TECHNOLOGY
Oxychlorination process uses liquid phase Kellogg's new process goes to homogeneous catalysis to avoid problems of gas-phase predecessors
152ND
ACS NATIONAL MEETING Industrial and Engineering Chemistry
152ND
ACS NATIONAL MEETING Petroleum Chemistry
If the advantages claimed by M. W. Kellogg for its new liquid-phase oxychlorination process hold up in practice, they should add even more luster to what has already become a popular route to vinyl chloride monomer. Like its gas-phase predecessors, the process ( DCE ), makes 1,2-dichloroethane which is then thermally cracked to produce vinyl chloride and by-product HC1. Unlike its gas-phase predecessors, Kellogg's new process employs liquid-phase homogeneous catalysis. So far, a Kellogg research and development group, which includes Marshall L. Spector, J. C. Yarze, Dr. Heinz Heinemann, Kenneth D. Miller, Leo Friend, and Leonard Wender, has worked with the process through the pilot plant stage. Comprehensive process flowsheets and detailed economics for a full-scale plant have been prepared, but Kellogg hasn't disclosed details of initial commercialization. Basically, the process involves simple chemistry and first-order reactions. Ethylene, hydrogen chloride, and oxygen react, catalyzed by an aqueous mixture of cupric and cuprous chlorides, to make DCE. The reaction appears to occur between complexed ethylene and cupric chloride, Kellogg says. The resulting cuprous chloride is oxidized back to cupric chloride with the oxygen and HC1. Thus, production of DCE and regeneration of catalyst take place simultaneously. The ability to use by-product HC1 for oxychlorination of more ethylene is what gives oxychlorination—gasphase or liquid-phase—its special appeal. And this is what has led a number of vinyl chloride producers, such as B. F. Goodrich Chemical, to take the oxychlorination route. Processes combined. Vinyl chloride has traditionally been made from ethylene and chlorine or from acetylene and HC1. The economic choice is basically one of feedstock costs, giving ethylene (at about 3 to 4 cents per pound) a husky edge over acetylene (at, say, 8 cents per pound). But the 76
C & E N S E P T . 26, 1966
ethylene route produces by-product HC1, for which there may be no outlet. Some producers have combined the processes, using by-product HC1 from an ethylene process to make more vinyl chloride in an acetylene process. Oxychlorination makes it possible to use the HC1 with ethylene; not only is the HC1 used, but only the lower cost feedstock is required. The gain in the economics, however, has been paid for in technical difficulty. Reactors used in the gasphase processes generally operate with supported metal halide catalysts. Large amounts of heat are generated at the catalyst surface, and hot spots tend to form. This makes temperature control difficult. It adversely affects selectivity of the reaction. And it can cause catalyst to vaporize. Since the Kellogg process operates in the liquid phase, this problem doesn't occur. Vaporization of water removes heat of reaction. No cooling surfaces are needed in the reactor, so there are no temperature gradients. Mr. Yarze described other advantages of the process during the Symposium on Homogeneous Catalysis, held by the Division of Industrial and Engineering Chemistry: • Selectivity of the reaction for DCE is high. Better than 96% on both HC1 and ethylene can be achieved in sustained operation.
• HC1 conversions are high. About 99% per pass can be achieved. • Operating conditions are relatively mild. The reactor operates at 340° to 360° F. and 250 to 275 p.s.i.g. • DCE product is quite pure. Hexachloroethane, which gives serious trouble in cracking DCE to vinyl chloride, is present at only about 3 p.p.m. An especially big advantage of the process is feedstock flexibility. HC1/ oxygen, chlorine, or HC1/oxygen and chlorine can be used as régénérants in any proportion. Moreover, the process will accept by-product HC1 from cracking of DCE without the need for removing contaminants such as acetylene. Of particular importance is the fact that the process can accept up to the entire chloride requirement in the form of aqueous HC1. This leaves the way open for a producer to buy cheap waste HC1, since such HC1 usually occurs and is shipped wet. The cost and handling problems involved in drying HC1 ordinarily rule out this source if dry HC1 is required. In operation of the process, ethylene and régénérants are fed to a reactor lined with prestressed brick and containing the promoted, aqueous cupric chloride/cuprous chloride catalyst solution. Chlorination and catalyst regeneration occur simultaneously at steady state.
These reactions . . . C 2 H 4 + 2 C u C I 2 -» C 2 H 4 CI 2 + 2 C u C I 2 C u C I + 2 H C I + V2O2 -> 2 C u C I 2 +
H20
. . . lead to a plant with these economics Raw m a t e r i a l
Ethylene HCI—fresh HCI—cracking Oxygen
Cost (cents per pound)
Pounds/pound DCE
cents/pound DCE
4.0 1.5 — 1.0
0.298 0.404 0.372 0.193
1.19 0.61
Raw material cost (cents per pound DCE) Other operating costs DCE manufacturing cost (cents per pound)
0.19 1.99 0.36 2.35
Kellogg oxychlorination takes liquid-phase route Ethylene recycle "*"Γ - '
| - » - Ethylene—»- J - * Purge (inerts) Ethylene recovery
-•Quench
Reactor
-+- Ethylene
Ethylene-J
Quench water
Oxygen -J Chlorine-J HCl , J
Recycle water τ
Liquid-liquid separator
1,2-Dichloroethane s product
Water purge
L
HCl absorber
Effluent gases from the reaetor go to a packed tower lined with prestressed brick where they are quenched with water. The liquid leaving the tower is cooled further and separated into aqueous and DCE phases. The aqueous phase is split. Part recycles to the tower as quench liquid, while the remainder recycles to the reactor following a purge equal to the amount of water made in the oxychlorination reaction. Water re cycled to the reactor first absorbs part of the HCl feed, entering the reactor as an aqueous HCl solution. DCE product is cooled further and flashed to separate out more water, which is purged, and dissolved ethylene, which is recycled. Un condensed gases from the quench tower recycle to the reactor, except for a purge stream to remove inerts. Eth ylene is recovered from the purge stream. Reactor designed. In developing a rational basis for reactor design, the Kellogg research and development group made extensive studies of mass transfer rates, chemical kinetics, water vapor pressure over the catalyst, selec tivity relationships, and flammability factors. Some of the chemistry was described by Mr. Spector during the Symposium on New Chemistry of Eth ylene, held by the Division of Petro leum Chemistry. Various concentrations of the cop per chlorides can be used in the reac tion. The range studied by Kellogg varied from 4.8M to 10M in total cop per concentration. In the commercial process, catalyst solution is maintained at a steady state cuprous/cupric ratio
Flash Water
by regeneration with oxygen and HCl in a 1:4 ratio. If an excess of HCl is allowed to build up in the catalyst solution, mak ing it acid, the reaction begins to shift toward more production of ethyl chlo ride. Normally, if HCl concentration is controlled to that needed for regen eration, selectivity for DCE remains high. Kellogg has been able to achieve above 99% in experiments. Chlorination reaction rate, Mr. Yarze explains, can be limited either by chemical kinetics or ethylene mass transfer, depending on ethylene par tial pressure, agitation, catalyst com position, and temperature. The Kel logg group has delineated the mass transfer and kinetic limiting regimes. Feed operations are carried out under conditions where chlorination kinetics, and not ethylene mass transfer, are controlling. For steady-state operation involving simultaneous chlorination and regen eration, both rates must be equal. If ethylene partial pressure and/or agi tation rate are kept high enough to en sure that ethylene mass transfer isn't limiting, the steady-state rate of DCE formation is a function of catalyst com position and, therefore, of catalyst re generation rate. Regeneration is usu ally limited by oxygen transfer, since both reaction and mass transfer of hy drogen chloride are very fast. The Kellogg group has developed a rate equation for the process in which STY—space time yield (expressed as moles of product per hour per liter of copper chloride solution)—is a func tion of total copper concentration, cuprie/cuprous ratio, and temperature.
The STY equation was developed from pilot plant data, which were ana lyzed by multiple regression tech niques. Mr. Spector emphasizes that the equation is empirical. STY is independent of conversion, although depletion of cupric chloride does have an appreciable effect on rate. Generally, reaction rate in creases with temperature. Above about 350° F., however, carbon diox ide begins to appear in the product gas stream indicating that unwajited reactions are taking place. The com mercial rHOcess is designed for an STY of 3.0. Production economics for Kellogg's plant vary widely, depending on whether the chloride requirement comes entirely from HCl or whether some chlorine is used. It also varies widely with cost of ethylene feed. Kellogg has worked out the econom ics on the basis of a 350 million poundper-year plant for DCE. Assuming all chloride comes from HCl—0.372 pound per pound DCE coming from DCE cracking, 0.404 pound per pound DCE supplied fresh—the raw material cost runs 1.99 cents per pound DCE. This assumes ethylene at 4 cents per pound and oxygen at 1 cent per pound. Adding in all other operating costs brings DCE manufacturing cost to 2.35 cents per pound. This includes catalysts and chemicals, utilities at typical rates, fixed charges at 18% per year of investment, two men per shift, and overhead and remaining costs at 100% of operating labor. The manufacturing cost goes up to 2.70 cents per pound DCE if chlorine rather than fresh HCl is used along with HCl from DCE cracking. Again, this assumes ethylene at 4 cents per pound, chlorine at $55 per ton. The effect of ethylene cost is equally pronounced. For the plant using HCl as the entire chloride requirement, with fresh HCl at 1.5 cents per pound, the DCE manufacturing cost is 2.35 cents per pound, if ethylene is 4 cents per pound. For 3 cent-per-pound eth ylene, DCE manufacturing cost is 2.05 cents per pound. If HCl is available at no cost, DCE manufacturing cost, using 4 cent-perpound ethylene, drops to 1.74 cents per pound. For 3 cent-per-pound eth ylene, it drops to 1.44 cents per pound. SEPT. 26, 1966 C&EN
77
Composite fibers lead to whisker composites 1 CO ND JLU/LND
ACS ACS NATIONAL MEETING Cellulose, Cellulose, Wood, Wood, and and Fiber Chemistry Chemistry
"We are approaching a new area, where high-performance fiber-rein forced composites will provide two-to threefold improvements in properties over conventional materials." Dr. James Economy of Carborundum ex pressed this optimistic view after de scribing a new process for making composites with high loadings of oriented silicon carbide whiskers (single crystal fibers). Now, he says, design engineers will be able to eval uate the structural characteristics of these materials. So far, whiskers possess the best combination of high strength and stiffness (modulus) with low weight and good temperature stability. The fact that they were not available in large quantities hindered their devel opment. When Carborundum started making silicon carbide whiskers on a commercial scale, Dr. Economy, Dr. L. C. Wohrer, and F. Frechette turned their efforts to finding ways to fabri cate composites. For the best reinforcing, other workers have shown, fibers should be long, oriented, and present in high loadings. Whiskers, though, are rela tively short fibers with very small diameters. It is difficult to pack them densely into a matrix with the de sired orientation without damaging the whiskers. Dr. Economy's group first tried con ventional plastics processing tech niques—casting, molding, extrusion. Orientation was only poor to fair, how ever, and the properties of the com posites improved only slightly. Whis ker concentrations were limited to less than 15% by volume; otherwise,
the fibers were damaged considerably. Spinning techniques did produce highly oriented composite fibers with up to 15% by volume of whiskers. Dry spinning of a polyethylene maleic anhydride polymer from acetone solu tion, for example, produced composite fibers with up to 12.5% whiskers. Wet spinning of a solution of polyacrylonitrile (PAN) in dimethylformamide gave composites with 15% whiskers. Concentrations of whiskers of at least 50% yielded porous com posites that could not be made into dense structures. The answer to high loadings, the Carborundum group found, was to use composite fibers as intermediates. PAN composite fibers, for example, were exposed to a temperature of 600° C. for a short time to remove the polymer matrix. The resulting nonbonded whisker yarn, which showed no loss in orientation, was sprayed with a solution of a resin such as a phenolic or an epoxy. Compres sion molding of this "prepreg" at pres sures up to 2000 p.s.i. produced composites with as much as 50% whiskers. Photomicrographs show a high degree of whisker orientation and no evidence of damage. The Carborundum group tested phenolic composites containing 30 to 49% SiC whiskers. These have very high flexural moduli, some as high as 11.5 million p.s.i., Dr. Economy says. The specific modulus is twice as high as that of uniaxial glass fiber composites and 50% higher than that of steel. The aver age flexural strength is close to 50,000 p.s.i. Dr. Economy believes that the whisker yarn has solved the fabrica tion problem. It has opened the way for engineers to study properties such as energy absorption, long timefatigue, dimensional stability, and di rectional strength and stiffness. With further development, he expects, com posites will improve greatly both in strength and modulus.
ORIENTED. Phenolic composite with 41.5% by volume silicon carbide whis kers shows high de gree of whisker orien tation at 1000 χ magnification
78 C&EN SEPT. 26, 1966
Lubrizol offers DAA, a specialty monomer Lubrizol Corp. will enter the specialty monomer field with commercializa tion of a new chemical, diacetone acrylamide (DAA). The Cleveland, Ohio, company, long a producer of additives for lubricating oils and fuels, has been recently expanding its spe cialty chemicals line which now in cludes corrosion control compounds, paint resins, and thixotropic agents. DAA will be the first vinyl monomer in its product mix. The monomer will initially be pro duced at the company's pilot-plant facilities in Wickliffe, Ohio, and mar keted by Lubrizol's plastic chemicals department. Synthesis route will be the reaction of acrylonitrile with ace tone in the presence of sulfuric acid. Projected commercial price should be about 50 cents per pound. Sample lots (minimum 10 pounds) are avail able at $1.75 per pound. The company feels that most com mercial applications of DAA will hinge on the unique solubility characteris tics of the monomer-polymer system and the many reactive sites available on the monomer. DAA's solubility in organics is similar to that of acrylamides in general—it dissolves easily in such common solvents as benzene, acetone, ethyl acetate, and hexanol. But unlike most substituted acrylamides, DAA is readily water soluble. The homopolymer, on the other hand, is water insoluble (although it is plasticized somewhat by water). This difference in water solubility suggests a possible advantage over other acrylamides as a flocculent for water treat ment. The monomer is very surface active, allowing emulsion polymerization to be carried out with a minimum of additional emulsifiers. The solid monomer can be polymerized by ultra violet or gamma radiation, and bulk polymerization can be initiated by heat alone, peroxides, or UV. Solution polymerization is possible with conventional free-radical initia tors in aqueous or nonaqueous sys tems, the company says. Homopolymers of DAA have a highly polar structure and may be useful as adhesives, bonding agents, and adhesion promoters. Films of the homopoly mer are UV-resistant and highly per meable to gases; they thus have po tential applications in "breathable" coatings and paints. DAA is a reactive monomer that copolymerizes with other vinyl mono mers. In addition to the reactive double bond, DAA has a keto group with reactive hydrogens adjacent to it.
