Chemical dehydration

Based upon raw material and intended application, the manufacturing of activated carbon falls into two mam categories thermal activation and chemical activation. In general, thermal activation involves the heating/gasification of carbon at high temperatures [13], while chemical activation is characterized by the chemical dehydration of the raw material at significantly lower temperatures [11,14],... 

Conditions for low temperature solution polymerizations of pyromellitic dianhydride (PMDA) have been developed for a wide variety of aromatic 1,4-phenylene [54, 55] and 4,4 -biphenylene [56-58] diamine monomers in a number of aprotic solvents to give high molecular weight prepolymers referred to as polyamic acids. Since the imidized structures are insoluble, they must be processed in the form of their polyamic acids which are subsequently imidized thermally or by chemical dehydrating agents. Although this procedure is acceptable for thin film or fibers, the fabrication of thick parts is complicated by the water of imidization. 

Tetrodotoxin, an extremely poisonous heterocycle present in Japanese puffer fish (various species of Spheroides), exerts its action by blocking the sodium ion channels in the peripheral nervous system. Chemically it has an adamantane-like structure, namely octahydro-12 - (hydroxymethyl) - 2 - imino-5,7,9,1 Oa-dimethano- 10aH-[ 1,3] -dioxo-cino-[6,5-d]pyrimidine-4,7,10,11,12-pentol. When chemically dehydrated, it rehydrates in dilute acid.73 Methanol, and ammonia, can add similarly. Because 2-amino-1,6-dihydropyrimidine forms the central part... 

Pharmaceutical Cosmetic Ingredients Specialty Chemicals Dehydrated Vegetables... 

These plastics, also known as pyrrones, are experimental materials prepared from aromatic dianhydrides and aromatic tetraamines. The polymer syntheses provide soluble prepolymers that are converted to the pyrrone structures by thermal or chemical dehydration. The precursors can be used to cast films or coatings, or can be molded under very high pressures into filled or unfilled forms. The pyrrones combine some of the best properties of the polybenzimidazoles and polyimides. The pyrrone films are exceptionally radiation resistant and retain their strength properties after 10,000 megarads of 1-MeV electrons. 

Synthesis of Polymers. Polyamic acid solutions were prepared by condensation of the aromatic anhydride and amine in N,N-dimethylacetamide (DMAc). Polyimide modified electrodes were made by casting or spin coating the precursor polyamic acid solution onto stainless steel or platinum substrates. Imidization was achieved by either heating the films to 400°C for 60 min or through a chemical dehydration process involving immersion in a 1 1 mixture of acetic anhydride and pyridine (6). BTDA-DAPI films were made by casting from a DMAc solution and heating to 100 C. 

Sperry et al. [39] reported capillary condensation up to 473 K in methanol/H2 mixtures for certain pressure ranges. They used a similar type of membrane as used by Uhlhorn, but treated with NaOH to poison the surface for chemical dehydration reactions. 

Prednisolone can be obtained with a chemical dehydration of hydrocortisone with selendioxide in tertiary butanol (2) or microbiologically through the dehydration action of corynebacterium simplex in zll,2-position (3, 4). A methanolic solution of the substrate was mixed with a 24 hours old bacteria... 

Fluid displacive resin-embedding of wet sediment is a passive procedure, samples are never physically dry and the fabric is supported by fluid throughout. Chemical dehydration prevents the cracking (common in vacuum dried sediment), and the technique requires no specialized drying, or resin-impregnating equipment. Water-saturated samples are more successfully embedded using fluid replacement than those which are partially dry. 

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