Aug- 3, 1965 c. E. P. v. VAN DEN BERG ETAL 3,193,777 PROCESS FOR PURIFYING POLYMERS Filed June '7, 1960 2 Sheets-Sheet l
FlG.l I
heoyy purified polymer “quid ' ' plus light liquid
_ roschig ring filling
pulsotor impure polymer plus light liquid plus alcohol heclvy liquid plus alcohol plus impurities
INVENTORS CORNEL/S E. PM “4N DEN BERG HENDR/K HENDR/KS MATH/A5 J G. MUYTJENS
3,198,777 United States Patent 0 ” 1C6, Patented Aug. 3, 1965
1 . 2 when the frequency of the pulsations is higher than 400 3,198,777 per minute. PROCESS FOR PURIFYENG POLYMERS The above mentioned obstructions in the column, i.e., Cornelis E. P. V. van den Berg, Hendrik Hendriks, and the contact promoting means, can consist, for example, Mathias J. G. Muytjens, all of Geleen, Netherlands, of inwardly extending bulges on the Wall of the column, assignors to Stamicarhon N.>‘V., Heerlen, Netherlands various types of column packings, or perforated plates. Filed June 7, 1960, Ser. No. 34,517 Preferably, use is made for this purpose of rings formed Claims priority, application Netherlands, June Ill, 1959, of polyole?ns, such as polyethylene. Compared with . ’ 5 3 (Zlaims. (Cl. 260-883) porcelain rings, these rings have the advantage that they are not wetted, or are only sightly wetted, by the heavier 10 This invention relates to a process for purifying poly liquid; they can be made so thin as to leave a free space’ mers in which the impurities-containing polymer together amounting to 60~70% of the volumeof the column. with a ?rst liquid is brought into contact with a second The volume displaced by one pulsation, calculated on liquid which is incompletely miscible with, and heavier the basis of an empty column, should preferably be suf than, the ?rst liquid and, thereupon, the polymer together ?ciently large so that the linear displacement of the liquid' with the first liquid is separated from the heavier liquid in the column equals one-?fth of the diameter of the which now contains the impurities. rings. When the displaced volume is smaller, the polymer A related process is known from Belgian Patent No. will be less puri?ed. Increasing the displaced volume to 567,031. This patent deals with the removal of catalyst the extent that the linear displacement becomes greater residues from hydrocarbon polymers formed by polym than about twice the ring diameter, does not give a erization with, for example, Ziegler catalysts at low pres further increase in the purity of the polymer. . sure. According to the disclosure in said Belgian patent, The distributing agent used in the polymerization, as the product formed during the polymerization is primarily ' gasoline or kerosine, is primarily'suitable for use as the brought into contact with an alcohol, as a result of which lighter liquid, while water is primarily used as the heavier the catalyst particles present in the product are de-acti liquid. It is preferred to add alcohol to a polymerization vated. Subsequently, a liquid immiscible with the dis product obtained with the aid of Ziegler catalysts, which tributing agent used in the polymerization is added, for results in a deactivation of the catalyst particles con example, water. The resulting bottom layer which con— tained therein. The entire mixture thus obtained is led tains a portion of the catalyst residue, is then separated into the base of the column, i.e., bottom—preferablyafter the catalyst particles and the alcohol have reacted with oil. 30 When the procedure described in the Belgian patent is each other for some time, say a few hours, at an elevated carried out on an industrial scale, there is encountered temperature-while water is fed into the top of the col—‘ the drawback that the extraction of the product resulting umn. The process is preferably carried out in‘such a from the polymerization has to be repeated many times in way that the quantity of Water passed through the column’ order to obtain a sufficiently pure polymer, necessitating in one hour amounts to 5-25 % by volume of the quan4 an extensive installation and a relatively considerable de tity of the lighter liquid passed through in one hour. gree of supervision. Moreover, the separation of the A slight amount of some acid, for example sulphuric heavier liquid on an industrial scale is dii?cult to realize acid or hydrochloric acid, or some base, for example in many cases. sodium hydroxide, can be preliminarily added to the alco The present invention provides a process by which the 40 hol or the water, if this should be desirable for achieving‘ above mentioned drawbacks can be overcome. In par proper de-activation or removal of catalyst residues from’ ticular, the invention provides a process by which poly a given polymerization product. With some hard-to mers, such as polyethylene, polypropylene or copolymers wash products, it is advantageous to ?rst treat the sus prepared with Ziegler catalysts can be puri?ed on a large pension with an acidulated alcohol, then to wash the mix scale and to a high degree with a relatively small installa ture with, water in the column and, thereupon, to sub tion and with little supervision. Other advantages result ject it successively to treatment with an alcoholic lye and ing from the process according to the present invention to washing with water in the column. will be pointed out below. In the case of some hard-to-wash products, use can The process for purifying polymers according to the also be made of a wetting agent. It is advantageous to‘ present invention-wherein the impuritiescontaining add this wetting agent to the water. polymers together with a ?rst liquid is brought into con It is a remarkable fact that the process according to tact with a second liquid which is incompletely miscible the invention can be carried out even when a liquid lighter with and heavier than the ?rst liquid, following which than the polymer itself is used as the heavier liquid, where the polymer together with the ?rst liquid is separated as the polymer is not dissolved. For example, when an from the heavier liquid containing the impuiities—is amount of water-containing methanol is added to a sus-' characterized in that the impurities-containing polymer pension of catalyst-containing Ziegler polyethylene (spe together with the ?rst liquid is continuously passed up ci?c gravity 0.96) in gasoline, there is formed a lower wards through a column provided with obstructions and layer having a .speci?c gravity of less than 0.96. Accord the heavier liquid is continuously passed downwards ingly, the polymer settles as far down as the bottom of through the said column in such a way that the lighter 60 the lower layer. However, if the above components are liquid forms a continuous phase in the column, while the treated according to the invention, then, the polymer re contents of the column are pulsated, preferably with a mains in the top layer in the form of a suspension or, at frequency of 50-400 pulsations per minute. any rate, a suspension of polymer in gasoline leaves‘ The above mentioned obstructions in the column, i.e., through the top of the column, while a polymer-free lower umn is obtained by controlling the discharge of the 65 layer, being speci?cally lighter than the polymer, is ob‘ heavier liquid from the base (bottom) of the column in tained from the base of the column. such a way, that the interface between the lighter and According to a preferred embodiment of the process of _ heavier liquids is in the bottom section of the column. the instant invention, the product obtained from the 130a‘ When the frequency of the pulsations is less than 50 lymerization and to which has been added a water-free‘ per minute and all other conditions are left unchanged, 70 or substantially water-free alcohol, such as methanol, eth a product of lesser purity is obtained. This also applies’ anol, isopropyl alcohol or a butanol, is fed into the bot-: 3,198,777 cl? 4 torn (base) of a ?rst pulsed column, while 4i—3’0% by vol Example 2 ume of water-containing methanol is introduced into the top of the column; thereupon, the methanol-containing The process is carried out in a cylindrical column hav product leaving through the top of the column is intro ing a diameter of 3.8 cm. and a height of 300 cm., ?lled duced into the base of a second pulsed column into which with the rings mentioned in Example 1. The column water is supplied through the top. communicates with a pulsator which imparts 105 pulsa ‘From the bottom of said second column, there is ob tions per minute to the column contents, the volume dis tained a water-containing methanol layer which, upon placed per minute being 10.5 ml. addition of water-free methanol, can be fed back to the A suspension of polyethylene in gasoline obtained by ?rst pulsed column. the Ziegler process, to which is added 33% by volume of This procedure has the advantage that the polymer is 10 methanol, is introduced into the base ‘of the column at the thoroughly puri?ed while, in the event the alcohol added rate of about 10 litres per hour. Water is fed into the top consists exclusively of methanol, the resulting lighter of the column at the rate of 2.4 litres per hour. The tem liquid contains so little methanol and water that, follow perature of the column contents is maintained at 43 ing removal of the polymer, the methanol and water 45° C. can be simply driven oft’ by blowing, say, l0‘—*20 litres of A polymer~free bottom layer, being speci?cally lighter nitrogen per litre through it. than the polymer, is discharged from the base of the col Following removal of the dissolved polymers contained umn at the rate of about 6 litres per hour, as a result of in the distributing agent, the latter can be re-used in the which the interface between the light and the heavy liquid polymerization operation without further puri?cation. lies in the bottom of the column. A slurry of the polymer The process according to the invention can also be ex 20 in gasoline leaves through the top of the column and, ecuted in ways other than those described above. For ex after separation of the gasoline, possesses a high degree of ample, the product obtained from ‘the polymerization, purity and whiteness. which still contains active catalyst particles, can be di Example 3 rectly introduced into the bottom of the column, while an alcohol containing a polar substance, say urea, is fed The process is carried out in a cylindrical column hav into the top of the column,the quantity of the polar sub ing a diameter of 2.4 cm. and a height of 80 cm., provided stance used being such that a more-phase system will be with constrictions. The column communicates with a bel~ formed.‘ In this Way, de-activation and simultaneous re lows pump which imparts about 200 pulsations per minute moval of the catalyst are eifected under water-free and to the column contents, the volume displaced per pulsa countercurrent conditions. It is also possible to use polar tion vbeing about 2 ml. substances other than urea, such as sulphuric acid, sodium A suspension of polyethylene in gasoline, obtained by hydroxide, sodium acetate, acetic acid, ethylene glycol or the polymerization of ethylene by the Ziegler process and glycerol. to which has been added 10% by volume of methanol, If desired, a polymer slurry puri?ed in the column can is fed into the base (bottom) of the column at the rate of be passed through a thickener, for example through a about 1 litre per hour. Water is introduced into the top cyclone. Methanol can be added to the thickened sus of the column at the rate of 1 litre per hour. The tem pension before ?ltering, if so desired; this has the advan perature of the column contents is maintained at 40 to tage that the ?lterability is improved, for example, in the 50° C. case of polypropylene. There is obtained in this way a A polymer-free bottom layer is discharged from the very compact installation in which the polymer can be 4.70 bottom of the column at the rate of about 1.1 litre per thoroughly puri?ed. hour, with the result that the interface between the light The following examples are given :by way of further ex~ and the heavy liquid lies in the base (bottom) of the‘ planation of the invention, butare not intended to restrict column. A suspension of' polymer in gasoline leaves it in any Way whatsoever. through the top of the column and, after separation of ' the gasoline, possesses a high degree of purity and white Example 1 ness. The gasoline contains no more than 0.0008% by The process is carried out in a cylindrical column 3.8 Weight of methanol. cm. in diameter and 300 cm. high, ?lled with polyethylene Example 4 Raschig rings having an inner diameter of 7 mm., an outer diameter of 10 mm. and a height of 10 mm. The column 50 The process is carried out in a cylindrical column hav communicates with a pulsator which imparts 220 pulsa ing a diameter of 20 cm. and a height of 200 cm., which tions per minute to the contents of the colummthe volume is ?lled with polyethylene Raschig rings of 12 mm. inner displaced by each pulsation being 7.5 ml. ' diameter, 16 mm. outer diameter and 15 mm. in height. 30% by volume of methanol is added to a suspension The column communicates with a pulsator which imparts of polyethylene in gasoline obtained by the Ziegler proc 200 pulsations to the column contents, the displaced vol ess; the mixture is introduced into the column at the rate ume per pulsation being 400 ml. of about 11 litres per hour. Water is fed into the top of A suspension of polyethylene in gasoline to which has the column at the rate of 1.2 litres per hour. The tem been added 20% by volume of methanol, is introduced perature of the column contents is maintained at 45— into the base of the column at the rate of 150 litres per 47° C. 60 hour. Water is fed into the top of the column at the A polymer-free bottom layer, being speci?cally lighter rate of 10 litres per hour. The temperature of the col than the polymer, is discharged from the base of the col umn contents is kept at 40—50° C. A polymer free bot umn at the rate of 4.5 litres .per hour, as a result of which tom layer, being speci?cally lighter than the polymer, is the interface between the light and the heavy liquid is in discharged from the bottom of the column at a rate of the base of the column. A suspension of the polymer in about 40 l. per hour, While the interface between the gasoline leaves through the top of the column and, after light and the heavy liquid lies in the bottom section of separation of the gasoline, possesses a high degree of the column. A suspension of polymer in gasoline leaves purity. Moreover, a plate pressed from this product ex through the top of the column and, after separation of hibits a high degree of whiteness. the gasoline, possesses a high degree of purity and white > If the non-ionogenic wetting agent sold under the trade 70 ness. The gasoline contains no more than 0.0007% by name “Lissapol” be added to the suspension obtained from weight of methanol. ‘ the polymerization, a product with approximately the same When the extraction of the polymer suspension is degree of whiteness is obtained. If this wetting agent be carried out on an industrial scale by a batch process, it is added to the water, then, there is obtained a product with extremely dir'licult to discharge the formed polymer-free an even slightly higher degree of whiteness. ' bottom layer. Moreover, even when the extraction hasv 3,198,777 5 been repeated twenty (20) times, the bottom layer still 2. Process according to claim 1, wherein the frequency shows an acid reaction, which indicates that chlorine of pulsations ranges from 50 to 400 pulsations per minute. compounds have been left behind in the polymer. 3. Process according to claim 1, wherein a distributing This is also re?ected in the lower degree of whiteness agent has been used in the preparation of the polymer, of a plate pressed from a polymer that has not been and said agent is used as the lighter liquid, while water puri?ed according to the present invention. In contrast is used as the heavier liquid. thereto, when the suspensions treated in the way de 4. Process according to claim 3, wherein an alcohol scribed in the examples are extracted with water, the is added to the product obtained from the polymerization, bottom layers are immediately obtained in acid-free form. and the resultant mixture is supplied to the column. In the above examples the invention is applied to sus 10 5. Process according to claim 3, wherein the quantity pensions of Ziegler-polyethylene. The process accord of water passed per hour through the column amounts to ing to the invention can also be applied to hard-to-wash 5—25% by volume of the quantity of lighter liquid passed suspensions, emulsions or solutions of polymers or co through the column per hour. polymers of other monomers, particularly the u-ole?ns, 6. Process according to claim 1, wherein the liquid such as propylene, l-butene, isobutene, styrene, butadiene, leaving the bottom section of the column has a speci?c isoprene or for example chloroprene. gravity lower than that of the polymer. The invention described above is still further illus 7. Process according to claim 1, wherein the product trated in the attached diagrammatic drawing, wherein removed from the top of the column is passed upward FIGURE 1 and FIGURE 2 represent ?owsheets of the in a second column countercurrent to a descending stream embodiments of the invention using one and two columns, 20 of a heavier liquid, the contents of the second column respectively. being likewise pulsated, whereby the polymer is sub We claim: jected to further puri?cation. 1. Process for purifying a polymer contaminated with 8. Process according to claim 3, wherein substantially impurities, comprising the following steps: continuously water-free methanol is added to the product obtained passing upward in a contacting zone, comprising an elon from the polymerization, the resultant mixture is sup gated column containing ?ow obstructing means and plied into the bottom section of the column, while meth having a polymer exit, the contaminated polymer to anol containing 4—30% by volumn water is passed into gether with a ?rst liquid countercurrent to a continuously the top section of the column, a methanol-containing downwardly moving second liquid, said second liquid product is removed from the column and is contacted in being heavier than and incompletely miscible with said 30 a second column in countercurrent fashion with water ?rst liquid; simultaneously pulsating the contents of the introduced at the top thereof, the contents of the second contacting zone, to maintain the polymer suspended in column being likewise subjected to pulsations. the lighter liquid and to insure passage of the polymer in the direction of said polymer exit whereby the im References ilited by the Examiner purities are transferred to the downwardly moving heavier liquid; continuously discharging from the bottom of the UNITED STATES PATENTS column a stream of the heavier liquid charged with im 2,742,381 4/56 Weiss et a1. ______23—31O purities; continuously controlling said discharge so that the interface between the lighter and the heavier liquids FOREIGN PATENTS lies in the bottom section of the column, whereby the 961,576 4/57 Germany. lighter liquid forms a continuous phase in the column; 567,031 5/58 Belgium. continuously removing the polymer substantially free of impurities from the top of the column, together with JOSEPH L. SCHOFER, Primary Examiner. the ?rst liquid and thereafter separating the puri?ed polymer from the ?rst liquid. 45 LESLIE H. GASTON, MORRIS LIEBMAN, Examiners. UNITED STATES ‘PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,198,777 August 3, 1965 Cornelis E. P. V. van den Berg et a1.
It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.
Column 1, line 64, for "The above mentioned obstructions in the column, i.e.," read -— The continuous phase of the lighter liquid in the-c401; --. Signed and sealed this 15th day of February 1966.
(SEAL) Attest:
ERNEST W. SW'IDER ‘EDWARD J. BRENNER Attesting Officer Commissioner of Patents