Chromium-based catalysts using

Yu, Xiuyuan Zhang, Wucheng Li, Na Zhou, Zhiyong. Iron and chromium-based catalyst used for preparation of 1,1,1,2-tetrafluoroethane. CN 1820845 A 20060823 (2006). 

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

Cocatalysts, such as diethylzinc and triethylboron, can be used to alter the molecular-weight distribution of the polymer (89). The same effect can also be had by varying the transition metal in the catalyst chromium-based catalyst systems produce polyethylenes with intermediate or broad molecular-weight distributions, but titanium catalysts tend to give rather narrow molecular-weight distributions. 

The commercial production of high-density polyethylene started almost at the same time in late 1956 by Phillips using a chromium-based catalyst in a medium-pressure process and by Hoechst using a Ziegler catalyst in a low-pressure process. Polypropylene production began in Montecatini and Hercules plants in 1957. Poly(l-butene) and poly(4-methyl-1-pentene) have been produced in small commercial quantities since about 1965. The commercial production of ethylene/propylene-based rubbers started in 1960 [241]. 

Chromocene (CrCp2) supported on silica is used to generate certain chromium-based catalysts for the polymerization of ethylene (e.g., Phillips and Union Carbide catalysts). The nature of the organometallic species responsible for the catalysis is not known with certainty, though it is noteworthy that some Crm alkyls such as [Cp Cr(CH2Ph)(THF)2]+BPh catalyze the polymerization of ethylene.19... 

Due to increasing environmental problems, the use of metal catalysts will gradually be reduced in the future the reduction in the early use of lead- and chromium-based catalysts is evidence of this. With stricter regulations governing the release of metals, the cost of catalyst recovery and environmental remediation is quickly making noncatalytic processes for the production of carboxylic acids preferable. Coupled with recent advances in the field of biocatalysis, metal-mediated oxidations may give way to alternative processes as we enter a new millennium of chemistry. 

Process description The INNOVENE S process utilizes a proprietary vertical slurry-loop reactor, as shown in the flow diagram. Two reactors are used for bimodal capability. Isobutane is normally used as the hydrocarbon diluent in the process, although hexane may be used as an alternative. The diluent is used as a catalyst carrier and as the polymerization reactor suspension and heat transfer medium. Hexene-1 and/or butene-1 can be used as a comonomer. Hydrogen is used for molecular weight control when using the Zieglerg catalyst platform. Titanium-based and chromium-based catalysts are both used. 

Sasol reported the use of a chromium-based catalyst (Cr salt, 2,5-dimethylpyrrole ligand) for the trimerization of ethylene into 1-hexene (P= 5 MPa, T= 115 °C) [18, 19]. According to Sasol, the IL of choice is l-ethyl-2,3-dimethylimidazolium chloride/ AlEtj containing an excess of AlEtj. When compared to typical homogeneous catalytic systems, the activity and yield in 1-hexene are lower. 

A typical chromium-based catalyst is prepared similarly. It is usually supported by a 9 1 of Si02 Al203 carrier. Either Cr(N03)3 9H20 or C1O3 solutions in nitric acid are used to impregnate the support. The nitrates are decomposed in air at 400 to 1000 An optimum chromium content... 

In the 1950s, two chromium-based eatalysts, Ziegler-Natta and Phillips, were introdueed for use in polymerisation reaetions. The Phillips eatalyst is part of the industrial development of polyethylene and is still in use today. Using these eatalysts as a template, researehers are developing chromium-based catalysts for the polymerisation of monomers other than ethene, including the formation of polycarbonates from epoxides and carbon dioxide. 

The oxidation of alcohols to carbonyl compounds is a fundamental reaction that has synthetic and chemical importance. Using chromium-based catalysts, researchers have developed several catalysts that have impacted alcohol oxidation reactions. Recently, homogeneous catalysts have had problems with catalyst/product separation and suffer from poor catalyst recyclability. Therefore, the quest for a resolution to this problem has led researchers to scaffold salen complexes onto a silica-based material such as MCM-41. Zhou et al. used an ion-exchangeable, layered polysiloxane support to immobili.se their sulfonato-(salen)Cr(m) complex. They reacted benzyl alcohol, cyclo-hexanol and -hexanol with hydrogen peroxide as oxidant in an ionic liquid at 40 °C. Several ionic liquids were investigated [BMImX (BMIm = 1-n-butyl-3-methylimidazolium X =PF6, BF4, NOs")] and compared for each substrate. 

According to the reaction temperature (Chen et al, 2008), the WGSR falls into two categories high-temperature shift catalyst (HTC) and low-temperature shift catalyst (LTC). The catalyst commonly used in the former is an iron-chromium-based catalyst, whereas a copper-zinc-based catalyst is frequently adopted in the latter. 

In the 1960s, scientists at the Union Carbide Corporation developed two additional silica-supported, chromium-based catalysts that are used in a gas-phase process for the manufacture of HDPE. One catalyst is based on... 

Although Phillips Petroleum did not commercialize a gas-phase process for the manufacture of polyethylene. Sailors and Hogan pointed out that the first commercial gas-phase process came on stream in 1964, with BASF using the licensed Phillips chromium-based catalyst [21]. BASF received U.S. Patent 3,300,457 on January 24, 1967 (filed on May 9, 1963), for a gas-phase process [37]. 

Chapters 2, 3 and 4 discuss each of the three catalyst types used today to manufacture polyethylene, with Chapter 2 devoted to titanium-based catalysts Chapter 3 to chromium-based catalysts and Chapter 4 to singlesite catalysts. These chapters would primarily appeal to scientists that are involved in developing ethylene polymerization catalysts. 

The particular features of phosphonium salts were exploited for a number of synthetic applications in 2014. Phosphonium chloride salts found applications as chlorine source and as modifiers for homogeneous catalyst systems. As an example, Muller, Rosenthal and co-workers reported the study of a chromium-based catalyst for the selective tri-merization of ethylene. A phosphonium precursor of the type i cyclo-(PR2CH2CH(OH) )2][Br]2) was used for the preparation of iron(n) complexes containing unsymmetrical P-N-P pincer ligands (Scheme 5). The group of Prof. Morris tested these compounds as catalysts for the asymmetric hydrogenation of ketones and imines. ... 

Twelve-membered rings have been obtained using coordination catalysts. The transJmns,ds-cyc. ododec2Lti ien.e has been prepared with a tetrabutyl titanate—diethylalurninum chloride catalyst (48,49) and with a chromium-based system (50). The trans,trans,trans-isom.e-i. has been prepared with a nickel system. 

Chromium Oxide-Based Catalysts. Chromium oxide-based catalysts were originally developed by Phillips Petroleum Company for the manufacture of HDPE resins subsequendy, they have been modified for ethylene—a-olefin copolymerisation reactions (10). These catalysts use a mixed sihca—titania support containing from 2 to 20 wt % of Ti. After the deposition of chromium species onto the support, the catalyst is first oxidised by an oxygen—air mixture and then reduced at increased temperatures with carbon monoxide. The catalyst systems used for ethylene copolymerisation consist of sohd catalysts and co-catalysts, ie, triaLkylboron or trialkyl aluminum compounds. Ethylene—a-olefin copolymers produced with these catalysts have very broad molecular weight distributions, characterised by M.Jin the 12—35 and MER in the 80—200 range. 

Silver-containing catalysts are used exclusively in all commercial ethylene oxide units, although the catalyst composition may vary considerably (129). Nonsdver-based catalysts such as platinum, palladium, chromium, nickel, cobalt, copper ketenide, gold, thorium, and antimony have been investigated, but are only of academic interest (98,130—135). Catalysts using any of the above metals either have very poor selectivities for ethylene oxide production at the conversion levels required for commercial operation, or combust ethylene completely at useful operating temperatures. 

Balthis and Bailar6 obtained tris (ethylenediamine) chromium-(III) complexes by the oxidation of chromium(II) solutions, using a procedure somewhat similar to that used for the synthesis of cobalt (III) com plexes. Mori7 described the preparation of hexaamminechromium(III) salts from the oxidation of chromium (II) salts in the presence of ammonia. The results obtained in both syntheses have been erratic.8,9 Berman noted that the foregoing syntheses are rendered dependable by the use of a catalyst of activated platinum on asbestos. Schaeffer,100 in a subsequent study, independently used colloidal platinum as a catalyst but reported some difficulty in separating it from the product.106 The procedures recommended and described here are based on the use of platinized asbestos as the catalyst. 

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