A low-smoke flame-retardant sampling heating composite pipe and its preparation method

Abstract

The present invention relates to a low-smoke flame-retardant sampling and heating composite pipe, which comprises, from the outside to the inside, a sheath layer, an aluminum foil layer, a glass fiber felt layer, a nano fireproof layer, an aluminum foil layer, a sampling tube and a heating tape. The two sampling tubes are attached to the outer surface of the same side of the heating tape. The outer surfaces of the sampling tube and the heating tape are wrapped with an aluminum foil layer, the outer surface of the aluminum foil layer is wrapped with a nano fireproof layer to form a tube core, the outer surface of the tube core is wrapped with a glass fiber felt layer, the outer surface of the glass fiber felt layer is covered with an aluminum foil layer, and the outer surface of the aluminum foil layer is covered with a sheath layer. The heating tape of the present invention adopts a reinforced explosion-proof constant power heating tape or a self-limiting temperature heating tape. The two sampling tubes are attached to one side of the heating tape to make the heating temperature more accurate. The aluminum foil layer is a double-sided aluminum foil, i.e., a shielding reflective film. The shielding layer formed thereby should maintain electrical continuity over the entire length of the composite pipe.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame-retardant composite pipe preparation, and in particular relates to a low-smoke flame-retardant sampling heating composite pipe and a preparation method thereof. Background Art

[0002] The heated sampling composite tube is a corrosion-resistant heated sampling composite tube used in the continuous monitoring system of flue gas emissions for heated sampling and transportation of gaseous pollutants and particulate matter emitted from various industrial production sites or to prevent liquefaction and condensation blockage. It is an important component for environmental monitoring and industrial instrument process monitoring. It consists of a group of corrosion-resistant, high-performance fluororesin conduits with self-limiting temperature heating cables or constant power heating cables and various wires laid in parallel, plus a special glass fiber insulation layer, and finally compounded with extruded polyethylene (PE) or polyvinyl chloride (PVC) as a protective jacket.

[0003] The structure of a conventional heating pipeline is that the heating tape and the sampling tube are directly attached together. The hot heating tape makes the temperature of the sample gas tube on the side in contact with the heating tape higher than the temperature on the other side, making the temperature uneven on the cross section of the sample gas tube. This causes the temperature of the sample gas in the sample gas tube to not fully reach the required temperature, or the temperature of one side of the sample gas tube is too high, making the sample gas tube easily damaged, which in turn causes condensation of the sample gas or adsorption of certain components in the sample gas, affecting subsequent analysis and detection. Summary of the Invention

[0004] In order to solve the technical problems mentioned in the background technology, the purpose of the present invention is to provide a low-smoke flame-retardant sampling heating composite pipe and a preparation method thereof.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A low-smoke flame-retardant sampling and heating composite pipe, which includes, from the outside to the inside, a sheath layer, an aluminum foil layer, a glass fiber felt layer, a nano fireproof layer, an aluminum foil layer, a sampling tube and a heating tape. The two sampling tubes are mounted on the outer surface of the same side of the heating tape. The outer surfaces of the sampling tube and the heating tape are wrapped with an aluminum foil layer, the outer surface of the aluminum foil layer is wrapped with a nano fireproof layer to form a tube core, the outer surface of the tube core is wrapped with a glass fiber felt layer, the outer surface of the glass fiber felt layer is covered with an aluminum foil layer, and the outer surface of the aluminum foil layer is covered with a sheath layer.

[0007] Furthermore, the nano fireproof layer is made of a nano fireproof material, and the nano fireproof material is made by the following steps:

[0008] Step S1, adding xylene to a three-necked flask, transferring it to a 95°C oil bath, slowly adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, stirring at a uniform speed for 30 minutes, adding paraformaldehyde, continuing stirring for 30 minutes, heating to 120°C, condensing and reflux reaction for 6 hours, filtering while hot, washing the filter cake three times with xylene, transferring it to a drying oven and drying it at 80°C for 10 hours to obtain intermediate 1, and controlling the amount ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, paraformaldehyde and xylene to be 43.10-43.25g:6g:120mL;

[0009] In step S1, paraformaldehyde reacts with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to form intermediate 1, the structure of which is shown below:

[0010]

[0011] Step S2, adding molybdenum disulfide and sodium nitrate to concentrated sulfuric acid under an ice-water bath, magnetically stirring and adding potassium permanganate in equal amounts three times, controlling the reaction temperature not to exceed 20°C, stirring at a uniform speed and reacting for 4 hours, heating to 35°C, continuing stirring for 30 minutes, slowly adding deionized water, stirring at a uniform speed for 20 minutes, adding 30% hydrogen peroxide by mass, filtering while hot, washing the filter cake with 5% hydrochloric acid by mass and deionized water until there is no sulfate ion in the filtrate, then drying at 65°C, dispersing in deionized water, and ultrasonically dispersing for 1 hour to obtain treated molybdenum disulfide, wherein the amount ratio of molybdenum disulfide, sodium nitrate, concentrated sulfuric acid, potassium permanganate, deionized water and hydrogen peroxide is controlled to be 2g:1g:20-25mL:3g:40-45mL:5g;

[0012] In step S2, the molybdenum disulfide is surface treated with a strong acid and a hydrogen oxidizing agent to introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups on the surface of the molybdenum disulfide, followed by ultrasonic dispersion to prepare a treated molybdenum disulfide with a lamellar structure;

[0013] Step S3, adding phosphorus oxychloride to N, N-dimethylformamide in an ice-water bath and a nitrogen atmosphere, stirring at a uniform speed for 15 minutes, adding triethylamine solution dropwise, stirring for 4 hours after the addition is completed, heating to 65°C, continuing stirring for 20 minutes, adding treated molybdenum disulfide, keeping warm and stirring at a uniform speed for 4 hours, adding the mixed solution of intermediate 1, keeping warm and stirring and reacting for 6 hours, filtering, washing with deionized water, and freeze-drying for 12 hours to obtain a matrix, controlling the amount ratio of phosphorus oxychloride, triethylamine solution, N, N-dimethylformamide, treated molybdenum disulfide and the mixed solution of intermediate 1 to be 0.05 mol: 10 mL: 50 mL: 1 g: 100 mL;

[0014] Step S4: Add the matrix and sodium hypophosphite to deionized water, ultrasonically stir for 1 hour, then transfer to a 90°C oil bath, stir for 30 minutes, slowly add the aluminum ion solution dropwise, heat to 90°C, stir at a constant speed for 6 hours, filter, and wash the filter cake with deionized water to obtain a nano fireproof material. The dosage ratio of the matrix, sodium hypophosphite, deionized water and aluminum ion solution is controlled to be 1g:7.5-8.0g:20mL:20mL.

[0015] In step S3, the intermediate 1 undergoes a covalent bond reaction with the oxygen-containing functional groups on the treated molybdenum disulfide, and is then inserted into the molybdenum disulfide sheet. Then, in step S4, the aluminum hypophosphite is hybridized on the matrix through a hydrothermal reaction to prepare a nano-fireproof material with excellent flame retardant properties. The nano-fireproof material can play an excellent physical barrier role during the combustion process, effectively catalyze the formation of carbon, hinder the thermal degradation of the polymer matrix, and inhibit the formation of smoke.

[0016] Furthermore, the triethylamine solution in step S3 is prepared by mixing triethylamine and N,N-dimethylformamide in a dosage ratio of 0.1 mol:10 mL.

[0017] Furthermore, the mixed solution of the intermediate 1 in step S3 is prepared by mixing the intermediate 1 and N,N-dimethylformamide in a ratio of 0.08-0.1 mol:100 mL.

[0018] Furthermore, the aluminum ion solution is prepared by mixing aluminum sulfate 18hydrate and deionized water in a dosage ratio of 4.502-4.505 g:20 mL.

[0019] Furthermore, the sheath layer is made of PVC material and is cold-resistant to -25°C.

[0020] Furthermore, the specification of the glass fiber felt layer is 50g / ㎡, and it is bidirectionally wrapped with 40 layers.

[0021] Furthermore, the sampling tube is a PTFE polytetrafluoroethylene tube with a diameter of 8 mm.

[0022] Furthermore, the two sampling tubes are mounted on the outer surface of the same side of the heating tape, and then an aluminum foil layer is wrapped around the outer surface of the sampling tube and the heating tape, and a nano fireproof layer is wrapped around the outer surface of the aluminum foil layer to form a tube core, and a glass fiber felt layer is wrapped around the outer surface of the tube core, and the outer surface of the glass fiber felt layer is covered with an aluminum foil layer, and the outer surface of the aluminum foil layer is covered with a sheath layer to form a low-smoke flame-retardant sampling and heating composite tube.

[0023] Beneficial effects of the present invention:

[0024] The present invention discloses a low-smoke flame-retardant sampling heating composite pipe, in which the heating tape adopts a reinforced explosion-proof constant power heating tape or a self-limiting temperature heating tape. Two sampling tubes are attached to one side of the heating tape to make the heating temperature more accurate. The aluminum foil layer is a double-sided aluminum foil, i.e., a shielding reflective film. The shielding layer formed thereby should maintain electrical continuity over the entire length of the composite pipe. In addition, a nano-fireproof layer is prepared by using nano-fireproof materials. During the preparation process, an intermediate 1 is first prepared. The intermediate 1 reacts with the oxygen-containing functional groups on the treated molybdenum disulfide by a covalent bond reaction and then is inserted into the molybdenum disulfide sheet layer. Subsequently, in step S4, aluminum hypophosphite is hybridized on the matrix by a hydrothermal reaction to prepare a nano-fireproof material with excellent flame-retardant properties. The nano-fireproof material can play an excellent physical barrier role during the combustion process, effectively catalyze the formation of carbon, hinder the thermal degradation of the polymer matrix, and inhibit the formation of smoke. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a low-smoke flame-retardant sampling and heating composite pipe of the present invention.

[0027] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0028] 1. Sheath layer; 2. Aluminum foil layer; 3. Glass fiber felt layer; 4. Nano fireproof layer; 5. Sampling tube; 6. Heating tape. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 any creative efforts shall fall within the scope of protection of the present invention.

[0030] Example 1

[0031] See also Figure 1As shown, the present invention provides a low-smoke flame-retardant sampling and heating composite pipe, which comprises, from the outside to the inside, a jacket layer 1, an aluminum foil layer 2, a glass fiber felt layer 3, a nano fireproof layer 4, an aluminum foil layer 2, a sampling tube 5 and a heating tape 6. The two sampling tubes 5 are attached to the outer surface of the heating tape 6 on the same side. The outer surfaces of the sampling tube 5 and the heating tape 6 are wrapped with the aluminum foil layer 2, and the outer surface of the aluminum foil layer 2 is wrapped with the nano fireproof layer 4 to form a tube core. The outer surface of the tube core is wrapped with a glass fiber felt layer 3, the outer surface of the glass fiber felt layer 3 is covered with the aluminum foil layer 2, and the outer surface of the aluminum foil layer 2 is covered with the jacket layer 1;

[0032] The low-smoke flame-retardant sampling heating composite pipe is manufactured by the following steps:

[0033] The two sampling tubes 5 are attached to the outer surface of the same side of the heating tape 6, and then an aluminum foil layer 2 is wrapped around the outer surface of the sampling tube 5 and the heating tape 6, and a nano fireproof layer 4 is wrapped around the outer surface of the aluminum foil layer 2 to form a tube core, and a glass fiber felt layer 3 is wrapped around the outer surface of the tube core, and the outer surface of the glass fiber felt layer 3 is covered with an aluminum foil layer 2, and the outer surface of the aluminum foil layer 2 is covered with a sheath layer 1 to form a low-smoke flame-retardant sampling and heating composite tube.

[0034] The nano fireproof layer is made of nano fireproof material, the sheath layer is made of PVC material, which is cold-resistant at -25°C, the specification of the glass fiber felt layer is 50g / ㎡, and it is wrapped in 40 layers in both directions, and the sampling tube is a PTFE polytetrafluoroethylene tube with a diameter of 8mm.

[0035] Example 2

[0036] The nano fireproof material is prepared by the following steps:

[0037] Step S1, adding xylene to a three-necked flask, transferring it to a 95°C oil bath, slowly adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, stirring at a uniform speed for 30 minutes, adding paraformaldehyde, continuing stirring for 30 minutes, heating to 120°C, condensing and reflux reaction for 6 hours, filtering while hot, washing the filter cake three times with xylene, transferring it to a drying oven and drying it at 80°C for 10 hours to obtain intermediate 1, and controlling the amount ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, paraformaldehyde and xylene to be 43.10:6g:120mL;

[0038] Step S2, adding molybdenum disulfide and sodium nitrate to concentrated sulfuric acid under an ice-water bath, magnetically stirring and adding potassium permanganate in equal amounts three times, controlling the reaction temperature not to exceed 20°C, stirring at a uniform speed and reacting for 4 hours, heating to 35°C, continuing stirring for 30 minutes, slowly adding deionized water, stirring at a uniform speed for 20 minutes, adding 30% hydrogen peroxide by mass, filtering while hot, washing the filter cake with 5% hydrochloric acid by mass and deionized water until there is no sulfate ion in the filtrate, then drying at 65°C, dispersing in deionized water, and ultrasonically dispersing for 1 hour to obtain treated molybdenum disulfide, controlling the amount ratio of molybdenum disulfide, sodium nitrate, concentrated sulfuric acid, potassium permanganate, deionized water and hydrogen peroxide to be 2g:1g:20mL:3g:40mL:5g;

[0039] Step S3, adding phosphorus oxychloride to N, N-dimethylformamide in an ice-water bath and a nitrogen atmosphere, stirring at a uniform speed for 15 minutes, adding triethylamine solution dropwise, stirring for 4 hours after the addition is completed, heating to 65°C, continuing stirring for 20 minutes, adding treated molybdenum disulfide, keeping warm and stirring at a uniform speed for 4 hours, adding the mixed solution of intermediate 1, keeping warm and stirring and reacting for 6 hours, filtering, washing with deionized water, and freeze-drying for 12 hours to obtain a matrix, controlling the amount ratio of phosphorus oxychloride, triethylamine solution, N, N-dimethylformamide, treated molybdenum disulfide and the mixed solution of intermediate 1 to be 0.05 mol: 10 mL: 50 mL: 1 g: 100 mL;

[0040] Step S4: Add the matrix and sodium hypophosphite to deionized water, ultrasonically stir for 1 hour, then transfer to a 90°C oil bath, stir for 30 minutes, slowly add aluminum ion solution dropwise, heat to 90°C, stir at a constant speed for 6 hours, filter, and wash the filter cake with deionized water to obtain a nano fireproof material. The dosage ratio of the matrix, sodium hypophosphite, deionized water and aluminum ion solution is controlled to be 1g:7.5g:20mL:20mL.

[0041] The triethylamine solution in step S3 is prepared by mixing triethylamine and N,N-dimethylformamide in a ratio of 0.1 mol:10 mL.

[0042] The mixed solution of the intermediate 1 in step S3 is prepared by mixing the intermediate 1 and N,N-dimethylformamide in a ratio of 0.08:100 mL.

[0043] The aluminum ion solution is prepared by mixing aluminum sulfate 18hydrate and deionized water in a dosage ratio of 4.502 g:20 mL.

[0044] Example 3

[0045] The nano fireproof material is prepared by the following steps:

[0046] Step S1, adding xylene to a three-necked flask, transferring it to a 95°C oil bath, slowly adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, stirring at a uniform speed for 30 minutes, adding paraformaldehyde, continuing stirring for 30 minutes, heating to 120°C, condensing and reflux reaction for 6 hours, filtering while hot, washing the filter cake three times with xylene, transferring it to a drying oven and drying it at 80°C for 10 hours to obtain intermediate 1, and controlling the amount ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, paraformaldehyde and xylene to be 43.20g:6g:120mL;

[0047] Step S2, adding molybdenum disulfide and sodium nitrate to concentrated sulfuric acid under an ice-water bath, magnetically stirring and adding potassium permanganate in equal amounts three times, controlling the reaction temperature not to exceed 20°C, stirring at a uniform speed and reacting for 4 hours, heating to 35°C, continuing stirring for 30 minutes, slowly adding deionized water, stirring at a uniform speed for 20 minutes, adding 30% hydrogen peroxide by mass, filtering while hot, washing the filter cake with 5% hydrochloric acid by mass and deionized water until there is no sulfate ion in the filtrate, then drying at 65°C, dispersing in deionized water, and ultrasonically dispersing for 1 hour to obtain treated molybdenum disulfide, wherein the amount ratio of molybdenum disulfide, sodium nitrate, concentrated sulfuric acid, potassium permanganate, deionized water and hydrogen peroxide is controlled to be 2g:1g:22mL:3g:43mL:5g;

[0048] Step S3, adding phosphorus oxychloride to N, N-dimethylformamide in an ice-water bath and a nitrogen atmosphere, stirring at a uniform speed for 15 minutes, adding triethylamine solution dropwise, stirring for 4 hours after the addition is completed, heating to 65°C, continuing stirring for 20 minutes, adding treated molybdenum disulfide, keeping warm and stirring at a uniform speed for 4 hours, adding the mixed solution of intermediate 1, keeping warm and stirring and reacting for 6 hours, filtering, washing with deionized water, and freeze-drying for 12 hours to obtain a matrix, controlling the amount ratio of phosphorus oxychloride, triethylamine solution, N, N-dimethylformamide, treated molybdenum disulfide and the mixed solution of intermediate 1 to be 0.05 mol: 10 mL: 50 mL: 1 g: 100 mL;

[0049] Step S4: Add the matrix and sodium hypophosphite to deionized water, ultrasonically stir for 1 hour, then transfer to a 90°C oil bath, stir for 30 minutes, slowly add aluminum ion solution dropwise, heat to 90°C, stir at a constant speed for 6 hours, filter, and wash the filter cake with deionized water to obtain a nano fireproof material. The dosage ratio of the matrix, sodium hypophosphite, deionized water and aluminum ion solution is controlled to be 1g:7.8g:20mL:20mL.

[0050] The triethylamine solution in step S3 is prepared by mixing triethylamine and N,N-dimethylformamide in a ratio of 0.1 mol:10 mL.

[0051] The mixed solution of the intermediate 1 in step S3 is prepared by mixing the intermediate 1 and N,N-dimethylformamide in a ratio of 0.09 mol:100 mL.

[0052] The aluminum ion solution is prepared by mixing aluminum sulfate 18hydrate and deionized water in a dosage ratio of 4.503 g:20 mL.

[0053] Example 4

[0054] The nano fireproof material is prepared by the following steps:

[0055] Step S1, adding xylene to a three-necked flask, transferring it to a 95°C oil bath, slowly adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, stirring at a uniform speed for 30 minutes, adding paraformaldehyde, continuing stirring for 30 minutes, heating to 120°C, condensing and reflux reaction for 6 hours, filtering while hot, washing the filter cake three times with xylene, transferring it to a drying oven and drying it at 80°C for 10 hours to obtain intermediate 1, and controlling the amount ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, paraformaldehyde and xylene to be 43.25g:6g:120mL;

[0056] Step S2, adding molybdenum disulfide and sodium nitrate to concentrated sulfuric acid under an ice-water bath, magnetically stirring and adding potassium permanganate in equal amounts three times, controlling the reaction temperature not to exceed 20°C, stirring at a uniform speed and reacting for 4 hours, heating to 35°C, continuing stirring for 30 minutes, slowly adding deionized water, stirring at a uniform speed for 20 minutes, adding 30% hydrogen peroxide by mass, filtering while hot, washing the filter cake with 5% hydrochloric acid by mass and deionized water until there is no sulfate ion in the filtrate, then drying at 65°C, dispersing in deionized water, and ultrasonically dispersing for 1 hour to obtain treated molybdenum disulfide, wherein the amount ratio of molybdenum disulfide, sodium nitrate, concentrated sulfuric acid, potassium permanganate, deionized water and hydrogen peroxide is controlled to be 2g:1g:25mL:3g:45mL:5g;

[0057] Step S3, adding phosphorus oxychloride to N, N-dimethylformamide in an ice-water bath and a nitrogen atmosphere, stirring at a uniform speed for 15 minutes, adding triethylamine solution dropwise, stirring for 4 hours after the addition is completed, heating to 65°C, continuing stirring for 20 minutes, adding treated molybdenum disulfide, keeping warm and stirring at a uniform speed for 4 hours, adding the mixed solution of intermediate 1, keeping warm and stirring and reacting for 6 hours, filtering, washing with deionized water, and freeze-drying for 12 hours to obtain a matrix, controlling the amount ratio of phosphorus oxychloride, triethylamine solution, N, N-dimethylformamide, treated molybdenum disulfide and the mixed solution of intermediate 1 to be 0.05 mol: 10 mL: 50 mL: 1 g: 100 mL;

[0058] Step S4: Add the matrix and sodium hypophosphite to deionized water, ultrasonically stir for 1 hour, then transfer to a 90°C oil bath, stir for 30 minutes, slowly add the aluminum ion solution dropwise, heat to 90°C, stir at a constant speed for 6 hours, filter, and wash the filter cake with deionized water to obtain a nano fireproof material. The dosage ratio of the matrix, sodium hypophosphite, deionized water and aluminum ion solution is controlled to be 1g:8.0g:20mL:20mL.

[0059] The triethylamine solution in step S3 is prepared by mixing triethylamine and N,N-dimethylformamide in a ratio of 0.1 mol:10 mL.

[0060] The mixed solution of the intermediate 1 in step S3 is prepared by mixing the intermediate 1 and N,N-dimethylformamide in a ratio of 0.1 mol:100 mL.

[0061] The aluminum ion solution is prepared by mixing aluminum sulfate 18hydrate and deionized water in a dosage ratio of 4.505 g:20 mL.

[0062] Comparative Example 1

[0063] Compared with Example 4, this comparative example uses a substrate as a nano fireproof material.

[0064] Comparative Example 2

[0065] This comparative example is a commercially available nano fireproof material.

[0066] The properties of the nano fireproof materials prepared in Examples 2-4 and Comparative Examples 1-2 were tested, and the results are shown in Table 1 below:

[0067] Table 1

[0068]

[0069] It can be seen from Table 1 above that the nano fireproof materials prepared in Examples 2-4 of the present invention have excellent fireproofing properties.

[0070] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0071] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A low-smoke flame-retardant sampling and heating composite pipe, comprising, from the outside to the inside, a sheath layer (1), an aluminum foil layer (2), a glass fiber felt layer (3), a nano fireproof layer (4), an aluminum foil layer (2), a sampling pipe (5) and a heating tape (6), characterized in that: The two sampling tubes (5) are mounted on the outer surface of the heating belt (6) on the same side. The outer surfaces of the sampling tubes (5) and the heating belt (6) are wrapped with an aluminum foil layer (2). The outer surface of the aluminum foil layer (2) is wrapped with a nano fireproof layer (4) to form a tube core. The outer surface of the tube core is wrapped with a glass fiber felt layer (3). The outer surface of the glass fiber felt layer (3) is covered with an aluminum foil layer (2). The outer surface of the aluminum foil layer (2) is covered with a sheath layer (1). The nano fireproof layer (4) is made of a nano fireproof material, and the nano fireproof material is made by the following steps: Step S1, adding xylene to a three-necked flask, transferring it to a 95°C oil bath, slowly adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, stirring at a uniform speed for 30 minutes, adding paraformaldehyde, continuing stirring for 30 minutes, heating to 120°C, condensing and reflux reaction for 6 hours, filtering while hot, washing the filter cake three times with xylene, transferring it to a drying oven and drying it at 80°C for 10 hours to obtain intermediate 1, and controlling the amount ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, paraformaldehyde and xylene to be 43.10-43.25g:6g:120mL; Step S2, adding molybdenum disulfide and sodium nitrate to concentrated sulfuric acid under an ice-water bath, magnetically stirring and adding potassium permanganate in equal amounts three times, controlling the reaction temperature not to exceed 20°C, stirring at a uniform speed and reacting for 4 hours, heating to 35°C, continuing stirring for 30 minutes, slowly adding deionized water, stirring at a uniform speed for 20 minutes, adding 30% hydrogen peroxide by mass, filtering while hot, washing the filter cake with 5% hydrochloric acid by mass and deionized water until there is no sulfate ion in the filtrate, then drying at 65°C, dispersing in deionized water, and ultrasonically dispersing for 1 hour to obtain treated molybdenum disulfide, wherein the amount ratio of molybdenum disulfide, sodium nitrate, concentrated sulfuric acid, potassium permanganate, deionized water and hydrogen peroxide is controlled to be 2g:1g:20-25mL:3g:40-45mL:5g; Step S3, adding phosphorus oxychloride to N, N-dimethylformamide in an ice-water bath and a nitrogen atmosphere, stirring at a uniform speed for 15 minutes, adding triethylamine solution dropwise, stirring for 4 hours after the addition is completed, heating to 65°C, continuing stirring for 20 minutes, adding treated molybdenum disulfide, keeping warm and stirring at a uniform speed for 4 hours, adding the mixed solution of intermediate 1, keeping warm and stirring and reacting for 6 hours, filtering, washing with deionized water, and freeze-drying for 12 hours to obtain a matrix, controlling the amount ratio of phosphorus oxychloride, triethylamine solution, N, N-dimethylformamide, treated molybdenum disulfide and the mixed solution of intermediate 1 to be 0.05 mol: 10 mL: 50 mL: 1 g: 100 mL; Step S4: Add the matrix and sodium hypophosphite to deionized water, ultrasonically stir for 1 hour, then transfer to a 90°C oil bath, stir for 30 minutes, slowly add the aluminum ion solution dropwise, heat to 90°C, stir at a constant speed for 6 hours, filter, and wash the filter cake with deionized water to obtain a nano fireproof material. The dosage ratio of the matrix, sodium hypophosphite, deionized water and aluminum ion solution is controlled to be 1g:7.5-8.0g:20mL:20mL.

2. The low-smoke flame-retardant sampling and heating composite pipe according to claim 1, characterized in that: The triethylamine solution in step S3 is prepared by mixing triethylamine and N,N-dimethylformamide in a dosage ratio of 0.1 mol:10 mL.

3. The low-smoke flame-retardant sampling and heating composite pipe according to claim 1, characterized in that: The mixed solution of the intermediate 1 in step S3 is prepared by mixing the intermediate 1 and N,N-dimethylformamide in a ratio of 0.08-0.1 mol:100 mL.

4. The low-smoke flame-retardant sampling and heating composite pipe according to claim 1, characterized in that: The aluminum ion solution is prepared by mixing aluminum sulfate 18hydrate and deionized water in a dosage ratio of 4.502-4.505 g:20 mL.

5. The low-smoke flame-retardant sampling and heating composite pipe according to claim 1, characterized in that: The sheath layer (1) is made of PVC material and is cold-resistant to -25°C.

6. The low-smoke flame-retardant sampling and heating composite pipe according to claim 1, characterized in that: The specification of the glass fiber felt layer (3) is 50g / ㎡, and it is wrapped in 40 layers in two directions.

7. The low-smoke flame-retardant sampling and heating composite pipe according to claim 1, characterized in that: The sampling tube (5) is a PTFE polytetrafluoroethylene tube with a diameter of 8 mm.

8. The method for preparing a low-smoke flame-retardant sampling heating composite tube according to claim 1, characterized in that: The method comprises the following steps: attaching two sampling tubes (5) to the outer surface of the heating belt (6) on the same side, then wrapping an aluminum foil layer (2) around the outer surface of the sampling tube (5) and the heating belt (6), wrapping a nano fireproof layer (4) around the outer surface of the aluminum foil layer (2) to form a tube core, wrapping a glass fiber felt layer (3) around the outer surface of the tube core, coating the outer surface of the glass fiber felt layer (3) with an aluminum foil layer (2), and coating the outer surface of the aluminum foil layer (2) with a sheath layer (1) to form a low-smoke flame-retardant sampling and heating composite tube.

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