Processing of alkyd resins

There are two major chemical processes used for manufacturing alkyds the fusion process and the azeotrope process (solvent process). The fusion process is an old method of manufacturing alkyd that involves fusing all components at elevated temperature. An inert gas is continuously purged in the system to avoid oxidation as well as to drive off water of the reaction. Alkyds made by this process are often darker in color. Due to the possibilities of sublimation of phthalic anhydride and loss of polyols, this process suffers from poor reproducibility. In the solvent process, poly condensation is carried out in the presence of a small quantity (5 to 10 % of reaction mass) of hydrocarbon solvents (normally xylene or toluene) in 

---

Figure 2. Equipment for solvent processing of alkyd resins. Courtesy of Hercules Inc. (Wilminton, Del.).

History of Alkyd Resins Functionality Theory and Synthesis Processing of Alkyd Resins... 

Monsanto Chemical Co., The Chemistry and Processing of Alkyd Resins, 1952. 

Another commercially important crosslinking process that involves unsaturated polymer precursors is the so-called drying of alkyd resins in paints. This process is not drying at all, at least not in the sense of mere loss of solvent to leave behind a solid residue. Instead, the main process is the conversion of high relative molar mass molecules to a crosslinked structure via... 

An aromatic compound which is employed along with glycerol in the production of alkyd resins is phthalic anhydride. The conventional process for the manufacture of this chemical has been from the catalytic oxidation of coal tar naphthalene, and annual production of the anhydride in recent years has been around 150,000,000 pounds. In 1946 production was started (4) in a plant of the Oronite Chemical Co. at Richmond, Calif., to produce phthalic anhydride by the oxidation of o-xylene produced in a hydroformer unit of the adjacent Standard Oil Co. of California refinery. The Oronite plant was reported to have a design capacity of 7,000,000 to 8,000,000 pounds per year of 99.7% pure phthalic anhydride. 

For each of the three principal componcnis of alkyd resins, the polybasic acids, the polyols, and the monobasic acids, there is a large variety to be chosen from. The selection of each of these ingredients affects the properties of the resin and may affect the choice of manufacturing processes, Thus, to both the resin manufacturers and die users, die selection of the proper ingredients is a significant decision. 

On the other hand, although o-phthalic acid, or rather its anhydride, had long been produced in enormous amounts for use in the manufacture of alkyd resins, the para derivative was less well known and not available on a large scale. The synthesis is a straightforward one, however, from p-xylene, which is oxidized to terephthalic acid, either by means of nitric acid in the older process or by air (catalyzed) in the newer one. In the early years this compound then was converted to the easily purified dimethyl ester in order to obtain a colorless polymer adequate for the manufacture of commercially acceptable fibers. 

Several industrial systems involve emulsions, of which the following are worthy of mention. Food emulsions include mayonnaise, salad creams, deserts, and beverages, while personal care and cosmetics emulsions include hand creams, lotions, hair sprays, and sunscreens. Agrochemical emulsions include self-emulsifiable oils that produce emulsions on dilution with water, emulsion concentrates with water as the continuous phase, and crop oil sprays. Pharmaceutical emulsions include anaesthetics (O/W emulsions), hpid emulsions, and double and multiple emulsions, while paints may involve emulsions of alkyd resins and latex. Some dry-cleaning formulations may contain water droplets emulsified in the dry cleaning oil that is necessary to remove soils and clays, while bitumen emulsions are prepared stable in their containers but coalesce to form a uniform fihn of bitumen when apphed with road chippings. In the oil industry, many crude oils (e.g.. North sea oil) contain water droplets that must be removed by coalescence followed by separation. In oil slick dispersion, the oil spilled from tankers must be emulsified and then separated, while the emulsification of waste oils is an important process for pollution control. 

There are two main methods for preparation of alkyd resins. In the first one, called the fatty acid process, a free fatty acid is coesterified directly with the dibasic acid and the polyol at 200-240 °C. The reaction may be carried out without a solvent by first heating in an inert atmosphere. At the end, an inert gas may be blown into the resin from the bottom of the reaction kettle to remove water and unreacted materials. As a modification of this, a small quantity of a solvent may be used to remove water of esterification continuously by azeotropic distillation with the aid of moisture traps. 

Found extensively in esterified form in animal and plant glycerides. Obt. on large scale by alkaline hydrol. of fats during soap manuf. and by other routes. Used in cosmetics, foods, tobacco processing and extensively in numerous industrial and domestic prods. Component of alkyd resins and polyurethanes. Syrup with sweet taste. d 5 1.265. Mp 17.8 . Bp 290 part, dec., Bp2o 182 . V. hygroscopic. Steam-volatile. Numerous glycerides are listed separately. 

Tables 14.22.1 and 14.22.2 provide data on releases and transfers from both polymer manufacturing and man-made fiber production in the USA. Carbon disulfide, methanol, xylene, and ethylene glycol are used in the largest quantities. Carbon disulfide is used in manufacture of regenerated cellulose and rayon. Ethylene glycol is used in the manufacture of polyethylene terephthalate, the manufacture of alkyd resins, and as cosolvent for cellulose ethers and esters. Methanol is used in several processes, the largest being in the production of polyester. This industry is the 10th largest contributor of VOC and 7th largest in releases and transfers.

The manufacture of alkyd resins usually involves alcoholysis of the oils with a polyhydric alcohol followed by a batch process in which the first step is the esterification to a specified end point and then solution into a solvent thinning tank. The esterification may be done in the absence (fusion process) or presence (solvent process) of solvent, but in both cases an inert gas (nitrogen or carbon dioxide) must be bubbled through the reaction mixture to facilitate removal of water of esterification and to minimize oxidation. 

As discussed earlier, the preparation of alkyd resins is essentially an esterification process in which the polybasic acids and polyhydric alcohols are reacted with various oils or fatty acids and modifying agents. When a fatty acid is used, the process chiefly involves direct esterification. When an oil is the fatty acid source, an alcoholysis or ester-exchange reaction between the oil and the polyhydric alcohol is usually carried out before the esterification step. 

Figure 2.8 Schematic representation of alcoholysis process for alkyd resins...

Figure 2.9 Schematic representation of acidolysis process for alkyd resins 2.3.1.3 Fatty acid process...

Glycerol is used as a raw material in the manufacure of alkyd resins, ester gums, polyurethane foams, polyols, nitroglycerine, pharmaceuticals, cosmetics, as humectant in tobacco processing, antifreeze agent, solvent, extractant, plasticizer, etc. 

---