An alternative for rigid foam production: Cyclopentane - a new insulation technology appropriate for developing countries
by Werner Wiegmann
Cyclopentane is a hydrocarbon which has no ozone depletion potential (ODP) or global warming potential (GWP). According to expert Werner Wiegmann, cyclopentane is a viable alternative to CFCs for the production of rigid polyurethane (PUR) foams not only in the industrialised countries, but also in the developing world.
Throughout the world, rigid polyurethane foam is one of the most widely used insulating materials for household, commercial and industrial refrigerators and freezers. Foaming of self- adhesive rigid foam systems enables a weight-saving sandwich construction to be produced in a single operation. The good thermal insulating properties permit an optimum relationship between effective and total volume. The use of CFC 11 as blowing agent for rigid foam is an important factor in achieving this good insulating effect. After the foaming process, CFC 11 remains in the closed cells of the rigid foam as insulating gas.
Due to its ozone depletion potential, CFC 11 is to be replaced by other blowing and insulating gases as soon as possible. CFC use is regulated by the Montreal Protocol. However, their substitution by hydrochlorofluorocarbons (HCFCs; e.g. 141b) as interim solution must be phased out between 1996 and 2030, to comply with a tightening-up of the rules at a reconvention of the Montreal Protocol Conference. In order to comply already today with all these national and international regulations, cyclopentane has become established in Germany as an effective and environmentally compatible option. By the end of 1994, almost all refrigeration appliance production lines in Western Europe will have switched over to using cyclopentane as blowing agent and insulating gas.
Partly halogenated hydrocarbons (HCFCs, e.g. 141b) have properties similar to those of CFC 11 and are also technically satisfactory as alternatives. Conversion of a production plant processing 141b blown polyurethane systems is expected to produce only minor problems. Unfortunately, however, the system does not achieve an ozone depletion potential of zero.
As chlorine-free alternatives, perfluoroalkanes (HFA) were the first substances to make their appearance as a feasible option to replace CFCs. However, besides the poor processibility of these emulsified components, they were found to have a relatively high greenhouse warming potential. So these substances are not very environmentally friendly either.
Another alternative is the hydrofluorocarbon HFC 134a, a product which is gaseous at ambient temperature and can therefore only be used with special additional metering machines. Due to the preforming effect, it usually shows poorer processibility, which in turn can lead to poorer thermal conductivity values. Also, the product obtained with this blowing agent is not halogen- free. It thus fails to satisfy the criteria for award of the "Blue Angel" seal of environmental compatibility.
Cyclopentane a viable alternative
Among the many compounds that may be considered as blowing agents for rigid foam, saturated aliphatic hydrocarbons, and specifically pentanes are most suitable. One reason for this is their favourable boiling point (Table 1). Another is their low solubility in the PUR foam matrix. The low thermal conductivity, which is especially important for the refrigerator industry, is maintained when cyclopentane is used. With cyclopentane, in combination with special tailor- made polyol formulations, the thermal conductivity values are almost as good as those of CFC produced foams.
With regard to ageing as compared to CFC 11, it was found that the thermal conductivity of a specimen containing cyclopentane was by approx. 5 % higher at the start of the study. During storage, however, the increase was less pronounced, and in aged foam specimens, the thermal conductivity of the foam containing cyclopentane was actually lower (Fig. 1).
The mechanical properties of the foam, such as its compressive strength, are retained. Long-term studies showed no reduction in strength, even with thermal stressing. Nor was any "softening" of the foam noted. This had been teared at first due to condensation of cyclopentane.
Unlike CFC 11, cyclopentane is a highly flammable liquid and its vapour forms explosive mixtures with air (Table 2).
As a result of adding e.g. 11% cyclopentane, the entire component is classified as flammable liquid. This means that for both, storage and processing of the components, safety precautions must be taken in accordance with statutory regulations of the individual countries. In Germany, for example, the following regulations are applicable:
• Regulation applicable to combustible liquids (VbF);
• Law on water resources management (WHG);
• Guidelines for avoidance of hazards due to explosive at mospheres (Explosion Protection Guidelines, Ex-RL).
For safety reasons, cyclopentane is added to the polyol component at the point of use on ordinary high-and lowpressure machines (Table 3).
One basic principle of safe and compliant use is that the combustible and explosive pentane-air mixture 15 avoided. This is accomplished principally by replacement of the air (exhaustion) and by appropriate measures known as "primary explosion protection". Essentially, this is achieved by:
• inertization of tanks and moulds;
• high air replacement rates (monitored) at mixing and foaming stations;
• potential equalizing (earthling) avoids generally the build up of hazardous static charges.
In the light of experience to date, the use of cyclopentane will require additional equipment for production plants in developing countries as well. Safety-related conversion will be necessary in the following critical areas:
• cyclopentane storage tank;
Plant conversion can be paid for out of the Multilateral Fund of the Montreal Protocol Conference, under the provisions for incremental cost. Developing countries can therefore propose projects for plant conversion to the Executive Committee of the Fund.
Personnel handling combustible liquids need to be trained. The responsible employer must ensure that employees receive basic instruction on the potential hazards and that this instruction is repeated in appropriate intervals. Guidelines for the pentane group of substances have been issued in various industrialised countries. For the sake of good order, they should be agreed upon with the competent supervisory authorities in the individual countries. Under the terms of the Multilateral Fund, training programmes may also be instituted as "projects".
Now that the European refrigerator industry has switched to cyclopentane, this development is attracting a great deal of attention worldwide. Meanwhile, production facilities in Japan, New Zealand and Korea are also being converted to use this new blowing and insulating method. There is no doubt that other industrialized countries will follow, and that this new BASF/Elastogran technology will soon also be introduced all over the world.
La plupart des fabricands allemande de réfrigérateurs ont entre temps renoncé aux C.F.C. pour la production des parois d'isolation de leurs réfrigérateurs et les ont remplacés par le mélange d'hydrocarbures cyclopentane. L'auteur, manager d'une entreprise allemande defabrication de mousses rigides, esqisse plus particulièrement les problèmes de sécurité liés à cette substance et décrit les transformations qui s'avéreront nécessaires pour les installations de production.
La mayoría de los fabricantes alemanes de frigoríficos han dejado de utilizar CFC pare la producción de las paredes aisladoras, sustituyéndolo por ciclopentano que es un hidrocarburo ciclánico. El autor - gerente de una empresa alemana fabricante de espuma rígida - describe los problemas de seguridad en relación con dicho material e indica los pasos a seguir pare el reequipamiento necesario de las instalaciones de producción.
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