Ind. Eng. Chem. Prod. Res. Dev. 1982, 27, 139-141
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SYMPOSIA SECTION
I . Symposium on Plastics for the 1980's R. D. Deanin, Chairman 181st National Meeting of the American Chemical Society Atlanta, Georgia, March 198 1
Novel Process for the ProductSon of Particulate Phenolic Resins Alba M. Reglna-Mazzuca,' W. Fong Ark, and Thomas R. Jones Union Carbkle Corporatlon, Coetlngs Materiels Dlvlsbn, Bound Brook, New Jersey 08805
A new process has been developed for produclng both thermosetting and thermoplastic phenolic powders. Based on proprietary Union Carbide technology, the process employs suspension polymerization to produce particles of the desired size. This process offers substantial reductions In energy coqsumption relative to conventional phenolic resin processes. The product is separated from the suspension and byproduct water by filtration, eliminating the energy intenshre batch distillation. Further energy savings are realized in eliminating the grirtdlng operation normally used to produce phenolic powders. The full range of conventional thermosetting and thermoplastic phenolic resins can be produced by this process. The process, from raw materials to dry powder, has been demonstrated in an integrated manufacturing facility.
Introduction The methods currently employed to produce phenolic resins are based on technology much of which was developed over 70 years ago when the commercial value of these phenol/formaldehyde products was first recognized (Brode, 1980). Since then, the demand for phenolics has grown in both volume and diversity. By varying formulation and processing conditions, a wide variety of physical properties are obtained, resulting in a broad range of applications. Depending on the exact manufacturing process used in the application, a phenolic resole (thermoset); a phenolic novolak (thermoplastic), or a combination is required in the form of a liquid, a solution, or a dry powder. Dry phenolic powders are used in a wide variety of applications, including waferboard, fiberbonding, foundry, friction materials, and molding materials. Conventional technology for their production involves bulk polymerization and resin solidification, followed by pulverization of the bulk resin. At Union Carbide, novel technology has been developed which employs suspension polymerization to produce both thermosetting and thermoplastic phenolic powders. These products represent a unique new class of phenolic resins known as phenolic thermospheres (PTS). The chemistry of PTS is presented elsewhere (Brode et al., 1981). This paper focuses on this novel process technology and its advantages over the conventional technology. PTS resins differ from conventional phenolics both in manufacturing technology and in pysicochemical characteristics. As a result, PTS technology offers both manufacturing cost savings and improved performance in certain applications. A broad-based patent containing both product and process claims has been granted to UCC. 0196-4321/82/1221-0139$01.25/0
Several foreign patents have also been granted on this technology. Although PTS was originally developed as replacement technology for conventional solid resoles, recent work has demonstrated that novolak resins can also be produced by the PTS process. Because PTS resole technology is essentially ready for commercialization, whereas novolak technology is just entering the pilot plant stage, this paper will focus on resoles unless otherwise indicated. A large-scale pilot plant for PTS resins manufacture has been operating since October, 1978. This unit has been used for process verification and production of market development quantities of material. The unit, which has a capacity of 750M to 1MM lb/yr, has been used to support customer trials requiring truckload quantities. Shown in Figure 1 is a comparison of conventional and PTS resole processes. The conventional one-step process consists of bulk reaction followed by dehydration in the same reactor. The dehydrated molten resin is then discharged to resin coolers, broken out into resin pans, and ultimately pulverized to the desired particle size. These manufacturing steps, particularly downstream of dehydration, are heavily labor intensive and involve considerable amounts of manual operation. In contrast, the PTS resin process consists of an aqueous suspension polymerization follwed by solid-liquid separation, drying, and a low-energy deagglomeration step. Two aspects of the PTS process are particularly noteworthy. First, all processing downstream of the batch suspension polymerization is continuous, thereby eliminating the manual labor associated with the conventional process. Second, particles of the desired size are actually 0 1982 American Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982 CONVENTIONAL RESOLE PROCESS
BULK REACTION
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DEHYDRATION
RESIN PANS
PRODUCT
PULVERIZATION
CONVENTIONAL PULVERIZED RESINS
2 5
P T S PROCESS
1
SUSPENSION POLYMERIZATION
t-1
SOLID/LIOUID SEPARATION
+I
0
DRYING
20
40
60
80
100
PARTICLE SIZE (MICRONS)
Figure 2. Comparison of particle size distributions of PTS and pulverized resins. PRODUCT
Figure 1. Comparison of processes. Table I. PTS Resins vs. Conventional Resoles conventional resoles PTS resins heat reactive heat reactive phenol-formaldehyde phenol-formaldehyde condensation polymers condensation polymers solid chunks free-flowing powder very uniform improved sinter and moisture
resistance
highly nonuniform highly sinterable
formed in the reaction stage and carried through the entire process as individual spheres.
Why PTS Resins? PTS resin technology offers many important advantages over conventional pulverized resins technology. Not only are the physicochemical properties of PTS resins superior to those of conventional resins, but also the PTS process allows excellent control and reproducibility of these properties. Furthermore, operating costs are significantly lower for the PTS process due to semicontinuous operation, shorter batch cycles, and reduced energy and labor requirements. Finally, the PTS process offers broad manufacturing flexibility in both product variety and reactor size. Physicochemical Properties The physicochemical properties of PTS and conventional one-step resins are compared in Table I. Both are phenol/formaldehyde condensation polymers and both are heat-reactive. However, the physical characteristics of the two materials are quite different from one another. Conventional one-steps are recovered in solid blocks or chunks and are, in general, highly nonuniform. PTS resins, on the other hand, are recovered as a free-flowing powder. Because of the nature of the process, the material is very uniform. Conventional resoles are highly sinterable, i.e., quite sensitive to temperature, pressure, and moisture. Few conventional phenolic reactive powders can be stored and handled without first incorporating anti-sintering agents and/or flow promoters. This is, however, a viable possibility for PTS resins because, due to their improved sinter and moisture resistance, they are easier to store and handle.
PTS Process Development As previously mentioned, the PTS process has been demonstrated in an integrated pilot plant facility. Hundreds of batches have been successfully processed in this pilot plant to provide material for customer field trials and to obtain data for process optimization and scale-up criteria. Several challenging engineering problems were encountered in the development program. In particular, due to difficulties in handling lower molecular weight resins, the solids recovery system required a substantial development program. As in many new processes, it was necessary not only to install a workable pilot plant system but also to develop an understanding of the important process parameters in order to optimize process conditions and to determine scale-up criteria. In defining these criteria, mathematical models were developed for the reaction step, the solid-liquid separation step, and the drying step. We shall not present these models here but rather highlight the process features that help make PTS technology superior to conventional pulverized resins technology. Property Control and Reproducibility In the PTS resins process both particle size and resin molecular weight can be more precisely controlled than in the conventional resoles process. This control results in excellent batch to batch reproducibility and in the ability to easily vary these properties. Particle size distributions of a PTS resin and a typical pulverized resin are compared in Figure 2. The particle size distribution is considerably narrower for the phenolic thermospheres than for the pulverized product. Furthermore, the mean particle size can be easily controlled by adjusting the formulation and reaction conditions. In the conventional process, where particle size is determined by grinding conditions, it is much more difficult to control particle size and/or vary it at will. Since molecular weight is a critical property of phenolic resoles, the improvements in molecular weight control and uniformity resulting from the PTS process are quite valuable. PTS resoles having a wide range of properties can be produced in our pilot unit. Products having gel times from 0 to 130 s and plate flows from no flow to 100 mm have been produced successfully. Molecular weight is heavily dependent on the extent of reaction. In the PTS process, the reaction can be quenched rapidly, whereas the conventional process depends on
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 2, 1982 141
Table 11. Reducing Manufacturing Costs feature
PTS process
conventional pulverized phenolics process
particle formation water removal reaction product automation potential
suspension polymerization filtration low viscosity aqueous slurry amenable to computer control
pulverization by mechanical grinding batch distillation high viscosity molten bulk resin difficult to automate
cooling of a reacting viscous molten mass to control molecular weight. For the latter, this often produces material with a large variation in molecular weight even within a given batch. In contrast, batch-to-batch reproducibility is outstanding for PTS resins. Process Economics The operating costs of a phenolic thermosphere facility are significantly lower than for conventional phenolic processes because of substantial reductions in energy and labor requirements. Table I1 lists the main features of the PTS process which contribute to these savings. The most important factor is particle formation. In the novel process, the particulates are formed during the reaction. No additional energy is required for particle formation. By way of contrast, in the conventional process, the particles are formed by mechanical pulverization. Pulverizing is highly labor and energy intensive and therefore costly. The second significant source of cost reduction is the method of water removal. The novel process employs a simple mechanical separation step to remove the bulk of the water from the particulate phase. The conventional process, on the other hand, employs batch dehydration using additional heat for vaporizing the water. This is both energy and time consuming. In addition to these features, PTS resin is much easier to handle than the conventional resin. The novel reaction yields a slurry which is low in viscosity and can be cooled and transferred with little operator intervention. For conventional resole products, typical industrial practice is to cool the resin in pans or plate and frame coolers. The resin is then broken down into smaller chunks by manual labor, again an expensive operation. Because little operator intervention is needed in the novel process, it is amenable to computer control. Computer control results in further labor cost savings and improved uniformity. The combined reductions in energy and labor intensity of this novel process have a significant impact on the process economics. The cost of resole production is reduced by several cents per pound of product by the PTS process. This advantage obviously becomes increasingly
important as the costs of energy and labor continue to rise. Furthermore, investment studies comparing the novel and conventional processes favor the novel process. Overall, then, the economics of the PTS process are significantly better than for current conventional processes.
Manufacturing Flexibility The PTS process lends itself to possible manufacture of both resoles and novolaks in much larger reactors than the 25W5000 gal reactors presently used throughout most of the phenolics industry. Both novolaks and resoles could be produced in the same reactor. The major efforts on PTS technology to date have been directed toward products having properties similar to established conventional pulverized resins. However, preparation of a number of specialized resins has been demonstrated at the laboratory and/or pilot plant scales. These include filled PTS resins, for which a US. patent has been granted, PTS resins for waferboard, PTS friction particles, and PTS foundry resins. A strong patent position is anticipated in several of these areas. Summary In summary, phenolic thermosphere technology has been developed at Union Carbide for producing both thermosetting and thermoplastic phenolic powders. Phenolic thermospheres exhibit physical properties superior to those of conventional resoles, while the PTS process offers substantial operating cost savings, better reproducibility, and increased manufacturing flexibility. We believe PTS technology is new, unique, and may well be the process of the future for manufacture of solid phenolic resins. Literature Cited Erode, G. L. In "Kirk-Othmer Encyclopedia of Chemical Technology", 3rd ed.; Wiley: New York, 1981; Voi. 17. Erode. G. L.; Kopf, P. W.; Chow, S. W. Ind. Eng. Chem. Prod. Res. D e v . 1982, In press.
Received for review September 3, 1981 Accepted February 8, 1982 Presented at the 181st National Meeting of the American Chemical Society, Mar 29,1981, Division of Organic Coatings and Plastics Chemistry.
