Process SystemsEngineering2003 B. Chenand A.W.Westerberg(editors) 9 2003 Publishedby ElsevierScienceB.V.
1460
TEACHING
CHEMICAL
PRODUCT DESIGN
G.D. Moggridge and E.L. Cussler*
University of Cambridge, Department of Chemical Engineering, Pembroke St, Sambridge CB2 3RA, UK. * University of Minnesota, Department of Chemical Engineering and Materials Science, Minneapolis, Minnesota 55455, USA.
ABSTRACT Chemical products depend for their function on a chemical or a chemical transformation and are usually of high value and manufactm'ed in low volumes, relative to commodity chemicals. In recent decades chemical products have started to play a much more prominent role in the chemical industry. Our teaching, however, remains concentrated on the commodity sector. We argue that university curricula need to be adapted to take account of changes in industry. We propose, in particular, that design teaching should take more account of the different requirements for designing chemical products. We propose a four step procedure as a template around which to organise ideas for designing chemical products.
INTRODUCTION The chemical industry has changed very rapidly over the past couple of decades. Calvin Cobb [1] has argued that this represents the latter stages of a long-wave Kondratieff cycle (the Automobile Era), typified by consolidation and mergers in an industry which has reached over-capacity after decades of rapid expansion. This makes the following words of P. V. Danckwerts in his presidential address to the Institution of Chemical Engineers in 1966 [2] as apt today as there were then: "'It would be a great mistake to think of the content of chemical engineering science as permanently foced. It is likely to alter greatly over the years, in response to the changing requirements of industry and to new scientific discoveries and ideas for their application."
CHANGES IN THE CHEMICAL INDUSTRY We examine synthetic fibres as an exemplar for the evolution of the chemical industry since the Second World War. From 1950 to 1970 increasing quantities of synthetic textile fibres were manufactured (see Table 1); while the production of natural fibres remained roughly constant, the production of synthetics grew by 20% per year. This growth rate is similar to that of the software industry today. Du Pont can be seen as the Microsoft of the 1950s. This was a golden age for chemicals.
1461
Cotton,
1948
1969
1989
4353
4285
4794
3480
8612
wool Synthetics .
.
92 .
.
.
.
.
Table 1 Growth of Textile Fibres From 1950 to 1970 synthetic fibre production grew about 20% per year. Since then growth has been 5% per year [3].
From 1970 to 1990, synthetic textile fibre production grew by less than 5% per year, about the same rate as the growth of the world population. From 1970 to 1990, the industry maintained profitability by using larger and larger facilities. Bigger profits came from consolidating production into bigger plants, designed for greater efficiency in making one particular product. Interest in computer-optimised design was a consequence of this consolidation. Such optimisation meant small producers were forced out. For example, the number of companies making vinyl chloride shrank from twelve in 1964 to only six in 1972 [2]. This trend continues. Having exhausted optimisation and restructuring as ways to stay profitable, chemical companies now have three remaining options. First, they can leave the chemical business. This option seems reasonable to a surprising number, including many petrochemical businesses. Second, chemical companies can focus exclusively on commodities. This seems a preferred strategy for some private companies, who may be better able to handle the ebb and flow of a commodity business. It implies a ruthless minimisation of research and focus on in-house efficiency. The third strategy open to chemical companies is to focus their growth on chemical products. Such chemical products, produced in much smaller volumes than commodities, typically have much higher added value. These higher added values mean that more research and higher profits are possible. Not surprisingly, many chemical companies are turning their attention to chemical products. One example is ICI, the mainstay of the British chemical industry for almost a century, which recently divested almost its entire commodity business to focus on higher added value products.
WHAT RESPONSE IS APPROPRIATE IN EDUCATION? We would maintain that the basic skills needed by chemical engineers are diverse and have not altered dramatically, despite these rapid changes in the chemical industry. Again this echoes the words of Danckwerts: "[C]hemical engineering science should not become exclusively identified with the "rigorous" subjects ... [W]e should be ready to use science to solve any of the problems of chemical engineering, however ill-formulated they may be ... [We] should take every opportunity to emphasise the versatility which our training provides. "
Based on the above discussion we make three assertions: 1. That the strong and rewarding identification of chemical engineering with the petrochemicals and commodity chemicals industries has led to our concentration on the "rigorous" subjects.
1462 2. That, as Danckwerts suggested, the skills of chemical engineering are highly versatile and can be applied to a wide range of industries. 3. That in recent years high value added products have become more important to the chemical industry. Our conclusion is that we need to increase the emphasis on the design of chemical products in our teaching, in order to reflect the changing nature of the chemical industry and the types of jobs our students go on to do.
WHAT ARE CHEMICAL PRODUCTS? We define high added value chemical products essentially by contrast with commodity chemicals, which have for so long been the mainstay of the chemical industry. Chemical products are designed and manufactured to achieve a specific effect, in which the crucial element is a chemical or a chemical transformation. In contrast, commodity products are specified chemically, and sold into a highly competitive global market for a wide range of uses. For high value added chemical products, function is key. For commodities, price is key. These differences between chemical products and commodities imply important differences in the way they are designed. Because chemical products are defined by function, the design procedure must start earlier; we cannot decide how to make something until we have decided what to make. A chemical engineer involved in chemical product design must expect to participate in the identification of a market opportunity, the generation of possible solutions and the selection of a suitable product, in addition to making manufacturing decisions. This holistic approach to design is in sharp contrast to traditional process design, in which a specification is dictated to the chemical engineer who then optimizes a process. Product design involves participation at a much earlier stage of product development, usually in a multi-disciplinary team. Since high value added chemical products are normally produced in low volume, they are typically manufactured by batch processing, often in campaigns in generic equipment used for many different products. As a result, much traditional process design becomes irrelevant. Heat integration cannot be achieved if several different products are to be made in batch in the same vessel. Control will often be rudimentary. Because margins are high, process optimisation is rarely an issue. Instead, time to market is critical. Because products usually have a short market lifetime, being first in the marketplace represents a major advantage. Product design therefore emphasises speed, not optimisation.
THE PRODUCT DESIGN PROCEDURE We have been concerned that product design was not receiving careful thought by chemical engineers. As a result, we collected our thoughts in a book, Chemical Product Design [4]. In developing the book, we wanted to be independent of case studies of particular products. Case studies can have considerable value: the design of a high performance lithium battery can help in understanding product design, just as the design of a styrene plant can be instructive in learning about process design. However, we all
1463 need to seek an understanding in the context of a broader philosophy, a template around which we can organise our thinking. The product design procedure we propose is a simple, four step design scheme. Similar schemes are said to be used in companies such as Du Pont, Motorola, and W. L. Gore. The four steps are: 1) Needs. What needs should the product fill? 2) Ideas. What different products could fill this need? 3) Selection. Which ideas are the most promising? 4) Manufacture. How can we make the product and test it critically? In defining "needs", we must identify who our customers are, a marketing function, and convert their requirements into quantitative specifications, an engineering task. In generating "ideas" to satisfy these needs, we must remember the industrial consensus that we will need up to one hundred ideas to get one successful product. In the "selection" of the best ideas for development, we use both qualitative matrix screening techniques, another business idea, and order-of-magnitude calculations, not detailed but firmly rooted in traditional engineering. In "manufacture", we proceed roughly along the lines of conventional process design, but with greater emphasis on speed and less on detail. While this simple template has worked for us, we expect that each of us will continue to improve it, just as we improve our ideas of process design. To understand how this four step procedure works in practice it is useful to look at how it might be applied to four very different chemically-based products: an amine for scrubbing acid gases, a pollution-preventing ink, an electrode separator for high performance batteries, and a ventilator for a carefully insulated house. These four products may seem to have nothing in common. The amine is chemically well defined: a single chemical species capable of selectively reacting with sulphur oxides. The ink is a chemical mixture, which includes a pigment and a polydisperse polymer 'resin' amongst other ingredients. The electrode separator provides a safeguard against explosion if the battery accidentally shorts out, by physically isolating the anode from the cathode. The ventilator both provides fresh air and recovers the energy saved by insulating the house in the first place. What these products do have in common is the procedure by which they may be designed. In each case, we begin by defining what we need. Next, we think of ideas to meet this need. We then select the best of these ideas. Finally, we decide what the product should look like and how it should be manufactured. We define chemical product design as this entire procedure. At the start of the procedure, when we are deciding what the product should do, we expect major input from both marketing and research, as well as from engineering. By the end of the procedure, when we are focused on the manufacturing process, we expect a reduced role for marketing, and a major effort from engineering. However, we believe that the entire effort is best viewed as a whole, carried out by integrated teams drawn from marketing, research and engineering. For the pollution preventing ink, our need is to reduce emissions of volatile solvents in the ink by 90%. Our ideas to meet this need include reformulating the polymer resin in the ink in two different ways. First, by using a polydisperse resin of broader molecular weight
1464 distribution, we can eliminate the need for volatile solvents in the ink itself. Thus there will be no emissions during printing. Second, by adding pendant carboxylic acid groups to the resin, we can make the resin not only an effective component of the ink but also an emulsifying agent in dilute base. If we wash the presses with dilute base, we can clean them without volatile solvents and without solvent-soaked shop rags. The manufacture of the new ink will be very similar to that used for the existing ink. Now consider the amine for scrubbing acid gases. Current acid gas treating often uses aqueous solutions of amines, like diethanolamine. After these solutions absorb acid gases like carbon dioxide and sulphur oxides, they are regenerated by heating. Though this heating gives an efficient regeneration, it can be expensive. The need is for amines that can be more easily regenerated. Our idea is to effect the regeneration with changes in pressure. We would absorb the acid gases at high pressure and regenerate the amines at low pressure, where the acid gases just bubble out of solution. In order to achieve this, we have little idea how to proceed, so we are forced to synthesise small amounts of a large number of sterically hindered amines. We will test all candidates to find the best ones. We will then manufacture the winners. Like many high value-added chemicals, these will be custom syntheses, made in batches in equipment used for a wide variety of products. This obviates the need for intensive process design in many of the chemical products which we are considering. The need for an electrode separator in lithium batteries arises from the increasingly high power densities achieved in modern batteries. They are small bombs which can be triggered by a dead short between anode and cathode. The need is to avoid explosion when the liquid in the battery boils due to being heated by such a short between the electrodes. Ideas on how to achieve this include efficient heat exchangers, using a dry cell, installing a blow out safety valve and increasing the separation between the electrodes. These are however rejected in favour of producing a self sealing polymer membrane separating the electrodes. This has holes in it and under normal operating conditions allows the free flow of electrolyte. However it has been pre-stressed such that on heating the holes close up and contact between the electrodes is broken. Here we have an example of a chemical product which is determined by its microstructure - the holes and the pre-stressing - rather than its chemical composition (many different polymers would be effective) Our final example of product design is house ventilation. Well insulated houses are energy efficient, costing little to heat, but they can exchange air at one tenth or less of the recommended rate. To get more flesh air, we can open a window, but this sacrifices our efforts at good insulation. The need is for a fresh air exchanger that captures the heat and humidity of our snug house, but exhausts stale air, with smells and carbon dioxide. Our idea is for an exchanger for both heat and water vapour for this energy efficient house. We can manufacture this in the same way as other low cost, cross flow heat exchangers. In this case our product is a device - not a chemical - that increases health and comfort in the house. Here we have four diverse examples of chemical products, all of which can be designed using the same four step procedure. We can identify three broad categories of chemical product; speciality chemicals, such as the amine; products whole function depend critically on their microstructure, like the electrode separator; and chemical devices, such as the house ventilator.
1465 CONCLUSION We believe that chemical product design merits increased emphasis because of major changes which have occurred in the chemical industry. We do not argue that the chemical engineer's concern with process design should disappear. Nor do we argue that most of the core curriculum of chemical engineering courses has become redundant. On the contrary we believe that the skills of chemical engineers are highly versatile and can be applied to the problems of designing chemical products as effectively as they have for so long been applied to chemical processes. What we do suggest is that we need to increase the emphasis on chemical products in our teaching of design. This implies an increased emphasis on speed over "rigour" in design, since getting a product to market is key rather than optimising the process for its production.
REFERENCES
[ 1]
C.B. Cobb, Chemical Engineering Progress (Feb 2001) 69-74.
[2]
P.V. Danckwerts, The Chemical Engineer (July/August 1966)155-159.
[3]
P. Spitz, Petrochemicals: the Rise of an Industry, Wiley, New York, 1988.
[4]
E.L. Cussler and G.D. Moggridge, Chemical Product Design, CUP 2001.