Method for reducing odor of slurry-process high-density polyethylene

Abstract

The invention discloses a method for reducing odor of slurry-method high-density polyethylene, which comprises the following steps: 1) firstly, judging the odor level of a sample by adopting an artificial odor evaluation method, and then measuring volatile components and content in the sample by adopting a gas chromatography-mass spectrometry method; 2) by taking CO2 as an internal standard, converting the content of each component in the VOC into the volume concentration in the smell evaluation bottle according to the density of the volatile gas, the volume of the headspace bottle and the volume of the smell evaluation bottle; 3) introducing the smell threshold value of each component in the volatile components, calculating the activity value of each component according to the volume concentration of each component in the smell evaluation bottle, and determining the contribution of each component to the smell; and 4) in combination with the characteristics of a slurry method high-density polyethylene process, proposing a suggestion for reducing the odor, and implementing the suggestion until the odor level is qualified. The method provided by the invention is convenient for quickly finding the odor source, is simple and easy to implement, has wide applicability, and can quickly reduce the odor of the slurry-method high-density polyethylene product.

Description

Technical Field

[0001] The invention belongs to the technical field of polyolefin resin odor treatment, is used for reducing the odor of stirred tank slurry process high-density polyethylene, and specifically relates to a method for reducing the odor of slurry process high-density polyethylene. Background Art

[0002] As environmental protection requirements become stricter, downstream users have increasingly strict requirements on the odor of chemical products, and need to produce odorless, low-odor or low-VOC synthetic resin products. High-density polyethylene has the characteristics of being non-toxic and non-absorbent, and is often used in the food packaging industry. For example, high-density polyethylene 5000S has now begun to be used to produce various products with high hygienic standards such as bottle caps and baby bottles, and the requirements for the odor of 5000S have gradually increased. The high-density polyethylene device currently used adopts a slurry preparation process. This process uses high-purity ethylene as the main raw material, propylene and l-butene as copolymers, hexane as solvent, and uses high-efficiency catalysts. Low-pressure polymerization is carried out at 70-85°C. The slurry obtained by polymerization is separated, dried, mixed and granulated to obtain various HDPE products with excellent performance. This process involves solvents in the polymerization process. In the subsequent product separation and solvent recovery process, trace amounts of solvents remain in the product, causing the product to often exceed the odor standard.

[0003] The odor of slurry high-density polyethylene samples is mainly generated by volatile gases (VOC) in the samples. Chinese patent CN 104297434B discloses a method for evaluating the odor of automotive interior parts. By adopting a larger sample volume and higher test requirements, the identification of the odor source is increased, and the contribution of the component assembly to the odor of the whole vehicle is more intuitively examined. The artificial odor evaluation method is used in the whole process. Chinese patent CN 112444617A discloses a method for evaluating the odor of polyolefin resins and its application. The method comprises the following steps: step 1) using an artificial odor evaluation method to grade the odor, and when the evaluated odor level is greater than the safe odor level, step 2 is performed; step 2) TVOC is measured, and when TVOC < evaluation threshold TVOC0, the evaluation is terminated; when TVOC ≥ evaluation threshold TVOC0, step 3 is performed; step 3) headspace injection gas chromatography mass spectrometry analysis is performed, and volatile organic compounds with boiling points of 20-200°C are screened from the results, and the top 2-5 volatile organic compounds with the largest peak areas are selected. This method only performs TVOC detection on the sample to determine the impact of volatile substances on the odor, but for different volatile gases, the odor thresholds vary greatly. Some gases have a relatively high content, but their odor thresholds are relatively large, and their impact on the odor is relatively small. Chinese patent CN112048127A discloses a method for removing odor and VOC from polypropylene composite materials. The method uses a process combining lactic acid and atomization extraction to effectively reduce polar and non-polar volatile organic compounds in polypropylene materials, improve the odor level of polypropylene composite materials and reduce the VOC content of composite materials. The method is mainly for polypropylene. Polypropylene polymerization generally adopts a bulk method without solvents, and introduces new substances such as lactic acid.

[0004] Therefore, it is imperative to develop odorless, low-VOC synthetic resin products. At the same time, it is necessary and urgent to establish an odor evaluation method for synthetic resin products and carry out evaluation work. Summary of the invention

[0005] The purpose of the present invention is to provide a method for reducing the odor of slurry-processed high-density polyethylene, which solves the problem that the odor evaluation method in the prior art has many limitations, it is difficult to accurately evaluate the odor level, and specifically solve the problem of retained odor.

[0006] The technical solution adopted by the present invention is a method for reducing the odor of slurry-process high-density polyethylene, which is implemented according to the following steps:

[0007] Step 1: firstly use the artificial odor evaluation method to determine the odor level of the sample, and then use the gas chromatography-mass spectrometry method to determine the volatile components and content in the sample;

[0008] Step 2, using CO2 as an internal standard, the content of each component in the VOC is converted into the volume concentration in the odor evaluation bottle through the density of the volatile gas, the volume of the headspace bottle and the volume of the odor evaluation bottle;

[0009] Step 3: Introduce the olfactory threshold of each component in the VOC, calculate the activity value of each component based on the volume concentration of each component in the odor evaluation bottle, and determine the contribution of each component to the odor;

[0010] Step 4: Based on the characteristics of the slurry high-density polyethylene process, propose suggestions for reducing odor and implement them until the odor level is qualified.

[0011] The beneficial effects of the present invention are that the concepts of internal standard, volatile substance odor threshold and activity value are introduced to digitize and concretize the contribution values ​​of various volatile components to the odor, which is convenient for quickly finding the odor source, is simple and easy to operate, has wide applicability, and can quickly reduce the odor of slurry process high-density polyethylene products. At the same time, combined with the production process characteristics of the product, suggestions and measures for reducing the odor are proposed and implemented to effectively reduce the odor of the product. After the method of the present invention is implemented, the slurry process high-density polyethylene sample can be reduced from an unqualified product with an odor level greater than 3.5 to a qualified product with an odor level less than 3.5 within 8 hours. DETAILED DESCRIPTION

[0012] The present invention is described in detail below in conjunction with specific implementation modes.

[0013] The present invention discloses a method for reducing the odor of slurry process high-density polyethylene. The polymerization mechanism of the slurry process high-density polyethylene process involved belongs to anionic coordination polymerization, and is composed of a catalyst configuration unit, a polymerization unit, a separation and drying unit, a solvent recovery unit, an extrusion granulation unit, and a packaging unit. The slurry process in slurry process high-density polyethylene is a method of mixing ethylene and aliphatic hydrocarbon solvents, adding titanium or chromium catalysts, and polymerizing ethylene under low pressure and low temperature. The solvent used in slurry process high-density polyethylene is aliphatic hydrocarbons, mainly hexane, pentane, isobutane and propane. The volatile gas mainly consists of hydrocarbon substances such as 2-methylpentane, 3-methylpentane, n-hexane, cyclohexane, methylcyclopentane, octane, decane and dodecane.

[0014] The composition of the solvent is shown in Table 1:

[0015] Table 1. Main composition of hexane solvent used in slurry high-density polyethylene

[0016] Components 2-Methylpentane 3-Methylpentane n-Hexane Dimethylpentane Methylcyclopentane Octane content% 1.27 9.49 73.52 0.58 14.72 0.42

[0017] The method for reducing the odor of slurry-process high-density polyethylene of the present invention is implemented according to the following steps:

[0018] Step 1: First, the odor level of the sample is determined by artificial odor evaluation method, and then the volatile components (VOC) and content in the sample are determined by gas chromatography-mass spectrometry;

[0019] Among them, the artificial odor evaluation method is implemented using the "High-density polyethylene resin odor detection-artificial sensory detection method (Q / SYLS1007-2021)".

[0020] The gas chromatography-mass spectrometry method (VOC detection method for short) adopts the "high-density polyethylene resin organic volatile detection gas / mass spectrometry detection method" to determine the volatile components and content in the sample.

[0021] Step 2, using CO2 as an internal standard, the content of each component in the VOC is converted into the volume concentration in the odor evaluation bottle through the density of the volatile gas, the volume of the headspace bottle and the volume of the odor evaluation bottle;

[0022] Step 3: Introduce the olfactory threshold of each component in the VOC, calculate the activity value of each component based on the volume concentration of each component in the odor evaluation bottle, and determine the contribution of each component to the odor;

[0023] The odor threshold is derived from the database of “malodorous substances and their odor threshold”; the density data is derived from the physical and chemical properties of each volatile gas.

[0024] The relationship between the odor activity value and the odor threshold is: the odor activity value is the ratio of the volume concentration of an individual substance in the sample to the odor threshold concentration of this substance.

[0025] The odor level of the sample is between 2.5-5, and the volatile gas is C6-C 16 The mass-to-nuclear ratio scanning range of volatile organic compounds is 40-550.

[0026] The density and odor threshold of each component in VOC are shown in Table 2:

[0027] Table 2. Odor threshold and density of each VOC component in the sample

[0028]

[0029] The unit of olfactory threshold is 10 -6 V / V, density unit is g / cm 3 .

[0030] Step 4: Based on the characteristics of the slurry high-density polyethylene process, propose suggestions for reducing odor and implement them to reduce the level of product odor until the odor level is qualified.

[0031] The working principle of the method of the present invention is that under the same heating temperature and time conditions, the samples in the headspace bottle and the odor bottle are pre-treated, the volatile compounds in the headspace bottle are carried into the gas chromatography column by the carrier gas, and the components in the sample are separated under certain conditions, and then enter the ion source of the mass spectrometer, and are ionized into ions in the ion source. After passing through the mass analyzer and the detector, the ions become mass spectrometry signals and are input into the computer. The computer can automatically add all the ion intensities of each mass spectrum to display the total ion intensity. The curve of the total ion intensity changing with time is the total ion chromatogram. The shape of the total ion chromatogram is consistent with the ordinary chromatogram, which can be considered as a chromatogram obtained by using the mass spectrum as a detector. The mass spectrum is compared with the spectrum in the NIST2011.L standard spectrum library of the United States to qualitatively identify the substances of volatile odor, determine each component in the volatile compound, and obtain the VOC result of the sample; the volatile compounds in the odor evaluation bottle are evaluated for odor, and the artificial odor evaluation result is obtained. Different substances in volatile compounds have quite different olfactory thresholds. Some substances have low content but very small olfactory thresholds and contribute greatly to the odor of the sample. Therefore, introducing the olfactory threshold of the compound can more accurately and objectively determine the contribution of each component in the volatile compound to the odor.

[0032] Experimental verification

[0033] The following eight examples are used to illustrate the evaluation process and odor reduction effect of the method of the present invention.

[0034] Step 1: The slurry process high-density polyethylene sample is graded by an artificial odor method, and the volatile components (VOC) and content in the sample are determined by gas chromatography-mass spectrometry. The specific results of the eight embodiments are shown in Table 3.

[0035] Table 3. VOC detection and odor evaluation results of high-density polyethylene samples with different odor levels

[0036]

[0037]

[0038] Step 2, using CO2 as the internal standard, the content of each component in VOC was converted into the volume concentration in the odor evaluation bottle by the density of the volatile odor, the volume of the headspace bottle and the volume of the odor evaluation bottle. The specific results are shown in Table 4; the concentration value unit is 10 -6 V / V.

[0039] Table 4. Concentration values ​​of each component in the VOC sample in the odor evaluation bottle

[0040]

[0041] Step 3, introduce the olfactory threshold of each component in the VOC, calculate the activity value of each component based on the volume concentration of each component in the odor evaluation bottle, and determine the contribution of each component to the odor. The results are shown in Table 5.

[0042] Table 5. Odor activity values ​​of each component in the VOC sample in the odor evaluation bottle

[0043]

[0044] Step 4: Based on the contribution of each component to the odor and the characteristics of the slurry process high-density polyethylene, suggestions for reducing the odor are proposed and implemented to obtain samples with lower odor, and the obtained samples are artificially evaluated for odor. The measures for reducing the odor of the samples corresponding to the 8 embodiments and the odor levels after implementation are as follows:

[0045] Example 1, the largest contribution to the sample odor is decane, followed by dodecane, and these two components are mainly derived from oligomers. Combined with the characteristics of the slurry high-density polyethylene process, first, under the premise of meeting production, reduce the amount of triethyl aluminum added; secondly, reduce the circulation volume of the mother liquor in the polymerization station, increase the reflux volume of the solvent recovery tower, and remove the oligomers in the mother liquor to the maximum extent; finally, increase the separation and drying circulation air volume under the premise of ensuring that no mist entrainment occurs, and increase the dryer unloading temperature according to the nature of the sample, which can effectively reduce the content of volatile components in the sample. After the implementation of the measures to reduce the odor, the odor level is 3.2.

[0046] Example 2, hexane contributes the most to the sample odor. Hexane comes from the solvent. Combined with the characteristics of the slurry process high-density polyethylene process, firstly, the separation and drying cycle air volume is increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the properties of the sample; secondly, the interval time of nitrogen backwashing of the powder bag filter is shortened, which can effectively reduce the content of volatile components in the sample. After the measures to reduce the odor are implemented, the odor level is 3.0.

[0047] In Example 3, the contents of n-hexane, methylcyclopentane and 3-methylpentane are relatively high. These three components are mainly derived from solvents; the contents of decane and dodecane exceed 100, which contributes to the odor to a certain extent. In combination with the characteristics of the slurry high-density polyethylene process, the separation and drying circulation air volume is first increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the properties of the sample; secondly, the circulation volume of the mother liquor in the polymerization station is reduced, the reflux volume of the solvent recovery tower is increased, and the oligomers in the mother liquor are removed to the maximum extent, which can effectively reduce the content of volatile components in the sample. After the measures to reduce the odor are implemented, the odor level is 3.3.

[0048] Example 4, n-hexane contributes the most to the odor of the sample, followed by methylcyclopentane, 3-methylpentane and decane, hexane comes from the solvent, methylcyclopentane, 3-methylpentane and decane come from the solvent and oligomers respectively. Combined with the characteristics of the slurry process of high-density polyethylene, firstly, the separation and drying circulation air volume is increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the nature of the sample; secondly, the powder bag filter nitrogen backwash interval is reduced; finally, the circulation volume of the mother liquor of the polymerization station is reduced, the reflux volume of the solvent recovery tower is increased, and the oligomers in the mother liquor are removed to the maximum extent, which can effectively reduce the content of volatile components in the sample. After the implementation of the measures to reduce the odor, the odor level is 3.3.

[0049] Example 5, n-hexane contributes the most to the odor of the sample, followed by methylcyclopentane, 3-methylpentane and decane, hexane comes from the solvent, methylcyclopentane, 3-methylpentane and decane come from the solvent and oligomers, respectively. Combined with the characteristics of the slurry process of high-density polyethylene, firstly, the separation and drying circulation air volume is increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the nature of the sample; secondly, the powder bag filter nitrogen backwash interval is shortened; finally, the circulation volume of the mother liquor of the polymerization station is reduced, the reflux volume of the solvent recovery tower is increased, and the oligomers in the mother liquor are removed to the maximum extent, which can effectively reduce the content of volatile components in the sample. After the implementation of measures to reduce the odor, the odor level is 3.4.

[0050] In Example 6, n-hexane contributes the most to the odor of the sample, followed by methylcyclopentane and 3-methylpentane. These three components mainly come from the solvent. In combination with the characteristics of the slurry high-density polyethylene process, the separation and drying circulation air volume is first increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the properties of the sample; secondly, the interval time of nitrogen backwashing of the powder bag filter is shortened to effectively reduce the content of volatile components in the sample. After the measures to reduce the odor are implemented, the odor level is 3.2.

[0051] In Example 7, n-hexane contributes the most to the odor of the sample, followed by methylcyclopentane and 3-methylpentane. These three components mainly come from the solvent. In combination with the characteristics of the slurry high-density polyethylene process, the separation and drying circulation air volume is first increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the nature of the sample; secondly, the interval time of nitrogen backwashing of the powder bag filter is shortened to effectively reduce the content of volatile components in the sample. After the measures to reduce the odor are implemented, the odor level is 3.3.

[0052] In Example 8, n-hexane contributes the most to the odor of the sample, followed by methylcyclopentane and 3-methylpentane. These three components mainly come from the solvent. In combination with the characteristics of the slurry high-density polyethylene process, the separation and drying circulation air volume is first increased under the premise of ensuring that no mist entrainment occurs, and the dryer unloading temperature is increased according to the properties of the sample; secondly, the interval time of nitrogen backwashing of the powder bag filter is shortened to effectively reduce the content of volatile components in the sample. After the measures to reduce the odor are implemented, the odor level is 3.4.

Claims

1. A method for reducing the odor of slurry-process high-density polyethylene, characterized in that the steps include: Step 1: firstly use the artificial odor evaluation method to determine the odor level of the sample, and then use the gas chromatography-mass spectrometry method to determine the volatile components and content in the sample; Step 2, using CO2 as an internal standard, the content of each component is converted into a volume concentration in the odor evaluation bottle by using the density of the volatile gas, the volume of the headspace bottle and the volume of the odor evaluation bottle; Step 3: Introduce the olfactory threshold of each component, calculate the activity value of each component according to the volume concentration of each component in the odor evaluation bottle, and determine the contribution of each component to the odor; Step 4: Based on the characteristics of the slurry high-density polyethylene process, propose suggestions for reducing odor and implement them until the odor level is qualified.

2. The method for reducing the odor of slurry-process high-density polyethylene according to claim 1, characterized in that: In step 1, the artificial odor evaluation method is implemented by "high-density polyethylene resin odor detection-artificial sensory detection method".

3. The method for reducing the odor of slurry-process high-density polyethylene according to claim 1, characterized in that: In step 1, the gas chromatography-mass spectrometry method adopts the "gas / mass spectrometry detection method for organic volatiles in high-density polyethylene resin" to determine the volatile components and contents in the sample.

4. The method for reducing the odor of slurry-process high-density polyethylene according to claim 1, characterized in that: In step 3, the odor threshold is derived from the "malodorous substances and their odor threshold" database; the density data is derived from the physical and chemical properties of each volatile gas; The relationship between the odor activity value and the odor threshold is: the odor activity value is the ratio of the volume concentration of an individual substance in the sample to the odor threshold concentration of this substance.

5. The method for reducing the odor of slurry-process high-density polyethylene according to claim 1, characterized in that: In step 3, the odor level of the sample is between 2.5-5, and the volatile gas is C6-C 16 The mass-to-nuclear ratio of volatile organic compounds is 40 to 550. The density and odor threshold of each component in VOC are shown in Table 2: Table 2. Odor threshold and density of each VOC component in the sample The unit of olfactory threshold is 10 -6 V / V, density unit is g / cm 3 .

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