activated by discrete activators have no large excess of alkylaluminum to scavenge poisons from the reaction medium, while common scavengers may hinder activity by consuming the expensive activator. 

The heterogeneous catalyst was prepared by reacting 0.5 g of silica containing MAO within the silica pores with 25 mg of complex 24 and 10 ml of additional toluene and 5 ml of additional MAO/toluene solution. The contents of this slurry were stirred and ethylene was added (1 atm) to initiate a prepolymerization process that was carried out to increase the total solids to 2.06 grams which were isolated by solvent evaporation in vacuo. The silica-supported catalyst was evaluated in a 2-liter reactor containing one liter of isobutane at 80°C, 35 bar total pressure with TIBA as cocatalyst. Linear polyethylene was produced with an M of 1470 and M M of 2.13 with a catalyst activity of 1309 Kg PE/g Cr/hr. These results clearly demonstrate that this particular single-site catalyst could be operated in commercial polyethylene manufacturing operations. 

DuPont introduced a commercial solution process in the 1960s with the tradename of Sclair that reportedly used a Ziegler-type catalyst based on both a vanadium compound (VCl or VOCI3) and a titanium compormd (TiCl ) in the presence of an aluminum alkyl cocatalyst. Operating conditions were above 200°C and 1,000 psi [42]. 

In the almost 60 years since the first patent on MA production by Weiss and Downs/ a flood of patent and nonpatent literature has been published. In the benzene oxidation route, vanadium oxide stands out to be the most common feature of all the catalysts. It appears that in the commercial production of MA from benzene, vanadium oxide or cocatalyst promoted vanadium oxide over a support is used (except SAVA process). Typical promoters used are oxides or salts of the following elements Mo, W, Bi, Sn, P, Ag, Cu, Na, B, Ti, and Ni. The V + Mo is most common. Other elements may also act as modifiers (see Ref. 15). 

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