CA1325003C - Ziegler-natta catalyst and a process for its preparation - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
ZIEGLER-NATTA CATALYST AND A PROCESS FOR ITS PREPARATION
A process for the preparation of a solid catalyst of the Ziegler-Natta type comprises precipitating the solid catalyst in a liquid hydrocarbon medium by reacting (A) a solution of a soluble magnesium alkoxide and (B) a transition metal halide which is a halide of Ti (IV), a halide of V (IV) or a halide of VO (III) in the presence of (C) at least one transition metal alkoxide which is free from halogen and soluble in liquid hydrocarbon. The precipitated solid catalyst consists of spheroidal particles having a mean diameter by mass of from 10 to 70 microns and a narrow particle size distribution such that the ratio of mean diameter by mass to the mean diameter by number is greater than 1.2 and smaller than 2Ø

Description

13 2 ~ O a 3 1/B181(2) ''.' ' zIFr~FR-NATTA CATALYST A~D A ~ S F3R ITS ~ ARATIoN
~ : -The present lnvention relates to a solil oat lyst of ~he ~ .
Ziegler-Natta type, suitable for the pol~merizaticn of ole~i~s, and .
to a process for preparing thls catalyst. ~hP sol~ cat l~st is ;~
erpeodsl1y suita~le for the polymerlzaticn o~ copolymer~tlon of etbylene in suspension in a liquil-bydroo&rbon medium or, preferably, in gaseous ~ .
It iS kn~n that ole~in polymerizatlon cat~lyst s~stems o~ the -~
Ziegler-Natta t~pe consist of a ~olld catalyst ornprlEirg at least : ; :
one compou~d o~ a traDsition metal belongi~g to sukgrcups IUb, Vb or - :
10 VIb of ~he Periodic Classlfioation o~ ~he ~leæ nts and a cocatalyst :.
ccmprising at least one OrgBlC et3111D oompound 0~ a metal kelonging : :
to group~ II or III of tbis Caa8si~ioatio!n.
~1gh-e~ficiency solii catslyst~ are knc~n wbi~h comprise at : -least one c ~ o~ a transit~o~ metal sudh as tit n~um or vaxadlum, and a maghes~m c ~ , suoh as a magnesium cklorlde ccmp~und. The co-catalyst is usually obDsen ~rcm organo~luminium or orga;aozi~ o~ . ~Che use o~ ioienay solid catalysts c~1r~i~ a ma~nes~um ~bloride is ~ m to have ~be din~d=t~ge o~
leavi~g hlghly chlor~nated a~d corrosi~e oatalyst re~idues in tbe polymers prQduced~ and so relatively large quantities of Deutrali~ing aL~d sta}Lllzl~g age~ts may have to ~e ad~ed to thEse polymers.
C3talysts prepared USiDg mngreslum aIks~ylates are also kIown ich may ove~c~me or at least mitlgate the problems associated with -.
~5 t ~ use Qf Illag~llm chlo 1~2~03 2 . .

British Fatent 1 306 001 ~c~-loses a process for prepari~g a polymerisation catalyst ccr~stlRg of (A) the reaotion produot obtainel by reaot ~ magnesium etbylate, titanium ~op¢opylate anl tltanium tetrachloridR in an inert dlap#rSl~g medium an~ (B) an :
or~anomet~ o o ~ .
Eritlsh patent 1 333 75~ ~1CrlOSes a prooess for (oo)polymerising alpha-olefins in the presenoe of a catalyst system oomprising the reaotlon p¢oduot of (A) a titaDium compounl ani (B) .. : :
an organoaluminium ccmpounl in whidh the titanium oompounl (A) is a . :.
10 reaotion product obtain3d by the aoti~n of a tetravalent - :-.
halogen-containing tita~ium oompouni on a oomllex metal alccholate or ~uocessively with.~fferent alcoholates. `
Europe~n patent applicati~n 0248593 dlscloses a p¢ooess for (co)polymRrising aD olefiD USiDg a Ziegler-Natta oatalyst in whi~h ~:
the solil catalyst oomponent ls obtained by treating a magnesium alkoxide with an eleotran dcnDr~ a s~licon aIkoxylate and a titaDium . :
ccmpound, e.g. titanium tetrachloride.
Europe~n patent application 0 113 ~57 ~l~nloses a Bolil ~-catalyst c~mpon~nt for produc~ng (co)polymeIs of olefins obtalned by .: .
20 oontaotlng a msgneæium or manganese al$oxlle wlth another ~lkoxide, ~.
such as tetrabutyl titanate, to obta~n a llquJI and-then reaoting this liqu1d with a fluid oomp¢islng a balogenat$ng agent treating wlth an ele tron donor to form a sol~i which is post-treated with a transition metal halide. Ihe post-treatment may 25 not be re~uired if the halogenating agent is a transition metal ~ .-halide.
US pat~nt 4638325 discloses a pYoceæs for prOdU~dDg a transition metal polymerisatian catalyst component comprisiDg reacti~g (i) a soluble magnesium al~rYy alkcxide sol~h~llqc~ in an orgaDic solvent with (ii) titanium tetrachlo¢ide.
~ ome of the processes which utllise msgnesium alkoeide in ~he preparation of solid catal~st require ths use o~ au in~ermsdlate magDeSium alkoxide solid support, w~ich ~aq bave to be prepared in a p~el~mdn3ry step. The quality of the oatalyæts produced USiDg such p~ocesses can ~e variable.

132~03 This labk of reprodlln~h1l~ty oan be bighly detrlmental to a polymerization process, erpe~1o1ly in gasecu8 phase, which is generally sensitive to variatlons i~ the quality o~ the catalysts employed.
It has been foNnd that when the preparation of the catalysts involves the use of an intermediate support based, for example, on magnesium alkoxide, the aotive co=pcu~d3 kased on traDsition metal8, such as titanium or vanadium, enter lnto thl8 801id 8upport nnly ;~
with difficulty. As a result o$ thiS, the ccmposition o$ the 10 catalyst Cb~npA in this manner ~n be relatively heterogeneous and ~
this heterogeneity oan adversely a$$e~t a polymerization prooes8 `
operating un~er stable con~itions. In faot, the polyxr partioles fo~msd from such oatalysts may _ave a tenleDDy to $all apart into f~n~. partioles wh~n the pol y ization progresses to a hih degree.
Solil oatalysts oompriæ~ng a magnesium aLkoæide gener~ly o~nsist of particles of i~l-de$ined shape w_ich produ~e polymer p~wlers wh~ch have a relatively low ~ulk density. Euc1ue:~cre, in most cases these solii catalysts have a relatively broad particle size distribution.
A rPl~ti~ely broad particle size di8tribution is particularly vant~geoUs when the ~olii catal~st is 1~cP~ in,a gas phase ~luidlsed b~d prooesS beogu~e fine partiole~ may be entrained out o$
the reactor with the fluldising ga~ and coarse particles may ættle ~t the bott~m of the reactor.
Tkus, there is a need for a high efficiency, low chlor oon~ent, solll catalyst which comprlses spheroiAA1 p2Iticles having a relatively naITow particle size distribution and whi~h is s~lta~le for use in iniustr~1 ole~in, poly~eslsatlon }rcocasea both in suspensio~ in a llquid h~drocarbcn and in, gaseous ph3se, particularly in a fl~ CP~ ~el. There i8 also a ~ for a simple process for produclng such a solid catalyst.
It has ncw keen foun~ that it is possible to prepare such a hig~, e~ficle~cy solid catalyst using a process wbich is simple, --q~ick aDd lne=pensl~e, since it oo~prises preoipitating the so~
c~talyst essent~lly in a c1n~le stage i.e. the so1~ catalyst is 4 13~003 obtainel directly from ccmpcun~s which are l~quid or in solution in : :
a liquid hydrocarbon. Tn particular, the prooess does not require the manufacture and the baD~ling of an intermedlate so'i~ support ~3sed on magnesium balide or magnesium ~lkoxide. Ihe solid cat lyst can be obtalned with exoellent repro~ucibility aDl high quality. :~-Furthermore, it is advantagecNæly in the form of partioles whose compositlon is relatively homogeneous from core to periphery aDd which h~ve a substantially spherical shape and a relatively narrow pa~ticle size distrlbution.
Thus, accor~ing to the present inNenti~n a process for the :
preparation of a sol1~ catalyst of the Ziegler-Natta type c~ -ising reacting a soluble magnesium alkoxide solu~ilised in a liquid j -hydrooarbon with a transiti~n metal ~ is characterised in tbat ~ -tbe solid cataly~t is prPQ1pitated in a liquid hydroc~rbon ~P~um by reacting the solution of m2gnesium alkoxide and transition metal h~ P in the presence of at least one alkoxide of a tr2~tion metal belonging to subgroup~ IVb, Ub or VIb o~ the Perlr~o Classlfioation o~ Elements, which transition metal ~lk~Xi~ iS free from halogen and is soluble in the liquil h~drocarbo~ medium and in that the transition metal halide is seleoted from the group consisting o~ halldes o~ titanlum (IV), h~l ~Pq of vanadium (IV) and ha~ideæ of VO(III). ~he pIecipitated solii oatalyst comprislng magneslum, transition m~tal, halogen and aIkoxide is ~ aoterised in that it is i~ the form of s~heroidal partioles having a mean : :
diameter by mass, nm, of from lO to qO microns and a narrow partiole size ~tribution su~h that the ratio of mean diameter by msss, Dm, to ~he mean diameter by DNmber, Dn, is great OE than 1.2 and ~maIlOE
th~n 2.0 aDd in that the catalyst con~ transition metal at lts ::
m3ximum valency or vanalyl grcups.
The solid cat lyst accor ~ to t;he present i~ve~tion does not . .
ccmpri~e a soli~ support, su~h as magneæium halide, magnesium alkoxide or a porous refractory oxide on which support a tr~n~tion metal compoucl is fixel or impregnated. Ins~ea~, the sol~d catalyst ~oco~dlng to the present invention is a precipltate, having a 35 sukst~ntially 1m1~orm composition from ths ¢ore to the periphery o~

5 132~0~3 ~ ~

the parti¢les anl comprising magnesium, halogen, alkoxide an~ a transitlon metal.
Although the solil cat lyst is not of the supported type, it is, surprisingly, in the form of sphero~ partioles. In this specification, the terms "spheroidal" or "spherioal" when used in rel~tion to the shape of the solid partioles, mean that the ratio of the m ~ l~n~.r diameter, D, to the minimum line~r diameter, d, :
is less ~han 2, preferably less than l.a. It is a great advantage for the p~rtioles to be sEheroidal because they are more traotable and can p¢oduoe polyolefln powders having improved flow prop OEties.
~hP surface of the SEherol~Al p2rticles is preferakly smooth but -~ -may, for example. resemble the surfaoe of a raspberTy. ;
~ n advantage of the prooess aocording to the present inventi~n for prod~ ng the soll~ catalyst is ~h~t it ccnsists essen~ of a single stage precipitation reacti~n.
Another advantagecus prcperty of the solid oatalyst produoad aeoor~ing to the process of the present i~vention is that it oomprises partloles having a relatively narrow particle a17~
~latributi~n sudh that the ratio of Dmlnn i8 ~reater th~n 1.2 and less than 2Ø Preferably, the ratio o~ nmAon is greater tban 1.4 a~d equal to or less than 1.8. It ha8 been found that the prooess produ oes few coarse p3~tlcles having a diameter greater than 2 x nm and also produces few fines having a dlamter le~8 than 0.2 x Dm. It ;
t~ posslble to produoe solid catalyst 0C~ by weight of whlch 25 con~sts Of partiolles f~ll1n~ with~n the ra~ge Dm + 10%. GbnOEally, the specifio surfaoe area of the par$ioles is from about 10 to ao m2/g ~1'). , ~ ore particularly, the ~nl1~ catalyst can contain magneslum, halogen anl ~ransition mRtal ~n proporticns ~uch that the atomic ratio of halogen to magnesium ~ from 1.7 to 2.3, preferably from 1.8 to a value less than 2.05, and the atomic ratio of transition met~l to magnesium is from 0.1 to O.S, preferably fIcm 0.12 to O.25. ~he ~lsgen co~tent by weiht of ~he so~ catalyst ls a~vantageously less than 50~, and more particularly is between 30~ -a~l 45~. Preferably, the solid catalys$ contains no electron d~nor -~ '' ':~ . '-6 132~0~3 ~

compound selected from the group oonsistlng of amines, amides, ph~pblres, sulphines, sulEhides, sulph~nes, ethers, thioethers, ~etones, aldebqdes, aloohols, thiols anl oarkoxylio acid esters. ~;
Xowever, if su~h an electron donor oompoun~ is used in the so~
catalyst, it is preferably usei in a small quantity, such that the molAr ratio of the electron donor ocmpouni to the tr~n~1tion metal is less than 0.2, preferakly less th3n O.l.
The sol1~ oatalyst acoordlng to the present inventlon has a relatively low h~logen oontent anl oonsequently does not result ln ~O high levels of corrosive resi~iues in the polyolefin produced USiDg th2 catalyst.
The subgroups of the Periodic Classification of the Elements r~ferred to tn this ~pecificatian are thDse citeli in "~an~book of Chem~:try ~n~ Physics", 55th editicn (1971-q2) by R.C. Weast, p~ by t'he Chmi~A7 ~ukber Co. (~SA).
~he prooess accordiDg to the E~resent invention iDNolv~s ths precipitaticn of the solld catalyst in a liqu~i ~ r~on medium which c~n be, for example, one o¢ more llquld hydrocarkcns, suoh as n-pentane, n-hexane or ~-o¢tane.
The tranSitiQn metal hal~ie employed 1n the preparation of the solll catalyst is prefera~ly seleot3i from titarium tetrAnhloride, vaDadl~m tetrachloride, vanadyl trichlor~, titaniu~ tetrabromide, vanadium tetrabrcmide and vanadyl tribromide. ~he balogenated :. :
tltanium and valadium co~çc~mls are liqu~d in the pure state, or ;~
2~ solukle in a liquid h~drocarbon ~n t~e ahsen¢e of any speoial : -solubllizlng agent. Ihey may be e~ploysd singly or as a mixtNre and may be used ln the pure state or, preferakly, in æolution in a liquid hydrocarbon such as D. hexane or n~heptane.
~he mag~eæium ~lknY~ US~i ln ~he pIesent i~Nention iæ used as ~ .
50 a solution in a liquid hydrocarbon. The magnesium ~lk~nl~ iS :
solu~le in the liq~ld hldrocarbon without the need for solu~Llldlg or ccmplexing agents such as a trausition metal alkcxide or ~lumini~m alkcæide. Ihe magnesium ~lkrYi~ can be dissolved in the liquid hydrocarbon medium i~ which the olid catalyæt is to be s5 precipitated. Alternativ~ly ~he magnesium alkoxide oan be pre-dissolved in a liquid hydrocarbon which oan be the same as or different from the liquid hydrocarbon ~Riium in which the solid catalyst is to be precipitatel ani then this solution of magnesium ~.lkoxide can be mixed wlth the liquil hydrocarbon medium. The magnesium alkcxide oan be used in the form of a solution in liquld hydrocarbon at a conoentration which is prefer~hly from 0.1 to 5 moles, preferably 0.1 to 2 moles per lltre of liquld hydrocarbon medium.
The magnesium dialkoxide can have the gener~l fo~mula Mg(o~1)(oR2) in which (ORl) and (oR2) are the same or ~fferent ~lkoxide or alkoxyalkoxide groups. Experienoe sh~ws that it is advant3geous to ;~
15 employ a magnesium ~AlkrN~P in which the groups (ORl) ani (oR2) ~:
are ~lkoxide groups ea~h of which conta~ns a 1~nP~r alkyl radi~
having from 6 to 12 carbon atoms or, preferably, a brarched alkyl ~-~
raAical having from 5 to 12 carbcn atoms, in palticular alkoxide -~
groups c~rrespo~dinB to the general formula .
' ' R3~(B4~CH20 ' in which R3 is an alkyl r~1cal oon~s~n~ng from 2 to ~ carbon atoms ;~ ~-and R4 is an aIkyl radi~l containing from 1 to 8 carbo~ atoms. m e -~
25 total ~umber of carbon atoms being fror 5 to 12. -~
It ~s also possible to employ advantagecusly a magneslum ~-oial~oYide in which the grcups (ORl) and (CR2) are clXoYyalboxlde ~ .:
groups co~taining an ether functlon and havlng from 4 to 12 carbon atoms, i~ particular correEpcnling to tbe geceral formula .--RgO OE(R6)CHzO

in which R6 is a h~droge~ atom and ~5 an alkyl radical con~ g from 2 to 10 c~r~on atcms, or else R6 is a methyl radical an~ R5 an aIkyl rA~cal cont~in1ng ~rcm 1 to ~ carbon atoms.

8 ~32500~ : ~

me magnesium dia1kn~ is preferakly chosen frcm di(2-methyl-1-pentoxy) ~ sium of formula :

Mg(ocH2~H(cH3)cH~cH2c95)2 di(2-ethy1-1-hexoxy)magnesium of for~ula Mg(OCH2CH(C92cHs)cH2cH2PH2cH5)2 and di(2-ethoxy-1-ethoxy)magnesium of formula Mg(ocH2cHzocH2~)2 ~h~ preparation of the solii catalyst a~cording to the prese~t invention must take place in the presenoe of at least one transitlon met 1 alkcxide which is a~ alkoxlde of an element belonging to sub- -:~
groups IVb, Ub or VIb of the Perir~1o Classification o~ the -~
Elements. The tr~nc1tio~ metal al~cxldes suitable for use i~ the ~
prooes~ of t~e prese~t inwention are rh~acterised by the fact that : -t~ey co~tain no halogen a~d tbat they are solu~le in li4~
hydrocar~on, even in the abEenoe of a~y solullllzl~g agent. In ;: -partl~ular, the transition m0tal ~lho;lde8 are ~oluble ln the liquld hyd~ocar~cn employed for formicg the solution of magneaium dialkc~ide or the liquid hydrocarbon medium in whlch the so~
catalyst is prepsred.
~hP transition metal alkoxide i8 prefera~ly va~adyl trioIhoxJ~e -~
or is a ccmpound of the formula Me(a~)x where ~e is the tr~nqition ~e~31, OP~ is a;n ~e group and x is an i nteger equal to the ma~ val~y of the transition metal. ~uitable tra~ition metal a~ nr~ e titanium tetraalk~, vanadium tetr ~krxide, . - .
ZirCODiUIII tetr~e a~l vanadyl tr~lk~, for ei~e tltaI~ium tetra-n-~Ld~3, vaI~adium tetra-~ld3, vaDadyl tri-n-propc~dde, ti~ium tetraiso~ro3?~de, vaI~adyl ~ -triisopTop~de, tita;nium tet~a-~utaxlde, vaDa~ium tetra-n-~tc~e ar~ va~dyl 132~003 Although the mechanlsm by which the soluble halogen-free : .
transition met~l aLkoxide is involvel in the formation of the sol~
catalyst is not accurately known at present, it has nevertheless been founl that its presence in the ccurse of the preparation of the so~l~ catalyst is lnd~speusable. e~pecl~lly for the puIpose of improving the particle c~ distribution of the catalyst anl of control~lng the sukstantially ~pherlcal shape of the partloles of g .
this catalyst. ~ .
It has been observed that it iS possikle to employ at least one 10 adlitional alkoxile o~ an elem~nt of ~Nkgroups IIIa or IVa of the :~:
Periodic Classlfication of elements. The P~tional ~lk~N~ should con~n no h logen, shculd not aot reduotively tcwaIds the - :-.
transition metal halide and mNst be soluble in the organio solvent ':: :
in the aksenoe of any solukLlisdng agent. Suitable additianal 15 aIkolides in~.lude boran alkaxide, allrn~n~um ~lkrYi~P and sil~Con.:.
alkoxide. In particular, it is possible to employ a boron triaIkoxide su~h as boron trietboxide or boron trlbutcxlde. It is ~:
also possible to employ an aluminlum trlaI}cxids such as alumlnium :-triisobutaxide or all~n1n~um tri-sec-butoxlde. More advantageously, it is possi~le to choose a silicc~ AlkrYi~P containlng no funotion acting reduotively towards a traDsition metal cr=pounl, in .:~
partlcular containing no Si-~ band and oorresEo~lLB to the general formNla . .
Si(R7)n(CRB)4-n . ~
. .
in which R7 ls a~ alkyl or aryl ~adUool con~n1ng up to 12 carb~n atoms, R~ is an alkyl radioal o~nt~1n1~g from 1 to 6 oarbon atoms ~-3n~ n is a numker e~ual to or greater tban 0 and s~aaler tha~ or ~ : :
equal to 3. It i,s p~ssdkle, for example, to employ a 1ltoon tetralkoxide su~h as ~11 tcon t~eI~etboxids, tl t oon tetra-n-propoxide or silicon tetralso$rol{xJdc, or else a ~t~ioon .lkoxide or trlalkrxi~e suih as met~hyl trlethnxyY11ure or ~hen~l trie~hnxy311aDe.
It ~as also keen o~served, surprisingly, that the properties .
- ,. :.
9 ~ `
~;
... .... ..

lo ~32~3 of the $oll~ catalyst as a whole and in particular the ~hape.
surface aspect anl particle size distribution are better when use is made of the combi~ation o~ the transitlon metal a ~ an~ the adlitional alkrn~
In order to obtain a soll~ oatalyst having the desired characteristics, it is advantageous to c3rry out itæ preparation in an inert liquid hydrocarbon medium which has the property of being a solvent for the magnesium ~l~.lknyi~P,, the transltion metal ll~e, the transitlon metal aIkoxide and the adiitional ~lk~R~P lf used.
One or more ~11phatio liquid hydrocarboDs æuch as n-hP-~PnP or n-heptane, ~y ltsel f or mixed, are generally emplGyed. I~ praoti oe, lt ls convenient to employ, in the llquid medium where the oatalyst is prepared, quantitites of llquid hydrooarb~n æuch that this meiium oontains between 0.05 and 5 moles of magnesium per litre. The preparation of the solld catalyst may, furthermore, be oarried out ln the presence of a ~11 quantity of an eleotron donor compoNnd ~ :
selected from the group cocelstl=g of amines, ~ Pq, pbo6lhlDe6, sulphnxides, sulphones, ethers, thioethers, ketcnes, aldeb~de~, alcohols, thiols a~d oarbcxylio aoid esters. The quantity of the eleotrosn donor oompound used during the preparation is fiuch th~t in the solli catalyst the molar ratio of the eleotron donor compound to ~ -the transltiosn metal is less than 0.2, more paIticularly less th~n 0.1. The electron donor compound is not an es8ential element of the present preparation. Its presenoe genes311y reduces the activity of the solid catalyst ~n the olef~n polymerisation. Preferakly, the solid ca~alyst is prepared ln the absence of su~h an electron donor compcunl. It is adu~ntage~us, moIeover, to carry out thls preparation at a temperature of from -20C to 100C, preferably from O~C to 80C.
The preparatiosn of the ~o~l~ catalyst consists essentially of a si~gle st~ge precipitation reaoticn. Tbe reaction is preferAhly carried GUt with stirring in the liquid hydrooarbc~ ~P~ium at a temperature in the ra~ge from -20C to 100C n~ing quantities subh that:

3& - the molar ra~io of the qua~tity of ~he magnesium dlalk~xl~e to ' ' ll :
~ 3 2 5 0 0 ~
.
the quantity of the transition metal h~ e is from 0.2 to 4, preferably from 0.5 to 2;
- the molar ratlo of the quantity of the transition metal ~ -:
alkcxide to the quantity of the traDsition metal hal1~e 1~ from . ~ .
0.05 to 5, preferably from 0.1 to 2, aD~ :
- the molar ratio of the y tity of the trA~1tion met 1 ;-alkoxide to the quantity of the ~A~ltirn~.l alkoxide, if used, is from 0.5 to 20, preferAhly from 1 to 10. : : `
Analysis of the ~olid catalyst shcws that thls produot contalns ~ :
one or more oc=pc=~ds of transition metal whioh have not been reduced. It shows, furthermore, that the quantity of transiticn me~al which is precipitatel with the magnesium dlil~=siie is relatively 13rge, since the lar ratio of the quantity of trans~tion metal to the qu~ntity of magnesium is from 0.1 to 0.3, preferAhly from 0.12 to 0.25. Mhat is more, analy~ls of the $o~
oatalyst ~lRo shows that the halogen oontent of thls catalyst ls .. ~ -rel~tively low, s~nce the ~olar ratio of the qu~ntity of halogen to -~
the qu mtity of magnesium ls ~rom 1.7 to 2.3, preferably frolm 1.8 to .: -n:
l~e~ th~n 2.05. In parti~ln~ has been noted that when this 20 molar ratio is too low, for exam¢le smaller than 1.7, the solid .. .
catalyst gives a polyetbylene o~ very low ~ulk density. . .: :
Ihe preparation of the solid oatal~st of the iDwention may be carried tNt acccDdi~g to varlous alternati~e pra3e*ure3. Given that .~ .
thls preparation consistR esse~tially of a preoipitation, the 25 t~pec~ Rt is aware that physical faotors such as the vlscoodty of : .
the medium, the type and rate of s ~ ing, the con~itions of use of ~: :
the varitJus ccnstituents, the Etlrrlqg and the contaot u~me c3n, :
everything ~ P being u ~ ged, play an important paIt in the t~hape, the structure, the size and the ~ icle size dIstributit~n of -. 0 the oatalyst particles.
~n particular, a solutit~n of the magnesium ~Alkrn~ in a liquid hydrocarb~n may be added slawly to a }ydrcc~rbcq mF~1um cont~n1ng the titanium or vanadium halide; the tr~nR~tion metal ~`~
alkoxide and adlltit~nal alkcxide, i~ used, being either present in .
35 the h~drt~c~rb~n nedium, or else belng added to thls medium at the :~
.. ..
11 ~

:. :-.

12 1 ~ 2 ~ 00 3 same time as the solution of the magnesium di01kcxlde, or else being intro~uced by hoth these metho simultanecusly.
It is also poss~h~e to adl the tltanium or vanadium hallde, the transition metal alkoxide an~ optionally an a~ditional aIkoxide of elements of sub-groups IIIa, IVa, slowly anl preferahly simultaneously to the liquil hydrocarbon medium coa~ n~ng the magnesium d1~lkoxide.
It is possible to adl the titanium or vanadium halides ~n~ a solution of magnesium ~1alkryi~p in a liquid hydrooarbon slowly an~
simultanecusly to the liquid h.~dr~rbon medium oo~taining the transition metal alkoxide and cptionally an additional alkoxide of t~R elements of sub-groups IIIa, or IVa.
In ~11 cases, lt is preferable that t~e additicn(s) oarried out in the hydrocarbon W~um should be relatively slow and shLNld take 15 approximately between l and 24 hcurs, preferakly bebwee~ 2 and lO
h~urs. After this or these sl~w addition(s), the mixture o~tained m3y advantageously be kept stlrred for a period of between l and lO
hours. The sol~ oatalyst which i8 thus preoipitated in the liquid hydrocar~n mcdium i8 pre~er~hly ENb~eoted to one or more wzshings :
with the aid of one or more inert llquid hydrooarb~ns and may be reoovered in the form o~ a dry powder, for example, by filtration or ::
by eYaporati~n o~ the liquii hydrooarbon(~).
m e solld oatalyst may be employed aB ~uch and ~1reotly in an olefin polymerisation or oopolymerisatian, partioularly of ethylene, -~
25 in suspension in a liquid hydrooarban, or in gaseous phase in a : ~-fl~ zed bed reactor, in the presenoe of a oocatalyst consisting of .
at least one organsmetallio oompound cc~tzl~drg a metal of groups II
or III of the Periodic Classification of the ~lements. ~he solid cat~lyst ma~ also be o~=wert~d i~to a prepolymer ~efore being usel 30 in a polymerisation. Tn this c3se, the prepolymer is obtalnsd ~y ~ -~riDging the sol~ ¢atalyst i~to ¢o~taot w~ith one or more olef1nq, preferably ethylene, i~ the presence of a cooatalyst oansisting of at least one above mentioned orga = etallic oompcu~d. ~he prepoly~er ma~ c~ntaln fram 1 to 200 g of poly~er, pre~erably from -~
35 10 to lQ0 g of polymer, per mole of tra;nsition met 1. Furt~nore, 13 132~003 .

it contains a quantity of cocat lyst such that the atomic ratio of the guantity of me W in the cocatalyst to the quantity of transition metal is from 0.1 to 10, preferably from 0.3 to 5. :.:
The cocatalyst is advantageously an organoaluminium compcund or an org_nozinc ccmpound. In all caæs, it may be used directly in thP polymerisation me~ium at the same time as the solil catalyst.
It may ~e partly or completely miæed with the catalyst or prepolymer : ~-before keing used in the polymerisation medium. :
The sol~d catalyst is particularly highly suitable for the 10 ma~ufacture of ethylene homopolymers or ethylene copolymers with at ~ -least one al~ha-olefin COD:t~lnlng from 3 to 8 carbon atoms, eSpeclAlly aocordiDg to a gas phase polymerisation process in a -. -fl~ P~ k~d reactor. Ihese eth~lene polymers or copolymers have a-~ -relatlvely narrow mol~ Ar weight distributl~n aDd a low k~logen content. ~n ~ ti~n, they are in the form of a pcwder cc~ tlng of substantially spherical par~icle~ which have a rarTow particle size distribution aD~ a high buIk denslty.
The followlng n~n-11m1ting EXamples i11ustrate the pres~nt :-iDvention. :
20 Example 1 - PreParation of a Catalyst ~B2 -.:
A solution (A) was pr~epared by ~tYing, at amhient temperature (200C) and un~er a nitrogen atmosphere, 230 ml of n-hexane, 61.1 ml :~ -of a solutlon cc~Ltalnlng 6B mlllimoles o~ tltanium tetrachloride in n-hexane and 9 ml of titanium tetra-r~prcpcxide aDd stlrring this 25 mixture for 50 mi~Lutes at ambient temperature. The mdxture was -introd~uced~, un~er a ritrogen atmosphere, irLto a 2 litre glA~
r~3ctor ~itted with a ~tirring system rotating at 550 revolutions per minute. 293 ml of a solutlcn ccn~A~n~ng lO0 mill~moles of .:
di(2-methylpe~Ltcxy)magnesium in n heeane were then s}owly added to ~he re~ctor over 550 minutes, at a l~form r3te, wlth stlrring, and at ambient temperature. At the enl of ~hls tlme, the mixture was stirred for a further one hsur. The sol~ catalyst (B) precipitated :.
was wæshel 5 tlmes with 500 ml of n-hexane at am~ient temperature. : :
It col~tainsd magnesium, tita~ium anl chlorine in such proportions ~5 that the atomlc ratio of titanium to magnesium was 0.16 aDd the 13 :
: . ..
,:'''," . ' ..... , .,, .. 1. ~ . .,- . " -, . , - . - :.

.,.. ., , .. . , .. ~ . ..

14 132~003 :~

atomic ratio of chlorine to m3gnesium was 1.95. m e soll~ oatalyst (B) consistel of spheroidal particles having a mean diameter b~ mass Dm of 31 microns anl a ratio of rh~Dn of 1.8 where Dn is the mean diameter by number.
The mea~ diameter by mass (rm) and the mean dlameter by number (Dn) of the particles were measured on the h~.cl~ of micIoscope `
examinatio~s with an OPTC~AK image analyser (Mlcro Neasurements ~-.
Ilmited GB). ~he measuring prinolple consists in ob ~ from the experimental stuly by optical miorosoopy of a population of particles a table of ahsolute frequencies showlng the n~mker (ni) of particles belonging to each class (i) of diameters, eaoh olas5 (i) : .
being characterised by an intermediate diameter ~di) comprised between the limits of the said class. AYocldl4g to the French Norm ~F X 11-630 of Ju~e l9Bl, Dm and ~n are glven by the follcwing fo~mula:
- mean diameter ~y mass:D~ ~ ~ ni (dl5~ di Di (di3) -- mean diameter by number: Dn - Di.di Di The ratio Dm:Dn characterises the particle slze distribution.
Measurement by the OPTO~K image analyser is performed by means of an inNeIted miorosoope which makes it pcsslkle to examine suspensions of p&rticles at an enlargement betwe~n 16x and 20ax. A
television camera picks up the i~ages giv~n by the inverted -mhcroscGpe aDd transmits them to a oomputer, whic~h analyses the image linP by 11nP and poi~t by po~nt on ea~h llnP 80 as to de~erm~ne the dimensions or diameters of the partiole~s and then to Exa~Ple 2 - PreParatl~n of a Catal~t (D~ - -Ihe procedure was the same as ~n Example 1, exoept that instæad --of employing the sol~1tion (A), a s ~ on (C) w used, which was prspared by mixing, at ambient temperature (20C) and under a nitrogen atmosphere, 230 ml of ~- ~ e, 61.1 ~1 of a solution oont~1ning ~6 mi 1 l 1~ole$ of titanium tetrachlori~e in n~hexane, 9 ml of titan~um tetra-nn-propoxide aDl 4.8 ml of phenyl trlethoeyElls=e 14 ~. .-:' ':.: ' 15 ~ 32~003 ~- ~

anl stirring this mixture for 30 minutes at ambient temperature. ~-The soll~ catalyst (D) preoipitated con~nP~ magnesium, tit~nlum anl ¢hlor~nP in such proportions that the atomi¢ ratio of `~
titanium to nagnesium was 0.12 anl the atcmi¢ ratio of chlor~nP to ma~nesium was 2.02. The solil ¢atalyæt (D) c~nsisted of spheroi~Al -~
particles having a msan diameter by msss nm of 35 microns and a ~. ;
ratio of nm/Dn of 1.4. . -~
Example 3 - Preparatlon of a Catalyst (F~
The prooedure was the same as i~ Example 1, exoept that inæ~ead 10 of employing the solution (A) a solution (E) was used, preparel by : . -mixing, at ambient t ~ rature (20C) and ~1n~ a nitro~en atmosphere, 250 ml of n-hÆeane, 61.1 ml of a soluti~n o~n~ ning ~6 : : .~t11 ~m~les o~ titanium tetrachlor~P in ~-heeane, 9 ml of titanium te~ra-n-PropoOEide and 4 ml of methyl triethcY~oilsoe, and by 15 stirring this mixtNre for 30 m~ln~tes at ambient temper~ture. ~;~
Ihe solid catalyst (F) preoipitated oontalned magnesium, ,.
titanium and ~hlorine i~ such proportions that the atomio ratlo of titanium to magnesium was 0.18 aDd the atcmio ratio of chlori~e to :. `
magnesium was 2.04. ~h~ solid catalyst CF) ccredstol o~ spheroidal 20 particles having a me~n ~ r by mass, Dm, of 32 mi~rons and a - .
ratio r~nn of 1.5.
ExamPle 4 - PreParation of a Cataly~t ~2 The pro~edure was the sa~e a~ in Example 1, exo~pt that instead of employlng the solution (A), a solution (G) was used, prepared ~y ~5 mixing, at amblent temperature (200C) an~ un~er nitrogen atmosehere, ~3D ml of n-hexane, 61.1 ml of a solution oon~n~ng 66 n~ les - ~:
of titanium tetra~hloride in n hexane, 9 ml of titaniu~
tetra-n-propcxile, 4 ml of meth~l trietbnxycil~Do and a.6 ml of 2-met~yl-1-pentanol, and stirring tbis mixture for 30 minutes at . :
ambient temperature.
The solid catalyst (X) Preoipltated contained magnesium, ~itaDium an~ chlor~n~ in such proporti n~ that the atomio ratio of tit~Dlum to magnesium was 0.14 and the atcmio ratio of chlorine to -magr~1um was 1.94. Ihe so~l~ catalyst (X) consistel of spheroidal .. :
particl2s having a ma~n ~A~Pter by mass, r~ of 30 microns and a ..

'. ' lff 132~003 ratio nm/Dn of 1.4.
Example 5 (ComParative) - PreRaratlon of a Catalyst_~J~ :
The prooedure was the same as ln Example 1, exoept that instead of employing the solution (A) a solutio~ (I) was used, preRared ky mixing, at ambient temperature (20C) anl unler nitrogen at-eopbere, 200 ml of n-hexane, 92.6 ml of a solution con~n~ng 100 ~ oles of titanium tetrachloride in n-hexane and 7.5 ml of ::
2-methyl-1-pentanol, anl by stirring this mixture for 30 minutes at -`
~mbient temperature. .
The solil catalyst (J) preoipltated oontalned magnesium, -. :
titanium and ~hlorine in such proportions that the atomio ratio of titaDium to magnesium was 0.06 and the atomio ratio of chlorlne to maghSium was 2.02. ~-c, this catalyst oontained a relatively low quantity o~ titanium relative to magnesium. Furthec~ore, the solid '' catalyst (J) consisted of paIticles having an lr~etel~lDste shape a ratlo rm~n of 2.
ExamPle 6 - PreRaration of a Catalvst (L~ ~
The prooedure was the ~amB as ~n Exampl~ 1, except that instead ,' o~ employing ~he solution (A), a soluti,on (E) was used, prepared by mlxlDg, at ambient temperature (20C) and under nlt ~ at~ccpherc, 210 ml of n,-hR$ane, 69.5 ml of a ~olutl~n ocDtyilllg 75 ~ les .' of titanium tetrachlorlde in n,hexane, 20.4 ml of ti O ~-.
tetra-n-propcxide, and 4 ml o~ metbyl erlctbosysll~a3, and stlrTin thls mixture for W mlnutes at a~bient tc~pesYtDre. .,;' A solld catalyst (L) preoipita W o~nt~nP~ magnesium, tita~iu~
aDl c~lorire in such p ~ oas that the atomlo ratio of titanium to mu~hP~um was 0.12 and the atomic ratlo of chlarlne to m3gnesium . ~ '~
was 1.83. The solid catal~st (L) oore~c w of elbærcddYl partloles , -having a m~an d$ameter by mass, nm, of 2~ r~k rc~a and a ratio nm/Da '''~' 30 of 1.5. , ,,:' Exam~le 7 - Preparation of a Catalvst (N) : ' ~he prooedure was the same as in ExamEle 1, except that instead :,'.' of employing the solution A, a solutio;n (M) was used, prep2red by - ~.
mixing, at ambient temperature (20C) and un~er rdtrogen atmosphere, ~ ~ :
~30 m~ o~ n-hexane, 61.1 ml of a solution oanta~ g 66 millimoles ','~
'~ ' . "~, 16 - ~ ' ~325~03 :

of titanium tetrachloride ln n-hexane, 11.2 ml of titanium tetra-n-~utcxide and 3.4 ml of methyltrieth~xyslll}e, and stirring this mixture for 30 mlnutes at ambient te~perature. :.:
m e solid catalyst (N) precipitated oontained magnesium, . .
titanlum and chlorine in such proportiocs that the atomic ratio of .:
titanium to magneslum was 0.17 aDl the atomic ratio of chlorlne to magnesium was 1.97. The solil catalyst (N) ccnsisted of spheroidal partlcles having a mean dlameter by mass, Dm, of 35 microns and a ~:
ratio nm/Dn of 1.4.
Example 8 - Preparation of a Catalyst (P~
100 ml of n-hexane anl 133 ml of a solution containlng 100 millimoles of di(2-methylpentoxy) magnesium in n-hexane were introduced under nitrogen atmssphere anl at ambient temperature (20C) into a 2 litre glasæ reaotor ~itted wit]h a stlrring system rotating at 350 revolutions per m~nute. A æolution (0) which had been prep&red by mlxing, at ambient temperature ani under nitrogen atmosphere, 50 ml o~ n-hPXPn~ 61.1 ml of a æolution oontaining ~6 millimoles o~ titacium tetr~hloride i~ n-hexane aDd 9 ml of titaDium tetra-n-prcloxids were tben introduoed into the reaotor slowly over 75 minuteæ and at a uIlform rate. At the enl of thiæ
tlme, the mlxture ~as ætirred ~or a further hcur. he solid catalyst (P) preoipitated was -~ashed 5 timeæ wit]h 500 ml of n-hexane at ambient temperature. The æolil catalyst oontained magnesium, tltanium and chlorine in such proportion~ that the ato~io ratlo of ~ltanium to magnesiu~ was 0.18 and tbe atomic ratio of chlor~nP to magDesium was 1.~ Che so~ld oatalyst (P) 019i~119i O:e SEiheToidal.
particles haYing a me~n diameter by mass, Dm, o~ 30 mioroDs an~ a ra~io ~n/nn of 1.8. .
Ex~mPle 9 - Polvm~isation o~ ~tsvlene in Su~sion in n-he~ne Ethylene was pol~merised i~ ~sion in n-bexane using tbe ~atalysts pro~uced in Examples 1 to 8.
2 litres of ~-bexa~e, 6 ~ n~es of trietbylalu~inium (TEA), and a quantity of catalyst correEpo~di~g to O.g ~ nle of -titanium were introduced under nitrogen into a 5 litre stalnless steel reaotor fitted with a stirring syBte~ rotatlng at 750 ':'. ' " ' ~, , .

1 i32~0'3 ~, revolutions per minute. ~hP reaotor was heated to 80C and hydrogen an~ ethylene were introduced therein. The pressure in the reactor was kept constant by the ~ tion of ethylene during the polymerisation. At the end of the polymerisation, the polymer W3S
~iltered off anl driffd. Ihe operating con~itions an~ the characteristics of the polymers o~taln3d are given in Table 1.
Table 1 Polymerisation o~ ~thvlene in susPension in n-hexane Catalyst _ PC2 Tlme Prodn, ~I 2.16 n Bulk (MPa) (MPa) (h) (g) (micro,ns) (g/10 mins) (g/c=t5~
_ _ ~ .
B 0.074 0.074 3 725 236 14 1.26 0.31 D O.06 0.10 3 421 227 7.8 1.27 0.44 F 0.1 O.07 3 537 281 10.3 1.34 O.39 ~ O.OB 0.11 3 285 135 lS 1.42 0.55 ~ (comp) 0.085 0.31 3 2B _ _ _ _ L 0.088 0.12 3 302 170 4.1 1.26 0.41 N O.OB 0.18 1.5 875 395 3.2 1,44 0.33 P 0.1 0.15 1.5 58~ 250 _ _ 0.29 pH2 : partlal pres6ure of hydrogen PC2 : paItial presæure of eth~lene Dm : mean diameter by mass o~ the pol y r particles MI2.16 : melt in~PY of the pol~mer, measured unler a load of 2.16 kg at 190C `-`
D : flow paræmeter o~ the polymer calculated ~occrdlDg to the equation:
n ~ log (MI8-5~Io-325)/1og (8.5/0.325) with MI8.5 and ~Io.325 being the melt lndioes of the polymer, measNred at lgOC un~er a load of 8.5 kg and 0.325 kg respectively The bulk density of the pol~mer powder was deter~ined aocor~ing to AS~M-D 1895A. :

~. ..
,:....

lg 132~003 Example 10 - PrePolvmerisation in Suspension in n-hexane 2 litres of n-hexane were introduoed u~er nitrogen into a 5 ;
litre st~nless steel reactor fltted with a stirring s~stem rotating at 750 revolutiQns Per minute. The reactor was heated to 70C and 20 millimoles of T~A and a quantity of soll~ catalyst (D) prepared in Example 2, corre#pondlng to 3 mt 11 ~oles of titanium were i~trodused therein. Hydrogen w then introduced therein so as to give a Partial pressure of hydrogen of 0.05 NPa, followed by ethylene at a uniform rate of 85 g/h for 280 minutes. At the enl o~ ~
10 this time the reactor content w transferred to a rotary evaporator ~ -anl the n-hexane was evaporated off lm~ reduced pressure. A
pr~polymer (Q) was thus obtain3d which w in the fo m of a powder ~ -cons~sting of spheroidal Particles~ having a narrow particle size distribution.
15 Example 11 - PolYmerlsation anl Copolymerisation of Ethvlene in ~-Gaseous Phase in a Mechanioallv Stirred Reaotor `
200 g of a dry and deaerated polyethylene powder, as a powder charge, followed by 2 m~ m~le3 of TEA, were introdu2ed un~Rr nitroge~ into a 2.5 litre staisless steel reactor fitted with a stirring system for dry powder, rotating at 2S0 revolutions per mlnute. 10 g of the prepolymer tQ) prepared in Ex~mple 10 an~ a gas m~Kture consisting of hydroge~ and ethylene, an~ in a seoond run, 4-meth~1-penteDe-l were then introduced therei~ at a total pressure of 0.8 MPa, kept const3nt by the further addition oi etbylene. ~he opera~ing conditions for the hcmopolymerisation and copolymerisation of ethylene a~d the characteristics o~ the polymRrs obtained are ; -given in Table 2. `~

19 "' ' . . ! ' ': .' ' ;'. ' ` ' ~ " . . :
.`. ` ' . . ': '.. , ` .'` ' : ' ,~,. , ' 13250~3 Table 2 Polymerisation anl CoPolvmerisation of Ethvlene in Gaseous Phase in a MechanicallY Stirred Reactor Temp. pX2/pC2 pC6/pC2 TimR Produ¢tion ~Ia-16 n ('C) (h) (g) (g/10 ~DS) ~0 0.67 0 3 257 7.4 1.24 85 0.15 0.5 3 272 1.3 1.26 PC6 : partial pressure of 4-methyl-1-pentene Example 12 - Polymerisation anl Copolymerisation of Fg~-ene in ~aseous Phase in a Fluidized Bed Reaotor 800 g of a dry ~n~ deaerated polyethylene powler were introduced, as a powder charge, into a fl~ bel reactor 20 om in diameter. Ihis powder was $1uldl2ed with the ali o$ an upwarl gas stream travelling at a velocity of 15 cm/s and ccl~dstlrg of a mixture of hydroge~, ethylene and 1n the f1~st two runs, but not ~n the third, l-butene, at a total pIessure o$ 1.5 ~Pa. 2 mllllmoles - -of TEA were th~n introduced ~lnto the reactor, followed ~y 30 g of the prepolymer (Q) prepared in ExEmple 10. The total pressure was -kept constant at 1.5 MPa by the ~ tion of ~urther ethylene anl, when used, ~utene. TEA was ~ntrodNoed into the reaotor sequentially during the polymerisation or ccpolymerisation. The operating con~itions for ~he polymerisation a~d copolymer~ation of ethylene, a~d the characte~istlcs o~ the polymeIs obtalned are given in Table 3. - -3~

ZO . :.

21 132~03 Table 3 - :Polymerication an~ Copolymerisation of Ethylene in Gaseous Phase ~ :
in a Fluidized Bed Reactor Temp. pH2/pC2 pC4/PC2 TEA ~P Prodn. MI2-16 n d (C)(addelsd) (h) (g) (g/10 mi~s) (g/cm5) : ~
. _ . . .
0.4 0.15 14 3 1 850 4.5 1.24 0.945 - :. :
0.15 0.35 12 2.5 1 260 2.1 1.26 0.~18 ~5 0.6 0 1~ 3.5 2 040 5 1.24 0.959 .:~ ' 15 PC4 : Partial pressure of l-butene .:;
d : density of the polymer determined aocording to ASTM D1505 ~

. ~
.: .

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:', '.
. -:.' :

. .

Claims (14)

1. A process for the preparation of a solid catalyst of the Ziegler-Natta type comprising reacting a soluble magnesium alkoxide solubilised in a liquid hydrocarbon with a transition metal halide characterised in that the solid catalyst is precipitated in a liquid hydrocarbon medium by reacting the solution of magnesium alkoxide and transition metal halide in the presence of at least one alkoxide of a transition metal belonging to sub-groups IVb, Vb or VIb of the Periodic Classification of Elements, which transition metal alkoxide is free from halogen and soluble in liquid hydrocarbon and in that the transition metal halide is selected from the group consisting of halides of titanium (IV), halides of vanadium (IV) and halides of VO
(III).

2. A process as claimed in claim 1 in which the magnesium dialkoxide has the general formula Mg (OR1)(OR2) in which (OR1) and (OR2) are the same or different and are alkoxide or alkoxyalkoxide groups selected from the group consisting of alkoxide groups comprising a linear alkyl radical having from 6 to 12 carbon atoms or a branched alkyl radical having from 5 to 12 carbon atoms and alkoxyalkoxide groups containing from 4 to 12 carbon atoms.

3. A process as claimed in claim 1 in which the transition metal alkoxide is a titanium tetraalkoxide, vanadium tetraalkoxide, zirconium tetraalkoxide or vanadyl trialkoxide.

4. A process as claimed in claim 1 in which the precipitation is carried out in the presence of at least one additional alkoxide of an element belonging to sub-groups IIIa or IVa of the Periodic Classification of Elements, the additional alkoxide being soluble in the liquid hydrocarbon medium, containing no halogen and having no function capable of acting reductively towards the transition metal halide.

5. A process as claimed in claim 4 in which the additional alkoxide is selected from the group consisting of a boron trialkoxide, an aluminium trialkoxide or a silicon alkoxide.

6. A process as claimed in claim 5 in which the additional alkoxide is a silicon alkoxide having the general formula Si(R7)n (CR8)4-n in which R7 is an alkyl or aryl radical containing up to 12 carbon atoms, R8 is an alkyl radical containing from 1 to 6 carbon atoms and n is a number from 0 to 3.

7. A process according to claim 1 in which the precipitation is carried out at a temperature in the range from -20 to 100°C using quantities such that:
(a) the molar ratio of magnesium dialkoxide to transition metal halide is from 0.2 to 4, and (b) the molar ratio of the transition metal alkoxide to transition metal halide is from 0.1 to 2.

8. A process as claimed in claim 7 and claim 4 in which the molar ratio of transition metal alkoxide to additional alkoxide is from 0.5 to 20.

9. A process as claimed in claim 1 in which the solid catalyst is separated from the hydrocarbon medium and consists of spheroidal particles having a mean diameter by mass, Dm, of from 10 to 70 microns and a narrow particle size distribution such that the ratio of mean diameter by mass to mean diameter by number, Dn, is greater than 1.2 and less than 2Ø

10. A process as claimed in claim 9 in which the solid catalyst separated from the liquid hydrocarbon medium has a particle size distribution such that 90% by weight of the solid catalyst consists of particles having a diameter in the range Dm ? 10%, where Dm is the mean diameter by mass.

11. A solid catalyst of the Ziegler-Natta type comprising magnesium, transition metal, halogen and alkoxide characterised in that the solid catalyst is a precipitate consiting of spheroidal particles having a mean diameter by mass from 10 to 70 microns and a ratio of mean diameter by mass, Dm to mean diameter by number, Dn, which is greater than 1.2 and smaller than 2.0 and in that the catalyst contains transition metal at its maximum valency or vanadyl groups.

12. A solid catalyst as claimed in ~ 11 in which the transition metal is selected from the group consisting of titanium IV, vanadium IV and vanadium V in a vanadyl group.

13. A solid catalyst as claimed in claim 11 in which the atomic ratio of halogen to magnesium is from 1.7 to 2.3 and the atomic ratio of transition metal to magnesium is from 0.1 to 0.3.

14. A solid catalyst as claimed in claim 11 which contains an electron donor compound selected from the group consisting of amines, amides, phosphines, sulphoxides, sulphones, ethers, thioethers, ketones, aldehydes, alcohols, thiols and carboxylic acid esters in a quantity such that the molar ratio of the electron donor compound to the transition metal is less than 0.2.