Quantitative detection and analysis method of waste plastic composition from domestic sources based on energy-quality balance

Abstract

The present invention discloses a quantitative detection and analysis method for the composition of waste plastics from living sources based on energy-quality balance, and uses the mass balance of sample elements and heat balance to infer the composition of the mixture, including: 1) establishing an overdetermined equation group of waste plastic element balance, heat balance, etc.; 2) collecting plastic samples and drying, crushing, and mixing them evenly; 3) weighing the samples, using instruments to detect the C / H / O element mass fraction, ash mass fraction, and calorific value, and obtaining a thermal analysis curve; 4) calculating the first-stage weight loss percentage and the second-stage melting peak area through the thermal analysis curve; 5) substituting the element and ash mass fraction, calorific value, first-stage weight loss percentage, and second-stage melting peak area obtained in steps 3) and 4) into the overdetermined equation group in step 1) to calculate the sample composition mass fraction. The present invention has good accuracy in the case where the element analysis, ash analysis, calorific value analysis, and thermal analysis methods are consistent.

Description

Technical Field

[0001] The present invention relates to the field of solid waste management, and in particular to a quantitative detection and analysis method for the composition of waste plastics from domestic sources based on energy-quality balance. Background Art

[0002] Plastic products are widely used in people's daily lives. Plastic waste accounts for 10-30% of domestic waste. In the mineralized waste in mined domestic waste landfills, plastic accounts for more than 50% of the combustible material. Clarifying the specific composition of plastic waste is of great significance for the disposal of waste plastics from domestic sources and their resource utilization.

[0003] Plastics from daily life mainly include five categories: polyethylene (PE), polypropylene (PP), polypropylene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). Other plastics such as nylon, PC, ABS, PLA, acrylic plastics, etc., as well as additives in plastic products, account for a very small proportion. For the detection of mixed plastic composition, the commonly used method is to preliminarily classify them according to appearance with the naked eye, and then use Fourier change infrared spectroscopy or Raman spectroscopy for qualitative detection, and further classify them in detail according to the material to obtain the mass proportion of each component. However, for waste plastics, a large number of samples need to be collected to ensure the representativeness of the sampling. The sampling steps are generally 1) collecting a large amount of waste plastics; 2) preliminary crushing and mixing; 3) collecting and analyzing samples. If the above method is used in step 1), the workload and cost are extremely high, and this method is also difficult to handle mixed material plastics, and the crushed plastics in step 3) cannot be manually classified.

[0004] For step 3), there are two main methods for analyzing the composition of the sample: thermogravimetric method and pyrolysis chromatography-mass spectrometry. Thermogravimetric method assumes that the thermogravimetric curve of the pyrolysis of mixed plastics is the sum of the thermogravimetric curves of each component in mass proportion. Pyrolysis chromatography-mass spectrometry determines the correlation equation between the specific indicator products generated by each material plastic under specific pyrolysis conditions and the chromatographic peak area of ​​the indicator products and the mass of the corresponding material plastic. It is believed that this equation is also applicable to mixed plastics. However, both methods ignore the significant effects of the interaction of the co-pyrolysis process of different plastics on the thermogravimetric process and product distribution, so the accuracy of the results is poor. Summary of the invention

[0005] The purpose of the present invention is to provide a quantitative detection and analysis method for the composition of waste plastics from domestic sources based on energy-quality balance in response to the deficiencies of the prior art.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] Domestic plastics mainly include five categories: polyethylene (PE), polypropylene (PP), polypropylene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). Other plastics such as nylon, PC, ABS, PLA, acrylic plastics, etc. and additives in plastic products account for a very small proportion, and their impact on the overall energy-quality balance model can be ignored. Therefore, waste plastics can be regarded as a mixture of water, pure plastic substances (PE\PP\PS\PVC\PET) and inert substances. Inert substances are non-combustible substances such as ash and soil that adhere to waste plastics during circulation, which are difficult to remove during the sampling process.

[0008] Based on the principle of energy-mass balance, for a mixture formed by mixing multiple substances in a certain proportion, the C\H\O element mass, ash mass, calorific value and total mass of the mixture should be the sum of the C\H\O element mass, ash mass, calorific value and total mass of each component substance added in mass proportion.

[0009] The thermogravimetric curves of five types of plastics from daily life, namely PE, PP, PS, PVC and PET, were tested. Only PVC had two weight loss peaks. The first-stage weight loss peak of PVC (temperature range 500-575K at a heating rate of 10°C / min) characterizes the chlorine precipitation process, and its termination temperature is earlier than the starting temperature of thermal decomposition of other plastics. It can be considered that the first-stage weight loss of PVC contained in the mixed plastic is not affected by other plastic components, and the corresponding weight loss (first-stage weight loss) of the thermogravimetric curve of the mixed plastic is proportional to the internal PVC mass. The schematic diagram of the first-stage weight loss peak of PVC is shown below: Figure 1 shown.

[0010] Inert substances are dust and dirt adhered to discarded plastics during circulation, which are difficult to remove during the sampling process and their pyrolysis weight loss can be ignored. The mass of mixed plastic ash can be considered as the sum of the mass of inert substances and the mass of each plastic ash in proportion to their mass.

[0011] The calorimetric curves of five kinds of plastics from daily life, PE, PP, PS, PVC, and PET, were tested. Only PE, PP, and PET had melting peaks. The melting peaks of PE and PET overlapped, while the melting peak of PP was independent (temperature range 420-445K at a heating rate of 10°C / min) and was not affected by other components. It can be considered that the melting peak in the corresponding temperature range of the calorimetric curve of the mixed plastic, i.e., the second-stage melting peak, is the PP melting peak, and the melting peak area is proportional to the internal PP mass. The schematic diagram of the PP melting peak is shown in the figure below: Figure 2 shown.

[0012] In summary, the mass of C\H\O elements, ash mass, calorific value, PVC first-stage weight loss, and PP melting heat are defined as characteristic quantities that are only related to the mass fraction of the components and are not affected by the interaction of other components in the same thermal conversion process. Under the same detection conditions, the energy-mass balance equation with the mass fraction of each characteristic quantity as the only unknown can be obtained.

[0013] The present invention proposes a quantitative detection and analysis method for the composition of waste plastics from living sources based on energy-quality balance, and the steps are as follows:

[0014] 1) Treat waste plastics from domestic sources as a mixture of water, pure plastic substances and inert substances, extract characteristic quantities that are not affected by the interaction after pyrolysis of various pure plastic substances; establish an energy-mass balance equation based on characteristic quantities with mass fraction as a bridge;

[0015] 2) Collect waste plastic samples from daily sources and dry, crush and mix them evenly;

[0016] 3) Weigh the pretreated plastic sample, detect the mass fraction of C / H / O elements using an element analyzer, detect the mass fraction of ash using an ash content meter, detect the calorific value using an oxygen bomb calorimeter, and detect the thermal analysis curve using a thermogravimetric analysis-calorimetric analysis combined instrument;

[0017] 4) Carry out thermal analysis curve data analysis to calculate the weight loss percentage of the first stage and the melting peak area of ​​the second stage;

[0018] 5) Substitute the C / H / O element mass fraction, ash mass fraction, calorific value, first-stage weight loss percentage and second-stage melting peak area obtained in steps 3) and 4) into the energy-mass balance equation in step 1), and calculate the mass fraction of the plastic sample composition using the weighted least squares method.

[0019] Furthermore, the energy-mass balance equation described in step 1) is obtained by the following method:

[0020] 1-1) The sampled waste plastics from living sources are considered to be a mixture of water, pure plastic substances PE\PP\PS\PVC\PET and inert substances. Inert substances are non-combustible substances that adhere to waste plastics during circulation and are difficult to remove during the sampling process;

[0021] 1-2) The C / H / O element mass, ash mass and calorific value of the waste plastic are the sum of the C / H / O element mass, ash mass and calorific value of each component in mass proportion. The weight loss of the waste plastic in the first stage of pyrolysis is proportional to the internal PVC mass, and the melting heat of the waste plastic in the second stage of pyrolysis is proportional to the internal PP mass. The energy-mass balance is constructed based on the above conditions;

[0022] Plastic PE\PP\PS\PVC\PET samples of analytical purity were used to detect the mass fraction of C / H / O elements using an element analyzer, the mass fraction of ash using an ash content meter, the calorific value using an oxygen bomb calorimeter, and the thermal analysis curve using a thermogravimetric analysis-calorimetric analysis combined instrument to determine the first-stage weight loss percentage of PVC plastic and the melting peak area of ​​PP plastic. The mass of C / H / O elements, ash mass, calorific value, weight loss in the first stage of pyrolysis, and melting heat in the second stage of pyrolysis were defined as characteristic quantities of plastics.

[0023] 1-3) Establish an energy-mass balance equation based on characteristic quantities with mass fraction as a bridge, that is, an overdetermined set of equations for the mass fraction of waste plastics from domestic sources.

[0024] Furthermore, the energy-mass balance equation established is:

[0025] Carbon mass balance:

[0026] TC=TC PE x PE +TC PP x PP +TC PS x PS +TC PVC x PVC +TC PET x PET

[0027] Hydrogen mass balance:

[0028] TH=TH PE x PE +TH PP x PP +TH PS x PS +TH PVC x PVC +TH PET x PET

[0029] Oxygen mass balance:

[0030] TO=TO PE x PE +TO PP x PP +TO PS x PS +TO PVC x PVC +TO PET x PET

[0031] Ash mass balance:

[0032] Ash=AshPE x PE +Ash PP x PP +Ash PS x PS +Ash PVC x PVC +Ash PET x PET +x NO

[0033] Total mass balance:

[0034] 1 = x PE +x PP +x PS +x PVC +x PET +x NO

[0035] Mass balance of pyrolysis loss:

[0036] TG mix_1 =TG PVC_1 x PVC

[0037] Energy balance of material calorific value:

[0038] TQ=TQ PE x PE +TQ PP x PP +TQ PS x PS +TQ PVC x PVC +TQ PET x PET

[0039] Pyrolysis melting heat energy balance:

[0040] DSC mix_2 =DSC pp x pp

[0041] Where TC / TH / TO is the mass fraction of C / H / O elements in the plastic sample measured in step 3), TC / TH / TO PE / PP / PS / PVC / PET is the mass fraction of C / H / O elements of various plastics measured in step 1-2), TQ is the calorific value of the plastic sample measured in step 3), TQ PE / PP / PS / PVC / PET is the calorific value of each type of plastic measured in step 1-2), Ash is the mass fraction of sample ash measured in step 3), Ash PE / PP / PS / PVC / PET is the ash mass fraction of various plastics measured in step 1-2), TG mix_1is the weight loss percentage of the plastic sample in the first stage calculated in step 4), TG PVC_1 The first-stage weight loss percentage of PVC plastic calculated in step 1-2), DSC mix_2 is the second stage melting peak area of ​​the plastic sample calculated in step 4), DSC PP is the peak area of ​​the second stage melting of PP plastic calculated in step 1-2), x PE / PP / PS / PVC / PET is the mass fraction of each type of plastic in the plastic sample, x No is the mass fraction of inert matter in the plastic sample.

[0042] Compared with the prior art, the advantages of the present invention are:

[0043] The present invention can quantitatively detect the specific composition of waste plastics from domestic sources. Compared with the mainstream spectral method, the energy-mass balance method adopted by the present invention has greatly reduced costs and workload, and can effectively detect mixed material plastics, which can be achieved through conventional equipment; compared with thermogravimetric method and pyrolysis chromatography-mass spectrometry, the method of the present invention eliminates the influence of the co-pyrolysis interaction of plastics of different materials on the thermal gravimetric process and product distribution, and has higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the first-stage weight loss peak of PVC;

[0045] Figure 2 Schematic diagram of PP melting peak;

[0046] Figure 3 This is a flow chart of a method for quantitatively detecting and analyzing the composition of waste plastics from domestic sources provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0048] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application are also intended to include plural forms, unless the context clearly indicates other meanings.

[0049] The embodiment of the present invention provides a quantitative detection and analysis method for the composition of waste plastics from living sources based on energy-quality balance, which is used to solve the problem that the mass fraction of the specific composition of waste plastics from living sources is difficult to determine, such as Figure 3 As shown, the following steps are included:

[0050] 1) Consider waste plastics from domestic sources as a mixture of water, pure plastic substances and inert substances, extract characteristic quantities that are not affected by the interaction after pyrolysis of various pure plastic substances; establish an energy-mass balance equation based on characteristic quantities with mass fraction as a bridge.

[0051] 2) Collect waste plastic samples from daily sources and dry, crush and mix them evenly;

[0052] 3) Weigh the pretreated plastic sample, detect the mass fraction of C / H / O elements using an element analyzer, detect the mass fraction of ash using an ash content meter, detect the calorific value using an oxygen bomb calorimeter, and detect the thermal analysis curve using a thermogravimetric analysis-calorimetric analysis combined instrument;

[0053] 4) Carry out thermal analysis curve data analysis to calculate the weight loss percentage of the first stage and the melting peak area of ​​the second stage;

[0054] 5) Substitute the C / H / O element mass fraction, ash mass fraction, calorific value, first-stage weight loss percentage and second-stage melting peak area obtained in steps 3) and 4) into the energy-mass balance equation in step 1), and calculate the mass fraction of the plastic sample composition using the weighted least squares method.

[0055] In one embodiment, the energy-mass balance equation is obtained by the following method:

[0056] 1-1) The sampled waste plastics from living sources are considered to be a mixture of water, pure plastic substances PE\PP\PS\PVC\PET and inert substances. Inert substances are non-combustible substances that adhere to waste plastics during circulation and are difficult to remove during the sampling process;

[0057] 1-2) The C / H / O element mass, ash mass and calorific value of the waste plastic are the sum of the C / H / O element mass, ash mass and calorific value of each component in mass proportion. The weight loss of the waste plastic in the first stage of pyrolysis is proportional to the internal PVC mass, and the melting heat of the waste plastic in the second stage of pyrolysis is proportional to the internal PP mass. The energy-mass balance is constructed based on the above conditions;

[0058] Purchase samples of PE\PP\PS\PVC\PET plastics from domestic sources, use an element analyzer to detect the mass fraction of C / H / O elements, use an ash analyzer to detect the mass fraction of ash, use an oxygen bomb calorimeter to detect the calorific value, use a thermogravimetric analysis-calorimetric analysis combined instrument to detect the thermal analysis curve and determine the first-stage weight loss percentage of PVC plastics and the melting peak area of ​​PP plastics, and define the C / H / O element mass, ash mass, calorific value, first-stage pyrolysis weight loss, and second-stage pyrolysis melting heat as characteristic quantities of plastics;

[0059] 1-3) Establish an energy-mass balance equation based on characteristic quantities with mass fraction as a bridge, that is, an overdetermined set of equations for the mass fraction of waste plastics from domestic sources.

[0060] The energy-mass balance equation established is as follows:

[0061] Carbon mass balance:

[0062] TC=TC PE x PE +TC PP x PP +TC PS x PS +TC PVC x PVC +TC PET x PET

[0063] Hydrogen mass balance:

[0064] TH=TH PE x PE +TH PP x PP +TH PS x PS +TH PVC x PVC +TH PET x PET

[0065] Oxygen mass balance:

[0066] TO=TO PE x PE +TO PP x PP +TO PS x PS +TO PVC x PVC +TO PET x PET

[0067] Ash mass balance:

[0068] Ash=Ash PE xPE +Ash PP x PP +Ash PS x PS +Ash PVC x PVC +Ash PET x PET +x NO

[0069] Total mass balance:

[0070] 1 = x PE +x PP +x PS +x PVC +x PET +x NO

[0071] Mass balance of pyrolysis loss:

[0072] TG mix_1 =TG PVC_1 x PVC

[0073] Energy balance of material calorific value:

[0074] TQ=TQ PE x PE +TQ PP x PP +TQ PS x PS +TQ PVC x PVC +TQ PET x PET

[0075] Pyrolysis melting heat energy balance:

[0076] DSC mix_2 =DSC pp x PP

[0077] Where TC / TH / TO is the mass fraction of C / H / O elements in the plastic sample measured in step 3), TC / TH / TO PE / PP / PS / PVC / PET is the mass fraction of C / H / O elements of various plastics measured in step 1-2), TQ is the calorific value of the plastic sample measured in step 3), TQ PE / PP / PS / PVC / PET is the calorific value of each type of plastic measured in step 1-2), Ash is the mass fraction of sample ash measured in step 3), Ash PE / PP / PS / PVC / PET is the ash mass fraction of various plastics measured in step 1-2), TG mix_1 is the weight loss percentage of the plastic sample in the first stage calculated in step 4), TG PVC_1The first-stage weight loss percentage of PVC plastic calculated in step 1-2), DSC mix_2 is the second stage melting peak area of ​​the plastic sample calculated in step 4), DSC PP is the peak area of ​​the second stage melting of PP plastic calculated in step 1-2), x PE / PP / PS / PVC / PET is the mass fraction of each type of plastic in the plastic sample, x No is the mass fraction of inert matter in the plastic sample.

[0078] A specific detection example is given below:

[0079] S1. Take analytically pure PE, PP, PS, PVC, and PET as pure plastic substances, take analytically pure SiO2 as an inert substance, and mix them according to the proportions in Table 1 to obtain three groups of simulated life source waste plastics, A, B, and C;

[0080] Table 1

[0081] PE PP PS PVC PET <![CDATA[SiO2]]> A 30 20 15 10 20 5 B 20 30 10 20 10 10 C 10 10 30 30 10 10

[0082] S2, the characteristic values ​​of each analytically pure PE, PP, PS, PVC, and PET are shown in Table 2;

[0083] Table 2

[0084] PE PP PS PVC PET Carbon mass fraction 85.49 85.74 91.85 38.02 63.05 Hydrogen mass fraction 13.23 13.85 7.51 4.13 3.95 Oxygen mass fraction 0 0 0 0 33 Calorific value 47.093 46.647 41.468 20.667 22.723 Ash mass fraction 0.035 0.036 0 0 0.041 PVC first stage weight loss percentage / / / 48.39 / PP pyrolysis second stage melting peak area / 10.79 / / /

[0085] S3, the characteristic values ​​of simulated household waste plastics ABC are shown in Table 3;

[0086] Table 3

[0087]

[0088]

[0089] S4. Using the weighted least squares method, the composition of waste plastics ABC from domestic sources was simulated and the estimated results are shown in Table 4. It can be seen that the error between the estimated results and the actual results is within 2%.

[0090] Table 4

[0091] PE PP PS PVC PET <![CDATA[SiO2]]> A 30.70 21.24 11.70 11.42 20.89 4.32 B 19.40 30.79 10.70 18.32 10.56 9.20 C 11.10 9.80 29.80 29.48 10.51 9.24

[0092] The above is only a preferred embodiment of the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A quantitative detection and analysis method for the composition of waste plastics from living sources based on energy-quality balance, characterized in that: The following steps are involved: 1) Consider waste plastics from domestic sources as a mixture of water, pure plastic substances and inert substances, extract characteristic quantities that are not affected by the interaction after pyrolysis of various pure plastic substances; establish an energy-mass balance equation based on characteristic quantities with mass fraction as a bridge; the energy-mass balance equation is obtained by the following method: 1-1) The sampled waste plastics from living sources are considered to be a mixture of water, pure plastic substances PE\PP\PS\PVC\PET and inert substances. Inert substances are non-combustible substances that adhere to waste plastics during circulation and are difficult to remove during the sampling process; 1-2) The C / H / O element mass, ash mass and calorific value of the waste plastic are the sum of the C / H / O element mass, ash mass and calorific value of each component in mass proportion. The weight loss of the waste plastic in the first stage of pyrolysis is proportional to the internal PVC mass, and the melting heat of the waste plastic in the second stage of pyrolysis is proportional to the internal PP mass; Purchase samples of PE\PP\PS\PVC\PET plastics from domestic sources, use an element analyzer to detect the mass fraction of C / H / O elements, use an ash analyzer to detect the mass fraction of ash, use an oxygen bomb calorimeter to detect the calorific value, use a thermogravimetric analysis-calorimetric analysis combined instrument to detect the thermal analysis curve and determine the first-stage weight loss percentage of PVC plastics and the melting peak area of ​​PP plastics, and define the C / H / O element mass, ash mass, calorific value, first-stage pyrolysis weight loss, and second-stage pyrolysis melting heat as characteristic quantities of plastics; 1-3) Establish an energy-mass balance equation based on characteristic quantities with mass fraction as a bridge, that is, an overdetermined equation group of mass fraction of waste plastics from living sources; the established energy-mass balance equation is specifically: Carbon mass balance: TC=TC PE x PE +TC PP x PP +TC PS x PS +TC PVC x PVC +TC PET x PET Hydrogen mass balance: TH=TH PE x PE +TH PP x PP +TH PS x PS +TH PVC x PVC +TH PET x PET Oxygen mass balance: TO=TO PE x PE +TO PP x PP +TO PS x PS +TO PVC x PVC +TO PET x PET Ash mass balance: Ash=Ash PE x PE +Ash PP x PP +Ash PS x PS +Ash PVC x PVC +Ash PET x PET +x No Total mass balance: 1=x PE +x PP +x PS +x PVC +x PET +x No Mass balance of pyrolysis loss: TG mix_1 =TG PVC_1 x PVC Energy balance of material calorific value: TQ=TQ PE x PE +TQ PP x PP +TQ PS x PS +TQ PVC x PVC +TQ PET x PET Pyrolysis melting heat energy balance: DSC mix_2 =DSC PP x PP Where TC / TH / TO is the mass fraction of C / H / O elements in the plastic sample measured in step 3), TC / TH / TO PE / PP / PS / PVC / PET is the mass fraction of C / H / O elements of various plastics measured in step 1-2), TQ is the calorific value of the plastic sample measured in step 3), TQ PE / PP / PS / PVC / PET is the calorific value of each type of plastic measured in step 1-2), Ash is the mass fraction of sample ash measured in step 3), ASh PE / PP / PS / PVC / PET is the ash mass fraction of various plastics measured in step 1-2), TG mix_1 is the weight loss percentage of the plastic sample in the first stage calculated in step 4), TG PVC_1 The first-stage weight loss percentage of PVC plastic calculated in step 1-2), DSC mix_2 is the second stage melting peak area of ​​the plastic sample calculated in step 4), DSC PP is the peak area of ​​the second stage melting of PP plastic calculated in step 1-2), x PE / PP / PS / PVC / PET is the mass fraction of each type of plastic in the plastic sample, x No is the mass fraction of inert matter in the plastic sample; 2) Collect waste plastic samples from daily sources and dry, crush and mix them evenly; 3) Weigh the pretreated plastic sample, detect the mass fraction of C / H / O elements using an element analyzer, detect the mass fraction of ash using an ash content meter, detect the calorific value using an oxygen bomb calorimeter, and detect the thermal analysis curve using a thermogravimetric analysis-calorimetric analysis combined instrument; 4) Carry out thermal analysis curve data analysis to calculate the weight loss percentage of the first stage and the melting peak area of ​​the second stage; 5) Substitute the C / H / O element mass fraction, ash mass fraction, calorific value, first-stage weight loss percentage and second-stage melting peak area obtained in steps 3) and 4) into the energy-mass balance equation in step 1), and calculate the mass fraction of the plastic sample composition using the weighted least squares method.

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