CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 5 879-880
Communications Is Melt Crystallization a Green Technology? Joachim Ulrich Martin-Luther-Universita¨ t Halle-Wittenberg, Fachbereich Ingenieurwissenschaften, Institut fu¨ r Verfahrenstechnik/TVT, D-06099 Halle (Saale), Germany Received December 1, 2003
ABSTRACT: The question of whether melt crystallization is a green technology is discussed. Besides an evaluation of technical reasons, examples from studies concerning the energy consumption in chemical industries in The Netherlands are used as arguments. Conclusions are as follows: (i) there are definitely positive indications that melt crystallization can be considered a green technology. (ii) Frame conditions by the society have a very strong influence on acceptance of a technology as a green technology. The question of what constitutes a green technology and whether melt crystallization can be considered as such a technology is raised again and again. To begin, there has to be an answer to the question of how green technology is defined. The following definition given here is certainly just an attempt; however, it should remain the basis for followup discussion: A green technology defines a production with the least intake of resources while simultaneously avoiding hazardous chemicals and technical risks. On the basis of this definition, the following features of a green separation process can be named: (i) low energy consumption (ii) no or little solid waste or waste liquid/gases (iii) no solvents (organic) - process liquids (iv) no recover treatment (v) no hazardous process materials (vi) no gas phase (vii) small size (volume) of equipment (viii) high selectivities Melt crystallization, in one way or another, offers all the above named features (according to, e.g., refs 1-4). In other words, melt crystallization is more than just a technology to help overcome separation or purification problems that cannot be carried out with sufficient quality by distillation or extraction, for example. The comparison of costs required is not easily possible, since political boundary conditions and local constraints do not allow such a “real” comparison. Therefore, a comparison of material and energy consumption costs as well as equipment costs is only possible if everything is transferred to some universal unit such as CO2 emission. Again, this is only a suggestion and would be an extreme effort to implement. The advantage of melt crystallization processes is clarified by looking at the energy consumption of a melt crystallization separation process, as shown in the data (Figures 1 and 2) of Ulrich et al.5 and Matsuoka et al.,6 which show the melting points of 4773 organic compounds and the type of phase diagrams of organic two-component
Figure 1. Distribution of melting points according to Ulrich, Glade, and Lu,5 based on the chemistry data bank of Merck, Germany.
Figure 2. Typical phase diagram types of binary organic systems, according to Matsuoka6 and data form ICT.
mixtures, respectively. The advantage is in the low temperature level required and the high purity (achievable) in one step (in the case of eutectic mixtures).
10.1021/cg0300432 CCC: $27.50 © 2004 American Chemical Society Published on Web 07/22/2004
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Communications
Table 1. Study of TNOa for The Netherlandsb
(iii) low energy consumption (iv) no solvents There are therefore, according to the definition given above, clear aspects of a “green” technology to be seen in the technology of melt crystallization. As a second conclusion two other statements have to be made: (i) The quality of the achieved product is primarily related to the use of a certain technology. (ii) The acceptance by society, the price of energy, and the policy toward waste determine the further use of a technology. In the end, despite all ideal definitions of green technologies with hypothetical measures for a comparison of resources, the question remains whether the real-life definition of a green technology is not given by the two last points stated in the second conclusion.
energy savings
a
component
(GJ/ton)
(%)
caprolactam phenol dimethylterephthalate
0.57 2.35 4.64
50 63 96
See refs 8 and 9. b Based on data of 1989.
Table 2. Energy Savings in One Crystallization Step Compared to Distillation component
energy savings (%)
benzene styrene
27 32
The energy advantage, however, only exists if the separation requires only one or, in some cases, two separation steps. In any other case, the advantages may be lost as shown by Wintermantel and Wellinghoff et al.7 Possible energy savings have been put in numbers for some compounds by Arkenbout et al.8 and de Goede9 as shown in Tables 1 and 2. According to these data, the total production capacities of bulk organics and organic fine chemicals in The Netherlands (general acceptance of melt crystallization technology) could lead to a total energy savings of 2.7 × 1015 J/year. There are also of course “nongreen” properties of melt crystallization, e.g.,: (i) Many processes are batch processes: They (a) need heating and cooling of product and equipment, and (b) need large size of equipment. (ii) Process temperatures below ambient conditions need a large amount of energy. As a first conclusion, it can therefore be stated: Melt crystallization has positive aspects in all of the following points: (i) high selectivity w pure products (ii) no gaseous phase, no recovery of solvents
References (1) Arkenbout, G. J. Melt Crystallization Technology; TECHNOMIC Publishing Company, Inc.: Lancaster, PA, 1995. (2) Mullin, J. W. Crystallization, 3rd ed.; Butterworth: London, 1993. (3) Rittner, S.; Steiner, R. Chem. Ing. Technol. 1985, 57, 91102. (4) Ulrich, J. In Handbook of Industrial Crystallization, 2nd ed.; Myerson, A. S., Ed.; Butterworth-Heinemann: Stoneham, 2002; pp 161-177. (5) Ulrich, J.; Glade, H.; Lu, J. Internal Report, Martin-LutherUniversity Halle-Wittenberg, Halle, Germany, 2000. (6) Matsuoka, M. Bunri Gijutsu 1977, 7, 245-249. (7) Wintermantel, K.; Wellinghoff, G. In Proceedings of the 11th Symposium on Industrial Crystallization; Mersmann, A., Ed.; 1990; pp 703-708. (8) Verdoes, D.; Arkenbout, G. J.; Bruinsma, O. S. L.; Koutsoukos, P. G.; Ulrich, J. Appl. Therm. Eng. 17 1997, 8-10, 879-888. (9) de Goede, R. Energy Effic. Process Technol. 1993, 1-14.
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