United States Patent Office Patented Apr
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2,979,495 United States Patent Office Patented Apr. 11, 1961 1. 2 a method whereby the used solvent or catalyst suspending agent in the Ziegler process for the polymerization of 2,979,495 polymerizable hydrocarbons is recovered in a purified ETHYLENE POLYMERIZATION PROCESS IN state for recycling to the process. WHICH THE KEROSENE SUSPENDING ME. 5 Other objects and advantages of the invention will DUM ES RECOVERED become apparent from the following description and ap pended claims. James V. Cavender, Jr., Texas City, Tex., assignor to According to the invention, solvent or catalyst suspend Monsantoporation of Chemical Delaware Company, St. Louis, Mo., a cor ing agent suitable for recycle to the catalyst preparation O step in the Ziegler process is prepared by subjecting used No Drawing. Fied May 14, 1956, Ser. No. 584,874 solvent or catalyst suspending agent to washing or scrub 2 Claims. (C. 260-94.9) bing with concentrated sulfuric acid. The acid-washed solvent can then be separated from the acid, washed with alkali to remove any residual traces of acid, dried, and This invention relates to the polymerization of hydro 5 distilled, or handled in any other conventional manner carbons. More particularly, it relates to an improvement to yield a product containing essentially no contaminants the process for the production of Ziegler-type polymers, so that it performs in a manner comparable to the fresh relating specifically to a method for cleaning up the cata solvent when employed in the polymerization reaction. lyst Suspending agent employed to render it suitable for The following example is presented as illustrative of recycle purposes. 20 the invention, but is not to be construed as limiting it in There has recently come into commercial prominence any manner other than it is limited in the appended claims. a process whereby ethylene and other polymerizable hy drocarbons may be polymerized at low temperatures and Example I preSSures to yield products of high molecular weight A polymerization run was made employing ethylene Superior in many respects to those produced by the high 25 as the feed material and kerosene as the solvent or catalyst pressure techniques previously practiced in the art. This suspending agent. Kerosene, purified by distillation to process has been made possible through the agency of remove any moisture present, was metered to a dry reac a type of catalyst developed by Dr. Karl Ziegler of the tion vessel and heated to 65° C. The catalyst, a mixture Max Planck Institute at Mulheim, Ruhr, Germany and of triisobutylaluminum and titanium tetrachloride, was has come to be commonly termed the "Ziegler process' 30 measured into the reaction vessel with stirring. Ethylene while the products so produced are as commonly referred was metered into the reactor near the bottom with agita to as "Ziegler-type polymers.” Many variations of the tion and the temperature of the reactor was maintained catalyst have been disclosed but probably the preferred at 65° C. by the use of cooling water. After all the group is that described in Belgian Patent No. 533,362, ethylene had been reacted, the reaction mixture was issued May 16, 1955, to Ziegler, the disclosure of which is 35 transferred to a quench tank containing isobutanol where incorporated herein by reference, namely, catalysts pre the catalyst complex was reacted with the isobutanol and pared by the interaction of a trialkylaluminum with a com thus dissolved in the mixed solvents. The quenched mix pound of a metal of group IV-B, V-B, or VI-B of the ture was heated to 97-100° C. for two hours, then was periodic system including thorium and uranium, and es cooled rapidly to 25-30° C. The quenched mixture was pecially compounds of titanium, zirconium and chromium. 40 filtered and the solid ethylene polymer therein was sep As the process is ordinarily conducted, the catalyst is arated, dried, densified, and packaged. suspended in a suitable liquid organic medium or solvent The resulting filtrate liquor or mixed solvents from and the polymerizable hydrocarbon is bubbled through the quench step containing a small amount of solids was the system at a temperature anywhere in the range from fractionated under reduced-pressure to remove isobutanol 0° C. to 100° C. Upon completion of the reaction, the 45 therefrom. The bottoms from this fractionation, rep polymer is recovered by first destroying the catalyst by resenting the used solvent and containing all the catalyst quenching it with an alcohol and then separating the solid residues, were fed over a 24-hour period at a rate of polymer from the reaction mixture by filtration or cen 100 lb. per hour together with concentrated sulfuric acid trifugation. Thereafter for practical and economic rea at a rate of 10 lb. per hour to a mixing pump where they sons, the catalyst suspending agent or solvent must be 50 were thoroughly and intimately contacted at ambient tem recovered for re-use. The state of purity required in the perature for a period of approximately 10 minutes. The solvent is critical. It is imperative that the used solvent resulting acid-kerosene mixture was transferred to a be recovered in an extremely pure state, since any im settling tank where the acid and kerosene separated into purity present in it such as water, acids, compounds with discrete layers during a settling time of approximately one active hydrogen, oxygen, etc., interfere seriously with 55 hour. The acid-washed kerosene was then drawn off and respect to formation of the active catalyst. Because the charged at a rate of 100 lb. per hour together with 10 lb. solvent in this case is contaminated with catalyst residues per hour of dilute sodium hydroxide (5%) to a mixing and frequently has a solids content up to as high as 1%, pump where the two were intimately mixed to neutralize some specific problems arise which are not encountered any traces of acid in the kerosene. The alkali-kerosene in the usual solvent recovery systems. Conventional dis 60 mixture was run into a separator for phase separation and tillation techniques which are practical can be used to the kerosene layer was withdrawn, heated under vacuum remove the major portion of the alcohol contained in the to distill off the water, and then fractionated under vacu mixed solvents of the reaction mixture, but they are not um to recover the pure kerosene. effective in removing other contaminants from the solvent. A sample of the kerosene so recovered was used in a Neither is distillation after water-washing of the con 65 polymerization run as the solvent or catalyst suspending taminated solvent an acceptable technique for produc agent as described above to make polyethylene. No ing useable material for recycling. It has now been dis difficulties of any kind were experienced in the polymer covered, however, that after it has been separated from ization process and the polymer produced was of a quality the quench medium, washing or scrubbing of the con comparable to that made when fresh kerosene was em taminated solvent with concentrated sulfuric acid will 70 ployed. render it sufficiently pure for re-use in the process. While the example describes the catalyst suspending It is an object of the invention, therefore, to provide agent or solvent as kerosene, the polymerizable hydrocar 3,979,495 3 4. born as ethylene, and the catalyst as a mixture of trialkyl metals, not with organo-metallic compounds but rather aluminum and titanium tetrachloride, the invention is by reducing agents such as: alkali metals, e.g., lithium, not to be considered as limited in its applicability to this Sodium, potassium; alkali hydrides, e.g., lithium hydride, particular system. ... Many variations may be made in the Sodium hydride; complex alkali aluminum and alkali process conditions and reactants, without departing from boron hydrides, e.g., lithium aluminum hydride; com the scope of the invention. For example, the catalysts plexes of alkali metal hydrides with boron triaryls or boric composition can be varied substantially from that de-r acid esters or boronic acid esters; and especially titanium scribed. In addition to the type catalyst disclosed in the and zirconium halides reduced by zinc or alkaline earth exampies and in the Belgian Patent No. 533,362 men metals or other earth metals including the rare earths, tioned earlier, other catalysts of the Ziegler type which O or hydrides of same; said reductions being effected in the differ in various ways from this one may be enployed. coImplete absence of oxygen, moisture, and compounds For example, instead of or in addition to the aluminum containing active hydrogen atoms as deterimined by the trialkyls, catalysts of the type described in the Belgian pat Zerewitinoff method. Polymers of low to medium molec ent can be made by reacting the various metal com ular weight can be obtained from ethylene and other pourids of groups V-B, W-B and VI-B disclosed therein monomers by using trialkylaluminums alone as catalysts, with aluminum compounds of the general formula RAIX2, especially in very small amounts, as well as dialkyl beryl where R is hydrogen or hydrocarbon, X means any other liums, trialkyl galliums, trialkyl indiums, monoalkylalu substituent including hydrogen or hydrocarbon, particu minum dihydrides, and the various other catalysts dis larly diaikyl or diary aluminum monohalides, also aiu closed by Ziegler in U.S. Patent No. 2,699,457. Attention, ... minum hydride, alkyl or aryl aluminum dihydrides, di 20 is further directed to the teaching of various of the fore- : alkyl or diaryl aluminum hydrides, alkyl or aryl alu going catalysts in Ziegler's Belgian Patents 534,792 and . minum dihydrides, alkyl or aryl aluminum dialkoxy or 534,888, the disclosures of which are hereby incorporated diaryioxy compounds, dialkyl or diaryl aluminum alkoxy herein by reference.