Professor Ken Toyokura: International Scientist, Sensei, and Friend

Piotr H. Karpinski
Eastman Kodak Company, Rochester, NY, USA

　　The International Symposium on Industrial Crystallization held at WASEDA University in Tokyo, 17 - 18 September, 1998 was intended to give an Overview of the Present Status for the 21st Century. This event was unique and impressive for many participants since it also brought back the numerous activities in this field during there decades, which today can be regarded as milestones in the development of crystallization to an important, world -wide industrially applied Separation Process.

　　Professor Ken Toyokura’s contribution to industrial crystallization was notably accompanied by building up world-wide contacts with both academic and industrial researchers. It is neither the objective of this short manuscript to make a historical review nor to repeat what was said and reported by his friends to honor the results of his work and particular efforts to overcome the complex problems of crystallizer design.

　　Almost thirty years ago, on April 15./ 16. 1969 a Symposium on Industrial Crystallization was organized by the Institution of Chemical Engineers at the Royal Society in London. In the same year at the general assembly of the EFCE in September the Working Party on Crystallization received final approval. The delegates of the WPC represented more than 20 countries, among them also Japan (!). At about the same time Professor Ken Toyokura had “nucleated” a small Working Party in Japan, which developed the exchange of experience between scientists and industry in the county about brought them abroad.

　　From the papers which were presented at the ACHEMA in 1970 the following three dealt with the design of industrial crystallizers:

　　The present status of crystallization from suspension was demonstrated by Professor J.M.Mullin in a covering lecture on “Laboratory Studies and the Design of Industrial Crystallizers”. The problems encountered in the design of industrial crystallizers were discussed and techniques were described for measuring basic data. Nucleation kinetics could be determined by using simple cooling methods for lab tests. Various crystal growth rate measurements were shown to be useful for the prediction of crystal habit modification from face growth velocities and for overall mass deposition rates for crystallizer design. In the conclusions it was noted that the role of laboratory studies as an aid to the measurement of crystallizer design data had been neglected in the past. Much more could be done to gather basic data on small scale apparatus in the laboratory. Of particular importance to the further development and research activities in crystallization was the last conclusion, will became a milestone in marking progress, the outlook to be able to design crystallizers from basic principles and avoiding scale-up from pilot plant tests.

　　This last conclusion was the idea which developed into a challenging task for Professor Ken Toyokura. In the following new methods for crystallizer design were proposed, that were suitable to overcome the scale-up problems which could not be solved by the criteria of hydraulic similarity (kinematic and dynamic) and maintaining the same geometry (shape) of the crystallizer.

　　Another paper came from Japan and was written by S. Saitoh, T. Imura and K. Kodama about a “Continuos Purifier by Crystallization“, it may be one of the most hopeful apparatus for separation of mixtures (of organic compounds) which have almost the same boiling points or high boiling points and when a product of high purity is required. The mechanism of this apparatus seems to be very similar to that a distillation tower by combining a recrystallization tower with a mechanically agitated counter-current washing column.

　　A different approach for solving the same problem was presented by A. Mutzenberg and K. Saxer who described a new process: Separation is achieved by means of a semi-continuous process where crystals and motherliquor formed by partial crystallization flow in counter-current.

　　This was the status at the end of the sixties and the outlook for starting into the seventies.

　　At the 5th Symposium on Industrial Crystallization (1972) in Prague the results of Professor Ken Toyokura’s “international driving force” became clearly visible: 4 papers on industrial crystallization were presented by various authors, 2 papers dealt with crystallizer design from test data and pilot plant results. The new methods to design continuous crystallizers were based on new dimensionless factors and characteristic factors of crystallization (C.F.C.) which are convenient for scale-up. The new factors as defined for individual types of crystallizers were obtained from dimensionless concentration and dimensionless crystal size, independent from the system, the absolute size of product crystals and any other factors. Two kinds of ideal crystallizer types were of particular interest: the conveying bed (like DTB crystallizer) and the well mixed bed (like a stirred tank). A number of other contributions on these topics can be observed in literature around that time, marking the design of the continuous classified bed type crystallizer (Krystal-Oslo).

　　Few years later at the 6th Symposium on Industrial Crystallization (1975) in Usti nad Labem the famous design chart was proposed to simplify the practical approach from the new design theories. Since Professor Ken Toyokura was frequently visiting his friends at universities and in industry in Europe he gave us the unique opportunity to fruitful discussions, exchange of experience and a better understanding of the complexity involved in the application of the design theories.

　　This year from 12 to 16 September the 14th Symposium on Industrial Crystallization will be at Cambridge University, UK and we look very much forward to meet Professor Ken Toyokura again, our Japanese friends and to continuation of the international exchange of experience between universities and industry in the successful applications of crystallization as a industrial Separation Process.

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The Spirit of Sakura

Elzbieta Karpinski

　　In August 1977, I arrived in Tokyo, joining my husband, Piotr karpinski, who was a recipient of a fellowship at Waseda University. Our two very young children, Michal, aged 3 and Zuzanka, aged 2, came with me. All I knew about Japan at my arrival was cherry blossom, kimono, green tea, chopsticks, and extreme sophistication, though entirely mysterious. During my first days in Tsurukawa, Machida-shi, where my husband was renting a small apartment, the Japanese mystery did not become any clearer, but my knowledge of the country become richer due to the warmest, never before experienced hospitality offered by Professor Ken Toyokura and his family.

　　In our native country, Poland, one may always count on the warmth and generosity of one’s closest family or intimate friends. Bosses, work cohorts or acquaintances are never thought to bring help, invite one to dinner, or be interested in one’s well-being. I was almost overwhelmed by the interest Professor Toyokura and his wife manifested in making sure that all of us stayed well, comfortable, and content. They went as far as to talk to our neighbors, seeing to that we had good company. I was only twenty six at that time, but I had some experience of living in countries different than my homeland; nevertheless, the sensation of comfort and affectionate protection was incomparable with any of my other foreign adventures before or after my stay in Japan. Professor Toyokura and his wife Hiroko invited us to their home repetitiously, taught me some secrets of their most refined cuisine, took us on New Year visits, patiently explained the aspects of the Japanese social life, offered a weekend in a most elegant resort, and more and more; the list is too long to itemize. They never showed us the slightest sign of annoyance or discouragement, and although we were not the only scholar family under their care, they made us feel very special, like members of their immediate family.

　　Twenty years have passed since that all too brief year, spent in the most beautiful country in the world, which I left in tears and with a mourning scar in my heart. Yet, thanks to Professor Toyokura and his family, our bond with Japan has remained alive. We had an honor to see them in our humble dwelling, recalling the best year of my lifetime in hopes of many years of continuing friendship.