Commercial Process Methods

The physical state of the polyethylene during the polymerization process varies depending on the type of process utilized in the manufaduring process and the molecular structure of the polyethylene produced. The polyethylene contained in the polymerization reactor may be in the molten state, a solid particle of polyethylene (referred to as granular polyethylene) or polyethylene which is dissolved in an organic solvent. In some cases. 

The specific polymerization conditions utilized in the manufacturing process determine the physical state. The polymerization conditions in the process are primarily the polymerization temperature, ethylene pressure, polyethylene composition (amoxmt of branching, molecular weight and molecular weight distribution) and type of solvent employed in the process. 

Commercial polyethylene is manufactured by either a high-pressure process or a low-pressure process summarized in Table 5.1. 

The low-pressure polymerization processes were originally used in a single reactor configuration, but since the 1970s more complex polymerization systems have been developed that utilize two or more reactors that are in parallel and/or in series. Consequently, the polymerization conditions in each reactor may be varied over a wide range so that the final polyethylene material manufactured has a complex molecular structure, which is designed to provide various premium-grades of polyethylene that are suited for specific markets and applications. 

High Pressure Either a tubular reactor or a stirred autoclave reactor. Operating pressure 15,000-40,000 psi at 150-250°C. 

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The aim of this volume and a first companion volume is to compile in one place a working knowledge of the polymer chemistry and physics of fluoropolymers with detailed descriptions of commercial processing methods. The books focus on providing a reference as well as a source for learning the basics for those involved in polymer manufacturing and part fabrication, as well as end-users of fiuoro-... 

Although Pd is cheaper than Rh and Pt, it is still expensive. In Pd(0)- or Pd(ll)-catalyzed reactions, particularly in commercial processes, repeated use of Pd catalysts is required. When the products are low-boiling, they can be separated from the catalyst by distillation. The Wacker process for the production of acetaldehyde is an example. For less volatile products, there are several approaches to the economical uses of Pd catalysts. As one method, an alkyldi-phenylphosphine 9, in which the alkyl group is a polyethylene chain, is prepared as shown. The Pd complex of this phosphine has low solubility in some organic solvents such as toluene at room temperature, and is soluble at higher temperature[28]. Pd(0)-catalyzed reactions such as an allylation reaction of nucleophiles using this complex as a catalyst proceed smoothly at higher temperatures. After the reaction, the Pd complex precipitates and is recovered when the reaction mixture is cooled. 

The preparation of fluoroaromatics by the reaction of KF with perhaloaromatics, primarily hexachloroben2ene, has received considerable attention. Two methods were developed and include either the use of an aprotic, polar solvent, such as /V-methy1pyrro1idinone (8), or no solvent (9). These methods plus findings that various fluoroaryl derivatives are effective fungicides (10) prompted development of a commercial process for the production of polyfluoroben2enes (11). The process uses a mixture of sodium and potassium fluorides or potassium fluoride alone in aprotic, polar solvents such as dimethyl sulfoxide or sulfolane. 

Manufacture. One commercial process features a three-stage saturation—rearomatization technique using benzene and fluorine gas as raw materials (73). Principal problems with this method are the complex nature of the process, its dependence on fluorine gas which is cosdy to produce, and the poor overall utilization of fluorine, because nearly one-half of the input fluorine is removed during the process. 

This direct method of preparing organ oHthium compounds is commonly used in commercial processes. 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Butene. Commercial production of 1-butene, as well as the manufacture of other linear a-olefins with even carbon atom numbers, is based on the ethylene oligomerization reaction. The reaction can be catalyzed by triethyl aluminum at 180—280°C and 15—30 MPa ( 150 300 atm) pressure (6) or by nickel-based catalysts at 80—120°C and 7—15 MPa pressure (7—9). Another commercially developed method includes ethylene dimerization with the Ziegler dimerization catalysts, (OR) —AIR, where R represents small alkyl groups (10). In addition, several processes are used to manufacture 1-butene from mixed butylene streams in refineries (11) (see BuTYLENEs). 

The oxidation of carbohydrates is the oldest method for oxahc acid manufacture. The reaction was discovered by Scheele in 1776, but was not successfully developed as a commercial process until the second quarter of the twentieth century. Technical advances in the manufacture of nitric acid, particularly in the recovery of nitrogen oxides in a form suitable for recycle, enabled its successful development. Thus 150 t of oxahc acid per month was produced from sugar by I. G. Earben (Germany) by the end of World War II. 

Synthesis. Exploratory research has produced a wide variety of odorants based on natural stmctures, chemicals analogous to naturals, and synthetic materials derived from available raw materials and economical processing. As in most areas of the chemical industry, the search for new and useful substances is made difficult by the many materials that have been patented and successfully commercialized (4). In the search for new aroma chemicals, many new materials are prepared for screening each year. Chemists who perform this work are involved in a creative exercise that takes its direction from the commercial sector in terms of desirable odor types and specific performance needs. Because of economic limitations, considerations of raw material costs and available processing methods may play a role eady in the exploratory work. 

Manufacture. Historically, ammonium nitrate was manufactured by a double decomposition method using sodium nitrate and either ammonium sulfate or ammonium chloride. Modem commercial processes, however, rely almost exclusively on the neutralization of nitric acid (qv), produced from ammonia through catalyzed oxidation, with ammonia. Manufacturers commonly use onsite ammonia although some ammonium nitrate is made from purchased ammonia. SoHd product used as fertilizer has been the predominant form produced. However, sale of ammonium nitrate as a component in urea—ammonium nitrate Hquid fertilizer has grown to where about half the ammonium nitrate produced is actually marketed as a solution. 

Methods of dkect reduction of chlorosilanes using hydrogen at high temperatures have historically been inefficient processes (68—70). Significant process innovations, involving the hydrogenation of siUcon tetrachloride over Si—Cu at less than 2.45 MPa (500 psi), proceed in good conversion (71,72) and allow commercial processes. 

The processing methods for siHcone mbber are similar to those used in the natural mbber industry (59,369—371). Polymer gum stock and fillers are compounded in a dough or Banbury-type mixer. Catalysts are added and additional compounding is completed on water-cooled roU mills. For small batches, the entire process can be carried out on a two-roU mill. Heat-cured siHcone mbber is commercially available as gum stock, reinforced gum, partially filled gum, uncatalyzed compounds, dispersions, and catalyzed compounds. The latter is ready for use without additional processing. Before being used, sihcone mbber is often freshened, ie, the compound is freshly worked on a mbber mill until it is a smooth continuous sheet. The freshening process eliminates the stmcturing problems associated with polymer—filler interactions. 

A number of processes have been devised for purifying thionyl chloride. A recommended laboratory method involves distillation from quinoline and boiled linseed oil. Commercial processes involve adding various high boiling olefins such as styrene (qv) to react with the sulfur chlorides to form adducts that remain in the distillation residue when the thionyl chloride is redistilled (179). Alternatively, sulfur can be fed into the top of the distillation column to react with the sulfur dichloride (180). Commercial thionyl chloride has a purity of 98—99.6% minimum, having sulfur dioxide, sulfur chlorides, and sulfuryl chloride as possible impurities. These can be determined by gas chromatography (181). 

Of the four commercial processes for the purification of carbon monoxide two processes are based on the absorption of carbon monoxide by salt solutions, the third uses either low temperature condensation or fractionation, and the fourth method utilizes the adsorption of carbon monoxide on a soHd adsorbent material. AH four processes use similar techniques to remove minor impurities. Particulates are removed in cyclones or by scmbbing. Scmbbing also removes any tars or heavy hydrocarbon fractions. Acid gases are removed by absorption in monoethanolamine, hot potassium carbonate, or by other patented removal processes. The purified gas stream is then sent to a carbon monoxide recovery section for final purification and by-product recovery. 

The widespread use of cinnamic derivatives has led to the pursuit of reUable methods for thek dkect synthesis. Commercial processes have focused on condensation reactions between ben2aldehyde and a number of active methylene compounds for assembly of the requisite carbon skeleton. The presence of a disubstituted carbon—carbon double bond in the sidechain of these chemicals also gives rise to the existence of two distinct stereoisomers, the cis or (Z)- and trans or (E)- isomers ... 

X-ray studies indicate that the vinyl chloride polymer as normally prepared in commercial processes is substantially amorphous although some small amount of crystallinity (about 5% as measured by X-ray diffraction methods) is present. It has been reported by Fuller d in 1940 and Natta and Carradini in 1956 that examination of the crystalline zones indicates a repeat distance of 5.1 A which is consistent with a syndiotactic (i.e. alternating) structure. Later studies using NMR techniques indicate that conventional PVC is about 55% syndiotactic and the rest largely atactic in structure. 

Waste products from a number of commercial processes can be used as cheap and readily available fillers for PCM. For example, lightweight structural materials may be obtained by filling various low-viscous resins with waste materials [4, 5]. Also by adding fillers to reprocessed polymers it is possible to improve their properties considerably and thus return them to service [6]. This method of waste utilization is not only economically feasible but also serves an ecological purpose, since it will help to protect the environment from contamination. The maximum percentage of the filler should in these cases be such as to assure reliable service of the article made from the PCM under specified conditions for a specified period of time. 

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