Foams, CFC

In flexible slabstock and molded polyurethane foam production, methylene chloride, CO2 (liquid or gas injection), and water are used as ABAs. In rigid insulation foams CFCs have been replaced with HFC-134a (sometimes blended with HFC 152a) or liquid CO2. In integral skin polyurethane products, CO2, water, and hydrocarbons are used for the purpose. 

Siace the pores ia an aerogel are comparable to, or smaller than, the mean free path of molecules at ambient conditions (about 70 nm), gaseous conduction of heat within them is iaefficient. Coupled with the fact that sohd conduction is suppressed due to the low density, a siUca aerogel has a typical thermal conductivity of 0.015 W/(m-K) without evacuation. This value is at least an order of magnitude lower than that of ordinary glass and considerably lower than that of CFC (chloro uorocarbon)-blown polyurethane foams (54). 

The use of CFCs as foam blowing agents has decreased 35% from 1986 levels. Polyurethanes, phenoHcs, extmded polystyrenes, and polyolefins are blown with CFCs, and in 1990 the building and appHance insulation markets represented about 88% of the 174,000 t of CFCs used in foams (see Foamed plastics). 

Economic Aspects. Manufacturing facilities for CFG alternatives are just now coming on line. The size of the markets for the alternatives is estimated to be quite large (several thousand t/yr), but it will not be as large as the prior markets for CFCs themselves. This is largely because of the higher cost of the alternatives, typically 3—5 times that of the incumbents. Low value-in-use appHcations which caimot support the cost of the alternatives will disappear or will switch to not-in-kind alternatives such as hydrocarbons for foam blowing. 

Research and development programs have been initiated by the cellular plastics industry to develop viable substitute blowing agents. These must have similar or improved properties to their CFC counterparts at a reasonable cost. Emphasis was initially placed on HCFC 123 and HCFC 141b, both having much shorter lifetimes and considerably less effect (up to 50 times) on o2one layer depletion (22). However, various options, including gas mixtures, water, or CO2 blown foams, continue to be studied ultimately to eliminate all CFCs and HCFCs. 

Phenolic foams - Phenolic foams can now be made using HCFC-141b, hydrocarbons, injected carbon dioxide, or HFC-152a instead of CFCs. In the long term, HFCs may be the predominant alternative. 

Chlorofluorocarbon-blown foam blocks are used to insulate the walls and roofs of some buildings, thus reducing heat losses and helping to conserve fossil fuels. In this area, polyurethane foam competes with polystyrene foam, which until recently was blown with dichlorodifluoromethane (CFC 12) but is now blown with a mixture of chlorodifluoromethane (HCFC 22) and 1 -chloro-l,l-difluoroethane (HCFC 142b). 

Dichlorofluoro-ethane (CCI2FCH5) The leading substitute blowing agent for CFC-11 in rigid foam insulation applications such as construction (commercial, residential, and public), appliances, and transport vehicles. 

Difluorochloro-ethane (CH5CCIF2) An effective replacement for CFC-12 in rigid polyurethane, polystyrene, and polyethylene foam insulation applications. Uses include both residential and commercial construction and process piping. 

Chlorotetrafluoro-ethane (CHCIFCF5) A potential medium pressure refrigerant for chiller applications. It is designed to replace CFC-12 as a diluent in sterilizing gas. A potential replacement for CFC-11 and-12 in rigid foam insulation applications. 

Much research is being conducted to find alternatives to CFCs with little or no effect on the ozone layer. Among these are HCFC-123 (HCCI2CF3) to replace Freon-11 and HCFC-22 (CHCIF2) to replace Freon-12 in such uses as air conditioning, refrigeration, aerosol, and foam. These compounds have a much lower ozone depletion value compared to Freon-11, which was assigned a value of 1. Ozone depletion values for HCFC-123 and HCFC-22 relative to Freon-11 equals 0.02 and 0.055, respectively. ... 

It should be noted that prior to 1987, total CFC emissions were made up from aerosol sprays, solvents and foam insulation, and that refrigerant emissions were about 10% of the total. However, all the different users have replaced CFCs with alternatives. 

Perhaps the most significant recent issue for the industry was the phase-out of CFCs as blowing agents resulting from the Montreal Protocol (1987) and Clean Air Act (1990).19 These regulations mandate specific timelines for discontinuation and, since foams comprise the bulk of polyurethane applications, have prompted a worldwide search for alternatives. Hydrochlorofluorocarbons, HFCs, and hydrocarbons (HCs) are now the blowing agents of choice. Which one is... 

Foam systems, non-CFC, 201 Ford hydroglycolysis process, 546 Formaldehyde... 

C05-0071. Freons (CFCs) are compounds that contain carbon, chlorine, and fluorine in various proportions. They are used as foaming agents, propellants, and refrigeration fluids. Freons are controversial because of the damage they do to the ozone layer in the stratosphere. A 2.55-g sample of a particular Freon in a 1.50-L bulb at 25.0 °C has a pressure of 262 torr. What is the molar mass and formula of the compound ... 

The term CFCs is a general abbreviation for ChloroFluoroCarbons. They have been extensively used since their discovery in the thirties, mainly as refrigerant, foam blowing agent, or solvent because of their unique properties (non toxic, non flammable, cheap). However, after the first warning of Rowland and Molina [1] in 1974 that CFCs could destroy the protective ozone layer, the world has moved rapidly towards a phase-out of CFCs. Because the destruction of stratospheric ozone would lead to an increase of harmful UV-B radiation reaching the earth s surface, the production and use of CFCs is prohibited (since January 1, 1995 in the European Union and since January 1, 1996 worldwide). 

Stripping of hazardous substances Mercury switches and other components containing particularly hazardous substances must be removed CFCs are recovered from the cooling circuit and PU foam with special equipment and appliances with varying degrees of automation ammonia is dissolved in water and separate disposal of waste oil (from compressors). 

Shredding and fractionation of the main unit takes place under partial vacuum in a special shredder. PU foamed with CFCs is pressed out as completely as possible. The vitiated air from the shredder and the press is cleaned through activated carbon and passed through a condensation cooling system. By this means, the foaming agent may be almost entirely recovered. 

Separation of the residual fractions is as follows separation of CFCs by condensation separation of expanded PS and PU foam by air classification separation of iron with a magnetic separator and separation of nonferrous metals with an eddy-current separator. 

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