CA1305281C - Control method of molecular weight of polypropylene - Google Patents
Control method of molecular weight of polypropyleneInfo
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- CA1305281C CA1305281C CA000525924A CA525924A CA1305281C CA 1305281 C CA1305281 C CA 1305281C CA 000525924 A CA000525924 A CA 000525924A CA 525924 A CA525924 A CA 525924A CA 1305281 C CA1305281 C CA 1305281C
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- propylene
- hydrogen
- reaction tank
- monomer
- molecular weight
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Abstract
ABSTRACT
Disclosed herein is a method for controlling the molecular weight of a propylene homo- or co-polymer at a constant level upon subjecting propylene alone or a mixture of propylene and another .alpha.-olefin copolymeri-zable with propylene as a monomer or monomer mixture to bulk polymerization in the presence of hydrogen as a molecular weight modifier in a reaction tank equipped with a reflux condenser. According to the present invention, it is possible to prepare continuously a propylene homo- or copolymer, the molecular weight of which is controlled at a desired level, by measuring moment by moment the quantity of heat removed from the reaction tank, calculating the amount of the monomer or monomer mixture polymerized in the reaction tank based on the thus-calculated quantity, determining in advance the relationship between molecular weights and the volumes of hydrogen consumption required per unit amounts of corresponding polypropylene homo- or co-polymers, calculating the volume of hydrogen which is to be introduced into the reaction tank 90 as to obtain polypropylene of a desired molecular weight from the above relationship and the above-calculated polymerized amount, and charging hydrogen into the reaction tank in accordance with the above-calculated volume of hydrogen which varies from time to time.
Disclosed herein is a method for controlling the molecular weight of a propylene homo- or co-polymer at a constant level upon subjecting propylene alone or a mixture of propylene and another .alpha.-olefin copolymeri-zable with propylene as a monomer or monomer mixture to bulk polymerization in the presence of hydrogen as a molecular weight modifier in a reaction tank equipped with a reflux condenser. According to the present invention, it is possible to prepare continuously a propylene homo- or copolymer, the molecular weight of which is controlled at a desired level, by measuring moment by moment the quantity of heat removed from the reaction tank, calculating the amount of the monomer or monomer mixture polymerized in the reaction tank based on the thus-calculated quantity, determining in advance the relationship between molecular weights and the volumes of hydrogen consumption required per unit amounts of corresponding polypropylene homo- or co-polymers, calculating the volume of hydrogen which is to be introduced into the reaction tank 90 as to obtain polypropylene of a desired molecular weight from the above relationship and the above-calculated polymerized amount, and charging hydrogen into the reaction tank in accordance with the above-calculated volume of hydrogen which varies from time to time.
Description
~1305Zt31 CONTROL METHOD OF
MOLECULAR WEIGHT OF POLYPROPYLENE
This invention relates to a process of the homo- or co-polymerization of propylene. Specifically, the present invention relates to a method for controlling the molecular weight of a propylene homo- or co-polymer which is obtained by subjecting propylene alone or a mixture of propylene and another d -olefin copolymeri-zable with propylene to bulk polymerization in the presence of hydrogen as a molecular weight modifier in a reaction tank equipped with a reflux condenser while using the propylene or mixture itself as a liquid medium too.
It has been well-known that upon polymerization of propylene in the presence of a Ziegler-Natta catalyst, the molecular weight of the resulting polypropylene can be controlled by adjusting the volume of hydrogen to be added during the polymerization [see, for example, J.
Polymer Sci., Ç2, 109 (1974)]. Since A
, .. . .
.
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there is a certain close relationship between the concentrations of hydrogen in vapor phases and the molecular weights of the resulting polypropylenes tsee, for example, J. Polymer Sci., Part AI, Vol. 8, 2717 S (1970)], polypropylene is usually prepared by controlling the concentration of hydrogen in a vapor phase at a constant level so that the molecular weight of the resulting polypropylene has a desired value.
When polypropylene is prepared by bulk 10 polymerization in a large reaction tank, it is difficult to remove the polymerization heat if the removal of heat is effected merely through the wall of the reaction tank or by means of a heat exchanger provided inside the reaction tank. Accordingly, it has lS also been known to use a reflux condenser which makes use of the latent heat of a liquid medium.
When polypropylene is subjected to bulk polymerlzation in a reaction tank equipped with the the ~
above-mentioned reflux condenser, the concentration of - ~ 20 hydrogen in a vapor phase however varies significantly in accordance with the load to the reflux condenser.
It is therefore necessary to repeat the introduction or ; discharge of hydrogen frequently into or out of the ; reaction tank in order to maintain the concentration of 25 hydrogen at a constant level in the vapor phase, that is, to control the molecular weight of the resulting ~,~' J ~ ~
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.: ~
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~3C~5~13i polymer. This means that a great deal of hydrogen is discharged and moreover, a large volume of propylene is also discharged along with the thus-discharged hydrogen, resulting in a problem that the above process is not preferred economically.
The present inventors have carried out an extensive investigation with a view toward providing a solution to the above-described problems. The investigation has now resulted in the finding of a process which allows to adjust, with good controll-ability, the molecular weight of polypropylene without loss of hydrogen and/or propylene, leading to completion of this invention.
The present invention is directed towards the provision of a process for the preparation of a propylene homo- or co-polymer of a controlled molecular weight without 1088 of raw materials.
In one aspect of this invention, there is thus provided a process for the preparation of a propylene homo- or co-polymer by subjecting propylene, or a mixture of propylene and another ~-olefin copolymeri-zable with propylene, as a monomer or monomer mixture to bulk polymerization at a constant temperature, in the presence of hydrogen as a molecular weight modifier, in a reaction tank equipped with a reflux condenser while using the propylene or mixture itself as a liquid medium and condensing vapor of the medium in the reflux condenser so as to remove at least a part of polymerization heat. The process comprises:
(a) measuring only the heat balance of the reaction tank in calculating the quantity of polymerization reaction heat generated in the reaction tank based on said measurement, not using detectable information of the concentration of hydrogen in the vapor phase of the reaction tank at all in this calculation and the following calculations and determinations and calculating the amo~nt of the monomer or monomer mixture polymerized in the reaction tank based on the thus-calculated quantity;
(b) determining in advance the relationship between molecular weights and the volume of hydrogen consumption required for the molecular weights with respect to propylene homo- or co-polymer;
~ c) determining the volume of hydrogen consumption required per unit amount of propylene alone or the mixture of propylene with another ~-olefin copolymerizable with propylene corresponding to a desired molecular weight of the propylene homo- or co-polymer; and (d) reacting ~he monomer or monomer mixture while controlling the volume of hydrogen, which is to be fed into the reaction tank, in accordance with variations in the volume of hydrogen required in the reaction tank as a product of the volume of the required hydrogen ,,., ,,, - , .
13~5~281 consumption and the above-calculated amount of the monomer or monomer mixture.
In the following description, there is reference to the accompanying drawings, in which:
FIGURE 1 shows one example of an apparatus suitable for use in the practice of the process of this invention;
FIGURE 2 is a diagrammatic representation of the relationship between the volume of hydrogen consumed in an exemplary polymerization process at a constant temperature and the intrinsic viscosity of the resulting polymer measured as its tetralin solution; and FIGURE 3 is a diagrammatic representation of the relationship between the reaction time periods in Examples and the concentrations of hydrogen in the reaction vessels and the intrinsic viscosities of the resulting polymers.
The term "another ~-olefin copolymerizable with propylene" as used herein means at least one of ethylene, butene-l, hexene-l, etc. and may also be called "copolymerizable d -olefin" hereinafter. When a propylene copolymer is prepared in accordance with the process of this invention, no particular limitation is imposed on the amount of the copolymerizable ~-olefin A
~131~
so long as the resulting polypropylene remains in a slurry state. However, the upper limit of the proportion of the copolymerizable ~-olefin other than propylene in each resulting polymer may generally be 5 about 40 wt.% or so. For the sake of convenience in describing the present invention, the term "propylene"
as used in the descriptive portion of the present specification other than the Examples should be interpreted to include not only propylene alone but 10 also a mixture of propylene and another a-olefin copolymerizable with propylene. Correspondingly, the term "polypropylene" as used in the descriptive portion of the present specification other than the Examples means not only propylene homopolymer but also the lS c,opolymer of the mixture.
For the following reasons, the process of this invention finds extremely important utility when propylene is polymerized in the presence of hydrogen as a molecular weight modifier in a reaction tank equipped 20 with a reflux condenser.
In a reaction tank having no reflux condenser, the vapor phase and liquid phase are maintained in vapor-liquid equilibrium and moreover, the vapor phase is in a substantially even state. Therefore, the 25 concentration of hydrogen in the vapor phase can be accurately determined if the gas of the vapor phase is 13~Z~
sampled and its hydrogen concentration is measured. It is hence possible to control the molecular weight of the resulting polypropylene by comparing the thus-detected hydrogen concentration with a desired hydrogen 5 concentration by conventionally-known desired comparator means and on the basis of the results of the comparison, by automatically controlling a feed valve of hydrogen to the reaction tank and thus always introducing a deficient volume of hydrogen into the 10 reaction vessel so as to maintain the concentration of hydrogen in the vapor phase substantially at a constant level.
However, the vapor phase and liquid phase are not always maintained in vapor-liquid equilibrium when 15 a polymerization is conducted by using a reaction vessel equipped with a reflux condenser. In addition, the concentration of hydrogen in the vapor phase varies considerably depending on the load to the reflux condenser along the passage of time as mentioned above.
20 As a result, it i8 impossible to control the molecular weight of the resulting polypropylene if a simple automatic controlling method such as that referred to above is relied upon.
As exemplary polymerization catalysts useful in 25 the practice of this invention, may be mentioned catalyst systems composed of conventionally-known , 13~SZ8~
transition metal catalysts and organometallic compounds. One or more stereoregularity improvers may also be used in combination if necessary or desirable.
Although not limited specifically to the following s exemplary polymerization catalysts, illustrative of the polymerization catalyst may include titanium trichloride obtained by reducing titanium tetrachloride with a reducing agent such as aluminum; organoaluminum ; or organomagnesium, those obtained by subjecting 10 titanium trichloride to activation treatments such as , . . .
its treatments with oxygen-containing organic compounds, titanium tetrachloride and the like , subsequent to its grinding; those formed of titanium trichloride or titanium tetrachloride supported on 15 carriers 9uch a9 magnesium chlorid-; etc. As exemplary organometallic compound~, may be mentioned organo-aluminums such as trialkylaluminums, dialkylaluminum :
halides, alkylaluminum sesquihalides and alkylaluminum dlhallde~ and organomagnesiums ~uch as dialkyl-20 agnesiu0s.
One embodiment of the present invention willhereinafter be described with reference to the accompanylng drawings.
FIGURE 1 illustrates one example of an apparatus 25 ~uitable for use in the practice of the process of this invention,~in whlch there are illustrated an agitator-~,:: , :
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13~S'~Bl g equipped reaction tank 1, a reflux condenser 2 in theform of a horizontal shell-and-tube heat exchanger, a jacket 3 for the reaction tank 1 and an inlet line 5 for the introduction of a slurry into the reaction tank 5 1. Where the reaction tank 1 is employed for single-tank polymerization or is used as the first tank upon polymerization in a plurality of tanks connected in series, the inlet line 5 is used for the introduction of a catalyst slurry. Where the reaction tank 1 is the 10 second or subsequent tank in such series reaction tanks, the inlet line 5 is employed for the introduc-tion of a reaction slurry from the preceding reaction tank. There are also shown a discharge line 6 for the removal of a slurry from the reaction tank 1, a charge 15 line 7 for the introduction of propylene and a catalyst, a sampling line 9 for the collection of gas from the vapor phase of the reaction tank 1, and a blower 18 adapted to recycle to the reaction tank 1 uncondensed gas which has not been condensed in the 20 reflux condenser 2 and is composed principally of hydrogen gas. Also illustrated are a detector 4-1 for the flow velocity and temperature of gas at the entrance to the reflux condenser 2, another detector 4-2 for the flow velocity and temperature of a 25 condensate returning to the reaction tank 1 subsequent to i~s recovery in the reflux condenser 2, a flow rate 13C~5281 regulating valve 4-3 for hydrogen gas to be introduced into the reaction tank 1, a further detector 4-4 for the flow velocity and temperature of cooling (or heating) water leaving the jacket 3, a still further s detector 4-5 for the flow rate and temperature of cooling (or heating) water to be introduced into the jacket 3, The following procedure may be followed by way of example in order to calculate the amount of a 10 monomer or monomer mixture polymerized per unit time in the reaction tank 1. Data signals a,b,c,d, which have been output from the detectors 4-1,4-2,4-4,4-S respec-tively, are input to a data processor 8, where the quantity of heat generated per unit time in the lS reaction tank 1 at the time of output of the data ~ignals i~ calculated by correcting the quantity of heat removed per the ~ame unit time from the reaction : tank 1, which has been calculated from the data signals - a,b,c,d, in accordance with the quantity of dissipated 20 heat whlch ha~ been calculated based on the overall : structure of the polymerization system and its : operational conditions. Since the relation~hip between polymerized amount of the monomer or monomer mixture and reaction heat can be known from the compo~ition of /
25 the thu~-polymerized monomer or monomer mixture in the manner known per se in the art, the above-mentioned , ~. .. .. .
13~5Z~
generated heat is converted further at the data Qrocessor 8 into the amount of the monomer or monomer mixture polymerized per unit time in the reaction tank 1.
Incidentally, the relationship between the molecular weight of polypropylene of a desired composition and the volume of hydrogen required for the preparation of the polypropylene varies in accordance with catalyst system, polymerization temperature and 10 the like, but as shown in FIGURE 2 by way of example, the relationship between the intrinsic viscosity of a polymer as measured in the form of its tetralin solution of 135C and the volume of hydrogen consumption per unit weight of the polymer can be 15 predetermined.
It is therefore possible to determine the volume of hydrogen reguired per unit amount of feed propylene by storing beforehand the above relational expression as an equation In the data processor 8 and then inputting 20 a desired polypropylene molecular weight in the data processor 8.
In the above-described manner, the volume of hydrogen required in the reaction tank 1 is hence calculated at the data processor 8 as the product of 25 the amount of the polymerized monomer or monomer mixture, which has been calculated in advance, and the , :, ' , ~, , -- 13~S2~
volume of hydrogen required for the unit amount of the feea polypropylene. Results o~ the operation are output as a signal e from the data processor 8. It is therefore possible to replenish the volume of consumed s hydrogen by changing the opening degree of the flow rate regulating valve for hydrogen gas in accordance with variations in the value of the signal e so as to control the volume of hydrogen to be introduced into the reaction tank 1, that is, to conduct the reaction 10 while maintaining the actual concentration of hydrogen in the reaction tank 1 substantialIy at a constant level. Accordingly, it seems to be possible to prepare polypropylene of a uniform molecular weight.
By the way, when the present invention is 15 applied to such a reaction ~y~tem that a plurality of tanks are connected in series to conduct continuous polymerization therein and the molecular weight of the resulting polymer i8 increased successively from one tank to the next tank, hydrogen is introduced and 20 di9charged from each of the tanks along with the :
~slurries which are introduced through the line S and diocharged through the line 6 respectively and contains 8aid hydrogen dissolved therein. It is hence necessary ~;~ to input information on the volume of the hydrogen in 25 the data processor 8 and to perform a correction on the -~; basis of the information.
~,:
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' '''':'~"' ' ' 13~5281 On the other hand, when a single-tank polymeri-zation process is effected in the above-described reaction tan~ l or a polymerization process is conducted by connecting in series a plurality of 5 reaction tanks, each, of the same type as the reaction tank 1, each of the reaction tanks has already been filled with a great deal of propylene not only as a liquid medium but also as a reaction raw material at the start-up time of the reaction. It is therefore 10 impossible to obtain a polymer of a desired molecular weight even if hydrogen is fed in accordance with the present invention, namely, in a volume correspond-ing to the amount of polymerized propylene which is calculated based on the measured and calculated 15 quantity of heat of the polymerization reaction. While taking into consideration the volume of hydrogen to be dissolved in the liquid propylene filled in each reaction tank at the start-up time and the volume of the vapor phase above the liquid medium, it is thus 20 necessary to charge at once hydrogen in a volume corresponding to the liquid propylene at the beginning ~o that the polymerization reaction is conducted. The molecular weight of the resulting polypropylene is then measured and compared with a desired value. Based on 25 the results of the comparison, a small amount of hydrogen or propylene is additionally charged in the .
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reaction tank. The above-described fine correctio~
procedure is repeated until the molecular weight of the resulting polypropylene reaches the desired value. The reaction is thereafter allowed to proceed further in 5 accordance with this invention, whereby polypropylene of a constant molecular weight can be prepaxed.
It is a reaction tank equipped with a reflux condenser that can be used in the practice of the present invention. No particular limitation is imposed 10 on the heat-removing capacity of the reflux condenser.
The present invention is particularly effective in a steady state, that is, when it is applied to a reaction tank the temperature of which is controlled by the removal of heat through the reflux condenser while the lS pregent invention is being practised.
According to the present invention, it is po~9ible to maintain the molecular weight of the resulting polypropylene at a constant level by introducing hydrogen in a volume corresponding to the 20 volume of it9 consumption into the reaction tank, since the volume of hydrogen consumption required upon providing polypropylene of a constant molecular weight is uniform per unit weight and the vapor phase and liquid phase are maintained in equilibrium on average 25 although the concentration of hydrogen in the vapor phase of the reaction tank varies depending upon the . ., ~ .
13~3$~
load to the reflux condenser and its apparent value changes considerably.
The present invention is extremely valuable from the industrial viewpoint because polypropylene of a constant molecular weight can be obtained with not only high efficiency but also good controllability by using a reaction tank equipped with a reflux condenser and conducting bulk polymerization of propylene in the presence of hydrogen as a molecular weight modifier in accordance with the process of this invention.
EXAMPLES:
Continuous bulk polymerization of liquid propylene was conducted at 70C in the presence of a catalyst composed of titanium trichloride and diethylaluminum chloride in a reaction tank having the structure shown in FIGURE 1 and an internal capacity of 40 m3 while using the liquid propylene as a medium.
Upon initiation of the polymerization, 3000 kg of propylene and 35 Nm3 of hydrogen were first charged in the reaction tank. Warm water was caused to flow through the jacket so as to heat the medium up to 70C. The polymerization reaction was then initiated while charging the catalyst and propylene at constant feed velocities (titanium trichloride: l.0 kg/hr, diethylaluminum chloride; 16 kg/hr, propylene: lO000 -" 13~SZ~l kg/hr). During the reaction, the reaction slurry was sampled from the reaction tank and the molecular weight of the resultant polypropylene was measured. The thus-measured molecular weight was compared with a predeter-5 mined value. The molecular weight of the resultingpolypropylene was adjusted substantially to the predetermined value by repeating several times a fine correction procedure in which a small amount of hydrogen was charged in the reaction tank on the basis 10 of the results of the above comparison. About 30 minutes were spent until the predetermined value was reached.
Continuous bulk polymerization of propylene was then conducted in accordance with the process of this 15 invention. Namely, propylene, titanium trichloride and diethylaluminum chloride were charged at constant feed velocities, namely, at 6000 kg/hr, 0.8 kg/hr and 8 kg/hr respectively into the reaction tank. At the same time, a slurry was charged out at about 6000 kg/hr 20 from the reaction tank so as to maintain the level of the slurry constant in the reaction tank. During this polymerization, data signals a,b,c,d were input from the detectors 4-1,4-2,4-4,4-5 into the data processor 8 to calculate the quantity of heat removed through the 25 jacket and reflux condenser. It was found to be 860 Mcal/hr. Furthermore, upon its correction by the ., ' ~ ~
13~15Z~l quantity of heat released from the system, the quantity of polymerization reaction heat generated in the reaction tank was 1,006 Mcal/hr, which corresponded to a polymerized propylene amount of 2,196 kg/hr.
The intrinsic viscosity corresponding to polypropylene of a desired molecular weight as measured in the form of its tetralin solution of 135C was found to be 1.73 and the volume of hydrogen required corresponding to the above-determined polymerized 10 propylene amount was found to be 1.152 Nm3/hr from FIGURE 2. A correction was performed in view of the volume of the hydrogen discharged along with the slurry from the reaction tank which volume was 0.845 Nm3/hr.
As a consequent, hydrogen was introduced into the ~. qq7 3 15 reaction tank at the rate of 1.977 Nm /hr through the flow rate regulating valve 4-3. By the way, the above operation, conver~ion and correction were all performed automatically by the data processor, and the system was operated in such a way that the molecular weight of the 20 polypropylene in the discharged slurry was automatically controlled by delivering the volume of hydrogen, which was to be introduced, as the signal e to the flow rate regulating valve 4-3.
The polymerization reaction was continued while 25 correcting the volume of hydrogen, which was to be introduced, at intervals of five minutes in accordance 13~52Bl with variations of the data signals a,b,c,d. Two hours later, the volume of the polymerized propylene reached 2,405 kg/hr. At that point of time, the charging rate of hydrogen was 1.323 Nm3/hr and the intrinsic 5 viscosity of the polymer sampled out from the discharged slurry as measured in the form of its tetralin solution of 135~C was 1.73 as desired.
The above reaction was continued for about 20 hours. FIGURE 3 diagrammatically illustrates 10 time-dependent variations in the concentration (vol.%) of hydrogen in the vapor phase sampled out through the line 9 as well as time-dependent variations in the intrinsic viscosity of polypropylene in the slurry discharged through the line 6. As understood from 15 PIG~RE 3, the intrinsic viscosity, namely, the molecular weight was controlled at a constant level although the concentration of hydrogen in the vapor phase varied.
By the way, about 65~ of the total quantity of 20 heat removed through the jacket and reflux condenser in a ~teady ~tate, namely, during the practice of the process of this invention was accounted for on average by reflux condenser.
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.
MOLECULAR WEIGHT OF POLYPROPYLENE
This invention relates to a process of the homo- or co-polymerization of propylene. Specifically, the present invention relates to a method for controlling the molecular weight of a propylene homo- or co-polymer which is obtained by subjecting propylene alone or a mixture of propylene and another d -olefin copolymeri-zable with propylene to bulk polymerization in the presence of hydrogen as a molecular weight modifier in a reaction tank equipped with a reflux condenser while using the propylene or mixture itself as a liquid medium too.
It has been well-known that upon polymerization of propylene in the presence of a Ziegler-Natta catalyst, the molecular weight of the resulting polypropylene can be controlled by adjusting the volume of hydrogen to be added during the polymerization [see, for example, J.
Polymer Sci., Ç2, 109 (1974)]. Since A
, .. . .
.
~3~
there is a certain close relationship between the concentrations of hydrogen in vapor phases and the molecular weights of the resulting polypropylenes tsee, for example, J. Polymer Sci., Part AI, Vol. 8, 2717 S (1970)], polypropylene is usually prepared by controlling the concentration of hydrogen in a vapor phase at a constant level so that the molecular weight of the resulting polypropylene has a desired value.
When polypropylene is prepared by bulk 10 polymerization in a large reaction tank, it is difficult to remove the polymerization heat if the removal of heat is effected merely through the wall of the reaction tank or by means of a heat exchanger provided inside the reaction tank. Accordingly, it has lS also been known to use a reflux condenser which makes use of the latent heat of a liquid medium.
When polypropylene is subjected to bulk polymerlzation in a reaction tank equipped with the the ~
above-mentioned reflux condenser, the concentration of - ~ 20 hydrogen in a vapor phase however varies significantly in accordance with the load to the reflux condenser.
It is therefore necessary to repeat the introduction or ; discharge of hydrogen frequently into or out of the ; reaction tank in order to maintain the concentration of 25 hydrogen at a constant level in the vapor phase, that is, to control the molecular weight of the resulting ~,~' J ~ ~
, :''; : :
.: ~
; . : ' -' -'.
' - ' ' ., .
~3C~5~13i polymer. This means that a great deal of hydrogen is discharged and moreover, a large volume of propylene is also discharged along with the thus-discharged hydrogen, resulting in a problem that the above process is not preferred economically.
The present inventors have carried out an extensive investigation with a view toward providing a solution to the above-described problems. The investigation has now resulted in the finding of a process which allows to adjust, with good controll-ability, the molecular weight of polypropylene without loss of hydrogen and/or propylene, leading to completion of this invention.
The present invention is directed towards the provision of a process for the preparation of a propylene homo- or co-polymer of a controlled molecular weight without 1088 of raw materials.
In one aspect of this invention, there is thus provided a process for the preparation of a propylene homo- or co-polymer by subjecting propylene, or a mixture of propylene and another ~-olefin copolymeri-zable with propylene, as a monomer or monomer mixture to bulk polymerization at a constant temperature, in the presence of hydrogen as a molecular weight modifier, in a reaction tank equipped with a reflux condenser while using the propylene or mixture itself as a liquid medium and condensing vapor of the medium in the reflux condenser so as to remove at least a part of polymerization heat. The process comprises:
(a) measuring only the heat balance of the reaction tank in calculating the quantity of polymerization reaction heat generated in the reaction tank based on said measurement, not using detectable information of the concentration of hydrogen in the vapor phase of the reaction tank at all in this calculation and the following calculations and determinations and calculating the amo~nt of the monomer or monomer mixture polymerized in the reaction tank based on the thus-calculated quantity;
(b) determining in advance the relationship between molecular weights and the volume of hydrogen consumption required for the molecular weights with respect to propylene homo- or co-polymer;
~ c) determining the volume of hydrogen consumption required per unit amount of propylene alone or the mixture of propylene with another ~-olefin copolymerizable with propylene corresponding to a desired molecular weight of the propylene homo- or co-polymer; and (d) reacting ~he monomer or monomer mixture while controlling the volume of hydrogen, which is to be fed into the reaction tank, in accordance with variations in the volume of hydrogen required in the reaction tank as a product of the volume of the required hydrogen ,,., ,,, - , .
13~5~281 consumption and the above-calculated amount of the monomer or monomer mixture.
In the following description, there is reference to the accompanying drawings, in which:
FIGURE 1 shows one example of an apparatus suitable for use in the practice of the process of this invention;
FIGURE 2 is a diagrammatic representation of the relationship between the volume of hydrogen consumed in an exemplary polymerization process at a constant temperature and the intrinsic viscosity of the resulting polymer measured as its tetralin solution; and FIGURE 3 is a diagrammatic representation of the relationship between the reaction time periods in Examples and the concentrations of hydrogen in the reaction vessels and the intrinsic viscosities of the resulting polymers.
The term "another ~-olefin copolymerizable with propylene" as used herein means at least one of ethylene, butene-l, hexene-l, etc. and may also be called "copolymerizable d -olefin" hereinafter. When a propylene copolymer is prepared in accordance with the process of this invention, no particular limitation is imposed on the amount of the copolymerizable ~-olefin A
~131~
so long as the resulting polypropylene remains in a slurry state. However, the upper limit of the proportion of the copolymerizable ~-olefin other than propylene in each resulting polymer may generally be 5 about 40 wt.% or so. For the sake of convenience in describing the present invention, the term "propylene"
as used in the descriptive portion of the present specification other than the Examples should be interpreted to include not only propylene alone but 10 also a mixture of propylene and another a-olefin copolymerizable with propylene. Correspondingly, the term "polypropylene" as used in the descriptive portion of the present specification other than the Examples means not only propylene homopolymer but also the lS c,opolymer of the mixture.
For the following reasons, the process of this invention finds extremely important utility when propylene is polymerized in the presence of hydrogen as a molecular weight modifier in a reaction tank equipped 20 with a reflux condenser.
In a reaction tank having no reflux condenser, the vapor phase and liquid phase are maintained in vapor-liquid equilibrium and moreover, the vapor phase is in a substantially even state. Therefore, the 25 concentration of hydrogen in the vapor phase can be accurately determined if the gas of the vapor phase is 13~Z~
sampled and its hydrogen concentration is measured. It is hence possible to control the molecular weight of the resulting polypropylene by comparing the thus-detected hydrogen concentration with a desired hydrogen 5 concentration by conventionally-known desired comparator means and on the basis of the results of the comparison, by automatically controlling a feed valve of hydrogen to the reaction tank and thus always introducing a deficient volume of hydrogen into the 10 reaction vessel so as to maintain the concentration of hydrogen in the vapor phase substantially at a constant level.
However, the vapor phase and liquid phase are not always maintained in vapor-liquid equilibrium when 15 a polymerization is conducted by using a reaction vessel equipped with a reflux condenser. In addition, the concentration of hydrogen in the vapor phase varies considerably depending on the load to the reflux condenser along the passage of time as mentioned above.
20 As a result, it i8 impossible to control the molecular weight of the resulting polypropylene if a simple automatic controlling method such as that referred to above is relied upon.
As exemplary polymerization catalysts useful in 25 the practice of this invention, may be mentioned catalyst systems composed of conventionally-known , 13~SZ8~
transition metal catalysts and organometallic compounds. One or more stereoregularity improvers may also be used in combination if necessary or desirable.
Although not limited specifically to the following s exemplary polymerization catalysts, illustrative of the polymerization catalyst may include titanium trichloride obtained by reducing titanium tetrachloride with a reducing agent such as aluminum; organoaluminum ; or organomagnesium, those obtained by subjecting 10 titanium trichloride to activation treatments such as , . . .
its treatments with oxygen-containing organic compounds, titanium tetrachloride and the like , subsequent to its grinding; those formed of titanium trichloride or titanium tetrachloride supported on 15 carriers 9uch a9 magnesium chlorid-; etc. As exemplary organometallic compound~, may be mentioned organo-aluminums such as trialkylaluminums, dialkylaluminum :
halides, alkylaluminum sesquihalides and alkylaluminum dlhallde~ and organomagnesiums ~uch as dialkyl-20 agnesiu0s.
One embodiment of the present invention willhereinafter be described with reference to the accompanylng drawings.
FIGURE 1 illustrates one example of an apparatus 25 ~uitable for use in the practice of the process of this invention,~in whlch there are illustrated an agitator-~,:: , :
' ::
: ~ :
13~S'~Bl g equipped reaction tank 1, a reflux condenser 2 in theform of a horizontal shell-and-tube heat exchanger, a jacket 3 for the reaction tank 1 and an inlet line 5 for the introduction of a slurry into the reaction tank 5 1. Where the reaction tank 1 is employed for single-tank polymerization or is used as the first tank upon polymerization in a plurality of tanks connected in series, the inlet line 5 is used for the introduction of a catalyst slurry. Where the reaction tank 1 is the 10 second or subsequent tank in such series reaction tanks, the inlet line 5 is employed for the introduc-tion of a reaction slurry from the preceding reaction tank. There are also shown a discharge line 6 for the removal of a slurry from the reaction tank 1, a charge 15 line 7 for the introduction of propylene and a catalyst, a sampling line 9 for the collection of gas from the vapor phase of the reaction tank 1, and a blower 18 adapted to recycle to the reaction tank 1 uncondensed gas which has not been condensed in the 20 reflux condenser 2 and is composed principally of hydrogen gas. Also illustrated are a detector 4-1 for the flow velocity and temperature of gas at the entrance to the reflux condenser 2, another detector 4-2 for the flow velocity and temperature of a 25 condensate returning to the reaction tank 1 subsequent to i~s recovery in the reflux condenser 2, a flow rate 13C~5281 regulating valve 4-3 for hydrogen gas to be introduced into the reaction tank 1, a further detector 4-4 for the flow velocity and temperature of cooling (or heating) water leaving the jacket 3, a still further s detector 4-5 for the flow rate and temperature of cooling (or heating) water to be introduced into the jacket 3, The following procedure may be followed by way of example in order to calculate the amount of a 10 monomer or monomer mixture polymerized per unit time in the reaction tank 1. Data signals a,b,c,d, which have been output from the detectors 4-1,4-2,4-4,4-S respec-tively, are input to a data processor 8, where the quantity of heat generated per unit time in the lS reaction tank 1 at the time of output of the data ~ignals i~ calculated by correcting the quantity of heat removed per the ~ame unit time from the reaction : tank 1, which has been calculated from the data signals - a,b,c,d, in accordance with the quantity of dissipated 20 heat whlch ha~ been calculated based on the overall : structure of the polymerization system and its : operational conditions. Since the relation~hip between polymerized amount of the monomer or monomer mixture and reaction heat can be known from the compo~ition of /
25 the thu~-polymerized monomer or monomer mixture in the manner known per se in the art, the above-mentioned , ~. .. .. .
13~5Z~
generated heat is converted further at the data Qrocessor 8 into the amount of the monomer or monomer mixture polymerized per unit time in the reaction tank 1.
Incidentally, the relationship between the molecular weight of polypropylene of a desired composition and the volume of hydrogen required for the preparation of the polypropylene varies in accordance with catalyst system, polymerization temperature and 10 the like, but as shown in FIGURE 2 by way of example, the relationship between the intrinsic viscosity of a polymer as measured in the form of its tetralin solution of 135C and the volume of hydrogen consumption per unit weight of the polymer can be 15 predetermined.
It is therefore possible to determine the volume of hydrogen reguired per unit amount of feed propylene by storing beforehand the above relational expression as an equation In the data processor 8 and then inputting 20 a desired polypropylene molecular weight in the data processor 8.
In the above-described manner, the volume of hydrogen required in the reaction tank 1 is hence calculated at the data processor 8 as the product of 25 the amount of the polymerized monomer or monomer mixture, which has been calculated in advance, and the , :, ' , ~, , -- 13~S2~
volume of hydrogen required for the unit amount of the feea polypropylene. Results o~ the operation are output as a signal e from the data processor 8. It is therefore possible to replenish the volume of consumed s hydrogen by changing the opening degree of the flow rate regulating valve for hydrogen gas in accordance with variations in the value of the signal e so as to control the volume of hydrogen to be introduced into the reaction tank 1, that is, to conduct the reaction 10 while maintaining the actual concentration of hydrogen in the reaction tank 1 substantialIy at a constant level. Accordingly, it seems to be possible to prepare polypropylene of a uniform molecular weight.
By the way, when the present invention is 15 applied to such a reaction ~y~tem that a plurality of tanks are connected in series to conduct continuous polymerization therein and the molecular weight of the resulting polymer i8 increased successively from one tank to the next tank, hydrogen is introduced and 20 di9charged from each of the tanks along with the :
~slurries which are introduced through the line S and diocharged through the line 6 respectively and contains 8aid hydrogen dissolved therein. It is hence necessary ~;~ to input information on the volume of the hydrogen in 25 the data processor 8 and to perform a correction on the -~; basis of the information.
~,:
: ~, . , :
:
' '''':'~"' ' ' 13~5281 On the other hand, when a single-tank polymeri-zation process is effected in the above-described reaction tan~ l or a polymerization process is conducted by connecting in series a plurality of 5 reaction tanks, each, of the same type as the reaction tank 1, each of the reaction tanks has already been filled with a great deal of propylene not only as a liquid medium but also as a reaction raw material at the start-up time of the reaction. It is therefore 10 impossible to obtain a polymer of a desired molecular weight even if hydrogen is fed in accordance with the present invention, namely, in a volume correspond-ing to the amount of polymerized propylene which is calculated based on the measured and calculated 15 quantity of heat of the polymerization reaction. While taking into consideration the volume of hydrogen to be dissolved in the liquid propylene filled in each reaction tank at the start-up time and the volume of the vapor phase above the liquid medium, it is thus 20 necessary to charge at once hydrogen in a volume corresponding to the liquid propylene at the beginning ~o that the polymerization reaction is conducted. The molecular weight of the resulting polypropylene is then measured and compared with a desired value. Based on 25 the results of the comparison, a small amount of hydrogen or propylene is additionally charged in the .
. - ,. , ~3~5;2bl~
reaction tank. The above-described fine correctio~
procedure is repeated until the molecular weight of the resulting polypropylene reaches the desired value. The reaction is thereafter allowed to proceed further in 5 accordance with this invention, whereby polypropylene of a constant molecular weight can be prepaxed.
It is a reaction tank equipped with a reflux condenser that can be used in the practice of the present invention. No particular limitation is imposed 10 on the heat-removing capacity of the reflux condenser.
The present invention is particularly effective in a steady state, that is, when it is applied to a reaction tank the temperature of which is controlled by the removal of heat through the reflux condenser while the lS pregent invention is being practised.
According to the present invention, it is po~9ible to maintain the molecular weight of the resulting polypropylene at a constant level by introducing hydrogen in a volume corresponding to the 20 volume of it9 consumption into the reaction tank, since the volume of hydrogen consumption required upon providing polypropylene of a constant molecular weight is uniform per unit weight and the vapor phase and liquid phase are maintained in equilibrium on average 25 although the concentration of hydrogen in the vapor phase of the reaction tank varies depending upon the . ., ~ .
13~3$~
load to the reflux condenser and its apparent value changes considerably.
The present invention is extremely valuable from the industrial viewpoint because polypropylene of a constant molecular weight can be obtained with not only high efficiency but also good controllability by using a reaction tank equipped with a reflux condenser and conducting bulk polymerization of propylene in the presence of hydrogen as a molecular weight modifier in accordance with the process of this invention.
EXAMPLES:
Continuous bulk polymerization of liquid propylene was conducted at 70C in the presence of a catalyst composed of titanium trichloride and diethylaluminum chloride in a reaction tank having the structure shown in FIGURE 1 and an internal capacity of 40 m3 while using the liquid propylene as a medium.
Upon initiation of the polymerization, 3000 kg of propylene and 35 Nm3 of hydrogen were first charged in the reaction tank. Warm water was caused to flow through the jacket so as to heat the medium up to 70C. The polymerization reaction was then initiated while charging the catalyst and propylene at constant feed velocities (titanium trichloride: l.0 kg/hr, diethylaluminum chloride; 16 kg/hr, propylene: lO000 -" 13~SZ~l kg/hr). During the reaction, the reaction slurry was sampled from the reaction tank and the molecular weight of the resultant polypropylene was measured. The thus-measured molecular weight was compared with a predeter-5 mined value. The molecular weight of the resultingpolypropylene was adjusted substantially to the predetermined value by repeating several times a fine correction procedure in which a small amount of hydrogen was charged in the reaction tank on the basis 10 of the results of the above comparison. About 30 minutes were spent until the predetermined value was reached.
Continuous bulk polymerization of propylene was then conducted in accordance with the process of this 15 invention. Namely, propylene, titanium trichloride and diethylaluminum chloride were charged at constant feed velocities, namely, at 6000 kg/hr, 0.8 kg/hr and 8 kg/hr respectively into the reaction tank. At the same time, a slurry was charged out at about 6000 kg/hr 20 from the reaction tank so as to maintain the level of the slurry constant in the reaction tank. During this polymerization, data signals a,b,c,d were input from the detectors 4-1,4-2,4-4,4-5 into the data processor 8 to calculate the quantity of heat removed through the 25 jacket and reflux condenser. It was found to be 860 Mcal/hr. Furthermore, upon its correction by the ., ' ~ ~
13~15Z~l quantity of heat released from the system, the quantity of polymerization reaction heat generated in the reaction tank was 1,006 Mcal/hr, which corresponded to a polymerized propylene amount of 2,196 kg/hr.
The intrinsic viscosity corresponding to polypropylene of a desired molecular weight as measured in the form of its tetralin solution of 135C was found to be 1.73 and the volume of hydrogen required corresponding to the above-determined polymerized 10 propylene amount was found to be 1.152 Nm3/hr from FIGURE 2. A correction was performed in view of the volume of the hydrogen discharged along with the slurry from the reaction tank which volume was 0.845 Nm3/hr.
As a consequent, hydrogen was introduced into the ~. qq7 3 15 reaction tank at the rate of 1.977 Nm /hr through the flow rate regulating valve 4-3. By the way, the above operation, conver~ion and correction were all performed automatically by the data processor, and the system was operated in such a way that the molecular weight of the 20 polypropylene in the discharged slurry was automatically controlled by delivering the volume of hydrogen, which was to be introduced, as the signal e to the flow rate regulating valve 4-3.
The polymerization reaction was continued while 25 correcting the volume of hydrogen, which was to be introduced, at intervals of five minutes in accordance 13~52Bl with variations of the data signals a,b,c,d. Two hours later, the volume of the polymerized propylene reached 2,405 kg/hr. At that point of time, the charging rate of hydrogen was 1.323 Nm3/hr and the intrinsic 5 viscosity of the polymer sampled out from the discharged slurry as measured in the form of its tetralin solution of 135~C was 1.73 as desired.
The above reaction was continued for about 20 hours. FIGURE 3 diagrammatically illustrates 10 time-dependent variations in the concentration (vol.%) of hydrogen in the vapor phase sampled out through the line 9 as well as time-dependent variations in the intrinsic viscosity of polypropylene in the slurry discharged through the line 6. As understood from 15 PIG~RE 3, the intrinsic viscosity, namely, the molecular weight was controlled at a constant level although the concentration of hydrogen in the vapor phase varied.
By the way, about 65~ of the total quantity of 20 heat removed through the jacket and reflux condenser in a ~teady ~tate, namely, during the practice of the process of this invention was accounted for on average by reflux condenser.
';
, ....
.
Claims (2)
1. A process for the preparation of a propylene homo-or co-polymer by subjecting propylene, or a mixture of propylene and another .alpha.-olefin copolymerizable with propylene as a monomer or monomer mixture to bulk polymerization at a constant temperature, in the presence of hydrogen as a molecular weight modifier, in a reaction tank equipped with a reflux condenser while using the propylene or mixture itself as a liquid medium and condensing vapor of the medium in the reflux condenser so as to remove at least a part of polymerization heat, which process consists of:
(a) measuring only the heat balance of the reaction tank in calculating the quantity of polymerization reaction heat generated in the reaction tank based on said measurement, not using detectable information of the concentration of hydrogen in the vapor phase of the reaction tank at all in this calculation and the following calculations and determinations, and calculating the amount of the monomer or monomer mixture polymerized in the reaction tank based on the thus-calculated quantity;
(b) determining in advance the relationship between molecular weights and the volume of hydrogen consumption required for the molecular weights with respect to propylene homo- or co-polymer;
(c) determining the volume of hydrogen consumption required per unit amount of propylene alone or the mixture of propylene with another .alpha.-olefin copolymerizable with propylene corresponding to a desired molecular weight of the propylene homo- or co-polymer; and (d) reacting the monomer or monomer mixture while controlling the volume of hydrogen, which is to be fed into the reaction tank, in accordance with variations in the volume of hydrogen required in the reaction tank as a product of the volume of the required hydrogen consumption and the above-calculated amount of the monomer or monomer mixture.
(a) measuring only the heat balance of the reaction tank in calculating the quantity of polymerization reaction heat generated in the reaction tank based on said measurement, not using detectable information of the concentration of hydrogen in the vapor phase of the reaction tank at all in this calculation and the following calculations and determinations, and calculating the amount of the monomer or monomer mixture polymerized in the reaction tank based on the thus-calculated quantity;
(b) determining in advance the relationship between molecular weights and the volume of hydrogen consumption required for the molecular weights with respect to propylene homo- or co-polymer;
(c) determining the volume of hydrogen consumption required per unit amount of propylene alone or the mixture of propylene with another .alpha.-olefin copolymerizable with propylene corresponding to a desired molecular weight of the propylene homo- or co-polymer; and (d) reacting the monomer or monomer mixture while controlling the volume of hydrogen, which is to be fed into the reaction tank, in accordance with variations in the volume of hydrogen required in the reaction tank as a product of the volume of the required hydrogen consumption and the above-calculated amount of the monomer or monomer mixture.
2. The process as claimed in Claim 1, wherein propylene is used as a sole monomer.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000525924A CA1305281C (en) | 1986-12-19 | 1986-12-19 | Control method of molecular weight of polypropylene |
| US07/258,052 US5098967A (en) | 1986-12-19 | 1988-10-17 | Method of controlling the molecular weight of polypropylene |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000525924A CA1305281C (en) | 1986-12-19 | 1986-12-19 | Control method of molecular weight of polypropylene |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1305281C true CA1305281C (en) | 1992-07-14 |
Family
ID=4134602
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000525924A Expired - Fee Related CA1305281C (en) | 1986-12-19 | 1986-12-19 | Control method of molecular weight of polypropylene |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1305281C (en) |
-
1986
- 1986-12-19 CA CA000525924A patent/CA1305281C/en not_active Expired - Fee Related
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