Oligomerization glycerol

The structure of these products is uncertain and probably depends on pH and concentrations in solution. The hydroxyl or carboxyl or both are bonded to the titanium. It is likely that most, if not all, of these products are oligomeric in nature, containing Ti—O—Ti titanoxane bonds (81). Thek aqueous solutions are stable at acidic or neutral pH. However, at pH ranges above 9.0, the solutions readily hydroly2e to form insoluble hydrated oxides of titanium. The alkaline stabiUty of these complexes can be improved by the addition of a polyol such as glycerol or sorbitol (83). These solutions are useful in the textile, leather (qv), and cosmetics (qv) industries (see Textiles). 

In a system of two parallel reactions (Fig. 10.4), selectivity is an important parameter to monitor. The measure of selectivity is defined here as the ratio of isobutene reacted to ethers / total amount of isobutene reacted . Glycerol is consumed only in the etherification reaction, so the selectivity is calculated with respect to isobutene. Depending on the extent of the reaction, the formation of an ether molecule consumes from one to three isobutene molecules, and oligomerization consumes from two to four isobutene molecules [8],... 

In the dimerization of isobutene, tertiary-butyl alcohol (TBA, 2-methyl-2-propanol) has a strong role in modifying the selectivity of the reaction to Cg hydrocarbons and limits further oligomerization to C12 and Ci6 hydrocarbons [34]. Also, in the etherification of glycerol with isobutene the addition of TBA has a clear effect on the selectivity and on hydrocarbon distribution. The selectivity to ethers increased and the fraction of the Cu and Ci6 hydrocarbons decreased while the concentration of TBA was increased from 0 to 2.6 mol.%. As a conclusion, the formation of C12 and C16 hydrocarbons can be prevented in two ways either TBA should be added to the reaction mixture or the reaction should be carried out at high temperatures [8]. 

In view of the use of glycerol as a chemical commodity for the production of chemical intermediates, an overview will be made of existing catalytic knowledge. More specifically, glycerol oxidation, dehydration, hydrogenolysis, oligomerization/polymerization, polyol formation, and formation of a few miscellaneous products will be dealt with. 

Multihydroxyl containing monomeric or oligomeric p-cyclodextrins (PCD) such as those attained by grafting with glycidyl ethers of protected polyols (glycerol and pentitols) appeared rather promising components for their amphiphilic character, connected to the presence of an hydrophobic pocket and an external hydrophilic shell with an amplified number of hydroxyl groups. 

Adipic acid (0.60 mol) and an oligomeric glycerol having a repeat unit of three, PG-3 (0.44 mol), were dissolved at 70°C in 80 ml of toluene and then treated with enzyme catalyst Novozym -435 (14 g). The mixture was polymerized for 9 hours at 70°C at 300 mbar to remove water formed during the reaction. The mixture was then concentrated and the product isolated as a honey-like, viscous, colorless to slightly yellowish polyester. The polyester was readily soluble in water. 

Larson, T.J., Schumacher, G. and Boos, W. (1982) Identification of the g/pT-encoded sn-glycerol-3-phosphate permease of Escherichia coli, an oligomeric integral membrane protein. Journal of Bacteriology 1 52, 1 008-1 021. 

Barrault J., Clacens J.-M., PouUloux Y., Selective oligomerization of glycerol over mesoporous catalysts. Top. Catal., 27(1-4), 2004, 137-142. 

Lipase CA catalyzed the polymerization of adipic acid and glycerol to give the oligomeric products (97). The presence of molecular sieves improved the molecular weight. 

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