Process for radical polymerization of olefins

Abstract

The invention relates to the field of high-pressure free radical polymerization, and discloses an olefin free radical polymerization method, the method is carried out in an olefin free radical polymerization device, and the olefin free radical polymerization device comprises i sections of reaction zones connected in series; wherein the first-section reaction zone comprises at least two tubular reactors which are connected in parallel; the method comprises the following steps: (1) preparing i initiator solutions, wherein each initiator solution contains at least one initiator; (2) respectively introducing the i initiator solutions through an inlet of the i-section reaction zone, introducing an olefin-containing reaction material through an inlet of the first-section reaction zone, and carrying out an olefin polymerization reaction; wherein i is any integer greater than or equal to 2. The method can improve the reaction efficiency of the olefin polymerization product, and reduce the consumption of the initiator and the residual amount of the initiator in the polymerization product.

Description

Technical Field

[0001] The invention relates to the field of high-pressure free radical polymerization, and in particular to a method for olefin free radical polymerization. Background Art

[0002] Polyolefins are produced by high-pressure free radical polymerization. Tubular technology has gradually become dominant because tubular reactors are easier to scale up and more economical in the polymerization process.

[0003] Reactor temperature distribution indicators such as reactor inlet temperature and reactor temperature peak are important factors affecting the molecular chain structure of the product. For example, when producing low-density polyethylene with a wide distribution, the reactor inlet temperature is usually lowered, the reactor temperature peak is increased, or the reaction pressure is reduced; when producing low-density polyethylene with a narrow distribution, the reactor inlet temperature is increased, the reaction temperature peak is appropriately reduced, or the reaction pressure is increased. Generally speaking, on the one hand, the reactor inlet temperature has a wide range of variation, and the reactor inlet temperature can be adjusted by passing different heating media into the preheater, such as pressurized hot water, low-pressure steam, medium-pressure steam and high-pressure steam. On the other hand, in order to produce low-density polyethylene with higher density for medical and food use, it is necessary to increase the reaction pressure and reduce the reactor temperature peak.

[0004] Since the decomposition reaction rate of the initiator basically follows the Arrhenius equation, the decomposition rate of the initiator increases rapidly as the reaction temperature increases. Therefore, it is necessary to select a suitable initiator formula to adapt to different temperature distributions. However, in industrial equipment, the initiator formula is often fixed, which will pose a greater risk to the equipment and products. On the one hand, poor initiator selection will lead to the inability to effectively initiate ethylene polymerization, resulting in a significant increase in initiator consumption. On the other hand, it will also lead to a high level of initiator residues in low-density polyethylene, affecting the antioxidant properties of the product. In addition, it should be pointed out that poor initiator selection will also lead to the production of ultra-high molecular weight polyethylene, thereby affecting the heat transfer efficiency of the tubular reactor and significantly reducing the production load of the device.

[0005] Therefore, there is a need for a method for olefin free radical polymerization that can improve the reaction efficiency of olefin polymerization products and reduce the initiator consumption and the residual initiator content in the polymerization products. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art in the process of high-pressure olefin polymerization, that is, the initiator usage method is not optimal when producing different grades of polyethylene or ethylene copolymers, resulting in low initiator efficiency, high initiator residue in the polymer, and poor aging resistance of the polymer. The present invention provides a method for olefin free radical polymerization, which can improve the initiator usage efficiency, reduce the initiator residue in the product, improve the efficiency of the reactor, and reduce the cost of olefin polymerization.

[0007] In order to achieve the above object, the present invention provides a method for olefin free radical polymerization in a first aspect, wherein the method is carried out in an olefin free radical polymerization device, wherein the olefin free radical polymerization device comprises i-stage reaction zones connected in series; wherein the first stage reaction zone comprises at least two tubular reactors connected in parallel;

[0008] The method comprises the following steps:

[0009] (1) preparing i initiator solutions, each initiator solution containing at least one initiator;

[0010] (2) introducing the i initiator solutions through the inlets of the i-stage reaction zones respectively, and introducing the olefin-containing reaction material through the inlet of the first stage reaction zone to carry out olefin polymerization reaction;

[0011] Wherein, i is any integer greater than or equal to 2.

[0012] Preferably, in step (2), the minimum decomposition temperature MIN (T d,i ) and the temperature T at the inlet of the reaction zone in,i The value of satisfies the following relationship:

[0013] (MIN(T d,i )-T in,i ) 2 ≤1600, preferably (MIN(T d,i )-T in,i ) 2 ≤400, more preferably (MIN(T d,i )-T in,i ) 2 ≤225;

[0014] Where i is the i-th reaction zone.

[0015] Preferably, in step (2), the initiator half-life in the initiator solution in the i-stage reaction zone is 0.01s and the maximum decomposition temperature MAX (T d,i ) and the maximum temperature of the reaction zone T max,i The value of satisfies the following relationship:

[0016] (MAX(T d,i )-T max,i ) 2 ≤1600, preferably (MAX(T d,i )-T max,i ) 2 ≤400;

[0017] Where i is the i-th reaction zone.

[0018] Through the above technical solution, the beneficial effects achieved by the present invention are as follows:

[0019] (1) The method for olefin free radical polymerization provided by the present invention can improve the use efficiency of the initiator, thereby reducing the amount of initiator used and reducing the cost of the high-pressure polymerization process;

[0020] (2) The method for olefin free radical polymerization provided by the present invention can preferably reduce the residual amount of initiator in the product and the content of oxygen-containing functional groups of the initiator in the reactor by matching the decomposition law of the initiator with the distribution law of the reaction temperature, thereby improving the heat aging resistance and antioxidant properties of the product;

[0021] (3) The method for olefin free radical polymerization provided by the present invention is preferably carried out in an olefin free radical polymerization device, which can reduce the content of ultra-high molecular weight polymer in the polymerization device, improve the heat transfer efficiency of the reactor and the production capacity of the device, and has good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a high-pressure free radical olefin polymerization apparatus.

[0023] Description of Reference Numerals

[0024] 1. Circulating material compressor 2. Primary compressor 3. Secondary compressor

[0025] 4a / 4b, preheater 5a / 5b / 6a / 6b / 6c, tubular reactor 7, high pressure relief valve

[0026] 8. Cooler 9. High-pressure separator 10. High-circulation circuit

[0027] 11. Low pressure separator 12. Low circulation circuit DETAILED DESCRIPTION

[0028] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0029] The first aspect of the present invention provides a method for olefin free radical polymerization, the method is carried out in an olefin free radical polymerization device, the olefin free radical polymerization device comprises i-stage reaction zones connected in series; wherein the first stage reaction zone comprises at least two tubular reactors connected in parallel;

[0030] The method comprises the following steps:

[0031] (1) preparing i initiator solutions, each initiator solution containing at least one initiator;

[0032] (2) introducing the i initiator solutions through the inlets of the i-stage reaction zones respectively, and introducing the olefin-containing reaction material through the inlet of the first stage reaction zone to carry out olefin polymerization reaction;

[0033] Wherein, i is any integer greater than or equal to 2.

[0034] In the present invention, preferably, Figure 1 As shown, the olefin free radical polymerization device includes a circulating material compressor 1, a primary compressor 2, a secondary compressor 3, a preheater 4a / 4b, a tubular reactor 5a / 5b, a tubular reactor 6a / 6b / 6c, a high-pressure relief valve 7, a cooler 8, a high-pressure separator 9, a high-circulation loop 10, a low-pressure separator 11 and a low-circulation loop 12 which are connected in sequence.

[0035] In the present invention, preferably, the olefin-containing reaction material enters through the primary compressor 2 and the secondary compressor 3, is fully mixed and divided into multiple streams and enter the tubular reactor 5a through the preheater 4a, and enters the tubular reactor 5b through the preheater 4b. The reaction monomer flow feed port ends of the tubular reactor 5a and the tubular reactor 5b are both provided with initiator feed ports. The first initiator solution is added through the initiator feed port to carry out high-pressure polymerization reaction with the olefin-containing reaction material. The reaction products of the tubular reactors 5a and 5b flow into the tubular reactors 6a, 6b and 6c connected in series to continue high-pressure free radical polymerization. The feed ports of the tubular reactors 6a, 6b and 6c are each provided with an initiator feed port, and the second to i-th initiator solutions are respectively introduced through the initiator feed ports to participate in the corresponding high-pressure free radical polymerization reaction.

[0036] The high-pressure polymerization product passes through the high-pressure relief valve 7 and the cooler 8 in sequence and flows into the high-pressure separator 9 to be separated into a gaseous fraction A and a liquid fraction A. The liquid fraction A flows into the low-pressure separator 11 to be separated into a gaseous fraction B and a polymer product. The gaseous fraction A is cooled and separated by the cooler and separator on the high circulation loop 10 to obtain unreacted monomers, which flow into the suction side of the secondary compressor. The gaseous fraction B is cooled and separated by the cooler and separator on the low circulation loop 12 to obtain unreacted monomers, which are compressed by the circulating material compressor 1 on the low circulation loop and flow into the suction side of the primary compressor.

[0037] In the present invention, the olefin free radical polymerization device is used to carry out high-pressure free radical polymerization reaction on the reaction materials containing olefins. The reaction materials containing olefins are divided into multiple streams and enter the parallel tubular reactors of the first reaction zone respectively. The i series-connected reaction zones are connected in sequence, wherein the material at the outlet of the previous reaction zone is fed to the inlet of the next reaction zone, and each of them carries out high-pressure free radical polymerization reaction.

[0038] In the present invention, by matching the decomposition law of the initiator with the distribution law of the reaction temperature, an initiator formula whose decomposition temperature can meet the temperature of the reaction zone is selected, and initiators matching the temperature of the reaction zone are used in different reaction zones, so that the use efficiency of the initiator can be improved, thereby reducing the amount of initiator used and reducing the cost of the high-pressure polymerization process.

[0039] In the present invention, as long as the purpose of the present invention can be achieved, there is no limit to the number of tubular reactors connected in parallel in the first reaction zone. In some preferred embodiments, the number of tubular reactors connected in parallel is 2-4.

[0040] In the present invention, as long as the purpose of the present invention can be achieved, the order of polymerization in each reaction zone is not limited, and they can be carried out simultaneously or at different times, as long as the polymerization product of the previous reaction zone flows into the next reaction zone as a raw material for high-pressure free radical polymerization.

[0041] In the present invention, the initiator solution has a common meaning in the art, and the initiator solution is used to initiate olefin free radical polymerization reaction.

[0042] According to the present invention, preferably, the initiator solution contains an initiator and a solvent.

[0043] In the present invention, the types of initiators and solvents in different initiator solutions in i kinds of initiator solutions, as well as the concentrations of the initiators can be the same or different, as long as the i kinds of initiator solutions are introduced into i series-connected reaction zones to achieve the purpose of the present invention. Preferably, the types of initiators in different initiator solutions in i kinds of initiator solutions are different.

[0044] According to the present invention, preferably, in step (1), the initiator is an organic peroxide, preferably at least one of a peroxyester, a peroxyketal, a peroxyketone and a peroxycarbonate.

[0045] According to the present invention, preferably, the decomposition temperature of the initiator with a half-life of 0.1 h is 80°C-170°C, preferably 85-160°C, and the melting point of the initiator is lower than 10°C.

[0046] In the present invention, the half-life of the initiator has a conventional definition in the art, for example, it refers to the time required for the initiator to decompose to half of the initial concentration at a certain temperature.

[0047] In the present invention, preferably, the initiator is selected from di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxyisopropyl carbonate, di-tert-butyl peroxide, di-tert-amyl peroxide, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane, tert-butyl cumyl peroxide or didecanoyl peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexane, tert-amyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxydiethyl acetate, diethyl isopropyl peroxide At least one of tert-butyl butyrate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-amyl peroxyneodecanoate, tert-amyl peroxypivalate, tert-butyl peroxyneodecanoate, tert-butyl permaleate, tert-butyl peroxypivalate, tert-butyl peroxyisononanoate, tert-butyl peroxybenzoate, methyl isobutyl ketone hydroperoxide, 3,6,9-triethyl-3,6,9-trimethyltriperoxycyclononane and 2,2-di(tert-butylperoxy)butane.

[0048] According to a preferred embodiment of the present invention, the initiator is selected from at least one of di-tert-butyl peroxide, tert-butyl perbenzoate, tert-butyl peroxy-2-ethylhexanoate, tert-amyl peroxy-2-ethylhexanoate and tert-butyl peroxypivalate.

[0049] According to the present invention, preferably, based on the total weight of the initiator solution, the initiator content in the initiator solution is 10-40 weight%, for example, the initiator content is 10 weight%, 15 weight%, 20 weight%, 25 weight%, 30 weight%, 35 weight%, 40 weight%, and any range composed of any two of them, preferably 15-30 weight%.

[0050] According to the present invention, preferably, in step (1), the initiator solutions each independently contain j initiators, j is any integer from 1 to 6, and j is preferably any integer from 1 to 5.

[0051] In the present invention, preferably, the number j of initiator types in different initiator solutions decreases or remains unchanged as the value of i increases.

[0052] In the present invention, preferably, the mass percentage of the content of each initiator in the initiator solution to the total initiator content in the initiator solution is not less than 10 weight %, preferably not less than 15 weight %.

[0053] According to the present invention, preferably, in step (1), the solvent of the initiator solution is an aliphatic hydrocarbon, preferably at least one of the alkanes of C6-C25, and more preferably at least one of the alkanes of C8-C15.

[0054] In the present invention, aliphatic hydrocarbon is selected as the solvent so that the initiator can initiate the free radical polymerization reaction in a dissolved form, so that the initiator can be better dispersed in the reaction material, thereby improving the utilization efficiency of the initiator.

[0055] According to a preferred embodiment of the present invention, the solvent of the initiator solution is selected from at least one of octane, decane and isododecane.

[0056] According to a preferred embodiment of the present invention, the solvent content in the initiator solution is 60-90 wt %, preferably 70-85 wt %, based on the total weight of the initiator solution.

[0057] In the present invention, the reaction zone is configured as i-stage reaction zones, and the reaction conditions of each reaction zone are independent of each other. By controlling the reaction temperature and reaction pressure of different reaction zones and matching them with the initiator solution, the initiation efficiency of the initiator is improved, the residual amount of initiator in the polymer is reduced, and the aging performance of the polymer is thereby improved.

[0058] In the present invention, the selection of initiators in the i initiator solutions matches the reaction temperature distribution of the corresponding reaction zones, ensuring that the selected initiators can initiate free radical polymerization reactions under appropriate reaction conditions, thereby improving the safety of the reaction, improving the efficiency of the initiators, and reducing the consumption of the initiators.

[0059] According to the present invention, preferably, in step (2), the value of i is any integer from 3 to 7, preferably any integer from 3 to 5.

[0060] According to the present invention, preferably, the reaction temperature in each of the i-stage reaction zones is independently 120-350°C, for example, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 310°C, 330°C, 350°C, and a range consisting of any of the above values, preferably 140-310°C.

[0061] According to the present invention, preferably, the reaction pressure in each of the i-stage reaction zones is independently 80-320 MPa, for example, 80 MPa, 100 MPa, 120 MPa, 140 MPa, 160 MPa, 180 MPa, 200 MPa, 220 MPa, 240 MPa, 260 MPa, 280 MPa, 300 MPa, 320 MPa, and a range consisting of any of the above values, preferably 120-280 MPa.

[0062] In the present invention, during the free radical polymerization reaction, the reaction temperature is in the range of 120-350°C. The addition of the free radical polymerization initiator will affect the polymerization temperature. In some embodiments of the present invention, the temperature of the material in the reactor at the injection position of the free radical polymerization initiator through the initiator feed port is recorded as the "temperature at the entrance of the reaction zone", recorded as T in,i .

[0063] In some embodiments of the present invention, among the j initiators in the i-th initiator solution, the initiator decomposition temperature with the lowest decomposition temperature when the initiator half-life is 1 s is taken as the minimum decomposition temperature of the initiator half-life of 1 s in the initiator solution in the i-stage reaction zone, and is recorded as MIN(T d,i ).

[0064] According to the present invention, preferably, in step (2), the minimum decomposition temperature MIN (T d,i ) and the temperature T at the inlet of the reaction zone in,i The value of satisfies the following relationship:

[0065] (MIN(T d,i )-T in,i ) 2 ≤1600, preferably (MIN(T d,i )-T in,i ) 2 ≤400, more preferably (MIN(T d,i )-T in,i ) 2 ≤225;

[0066] Where i is the i-th reaction zone.

[0067] In the present invention, the minimum decomposition temperature MIN (T d,i ) and the temperature T at the inlet of the reaction zone in,i A specific relationship is satisfied so that the initiator decomposition rate and the reactor temperature match, thereby reducing the initiator consumption at the reactor inlet.

[0068] In the present invention, the consumption of the initiator is the total mass of pure initiator consumed to produce a unit mass of polymerization product.

[0069] In some embodiments of the present invention, the highest temperature of the material in the reactor during the free radical polymerization reaction in the reaction zone is recorded as the "highest temperature in the reaction zone", denoted as T max,i .

[0070] In some embodiments of the present invention, among the j initiators in the i-th initiator solution, the decomposition temperature of the initiator with the maximum decomposition temperature when the initiator half-life is 0.01 s is taken as the maximum decomposition temperature of the initiator in the initiator solution in the i-stage reaction zone when the initiator half-life is 0.01 s, and is recorded as MAX(T d,i ).

[0071] According to the present invention, preferably, in step (2), the maximum decomposition temperature of the initiator solution in the i-stage reaction zone with a half-life of 0.01s is MAX (T d,i ) and the maximum temperature of the reaction zone T max,i The following relations are satisfied:

[0072] (MAX(T d,i )-T max,i ) 2 ≤1600, preferably (MAX(T d,i )-T max,i ) 2 ≤400;

[0073] Where i is the i-th reaction zone.

[0074] In the present invention, the initiator half-life in the initiator solution is controlled to be the maximum decomposition temperature MAX (T d,i ) and the maximum temperature of the reaction zone T max,i When a specific relationship is satisfied, the amount of initiator used at the position where the highest temperature is located in the reactor temperature curve can be reduced.

[0075] According to the present invention, preferably, in step (2), the olefin-containing reaction material comprises reaction monomers and an optionally added molecular weight regulator, and the reaction monomers include olefin monomers and an optionally added comonomer.

[0076] In the present invention, the olefin monomer includes one or more of R2C=CR2 type monoolefin compounds, conjugated dienes, and non-conjugated dienes, wherein R is independently H, alkane or halogen.

[0077] In the present invention, the comonomer is a conventional comonomer in the art that can be free radical copolymerized with an olefin monomer under high pressure. Preferably, the comonomer is selected from at least one of α, β-unsaturated C3-C8 carboxylic acid, a derivative of α, β-unsaturated C3-C8 carboxylic acid and 1-olefin.

[0078] In the present invention, preferably, the comonomer is selected from at least one of α, β-unsaturated C3-C8 carboxylic acids, such as olefinic acid, methacrylic acid, maleic acid and fumaric acid; the derivative of the α, β-unsaturated C3-C8 carboxylic acid is preferably an unsaturated C3-C5 carboxylic acid ester or anhydride, such as at least one of methyl methacrylate, n-butyl methacrylate or tert-butyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, methacrylic anhydride and maleic anhydride; the 1-olefin is selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 1-decene.

[0079] In the present invention, preferably, the comonomer is at least one selected from propylene, 1-hexene, acrylic acid, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, vinyl acetate and vinyl acrylate.

[0080] In the present invention, preferably, when the olefin monomer is ethylene and there is no comonomer, the product prepared by the method described in the present invention is low-density polyethylene.

[0081] According to the present invention, as long as the purpose of the present invention can be achieved, the feed amount of each initiator can be selected as needed, and there is no special restriction in the present invention. According to a preferred embodiment of the present invention, the mass ratio of the total mass of the initiator to the olefin monomer in the mixed material obtained by mixing the initiator with the reaction material after entering the reactor is 0.00005-0.001:1, preferably 0.0001-0.0005:1.

[0082] In the present invention, preferably, based on weight, the initiator in the i-th stage reaction zone accounts for 5-50 weight %, preferably 7-45 weight % of the total initiators.

[0083] According to the present invention, preferably, in step (2), the molecular weight regulator is selected from at least one of aliphatic hydrocarbons, olefins, ketones, aldehydes, alcohols and hydrogen.

[0084] In the present invention, the ketone is selected from at least one of acetone, methyl ethyl ketone (2-butanone), methyl isobutyl ketone, methyl isoamyl ketone, diethyl ketone and diamyl ketone; the aldehyde is selected from at least one of formaldehyde, acetaldehyde and propionaldehyde; the alcohol is selected from at least one of methanol, ethanol, propanol, isopropanol and butanol.

[0085] In some preferred embodiments of the present invention, the molecular weight regulator is selected from at least one of ethane, propane, butane, propylene, 1-butene, propionaldehyde and hydrogen.

[0086] In the present invention, as long as the purpose of the present invention can be achieved, the amount of the molecular weight regulator added can be selected as needed.

[0087] In the present invention, preferably, the molecular weight regulator is added to the multi-stage reactor to change the molecular weight of the polymer to be prepared, which can reduce the content of ultra-high molecular weight polymer in the polymerization device, improve the heat transfer efficiency of the reactor and the production capacity of the device, and has good economic benefits.

[0088] In the present invention, those skilled in the art can adjust the method of the present invention according to the changes in the devices required by different embodiments of the present invention, and no further details will be given here.

[0089] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, the heat aging test results are measured in a high and low temperature aging test chamber according to GJB 150.3A-2009.

[0090] Example 1

[0091] exist Figure 1 The high-pressure free radical olefin polymerization device shown in the figure carries out ethylene free radical polymerization reaction. The reaction zone in series in the figure contains 4 reaction zones, wherein the first reaction zone contains two parallel tubular reactors (first reactor A, first reactor B). The length of the first reaction zone is 560m, and the inner diameter is 0.032m. The length of the second to fourth reaction zones is 400m, and the inner diameter is 0.045m.

[0092] (1) mixing the following initiator combinations with isododecane to obtain four initiator solutions, wherein the content of isododecane in the four initiator solutions is 80 wt %;

[0093] In the following initiators, DTBP is di-tert-butyl peroxide, TBPB is tert-butyl peroxybenzoate, TBPEH is tert-butyl peroxy-2-ethylhexanoate, and TAPEH is tert-amyl peroxy-2-ethylhexanoate;

[0094] The mass ratio of initiator in the first reaction zone: DTBP / TBPB / TBPEH / TAPEH is 2:5:4:3;

[0095] The mass ratio of initiator in the second reaction zone: DTBP / TBPB / TBPEH is 2:5:4;

[0096] The mass ratio of initiator: DTBP / TBPB in the third reaction zone is 4:1;

[0097] Initiator in the fourth reaction zone: DTBP;

[0098] (2) feeding the initiator solution into the inlets of the first to fourth reaction zones respectively, introducing ethylene monomer through the inlet of the first reaction zone, the ethylene monomer addition amount is 45 tons per hour, the molecular weight regulator is propylene, the addition amount is 75 kg per hour, the reaction pressure of the reaction zone is 260 MPa, the temperature of each reaction zone in Example 1 is as shown in Table 1, and performing ethylene polymerization reaction to obtain low density polyethylene;

[0099] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this embodiment are shown in Table 8.

[0100] Table 1

[0101] Reaction zone (i) 1A 1B 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 174 174 182 207 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 308 308 308 308 308 <![CDATA[T in，i ,℃]]> 160 160 192 217 242 <![CDATA[T max，i ,℃]]> 295 295 305 305 295 Pure initiator dosage, kg / h 1.928 1.898 5.448 1.605 0.859

[0102] Example 2

[0103] Ethylene free radical polymerization was carried out according to the method of Example 1, which was different from Example 1 in that:

[0104] (1) changing the ratio of the initiator in the initiator solution from the second stage to the fourth stage of the reaction zone;

[0105] The mass ratio of initiator: DTBP / TBPB in the second reaction zone is 2:5;

[0106] Initiator in the third reaction zone: DTBP;

[0107] Initiator in the fourth reaction zone: DTBP;

[0108] (2) The temperature of each reaction zone in Example 2 is as shown in Table 2, and ethylene polymerization reaction is carried out to obtain low-density polyethylene;

[0109] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this embodiment are shown in Table 8.

[0110] Table 2

[0111] Reaction Zone 1A 1B 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 174 174 207 235 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 308 308 308 308 308 <![CDATA[T in，i ,℃]]> 160 160 192 220 242 <![CDATA[T max，i ,℃]]> 295 295 305 305 295 Pure initiator dosage, kg / h 1.928 1.898 3.221 1.373 0.845

[0112] Example 3

[0113] Ethylene free radical polymerization was carried out according to the method of Example 1, which was different from Example 1 in that:

[0114] (1) changing the ratio of the initiator in the initiator solution in the first to fourth reaction zones;

[0115] The mass ratio of initiator in the first reaction zone: DTBP / TBPB / TBPEH is 2:5:4;

[0116] The mass ratio of initiator: DTBP / TBPB in the second reaction zone is 2:5;

[0117] Initiator in the third reaction zone: DTBP;

[0118] Initiator in the fourth reaction zone: DTBP;

[0119] (2) The inlet temperature of the first reaction zone is 190° C. The temperatures of the reaction zones in Example 3 are shown in Table 3. Ethylene polymerization is performed to obtain low-density polyethylene;

[0120] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this embodiment are shown in Table 8.

[0121] Table 3

[0122] Reaction Zone 1A 1B 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 182 182 207 235 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 308 308 308 308 308 <![CDATA[T in，i ,℃]]> 190 190 190 220 243 <![CDATA[T max，i ,℃]]> 295 295 305 305 295 Pure initiator dosage, kg / h 1.38 1.34 3.815 1.32 0.8

[0123] Example 4

[0124] Ethylene free radical polymerization was carried out according to the method of Example 1, which was different from Example 1 in that:

[0125] (1) The mass ratio of initiator in the first reaction zone: DTBP / TBPB / TBPEH / TAPEH is 2:5:4:3

[0126] The mass ratio of initiator in the second reaction zone: DTBP / TBPB / TBPEH / TAPEH is 2:5:4:3

[0127] The mass ratio of initiator in the third reaction zone: DTBP / TBPB / TBPEH / TAPEH is 4:1:1:1

[0128] Initiator in the fourth reaction zone: DTBP;

[0129] (2) The temperature of each reaction zone in Example 4 is as shown in Table 4, and ethylene polymerization reaction is carried out to obtain low-density polyethylene;

[0130] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this embodiment are shown in Table 8.

[0131] Table 4

[0132] Reaction Zone 1A 1B 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 174 174 174 174 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 308 308 308 308 308 <![CDATA[T in,i ,℃]]> 160 160 192 218 241 <![CDATA[T max,i ,℃]]> 295 295 305 305 295 Pure initiator dosage, kg / h 1.928 1.898 6.581 2.125 0.872

[0133] Example 5

[0134] Ethylene free radical polymerization was carried out according to the method of Example 1, which was different from Example 1 in that:

[0135] (1) The mass ratio of initiator in the first reaction zone: TBPB / TBPEH / TAPEH is 5:4:3

[0136] The mass ratio of initiator in the second reaction zone: DTBP / TBPB / TBPEH / TAPEH is 2:5:4

[0137] The mass ratio of initiator in the third reaction zone: DTBP / TBPB is 4:1

[0138] Initiator in the fourth reaction zone: DTBP;

[0139] (2) The temperature of each reaction zone in Example 5 is shown in Table 5, and ethylene polymerization reaction is carried out to obtain low-density polyethylene;

[0140] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this embodiment are shown in Table 8.

[0141] Table 5

[0142] Reaction Zone 1A 1B 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 174 174 182 207 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 273 273 308 308 308 <![CDATA[T in，i ,℃]]> 160 160 189 219 242 <![CDATA[T max，i ,℃]]> 295 295 305 305 295 Pure initiator dosage, kg / h 11.01 10.802 5.4 1.564 0.838

[0143] Comparative Example 1

[0144] Ethylene free radical polymerization was carried out according to the method of Example 1, which was different from Example 3 in that:

[0145] The first reaction zone of the multi-stage tubular reactor has only one flow channel for the reaction materials.

[0146] (1) changing the ratio of the initiator in the initiator solution in the first to fourth reaction zones, wherein TBPPI is tert-butyl peroxypivalate;

[0147] The mass ratio of initiator in the first reaction zone: DTBP / TBPB / TBPEH / TAPEH / TBPPI is 2:5:4:4:4

[0148] The mass ratio of initiator in the second reaction zone: DTBP / TBPB / TBPEH / TAPEH is 2:5:4:4

[0149] The mass ratio of initiator in the third reaction zone: DTBP / TBPB is 2:5

[0150] Initiator in the fourth reaction zone: DTBP;

[0151] (2) The temperature of each reaction zone in Comparative Example 1 is shown in Table 6, and ethylene polymerization reaction is carried out to obtain low-density polyethylene;

[0152] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this embodiment are shown in Table 8.

[0153] Table 6

[0154] Reaction Zone 1 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 156 174 207 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 308 308 308 308 <![CDATA[T in,i ,℃]]> 190 201 217 241 <![CDATA[T max,i ,℃]]> 300 300 300 295 Pure initiator dosage, kg / h 3.884 6.238 2.098 0.814

[0155] Comparative Example 2

[0156] Ethylene free radical polymerization was carried out according to the method of Example 1, which was different from Example 1 in that:

[0157] (1) The same initiator solution is used in the four reaction zones, wherein the solvent in the initiator solution is decane, the mass fraction of decane is 25 wt %, and the mass ratio of the initiator in the first to fourth reaction zones: DTBP / TBPB / TBPEH / TAPEH is 2:5:4:3;

[0158] (2) The temperature of each reaction zone in Comparative Example 2 is shown in Table 7, and ethylene polymerization reaction is carried out to obtain low-density polyethylene;

[0159] The initiator consumption (kg initiator / ton polyethylene) and the average hourly output (kg / h) of the product of this comparative example are shown in Table 8.

[0160] Table 7

[0161] Reaction Zone 1A 1B 2 3 4 <![CDATA[MIN(T d,i) (1s),℃]]> 174 174 182 207 235 <![CDATA[MAX(T d,i )(0.01s),℃]]> 308 308 308 308 308 <![CDATA[T in，i ,℃]]> 160 160 192 218 239 <![CDATA[T max，i ,℃]]> 295 295 305 305 295 Pure initiator dosage, kg / h 1.928 1.898 6.581 5.757 3.720

[0162] Test Example 1

[0163] The products prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to a heat aging test. According to GJB 150.3A-2009, a high-temperature thermal oxidation aging test at 80°C was carried out in a high and low temperature aging test chamber. The test period was 64 days, 5 samples were taken in parallel, and the average value of the decrease rate of the flexural modulus after 64 days of heat aging was calculated. The results of the heat aging test are shown in Table 8.

[0164] Table 8

[0165]

[0166] It can be seen from the test results that by using the olefin free radical polymerization method proposed in the present invention, the consumption of initiator in Examples 1-3 is lower, and the decrease rate of the flexural modulus after heat aging for 64 days is also lower, achieving the effect of low initiator residue in the product and significantly improved heat aging resistance, which is extremely economical.

[0167] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for free radical polymerization of olefins, characterized in that: The method is carried out in an olefin free radical polymerization device, which comprises i-stage reaction zones connected in series; wherein the first stage reaction zone comprises at least two tubular reactors connected in parallel; The method comprises the following steps: (1) preparing i initiator solutions, each initiator solution containing at least one initiator; (2) introducing the i initiator solutions through the inlets of the i-stage reaction zones respectively, and introducing the olefin-containing reaction material through the inlet of the first stage reaction zone to carry out olefin polymerization reaction; Wherein, i is any integer greater than or equal to 2.

2. The method according to claim 1, wherein: In step (1), the initiator is an organic peroxide, preferably at least one selected from peroxyesters, peroxyketals, peroxyketones and peroxycarbonates; Preferably, the decomposition temperature of the initiator with a half-life of 0.1 h is 80°C-170°C, preferably 85-160°C, and the melting point of the initiator is lower than 10°C; Preferably, the initiator content in the initiator solution is 10-40 wt %, preferably 15-30 wt %, based on the total weight of the initiator solution.

3. The method according to claim 1 or 2, wherein: In step (1), the initiator solutions each independently contain j initiators, where j is any integer from 1 to 6, and preferably j is any integer from 1 to 5.

4. The method according to any one of claims 1 to 3, wherein: In step (1), the solvent of the initiator solution is an aliphatic hydrocarbon, preferably at least one of the alkanes of C6-C25, and more preferably at least one of the alkanes of C8-C15.

5. The method according to any one of claims 1 to 4, wherein: In step (2), the value of i is any integer from 3 to 7, preferably any integer from 3 to 5.

6. The method according to any one of claims 1 to 5, wherein: The reaction conditions of the i-stage reaction zone independently include: reaction temperature of 120-350°C, preferably 140-310°C, reaction pressure of 80-320MPa, preferably 120-280MPa.

7. The method according to any one of claims 1 to 6, wherein: In step (2), the minimum decomposition temperature MIN (T d,i ) and the temperature T at the inlet of the reaction zone in,i The value of satisfies the following relationship: (MIN(T d,i )-T in,i ) 2 ≤1600, preferably (MIN(T d,i )-T in,i ) 2 ≤400, more preferably (MIN(T d,i )-T in,i ) 2 ≤225; Where i is the i-th reaction zone.

8. The method according to any one of claims 1 to 7, wherein: In step (2), the initiator half-life in the initiator solution in the i-stage reaction zone is 0.01s and the maximum decomposition temperature MAX (T d,i ) and the maximum temperature of the reaction zone T max,i The value of satisfies the following relationship: (MAX(T d,i )-T max,i ) 2 ≤1600, preferably (MAX(T d,i )-T max,i ) 2 ≤400; Where i is the i-th reaction zone.

9. The method according to any one of claims 1 to 8, wherein: In step (2), the olefin-containing reaction material comprises reaction monomers and an optionally added molecular weight regulator, and the reaction monomers include olefin monomers and an optionally added comonomer; Preferably, the comonomer is selected from at least one of α,β-unsaturated C3-C8 carboxylic acids, derivatives of α,β-unsaturated C3-C8 carboxylic acids and 1-olefins; preferably selected from at least one of vinyl acetate, 1-hexene, acrylic acid, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, vinyl acetate and vinyl acrylate; Preferably, the mass ratio of the total mass of the initiator to the olefin monomer in the mixed material obtained after the initiator enters the reactor is 0.00005-0.001:1, preferably 0.0001-0.0005:

1.

10. The method according to claim 9, wherein: In step (2), the molecular weight regulator is selected from at least one of aliphatic hydrocarbons, olefins, ketones, alcohols and hydrogen, preferably selected from at least one of ethane, propane, butane, propylene, 1-butene, propionaldehyde and hydrogen.

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