Chemistry, process

PBT can be made by using both batch and continuous processes. Early commercial processes were DMT-based batch processes that involved two distinct 

Ester interchange and transesterification reactions are thermochemically neutral reactions which may be driven in the desired direction through the use of excess diol and by removal of volatile byproducts from the system. 

The key disadvantage of using excess BDO is that the raw material could be wasted unless efficiently recycled. 

The second, i.e. polycondensation (transesterification) stage, begins when vacuum is applied to the system to drive molecular weight build by removal of 

As the polymer melt builds molecular weight, it becomes more viscous. Toward the end of the reaction where the final molecular weight is achieved, stirring of the polymer requires specially designed reactor systems. Many large scale, commercial PBT plants currently employ a continuous DMT-based process. 

Isomerization reactions (reaction class 2) give an important pathway for high-octane components in the gasoline. This class of reactions is critical for producing high-octane components in the gasoline products. In addition, we find more valuable iso-butene components due to the isomerization of butanes. The isoparaffins from the isomerization class of reactions also reduce the cloud point of the diesel product [1]. 

Description General reaction formula for reactants and products 

Naphthenes (cydoparaffins) cracked to olefins and smaller naphthenes C(m+n)H2(m+n) (Naphthene) CniH2m (Naphthene) + C Hj (Olefin) 

Olefin bond shift X-CnH2n y-QiHjn (x and y are different locations of the olefin) 

Cyclo-hexane to Cyclo-pentane CjH,2 (Naphthene) C5H9-CH3 (Naphthene) 

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Two Other chemical processes that rely on hydrothermal processing chemistry are wet oxidation and supercritical water oxidation (SCWO). The former process was developed in the late 1940s and early 1950s (3). The primary, initial appHcation was spent pulp (qv) mill Hquor. Shordy after its inception, the process was utilized for the treatment of industrial and municipal sludge. Wet oxidation is a term that is used to describe all hydrothermal oxidation processes carried out at temperatures below the critical temperature of water (374°C), whereas SCWO reactions take place above this temperature. 

Process Chemistry. Manganese is combined with oxygen in its ores (see Table 3) and carbon is the most economical reducing agent for oxides. Therefore, the essential characteristics of manganese metallurgy is evident from examination of the interactions between manganese oxides and... 

Causticization, the reaction of hydrated lime [1305-62-0], Ca(OH)2, with sodium carbonate to regenerate sodium hydroxide and precipitate calcium carbonate, is an important part of the Bayer process chemistry. 

Alternatives to the methyl chloride dkect process have been reviewed (31). Processes to make phenyl and ethyl siUcones have employed dkect-process chemistry. Phenyl chloride has been used in place of methyl chloride to make phenylchlorosilanes (15). In addition, phenylchlorosilanes are produced by the reaction of benzene, HSiCl, and BCl (17,31). EthylsiUcones have been made primarily in the CIS, where the dkect process is carried out with ethyl chloride in place of methyl chloride (32). Vinyl chloride can also be used in the dkect process to produce vinylchlorosilanes (31). Alternative methods for making vinylchlorosilanes include reaction of vinyl chloride with HSiCl or the platinum-catalyzed hydrosilylation of acetjdene with HSiCl. ... 

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

The hydroxyl group of the resulting phenol is situated immediately adjacent to where the carboxyl group was previously located. This same Hquid-phase copper oxidation process chemistry has been suggested for the production of cresols by the oxidation of toluic acids. y -Cresol would be formed by the oxidation of either ortho or para toluic acids a mixture of 0- and -cresols would be produced from y -toluic acid (6). A process involving the vapor-phase catalytic oxidation of benzoic acid to phenol has been proposed, but no plants have ever been built utilizing this technology (27). 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

L. F. A. Mason, Photographic Processing Chemistry, Focal Press, London, 1966. 

The integral film format required different processing chemistry and film components from those used previously. The processed film unit needed to contain all of the reaction products along with the final color image. Polaroid followed the original SX-70 film with Time-Zero SX-70 film (1979), 600 film (1981), Spectra film (1986), and 600 Plus film (1988). 

AH ethylene oxide direct-oxidation plants are based on the original process chemistry discovered by Lefort in 1931 (7,8). The main reaction is as follows ... 

Reactive Chemicals Reviews The process chemistry is reviewed for evidence of exotherms, shock sensitivity, and other insta-bihty, with emphasis on possible exothermic reactions. It is especially important to consider pressure effects— Pressure blows up people, not temperature The pumose of this review is to prevent unexpected and uncontrolled chemical reactions. Reviewers should be knowledgeable people in the field of reactive chemicals and include people from loss prevention, manufacturing, and research. 

Our Electronic Chemicals group is an industry leader in most basic manufacturing of Wet Process Chemistries, from UHP Straights (100 ppt qualities). Custom formulated Wet Etch, Solvents and Solvent Blends, and Cleaning Products. 

Frequently a piece of equipment is used in different processes during its lifecycle. This could result in process conditions that exceed the safe operating limits of the equipment. Equipment inspection may provide a poor prediction of the equipment s useful life and reliability, due to the change of material handled or change in process chemistry over the life of equipment. Batch operations are also characterized by frequent start-up and shut-down of equipment. This can lead to accelerated equipment aging and may lead to equipment failure. This chapter presents issues and concerns related to the safe design, operation, and maintenance of various pieces of equipment in batch reaction systems, and provides potential solutions. 

Understanding the chemistry of the process also provides the greatest opportunity in applying the principles of inherent safety at the chemical synthesis stage. Process chemistry greatly determines the potential impact of the processing facility on people and the environment. It also determines such important safety variables as inventory, ancillary unit operations, by-product disposal, etc. Creative design and selection of process chemistry can result in the use of inherently safer chemicals, a reduction in the inventories of hazardous chemicals and/or a minimization of waste treatment requirements. 

Process chemistry issues and their effects on batch reaction systems safety are presented in Table 2, beginning on page 11. This table is meant to be illustrative but not comprehensive. 

Process chemistry should be selected to fit existing batch equipment. 

Listed below are safety practices aimed at minimizing the incidents caused by process chemistry issues. 

Select a process chemistry or synthesis route that is inherently safer. 

Document safety issues pertaining to process chemistry... 

Select a process chemistry or synthesis route that is inherently safer (e.g., nontoxic, nonflammable materials, less severe operating condition)... 

Ensure that the equipment is able to handle the new process chemistry, and that the demands of the new process on ancillary units are also met... 

Equipment inspec- Reevaluate and possibly reset inspection intervals tion may provide a when equipment is used for handling different poor prediction of chemistry equipment safety, Perform management of change review due to change of material handled or change in process chemistry over the life of equipment. ... 

Only catalysts that are completely inactive within reasonable condition should be rejected. Finding better conditions for a catalyst that shows some promise is best left for the catalyst manufacturer or the investigator. Those most familiar with process chemistry and recycle reactors will be best able to find the optimum condition for a promising catalyst. 

Fig ure 4-25. A loop reaotor produotion system. (Source M. Wilkinson and K. Geddes, An Award Winning Process." Chemistry in Britain, December, 1050-1052, 1993.)... 

Basic process chemistry using less hazardous materials and chemical reactions offers the greatest potential for improving inherent safety in the chemical industry. Alternate chemistry may use less hazardous raw material or intermediates, reduced inventories of hazardous materials, or less severe processing conditions. Identification of catalysts to enhance reaction selectivity or to allow desired reactions to be carried out at a lower temperature or pressure is often a key to development of inherently safer chemical synthesis routes. Some specific examples of innovations in process chemistry which result in inherently safer processes include ... 

A United States Environmental Protection Agency report (Lin et al., 1994) contains an extensive review of inherently safer process chemistry options which have been discussed in the literature. This report includes chemistry options which have been investigated in the laboratory, as well as some which have advanced to pilot plant and even to production scale. 

To apply inherent safety appropriately, research chemists must make an in-depth investigation into the process chemistry and into the entire process that may develop based on that chemistry. An adequate investigation necessitates input from a diverse team of people, including research chemists and business, engineering, safety, environmental personnel. They must consider the impact that the use of a particular process chemistry will have on a wide range of populations. These include the ultimate customer of the product, process operating personnel, the general public, and potentially impacted plant and animal populations. To chose the "inherently safest chemistry, the team needs to take into account ... 

Research management has the responsibility to create a working environment that promotes, encourages, rewards, and facilitates the application of inherent safety in the development of process chemistries. 

The wide array of choices available to research chemists necessitates a diligent search for hazards to select the inherently safest chemistry. One of the means to search for hazards is to conduct a literature search, looking in particular for reports of incidents occurring in processes using the same or similar process chemistry being considered. 

Parshall (1989) notes that product liability issues are complex and varied. An attorney knowledgeable in product liability issues may be an important contributor to process hazards discussions if such issues may affect the advisability of a proposed process chemistry. 

The life cycle cost of a process is the net total of all expenses incurred over the entire lifetime of a process. The choice of process chemistry can dramatically affect this life cycle cost. A quantitative life cycle cost cannot be estimated with sufficient accuracy to be of practical value. There is benefit, however, in making a qualitative estimate of the life cycle costs of competing chemistries. Implicit in any estimate of life cycle cost is the estimate of risk. One alternative may seem more attractive than another until the risks associated with product liability issues, environmental concerns, and process hazards are given due consideration. Value of life concepts and cost-benefit analyses (CCPS, 1995a, pp. 23-27 and Chapter 8) are useful in predicting and comparing the life cycle costs of alternatives. 

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