CN117343225A - A method for converting low melt flow rate polyethylene into high melt flow rate polyethylene - Google Patents
A method for converting low melt flow rate polyethylene into high melt flow rate polyethylene Download PDFInfo
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Abstract
本发明公开了一种低熔体流动速率聚乙烯转产高熔体流动速率聚乙烯的方法，该方法在转产时，短时间内同时加入远超正常生产时所需主催化剂、助催化剂和氢气，并且主催化剂、助催化剂、氢气采取不同的过调比例，通过快速调整催化剂加入量、助催化剂加入量、氢气加入量、α‑烯烃进料量等工艺参数，有效缩短转产时间，减少了过渡料的产生。The invention discloses a method for converting low melt flow rate polyethylene to high melt flow rate polyethylene. In this method, during the production conversion, a main catalyst, a cocatalyst and hydrogen gas that are far exceeding those required for normal production are simultaneously added in a short period of time. And the main catalyst, co-catalyst, and hydrogen adopt different over-adjustment ratios. By quickly adjusting the catalyst addition amount, co-catalyst addition amount, hydrogen addition amount, α-olefin feed amount and other process parameters, the conversion time is effectively shortened and the transition material is reduced. of production.
Description
Technical Field
The invention relates to the technical field of polyethylene technology, in particular to a method for converting low melt flow rate polyethylene into high melt flow rate polyethylene.
Background
Climate change is a global problem faced by humans, and as carbon dioxide is emitted from various countries, greenhouse gases are increased, which forms a threat to life systems. Under the background, the emission of greenhouse gases is reduced in a global agreement mode in all countries of the world, and energy conservation and consumption reduction are important means for reducing the emission of the greenhouse gases. The processing temperature is reduced, the molding period is shortened, the economic benefit is improved, and the energy consumption is reduced at the same time in the molding and processing process of the plastic product. In the production process of plastic products, the processing efficiency is generally required to be improved, the resin has better fluidity, and the fluidity requirements of large-sized injection molding parts and thin-wall injection molding parts on the resin are higher.
The common fields of polyethylene resin are packaging materials, containers, pipelines, monofilaments, wires, cables, daily necessities and the like, the melt flow rate of most polyethylene products is below 10g/10min, and the high-flow polyethylene resin products are few. CN201310350586.X discloses a preparation method of high-melt-index low-density polyethylene with melt index range of 42-60 g/10min. On a tubular high-pressure polymerization process device, proper addition proportion is selected between main flow and side flow of ethylene feeding material by selecting proper initiator, molecular weight regulator and proper usage amount, and proper polymerization pressure and polymerization temperature are selected to achieve the purpose. Industrial production of coal-based high fluidity LLDPE DNDA-8320 (synthetic resin and Plastic)Batch 2021, 38 (2): 42 Disclosure of the production of a pharmaceutical composition by increasing H 2 A process for the production of LLDPE having a melt flow rate of 20g/10min. The flow rate of the commercial high-flow HDPE special material is generally below 30g/10 min.
With the increasing demand of the market for polyolefin products, manufacturers are not limited to the production of single resin grades, and often need to switch the grades of the products to grades with vigorous market demands in order to gain advantages in market competition. With this is a series of problems such as reduced normal production time, generation of transition waste, etc. Because the melt flow rate of most products of polyethylene resin is low, when the high melt flow rate products are industrially developed and produced, the difference of product performance indexes is large, the switching time is long, the economic benefit is reduced by the produced transition materials, and effective product switching measures are needed to be adopted, so that the transfer time of the polyethylene products is shortened, and the transition materials are reduced.
CN202110120057.5 discloses a polyethylene polymerization switching method of a low pressure gas phase fluidized bed polyethylene process, comprising a process a of switching from producing PE-ML-63D082 polyethylene to producing PE-ML-57D075 polyethylene, and a process B of switching from producing PE-ML-57D075 polyethylene to producing PE-L-FB-20D20 polyethylene; 1-butene is introduced in the process A, diethyl aluminum chloride is introduced in the process B, wherein the processes A and B are realized through component and parameter adjustment. The process incorporates an intermediate product having a melt flow rate of 7.5g/10min during the switch from a product having a melt flow rate of 8.2g/10min to a product having a melt flow rate of 2.0g/10min.
CN202110623223.3 discloses a polymerization switching method for producing polyethylene, which comprises: carrying out copolymerization reaction in the presence of hydrogen, ethylene, 1-butene, a catalyst and a first cocatalyst and a second cocatalyst to produce first polyethylene; adjusting the ethylene feed amount, the 1-butene feed amount, the molar ratio of hydrogen to ethylene, the polymerization pressure, the polymerization temperature, the ethylene partial pressure, the dew point temperature, the catalyst feed amount, the first cocatalyst feed amount and the second cocatalyst feed amount so that when the density and the melt index of the obtained polymer product reach the set values,switching to polymerization to obtain second polyethylene; wherein the first polyethylene has a density of 0.917-0.923g/cm 3 A melt index of 1.5-2.5g/10min at 190℃and a load of 2.16 kg; the second polyethylene has a density of 0.96-0.966g/cm 3 The melt index at 190℃and 2.16kg load is 6.2-10.2g/10min. In the method, catalyst addition is needed to be suspended for a period of time in the switching and production transferring process, and a cocatalyst is added for adjustment, so that the transition material quantity in the process is reduced, but the product switching time is as long as 26 hours.
The above methods are all gas-phase fluidized bed brand switching technology, and the density difference of the products is large, and the melt flow rate is still far lower than 20g/10min.
The slurry brand switching research results reported in the prior publication are mainly concentrated in the university research units, and the main method of research is to build a product quality model and then solve the dynamic optimization problem. Also, those skilled in the art of polyethylene production have published studies on the method of controlling melt flow rate during the high density polyethylene brand switching process based on production experience. The general operation of the low to high melt flow rate switching in slurry processes is described, for example, in the literature "control of the melt flow rate of high density polyethylene" ("petrochemical technology" 2021, (8): 109-111): 1) fully opening a regulating valve of hydrogen, largely introducing hydrogen, 2) then taking 30-40 min to make the feeding amount of the catalyst 120% of the feeding amount of the catalyst with the standard post-switching brand, and continuously operating for 1.5-2.0 h, wherein the concentration of the catalyst in the polymerization kettle can reach the concentration required by the post-switching brand, and 3) then regulating the feeding amount of the catalyst back to the standard value. 4) When the hydrogen-ethylene ratio (molar ratio) is gradually increased to about 10% higher than the normal operation value, the feeding amount of hydrogen is then adjusted back to the normal value, the hydrogen-ethylene ratio (molar ratio) is kept unchanged basically for 2 hours, and then the catalyst amount is increased or decreased according to the change condition of the pressure.
The main problem of the above studies is that the inter-grade melt flow rate of the study is less different and has poor applicability in the conversion of high melt flow rate products. Meanwhile, in order to avoid the risk of local sudden aggregation caused by the rise of the kettle temperature when the catalyst is greatly lifted, besides the time for exceeding the feeding amount of the catalyst can be prolonged by controlling the lifting speed of the catalyst amount, a large amount of hydrogen is added in advance, and then the exceeding hydrogen feeding amount is returned and the hydrogen-ethylene ratio is kept for a period of time, so that the brand switching time is prolonged.
Disclosure of Invention
The invention aims to provide a polyethylene transfer method, which aims to solve the problems of long switching time and excessive transition materials in the polyethylene transfer process in the prior art.
In order to achieve the above object, the present invention provides a method for converting low melt flow rate polyethylene into high melt flow rate polyethylene, wherein the low melt flow rate polyethylene is prepared by a slurry process, the melt flow rate is less than 2.5g/10min, during the conversion, the feeding amount of ethylene and alpha-olefin is unchanged, the feeding amount of main catalyst, cocatalyst and hydrogen are simultaneously adjusted to convert the feeding amount of the high melt flow rate polyethylene, the feeding amount of the main catalyst is adjusted to 120-160% of the feeding amount of the main catalyst required for stably producing the high melt flow rate polyethylene, the feeding amount mole ratio of cocatalyst and the main catalyst is adjusted to 110-130% of the feeding amount mole ratio of cocatalyst and the main catalyst required for stably producing the high melt flow rate polyethylene, the feeding amount of hydrogen is adjusted to 120-170% of the hydrogen required for stably producing the high melt flow rate polyethylene, and after the adjusting conditions, the feeding amount of the main catalyst, the cocatalyst and the hydrogen are adjusted to reach more than 80% of the lower limit of the target high melt flow rate; when the melt flow rate of the obtained polyethylene powder reaches 90-95% of the lower limit of the target high melt flow rate after the conditions are adjusted, adjusting the alpha-olefin feeding amount to a feeding amount range for stably producing high melt flow rate polyethylene, and enabling the density of the obtained polyethylene powder to reach the requirement of a target product;
wherein the feeding amount mole ratio of the cocatalyst and the main catalyst is calculated as the mole ratio of aluminum to titanium.
The invention relates to a method for converting low melt flow rate polyethylene into high melt flow rate polyethylene, wherein the active ingredient of a main catalyst is titanium tetrachloride; the cocatalyst is one or more of triethylaluminum, n-butylaluminum, isobutylaluminum, tripropylaluminum, dihexylaluminum dichloride and triisobutylaluminum.
The method for converting the low melt flow rate polyethylene into the high melt flow rate polyethylene has the density of 0.950-0.956g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.951-0.954g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 0.8-1.3g/10min, preferably 0.9-1.2g/10min.
The method for converting the low melt flow rate polyethylene into the high melt flow rate polyethylene has the density of 0.950-0.954g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.951-0.953g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 1.8-2.2g/10min, preferably 1.9-2.0g/10min.
The method for converting the low melt flow rate polyethylene into the high melt flow rate polyethylene has the density of 0.948-0.965g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.955-0.963g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and a load of 2.16kg is 10-100g/10min, preferably 20-80g/10min.
The polymerization conditions of the method for preparing the low melt flow rate polyethylene are that the Ti content in a production device is 0.010-0.015 mmol/L, the Al-Ti ratio is 30-50, the hydrogen/ethylene volume ratio is 0.4-0.7, the temperature of a reaction kettle is 78-88 ℃, the alpha-olefin/ethylene mass ratio is 0.011-0.015, and the pressure of the reaction kettle is 0.38-0.48 MPa.
The polymerization conditions of the method for transferring the low melt flow rate polyethylene to the high melt flow rate polyethylene are that the Ti content in the production device is 0.025-0.038 mmol/L, the Al-Ti ratio is 20-35, the hydrogen/ethylene volume ratio is 1.5-3.0, the alpha-olefin/ethylene mass ratio is 0.002-0.01, the temperature of the reaction kettle is 75-90 ℃, and the pressure of the reaction kettle is 0.55-0.90 MPa.
The initial operation condition of the method for transferring the low melt flow rate polyethylene to the high melt flow rate polyethylene is that the Ti content in the production device is 0.030-0.060 mmol/L, the Al-Ti ratio is 22-45, the hydrogen/ethylene volume ratio is 1.8-5.0, the temperature of the reaction kettle is 75-90 ℃, and the pressure of the reaction kettle is 0.55-0.90 MPa.
The method for converting the low melt flow rate polyethylene into the high melt flow rate polyethylene comprises the step of converting the low melt flow rate polyethylene into the high melt flow rate polyethylene, wherein the alpha-olefin is the alpha-olefin with 3-8 carbon atoms, preferably the alpha-olefin with 4-8 carbon atoms.
The invention has the beneficial effects that:
(1) In the method, polymerization switching is carried out in a continuous state, so that the influence of parking plate number switching or reduction of production load on ethylene balance, disqualified materials generated by parking and yield loss are avoided;
(2) In the method, the conversion time is effectively shortened and the generation of transition materials is reduced by rapidly adjusting the technological parameters such as the addition of the catalyst, the addition of the cocatalyst, the addition of the hydrogen, the addition of the alpha-olefin and the like;
(3) In the method, the catalyst addition amount, the cocatalyst addition amount and the hydrogen addition amount are cooperatively and rapidly adjusted, so that the great fluctuation of the reactor temperature in the process of transferring and switching is avoided, and the risk of 'flying temperature' of the reactor is reduced.
Compared with the prior art, the transfer method of polyethylene provided by the invention can quickly transfer the high melt flow rate product in the production process of polyethylene, can shorten the transfer time, reduce transition materials in the transfer process, and quickly enable the performances of the product such as the melt flow rate and the like to meet the technical index requirements.
Detailed Description
The present invention will be specifically described below by way of examples. It is noted herein that the following examples are given solely for the purpose of illustration and are not to be construed as limiting the scope of the invention, as many insubstantial modifications and variations of the invention will become apparent to those skilled in the art in light of the above disclosure.
The method for converting low melt flow rate polyethylene into high melt flow rate polyethylene comprises the steps of preparing the low melt flow rate polyethylene by a slurry method, wherein the melt flow rate is less than 2.5g/10min, during conversion, ethylene and alpha-olefin feeding amount is unchanged, simultaneously converting the feeding amount of a main catalyst, a cocatalyst and hydrogen into the high melt flow rate polyethylene, regulating the feeding amount of the main catalyst to 120-160% of the feeding amount of the main catalyst required for stably producing the high melt flow rate polyethylene, regulating the feeding amount mole ratio of the cocatalyst to the main catalyst to 110-130% of the feeding amount of the cocatalyst required for stably producing the high melt flow rate polyethylene, regulating the feeding amount of hydrogen to 120-170% of the hydrogen required for stably producing the high melt flow rate polyethylene, and regulating the feeding amount of the main catalyst, the cocatalyst and the hydrogen to the feeding amount range of the high melt flow rate polyethylene powder obtained after regulating the melt flow rate of the polyethylene powder reaches more than 80% of the lower limit of the target high melt flow rate; when the melt flow rate of the obtained polyethylene powder reaches 90-95% of the lower limit of the target high melt flow rate after the conditions are adjusted, adjusting the alpha-olefin feeding amount to a feeding amount range for stably producing high melt flow rate polyethylene, and enabling the density of the obtained polyethylene powder to reach the requirement of a target product;
wherein the feeding amount mole ratio of the cocatalyst and the main catalyst is calculated as the mole ratio of aluminum to titanium.
The order of adjusting the feeding amount of the main catalyst, the feeding amount of the cocatalyst and the feeding amount of the hydrogen to the feeding amount range for stably producing the high melt flow rate polyethylene and the feeding amount of the alpha-olefin to the feeding amount range for stably producing the high melt flow rate polyethylene is not different. If the melt flow rate of the polyethylene powder reaches 85% of the lower limit of the target high melt flow rate, firstly adjusting the feeding amount of the main catalyst, the feeding amount of the cocatalyst and the feeding amount of hydrogen to the feeding amount range for stably producing the high melt flow rate polyethylene, and when the melt flow rate of the polyethylene powder reaches 90% of the lower limit of the target high melt flow rate, adjusting the feeding amount of alpha-olefin to the feeding amount range for stably producing the high melt flow rate polyethylene; or when the melt flow rate of the polyethylene powder reaches 92% of the lower limit of the target high melt flow rate, firstly adjusting the feeding amount of the alpha-olefin to a feeding amount range for stably producing the high melt flow rate polyethylene, then adjusting the feeding amount of the main catalyst, the feeding amount of the cocatalyst and the feeding amount of the hydrogen to a feeding amount range for stably producing the high melt flow rate polyethylene, or firstly adjusting the feeding amount of the main catalyst, the feeding amount of the cocatalyst and the feeding amount of the hydrogen to a feeding amount range for stably producing the high melt flow rate polyethylene, then adjusting the feeding amount of the alpha-olefin to a feeding amount range for stably producing the high melt flow rate polyethylene, or simultaneously adjusting the feeding amount of the main catalyst, the feeding amount of the cocatalyst and the feeding amount of the hydrogen to a feeding amount range for stably producing the high melt flow rate polyethylene.
The invention uses slurry method polyethylene process to prepare low melt flow rate polyethylene and high melt flow rate polyethylene, the catalyst is various catalysts suitable for catalyzing ethylene polymerization, preferably Ziegler-Natta catalyst commonly used in the field, comprising main catalyst and cocatalyst, the main component of the main catalyst is titanium tetrachloride, the main component of the cocatalyst is triethylaluminum, and a small amount of n-butyl aluminum, isobutyl aluminum and tripropyl aluminum. Aluminum hexyl dichloride, triisobutyl aluminum, and the like can also be used. High-purity ethylene, propylene or butene-1 is used as a raw material, hexane is used as a solvent, and hydrogen is used as a molecular weight regulator. The catalyst addition is adjusted and controlled according to the Ti content in the slurry reactor. The cocatalyst amount is regulated and controlled according to the aluminum-titanium ratio in the slurry reaction kettle. The hydrogen addition amount is regulated and controlled according to the volume ratio of hydrogen to ethylene in the gas phase of the slurry reaction kettle.
The density of the low melt flow rate polyethylene of the present invention is from 0.950 to 0.956g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.951-0.954g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 0.8-1.3g/10min, preferably 0.9-1.2g/10min.
The density of the low melt flow rate polyethylene of the invention is 0.950-0.954g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.951-0.953g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 1.8-2.2g/10min, preferably 1.9-2.0g/10min.
The invention is of middle and high gradeThe density of the melt flow rate polyethylene is 0.948-0.965g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.955-0.963g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and a load of 2.16kg is 10-100g/10min, preferably 20-80g/10min.
The polymerization condition for preparing the low melt flow rate polyethylene is that the Ti content in a production device is 0.010-0.015 mmol/L, the Al-Ti ratio is 30-50, the hydrogen/ethylene volume ratio is 0.4-0.7, the temperature of a reaction kettle is 78-88 ℃, the alpha-olefin/ethylene mass ratio is 0.011-0.015, and the pressure of the reaction kettle is 0.38-0.48 MPa.
The polymerization condition for stably producing the high melt flow rate polyethylene is that the Ti content in a production device is 0.025-0.038 mmol/L, the Al-Ti ratio is 20-35, the hydrogen/ethylene volume ratio is 1.5-3.0, the alpha-olefin/ethylene mass ratio is 0.002-0.01, the temperature of a reaction kettle is 75-90 ℃, and the pressure of the reaction kettle is 0.55-0.90 MPa.
The initial operation condition of the invention when transferring to produce high melt flow rate polyethylene is that the Ti content in the production device is 0.030-0.060 mmol/L, the Al-Ti ratio is 22-45, the hydrogen/ethylene volume ratio is 1.8-5.0, the temperature of the reaction kettle is 75-90 ℃, and the pressure of the reaction kettle is 0.55-0.90 MPa.
The alpha-olefin in the present invention is an alpha-olefin having 3 to 8 carbon atoms, preferably an alpha-olefin having 4 to 8 carbon atoms.
In the prior art, small ranges of melt flow rate are typically adjusted by adjusting the hydrogen/ethylene molar ratio and large ranges of melt flow rate are adjusted by catalyst feed. The cocatalyst generally maintains a certain proportion with the main catalyst according to different product brands.
When the melt flow rate of the product needs to be greatly improved, the addition amount of the catalyst needs to be greatly increased to improve the reaction temperature, but when the reaction temperature is increased and the catalyst amount is increased, the reaction intensity is improved, a large amount of heat can be released in a short time, the temperature of the reaction kettle is increased due to improper control, and the generated polymer powder begins to expand to cause explosion and aggregation accidents, so that the production cannot be normally carried out. To smooth the reaction, the slow increase of the catalyst addition is a conventional practice except for taking measures to enhance heat removalBy means of the method, the conversion switching time is increased by slowly increasing the catalyst addition amount, and in order to reduce the amount of transition materials, the production is stopped or the production load is reduced, so that the yield and economic benefit of the device are reduced, and the ethylene balance of the whole production chain is adversely affected. The hydrogen is introduced into the reactor in large quantity, and then the feeding quantity of the catalyst is introduced into the reactor to make the catalyst concentration in the polymerization reactor reach the required concentration of the switched brand, and for TiCl, the feeding quantity of the catalyst is introduced into the reactor to make the catalyst concentration reach 120% of the feeding quantity of the switched brand normal catalyst 4 -Al(C 2 H 5 ) 3 Catalyst system, with H 2 The activity gradually decreases with increasing addition. This is because hydrogen is adsorbed on the catalyst surface, making it difficult for monomer ethylene to contact the catalyst surface, resulting in a decrease in chain growth constant, and the reaction is difficult to proceed.
According to the research of the inventor, in the process of switching a slurry process polyethylene production device to produce a high melt flow rate product, the catalyst feeding amount, the cocatalyst feeding amount, the hydrogen feeding amount and the alpha-olefin feeding amount are cooperatively regulated, namely, a main catalyst, an cocatalyst and hydrogen required in far and ultra-normal production are simultaneously added in a short time in the first step, and different overshoot ratios are adopted for the main catalyst, the cocatalyst and the hydrogen, namely, the catalyst feeding amount is 20-60% higher than the stable production catalyst feeding amount, the cocatalyst feeding amount is 10-30% higher than the stable production cocatalyst feeding amount, and the hydrogen feeding amount is 20-70% higher than the stable production hydrogen feeding amount. And in the second step, after the melt flow rate of the polyethylene powder reaches the index lower limit of 90-95%, the alpha-olefin feeding amount is regulated to a stable production range. And thirdly, reducing the addition amount of the catalyst, the cocatalyst and the hydrogen to a stable production value. The whole transfer time is shortened to 3-5 hours. The catalyst and hydrogen are gradually increased to the indexes required in stable production in the prior art, the reaction is waited until the melt flow rate reaches the index range, and the conversion time is more than 15 hours.
Compared with the prior art that a large amount of hydrogen is firstly added to inhibit the reaction activity of the catalyst and then the excessive catalyst is added, the excessive catalyst is added with 20 to 60 percent of main catalyst and 10 to 30 percent of cocatalyst, and the hydrogen content is 20 to 70 percent higher than that of the hydrogen produced stably. Chain transfer to the cocatalyst also occurs with the growing polymer long chain, and the polymerization is temporarily terminated, avoiding the formation of high molecular weight products. The cocatalyst is an important component of an ethylene polymerization catalytic system, the formation speed of an active center in the catalytic system can be regulated and controlled through the cooperative control of the overshoot proportion of the cocatalyst and the main catalyst, and meanwhile, the proper hydrogen addition amount is matched to form the balance of the active center, the transfer of a polymer chain and the chain termination, and the polymerization degree of a polyethylene molecular chain is controlled on the premise of stable release of the catalytic activity, so that a high-melting-finger polymerization product is obtained.
In the present invention, the process of switching from producing a low melt flow rate polyethylene to polymerizing to a high melt flow rate polyethylene may be performed in a slurry process polyethylene apparatus (preferably a tank slurry), and the adjustment of the respective parameters may be performed in a stepwise adjustment manner in a continuous production state, for example, the method may comprise the steps of:
(1) And synchronously improving the entering amount of the main catalyst, the cocatalyst and the hydrogen to the brand switching control range within 15 minutes. The catalyst inlet amount is 20-60% higher than the stable production catalyst inlet amount, the promoter inlet amount is 10-30% higher than the stable production promoter inlet amount, and the hydrogen adding amount is 20-70% higher than the stable production hydrogen adding amount. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 4 to 5 hours/time to 0.5 hours/time.
(2) After the melt flow rate of the polyethylene powder reaches the lower limit of 90-95%, the feeding amount of alpha-olefin is regulated to make the density in the product index range.
(3) And (3) after the step (1) is finished for 2 hours, synchronously reducing the entering amount of the catalyst, the cocatalyst and the hydrogen to the stable production control range of the brand.
(4) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 0.5 hours/time to 4-5 hours/time.
The following examples are given to illustrate the technical scheme of the present invention in further detail, but it is necessary to point out that the following examples are only for the description of the present invention and are not to be construed as limiting the scope of the present invention.
Example 1
In a triple well oiled CX process kettle slurry process polyethylene apparatus, a conversion of low melt flow rate polyethylene to high melt flow rate polyethylene is performed wherein:
the density of the low melt flow rate polymer product was 0.952g/cm 3 The melt index at 190℃and a load of 2.16kg was 1.0g/10min.
The high melt flow rate polymer product has a density index of 0.952 to 0.956g/cm 3 The melt index of the polymer product at 190 ℃ and a load of 2.16kg is 20-24g/10min.
The transfer switching process is as follows:
(1) The method comprises the steps of refining polymerization-grade ethylene, pressurizing the refined ethylene into a reaction kettle, adding hexane as a solvent, and simultaneously adding a main catalyst, a cocatalyst and hydrogen to carry out polymerization reaction, wherein the operation conditions of the low melt flow rate product are as follows before the low melt flow rate product is switched to produce a high melt flow rate product: the Ti content in the slurry reactor was 0.013mmol/L, the Al-Ti ratio was 40, the hydrogen/ethylene volume ratio was 0.6, the propylene feed amount (relative to the ethylene feed) mass fraction was 1.3%, the reactor temperature was 85℃and the reactor pressure was 0.45MPa.
(2) And synchronously improving the entering amount of the main catalyst, the cocatalyst and the hydrogen to the brand switching control range within 15 minutes. The operating conditions include: the Ti content in the slurry reactor was 0.039mmol/L, the Al-Ti ratio was 36, the hydrogen/ethylene volume ratio was 2.9, the propylene feed amount (relative to the ethylene feed) mass fraction was 1.3%, the reactor temperature was 82℃and the reactor pressure was 0.65MPa. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 4 to 5 hours/time to 0.5 hours/time.
(3) In polyethylene powderAfter the melt flow rate of the material reaches 18.2g/10min, the mass fraction of the propylene feeding amount (relative to the ethylene feeding amount) is adjusted to be 1.0 percent, so that the density of the polyethylene powder is between 0.952 and 0.956g/cm 3 Synchronously reducing the entering amount of the catalyst, the cocatalyst and the hydrogen to the stable production control range of the brand. The operating conditions include: the Ti content in the slurry reactor was 0.030mmol/L, the Al-Ti ratio was 30, the hydrogen/ethylene volume ratio was 2.1, the propylene feed amount (relative to the ethylene feed) mass fraction was 1.0%, the reactor temperature was 85℃and the reactor pressure was 0.60MPa.
(5) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 0.5 hours/time to 4-5 hours/time.
The transfer switching completion time was 3.6 hours.
Example 2
In a hurst kettle type slurry process polyethylene apparatus, a conversion of low melt flow rate polyethylene to high melt flow rate polyethylene is performed wherein:
the density of the low melt flow rate polymer product was 0.951g/cm 3 The melt index at 190℃and a load of 2.16kg was 2.2g/10min.
The high melt flow rate polymer product has a density index of 0.956 to 0.960g/cm 3 The melt index of the polymer product at 190 ℃ and a load of 2.16kg is 80-99g/10min.
The transfer switching process is as follows:
(1) The method comprises the steps of refining polymerization-grade ethylene, pressurizing the refined ethylene into a reaction kettle, adding hexane as a solvent, and simultaneously adding a main catalyst, a cocatalyst and hydrogen to carry out polymerization reaction, wherein the operation conditions of the low melt flow rate product are as follows before the low melt flow rate product is switched to produce a high melt flow rate product: the Ti content in the slurry reactor was 0.015mmol/L, the Al-Ti ratio was 31, the hydrogen/ethylene volume ratio was 0.7, the propylene feed (relative to the ethylene feed) mass fraction was 1.4%, the reactor temperature was 86℃and the reactor pressure was 0.40MPa.
(2) And synchronously improving the entering amount of the main catalyst, the cocatalyst and the hydrogen to the brand switching control range within 15 minutes. The operating conditions include: the Ti content in the slurry reactor was 0.057mmol/L, the Al-Ti ratio was 24, the hydrogen/ethylene volume ratio was 4.9, the propylene feed amount (relative to the ethylene feed) mass fraction was 1.4%, the reactor temperature was 86℃and the reactor pressure was 0.80MPa. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 4 to 5 hours/time to 0.5 hours/time.
(3) After the melt flow rate of the polyethylene powder reaches 65g/10min, the entering amount of the catalyst, the cocatalyst and the hydrogen is reduced to the stable production control range of the brand. The operating conditions include: the Ti content in the slurry reaction kettle is 0.036mmol/L, the Al-Ti ratio is 21, the hydrogen-ethylene volume ratio is 2.9, the reaction kettle temperature is 88 ℃, and the reaction kettle pressure is 0.89MPa
(4) After the melt flow rate of the polyethylene powder reaches 75g/10min, the mass fraction of the propylene feeding amount relative to the ethylene feeding amount is regulated to be 0.6 percent, so that the density of the polyethylene powder is between 0.956 and 0.960g/cm 3 。
(5) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 0.5 hours/time to 4-5 hours/time.
The transfer switching completion time was 4.1 hours.
Example 3
In a triple well oiled kettle type slurry process polyethylene apparatus, converting a low melt flow rate polyethylene to a high melt flow rate polyethylene, wherein:
the density of the low melt flow rate polymer product was 0.950g/cm 3 The melt index at 190℃and a load of 2.16kg was 0.60g/10min.
The high melt flow rate polymer product has a density index of 0.960 to 0.963g/cm 3 The melt index of the polymer product at 190 ℃ and a load of 2.16kg is 45-55g/10min.
The transfer switching process is as follows:
(1) The method comprises the steps of refining polymerization-grade ethylene, pressurizing the refined ethylene into a reaction kettle, adding hexane as a solvent, and simultaneously adding a main catalyst, a cocatalyst and hydrogen to carry out polymerization reaction, wherein the operation conditions of the low melt flow rate product are as follows before the low melt flow rate product is switched to produce a high melt flow rate product: the Ti content in the slurry reaction kettle is 0.010mmol/L, the Al-Ti ratio is 48, the hydrogen/ethylene volume ratio is 0.5, the mass fraction of butene-1 feed (relative to ethylene feed) is 1.1%, the temperature of the reaction kettle is 84 ℃, and the pressure of the reaction kettle is 0.38MPa.
(2) And synchronously improving the entering amount of the main catalyst, the cocatalyst and the hydrogen to the brand switching control range within 15 minutes. The operating conditions include: the Ti content in the slurry reaction kettle is 0.040mmol/L, the Al-Ti ratio is 32, the hydrogen/ethylene volume ratio is 3.0, the mass fraction of butene-1 feed (relative to ethylene feed) is 1.1%, the temperature of the reaction kettle is 84 ℃, and the pressure of the reaction kettle is 0.70MPa. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 4 to 5 hours/time to 0.5 hours/time.
(3) After the melt flow rate of the polyethylene powder reaches 41g/10min, the mass fraction of the butene-1 feeding amount (relative to the ethylene feeding) is regulated to be 0.2 percent, so that the density of the polyethylene powder is between 0.960 and 0.963g/cm 3 。
(4) After the melt flow rate of the polyethylene powder reaches 43g/10min, the inlet amount of the catalyst, the cocatalyst and the hydrogen is reduced to the stable production control range of the brand. The operating conditions include: the Ti content in the slurry reaction kettle is 0.033mmol/L, the Al-Ti ratio is 25, the hydrogen/ethylene volume ratio is 2.4, the mass fraction of butene-1 feed (relative to ethylene feed) is 0.2%, the reaction kettle temperature is 86 ℃, and the reaction kettle pressure is 0.70MPa.
(5) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 0.5 hours/time to 4-5 hours/time.
The transfer switching completion time was 4.3 hours.
Comparative example 1
In a triple well oiled CX process kettle slurry process polyethylene apparatus, a conversion of low melt flow rate polyethylene to high melt flow rate polyethylene is performed wherein:
low melt flow rate polymer productHas a density of 0.952g/cm 3 The melt index at 190℃and a load of 2.16kg was 1.0g/10min.
The high melt flow rate polymer product has a density index of 0.952 to 0.956g/cm 3 The melt index of the polymer product at 190 ℃ and a load of 2.16kg is 20-24g/10min.
The transfer switching process is as follows:
(1) The method comprises the steps of refining polymerization-grade ethylene, pressurizing the refined ethylene into a reaction kettle, adding hexane as a solvent, and simultaneously adding a main catalyst, a cocatalyst and hydrogen to carry out polymerization reaction, wherein the operation conditions of the low melt flow rate product are as follows before the low melt flow rate product is switched to produce a high melt flow rate product: the Ti content in the slurry reaction kettle is 0.010mmol/L, the Al-Ti ratio is 50, the hydrogen/ethylene volume ratio is 0.6, the mass fraction of propylene feeding amount (relative to ethylene feeding) is 1.3%, the temperature of the reaction kettle is 85 ℃, and the pressure of the reaction kettle is 0.45MPa.
(2) Gradually increasing the main catalyst amount to ensure that the Ti content in the slurry reaction kettle is 0.030mmol/L and the aluminum-titanium ratio is 30, monitoring the temperature of the reaction kettle to ensure that the temperature is 80-88 ℃, and avoiding the explosion polymerization caused by the 'flying temperature' which occurs too quickly. The analysis frequency of the melt flow rate of the polyethylene powder in the process is adjusted from 4-5 hours/time to 2 hours/time.
(3) After 5 hours, the main catalyst dosage reaches the requirement, and the hydrogen addition amount is started to be increased to enable the volume ratio of hydrogen to ethylene to be 2.1, and the analysis frequency of the melt flow rate of the polyethylene powder in the process is adjusted to be 0.5 hours/time from 4 to 5 hours/time.
(4) After 9 hours, the melt flow rate of the polyethylene powder reaches the index of 22g/10min, and the feeding amount of propylene is adjusted to ensure that the density is between 0.952 and 0.956g/cm 3 。
(5) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 0.5 hours/time to 4-5 hours/time.
The transfer switching completion time was 12 hours.
Comparative example 2
In a hurst kettle type slurry process polyethylene apparatus, a conversion of low melt flow rate polyethylene to high melt flow rate polyethylene is performed wherein:
the density of the low melt flow rate polymer product was 0.951g/cm 3 The melt index at 190℃and a load of 2.16kg was 2.2g/10min.
The high melt flow rate polymer product has a density index of 0.956 to 0.960g/cm 3 The melt index of the polymer product at 190 ℃ and a load of 2.16kg is 80-99g/10min.
The transfer switching process is as follows:
(1) The method comprises the steps of refining polymerization-grade ethylene, pressurizing the refined ethylene into a reaction kettle, adding hexane as a solvent, and simultaneously adding a main catalyst, a cocatalyst and hydrogen to carry out polymerization reaction, wherein the operation conditions of the low melt flow rate product are as follows before the low melt flow rate product is switched to produce a high melt flow rate product: the Ti content in the slurry reactor was 0.015mmol/L, the Al-Ti ratio was 31, the hydrogen/ethylene volume ratio was 0.7, the propylene feed (relative to the ethylene feed) mass fraction was 1.4%, the reactor temperature was 86℃and the reactor pressure was 0.40MPa.
(2) The regulating valve of hydrogen is fully opened, a large amount of hydrogen is introduced, then the feeding amount of the main catalyst is increased by 120 percent of the feeding amount of the switched standard main catalyst (the Ti content in the slurry reaction kettle is 0.043 mmol/L), the aluminum-titanium ratio is adjusted by the same proportion (the 120 percent of the normal feeding amount is 25), the operation is continued for 1.5 to 2.0 hours, the concentration of the main catalyst in the polymerization kettle can reach the concentration required by the switched standard, and then the feeding amount of the main catalyst is adjusted back to the normal value. The Ti content in the slurry reactor was 0.036mmol/L, the Al-Ti ratio was 21, the hydrogen/ethylene volume ratio was 2.9, the propylene feed amount (relative to the ethylene feed) mass fraction was 0.6%, the reactor temperature was 88℃and the reactor pressure was 0.89MPa.
(3) When the hydrogen-ethylene volume ratio is gradually increased to about 10 percent (3.2) higher than the normal operation value, the feeding amount of hydrogen is regulated back to the normal value, the hydrogen-ethylene ratio is kept basically unchanged for 2 hours, and then the catalyst amount is increased or decreased according to the pressure change condition.
(4) The melt flow rate of polyethylene powder reaches the fingerAfter the standard of 80g/10min, the propylene feeding amount is adjusted to be between 0.956 and 0.960g/cm 3 。
(5) Synchronously reducing the entering amount of the main catalyst, the cocatalyst and the hydrogen to the stable production control range of the brand. The operating conditions include: the Ti content in the slurry reactor was 0.036mmol/L, the Al-Ti ratio was 21, the hydrogen/ethylene volume ratio was 2.9, the propylene feed amount (relative to the ethylene feed) mass fraction was 0.6%, the reactor temperature was 88℃and the reactor pressure was 0.89MPa.
(5) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The transfer switching completion time was 9.4 hours.
Comparative example 3
In a triple well oiled kettle type slurry process polyethylene apparatus, converting a low melt flow rate polyethylene to a high melt flow rate polyethylene, wherein:
the density of the low melt flow rate polymer product was 0.950g/cm 3 The melt index at 190℃and a load of 2.16kg was 0.60g/10min.
The high melt flow rate polymer product has a density index of 0.960 to 0.963g/cm 3 The melt index of the polymer product at 190 ℃ and a load of 2.16kg is 45-55g/10min.
The transfer switching process is as follows:
(1) The method comprises the steps of refining polymerization-grade ethylene, pressurizing the refined ethylene into a reaction kettle, adding hexane as a solvent, and simultaneously adding a main catalyst, a cocatalyst and hydrogen to carry out polymerization reaction, wherein the operation conditions of the low melt flow rate product are as follows before the low melt flow rate product is switched to produce a high melt flow rate product: the Ti content in the slurry reaction kettle is 0.010mmol/L, the Al-Ti ratio is 48, the hydrogen/ethylene volume ratio is 0.5, the mass fraction of butene-1 feed (relative to ethylene feed) is 1.1%, the temperature of the reaction kettle is 84 ℃, and the pressure of the reaction kettle is 0.38MPa.
(2) And synchronously improving the entering amount of the main catalyst, the cocatalyst and the hydrogen to the brand switching control range within 30 minutes. The operating conditions include: the Ti content in the slurry reaction kettle is 0.040mmol/L, the Al-Ti ratio is 25, the hydrogen/ethylene volume ratio is 3.0, the mass fraction of butene-1 feed (relative to ethylene feed) is 1.1%, the temperature of the reaction kettle is 84 ℃, and the pressure of the reaction kettle is 0.70MPa. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 4 to 5 hours/time to 0.5 hours/time.
(3) After the melt flow rate of the polyethylene powder reaches 41g/10min, the mass fraction of the butene-1 feeding amount (relative to the ethylene feeding) is regulated to be 0.2 percent, so that the density of the polyethylene powder is between 0.960 and 0.963g/cm 3 . Then the main catalyst and the hydrogen entering amount are reduced to the stable production control range of the brand. The operating conditions include: the Ti content in the slurry reaction kettle is 0.033mmol/L, the Al-Ti ratio is 25, the hydrogen/ethylene volume ratio is 2.4, the mass fraction of butene-1 feed (relative to ethylene feed) is 0.2%, the reaction kettle temperature is 86 ℃, and the reaction kettle pressure is 0.70MPa.
(4) And (3) carrying out small-range adjustment on the polymerization parameters according to the production condition, so that the product performance is within the index range. The melt flow rate analysis frequency of the polyethylene powder was adjusted from 0.5 hours/time to 4-5 hours/time.
The transfer switching completion time was 9.8 hours.
As can be seen from comparison of examples 1 and 2 with comparative examples 1 and 2, by using the polyethylene conversion method of the present invention, the conversion time is greatly shortened by synergistically adjusting the main catalyst feed amount, the cocatalyst feed amount, and the hydrogen/ethylene volume ratio, i.e., rapidly increasing the catalyst, cocatalyst and hydrogen feed amount, during the conversion from a low melt flow rate product to a high melt flow rate product, while avoiding a significant increase in the reactor temperature, by rapidly establishing the polymerization reaction, by gradually increasing the catalyst and adding an excess of hydrogen followed by increasing the catalyst overshoot over the prior art. From the comparison of example 3 and comparative example 3, it is evident that the catalyst and hydrogen feeds are increased simultaneously, but the cocatalyst feeds are not synergistically regulated, and that it takes longer to complete the switch to the high melt flow rate target product due to imbalance in active center and polymer chain transfer, chain termination in the reactor, and uneven release of catalytic activity.
Of course, the present invention is capable of other various embodiments and its several details are capable of modification and variation in light of the present invention by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. The method for converting low melt flow rate polyethylene into high melt flow rate polyethylene is characterized in that the low melt flow rate polyethylene is prepared by a slurry method, the melt flow rate is less than 2.5g/10min, when the conversion is carried out, the feeding amount of ethylene and alpha-olefin is unchanged, the feeding amount of a main catalyst, a cocatalyst and hydrogen is regulated, the feeding amount of the main catalyst is regulated to 120-160% of the feeding amount of the main catalyst required for stably producing high melt flow rate polyethylene, the feeding amount mole ratio of the cocatalyst and the main catalyst is regulated to 110-130% of the feeding amount mole ratio of the cocatalyst and the main catalyst required for stably producing high melt flow rate polyethylene, the feeding amount of hydrogen is regulated to 120-170% of the hydrogen required for stably producing high melt flow rate polyethylene, and after the melt flow rate of polyethylene powder reaches more than 80% of the lower limit of the target high melt flow rate, the feeding amount of the main catalyst, the cocatalyst and the hydrogen are regulated to the feeding amount range of stably producing high melt flow rate polyethylene; when the melt flow rate of the obtained polyethylene powder reaches 90-95% of the lower limit of the target high melt flow rate after the conditions are adjusted, adjusting the alpha-olefin feeding amount to a feeding amount range for stably producing high melt flow rate polyethylene, and enabling the density of the obtained polyethylene powder to reach the requirement of a target product;
wherein the feeding amount mole ratio of the cocatalyst and the main catalyst is calculated as the mole ratio of aluminum to titanium.
2. The method of converting a low melt flow rate polyethylene to a high melt flow rate polyethylene according to claim 1, wherein said primary catalyst active ingredient is titanium tetrachloride; the cocatalyst is one or more of triethylaluminum, n-butylaluminum, isobutylaluminum, tripropylaluminum, dihexylaluminum dichloride and triisobutylaluminum.
3. The method of converting a low melt flow rate polyethylene to a high melt flow rate polyethylene according to claim 1, wherein the low melt flow rate polyethylene has a density of from 0.950 to 0.956g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.951-0.954g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 0.8-1.3g/10min, preferably 0.9-1.2g/10min.
4. The method for converting a low melt flow rate polyethylene to a high melt flow rate polyethylene according to claim 1, wherein the low melt flow rate polyethylene has a density of from 0.950 to 0.954g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.951-0.953g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 1.8-2.2g/10min, preferably 1.9-2.0g/10min.
5. The method of converting a low melt flow rate polyethylene to a high melt flow rate polyethylene according to claim 1, wherein the high melt flow rate polyethylene has a density of from 0.948 to 0.965g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Preferably 0.955-0.963g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and a load of 2.16kg is 10-100g/10min, preferably 20-80g/10min.
6. The method for converting low melt flow rate polyethylene into high melt flow rate polyethylene according to claim 1, wherein the polymerization conditions for preparing the low melt flow rate polyethylene are that the Ti content in the production device is 0.010-0.015 mmol/L, the Al-Ti ratio is 30-50, the hydrogen/ethylene volume ratio is 0.4-0.7, the alpha-olefin/ethylene mass ratio is 0.011-0.015, the reaction kettle temperature is 78-88 ℃, and the reaction kettle pressure is 0.38-0.48 MPa.
7. The method for converting low melt flow rate polyethylene into high melt flow rate polyethylene according to claim 1, wherein polymerization conditions for stably producing high melt flow rate polyethylene are that the Ti content in the production device is 0.025-0.038 mmol/L, the aluminum-titanium ratio is 20-35, the hydrogen/ethylene volume ratio is 1.5-3.0, the α -olefin/ethylene mass ratio is 0.002-0.01, the reactor temperature is 75-90 ℃, and the reactor pressure is 0.55-0.90 MPa.
8. The method for converting low melt flow rate polyethylene into high melt flow rate polyethylene according to claim 1, wherein the initial operating conditions for converting high melt flow rate polyethylene are a Ti content of 0.030 to 0.060mmol/L, an aluminum to titanium ratio of 22 to 45, and a hydrogen to ethylene volume ratio of 1.8 to 5.0 in the production apparatus.
9. The method for converting low melt flow rate polyethylene into high melt flow rate polyethylene according to claim 8, wherein the temperature of the reaction kettle is 75-90 ℃ and the pressure of the reaction kettle is 0.55-0.90 MPa when converting the high melt flow rate polyethylene.
10. The method of converting a low melt flow rate polyethylene to a high melt flow rate polyethylene according to claim 1, wherein the alpha-olefin is an alpha-olefin of 3 to 8 carbon atoms, preferably an alpha-olefin of 4 to 8 carbon atoms.
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| CN118994458A (en) * | 2024-10-24 | 2024-11-22 | 新疆独山子石油化工有限公司 | Production method of transition material for reducing chromium-based polyethylene to metallocene polyethylene |
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