PHEXOL

C 0 L L A E3 0 R A T I V E

REPO R T

enol Continuous chlorination unit for manufacturing chlorobenzene

PHEXOL is to the organic chemical Capacity heads f o r business what caustic is to inorganic said Dow Chemical’s the billion pound- chemistry”-so late illustrious founder, Dr. H. H. Dow, back in 1915. But even he likely p e r - y e a r m a r k . way would be taken somewhat aback by the of phenol business today. This N e w e r p r o c e s s e s size year’s final tally could see synthetic phenol production near the 725 milliona b o u n d , b u t t h e pound level, up more than 1170 from 1959. And by 1965, output should grand-daddy of them grow over 900 million pounds, and poscloser t o one billion pounds annuall-Dow’s chloro- sibly ally. Tack on to this the steady 40 to 45 million pounds of natural phenol benzene route-still turned out every year, and you have big chemical business in any man’s language. has the lead in total And, despite persisting warnings of building overcapacity-U.S. synthetic phenol output phenol capacity is 735 million pounds per year and fast reaching for the billion-pound level-producers are having another go-around at expansion. Items:

LOUlS A . AGNELLO, Associate Editor, in collaboration with WILLIAM

H. WILLIAMS,

The Dow Chemical Co. Midland, Mich.

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e Dow Chemical is putting up a 36 million-pound plant at Kalama. M-ash., using a new, closelv-guarded toluene oxidation route and this year has completed a 2 5 million addition to phenol capacity at Midland. hlich. o Reichhold Chemicals is hiking its phenol capacity a t Tuscaloosa, Ala., from 60 to 90 million pounds, and has published that it is building another 60 million-pound unit a t Tacoma, Wash. e Allied Chemical is afoot with a 40 to 50 million-pound expansion a1 Frankford, Pa.

INDUSTRIAL AND ENGINEERING CHEMISTRY

e Union Carbide has a 25 millionpound expansion under way at Marietta, Ohio. Hooker Chemical will put up a 30 to 60 million-pound phenol plant at South Shore, Ky. o Monsanto, at press time, unveiled plans for a 50 to 75 million-pound unit plant a t Texas City, Tex.

Markets

Phenolic resins absorbs roughly 55yc of phenol output [IND.ENG. CHEM. 52, Yo. 6, 33A (June 1960)l. Over the long run, these resins should show a 3 to 4% annual growth. But they are highly sensitive to business conditions in the hard goods industries. S o w with these industries enjoying good times, demand runs high for such items as foundry resins, laminates, molded parts, and other phenolics. Phenolic binders for plywood and decorative laminates are two likely looking growth prospects. The year 1960 should see phenolic resin sales climb to a record high of some 650 million pounds, for a respectable 11% gain over 1959. More than a third of all phenol produced goes as a chemical intermediate for other than “phenolic resins.” Epoxy resins, polycarbonates, alkylated phenols for detergents, aspirin, chlorinated phenols-these are just some of its destinations. The petroleum industry takes most of the remaining phenol output for solvent refining and additives.

Chemical Routes

T o keep pace with phenol’s growing industrial importance has come a spate of processes. These have been pruned to the four now in commercial use in the U.S. Routes and their users:

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0 Chlorobenzene hydrolysis-monochlorobenzene reacts with water and caustic in liquid phase to give phenol, phenyl phenols, diphenyl ether, and sodium chloride-Dow Chemical. 0 Benzene sulfonation-benzene, sulfuric acid, and caustic soda form phenol, sodium sulfite, and sodium sulfateMonsanto Chemical and Reichhold Chemical, 0 Raschig-vapor phase catalytic airoxidation of aqueous hydrochloric acid to form chlorine and its immediate conversion to chlorobenzenes, which are catalytically hydrolyzed by steam to phenol and hydrochloric acid with minor amounts of chlorinated phenols and diphenyl compounds-Hooker Chemical and Union Carbide. Cumene peroxidation-cumene upon oxidation yields phenol, acetone, acetophenone, and some a-methyl styreneOronite Chemical, Allied Chemical, Hercules Powder, and Shell Chemical.

Each of these has its own features and drawbacks. Take the chlorobenzene process. Versatility is its strong-pointelectric power and coproducts, its key. The benzene sulfonate route is fine,

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provided you locate the plant close to ready outlets, such as paper mills, for by-product sulfites and sulfates. The Raschig process boasts relatively few by-products, but it demands largescale and continuous operation to be economical. With cumene peroxidation-process showing biggest growth deciding over the past 10 years-the factor is incremental propylene and availability of acetone markets. DOW’SKalama plant, now under construction, could prove to be the longsought solution to the two major problems plaguing phenol producers: dependence on benzene, and excessive by-products. The process takes toluene through a two-stage oxidation to phenol. First step oxidizes toluene to benzoic acid, part of which is then oxidized to phenol and unreacted benzoic is recycled to this second stage. Its selling points are obvious: Toluene is cheaper than benzene (25 cents against benzene’s 34 cents per gallon) and more available, output of hard-to-get-rid-of by-products is pared to the bone, and waste from the process is virtually nil. Developed by Dow [main patent U.S. 2,727,926 (December 20, 1955); reissued No. 24,848 (July 26, 1 9 6 0 ) ] , the process is also licensed under California Research Corp. patent No. 2,762,838. Not to be out-done, Scientific Design Co. (SD) announced this summer that HCI

it had solved the riddle of direct oxidation of benzene to phenol. But the company has said little about process specifics. If successful on a commercial scale, they indicate the route could mean phenol production with virtually no by-products. But some industry observers are skeptical-point out that various vapor phase benzene oxidation schemes have been tried and abandoned over the years because of low yields. But, with confidence undampened, S D claims that commercial units using the new process will not be long in coming. The company hints that the new route probably will be more popular for smaller overseas plants, rather than the larger domestic units. Attractions : low capital outlay and few, if any, by-products to be disposed of. Chlorobenzene

Is Still Tops

Dow Chemical is the world’s largest phenol producer, and by the same token, probably its biggest benzene customer. More phenol is produced by its chlorobenzene process than by any other single route. Dow’s installed phenol capacity (all via chlorobenzene) stands at 235 million pounds per year. This process, first put on stream commercially in 1926, has weathered the years because of a number of factors. First there is the geographic location of the plant and its raw materials ad-

HCI TO-ABSORBERS OR COMPRESSORS

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BENZENE

BENZENE STORAGE

MONOCHLOROBENZENE TO STORAGE

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CAKE p-DICH LOROBENZENE TO T R ICH LO RO B E NZ E M E

Flowsheet for the manufacture of chlorobenzene, The Dow Chemical Co., Midland Mich. VOL. 52, NO. 1 1

NOVEMBER 1960

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INDUSTRIAL AND ENGINEERING CHEMISTRY

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Staff-Industry vantages. Situated in Midland, Mich., in an area where salt brine wells abound, it is assured of an unlimited supply of caustic and chlorine-one of the key economic factors. Just 15 miles from Saginaw Bay, the plant can get lowfreight water-borne shipments of benzene from both domestic and overseas suppliers. The benzene is then piped underground from the port of Bay City, Mich., to the plant. But perhaps of equal importance is the process’s versatility. It is a main artery to a host of DOW’S other commercial chemicals. Among them : alkylphenols, bisphenols, phenyl phenols, chlorinated phenols, salicylates, Dowtherm A (a eutectic mixture of diphenyl and diphenyl oxide sold as a heat transfer medium), hydrochloric acid aniline, and ammonia. In its barest form, DOW’S chlorobenzene process for phenol is a twostage operation: chlorination of benzene to get monochlorobenzene, followed by hydrolysis of monochlorobenzene to get phenol. First stage uses gaseous chlorine and a Friedel-Craft catalyst to substitute chlorine for the hydrogen of the benzene ring. Then, by hydrolysis with aqueous caustic and neutralization of the resulting sodium phenolate, the monochlorobenzene is converted to phenol. Chlorobenzene Production

Benzene, as purchased, feeds from storage to a drying column at a rate of over 200 gallons a minute. Here, it is azeotropically dried at 69’ C. atmospheric pressure to reduce its moisture content from approximately 0.5% to 30 to 35 p.p.m. Dow takes off 10 to 1570 overhead to ensure that virtually all moisture has been removed from the feed stock. The dried benzene moves next to scrubber columns packed with steel rings to scrub out the last traces of chlorine gas from the hydrochloric acid stream. Now partially chlorinated, the benzene goes to the chlorinator to complete the reaction :

Gaseous chlorine under pressure (10 to 15 p s i . ) enters the process directly from Dow electrolytic cells in a closed system. The chlorobenzene plant can use u p to 800,000 pounds of chlorine a d.ay. The chlorine, by means of a rate feed controller, regulates benzene flow to the chlorinators (about 200 gallons per minute) and it also determines the proportion of mono- and dichlorobenzene produced.

T h e chlorinator operates a t 80’ C. and 16 p.s.i.a. Initially, the reaction needs anhydrous ferric chloride as catalyst for chlorination. Once the reaction is under way, there is enough ferric chloride produced from the steel rings in the system to provide the catalytic action. T o furnish this, some 30 to 50% of the product stream leaving the chlorinator is recycled to feed. As it leaves the chlorinator, the product stream (called “chlorinated oil”) contains some 30 to 50% unreacted benzene, 30 to 50% monochlorobenzene, and from 3% to 12y0 dichlorobenzenes. I t also holds some HC1 in solution. The stream moves on to an aqueous HCl scrubber to extract FeC13 and most of the dissolved hydrogen chloride, and is then treated with a 20% caustic solution to neutralize the last traces of dissolved HC1. By-product gaseous HCl from the chlorinator is refrigerated to recover benzene, and then either compressed and distributed as anhydrous gas to other units in the area--e.g., for liquefaction, and sale-or dissolved to produce a 35% aqueous solution for captive use and some outside sale. Eight Karbate units absorb the HC1 in water to produce constant percentage HC1 solution of whatever strength desired. During this operation, the heat of absorption drives off traces of hydrocarbons to atmospheric vents. Rubber-lined equipment then guides the HC1 solution through activated charcoal filters to remove the last traces of organics. The now neutralized chlorinated benzene stream is pumped to conventional bubble cap fractionating columns to separate the various components. The first column-a seven-plate unit operating a t atmospheric pressure and 80 to 100’ C.-separates unreacted benzene and the chlorinated benzene products from tars (chlorinated toluenes, thiophene, sulfur compounds, and straightchained high boiling hydrocarbons which result from impurities present in the benzene) which are then burned. The vaporous top product passes on to a 15-tray atmospheric column to strip off the unreacted benzene. The overhead product is a benzene cut containing about 9870 benzene and 2y0 monochlorobenzene. Recovered benzene is recycled to feed with new benzene at the initial drying stage. T h e bottoms consist essentially of monoand dichlorobenzenes which are pumped to the monochlorobenzene finishing column, a 30-tray unit operating a t 132’ C. and 15 p.s.i.a. Monochlorobenzene is the overhead product, which is for sale or transfer for Dow consumption. The bottoms portion-approximately 3OY0 monochlorobenzene,

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25% o-dichlorobenzene, and 45% pdichlorobenzene-is pumped to a 12tray column operating a t 3 p.s.i.a. and 100’ C. where the monochlorobenzene is the overhead product and it is returned to the monochlor column, the bottoms are pumped to the dichlorobenzene continuous distillation column where at about 2 p.s.i.a. and 150’ C. the ortho isomer is separated from the meta-para by fractionation. The meta-para fraction, leaving the top of the column, goes to a crystallizer where finished #-dichlorobenzene is produced with a congealing point of about 53’ C. T h e mother liquor is recycled to the dichlorobenzene column except for a portion that is continuously fed to the trichlorobenzene process. The bottoms are primarily o-dichlorobenzene and are flashed to produce technical o-dichlorobenzene and the residues from this flash distillation are the raw material for the manufacture of trichlorobenzene. Phenol

At the phenol plant, aqueous caustic soda solution, diphenyl ether, and monochlorobenzene are fed through a ratio feed controller to centrifugal mixing pumps. A battery of hydraulic pumps increases pressure on the mixture from 75 to about 4000 p.s.i.g., and forces

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An automatic freezing point recorder, developed b y Dow technicians, i s used in the primary phenol process VGL. 52, NO. 11

NOVEMBER 1960

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Storage tanks and interconnecting process pipelines (foreground) for continuous distillation unit for separating monochlorobenzene in the background

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A Continuous distillation unit for separating chlorobenzene

b Continuous distillation unit for separating monochlorobenzene from other compounds resulting from chlorination of benzene

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and p-di-

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A A Dow phenol purification unit with nickel and nickel-clad construction used in critical parts of fractionating columns, condenser, piping, and tankage

+ HCl-HzO CaHsOH + NaCl HzO C6HjC6H40Na+ HC1 --+ CsH&sHaOH + NaCl

it into tubular autoclaves. Each autoclave contains about a mile of pipe of gradually increasing diameter (the material expands as the reaction proceeds). Residence time for the reaction (10 to 30 minutes) is determined by the pumping speed through the autoclave and by the product mix required for sale. T o start the reaction, the autoclaves are gas-fired to approximately 340' C. Once under way, the heat of reaction is sufficient to exchange heat to the incoming liquid and maintain a reaction temperature of 370' to 385' C. The caustic's molecular and aqueous concentration varies from 2 to 2.5 moles per mole of chlorobenzene plus phenyl ether and from 10 to 20% solution, depending upon the ratio of productsphenol, phenyl phenols, and diphenyl etheraesired. The reaction products consist of an aqueous layer containing sodium phenolates and soldium chloride, and an oil phase of unreacted chlorobenzene and diphenyl ether which is recycled or processed for sale. c1

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Again two layers are formed: an oil layer of phenols, and a water layer containing dissolved by-product NaC1. Separated in a decanter, the water layer is extracted with benzene until it contains approximately 100 p.p.m. of phenol. The benzene extract is contacted with the aqueous product stream in the first extractor to recover the phenol. The oil, or phenol layer, is feed stock for the phenol stills. Since this feed contains some water and dissolved NaCI, it first goes to a drying column where it is azeotropically dried, the bottoms are pumped through a salt filter, and then to the finishing column operating at approximately 1.5 p.s.i.a. Because of its sensitivity to iron in the presence of moisture and oxygen the purified phenol is stored in ONa

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Product stream runs into a gravitytype decanter where the oil phase rises to the top, and is drawn off for recycle through the autoclaves or sent to a series of stills for separation. At the stills water and unreacted monochlorobenzene form the first fraction which recycles through the autoclaves, followed by a very small naphthalene cut, and then the diphenyl ether distills as the main product. Bottoms consist principally of phenyl phenols and phenyl diphenyl ethers. Diphenyl ether subsequently is purified further by crystallization and color distillation for transfer within Dow or for sale as a chemical intermediate, a perfume, and to make Dowtherm A-a heat transfer product composed of diphenyl (25%) and diphenyl ether (757,). The water phase from the autoclave is first extracted with benzene to remove diphenyl ether and then acidified with HCI to liberate phenol and phenyl phenols from their sodium salts.

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nickel, or glass-lined tanks until packaged for shipment. Bottoms-about 1570 crude phenol, 85% ortho- and para-phenyl phenols, and a trace of alkyl phenols-from the finishing columns is pumped to batch distillation units where it is separated into: phenol, alkylphenols, ortho-, metapara-, and para-phenyl phenols.

Automatic titrating machine or p H adjuster used in the primary phenol process. The pH adjuster was originally developed b y Dow's Physical Research Laboratory for use in this plant

Its Future Assured

With phenol an integral component of the spiraling chemical economy, its future looks secure for a long time to come. But competition is keen. Major producers are continuously re-evaluating production economies with a sharp eye toward further trimming costs. Out of these investigations could come new, improved, and perhaps more versatile phenol processes. But in Dow's scheme of things the chlorobenzene route will continue to play its vital role

INDUSTRIAL AND ENGINEERING CHEMISTRY

as one of the main pipelines to the company's huge phenol family. Acknowledgment

One author extends his sincere appreciation to Gordon Sears, M. S. Putnam, and J . T. Lundquisr and for their assistance, and to the Dow Chemical Co. for permission to publish the article.