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Selle, S. J.; Hess, L. L.; Sondreai. E. A. 1975 Meeting of the Air Pollution Control Association, Boston, MA, June 1975; Paper No. 75-02-5. Stearns, C. A.; Kohn, F. J.; Rosner, D. E. “Combustlon System Processes Leading to Corrosive Deposits”; US. DOE Report, DOEINASA12493-27, 1981. Weaver, J. N. ”Analytical Methods for Coal and Coal Products”, Kan, C., Ed.; Academic Press: New York, 1978; Vol. 1, pp 377-401.
final paper. Also, thanks to Associated Western Universities and DOE for grant support to P. L. Holm. Literature Cited AbdeCBaset, M. 6.; Yarzab, R. F.; Given, P. H. Fuel 1978, 57, 89. Bear. F. E. I n “Chemlstry of the Soil”, 2nd ed.,ACS Monograph Series, No. 160, Reinhokl Publishing Corp.: New York, 1964; p 320. Benson, S. A,; Karner, F. R.; Goblirsch, G. M.; Brekke, D. W. Am. Chem. Soc.Dlv. Fuel Chem., Prepr. 1982, 27(1), 174-181. Durie. R. A.; Sternhell, S. A M . J. Appl. Scl. 1958, 9 , 360. Finkelman, R. B. “Atomic and Nuclear Methods in Fossil Energy Research”, Filby, R. H., Ed.; Plenum Press: New York, 1982; p 141. Goblirsch, G. M.; Sondreal, E. A. “Proceedings, Technology and Use of Lignite”; Bureau of Mines-University of North Dakota Symposium, Grand Forks, ND, May 1979, GFETC/IC79/1. Lakatos. 8.; Meisel, J.; Mady, G.; Vinkler, P.; Sipos, S. Proceedings of the Fourth International Peat Congress, Otanieml, Finland, 1972; Vol. 4, p 341. Low-Rank Coal Study, National Needs for Resource DevelopmentResource Characterization. US. DOE Report DOE/FC/10066-T1, Nov 1980; Voi. 2, p 95. Miller, R. N.; Given, P. H. “Ash Deposits and Corrosion Due to Impurities in Combustion Gases”, Bryers, R. H., Ed.; Hemisphere Publishing Corp; Washington, DC, 1977; p 39. Mlller, R. N.; Yarzab, R. F.; Given, P. H. Fuel 1979, 58, 4. Miller, R. N.; Given, P. H. “A Geochemical Study of the Inorganic Constituents In Some Low-Rank Coals”; US. DOE Report FE-2494-TR-1, 1979. Rindt, D. K.; Jones, M. L.; Schobert, H. H. The Engineering Foundation Conference, Henniker, NH, July 1981. Salmon, J. E.; Hale, D. K. “Ion Exchange, A Laboratory Manual”; Academic Press: New York, 1959; p 31.
Received for review December 5 , 1983 Revised manuscript received August 2, 1984 Accepted August 23, 1984
This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process or service by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation,or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
An Improved Gas-Phase Polypropylene Process James F. Ross’ and Wllllam A. Bowles Northern Petrochemical Company, Morris, Illinois 60450
Gas-phase polymerization of propylene to high isotactic homopolymers, random copolymers, and impact copolymers has been commercial in the U.S. since 1977. The process incorporates technological improvements including high activity, high stereospecific catalyst, and continuous in-process catalyst deactivation. I t produces homopolymers with 97+ % heptane insolubles, melt flow rates from fractional to 50+, and a wide range of copolymers. Rapid technological progress was made in developing these improvements through an integrated lOOO-ton/year pilot plant in the US. to complement similar facilities in Germany. A process description and schematic flow plan for the process, typical product properties, and comparative economics are discussed.
Introduction Polypropylene plastics, as we know them today, were first manufactured in Italy by Montecatini (now Montedison) in 1957. This was within five years of the discovery that transition metal catalysts could produce crystalline thermoplastic polypropylene. Production was begun in the United States within a year. Other manufacturers followed rapidly until today, 27 years after its initial appearance, there is capacity for 7 million tons per year worldwide and about 2.5 million tons annually in the U.S. (Plast. World, 1982). This level of capacity by no means indicates that propylene polymerization is a mature technology. On the contrary, many analysts indicate that polypropylene is still a growth polymer (Plast. World, 1981a,b; Mod. Plast., 1982). There are large market areas that polypropylene has only begun to penetrate. In automotive, appliance, fiber, and packaging markets, for example, polypropylene’s combination of good (and sometimes unique) physical properties, ease of fabrication, and low price is gradually making it the preferred material in areas previously dominated by competitive polymers and even metals. A new and rapidly growing market for polypropylene is in impact copolymers. These materials combine impact resistance, stability, and processibility with a lower cost than com0196-4321 18511224-0149$01.50/0
petitive materials. As such, they are receiving a great amount of attention for such critical uses as fender liners and dashboards, dishwasher tubs, etc. As the markets for polypropylene have grown, so has the technology to manufacture these polymers. Old facilities are being modernized, simplified and improved. New processes have been developed which are more versatile, simple, and economical (Brockmeier, 1981; Brockmeier and Lin, 1979; Chriswell, 1983; Cipriani and Trischman, 1981; Goodall, 1981; Luciani et al., 1981; Miro and Kaus, 1981; Short, 1980; Sinclair, 1981). One such recent development has been brought to commercial use by Northern Petrochemical Co. (a wholly owned subsidiary of Internorth, Inc.). This development evolved from BASF gas-phase technology, and it incorporates several improvements made that are unique to Northern Petrochemical’s plant. This plant, depicted in Figure 1,has been designed to emphasize the synthesis of copolymers, both random and impact. These latter grades are unique in being made by synthesis, rather than blending. The various polypropylene processes in use today can be conveniently characterized by the medium in which polymerization takes place: inert diluent, liquefied monomer, and gas phase. Inert diluent or “slurry” processes were until recently the only ones developed commercially; 0 1985 American
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Figure 1. Gas-phase polypropylene plant, Morris, IL
liquefied monomer or 'bulk" and gas-phase processes represent newer technologies that are simpler, less costly, and more energy efficient. Diluent slurry processes too have recently undergone radical improvements and still represent the majority of the polypropylene plants in operation today. The simplifications that are inherent in modern polypropylene processes are illustrated in Figure 2. Here a simplified block flow diagram of a typical conventional slurry process is compared t o diagrams for modern hulk and gas-phase flow processes. Several of the extra process steps for conventional slurry relate directly to extremely stringent purity requirements for the inert diluent; these process steps are unique to inert diluent processes. Most of the extra steps shown in Figure 2 are a direct result of the relative inefficiency of the only catalysts available until recently. Traditional polypropylene catalysts have hasic shortcomings that complicate processes employing them. Compared to recent modified and supported catalysts, CONVENTIONAL SLURRY
traditional j3 and y crystalline forms of T i Q are marginally stereospecific and much less active (Galli, 1980; Goodall, 1981; Luciani et al., 1981). Under commercial conditions, these older catalystsproduce polypropylene homopolymers with a composition of approximately 90% crystalline, isotactic polymer and 10% soluble, amorphous atactic polymer. For many applications the market demands homopolymers with a maximum atactic content of about 5%. Consequently, older processes included equipment t o separate excess atactic from the desired product and to recover diluent from the atactic fraction. In some cases atactic material could he further purified for sale into rather limited markets. Alternately, in an integrated petroleum refining operation it would be visbroken to no. 6 fuel oil. Some of the new catalysts are more stereospecific, giving atactic contents of about 5%. As a result, many new or existing plants can eliminate atactic removal and its ancillary operations by use of these catalysts (Brockmeier, 1981; Cipriani and Trischman, 1981). The older generation catalysts could only produce up to about 1000 weights of polymer per weight of catalyst. Stated differently, catalyst residues amounted to several hundred parts per million in polymer product. These residues had t o he removed to obtain a saleable product hecause these levels of catalyst residues are generally acidic and often abrasive. They cause product degradationcolor, odor, loss of physicals-as well as corrosiveJerosive problems downstream and in customer's equipment. T o reduce catalyst residues to acceptable levels, elaborate solvent-deashing procedures were necessary. Alcohols or weak aqueous bases, sometimes with chelating agents, were employed. Because of deashing, polypropylene plants included additional steps of polymer separation and drying, solvent repurification and recycle, and residue disposal. Recently, however, radically improved catalysts are becoming commercially available. These are sufficiently active to allow simplification and even elimination of polymer deashing under certain conditions (Brockmeier,
MODERN BULK
GAS PHASE
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Figure 3. Original Novolen process schematic diagram.
1981; Cipriani and Trischman, 1981). With the develop ment of higher activity, more stereospecific catalysts, gas-phase polymerization of propylene became commercially feasible. Gas-phase polymerization affords a further simplification over modern bulk polymerization in that polymer degassing and the transfer, recovery, and repurification of large quantities of an excess volatile liquid phase are eliminated. Polymer is produced directly, and transported, as a fluidizahle powder. In addition, certain copolymers can be more easily produced in the gas phase than in any liquid medium. Gas-phase polymerization, per se, is not new. In the 1960'8, processes were developed for gas-phase polymerization of ethylene by use of transition metal catalysts (Batleman, 1975). Application of this technique to propylene polymerization, however, was delayed because the real economic benefits of gas-phase operation were negated where atactic and catalyst removal steps were necessary. Such problems did not affect high density polyethylene because ethylene is manyfold more reactive than propylene and stereospecificity is not a factor in polyethylene. In summary then, the success of any gas-phase polymerization process for polypropylene hinges on three factors: (1)high catalyst stereospecificity,(2) high catalyst activity, and (3) translation of gas-phase technology to polypropylene. The improved process evolved in three major stages over more than a decade of industrial development. These stages and the dates for their implementation on a commercial scale are: original Novolen polypropylene process (1969), second BASF gas-phaseprocess (1977), and improved gas-phaseprocess incorporating NF'C and BASF technology (1980).
Original Novolen Polypropylene Process During the middle 1960's Badische Anilin-und SodaFabrik, A.G. (now BASF Aktiengesellschaft) in Ludwigshafen, West Germany, had developed improved catalysts that made gas-phase polymerization of polypropylene economically possible for the first time. Yields were high (50-60 kg of polymer/g of Ti) and the resulting stereospecificity of 8 5 9 0 % was not only adequate for many applications but desirable for certain specialized uses. Simultaneous development work on mechanical aspects of the process was carried out a t Ludwigshafen to take advantage of operating experience with gas-phase polyethylene that had previously been developed by BASF (Wisseroth, 1969). A 24000-ton per year plant was built using BASF technology at Rheinische Olefinwerke (ROW) in Wesseling, West Germany. This plant came on stream in 1969 and has been in operation since then producing BASF's 1300 series of Novolen polypropylene resins (Oil Gas J., 1970). A schematic flow plan of this process is shown in Figure 3. The process is extremely simple. Polymerizationgrade propylene is first passed over adsorbent beds primarily to
Table 1. Original Novoleu Polypropylene Process. Typical Product Properties ASTM polymer type test method 1320HX 1320LX 1300EX MFR, dg/min D-1238-L 2 6 0.5 tensile yield, psi D-638 3200 3100 3500 tensile yield, N/mm2 22.2 21.3 24.3 elongation yield, % D-638 30 36 37 flex Modulus, kpsi D-790 83 75 91 flex modulus (1% s), 570 520 630 N/mm2 izod'impact, 23 ' C D-256 1.5 1.3 2.8 notched, ft-lb/in. izod impact, J/m 80 70 150 hardness, Rockwell R D-785 87 88 82 deflect temp, 66 psi D-648 84 82 83 (0.46 N/mmz), "C
protect the polypropylene plant from any loss of activity resulting from possible transient upsets in the purity of supplied monomer. This purified monomer and the catalyst components are introduced into a stirred polymerization reactor that operates essentially as a mechanically fluidized powder bed. The mechanical design of the agitator and the orientation of the various feed streams are critical design parameters upon which the smooth operation of the gas-phase reactor depends. A turbulent bed of powdered polymer is maintained in the polymerization reactors by automatic level control which vents off, periodically, a suspension of polymer powder in carrier gas. This stream enters a let-down vessel where disengaged gas is ultimately returned to the process while the powder continues into extrusion storage hoppers. Heat of polymerization is removed largely by condensing unreacted monomer in a separate cooling loop and introducing liquefied monomer back into the reactor where it immediately vaporizes. There are no facilities necessary for lowering the polymer atactic content nor for deashing. However, residual activity in the catalyst is killed by special additives during extrusion to give stable, corrosion-free products. Polymer products from this plant are widely used in European film and molding markets where the higher atactic content of the product is an asset. These markets include areas generally preempted by random copolymers in the United States. Physical properties of typical homopolymers produced in the original Novolen propylene process are given in Table I.
Second Base Gas-Phase Process Continued research and development at Ludwigshafen, coupled with operating experience in the ROW plant, led, in the early 1970'9, to an improved gas-phase polypropylene process. Catalyst modifiers were developed that significantly raised stereospecificity to 95+%, albeit a t a somewhat lower, though still acceptable, catalyst activity (Schick, 1976; Wisseroth, 1977). Productivities of 15-20 kg/g of titanium were readily obtained both in the laboratory and in continuous pilot and semiworks plants. Additional development work in smaller continuous pilot plants had indicated that these newly developed catalysts were also suitable for producing random and impact grade copolymers. In 1977, in a newly constructed facility a t ROW, initial commercial production of this new polypropylene (Novolen 1100 series polypropylene) was begun. This production wm followed within 6 months by Northem Petrochemical Co. (NPC), at Morris, IL, with their Norchem resins. Subsequently, Imperial Chemical Industries took a license to construct plants at Rozenberg (Holland) and Wilton (England), while IC1 Australia constructed a
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Figure 4. Improved gas-phase process schematic flow diagram.
unit at Botany Bay. Another plant has been licensed for Petroquimica Cuyo in Argentina. Today plants employing the basic technology of the improved BASF process are in operation, or under construction, with nameplate capacity in excess of 350000 tons/year. Improved Gas-Phase Process During 1976, Northern Petrochemical Co.constructed a loo0 ton/year completely integrated pilot plant as part of their Morris, IL, complex. This unit is capable of producing not only homopolymers but also random and impact grade copolymers. This unit complemented existing similar and smaller capacity pilot plants as well as the semicommercial unit that BASF was operating at Ludwigshafen. This replication of research and development facilities allowed extremely rapid advances in process modifications that have been incorporated into the Commercial Polypropylene Plant at Morris, IL. These modifications provide: improved high activity, high stereospecific catalyst; space-time yields of 4.W.5 T/m3 D (metric tons per cubic meter of reactor volume per day) stereospecific homopolymer: 97+% heptane insolubles; continuous in-process catalyst deactivation: full range of homopolymers-fractional through 50+ melt flow rate (MFR); and a wide range of copolymers. The Morris plant, as it exists today, retains much of the simplicity of its predecessors, but i t is far more versatile. The flow plan of this unit is basically unchanged, but it has been expanded to allow production of various copolymer types. Continuousin-process catalyst deactivation has replaced the alternate process step of extruder deactivation. As before, there are no diluent facilities, no atactic removal, no deashing, and no polymer drying. Process Description Until now, there has been no detailed description of an operating commercial gas-phase polypropylene process. The schematic flow plan of the improved configuration to produce homopolymers, random copolymer, and impact grades, is shown in Figure 4. Polymerization grade propylene monomer and ethylene comonomer, when used, are i n d i v i d d y passed through desiccant beds to maintain the high level of purity required by the active catalyst. The necessary level of propylene purity is shown in Table 11. Catalyst and cocatalyst are metered into the reactor, together with hydrogen for control of melt flow rate. As with other gas-phase processes based on BASF technology, the reactor employs a spiral agitator of special proprietary design to maintain a turbulent mechanically fluidized bed of polymer powder. Again, heat of polymerization is removed through an extemal cooling loop where unconverted
Table 11. Gas-Phase Polypropylene Monomer Purity Specifications min max major components, mol% propylene 99.5 propane 0.5 methane and ethane 0.04 trace components, ppm ethylene 45 acetylene, methyl acetylene, prapadiene 6 10 C,+
co
co*
5 5 5 10 10 2 5
monomer vapors are condensed and returned to the reactor, largely as a liquid. This liquid flashes on entering the reactor 80 that polymerization truly takes place in the gas phase. When producing homopolymers or random copolymers, only one reactor is needed, although two in series can be employed, when desired, to effect subtle changes in molecular weight distribution, or to increase throughput. In the primary reactor, propylene, hydrogen, and catalysts are individually metered t o maintain the desired combination of reactor pressure, product melt flow rate, and production throughput. When random copolymers are being produced, comonomeric ethylene is metered into the reactor to maintain desired product ethylene content. The sophisticated control system, a combination of flow, pressure, temperature, and compoaition analysis, maintains a constant environment in the reactor, and consequently constant properties in the product. Polymerization conditions maintained in the primary reactor are 2-3 MPa (3-50 psig), 7&100 OC, and 0.5-3 mol % hydrogen. Catalyst is TiC1, and DEAC, plus proprietary activators a t a mole ratio of 5-10 DEAC/Ti. Titanium catalyst rate is sufficient t o maintain residual Ti contents of approximately 2&50 ppm in polymer. For the production of impact grades, two reactors are used in series. Product from the primary reactor is introduced into the secondary reactor rather than into a pressure let-down drum. Additional monomer, comonomer, hydrogen, and catalyst, as necessary, are metered into the secondary reactor to produce the intimate physical mixtures of polymers that are necessary to achieve high impact values. In the secondary reactor, heat of polym-
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Table 111. Energy Requirements of Polypropylene Processes." Energy Equivalents, MJ/kg Drocesa traditional modern modern gas slurry slurry bulk phase utilities 9.9 5.1 2.5 0.5 steam 6.3 5.9 5.7 5.7 electricity 2.4 2.0 excess monomer 2.9 2.0 consumption, fuel equiv solvent diluent losses, fuel 0.9 0.5 0.5 equiv 8.1 equiv energy consumption 20.0 13.4 11.0 re1 energy consumption 2.5 1.7 1.4 1.0 "Adapted from Brockmeier (1981).
erization is removed by recirculating reactor gas through a refrigeration loop. In the secondary reactor, pressures of 0.7-2 MPa (100-300 psig) and temperatures of 40-70 "C are maintained. Polymer product, together with a small amount of carrier gas, leaves the reactor under level control into the pressure let-down drum where low-pressure recycle gas, consisting largely of unreacted monomers, is flashed off for recycling. Polymer product is conveyed through the proprietary in-process catalyst deactivation unit and then is pelletized in the presence of selected additives ready for packaging and shipping. Catalyst is prepared and activated in a separate area of the plant. This gas-phase polypropylene process is both versatile and simple. The inherent simplicity of the process allows control of critical polymer properties through feed-forward control of reactor variables. In addition to allowing close control of polymer properties, the simplicity of the process means reliable operation, lower energy requirements, and minimum anti-pollution requirements. The reliability of the improved process has been amply demonstrated on a commercial scale. Reactor run lengths are routinely measured in months, even for copolymers. Fouling of reactor walls is nonexistent, primarily because of (a) turbulence in the mechanically fluidized powder bed and (b) the docile, forgiving nature of the catalyst. This gas phase process requires less energy per unit of output compared to slurry or liquid pool processes, primarily because there is no diluent or wash liquid and, therefore, no energy requirements for initial purification, separation, and repurification of these streams. A comparison of energy consumption has been published by Brockmeier (1981). He shows that gas-phase energy requirements are less than half the requirements for traditional slurry processes and significantly lower than modern slurry or bulk processes where deashing or atactic removal have been eliminated. As can be seen in Table
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111,the principal savings in energy result from less usage of steam and lower losses in hydrocarbons, both monomer and diluent, with their equivalent fuel value. Electricity, mainly to power extruders, is the single largest energy use in the gas phase, but this is common to all processes marking pellets rather than powder. Another gas-phase polypropylene process has recently been announced that employs gas-fluidized reactors (Chem. and Eng. News, 1983). Energy requirements for this other process should be somewhat greater for equivalent homopolymer product. We have calculated that the energy required to compress and circulate recycle gas is approximately three times greater than the energy needed for the reactor agitator and recycle pumps in the present process. In addition, because reactor cooling is effected by circulating a liquid, there is no need to maintain a large disengaging space above the polymer bed. Almost all the volume of the reactor is bed volume, and consequently, at equivalent throughput, the reactor size is much smaller. Environmentally, this process does not have diluent losses, atactic polymer, nor catalyst residue streams to dispose of. It does not utilize a large inventory of liquid monomer; hence, emissions through leaks in equipment, valves, or piping are minimal. Product Properties Polymer products made at the Morris plant are unique in many respects and have gained wide acceptance in the marketplace. These unique properties of Norchem polypropylene result primarily from: gas-phase operation, per se, catalyst deactivation, and nature of the catalyst. Typical properties of homopolymer, random copolymer, and impact copolymer are listed in Table IV. Because polymerization is conducted in the gas phase, there are no solvent residues or solvent odor. Wet or glassy pellets are not a problem. Pellets are consistently neutral and noncorrosive. There is no acidic deashing that can leave corrosive residues in the polymer. Neither are there basic neutralization residues that can interact with stabilizers to form colored bodies on reprocessing. The proprietary catalyst deactivation step of the improved process is extremely effective. Catalyst residues in the polymer are innocuous, inert, and in such a finely dispersed state that they cause no extrusion buildup on fine screens. Product pellets are exceptionally clean, white, and stable. This stability has resulted in long-term heat aging grades with lives of over 120 days at 150 "C in oxidation oven testing. Furthermore, these grades have been given the highest UL rating of all polypropylenes-125 OC. The catalyst used in the improved gas-phase process contributes strongly to polymer properties. Homopolymers as synthesized have an exceptionally high isotactic index. Heptane insolubles of 97+% are obtained throughout the
Table IV. Gas-Phase Polypropylene Properties. Typical Product Properties of Norchem Resins polymer grade 8420HK ASTM 8004MR 8310GO test method (homo) (random) (impact) 12 10 7 D-1238-L MFR, dg/min 5100 3700 3800 D-638 tensile yield, psi 25.5 35 26 tensile yield, N/mm2 20 18 D-638 16 elongation yield, 70 130 D-790 210 100 flex modulus (1%s), kpsi 690 900 1450 flex modulus, N/mm2 2.5 D-256 0.7 0.5 izod impact, 23 "C, notched, ft-lb/in. 133 40 27 izod impact, J / m 16.0 D-256 12.5 4.0 izod impact, -18 " C , unnotched, ft-lb/in. 850 660 210 izod impact, J / m D-785 85 90 104 hardness, Rockwell R 90 110 D-648 90 heat deflection at 66 psi (0.46 N/mm2), "C
8752HJ (super impact) 2 3200
22 20 100 690 14.0 750 40.0 2120
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complete range of melt flows now commercially available-from fractional to over 30 MFR. Because of this high isotacticity, homopolymers are consistently strong and stiff-with tensile strengths in excess of 35 MN/m2 (5000 psi) and flexural moduli over 1400 MN/m2 (200000 psi). There is no measurable drop-off in physical properties as melt flow is increased, even past 30 MFR. The high isotacticity also means that all homopolymers are gel-free and meet FDA extractables standards for resins that may be processed for uses involving contact with foods. Random copolymers are produced commercially containing up to 4-5% ethylene at melt flow rates to 10 MFR. As ethylene content is increased, these copolymers exhibit increasing impact strengths, clarity, and gloss, with a simultaneous decrease in stiffness. Random copolymers are also gel free. This combination of properties has earned wide acceptance in injection molded housewares, blowmolded hot-fill bottles, and clarity film applications. Impact copolymers made with NPC’s catalyst cover a wide range of types. Synthesis conditions can be chosen to emphasize easy processing (high melt flow) at a given impact level. On the other hand, conditions can be altered to emphasize optical properties for housewares applications, while still retaining stiffness and impact resistance. Impact grades with room temperature notched Izod values up to 1060 J / m (20 ft-lb/in.) are commercially available. Both these polymers and their method of manufacture have been patented (Ross, 1983). These impact copolymers offer not only the best Izod impacts in the industry, but also the advantages of high melt flow rates for ease of processibility and a good balance of stiffness and other physical properties. These copolymers are currently generating extreme interest in the automotive industry due to their ability to offer cost savings in cycle time, while providing the strength and dimensional stability for automotive applications. Homo- and copolymers with controlled rheology can also be produced having narrower molecular weight distribution than synthesized resins. Controlled rheology homopolymers retain similar isotacticity and physical properties compared to synthesized material of the same melt flow rate. Because of their narrower molecular weight distribution, controlled rheology homopolymers give faster molding cycles and less warpage in fast-cycle injection molding applications.
Economics A comparison of capital investments and operating costs for various types of polypropylene processes has been made by Brockmeier (1981). His analysis shows that the second BASF gas-phase process is about a standoff in both capital and operating costs compared to modern diluent and bulk processes. All these modern processes are significant improvements over the older slurry process. Alternate confidential studies confirm the general conclusions of Brockmeier’s analysis, though they indicate somewhat different absolute values for capital and operating expense. The relative ranking of the process types is the same. When the improvements of the present homopolymer process are taken into account, the scales tip heavily in favor of this process. Both capital and operating costs are significantly lower than for the best available competitive process. If copolymer processes are compared, the economic advantages of the improved process are even more pronounced. Incremental equipment to manufacture the gamut of impact and random copolymers is minimal, adding no more than 5 1 0 % to investment and essentially only the incremental cost of comonomer feedstock to operating costs. Registry No. Polypropylene (homopolymer), 9003-07-0.
Literature Cited Batleman, H. L. Ptast. Eng. 1975, 37(4), 73. Brockmeier, N. F. Mich. Mol. Inst. Sympos., Midland, MI, 1981. Brockmeier, N. F.; Lin, C. H. AlChE 86th Annual Meeting, Houston, TX, 1979. Chem. Eng. News 1983, 61(46), 5. Chriswell, L. I.Chem. Eng. Prog. 1983, 79(4), 84. Cipriani, C.; Trischman, C. A. Reg. Tech. Conf. SPE, Houston, TX, 1981. Gaiii, P. Struct. Order. Poly. Int. Sympos. Macromol. Florence, Italy, 1980. Goodall, B. L. Mich. Mol. Inst. Sympos, Midland, MI, 1981. Luciani, L.; Monini, A,; Zaffagnini, D. Ann. Tech. Conf. SPE, New Orleans, LA, 1981. Miro, N. D.; Kaus, M. J. Reg. Tech. Conf. SPE. Houston, TX, 1981. Mod. Plast. 1982, 59(5),58. Oil Gas J . 1970, 68, 64. Plast. World 198la, 39(2), 14. Plast. World 1981b, 39(9), 98. Plast. WorM 1982, 40(1), 8. Ross, J. F. US. Patent 4375531, 1983. Schick, H. Centennial Meeting, American Chemical Society, New York, April 1976. Short, J. N. Ind. Res. Dev. 1980, 22, 109. Sinclalr, K. B. Reg. Tech. Conf. SPE, Houston, TX, 1981. Wlsseroth, K. Angew Macromol. Chem. 1989, 8. 41. Wisseroth, K. Chem. Ztg. 1877, 101 271.
Received for review June 25, 1984 Accepted October 1, 1984
