Methanolysis process

Dimethyl dichi orosilane can also be converted into sdoxane sdanol-stopped oligomers by a methanolysis process (eq. 8). 

In contrast to the hydrolysis technology, the methanolysis process allows for the one-step synthesis of organosdoxane oligomers and methyl chloride without formation of hydrochloric acid (64,65). The continuous methanolysis can also yield quantitatively linear sdanol-stopped oligomers by recycle of the cycHc fraction into the hydrolysis loop. 

Gamble et al.46 devised a glycolysis-methanolysis process which involves first dissolving PET in a mixture of EG, TPA, and dimethyl terephthalate oligomers (this stream actually is obtained from the molten PET formed in the polymerization process) at 230-290°C. The product stream is then reacted with superheated methanol at temperatures between 250 and 290°C to form a product mixture which is rich in dimethyl terephthalate. Most of the contaminants remain in the first reactor, which enables the process to produce high-purity dimethyl terephthalate. 

The important question of comparative value, mentioned earlier in Section 6, now must be considered. The material output of each process per unit of feed is estimated and multiplied by the market price of the material to arrive at a value of product. The output of the methanolysis processes, DMT and EG, are shown as a methanolysis-type product value in Table 16.5. The stoichiometric ratios are adjusted with a presumed 99 % recovery of DMT and 93 % recovery of EG. The output of the hydrolysis processes, TPA and EG, have the stoichiometric ratios adjusted for a presumed 99 % recovery of TPA and 93 % recovery of EG. The glycolysis processes, including methanolysis/BHET hybrid, are valued at 99 % recovery of terephthalic acid, 95 % recovery of ethylene glycol, and a US 0.022/kg esterification credit for making BHET. The EG recovery is higher for glycolysis-type products because of less loss of useful moieties. The three... 

The methanolysis process was patented in 1957 by DnPont [10], Since 1960 several processes have been developed [11, 12], The methanolysis process makes use of several steps. At first the PET is dissolved and partially glycolyzed. By this first step the pressnre of the subseqnent methanolysis can be reduced. The resulting DMT and EG are purified by crystallization and distillation (Figure 25.4). 

The methanolysis process can be performed batchwise (Figure 25.4) or continuously (Figure 25.5). In both cases the PET is molten. After that the melt is treated with methanol... 

Linear short-chain dimethylsiloxanes (oligomers) from hydrolysis or methanolysis processes are utilized as the starting material in the manufacture of polydiorganosiloxanes by polycondensation. If linear siloxane polymers are required, dimethyldichlorosilane with a high purity is necessary, since distillalive processing of siloxane diols is not possible due to their tendency to condensation (with cleavage of water). 

Methanol produced in the reaction also became a factor, as it reacted with the fully substituted hydrazine compound 9. Methanolysis tended to occur mainly at N-1. This allowed for selective production of either 8 or 9 by adding or removing methanol respectively, facilitating or circumventing the methanolysis process (Table 10, entries 2 and 3). 

Fatty acid methyl esters (FAMEs) were produeed by aeidie methanolysis of mitochondrial membrane hpids [11] or itsing one-step methylation of fatty aeids, exeluding the extraction of hpids [12]. The MEFAwere puriCfedby the method of thin layer chromatography on the siliea plates and hexanol elution. For a quantitative eontrol of the methanolysis process. An internal standard— pentadecane was used. 

Polyester can be recovered from contaminated polyester waste which contains non-polyester components. The waste may be polyester blended with cotton or other fibers, polyester magnetic tapes, or coated polyester films and engineering resins. The waste is dissolved in dimethylterephthalate, methyl-p-toluate or dimethylisophthalate. The eon-taminants are filtered from solution and polyester is reeovered by erystallization or used as a feedstock in a methanolysis process which forms dimethylterephthalate and alkylene glycol. 

A high temperature and pressure hydrolysis breakdown of PET has also been patented by Eastman which is said to be environmentally friendly but capable of providing conversion yields close to those associated with the usually more efficient methanolysis process [176],... 

Intellectual property assigned to Hoechst covers hydrolysis [190-192], methanolysis [193,194] and a method of purifying recovered EG fractions via solvent extraction in xylene [195]. The hydrolysis process is carried out in large volumes of water at high pressure and temperature, typically 4.2 MPa and 250 °C, with residence times of 2-3 hours. The methanolysis process differs from other known versions of this approach in that the polyester is first reacted (preferably in the melt) with a transesterification catalyst and that methanolysis is carried out on the resulting breakdown products. This is said to allow the second stage to be carried out under milder conditions. 

Asahi Carry out chemical recycling of PET bottles and post-industrial fibre waste. A methanolysis process termed Ecosensor is used to produce DMTA and EG, and is claimed to provide high-purity products which are used in fibre applications ( bottle to fleece system). No intellectual property has been found directly assigned to this company, which suggests that the process may be licensed from another concern. The website is tvtvw.ashai-kasei.co.jp. 

The imididazolidinone 180 (10-20 mol%, Fig. 4.35) catalyzed the homo-aldol dimerization process of an aldehyde and also the cross-aldol reaction between eno-lizable aldehydes (5, source of nucleophile, 10 equiv.) and aromatic aldehydes (2, electrophile). For both cases, the yields were high (58-90%), the anti-diastereo-selectivity was moderated (60-86% de) and the enantioselectivity was excellent (91-97% ee). To prevent a hemiacetal reaction of the initial aldol product 29 with another equivalent of aldehyde, the reaction was quenched by a methanolysis process to form the corresponding dimethyl acetal [259]. 

The first of these processes to receive a letter of nonobjection from the U.S. FDA was Goodyear s glycolysis process in 1991 (later sold to Shell). Later that same year Eastman Chemical and Hoechst-Celanese received approval for their methanolysis processes. The glycolysis processes typically produce partial depolymerization, which is followed by purification and repolymerization. Methanolysis processes provide full depolymerization, followed by purification by crystallization and then repolymerization. Glycolysis cannot remove colorants and certain impurities which can be removed by methanolysis. DuPont also operated a methanolysis facility for recycling PET, but indicated recently that it is discontinuing the operation for economic reasons. 

Barbuzzi et al. [28] analyzed a copolymer with 3-hydroxybutyrate (3HB) and 3-mercaptopropionate (3MP) or 3-mercaptobutyrate (SMB) units by ESI-MS. The samples were partially methanolyzed.The methanolysis process can be modeled as a random scission, which is known to broaden the MMD and, in fact, the polydispersity index is not small. For obvious reasons, it would be interesting to analyze the native copolymer prior to partial degradation by methanolysis. 

Methanolysis Eastman Kodak Co. patented a batch methanolysis process for recovering EG and DMT from ground scrap PET bottles including contaminants such as polyolefin bottom cups, aluminum bottle caps, labels, and adhesive by dissolving the scrap in oligomers of the same monomer and passing superheated methanol through the solution [9]... 

More contaminated PET-film waste must be degraded into the starting monomers, which can be separated and re-pol5Tnerized afterwards, of course, at a higher cost. At present, only the methanolysis process is exploited industrially, as opposed to hydrolysis processes, which are kept in reserve. 

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