TOKYO GAS TOP > Technical development > For the stable production of city gas > New Environmental-Friendly CFC-Free Insulation

New Environmental-Friendly CFC-Free Insulation


Facilities that handle very low temperature fluids such as LNG and liquid nitrogen are insulated with hard polyurethane foam (PUF), which is manufactured using HCFC-141b hydro-chlorofluorocarbon. However, with regard to chlorofluorocarbons (CFCs), which the global community has placed stringent regulations upon due to the fact that they strongly contribute to the greenhouse effect through their harmful impact upon the ozone layer, Tokyo Gas made the decision to avoid using them whenever possible.

Subsequently, Tokyo Gas developed a new type of environmentally-friendly insulation that has since been widely adopted which uses carbon dioxide as a foaming agent instead of CFCs. This insulation is still compatible with existing equipment, and it performs as well as conventional insulation in terms of cost, delivery time, time required for installation, etc.

Development of CO2-foamed PUF to assist phase-out of CFCs

The main ingredients of PUF are polyol and polyisocyanate, from which a high-polymer polyurethane is generated by addition polymerization. When CFC is used as a foaming agent, the heat of reaction from the generation of urethane resin causes the CFC to evaporate, foaming and hardening the PUF.
When water is added instead of CFC, on the other hand, carbon dioxide is generated by the reaction of water and polyisocyanate. This phenomenon is used to obtain CO2-foamed PUF. Some of the urethane resin is also bonded by urea bonds generated at this time.
As carbon dioxide has a higher thermal conductivity than CFC and the urea bonds generated when carbon dioxide gas is generated are less flexible than the urethane bonds, it was hard to obtain good PUF by this method. In order to produce CO2-foamed PUF of sufficient quality for practical use, therefore, we proceeded by studying combinations of types and quantities of the principal ingredients (polysol and polyisocyanate) and various additives in order to improve the physical properties of the end product.
Difference between foaming reactions
Previous insulation
(HCFC-141b-blown PUF)
New insulation (CO2-blown PUF)

Insulation Performance

PUF contains countless fine closed cells. In order to lower the thermal conductivity of CO2-blown PUF, it is necessary to reduce the level of heat radiation between these cells and make the cells smaller. By researching and adjusting the combination of mainly undiluted polyurethane solution with other ingredients, the cellular diameter of CO2-blown PUF was approximately halved compared with conventional insulation, and the new insulator satisfies the thermal conductivity requirements laid down in the Japan Gas Association’s “Recommended Practice for LNG In-Ground Storage.” The new PUF’s tensile, compressive, shear, and bending strength and creep characteristics are also on a par with those of conventional insulator, is adopted not only by Tokyo Gas, but also in the gas industry in Japan.
Thermal conductivity of new insulator


PUF seen under an electron microscope
Previous insulation ( HCFC-141b-blown PUF ) New insulation (CO2-blown PUF)

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