Dehydration with glycols

Worley, M. S., 1967, Super-dehydration with Glycols, Proc. Gas Conditioning Conf, University of Oklahoma, Norman, OK. 

If a-phellandrene be oxidised by potassium permanganate, the principal body resulting is a-oxy-/3-isopropyl glutaric acid. If /3-phellandrene be oxidised, closely related acids result, but if a 1 per cent, solution of permanganate be used and the oxidation effected very carefully in the cold, with the terpene always in excess, a glycol, CjoHjg(OH)2, results, which when dehydrated with dilute sulphuric acid yields tetrahydro-cuminic aldehyde. 

Polyester synthesis was carried out hy insertion-dehydration of glycols into polyanhydrides using lipase CA as catalyst (Scheme 6). The insertion of 1,8-octanediol into poly(azelaic anhydride) took place at 30-60°C to give the corresponding polyester with molecular weight of several thousands. Effects of the reaction parameters on the polymer yield and molecular weight were systematically investigated. The dehydration reachon also proceeded in water. The reaction behaviors depended on the monomer structure and reaction media. 

In a similar manner, coccinelline (99) and precoccinelline (100) have been synthesized from 2,6-lutidine (351) (336,450). Thus, treatment of the monolithium derivative (153) of 351 with P-bromopropionaldehyde dimethylacetal gave an acetal, which was converted to the keto acetal (412) by treatment with phenyllithium and acetonitrile. Reaction of 412 with ethylene glycol and p-toluenesulfonic acid followed by reduction with sodium-isoamyl alcohol gave the cw-piperidine (413). Hydrolysis of 413 with 5% HCl gave the tricyclic acetal (414) which was transformed to a separable 1 1 mixture of the ketones (415 and 416) by treatment with pyrrolidine-acetic acid. Reaction of ketone 416 with methyllithium followed by dehydration with thionyl chloride afforded the rather unstable olefin (417) which on catalytic hydrogenation over platinum oxide in methanol gave precoccinelline (100). Oxidation of 100 with m-chloroperbenzoic acid yielded coccinelline (99) (Scheme 52) (336,450). 

Ethanediol (ethylene glycol) [5g] Commercial products are pure enough for most purposes. In order to remove water of 2000 ppm, the ethanediol is dehydrated with sodium sulfate anhydride and distilled twice at reduced pressure in a dry nitrogen atmosphere in order to avoid oxidation to aldehyde. 

The synthesis of the C29-C51 EF segment 518 started with olefin 508 having three chiral centers, prepared by utilizing crotyl- and allyl-boronate chemistry (Scheme 73). Oxidative cleavage of olefin 508, debenzylation, and dehydration afforded glycol 509, which was converted into iodoglycal 510 by the Freisen method. 

Esterified nonionic surfactants are prepared from ether-containing polyhydric alcohols that include derivatives of EO and PO snch as polyethylene glycol (PEG), polypropylene glycol (PPG), EO/PO block copolymers, polyglycerin that is prepared by thermal dehydration with basic catalyst, and ethoxylated glycerin (Schane 1.9). 

Various combinations of dicarboxylic acid and their activated derivatives with glycols have been reacted enzymatically to generate biodegradable polyesters under mild reaction conditions (Table 12.2), in accordance with the following general scheme of dehydration polycondensation mode (Scheme 12.3) [7]. 

Note CO2 removal was followed by dehydration with triethylene glycoL ... 

Though membranes are widely used for air dehydration, it seems that this technology is not yet very widely accepted by the industry for gas dehydration applications. The main reason for this is that part of the methane processed through membrane modules is lost in the permeate, which does not happen with glycol-based processes. 

The most common contaminants in produced gas are carbon dioxide (COj) and hydrogen sulphide (HjS). Both can combine with free water to cause corrosion and H2S is extremely toxic even in very small amounts (less than 0.01% volume can be fatal if inhaled). Because of the equipment required, extraction is performed onshore whenever possible, and providing gas is dehydrated, most pipeline corrosion problems can be avoided. However, if third party pipelines are used it may be necessary to perform some extraction on site prior to evacuation to meet pipeline owner specifications. Extraction of CO2 and H2S is normally performed by absorption in contact towers like those used for dehydration, though other solvents are used instead of glycol. 

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