Heat transfer oils

Heat-transfer media Heat-transfer medium Heat-transfer oils Heat-transfer view Heat treating polyester Heat treatment Heavy crude oil Heavy-duty engines Heavy fuel oil Heavy gas oil Heavy metal Heavy metals... 

Mixtures containing various concentrations of mono-, di-, and polyisopropylnaphthalenes have been prepared by treating molten naphthalene with concentrated sulfuric acid and propjiene at 150—200°C followed by distillation (39). Products comprised of such isomeric mixtures have extremely low pour points, ie, ca —50° C, are excellent multipurpose solvents, and have been evaluated as possible Hquid-phase heat-transfer oils. 

Silicone Fluids. Sihcone fluids are used in a wide variety of appHcations, including damping fluids, dielectric fluids, poHshes, cosmetic and personal care additives, textile finishes, hydraiflic fluids, paint additives, and heat-transfer oils. Polydimethylsiloxane oils are manufactured by the equihbrium polymerisation of cycHc or linear dimethyl silicone precursors. Trifunctional organosilane end groups, typically trimethylsilyl (M), are used, and the ratio of end group to chain units (D), ie, M/D, controls the ultimate average molecular weight and viscosity (112). Low viscosity fluids,... 

Heat-transfer oil Aqueous solution Stainless steel 40-170 230-965... 

Heat-transfer oil Aqueous solution Glass-lined CS 25-70 140-400... 

Table 4.15 gives typical properties of some fluids. For other fluids, contact the manufacturer for exact data. With heat transfer oils, care must be taken that chemical changes such as carbonization do not take place. 

Some hot (370°C) pipework was supported by spring hangers to minimize stress as it was heated and cooled. The atmosphere was corrosive, and the spring hangers became impaired. They were removed, and the pipework was left solidly supported. It could not withstand the stress, and a condenser fractured hot heat-transfer oil was released and caught fire. 

Small cocks have often been knocked open or have vibrated open. They should never be used as the sole isolation valve (and preferably not at all) on lines carrying hazardous materials, particularly flammable or toxic liquids, at pressures above their atmospheric boiling points (for example, liquefied flammable gases or most heat transfer oils v./hen hot). These liquids turn to vapor and spray when they leak and can spread long distances. 

The furnace was fitted with interlocks that should have isolated the fuel supply if the tube wall temperature or the pressure of the heat transfer oil got too high. Neither interlock worked, and neither had been tested or maintained. The set-point of the high tube wall interlock had been raised far above its original set-point, from 433°C to 870°C, a simple way of putting it out of action [15]. Changing the set-point of an interlock is a modification and should be allowed only when the equipment is capable of withstanding the new conditions (see Chapter 2). 

A similar incident occurred on another furnace when the heat transfer oil froze inside the furnace during unusually cold weather. Outside the furnace, the lines were steam-traced. The operating team decided to thaw the frozen oil by lighting one of the burners... 

HEAVY OILS (INCLUDING HEAT TRANSFER OILS)... 

This term is used to describe oils that have a flash point above ambient temperature. They will therefore not burn or explode at ambient temperature but will do so when hot. Unfortunately many people do not realize this and treat heavy oils with a disrespect that they would never apply to gasoline, as shown by the incidents described below. Another incident was described in Section 12.2 (c). Heavy oils are widely used as fuel oils, solvents, lubricants, and heat transfer oils, as well as process materials. 

In another ineident of the same nature, the oil caught fire. A furnace supplied heat transfer oil to four reboilers. One was isolated for repair and then pressure-tested. The water was drained out of the shell, but the drain valve was 8 in. above the bottom tube plate, and so a layer of water was left in the reboiler (Figure 12-2). 

When the reboiler was brought back on line, the water was swept into the heat transfer oil lines and immediately vaporized. This set up a liquid hammer, which burst the surge tank. It was estimated that this required a gauge pressure of 450 psi (30 bar). The top of the vessel was blown off in one piece, and the rest of the vessel was split into 20 pieces. The hot oil formed a cloud of fine mist, which ignited immediately, forming a fireball 35 m in diameter. (Mists can explode at temperatures below the flash point of the bulk liquid see Section 19.5.)... 

In new plants, water should be considered as a heat transfer medium instead of oil. A decision to use water has to be made early in the design because the operating pressure will be higher. Although this will add to the cost, there will be savings in lower fire protection costs. In some plants the heat transfer oil is a bigger fire hazard than the process materials [9-1IJ. 

The heat transfer oil control valve was leaking. Unknown to the operators, the boiler temperature rose from 75°C to 143°C, the boiling point of the contents. Finally, bumping in the boiler caused about 0.2 ton of liquid to be discharged through the vent. 

Glycol.diacetate.. . Glycol diformate., , Heat transfer oils Heavy paraffinic. Light paraffinic.. 

Material of Construction (Barrier Material) Heating Water with Steam Heating Water with Heat Transfer Oil CooHng Organic Liqitid with Water Cooling Viscous Organic Liqitid with Water... 

Where high operating temperatures are required, high-temperature thermal fluid systems may be used instead of pressurized water or steam systems. These systems operate at atmospheric pressure using non-toxic media such as petroleum oil for temperatures up to 300°C or synthetic chemical mixtures where temperatures in excess of this are required (up to 400°C). Some advantages and disadvantages of thermal fluid or heat transfer oil systems are listed below. 

At 220°C a water-paraffin mixture is distilled off in a circulating evaporator (8). The product mixture passes to a second circulating evaporator (9) where the paraffin is stripped at 270°C with overheated water vapor, and finally the paraffin content in the resulting alkanesulfonate melt is further reduced by vapor stripping in a packed column (10). A heat transfer oil dissipates excess heat. 

Older appliances (such as ovens) still sometimes contain asbestos. A waste from which asbestos fibers may be released is classified as a hazardous waste and must be disposed of as specified in the appropriate environmental laws. The heat-transfer oils of older types of mobile convector heaters still sometimes contain PCBs. These fluids must be disposed of as hazardous waste. 

The Jacobs-Gould intramolecular cyclization of diethyl N-(6-methyl-2-pyridyl)amino-methylenemalonate to 3-ethoxycarbonyl-7-methyl-l,8-naphthyrid-4-one is another reaction ideally suited to microwave heating, although conductively heated equipment was employed for laboratory-scale experiments [45]. The product is a key intermediate in the synthesis of nalidixic acid, the first of the quinolone antibacterials. The process usually is conducted at temperatures of 200-250 °C and in high dilution, with heat transfer oils such as the eutectic mixture of diphenyl ether and biphenyl. However, it proceeded rapidly, predictably and controllably under solvent-free conditions. 

Scheme 2.9 Jacobs-Gould reaction in the absence of heat-transfer oil.

Interestingly, the Fischer indole synthesis does not easily proceed from acetaldehyde to afford indole. Usually, indole-2-carboxylic acid is prepared from phenylhydrazine with a pyruvate ester followed by hydrolysis. Traditional methods for decarboxylation of indole-2-carboxylic acid to form indole are not environmentally benign. They include pyrolysis or heating with copper-bronze powder, copper(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. 

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