CA1070048A - Process for recycling hydrogen when making blends of olefin copolymers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A continuous process for recycling hydrogen for reuse in making blends of olefin copolymers of high and low molecular weights which comprises copolymerizing ethylene with at least one higher olefin monomer in a solvent in separate reactors in the presence of a coordination catalyst, at least one, but not all, of said reactors containing hydro-gen in an amount sufficient to produce low molecular weight copolymer. The resulting solutions of high and low molecular weight copolymers are mixed, unreacted monomers and hydrogen are flashed from the mixture, and the copolymer blend is isolated from the unflashed residue. The flashed gaseous unreacted monomers and hydrogen are circulated together through a staged absorption column under superatmospheric pressure and simultaneously solvent is passed through said column in order to absorb monomer in the solvent and thus separate unabsorbable hydrogen gas from the monomers for recycle to a polymerization reactor in the system for making low molecular weight copolymer component.

Description

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Back~round of the Inven~ion This invention relates to a process for making a blend of olefin copolymers having different molecular weights and, more particularly, to such a process in which gaseous hydrogen is recovered for reuse as a chain-transfer agent in a single monomer recovery and recycle system for making blends of high and low molecular weight olefin copolymers.
Copolymers prepared by copolymerizing ethylene ~ith a higher olefin, e.g.~, propylene and, op~ionally, nonconjugated dienes, are well known commercial products.
Efficient manufacture of these products requires a copolymer synthesis process which involves continuously feeding a coordirlation catalyst and monomers to a reactor having a liquid phase where copolymerization occurs, continuously removing a portion of this liquid (containing a mixture of copolymer, tmreacted monomers, catalyst residue and solvent) in order to isolate the copol~m r product, recovering unreacted monomers and solvent and recycling them to the reactor.
I$ is known that blends of high and low molecular weight olefin copolymers display better processing properties than do the high or low molecular weight copolymers themselves.
Therefore, suitable copolymer components for these blends are prepared by using chain-transfer agents such as hydrogen in the reactor liquid phase during copol~meriæation therein to control the molecular weig~t of the copolymer being fonmed.
The chain-transfPr agent tenminates the growth of the copolymer molecule by displacing the coordination catalyst without deactivating it; a catalyst site is thereby made .

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available for making a new copolymer molecule. The higher the concentration of the chain-transfer agent in the reactor liquid phase, the lower the molecular weight of the resulting polymer. Chain-transfer agents are especially attractive to use to control molecular weight of copolymers because they do not alter the copolymer composition.
In order to produce blends of olefin copolymers having different molecular weights usually two continuous reactors, operating simult~aneously, are used in which the hydrogen concentrations in the liquid phases are different.
Usually, at least about 10% by weight of the total copolymer blend is made in each reactor.
A~ter the polymer blend is made it can be sep-arated from unreacted monomers and hydrogen in a conventional manner by flashing, for example, in a stripper. However~
a serious problem arises concerning reuse of hydrogen and unreacted monomers. Due to the large proportion of mono-mers in the resulting stripper off-gas mixture, one cannot split and recycle the gaseous mixture among the reactors in order to maintain the desired hydrogen concentrations in the liquid reaction zones and, at the same time, main-tain the monomer concentration ratios desired therein.
If the off-gas stream is split to apportion the hydrogen properly, incorrect monomer ratios result; if the stream is split to apportion the monomers properly, then hydrogen distribution is unsatisfactory. There is no practical or commercially feasible t~chnique for apportioning the hydro-~en in the off-gas stream to a reactor in which high molecular weight polymer is being made without first purging to the atmosphere mos~ of the stripper off-gas ~tream being recycled, thereby losing not only hydrogen but substantial amounts of increasingly scarce and expensive ~mreacted monomersO Accordingly, there is a need for a process in which hydrogen can be recovered and recycled ln preselected concentrations to separate reactors to regulate molecular weight of the copolymer components of a blend and at the same time permit independent product composition control so that a preselected ratio of monomer units is contained in the copolymers.
Summary of the Invention The present invention provides a process for making a blend of copolymers wherein said copolymer components of the blend have diferent molecular weights, and to such a process in which the chain~transfer agent, hydrogen, and unreacted monomers are recycled to the copolymerization reactors for reuse in the system. By "copolymer component" is meant the copolymer produced in a single copolymerization reactor.
More particularly, the present invention is directed to a continuous process for making blends of high and low molecular weight copolymers and recycling the chain-transfer agent, gaseous hydrogen,or reuse in the process, said process com-prising polymerizing ethylene and at least one higher olefin monomer iTI a solvent for the monomers in separate reactors in the presence of a coordination catalyst, at least one, but not all, of said reactors containing the chain-transfer agent hydrogen in an amount sufficient to produce low molecular w~ight copolymer, mixing the resulting solution o~ high and low molecular weight copolymers, flashing unreacted monomers and hydrogen from the mlxture, and isolating the blend o~ high and lo~ molecular weight .

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copolymers from the unflashed residue, the improvement which comprises circulating the flashed gaseous unreacted monomers and hydrogen together through a staged absorption column and simultaneously passing fresh or recycle solvent through said column to absorb monomer gas in ~he solvent and thus separate unabsorbable hydrogen gas from monomers and recycling hydrogen in the system to a polymerization reactor for making low molecular weight copolymer. Usually the solvent used is a hydrocarbon; the gaseous hydrogen and unreacted monomers are passed countercurrent to the flow of solvent in the absorption column; and the monomers are ethylene and propylene. The partitioning cf hydrogen from monomers permits the recycling of hydrogen and monomers in preselected amounts to polymerization reactors so that molecular weight and product composition can be controlled.
Detailed Description o~ the Invention The invention can be more readily understood by referring to the schematic drawing in ~onnection wit~
the detailed descrîption of making blends of olefin copoly-mers having different molecular weights, and th~ recoverya~d recycle of the hydrogen chain-transfer agent and monomers for reuse in the system.
The drawing depicts a representative process of the present invention illustrating two reactors in series with a common monomer recovery and recycle system. The concentration of hydrogen in the reactor liquid phase producing the low molecular weight copolymer is at least about three times greater than the concentration of hydrogen in the reactor liquid phase producing the high molecular 3~

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weight copolymer. The monomers to be polymeri2ed are added to evaporatively cooled reactor 1 together with the coordi~
~ation catalyst7 hydrogen, and solvent. The c~polymerization reaction is conducted therein in a conventional manner and a solution of the resulting high molecular weight copolymer is circulated to liquid-full reactor 2 through line 3 by means o~ pump 4. While copolymerization is occurring in reactor 1, monomers, coordination catalyst, make up hydrogen and solvent are, at the same time9 being independently fed through appropriate lines to upstream reactor 2, where copolymerization is also occurring in the presence of recycled hydrogen to produce the low molecular weight copolymer component needed to make a blend of copolymers A solution of the resulting blend of high and low molecular weight copolymer is passed through line 5 to stripper 6 where unreacted monomers and hydrogen are removed as gases by contact with a hot gas stream flowing through line 24.
The hydrogen and gaseous monomers are circulated via line 7 to a compressor and a series of condensers and thence to line 11 and into staged absorption column 13.
The residual polymer blend, together with solvent and monomers, is removed as liquid through line 8 and after flashing in separator 17 (to remove some of the remaining monomers) is fed to a product isolation area via line 18.
There the blend of polymers is separated from solvent in a conventional manner. Solvent is recovered, dried, and ~eturned to a recycle solvent feed system supplying solvent to stripper 6 (via line 24) and to staged absorption column 13 (via line 22). In the product isolation area (not depicted), the copolym~r blend is dried and packaged.

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The off gases from stripper 6 are primarily unreacted monomers and hydrogen. The mixture of hydrogen and monomer gas passes through line 7 to the first stage of a compressor 12A. Gas from the first stage is fed to an interstage cooler-condenser 23 and condenser separator 16 from which condensate is removed via line 10 for recycle. The remaining gas flows via line 9 to the second stage of the compressor 12B. From there the gas mixture is fed via line 11 to staged absorption column 13 (at or near the bottom). As the mixture of gases under superatmospheric pressure contacts the liquid recycle solvent in absorption column 13, the monomer gas transfers to the liquid by dissolving therein and hydrogen gas is partitioned. Most of the hydrogen is unabsorbed by the liquid stream entering through line 22 and thus exits at or near the top of staged absorption column 13 through vapor line 14 to be recycled to downstream reactor 2 in which low molecular weight copolymer is being made. The solvent, together with absorbed monomer gases, exits ~O through line 15 at or near the bottom of absorption column 13 and is recycled to upstream reactor 1 in which high molecular weight copolymer is bei.ng made. The small amount of hydrogen absorbed by liquid stream 15 thus is returned ~o reactor 1.
Occasionally, a small purge of the gas in the system is necessary in order to keep adventitious inerts ~uch ~s nitrogen, methaneg ethane and propane from accumu-I;ltin~. The p~lrge rate is set to maintain a steady-state l~v~l of inerts throughout the system by removing these t .

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components 9 for example, from upstream reactor 1, at the rate they are introduced into the system.
Alternatively, the polymerization reactors can be in parallel arrangement with respect: to the feed of reactants in which case the polymers are blended in stripper 6 where polymer and solvent are separated from unreacted monomer and gaseous hydrogen The invention is useful for making blends of copolymers containing ethylene units (usually containing less than about 85% ethylene by weight) and units of at least one higher olefin. Generally, the olefin is a higher alpha-olefin that can be represented by the formula RCH2-CH~CH2, where R is hydrogen or an alkyl group of 1-15, pre~erably 1-4, carbon atoms; propylene is particu-larly preferred. Preferred copolymers are the well known EPM and EPDM rubbers, i.e., ethylene/propylene dipolymers and ethylene/propylene/nonconjugated diene ter-polymers in which the diene contains only one polymerizable double bond and usually has 6-22 carbon atoms. Representative dienes include: open-chain aliphatic dienes such as 1,4-hexadiene; dicyclopentadienes, such as dicyclopentadiene;
alkylidene norbornenes such as 5-methylene-2-norbornene and 5-ethylidene-2-norbornene; 5-alkyl-2,5-norbornadienes æuch as 5-ethyl-2-5-norbornadiene; and 5-alkenyl-2-norbornene such as 5-(1'-propenyl)-2-norbornene. More than one nonconjugated diene monomer can be incorporated in the copolymer. Copol-ymers can also contain units derlved from a direactive diene used in small proportions to induce branching but insufficient to provide sulfur-curability or cause gelation. The copolymers may contain units of trienes such as 1,4,6-octatriene and - . ~ - . .. .

1,6,8-decatriene. Along with, or in place of the polyene units, there may be units of copolymeriæable olefins con-taining functional polar groups. Examples of such olefins include 2-hydroxy-5-norbornene, and 2 hydroxymethyl-5-norbornene; CH2-CH(CH2)nY where n = 0-20 and Y a carboxyl, ester, amide~ sulfonyl chloride, hydroxy (or dihydroxy) phenyl or their ethers;

¢~(CH2)nNH2 where n : 0-20;

~ CH2~nX where n = 0-20 and X - carboxyl~ amido, and cyano; functional derivatives of an unsaturated carboxylic acid having 3-20 carbon atoms, e.g., amides, nitriles, and anhydrides, and esters of lower alkanols.
Any of the well known coordination catalysts (Zieglsr type) use~ul for producing ethylene copolymers such as ethylene/propylene copolymers or ethylene/propylene/
nonconjugated diene terpolymers, can be used in the process o~ this invention. These catalysts gener~lly comprise a con)bination of transition metal con-pounds, us~lally vanadium cr titanium compounds such as VOC13, VC14, vanndium tris(ace-~yl~cetonate) and TiCl~ and organomet~llic reducing agents,particularly compounds oX metals of Groups I-III o~ the Periodic Table, organoaluminum compounds being preferred.
Examples of the latter include alkylaluminum chlorides, dichlorides ? and sesquichlorides such as diisobutylaluminum chloride and isobutylaluminum sesquichloride. The catalyst may be premixed or formed in situ in the copolymerization reactor.

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The copolymerization is desirably carried out at a temperature o~ less than about 100C.g especially when a vanadium catalyst is utilized, to avoid rapid deterior-ation of the catalyst. Preferably, the polymerization reaction is conducted at about 20-80C., the particular temperature being chosen to provide a convenient reaction rate and to achieve good catalyst e~iciency. Conventional pressures are utilized, usually at least about 10% by weight of total copolymer component is made in each reactor.
Any conventional solvent for the monomers can be used in the present process. Hydrocarbons, especially saturated hydrocarbons having 5 to 10 carbon atoms such as pentane, heptane, hexane, cyclohexane, octane, and decane, are preferred because o~ their high ~olatility.
The amount of hydrogen in the liquid phase in each reactor regulates the molecular weight of the resultant copolymer componen~. The difference in molecular weight between the copolymer components of the blend can be expressed as a ratio. Generally~ the ratio of the inherent viscosity of the high molecular weight copolymer component in deciliters per gram to the inherent viscosity o the 1QW moleculnr weight copolymer component in deciliters per gram is at lea~t about 1.5. Although the particular molecular weight of the copolymer component can vary widely3 the inherent viscosity of the eopolymer components of the blend are usually within a range of from about 0.2 deciliters per gram to about 4.5 deciliters per gram, the ratio of the inherent viscosity of the high molecular weight component of the blend to the inherent viscosity of the low molecular weight component of the blend being at least about 1.5. The inherent 1 ~ 7 0 ~ ~ ~
viscosity of a copolymer solution is determined by measuring to ~ 0.1 seconds efflux times o~ 10 ml. of a solution of 0.1 ~ 0.001 gram of copolymer in 100.0 ml. of tetrachloro~
ethylene at 30C. Replicate measuremen-ts are made in a Cannon Fenske type viscometer until three consecutive efflux times agree within 0.3 seconds An identical determination is made with tetrachloroethylene solvent Inherent viscosiLy in deciliters per gram is calculated as follows:
~n . ln (sample efflux time/solvent efflux time ~ lnh - concen'tration~o~f cop'olymers (grams per 10-0 ml.) where "ln" is the logarithm to the base ~.
To obtain the desired variation in molecular weight, usually, the hydrogen concentration in the liquid phase of the reactor in which low molecular weight copolymer is being made is at least about 3 times that of the hydrogen concentration in the liquid phase in the reactor in which the high molecular weight copolymer is being made. Other factors being comparable, it should be rememb~red that factors other than hydrogen can have an effect upon the molecular weight;
for example, low rea~tor temperatures and high ethylene monomer concentrations favor high molecular weights.
The copolymer components of the blend can be polymerized in a plurality of separate reactors, but usually two reactors are used. Utilizing more than two reactors is more costly and without an attendant increase in benefits.
The hydrogen and monomers, usually ethylene and propylene, in the gaseous state are con~acted with solvent in a staged absorption column. The solvent absorbs gaseous ~onomer in preference to hydrogen. Therefore, the hydrogen is partitioned or separated from the ~aseous monomer that ,, , , ~ , ~. ' ' , , dissolves in or is absorbed by the solvent and is recycled to the liquid phase of a polymerization reactor in which low molecular weight polyolefin copolymer is being made.
Generally, the absorption of monomers and partitioning o~
the hydrogen from them is conducted in a staged system having at least two theoretical equilibrium s~ages at superatmos~
pheric pressure. Pressures and temperatures can be selected over a wide range consistent with the continuous process.
Usually, the pressure in the absorption column is from about

2 atmospheres ~absolute) to 40 atmospheres (absolute) and the temperature in the column is between -40C. and ~150C.
Generally, for efficiency of operation, the staged absorp-tion column is one in which gaseous hydrogen and unreacted monomer are passed countercurrent to the flow of solvent.
However, cocurrent contact can also be used.
The present invention provides a unique way in which hydrogen is recovered and selectively recycled to one or more s-taged continuous polymerization reactors. Hydrogen is removed from the downstream reactor effluent in the staged absorption column and returned to th2 downstream reactor, only a small raction being sent to the upstream reactor.
Thus, a 1~ hydrogen concentration can be maintalnccl in the upstream ~actor, so that high molecular weight COpolymer is produced; at the same time a high co~centratiOn of hydrogen can be maintained in the downstre~m reactor so ~hat the desired low molecular weight copolymer can be produced ht the sa~e time the unreacted monomerS can be recyclcd ~o the pol~merization reactors in preselected amounts so that all important product composition is controlled without loss of m~nomer ~ 7 ~

The hydrogen inventory in the entire sys~em is maintained in a steady state by conventional means.
Additional hydrogen is introduced at the same ra~e as hydrogen is lost during the purging of inerts. Since the upstream reactor is evaporativelY coo:led, there is a con-ventiona1 cooling loop for recycle of the vaporized monomers;
hydrogen in the reactor off-gas trave-Ls through the cooling loop, most of it returning by a gas recycle line, a small amount going back by liquid recycle lines and, as mentioned above, ~ still smaller amount leaving ~he sys~em in the purge line.
For a more detailed and clearer understanding O~
the invention~ the following exaMple illustrates a preferred embodiment of the invention.
Example A 60/40 w/w blend of high and low molecular wei~ht ethylene/propylene/l14-hexadiene copolymers is prepared using two reactors in series which share a commOn ry and recycle system. I`he high molecular weight CPlymer (inherent viscosity 3.5 deciliters/gram~ is made in evaporatively cooled reactor l; the low molecular weight copolymer (inherent viscosity 0.9 deciliters/gram) is made downstream in liquid-full reactor 2 in the presence of the high molecular weight copolymer. A solution of the resulting blend is passed through countercurrent staged stripper 6,-residual polymer solution going to polymer lsolation while stripper off-gas (containing hydrogen, hex~ne solvent, and most of the ethylene and propylene) ~ is circulated to countercurrent staged absorption column 13 w~ere 94% vf the hydrogen is partitioned and returned as gas to reactor 2, 6% of the hydrogen being absorbed in liquid for recycle to reactor 1 Specifically, make-up ethylene gas and propylene liquid are contînuously introduced into evaporatively cooled reactor 1 at the rates of 5777 lbs./hr. and 5597 lbs./hr., respectively. Methane (0.3 lb./hr.) and ethane ~2.0 lbs./
hr.) are present in ethylene; methane (0.9 lb./hr.), ethane ~13 lbs./hr.) and propane (45.7 lbs./hr.) are present in propylene. Reactor 1 is operated at 20C. under a pressure of 7.83 atmospheres (absolute) with a residence time of 30 minutes. Unreac~ed liquid monomers and solvent from countercurrent staged absorption column 13 are continu-ously recycled via 15 to upstream reac~or 1 at l3.2C. at the following rates ethylene - 2,986 lbs./hr.; propylene -45,670 lbs~/hr.; 1,4-hexadiene 5,558 lbs./hr.; hexane solven~ - 120,842 lbs./hr.; hydrogen - 0.48 lb./hr.;
cthane - 283.6 lbs./hr.; propane - 3461.2 lbs./hr.;
nitrogen - 6.9 lbs./hr.; methane - 2.0 lbs./hr. Recycled l~4-hexadiene - 199 lbs./hr.- and recycled hexane - 4,800 lb8./hr. - are added (via a line not depicted) to reactor 1 at -15~C.~ together with fresh premixed eoordination cataly~t made by combining VCl~ (12.84 lbs.thr.) and diiso-butylaluminum monochloride (52.85 lbs./hr.); nitrogen -0.7 lb./hr , enters as ~n inert component of these streams.
; ~bout 8,500 lbs./hr. of high molecular weight copolymer having an inherent viscosity of about 3.5 decilite~s/
~ram is made in upstream reactor 1. The elastomeric copolymer contains about S9.8% ethylene units 5 36% propylene units, and 4.2% total 1,4-hexadiene units by ~eight. The hydrogen eoncentration in the liquid phase in reactor 1 is 0.000013 mole frac~ion.

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The off-gas from reactor 1 is circulated to the evaporative cooling loop at the following rates: ethylene -289426 lbs. /hr.; propylene - 84,368 lbs . /hr.; 1,4-hexadiene -316 lbs . /hr.; hexane - 7,357 lbs . /hr.; e~hane - 1,878 lbs./
hr.; propane - 6, 642 lbs . /hr,; nitrogen - 309. 6 lbs . /hr,;
methane - 83, 2 lbs . /hr,; and hydrogen - 22.3 lbs . /hr, After being compressed and partly condensed the components flow to vapor/liquid separators operated at 40C. and 27.8 atmospheres (absolute). A portion of the vapor is purged at the followi.ng rates: ethylene - 264 lbs./hr.;
propylene - 433 lbs . /hr.; 1,4-hexadiene - 0.1 lb . /hr.;
hexane - 3 lhs./hr.; ethane - 15 lbs . /hr,; propane - 31,9 lbs,/hr,; nitrogen - 5.2 lbs,/hr,; methane - 1~2 lbs./hr,;
and hydrogen - 0.4 lb./hr,; and the balance is recirculated to reactor 1, The liquid effluent from upstream evaporatively cooled reactor 1 is pumped directly to liquid-full reactor 2, Make-up ethylene vapor (2,945 lbs,/hr,) and make-up hydrogen (0.4 lb./hr. replacing that lost in the purge) are added townstream of the p~mp at 30C, and 21 atmospheres ~absolute), Recycle vapor line 14 containing hydrogen from countercurrent staged absorption column 13 enters downstream reactor 2 at 55,8C, and 15,2 atmospheres (absolute) at the following rates: ethylene - 386 lbs./hr,; propylene - 565.7 lbs,/hr,;
194-hexadiene - 6,2 lbs./hr.; hexane - 141 lbs./hr.;
hydrogen - 8,3 lbs./hr.; ethane - 15 lbs./hr,; propane -36 lbs,thr,; nitrogen - 24,8 lbs,/hr.; methane - 3 lbs./hr.
Fresh premixed coordination catalyst mad~ by combining VC14 -22.52 lbs./hr., and diisobutylaluminum monochloride -92.67 lbs./hr. enter down~tream reactor 2 at -15C. and .

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18.4 atmospheres ~absolute). This catalyst is carried in a liquid stream containing recycle 1,4-hexadiene - 199 lbs./
hr.; recycle hexane - 4,800 lbs./hr.; and recycle nitrogen -0.7 lbs./hr.
Reactor 2 is opera~ed at 58C. under a pressure of 14.6 atmospheres (absolute~ with a residence time of 10 min-utes, Abowt 5,625 lbs /hr. of low molecular weight elasto-meric copolymer having an inherent viscosity of about 0.9 and containing about 60.1% ethylene units, 35.8% propylene units, and 4.1% total 1,4-hexadiene units by weight is produced. The hydro~en concentration in reactor 2 wh~ch is liquid full is 0.0015 mole fraction.
The liquid effluent from liquid full downstream reactor 2, containing both high and low molecular weight copolymer, hexane solvent, unreacted monomers, hydrogen (8.8 pounds per hour), spent catalyst, ethane, propane, nitrogen, and methane is passed through a valve and enters the top of countercurrent staged stripper 6 under a pressure of 14.6 atmospheres (absolute) and at a temperature of 58C.
The liquid effluent contacts hot vapors of recycle 1,4-hexadiene ~4,958 lbs./hr.) and hexane (119,704 lbs./hr.) that are fed to the bottom of stripper 6 from heater 25 via gas stream line 24 at 185C. and 37 atmospheres (absolute). The stripping column contains the equivalent of three theoretical equilibrium stages. The copolymer ; blend containing large quantities of hexane solvent and 1,4-hexadiene passes downwardly through stripper 6 and exits via line 8 at 109C. and 4.1 atmospheres ~absolute).
The rate of flow is as follows: ethylene - 5.5 lbs./hr ;
propylene - 1~300 lbs./hr.; l,~-hexadiene - 9~565 lbs./hr.;

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hexane - 231,603 lbs./hr.; ethane - 1.2 lbs./hr.; propane -140 lbs./hr.; and copolymer - 14,125 lbs./hr. The stream from line 8 is flashed via valve V into separator 17 at 66C. and one atmosphere (absolute) to remove residual un-reacted volatile monomers. Liquid stream in line 18 (con-taining 0.1 lb./hr. ethyleneg 111.3 lbs./hr. propylene, 6494 lbs./hr. 1,4-hexadiene, 156,650 lbs./hr. hexane, 13.8 lbs./hr. propane, and 14,125 lbs./hr.of copolymer) is sent to product isolation where it is steam s~ripped and isolated in a conventional manner. The recycle hcxane and 1,4-hexa-diene are dried and returned to the pro~ess.
Vapor stream 19 from separator 17 is cooled to 40C. and condensed in recovery condenser 20 and combined vi~ line 21 with ~he recycle solvent fed to absorption ~olumll 13. The flow rates in stream 19 are: ethylPne, 5.4 l~s./hr.; ethane, 1 2 lbs./hr.; propylene, 1188.7 lbs./
l~r ; ~ropane, 126.2 lbs./hr.; 1,4-hexadiene, 3,071 lbs./hr.;
h~xane, 74,953 lbs./hr.
The ~low rates in gas stream 7 leaving counter-current s~aged stripper 6 are: ethylene, 3~366.5 lbs./hr.;
ethane, 297.4 lbs./hr.; propylene, 45,047 lbs./hr.;
propane, 3,371 lbs./hr.; 1,4-hexadiene, 769 lbs /hr.;
hexane, 18,681 lbs./hr.; nitrogen, 27.9 lbs./hr., methane, 5.0 lbs.~hr.; and hydroge~, 8.8 lbs./hr.; the temperature is 49C.; the pressure i5 3.4 atmospheres (absolute).
The gas stream is sent to the first stage o~ a compressor 12A and then to the interstage condenser-separator 16 where gas and liquid are separated. The gas stream exiting via line 9 enters the second stage of the compressor 12B, where it is further compressed, and then fed by way of line . , ~ . . .

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11 to the bottom of countercurrent staged absorption column 13. Flow rates of the stream in line 11 are: ethylene,

3,137.5 lbs./hr.; ethane, 268 lbs /hr.; propylene, 35,700 lbs./hr.; propane, 2,58~ lbs./hr.; 1,4-hexadiene, 111 lbs./
hr.; hexane, 2,685 lbs./hr.; nitrogen, 27.7 lbs./hr.;
methane, 5.0 lbs./hr.; and hydrogen, 8.8 lbs/hr. The temperature of the stream is 66C. and the pressure 16.3 atmospheres (absolute). The condensate stream in line 10 ~rom condenser-separator 16 contains ethylene (229 lbs./hr.), ethane (29O4 lbs./hr.), propylene (9,347 lbs./hr.), propane (783 lbs./hr.), 1,4-hexadiene (658 lbs./
hr.), hexane (15,9~6 lbs./hr.), nitrogen (0.2 lb./hr.), and methane (0.1 lb./hr.~ This condensate stream is combined with recycle solvent and condensates from the recovery condenser _ and fed via line 22 to the top of ab-sorption column 13. The combined liquid flow rates are:
ethylene - 234.5 lbs./hr.; propylene - 10,535.7 lbs./hr.;
1,4-hexadiene - 5,453 lbs./hr. (including 589.7 lbs./hr.
make-up monomer); hexane - 11~,298 lbs./hr.; ethane - 30.6 lbs./hr.; propane ~ 909.2 lbs./hr.; and nitrogen 4.0 lbs./
hr. The stream in line 22 enters the column 13 at 37~9C.
and 16.3 atmospheres (absolute). Recycled solvent and llquid monomers passing downwardly through the column absorb the gaseous monomers and a small amount of hydrogen that are ascending through the column The column contains the equivalent of three theoretical equilibrium stages. This liquid mixture exi-ts at the bottom o~ absorption column 13 via line 15, is passed through two heat exchangers, and is returned as liquid to reactor 1. The composition of the liquid stream leaving absorption column 13 at a t:emper~ture ~ 7~
of 74C. and a pressure of 15.7 atmospheres (absolut~) is as follows: ethylene - 2,986 lbs./hr.; propylene - 45~670 lbs./hr.; hexadiene - 5,558 lbs./hr.; hexane - 120,842 lbs /
hr; and hydrogen - 0.48 lb./hr; ethane - 283.6 lbs./hr.;
propane 3,461 lbs./hr.; nitrogen - 6.9 lbs./hr.; and methane - 2.0 lbs./hr.
The bulk of the hydrogen remains unabsorbed and leaves the top of countercurrent staged absorption column 13 by way of gas recycle vapor line 14 at the rate of 8.3 pounds per hour and is returned to reactor 2 wherein the low molecular weight copolymer component of the copolymer blend is made. The composition of the gaseous stream leaving thé column via vapor line 14 under a pressure of 15 2 atmospheres (absolute) and a temperature of 55.8C.
is as follows: ethylene - 386 lbs./hr.; propylene -565.7 lbs./hr.; 1,4-hexadiene - 6.2 lbs./hr.; hexane -141 lbs./hr.; hydrogen - 8.3 lbs./hr.; ethane - 15 lbs./hr.;
propane - 36 lbs./hr.; nitrogen - 24~8 lbs./hr.; and methane - 3 lbs./hr.
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The procedure described above in the working example is repeated in order to make a 60/40 w/w blend of high (3.5 inherent viscosity) and low (0.9 inherent viscosity) molecular weight ethylene/propylene/1,4-hexa-diene copolymers having t~e same product composition and in the same quantity, wîth the major exception being that the countercurrent staged absorption colun~ is omitted ~rom the process and, accordingly, hydrogen, uTIreacted monomers and solvent leaving the vapor/liquid separator are recycled to reactor 1.

It is necessary to introduce into reactor 1 makeup ethylene gas at 30C. and propylene liquid at 35C.
at flow rates of 10,522 lbs./hr and 13,674 lbs./hr., respectively. (The great increase in amounts, relative to those o~ ~he above working example~ reflect thP wasteful gas purging required in the comparative example because of the absence of the countercurrent staged absorption column.) Other variations made in the process are as follows. Recycled liquid components from the monomer recovery system are supplied continuously to reactor 1 at 13~C. and 7.57 atms. (absolu~e) pressure at the following flow rates: ethylene - 3,413 lbs./hr.; propylene - 46,167 lbs.~hr.; 1,4-hexadiene - 5,624 lbs./hr.; hydrogen -8.8 lbs./hr.; hcxane - 122~285 lbs./hr.; ethane - 33.5 lbs./
hr.; propane - 1733 lbs./hr.; nitrogen - 4.8 lbs./hr ;
and methane - 0.2 lb./hr.
Additional liquid components at -15C. are supplied ~o reactor 1 by a separa~e stream at the following rates: recycled 1,4-hexadiene - 197 lbs./hr.; recycled hexane - 4,802 lbs. Ihr .; nitrogen - 0.7 lb./hr.; fresh premixed coordination catalyst made by combining the VC14 -12,84 lbs./hr.; and diisobutylaluminum chloride - 52.85 lbs./hr.
The mole fraction of hydrogen in the liquid phase in reactor 1 is 0.000013.
The off-gas from reactor 1 is circulated through e~aporative cooling loop where the gas is compressed, partly condensed, and treated in vapor/liquid separators.
A portion of the separator vapor must be purged to main-tain a steady state of iner~s and hydrogen in the over~ll 1~ 7 ~

system. The loss occurs at the following rates: ethylene -5,383 lbs./hr~; propylene - 8,477 lbs./hr.; 1,4-hexadiene -3 lbs./hr.; hydrogen - 8.7 lbs./hr.; hexane solvent -67 lbs./hr.; ethane - 33.6 lbs./hr.; propane - 294 lbs./
hr.; nitrogen - 5.4 lbs./hr~; and methane - 2.6 lbs./hr.
The liquid effluent in evaporatively cooled reactor 1 is pumped to liquid-full reactor 2 and is joined by a make-up stream supplying 3,338 lbs./hr. of ethylene and 8.7 lbs./
hr. of hydrogen at 30C. and 2 atms. (absolute) pressure.
(No recycle vapor is supplied to reactor 2.) A liquid re-cycle stream enters reactor 2 and contains 1,4-hexadiene -197 lbs./hr.; hexane - 4,802 lbs.fhr.; nitrogen - 0.7 lb./hr.;
fresh premixed coordination catalyst made by combining VC14 -22.52 lbs./hr. and diisobutylaluminumchloride - 92.67 lbs./
hr. Hydrogen is present in the liquid phase in reactor 2 at a concentration of 0. 0015 mole fraction.
The liquid effluent rom liquid-full downstream reactor 2 containing both high and low molecular weight copolymer, hexane solvent, unreacted monomers, hydrogen, spent catalyst, ethane, propane, nitrogen, and methane is ; passed through a valve and enters the top of the counter~
current staged stripper under a pressure of 14.6 atms.
(absolute) and at a temperature of 58C. The liquid effluent from the reactor contacts hot vapors of recycle 1,4~hexadiene (4,822 lbs./hr.) and hexane (118,350 lbs./hr.) entering the bottom of the stripper. The stripper contains the equivalent of three theoretical equilibrium stages. The copolymer blend containing large quantities of hexane solvent and 1~4 hexadiene passes downwardly through the stripper exiting in line 8. The n~n-volatilized liquid exiting from the stripper flows at . : .

108C. and 4.1 atmospheres (absolute) at the following rates: ethylene - 7.2 lbs./hr.; propylene - 1,571 lbs./hr.;
1~4-hexadiene - 9,560 lbs./hr.; hexane - 233,57~ lbs /hr.;
ethane - 0.2 lb./hr.; propane - 83 lbs./hr.; and copolymer -14,125 lbs./hr. The mixture is flashed to atmospheric pressure and the resulting gas/liquid mixLure passes to a vaporjliquid separator at 66C. The liquid polymer solution is isolated and the gas from the separator is condensed at 40C. and recycled to reactor 1.
The off-gases from the stripper flow at 47C. and 3.4 atms. (absolute) pressure at the following rates:
ethylene, 34,062 l~s./hr.; propylene, 44,733 lbs./hr.;
1,4-hexadiene, 689 lbs./hr.; hexane, 163598 lbs./hr.;
ethane, 33.3 lbs./hr.; propane, 1658 lbs./hr.; nitrogen, 0.1 lb./hr.; methane, 0.2 lb./hr.; and hydrogen, 8.8 lbs./hr.
The stream is co~pressed and partly condensed and is passed ~o a liquid/vapor separator. The liquid is recycled to reactor 1 and the vapor is compressed and raturned to reactor 1.
It can be seen from a comparison between the working example and the control that an outstanding advantage of this invention is its efficient use of hydrogen~ volatile monomers and solvent. Most important, the working example of the present invention illustrates that only 0.4 pound per hour of hydrogen is lost from the polymerization system.
In contrast, in the control a loss of ~.7 pounds per hour of hydrogen occurs. Further, in the control process recycle of monomer containing an excessive amount of hydrogen to either reactor cannot be done because the ratio of hydrogen is excessive or making high molecular weight copolymer, and the ratio of monomer is excessive for making low molecular weight copolymer. The stream con~aining hydrogen in the control must be vented in order to purge the unit so that high molecular weight copol~ner can be produced and the hydrogen inventory in the en~ire system be held at steady state. Thus, not only hydrogen is lost, but also ; valuable volatile monomers and solvent.
In both the working example and the control disclosed herein each process produces 14~125 pounds of copolymer during each hour. From the data given in the experiments it can be calculated that the control requires that 12,863 pounds per hour of volatile monomers be purged from the system to make the high and low molecular weight copolymer blend, as contrasted to 6~7.1 pounds per hour using the process of the present invention. Stated differ-ently, the monomers purged per pound of copolymer using the control has a value of 1, whereas using the method of the present invention the value is about 0. 05. Since better utilization of valuable hydrogen and increasingly scarce petroleum feedstock is împortant from both the economic standpoint and one of conservation, this invention provides a process for making blends of high and low molecular weight copolymers that results in substantial s~v~ngs.

Claims (13)

What is claimed is:

1. In a continuous process for making blends of high and low molecular weight copolymers and recycling the chain-transfer agent gaseous hydrogen for reuse in the process, said process comprising polymerizing ethylene and at least one higher olefin monomer in a solvent for the monomers in sep-arate polymerization reactors in the presence of a coordina-tion catalyst, at least one, but not all, of said reactors containing the chain-transfer agent hydrogen in an amount sufficient to produce low molecular weight copolymer, mixing the resulting solution of high and low molecular weight copolymers, flashing unreacted monomers and hydrogen from the mixture and isolating the blend of high and low molecular weight copolymers and solvent from the unflashed residue, the improvement which comprises circulating the flashed gaseous unreacted monomers and hydrogen together through a staged absorption column and simultaneously passing fresh or recycle solvent through said column to absorb monomer gas in the solvent and thus separate unabsorbable hydrogen gas from monomers and recycling hydrogen in the system to a polymerization reactor for making low molecular weight copolymer

2. A process of claim 1 wherein gaseous hydrogen and unreacted monomer are passed countercurrent to the flow of solvent in the absorption column.

3. A process of claim 2 wherein the solvent is a hydrocarbon.

4. A process of claim 2 wherein the solvent is hexane.

A process of claim 2 wherein the solvent contains unreacted monomer.

6. A process of claim 2 wherein the coordination catalyst contains vanadium.

7. A process of claim 2 wherein the higher olefin is propylene.

8. A process of claim 7 wherein the copolymer contains units of a nonconjugated diene.

9. A process of claim 8 wherein the nonconjugated diene is 1,4-hexadiene.

10. A process of claim 8 wherein the nonconjugated diene is ethylene norbornene.

11. A process of claim 2 wherein two polymer-ization reactors are used.

12. A process of claim 2 wherein two polymer-ization reactors are used in series.

13. A process of claim 2 wherein the pressure employed in the absorption column is about from 2 to 40 atmospheres (absolute).