FR2525612A1 - PROCESS FOR PRODUCING LOW-DENSITY LINEAR POLYETHYLENE - Google Patents

Abstract

THE INVENTION RELATES TO POLYMER CHEMISTRY. IT CONCERNS A PROCESS FOR THE PRODUCTION OF A LOW-DENSITY LINEAR POLYETHYLENE (PELBD) BY USING SUSPENSION POLYMERIZATION TECHNIQUES INVOLVING THE POLYMERIZATION OF ETHYLENE AND BUTENE-1 IN THE PRESENCE OF A LIQUID THINNER IN C INERTE. CATALYST SYSTEM IN THE FORM OF AN ORGANIC COMPOUND OF ALUMINUM AND A CATALYST COMPONENT CONSISTING OF A TITANIUM HALOGENIDE SUPPORTED ON A MAGNESIUM HALOGENIDE. THE PROCESS IS REMARKABLY FLEXIBLE IN THAT IT CAN BE IMPLEMENTED WITH VARIOUS CATALYSTS, WITHOUT AFFECTING THE OPERATIONAL STABILITY.

Description

Low density linear polyethylene (sometimes

  hereinafter referred to as PELBD) can be produced by

  suspension polymerization by reacting ethylene and a small amount of another α-olefinic monomer such as butene-1 in the presence of a catalyst composition and using a hydrocarbon, for example hexane or heptane, as liquid diluent These

  suspension polymerization processes are linked to several

  For example, the solubility of

  copolymer in the diluent under the operating conditions leads to an unfavorable rise in the

  viscosity of said diluent and adversely limits the

  centration of the polymeric solids that may be present in the suspension as well as the performance

  space-time of the process These disadvantages were

  with some details in the United States patent

  No. 4,298,713, and said patent offers a

  development of linear polyethylene production

  low density using a catalyst formed from a

  poses a catalyst containing a halogen fixed on a

  layer of magnesium and an organic aluminum compound.

  The suspension polymerization is conducted in the presence of an inert diluent of relatively high boiling point such as hexane or heptane. The performance improvements disclosed would be achieved by conducting the process in at least two stages and by limiting the concentration of ethylene in the

  monomer charge of the first stage at an unex-

not more than 10 mole%.

  A disadvantage of the process mentioned above when it is suitable for a continuous operation on an industrial scale is the need for the presence of at least two reactors, namely one for each stage, which raises

  considerably the cost of the process and the product.

  U.S. Patent No. 4,294,947

  a single-step process for the production of

  copolymers of ethylene and butene-1 under suspension polymerization conditions, using

25256 12

  a Ziegler catalyst containing unfixed vanadium

  on a support The recommended liquid diluent is the butene-

  1; however, the scope of the invention extends to the use

  A C 4 fraction containing other C 4 components which have an inert behavior with respect to the polymerization catalyst. The patent shows that lower yields and lower catalyst efficiencies are obtained when the diluent is used. is a mixture of butene-1 with

other inert components in C 4.

  An important disadvantage of the use of pure butene-1 as a diluent is the lack of flexibility of the process. Because it is necessary to raise the pressure

  partial ethylene to establish the butene molar ratio

  1 / ethylene necessary to obtain a polymeric product

  of desired density, the working temperature must be low enough to prevent the critical temperature of the reaction mixture from being reached at temperatures above the critical temperature, the suspension conditions cease to exist, the operations

  become unstable and we obtain a non-uni-

  form. One of the aims of the present invention is therefore

  to propose a production process in suspension of poly-

  linear low density ethylene, in which

  stable conditions are achieved over a wide range of

operative procedures.

  Another goal is to find a process that can

  be used with various catalyst compositions.

  Another object of the invention is to allow a simple selection of catalysts that can be used

in the prôcédé.

  Other features and advantages of the

  will appear from the detailed description which will

  to follow. In accordance with the present invention, there is provided a continuous process for producing a low density linear polyethylene resin, which comprises copolymerizing ethylene and butene-1 in the presence of an inert C 4 diluent at a pressure at least sufficient to maintain the C 4 thinner in the liquid phase

  and up to about 3.5 M Pa gauge, a temperature of

  from about 54 to about 770 ° C. and an absolute partial pressure of ethylene (Pp -) ranging from about 0.35 to about 2.45 M Pa using a catalyst having a reactivity index r included in the range from about 0.0325 to

  about 0.0500 and containing (a) an organic aluminum compound

  and (b) a titanium halide as a catalytic component

  on a magnesium halide, to maintain a molar ratio Xc of butene-1 to C 4 hydrocarbon total of at least approximately the value calculated from the formula

.1205

XC 4 = (Pp 2) (10) r 4 C 2

  but not exceeding about 0.8, and to collect a poly-

  linear low density ethylene having a maximum density

about 0.935.

  In the accompanying drawings, FIGS.

  explain themselves the limits of the pre-

  invention with regard to operational parameters.

  tional. The catalyst composition used in the process may comprise any of the recently developed high activity titanium halide / magnesium compound catalyst components and cocatalyst components of organoaluminum compounds described, for example, in the US Pat. United States of America No. 3,830,787, No. 3,953,414, No. 4,051,313,

  No. 4,115,319, No. 4,149,990, No. 4,218,339, No. 4,220,554,

  Nos. 4,226,741, 4,252,670, 4,255,544 and 4,263,169;

  Nos. 4,298,713 and 4,301,029, provided that the reactivity index of the catalyst composition falls between about 0.0325 and about 0.0500.

  Property will be discussed in detail in the following.

  The component (a) of the catalyst composition is an alkyl aluminum whose alkyl groups comprise 1 to 8 carbon atoms. It is advantageously chosen from trialkyl aluminum, dialkyl aluminum halide.

  or mixtures thereof The preferred halide is chloride.

  Examples of suitable alkylaluminums are diethylaluminum chloride, di-n-butylaluminum chloride,

  triethylaluminum, trimethylaluminum, tri-n-

  butyl aluminum, triisobutyl aluminum, triisohexyl-

  aluminum, tri-n-octyl aluminum, triiso-octyl-

  aluminum case 6, aluminum alkyl can be

  plexed with an electron donor before its introduction into the polymerization reactor The donors are preferably selected from diamines or diesters of carboxylic acids, including esters of aromatic acids. Some representative examples of these compounds

  are methyl and ethyl benzoate, p-methoxy-

  methyl and ethyl benzoate, diethyl carbonate, ethyl acetate, dimethyl maleate, triethyl borate, ethyl ochlorobenzoate, ethyl naphthenate, methyl p-toluate, ethyl toluate, ethyl p-benzoxybenzoate, ethyl cyclohexanoate, ethyl pivalate, NN, N ', N'-tetramethylenediamine, 1,1,4-trimethylpiperazine, 2,5-dimethylpiperazine, dimethylpiperazine, etc. The molar ratio of aluminum alkyl to electron donor should be limited to a range of about 2 to

  about 5 Solutions of the electron donor and the com-

  aluminum alkylate in a hydrocarbon such as

  hexane or heptane are preferably

  reaction for a certain period, usually less than 1 hour before the mixture is introduced into the

  polymerization reaction zone.

  The method of preparation of component (b) of the catalyst composition is not critical to the process of the present invention and one can be used.

  any of the various techniques known in the prior art

  Normally, these techniques involve the reaction of a titanium compound, for example a titanium halide or a titanium oxyhalide, with a magnesium compound.

  such as a halide, alcoholate, haloalkoxide, carboxy-

  Other methods include reacting the aforementioned magnesium compounds with an electron donor, a silicon compound, an organoaluminum compound, followed by a

  Another reaction step with the titanium compound,

  followed by a second reaction step, wherein the product is treated, for example, with a halogen-containing silicon compound, an electron donor, etc. The halogen of the respective halides can be chlorine, bromine or iodine, the halogen of choice being chlorine. The electron donor, if it is used in the formation of a complex, is advantageously chosen.

  between the inorganic and organic oxygen esters of

  Examples of these compounds are esters of aromatic carboxylic acids such as benzoic acid, pmethoxybenzoic acid and p-toluic acid and in particular the alkyl esters of these acids;

  alkylenediamines, for example N, N, N ', N'-tetramethyl-

  The molar ratio of magnesium to electron donor is equal to or greater than 1 and preferably from 2 to 10. Generally, the content of titanium, expressed as titanium metal, ranges from 0.1 to 20% by weight in the catalyst component. attached to a support Processing steps may also be included in the preparation to obtain component (b) in the form

spherical or spheroidal.

  Processes for preparing the catalyst component

  of a titanium halide fixed on magnesium

  are described in detail in the patents listed above.

  The determination of the catalyst reactivity index is advantageously carried out in a reactor of the type of an autoclave equipped with a paddle stirrer, a cooling jacket for at least partial adjustment of the reactor temperature, intake ports of the catalyst components, triethylaluminum and titanium halide, ethylene, hydrogen, butene-1 and butane feeders used as diluent, steam equipped with a condenser and return ducts for the recycling of condensate and cooled gases After compression, the gases are introduced below the surface of the liquid in the reactor The product suspension is drawn off by a valve disposed in a pipe located at the bottom or near the bottom of the autoclave A small pipe is also provided at or near the top of the reactor to extract a small stream of water. scent sent to a gas chromatograph to continuously monitor the concentrations of the components, namely ethylene,

  hydrogen, butene-1 and butane, in the space of the

  The conditions to be maintained in the reactor at steady state are as follows: Temperature, OC 65.5 Absolute pressure of ethylene, M Pa 1.4 Hydrogen, mole% Total molar ratio C 4 / C 4 0.1: 1 Residence time-hours 2 Speed of the catalyst to titanium sufficient that there is 30% of polymer in the suspension contained in the reactor Alkyl-aluminum-% by weight based on the total weight contained in the reactor 0.1 After a brief drying step, the density d 01 of the polymer product is determined and finally the reactivity index r is determined according to the relationship

r = 0.3029 (d 01 0.8145).

  If the measured density of 1 is equal to or greater than a density of 0.945 g / cm 3, it is recommended to carry out the test under slightly modified conditions, that is to say by raising the ratio X c to 0 , 5, then determining the reactivity index r after the relationship

r = 0.3843 (d 0.5 0.8145).

  It is not necessary to condense and recycle

  If the conditions in the vapor space of the autoclave are at the values set out above, the aerial vapors of the reactor should be discarded. We can also drive the test, when that is

  advantageous, by discontinuous polymerization in the conditions

given.

  Components (a) and (b) of the catalyst are

  charged separately in the reaction zone Aluminum-

  alkyl is introduced in amounts ranging from about 0.025 to about 0.3% by weight based on the total weight of

  monomers and diluent charged to the reaction zone.

  The weight ratio of the titanium metal monomer charge is usually in the range of 50,000 to 1,500,000. The catalyst's preferred reactivity index

  should range from about 0.0325 to about 0.0425.

  The temperatures at which LLDPE formation is to be conducted should be in the narrow range of about 54 to about 770 ° C and especially about 63 to about 680 ° C pressures should be sufficient

  for there to be the proper partial pressure of ethyl-

  and to maintain the C 4 hydrocarbon diluent and

  the butene-1 monomer in liquid phase, the pressure manometer

  typically from about 1.92 to about 3.5 M Pa.

  and preferably from about 2.1 to about 3.15 M Pa.

  fraction of ethylene, which can be maintained to an absolute pressure of 2.45 M Pa at reactor pressures in the upper region of the total

  pressures, is advantageously in the range of

  The average residence time in the reactor can range from about 0.5 to about 10 hours and preferably from about 1.0 to about 4 hours. in polymeric solids

  the suspension in the reactor is usually

  between about 15 and about 50 percent by weight

  and preferably between 20 and about 40% by weight.

B

  The minimum total butene-1 / C 4 (XC) ratio

  can be calculated from the relationship: 4

-0.1055

X C = (Ppc) (10) r

24 2

  For ratios above this minimum, LLDPE products usually have lower densities

or equal to about 0.920 g / cm 3.

  The reaction is continuous and the charges of mono-

  the diluent and the catalyst components are continuously fed into the reactor and a suspension of polymeric product and liquid C 4 products is

  withdrawn, advantageously by a cyclic discharge valve

  That simulates a continuous operation Various modifiers such as hydrogen can be added to modify the properties of the polymeric product These modifiers and their use are well known in the prior art

  and it is not necessary to give a description

  When hydrogen is used to increase the rate of flow of the product, its concentration is usually maintained between about 5 and about 40 mole percent based on the composition of the vapor phase contained therein.

in the reactor.

  C 4 thinner is usually butane

  normal, but it may also be any other hydrocarbon

  inert C 4 bure such as isobutane or mixtures of

these inert compounds.

  Due to the generally high productivity

  of the catalyst fixed on a support, expressed in kg of poly-

  mother produced by kg of titanium metal, it is not

  necessary to remove the catalyst residues from the poly-

  mother in a demineralization operation, as it is

the case of a conventional catalyst.

  When a titanium halide of spherical or spheroidal form is used as the catalyst component, the product polymer is also recovered in forms which avoid the need for subsequent granulation or pelletization of the polymeric product prior to its production.

shipping to the user.

  Various additives may possibly be incor-

  PELBD-resin pores, such as fibers, fillers, antioxidants, metal deactivators, heat and light stabilizers, dyes, pigments, lubricants, etc. The LLDPE obtained as a product in this process is endowed with excellent physical properties which make it interesting to use for various applications, for example in the manufacture of cast and blown film, coatings of metal cables and films, household utensils molded, etc. The product LLDPE can be used alone or in combination with other polymers

  such as a conventional low density polyethylene, a

  ethylene-vinyl acetate, and many others.

  One of the main advantages of the invention

  is the remarkable facility with which the process

  tinu can be influenced to obtain a product of

  desired density at favorable productivity rates.

  Any significant deviation of the density from the desired value can be easily corrected by a simple adjustment of the ratio of butene-1 to the total charge C 4; for example in the case of densities too low, the ratio must be lowered, and vice versa Similarly, by the appropriate setting

  of the above-mentioned report, one accomplishes the same

  product in one product from one density to another, with a minimum of

  changes in the operating conditions and without

  In particular, the total pressure, the flow rate of the ethylene feedstock and the partial pressure, the flow rate of the hydrogen feed (if used), the catalyst speed and the reactor temperature can be kept in

  substantially constant conditions, whereas the

  The desired density is obtained by controlling the butene-1 concentration in the hydrocarbon feedstock.

C 4 total.

  Another advantage, probably even more

  important part of the process of the invention lies in its excellent

  slow flexibility in the use of various

  catalysts from many different sources.

  When going from one system from one catalyst to another, all you need to do is determine the reactivity index

  of the new catalyst and then adjust accordingly.

  laying total butene-1 / C 4 ratios while maintaining other operating conditions substantially at their respective levels.

respective previous ones.

  Another advantage of the process of the invention lies in the high productivity rates per unit volume of the reactor, i.e. the space-time yield, which can be obtained because of the lower solubility of the reactor. polymer in C 4 hydrocarbons compared to those of hexane and heptane This in turn allows the process to be carried out at high concentrations

  in solid polymer in the suspension.

  The following examples further illustrate the

advantages obtained by the invention.

EXAMPLES 1-6

  The tests were conducted in operations

  in large scale pilot plant using

  reading a process and apparatus essentially similar to those described with respect to the

  determining the reactivity index of the catalyst.

  The catalyst system that had a reactivity index

  0,0400 consisted of triethyl aluminum and a catalytic

  magnesium chloride and titanium chloride

  containing about 15% by weight of titanium and prepared

  According to the process described in US Pat. No. 4,218,339, the speed of the recycle gas in each of the tests was about 167 m 3 / hr.

  contact time was 2 hours Other data of interest

  Examples 1 and 2 were conducted in the absence of inert diluent and, as a result of the desired increase in the amount of ethylene reactant, the system became unstable at room temperature. moderate reactor

  60 ° C and serious operational difficulties were encountered.

  countries. Examples 3-6 were conducted within the limits of the invention and gave excellent stability of the

  The effect on density by increasing the

  the concentration of butene-1 in the products

  in C 4 totals is largely illustrated by these examples.

Example

  Temperature, C Manometric pressure, M Pa Ethylene, kg / h Butene-1, kg / h Butane, kg / h Hydrogen, moles% Absolute pressure of ethylene, M Pa Total molar ratio butene-1 / C 4 Al / Ti ratio Concentrations, solids,% by weight

Productivity kg of poly-

  mother / kg Ti Production rate, kg / h Melting index, g / 10 min Density, g / cm 3

T A B L E A U I

Comparative 1 Comparative 2

65.5

4.17 4.15

22.4 13.4

(1) (1)

13.4 11.6

  2.98 1.0 O (1) 000 (1) 0.7 0.927 2.73 1.0 (1)

67,600

  8.9 0.6 0.920 62.8 2.66 7.8 19.8 16.9 16.6 1.60 0.268

1.83 1.79 1.71

0.537 0.574

94.6 97.5

13.9 29.6 20.7 26

64,250

  6.7 0.8 0.931 (1) No specific data are available due to unstable conditions M 66.1 2.66 14.7 7.5 7.2, 7.5, 5.65 13 , 9 7.1 6, 0, 8 2.60 11.2 7.9 6.5 18.9 0.60 N

116,400

16.4 0.94 0.923

118,600

11.2 0.9 0.921

76,600

13.5 1.6 0.919

Examples 7-11

  These tests were conducted essentially from

  the manner indicated above, with the difference that the system

  The catalyst had a reactivity index of 0.0358, the titanium chloride / magnesium chloride component had a titanium content of 2.5% and had been prepared

  by the process described in the United States patent of

  No 3 953 414 The speed of the recycle gas was

  of 87.5 m 3 / h in example 10 and 166 m 3 / h in the example

  The results of these tests are reproduced on

Table II.

Example

  Temperature, C Manometric pressure, M Pa Ethylene, kg / h Butene-1, kg / h Butane, kg / h Hydrogen, moles% Absolute pressure of ethylene, M Pa Total molar ratio butene-1 / C 4 Al / Ti ratio Solid concentration,% by weight

Productivity kg of poly-

  mother / kg Ti Production rate, kg / h Melting index, g / 10 min Density, g / cm 3

TABLE

  , 2.59 13.9 1.57 3.51 12.9 1.71 0.265

952,000

17.05 1.0 0.920

WATER II

  , 2.59 14.5 3.01 1.30 27.7 1.34 0.234 32.3

628,000

  17.77 0.920, 2.59 12.8 1.35 3.24, 4 1.13 0.096 29.2

420,000

  , 57 0.935 62.8 2.03 13.9 4.99 6.48 9.6 1.29 0.175 34.4

706,000

  18.58 0.9 0.921 1 1 62.8 2.03 14.8 4.00 4.00 9.7 1.22 0.238 32.5

536,000

1.4 0.916 ril t; 1 r%) n A

Claims (11)

  A continuous process for producing a linear low density polyethylene resin, characterized by comprising: copolymerizing ethylene and butene-1 in the presence of an inert C 4 extender at a pressure of less sufficient to maintain the C 4 thinner in the liquid phase   and up to about 3.5 M Pa gauge, a temperature of   from about 54 to about 77 C and an absolute partial pressure of ethylene (PPC-) ranging from about 0.35 to about 2.45 M Pa using a catalyst having a reactivity index r in the range of about 0.0325 to   about 0.0500 and containing (a) an organic aluminum compound   and (b) a titanium halide as a catalytic component   on a magnesium halide, maintaining a molar ratio XC of butene-1 to total C 4 hydrocarbon at least approximately the value calculated from the formula -0.1205 Xc 4 (P Pc) (pp) 10) r C 4 -2   but not exceeding about 0.8, and to collect a poly-   linear low density ethylene having a maximum density about 0.935.   Process according to claim 1, characterized   characterized in that the minimum XC ratio is calculated according to the formula: .1055   XC 4 = (PPC 2) (10) A process according to claim 1, characterized in that the reactivity ratio is between about 0.0325 and about 0.0425.   4. Process according to claim 1, characterized   rised in that the temperature is maintained between 63 and about 68 C.   Process according to Claim 1, characterized in that the absolute partial pressure of ethylene   is maintained between about 1.05 and about 1.92 M Pa.   Process according to claim 1, characterized   in that the total gauge pressure is now   held between about 2.1 and about 3.15 M Pa.   The method of claim 1, wherein   in that the length of stay is between 1.0 and about 4 hours.   The method of claim 1, wherein   in that the solid polymer content of the suspension   in the reactor is between about 15 and about 50% by weight and preferably between about and about 40% by weight.   The method of claim 1, wherein   in that hydrogen is present at a concentration   from about 5 to about 40 mole% in the steam.   Process according to claim 1,   characterized in that the diluent is n-butane.   The process of claim 1, wherein   in that the halide of component (b) is a chloride.   Process according to claim 1, characterized   in that the organic aluminum compound is a   trialkyl-aluminum, preferably triethylaluminum.   The method of claim 1, wherein   in that component (b) is in spherical form or spheroid.