-Plastics coated steel drums for carbon tetrachloride and U.S.P. glycol. Polyethylene is also used in the form of gaskets, bungs, and spouts for steel drums as well as bottles and carboys for corrosive chemicals. Teflon finds application aa a cap liner for bromine bottles. MISCELLANEOUS PLASTIC APPLICATIONS
Plastics in the form of industrial clothing and filter cloths woven from synthetic fibers provide chemical resistance to acids, alkalies, and the halogens. Experiments are being conducted with blow-out windows formed from high impact modified polystyrene. Styrofoam is used in the same way and poly(methy1 methacrylate) sheeting, in similar fashion, serves as protective shields. Vinyl plastisol is very effective in prolonging the service life of metal stair treads, decking, and grating in atmospheres containing a combination of acid and aromatic solvent vapors. The modification of concrete with styrene-butadiene latex results in greater acid resistance and is used in the construction of electrolytic cells, pump bases, and gutters. For some time now the excellent durability of the vinyltoluene and styrene modified drying oils and alkyds has been utilized in exterior maintenance paints to obtain resistance to chemical plant atmosphere. Protective coatings based on rubber hydrochloride and the vinyl resins are also very good for this application.
,
I
CONCLUSION
The cost of a plastic material is obviously a major consideration in arriving at its use. Further, it is well known and generally accepted that price will largely determine the volume of a product which will be consumed. Therefore, one should be able to arrive a t some semiquantitative relationships ( 2 ) by use of available statistical information. In Figure 12 an industrial trend line has been drawn by plotting price per pound versus pounds consumed for a representative group of large volume industrial products. Similarly, a plastics trend line can be drawn using data for the
Construction Materials
major plastics families. Price-volume considerations of this sort are certainly subject to such factors as complexity of distribution before the product reaches the ultimate consumer, maturity of the development, availability of raw materials, and production limitations. Nonetheless, it is believed that the trend lines are sufficiently accurate to permit some useful generalizations. Plastics are relatively new materials as compared with the industrial products and have not reached their full utilization. Therefore, one can conclude from Figure 12 that, a t current prices, the consumption of plastics can be expected to grow until the industrial trend line is reached. Further growth will then require price decreases. If, on the other hand, the price per unit volume is plottedversus consumption, as shown in Figure 13, it immediately becomes apparent that the price of plastic materials is already competitive with many of the industrial products. Then, by continued emphasis on improving the performance of plastics on a unit volume basis, we can expect them to enjoy a substantial growth before reaching the industrial trend line and without further price decreases. This would appear to be a realistic conclusion since, for most of the plastic materials, major price decreases' do not seem likely in the foreseeable future. ACKNOWLEDGMENT
The author wishes to extend his appreciation to the various members of the production, waste disposal, and engineering departments of The Dow Chemical Co., as well as the plastics sales and technical service staffs who contributed the bulk of the information which is described here. LITERATURE CITED
(1) Chamberlin, R. S., Lake, D. E., and Dulmage, F. E., Dow Chemical Co., U. 9. Patent applied for.
(2) Roche, A. F., Jr., Ibid.,unpublished information, November 1951. R H I C ~ I Vfor E Dreview September 17, 1954.
ACCHIPTHID Marah 31, 1955.
Fine Chemicals Plants JOHN R. YOST, JR.', AND A. J. SARGENT Merck & Co., Inc., Rahway, N. J .
T
=
HE choice of materials of construction for fine chemicals manufacturing equipment is influenced by several factors. The usual process requires resistance to chemicals and solvents both of which are apt to be difficult to handle. Then, too, production schedules may require that certain units produce several products or intermediates; or equipment from a previous process may be incorporated into present installation. Also, the extreme variety of chemicals and solvents used and the versatility required of the equipment for its economic use impose many limitations on the initial choice of materials. There is the further factor which takes into consideration the corrosion of process equipment as a function of contamination of the product. Many times a construction material would be suitable, based on the expected life of that particular piece, but quality specifications on the product preclude its use. Engineers in the pharmaceutical industry have thus been in a unique position pertaining to the specification and selection of materials of construction. The high cost of raw materials and intermediates used to manufacture a product often minimizes the effect of choosing unusual and expensive materials. At the same 1 Present address, E. R. Pquibb & Sons Div. of Olin-Mathieson Gorp., New Brunswick, N. J.
July 1955
time, it is necessary to move with considerable speed to put a process into operation, and hence availability of construction materials is an important factor concerning their use. As a result, we have experimented with many of the newer materials available, particularly the many plastics recently introduced, in an effort to meet quality and process demands. These considerations have generally led to the use of glass-lined steel and stainless steel for major pieces of equipment. Even in this area, however, plastics have helped t o solve rough problems and are daily solving more. The greatest uses that the fine chemical industry has found for plastics and plastic materials have been as gaskets, packings, fittings, pipes. valves, ducts, filter cloths, and containers. It is in these uses that the inherent value of plastics is best utilizedtheir extreme adaptability as to shape and size, the range of hardness (and softness) of given materials, and their inertnessand often times a t a cost that permits throw away usage. Plastics in the pharmaceutical or fine chemical field, in addition to many of the already widely known common uses, provide a wide variety of application. For the purposes of this discussion, we have assumed four categories as representing the horizon of
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plaastics in our industry. These use categories may, in general, be broken down as follows: 1. Process equipment 2. Gaskets, packings, and bearings 3. Piping and valves 4. Special applications as: a. Coatings and duct work b. Filter media c. Containers d. Miscellaneous applications PROCESS EQUIPMENT
Process equipment constructed of plastics, as such, does not have a large place in the fine chemicals industry, inasmuch as glass-lined steel and stainless steel equipment do hold a dominant place in processing operations. However, this is not to say that plastics do not play a big part in most of the operations. They do, but in a different sense of the word. Such equipment as coated tanks, Karbate heat exchangers, rubber-lined tanks and centrifugals all are used extensively where a corrosion-resisting or metal-free operating environment is required. Coated tanks, generally of the phenolic resins, such as Heresite or Lithcote, are used for mild acid conditions or for storage of such materials aa require a metal-free contact surface. These tanks are usually limited to certain size categories; for best results, the tank construction and surface must be so detailed as to allow for the optimum coating condition. Larger tanks, although not uncommon-e.g., 15,000- to 25,000-gallon capacity, have been successfully coated, but the use factor on such tanks is always subject to question because of imperfection or lack of continuity in coating large surfaces. Spark testing, as is common with glasslined steel, is of some value in these instances, but again the test is not conclusive. The problem of coating large conventional type storage tanks is shown in the following case history which resulted in the failure of a coated tank more from a mechanical fault than a lack of chemical resistance. Not too long ago, a large tank farm, including several Heresitelined, 16,000- t o 25,000-gallon storage tanks, was installed in connection with a large process installation. Most of the Heresitelined, carbon steel tanks were for the storage of glacial and CDT grade acetic acid. Heresite was chosen in this case because stainless steel tanks were unavailable a t the time and because laboratory tests on the coating confirmed its chemical suitability. The coated tanks were designed to allow for optimum coating conditions and the manufacturer was cautioned about the application of coating and subsequent use of the tanks. In fact, before tanka were shipped, the coating was spark tested. The tanks were then carefully installed a t the plant site and equally carefully piped up. Unfortunately, when installing the sump pump, the pump casing scratched the edge of the sump pit because of misalignment of the pit and the pump manway. Affected areas were field patched and the tanks put in service. The CDT acid after a short period of time showed the presence of iron which could not be tolerated in the process, This material was then transferred to another tank and a crude acetic acid stored in its place. Roughly 12 months later, this tank developed a leak and had to be taken out of service. Inspection of the tank showed that the coating was attacked in several areas as characterized by long gouges in the lining. In general, the major part of the coating was in good condition with no evidence of attack. The other lined tanks used for similar acid storage were later inspected and all were undergoing attack and had to be removed from acid service. Here, in this instance, we feel that, although the coating apparently could withstand the corrosive condition, the problem of successfully coating a large continuous area had not been completely resolved. One pharmaceutical manufacturer states that they use plastic coatings only on open tanks that can be inspected periodically. Generally, a coated tank must be considered as a special case and not as a definite alternate to more expensive permanent alloy steel or glass-lined steel tanks. Heresite-lined air dryers have worked out well where corrosive fumes or solvents are liberated from a wet cake. 1350
Karbate (resin-bonded graphite), because of its relative inertness, is finding extensive use in our industry in the form of condensers, pumps, heat exchangers, vacuum jets, and the like. Heat exchangers of this material possess good corrosion-resistant qualities and are relatively trouble free, providing thermal and mechanical shock are eliminated. Haveg (a molded asbestos material) has been fabricated into many types of process equipment and a Haveg centrifugal pump was used successfully for the continuous circulation of a dilute hydrochloric acid solution. The use of Phenoline 300 (a modified phenolic coating) for lining of tanks and filters has allowed for use of corrosives with a fairly high degree of success. Phenoline 300 can be field applied; and when proper attention is given to the application, the over-all usefulness of equipment can be increased greatly. In fact, in one of our installations, a process development required that corrosionresistant equipment be employed for the operation. By applying Phenoline 300 to various tanks, filters, etc., much of the previous equipment could be adapted to the new process. New modifications of this resin are reported to be used successfully for certain fermentation operations. Haveg filters and scrubbing towers have also met with successful application. Other uses of plastics in process equipment are somewhat remote, but many novel and worth-while applications have resulted from shortcomings in an existing piece of equipment. For example, a stainless steel centrifuge basket was coated with Amercoat 74 (epon resin) for the successful handling of a hydrochloric acid and solvent slurry. In another case, a centrifuge, this time a continuous sterile unit, plugged a t the chute when the wet cake was cut from the basket. By coating the chute with Teflon, the smooth waxy surface, thus produced, allowed the cake to discharge freely. In another instance, the gasket material on a Selas candle unit was changed to one made of silicone rubber. Selas candles do not stick to this material or to the stainless steel plates, whereas Teflon and Neoprene do, and a t the same time, the latter materials are too hard for best results. The silicone rubber allowed the candles to be removed for cleaning without breakage. Other modifications to standard process equipment include placing Teflon sheet on the blades of a vessel baffle to increase the degree of agitation. The solution in this case was highly corrosive (solvent plus acid) and Teflon, other than glass, was about the only material able to withstand the corrosive action. The resultant agitation in this instance gave the improved yield that had been earlier predicted by laboratory agitation studies. Another agitation modification using a Teflon sheet as a scraperblade attachment to the vessel agitation resulted in a product with the proper bulk density. Previously this operation had been carried out with hand agitation, using paddles and scraper blade, but a change to large scale production equipment resulted in a poor quality product and yield loss because of material held in solution. By providing a scraper-blade attachment to the standard equipment, the problem of bulk density was solved and the yield of desired product increased. I n still another instance of applying plastics to process equipment, a Koroseal tank lining proved to be the answer to a very corrosive solution problem. In this case. an oxidation reaction at 70" to 80" C. in sodium hypochlorite solution was to be carried out. Of 20 metallic materials tested, only titanium was satisfactory, but it was too expensive and relatively unavailable. Instead a Koroseal-lined carbon steel tank was used, and it has worked successfully for the past several years. GASKETS, PACKINGS, AND BEARINGS
The most widely used gasket material of the newer synthetics is the polyfluorohydrocarbon type (Teflon). Its smooth surface and ability to withstand steam sterilization make it very useful; although the initial expense is greater, this is usually more than offset by increased gasket life. At present, Teflon is not particu-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7
Plastics Construction Materials Manufacture of fine chemicals uses a wide range of reactants and solvents.
A n individual unit may be scheduled to produce several products or intermediates. These conditions present special problems of corrosion and product contamination. To help combat these problems, there is an increasing trend toward the use of plastics in process equipment. Materials of construction for the major pieces of equipment are generally glass-lined steel or stainless steel. Plastic and plastic-impregnated materials, which can be fabricated in many forms, find their greatest use in gaskets, packings, fittings, valves, and pipes. Synthetic materials have found application in filter media which are inert and which aid in keeping products clean. Plastics also are used extensively in sterile processing units and for containers. The ability to apply protective coatings to existing equipment and to make field repairs has greatly enhanced the use of plastics. Development of plastic materials which maintain their properties above looo C. would greatly multiply their use.
larly suited for applications requiring flexing or resiliency, but it is becohing standard for the packing of pumps and valves in corrosive service. Teflon envelope gaskets, with Neoprene or asbestos fillers, are widely used on process vessels. Teflon snapon gaskets have solved the problem of suitable gasketing for the miles of glass pipe in the industry. A few instances that point out the extreme range of service of this material follow: The first is its use in reactor gaskets. A reaction is carried out in a high temperature, high pressure tubular-type reactor where alloy tubes are rolled into an alloy tube sheet. Difficulties were encountered in getting the liquid feed (containing dilute nitric acid at room temperature) to distribute properly among the tubes. The use of orifices before each tube seemed to answer the distribution problem, but the mechanics of doing this were difficult. Since the tubes were off-round and since any mechanical stressing of the tubes or sheet wm to be avoided, using plugs or the like was ruled out. The tubes extended about inch beyond the tube sheet. The final solution was to use individual Teflon gaskets around each tube to make an orifice cup to fit as snugly as possible around each tube and then to hold these cups on with a a/4-inch stainless steel plate bolted to the tube sheet. In another installation, a nitric acid stripping column operated a t 100 C. and 125 pounds per square inch. The flanges used permitted only a small bearing surface. Conventional gaskets leaked badly, and Teflon-coated asbestos also leaked. Solid Teflon was the best solution, although not a perfect one, as it flowed gradually so that the flanges had to be continually tightened and the gaskets replaced every few months. Teflon has been used for such items as a foot bearing for the agitator in a hydrogenation reaction and as a seat for safety valves on various autoclaves. Kel F (fluorochlorohydrocarbon) rupture disks have been used on other corrosive applications. An interesting application was the gasketing of nozzles on a glass-lined steel vessel producing hydriodic acid. Because of the low bolt stress available, Teflon envelope gaskets could not be and in due time, compressed enough to fill all the leakage of acid vapors occurred. These vapors then condensed and corroded between the glass lining and metal bond and caused severe damage to the vessel. The service required resistance to strong acid a t 110" to 120" C. From a whole list of materials tested, only a synthetic rubber and a vinyl (Tygon) formulation showed any promise, and the surface of synthetic rubber crazed. Plant testa on the Tygon gasket are under way, and this material s e e m satisfactory. Another common problem is gasketing against chlorinated hydrocarbon solvents. Here Teflon and Resistoflex have found usage. In mother case, a pump was needed to handle dilute nitric acid a t room temperature and high pressure. The original design called for a porcelain bearing, but this cracked, and other materials O
*
July 1955
were tried. Kel F gave fair service but gradually flaked. Nylon was not resistant to the corrosive conditions. Finally, an epoxide resin (Hysol) was tried and succeeded but it was not used because this material is quite brittle. Teflon-impregnated blue African asbestos was the packing material ultimately used. PIPING AND VALVES
Plastics piping and valve applications in the pharmaceutical field have not attained the volume of uses currently discussed in the petroleum or paper industries. Of the more common typese.g., polyethylene, Tenite butyrate, saran, and Uscolite-the material enjoying the largest use is saran. This material is perhaps the most versatile, economical, and currently available. Saran-lined pipe is equally suitable for permanent process liquid lines and corrosive liquor transfer. Straight saran pipe is thought of in applications of a temporary or minor nature. This is so because of temperature limitations and the necessity for angleiron support, which is usually a costly installation procedure. Therefore, other materials of construction-glass, porcelain, or stainless steel-are more generally used for rough, corrosive, or contaminant-free service. On the other hand, saran-lined pipe is relatively easily installed, and, although swollen by some chemicals, the over-all resistance of this material is surprising. Even though partially attacked by various organic solvents, this piping can be used where exposure is intermittent and a water flush can follow the process operation. Many of our chemical operations, therefore, employ the more common types of plastics piping, but by and large the volume is spotty, and so no generalizations can be made. Certainly as new resins or modified existing resins are made available and position tested, the probability for increased use of plastics piping in our industry will be great. From a design point of view, the economic advantages of using suitable plastics piping over porcelain or stainless steel should make this field one of high promise. Plastic valves thus far have met with mixed success. Most of the all-plastic materials swell to the point where use with organic solvents renders valves inoperable. Plug valves of metallic bodies and a Teflon plug are well regarded under very severe service conditons. All metallic valves under the same conditions have either been badly scored or galled, which is not the case with a Teflon plug valve. Teflon or Kel F diaphragm valves of the Grinnell-Saunders type have also been used extensively on our process operations. Vralvea of this type with a Teflon diaphragm backed up with Neoprene have generally replaced the stainless steel gate valves used in sterile operations. Stainless steel valves were subject to galling and did not maintain a sterile condition. The use of Teflon diaphragms in this application allows for steam sterilization and
INDUSTRIAL AND ENGINEERING CHEMISTRY
1351
continuity of sterile operation. These diaphragm valves are not the complete answer to the problem, however, because of the poor flex life of the diaphragm. Perhaps additional formulation or modification of these materials will overcome this shortcoming. Plastic-based lubricants for plug value service have recently extended the use of these valves and undoubtedly will add to the over-all usefulness of valves of this type. Resin-base valve lubricants are now in wide use and are extending the range of application of plastic valves. SPECIAL APPLICATIONS
The first consideration under special applications is the use of plastics in duct work. Hydrochloric acid fumes have been handled successfully for several years in duct work of Fiberglas mat impregnated and bonded with polyester resins (Pla-tank). Coatings of this type have not been as effective as solid material. Uscolite (a styrene-acrylonitrile copolymer) has also been used successfully for hydrochloric acid ducts, but it is more expensive than the polyester. Baked phenolic coatings have performed successfully for acid blowers and fume ducts, but their tendency to chip has led to their replacement with rubber-painted ducts or other materials. Acetic acid vapors are handled with Permanite ducts as the polyesters were attacked by the vapors. Plastics are also used in the fine chemicals industry as filter media. Such materials as Orlon, nylon, saran, Dynel, Vinyon and more recently polyethylene are used as filter cloth or centrifuge bag materials. These materials have very good resistance to corrosive solutions, particularly acid solution, and are a great aid in keeping products clean and free from lint. Other characteristics that tend to be overlooked are the good tensile strength of these fibera, particularly nylon, and their good abrasion and shrink resistance. One disadvantage is the low softening point (about 65' C.) of such fibers as Vinyon and saran. These materials must serve as effective gasketing materials and must be able to withstand high operating pressures as well as severe mechanical wear at the gasket edges. One severe application has to do with a slurry containing 201, bromine in organic solvents. Dynel was used for some time with good results, but a switch was made to a polyethylene media, which has greater strength. Orlon has proved a very versatile material. Saran is limited because of physical weakness. Nylon is cheaper than other but is not resistant to acids. An important use of plastics is in the fabrication of all types of containers. Nearly all the drug products and intermediates are now drummed in polyethylenelined containers to prevent contamination and corrosion. These liners, however, are somewhat susceptible to flex cracking. Other drums are coated with vinyl or phenolic coatings. Orlon and nylon bags are used for handling some of the vitamin products. The caps and seals of many product bottles are polystyrene or celloseal. Other containers are sprayed with plastic materials, such as silicones,to make them drain freely. One pharmaceutical formulator has extensively pioneered the use of plastics for containers, tubes, and dispensers and has set up ita own plastics molding machine to assist in the design and development of such items. Heretofore, the usual conflicts between designer and fabricator or molder were a problem in that a long period of time was expended in compromising the design to that which a molding company felt they could make. This loss of time has been alleviated by dovetailing design and fabrication through use of their own experimental machine to iron out these problems before a final container design is agreed on. This sort of treatment in container or package development has been particularly fruitful and points up the need for close cooperation between designer and molder t o expand the over-all usefulness of plastic containers. A n interesting development in the field of containers was the use of a plastic sheath or bag to house a very reactive intermediate 1352
that could be introduced into a process vessel in a sealed condition where the solvent vehicle would dissolve the plastic container. This chemical intermediate was highly sensitive to atmospheric moisture, and safety considerations dictated that production personnel handle i t in a sealed container and by remote control, The search for a plastic material that was resistant to moisture penetration, but yet soluble in the organic solvent although unreactive with other chemicals consumed in the reaction, led to testing a material known as S-60 or Parapol. This plastic, which is a copolymer of styrene and isobutylene, was made into lay-flat tubing, subsequently cut and heat sealed, and then put into a metal can to hold a given amount of the chemical compound. In the process operation, the can was opened by remote control behind a barrier, and the plastic bag was transferred to the reactor by inverting the can through a side-entering manhole. By application of a suitable plastic container, a chemical process was thus able to use a new and more reactive chemical than had previously been possible; this resulted in high process yields and lower product costs. There are numerous plastics uses which fall in the miscellaneous category, such as, paints of all kinds, scoops, beakers and funnels, label protection, face shields, and asphaltic insulation. Plastics are used particularly in sterile operating areas. Vinylite sleevelets are worn by the operators in sterile processing, and the sterile cubicles have methacrylate windows. Nylon is used in uniforms and for back-up filters in air-treating units. Silicone coatings on the walls of bottles reduce the interfacial tension of liquid and make it drain better. Silicones are also finding use as antifoam agents. Molded plastics in sheet or block form are readily machined. Saran and Teflon sheets have been fabricated into rotameter stops, plate filters, laboratory agitator blades, and other experimental mechanical items. The fine chemical field offers many challenges to the plastic industry. There is a tendency for production men to look with more favor on a plastic coating system that can be repaired in the field than on one which must receive special handling in the shop. Thus, coatings which can be applied without baking or special equipment will gain favor, particularly as new ones come closer to matching the chemical resistance of baked coatings. Another factor of extreme importance is surface preparation. It is sometimes next to impossible to prepare an existing piece of equipment properly often because of internal features, such as lap welds and sharp corners which interfere. The poor results which are apt to follow such attempts do not advance the case for plastic materials. Coating applicators also look for a practical and more trustworthy method for testing the continuity of surface in coatings and linings. Temperature limitation is frequently encountered when one is considering the use of plastics. Some rigid substances are exceptions, but generally 70" to 80" C. marks the upper range where they can be considered. A large number of organic reactions that we are concerned with are carried out above this temperature and, in fact, the trend is to higher temperatures and pressures. It would seem to be a fertile development area for plastic manufacturers to devote research to increasing the usable temperature range of their materials. Recent examples of this progress are the irradiation of polyethylene to increase its form stability to about 150' C., the development of a new trifluorochloroethylene polymer with rubberlike characteristics, superior chemical properties, and heat resistance to about 200' C., and several silicone rubbers good to about 280 C. O
ACKNOWLEDGMENT
The authors acknowledge the many useful contributions concerning plastics application submitted by Eli Lilly & CO., Abbott Laboratories, the Squibb Institute for Medical Research, Charles Pfizer & Co., and the Upjohn Go. RUCEIVH~D for review September 17, 1954.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACCEPTEDFebruary 21, 1955.
Vol. 47, No, 7
