Cross-linked aromatics

A considerable number of non-cross-linked aromatic and heterocyclic polymers has been produced. These include polyaromatic ketones, aromatic and heterocyclic polyanhydrides, polythiazoles, polypyrazoles, polytriazoles, poly-quinoxalines, polyketoquinolines, polybenzimidazoles, polyhydantoins, and polyimides. Of these the last two have achieved some technical significance, and have already been considered in Chapters 21 and 18 respectively. The most important polyimides are obtained by reacting pyromellitic dianhydride with an aromatic diamine to give a product of general structure (Figure 29.17). 

An example of oxidative cross-linking takes place during vancomycin biosynthesis three cytochrome P450 enzymes—which use the same heme cofactor as the cytochromes from the primary metabolic electron transport chain—cross-link aromatic rings in its scaffold to form its rigid cup-like shape (29, 30). 

F 2. — Cross-linked aromatic vinyl co-polymers. Brit. Pat. 885.720 (1961). 

This investigation was extended to wood and lignin chars prepared at 400 °C to determine the effect of preexisting aromatic nuclei of lignin in the charring reactions. The permanganate oxidation analysis indicated that these chars, like cellulose chars, have considerably condensed or cross-linked aromatic structures, even at 400 C. The NMR data also showed that the chars from similar cellulose, wood. 

Hirose et al. [1] suggested an approximately linear relationship between membrane surface roughness and permeate flux for TFC RO membranes with six different cross-Hnked aromatic polyamide skin layers. On a polysulfone (PSf) substrate, cross-linked aromatic polyamides were formed at a water/solvent interface using m-phenylene diamine (MPD) and 1,3,5-benzenetricarbonyl trichloride as monomers. Isopropyl alcohol content in the aqueous amine phase was changed from 0 to 60 wt.% to control the interfacial surface tension, which eventually led to different surface roughness values. 

Desal-5 DL Cross-linked aromatic polyamide 42 44" GE Osmonics... 

The lignin biopolymer consists of a complex network of cross-linked aromatic molecules, which serves to inhibit the absorption of water through cell walls. The structure and chemical composition of lignin are determined by the type and age of the plant from which the lignin is isolated (White et al., 2011). 

Can the component of coke yield from cross-linked aromatics be... 

The formation of cross-linked aromatic rings can be reduced by lowering the coke drum pressure, raising the coke drum outlet temperature, improving the vacuum tower operation, and by adding steam to the coke drum. 

A reduction in coke production cannot be made without producing more shot coke. A certain amount of cross-linked aromatic coke, mixed with the asphaltic coke, is necessary to turn shot coke into sponge coke. This increases total coke production. 

Shot coke formation is increased because recycling light gas oil raises the coke drum vapor outlet temperature and reduces the production of cross-linked aromatic coke. This concentrates the asphaltic coke. 

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