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IN THE LATE 1980s, the chemicals industry faced an unprecedented challenge. Environmental alarm over the apparent depletion of the ozone layer brought demands for a ban on the use of chlorofluorocarbons. An international agreement in 1987, the Montreal Protocol, ratified these concerns and called for cuts in the production of CFCs that gave the industry very little time in which to develop safe, effective replacements. The protocol demanded a freeze in the production and consumption of CFCs at 1986 levels by 1990; a reduction to 80 per cent of those levels by 1994; and a reduction to 50 per cent of the levels by 1999. (It also wanted a freeze in the production and consumption of halons at 1986 levels from 1992.) The task seemed impossible.

CFCs have been around for more than 50 years, and manufacturers have come to rely on them, designing and perfecting their appliances around the continuing use of these chemicals. CFCs make ideal refrigerants for homes and industry, solvents for cleaning and sterilising and blowing agents for insulation foam. Sales of CFCs worldwide now total about Pounds sterling 1 billion a year.

The Montreal Protocol challenged the chemicals industry – and the appliances manufacturers it serves – to telescope decades of experience into a few years: by 1991, the first replacements for CFCs had to be ready to use. Next week in London, Britain hosts a conference for the United Nations Environment Programme at which international working groups will prepare the ground for a revision of the 1987 protocol. The occasion provides industrialists with the opportunity to highlight the difficulties they faced with the last agreement and likely problems if new demands are even more ambitious. Recommendations from the working groups will form the agenda for the ‘Second meeting of the parties to the Montreal Protocol on substances that deplete the ozone layer’, which follows from 27 to 29 June. At this meeting, national delegations led by environment ministers will gather in sessions to negotiate the terms of a new agreement. They will also discuss ways of encouraging more countries to sign the protocol and methods of financing their proposals.

It usually takes the chemicals industry between 7 and 10 years to bring a new product onto the market. A chemist first identifies the class of compound that would meet the technical needs of the customer, and a series of evaluation tests follow one another logically. Toxicologists assess the health hazards and then, if there are no problems, the customers consider whether the compounds are likely to yield the products they want. Development chemists in the laboratory and process and mechanical engineers then begin to devise the best way of making the compounds, while scientists investigate their potential impact on the environment.

As confidence in the product grows, industry invests more money in the project and scaled-down versions of the production plant are built. These may cost several million pounds, but they help the engineers to improve their design and they provide samples for customers to develop their appliances and for more toxicological testing. The final stage involves completing the design, gaining planning permission, building and commissioning the plant.

Clearly, there was no time for this standard approach in developing alternatives to CFCs. Industry had to run the evaluation tests and programmes in parallel, collaborate more than is usual and make the most of the research that began in the late 1970s. (This research was a response to the widespread concern that followed publication in 1974 of studies by Sherwood Rowland, professor of chemistry at the University of California: he linked CFCs to a depletion of stratospheric ozone. The research became a low priority, however, as those early fears subsided substantially because of the lack of evidence. Then, in 1985, Joe Farman of the British Antarctic Survey published evidence of a ‘hole’ in the ozone layer over Antarctica.)

At ICI, after the Montreal Protocol, we established a large team of engineers and chemists to work closely together on the new compounds’ safety, suitability and production. The team is more than 100 strong and adds between Pounds sterling 50 million and Pounds sterling 100 million to the company’s research budget. It meets tight deadlines by setting priorities and by good communication. Energy and commitment are essential among its members. These front-line scientists and technologists must also integrate into their studies work being done by other teams at ICI on special aspects of the project. The support groups, for example, provide information on the physical properties of the new compounds and data on vapour/liquid equilibrium (VLE) characteristics that are essential for designing the production plant. They assess the materials that appliances using the new compounds will be made of and they design and build experimental rigs to see how these modified appliances will perform.

One of the most pressing problems was in recruiting and training sufficient numbers of staff quickly to become effective working members of the team. During the first 18 months of the project, we had to increase the number of chemists in the team from 10 to 60 and the number of process engineers by a similar ratio. As the project nears completion, we need to integrate many more different disciplines into the team, including control, mechanical and design engineers.

The early research, started in the 1970s, gave the project a head start. Several chemicals companies identified hydrofluoroalkanes (HFAs), often referred to as hydrofluorocarbons (HFCs), and hydrochlorofluorocarbons (HCFCs) as classes of compounds that showed the most promise as alternatives to CFCs. In these, hydrogen replaces all or some of the chlorine, which is the element implicated in a complex set of theoretical chemical reactions in the stratosphere that could lead to the depletion of the ozone layer. ICI is concentrating on HFA-134a (CF₃CH₂F) as a replacement for CFC-12 (CF₂Cl₂), which is used as a refrigerant, and on HCFC-123 (CF3CHCl2), among others, as a replacement for CFC-11 (CFCl₃), which is used both as a refrigerant and as a blowing agent. ICI and other companies are also investigating HCFC-124 (CF₃CHFCl) and HFA-125 (CF₃CHF₂) as refrigerants. Last year, CFC-11 and CFC-12 represented 70 per cent of the total sales of CFCs.

To help to speed the project along, the chemicals industry set up two consortia. The Programme for Alternative Fluorocarbon Toxicity Testing, established in January 1988, enabled toxicological tests to begin. PAFT defined the method of testing, provided samples and oversaw the tests. The Alternative Fluorocarbons Environmental Acceptability Studies (AFEAS) consortium, established in November 1988, began investigating the likely impact of the new compounds after their release into the environment.

Of the alternatives that ICI is investigating, the most advanced at this stage is HFA-134a. A new production plant at Runcorn in Cheshire will begin to manufacture the compound commercially from the beginning of next year: the company has not publicised its capacity. Another plant will follow in the US to meet the cutbacks demanded in 1993.

The introduction of HFA-134a, to which ICI has given the trade name KLEA, will mirror that of CFC-12 in the 1930s. CFC-12 was not a simple ‘drop-in’ replacement for the refrigerants of the time: the industry had to modify its appliances. It did so willingly because CFC-12 was less toxic and less flammable than the existing refrigerants, such as sulphur dioxide, methyl chloride and ammonia.

The switch to HFA-134a dictates the need for extensive R&D programmes throughout the refrigeration and air conditioning industries to ensure that systems continue to have the reliability and performance that customers expect. Finding such replacements for all the CFCs is not always easy. Manufacturers of CFCs are having a lot of trouble trying to find a substitute for the solvent CFC-113 (CF₂ClCFCl₂). They have come up with several proposals but the perfect substitute is proving elusive. CFC-113 is extremely good at its job; it combines just the right level of cleaning power with other favourable physical properties, such as a convenient evaporation temperature. This makes it the most widely used solvent for cleaning intricate electronics components. Alternatives either have the ideal boiling point but are too strong and damage components, or they have the correct strength but do not evaporate at the temperature they need to.

Two of the key properties we had to consider for HFA-134a were its solubility in a lubricant and its stability. Refrigeration systems generally contain a refrigerant, in gas or liquid form, and a lubricant, mixed together. Refrigerant and lubricant do not have to be able to mix, but it is a considerable benefit. Solubility over broad ranges of temperature, pressure and composition helps to ensure, for instance, that the lubricant reaches the bearings of the compressor, which is the most hard worked component of a refrigeration system. Solubility also helps the lubricant to return to the compressor from the refrigeration system, rather than build up on the surfaces of the evaporator’s heat exchanger. As a result, many companies making refrigerators, freezers and air-conditioning systems have designed their equipment on the basis that the refrigerant and the lubricant stay mixed together.

Mineral oil is the traditional lubricant because it is cheap, and soluble in CFC-12 over a wide range of conditions. It is also available in a range of viscosities to match different applications. But mineral oil and HFA-134a do not mix at all. This is because HFA-134a molecules are more polar than those of CFC-12 – the distribution of electrons is more uneven, giving the HFA-134a molecules a greater unbalanced charge – which makes them less soluble in non-polar lubricants, such as mineral oil. The result was that we had to find a new lubricant, which in turn meant that our customers would have to consider whether their equipment needed modification. Clearly, in terms of tight timescales and stringent standards, the problems that the refrigeration and air-conditioning industries face are as challenging as those that we confront in supplying the new refrigerants.

Because the suppliers and users of alternatives to CFCs have common concerns, good communications between the two are essential. With this in mind, ICI set up a new laboratory to investigate the performance of modified appliances, even though the company is primarily a producer of refrigerants and lubricants. The aim is to provide equipment manufacturers with as much information as possible on the new chemicals. Researchers at the ICI laboratories study lubrication, the compatibility between the new refrigerant and the materials used to build the equipment, and the energy efficiency of the modified appliances.

Two of the first questions raised by the industry were whether HFA-134a is stable in appliances, and how its stability compares with CFC-12. From laboratory tests, researchers at ICI have found that HFA-134a is more stable than CFC-12. These so-called ‘sealed tube’ tests conform to the standards of the American Society of Heating, Refrigerating and Air Conditioning Engineers. Researchers used a stainless steel autoclave, which is capable of withstanding high pressures, and tested a mixture of equal parts lubricant and refrigerant, at a temperature of 175 Degree C for 14 days. This was done in the presence of copper, aluminium, iron and zinc, all metals typically used in refrigeration systems, that were insulated to prevent electrochemical corrosion.

Subsequent analysis confirmed the stability of HFA-134a in three ways. The composition of the refrigerant mixture did not change; in contrast, 0.1 per cent of CFC-12 in mineral oil decomposed to HCFC-22 (CHF₂Cl). The concentration of fluoride ions remained unchanged at less than 2 parts per million; in contrast, the concentration of chloride ions in a mixture of CFC-12 and mineral oil increased from 10ppm to 100ppm. Corrosion of the metal surfaces was below the detection limit of 0.01 millimetres per year and there was no dissolution and redeposition of copper on the other metal surfaces; in contrast, chlorides formed on the surfaces of the metal samples in the CFC-12/mineral oil mixture and there was copper plating.

Researchers also confirmed that HFA-134a does not react with two classes of material that they were evaluating as lubricants, polyalkylene glycols (PAGs) and esters. These are synthetic lubricants that operate best over different temperature ranges. ICI knows how to formulate and to manufacture these products for the petrochemicals industry but not yet for refrigeration systems, which have never used these lubricants. The overall balance of the lubricants’ properties (for example, their solubility in refrigerant, their compatibility with materials used to build components, the amount of water they absorb and their resistance to electrical currents) means that the choice of base stock, or main ingredient, and the formulation will vary between customers. Both PAGs and esters are being considered by the automotive air-conditioning industry and by domestic appliances manufacturers, which require different balances of lubricant properties.

As part of ICI’s continuing evaluation of both lubricants, the company built experimental rigs to test the performance of components of refrigeration systems, particularly the compressors. After testing, researchers stripped down the compressors and assessed them for wear. They then compared the results with those from compressors that used mixtures of CFC-12 and mineral oil.

At the same time, ICI is refining its understanding of lubrication in the new refrigeration systems by improving the diagnostic tests of the performance of a lubricant in operation. These tests include, for example, monitoring the lubrication of four metal balls in a sample, which simulates the performance of the lubricant in a compressor. The aim is to give chemists some idea of how they might improve the lubricant and to understand how the different metal bearings of a compressor are likely to perform.

More immediately, the company is monitoring how the new lubricants perform over the long term. This will determine how far different compressors have to be redesigned. Although the chemicals industry is confident that a suitable lubricant is in sight, work to improve the performance of lubricants will continue for some time.

Over the past couple of years, the chemicals industry has also been looking at the energy efficiency of systems, particularly domestic refrigerators, that will use new refrigerant gases. The aim is not simply to compare the efficiencies of CFC-12 and HFA-134a and to accept a poorer performance in existing equipment; it is to modify equipment to match the properties of the new refrigerants.

The chemical structure of HFA-134a enables the new refrigerant to transfer more heat than CFC-12 – between 30 and 40 per cent more. In the future, if manufacturers redesign the condenser and the evaporator of a refrigerator’s heat exchanger to take advantage of this characteristic, it should be possible to improve the machine’s overall performance.

As part of its own studies into energy efficiency, ICI is investigating how a lubricant’s properties, such as viscosity, miscibility, solubility and dispersibility in HFA-134a, affect performance. The industry has no doubt that refrigerators and freezers designed to use HFA-134a will not use any more electrical power than equivalent models running on CFC-12.

The new mixture’s effect on the materials used to build refrigeration systems will partly determine the reliability of the modified equipment. Manufacturers use a broad range of metals, plastics and elastomers, and these must be compatible with the new refrigerants and lubricants. Tests to ensure compatibility are similar to those used to assess the mixture’s stability, though at temperatures appropriate to the particular materials. For plastics and elastomers, the properties of interest are changes in volume, both swelling and shrinking, tensile strength and hardness. The important properties for metals are rates of corrosion and surface changes.

From ‘sealed-tube’ tests in the laboratory, researchers can compare results with those obtained from tests of the same materials in a mixture of mineral oil and CFC-12. This will give them an idea of the modified equipment’s reliability, which they are refining with data from simulations of the product’s life. In the laboratories at ICI, researchers are testing both PAG and ester lubricants on a wide range of materials and sharing these results with appliances manufacturers.

The phasing out of CFCs has meant a period of rapid change for the chemicals, refrigeration and air conditioning industries, and indeed all users of these ubiquitous chemicals. One solution will be HFA-134a, which is gaining wide acceptance as the appropriate replacement for CFC-12 in domestic refrigerators and air conditioning systems for vehicles. The industry is sure that the refrigerators and freezers designed for HFA-134a will be as efficient as their predecessors – not a bad record for three years’ work.

Hugo Steven and Andy Lindley work for ICI as industrial chemists. Steven heads the research team that is formulating and developing alternatives to CFCs. Lindley, a member of that team, assesses whether the potential substitutes are practical.