Vapor phase oxidation silica

There are four principal processes that may be used to manufacture the glass body that is drawn into today s optical fiber. "Outside" processes—outside vapor-phase oxidation and vertical axial deposition— produce layered deposits, of doped silica by varying the concentration of SiCl4 and dopants passing through a torch. The resulting "soot" of doped silica is deposited and partially sintered to form a porous silica boule. Next, the boule is sintered to a pore-free glass rod of exquisite purity and transparency. 

The newest and most commercially successful process involves vapor phase oxidation of propylene to AA followed by esterification to the acrylate of your choice. Chemical grade propylene (90—95% purity) is premixed with steam and oxygen and then reacted at 650—700°F and 60—70 psi over a molybdate-cobait or nickel metal oxide catalyst on a silica support to give acrolein (CH2=CH-CHO), an intermediate oxidation product on the way to AA. Other catalysts based on cobalt-molybdenum vanadium oxides are sometimes used for the acrolein oxidation step. 

The direct oxidation of propylene by molecular oxygen is a low-selective reaction. The propylene oxide yield can be raised by limiting the conversion rate to a low value, about 10 to 15 per cent, by using more selective catalysts, or by achieving co-oxidation with a more oxidizable compound than propylene (acetaldehyde, isobutyraldehyde etc.). Many patents have been Hied concerning this process, but without any industrial implementation. Among them is the liquid phase oxidation of propylene on a rare earth oxide catalyst deposited on silica gel (USSR), or in the presence of molybdenum complexes in chlorobenzene or benzene (JFP Instiiut Francois du Petrole. Jefferson ChemicalX vapor phase oxidation on modified silver catalysts (BP British Petroleum IFP, or on ... 

Monochlorohenzene is also produced in a vapor-phase process at approximately 300°C. The hy-product HCl goes into a regenerative oxychlorination reactor. The catalyst is a promoted copper oxide on a silica carrier ... 

Phenylacetaldehyde can be obtained in high yield by vapor-phase isomerization of styrene oxide, for example, with alkali-treated silica-alumina [147]. Another process starts from phenylethane-l,2-diol, which can be converted into phenylacetaldehyde in high yield. The reaction is performed in the vapor phase in the presence of an acidic silica alumina catalyst [148]. 

TFSA satisfies all these requirements for hydrophilic silicone surfaces. Using silica as a model for extensively oxidized silicone surfaces, we showed that silylation with vapor phase TFSA took place at room temperature under scrupulously dry conditions. In contrast, others have found for the more conventional silylating agents, the methylchlorosilanes and the methylmethoxy-silanes, that no reaction occurred at temperature below 200°C under similar dry conditions [38]. 

Ethylamines. Mono-, di-, and triethyl amines, produced by catalytic reaction of ethanol with ammonia (330), are a significant oudet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, silica, or silica—alumina.. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethyl amine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give IV-ethylpiperidine [766-09-6] (332). 

An inert gas is bubbled through the sample. The volatile hydrocarbons are transferred into the vapor phase and trapped over a sorbent bed containing 2,6-diphenylene oxide polymer (Tenax GC). A methyl silicone (3% OV-1 on Chromosorb-W, 60/80 mesh) packing protects the trapping material from contamination. Other adsorbents such as Carbopack B and Carbosieve S III may also be used. If pentane and other low boiling hydrocarbons need to be detected, the sorbent trap should be filled with activated charcoal, silica gel, and Tenax, respectively, in equal amounts. 

H. van Bekkum et al. (17) reported that the alpha-pinene oxide 9 can be succesfully converted to campholenic aldehyde 10 (Eq. 15.2.5) in the presence of a BEA-zeolite. Ti-BEA proves to be an excellent catalyst for the rearrangement of a-pinene oxide to campholenic aldehyde in both the liquid and vapor phase. This is mainly attributed to the presence of isolated, well-dispersed titanium sites in a Bronsted-acid-free silica matrix. Furthermore, the unique molecularsized pore structure of the zeolite may enhance selectivity by shape-selectivity. 

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythdtol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is followed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerytliritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45 °C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on silica gel gives acrolein [107-02-8] (59). 

Shiraga and Uddin [6] carried out thermal and catalytic degradation of mixed plastic containing PVC. The solid acid catalyst employed in this study is silica-alumina with a chlorine sorbent such as goethite hydrated Iron Oxide FeO (OH). The dechlorination ability effects of contact mode, liquid phase contact, (LP) or vapor phase contact (VP) were studied. Dechlorination results show that the vapor phase contact was more effective for chlorine removal. 

To prepare a titanated catalyst, surface silanol groups on the silica react with a titanium ester or halide. Unreacted organic or halide groups left on the Ti are then replaced by oxide during subsequent calcination. Titanation can be accomplished in various solvents, such as hydrocarbons, alcohols, or even sometimes water, or by vapor-phase deposition. The simplicity of the approach allows any commercial silica to be so modified with up to 5-8 wt% Ti, at which point (depending on the surface area) saturation is reached. Catalyst manufacturers practice titanation but some procedures have also been developed by many polyethylene producers as well. These recipes can be practiced in a commercial polyethylene plant, because the titanium compound is applied as a vapor during the catalyst activation step. 

The first industrial plant using n-butane to manufacture maleic anhydride was started up by Monsanto in 1984. At the time, 20 per cent of the maleic anhydride production capacity of this company switched from benzene to butane. Since then, three other manufacturers in the United States (Amoco, Ashland and Denka Chemical), and two in Western Europe (Bayer and Huh) have followed a similar procedure, so that ail maleic anhydride produced today in the United States is based on butane feedstock and nearly 50 per cent of worldwide installed capacity operates by this method. The n-butane is oxidized in the vapor phase, in a multi-tube reactor, on a fixed bed of catalyst based on phosphorus, vanadium and iron, deposited on a silica/alumina support... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethylamine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcoholic solution of ammonia and the mixture is heated to 50-75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated silica—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH3CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

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