CN112881144B

CN112881144B - Pretreatment device for enrichment and analysis process of volatile organic compounds in atmosphere

Info

Publication number: CN112881144B
Application number: CN202110072751.4A
Authority: CN
Inventors: 曾立民; 郭鹏; 于雪娜
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2021-01-20
Filing date: 2021-01-20
Publication date: 2022-05-20
Anticipated expiration: 2041-01-20
Also published as: CN112881144A

Abstract

The invention discloses a pretreatment device for an enrichment and analysis process of volatile organic compounds in atmosphere, wherein the distance between a VOCs collecting pipe and a refrigeration part is regulated and controlled by a distance regulation and control component in the operation of the device, so that the temperature of a cold block is influenced as little as possible by the hot VOCs collecting pipe during thermal analysis, and the integral energy utilization efficiency of the device is improved; when the cryoadsorption, VOCs catches the pipe and can laminate with cold block fast, will catch the pipe temperature more fast and reduce to the assigned temperature, save the time of catching the pipe cooling. Moreover, the pretreatment device has a simple and small structure, is easy to operate, can perform enrichment analysis operation on a plurality of collecting pipes simultaneously, and can be used for conventional detection or field observation.

Description

Pretreatment device for enrichment and analysis process of volatile organic compounds in atmosphere

Technical Field

The invention relates to a pretreatment device of a measuring system for volatile organic compounds in the atmosphere, in particular to a pretreatment device of an enrichment and analysis process in the measuring system for the volatile organic compounds in the atmosphere.

Background

Volatile Organic Compounds (VOCs) are Compounds commonly existing in the atmosphere, have high saturated vapor pressure and low boiling point, and can react with free radicals in the atmosphere to promote O₃To cause photochemical contamination; meanwhile, part of VOC can be distributed into atmospheric particulates through a gas-solid phase, so that the VOCs have important research significance under the background of atmospheric combined pollution in China.

The monitoring method of the VOCs can be divided into two types of off-line monitoring and on-line monitoring, including four processes of sampling, pre-concentration, separation and detection, wherein the pre-concentration process is also called as a pretreatment process, and the process has a great influence on the accuracy of subsequent separation and detection results. The method of the pre-concentration process can be divided into a solvent analysis method and a thermal analysis method, the solvent analysis method has relatively low cost, but the volume of the analysis liquid is far larger than the volume of the sample, so that the analysis sensitivity can be reduced, and meanwhile, certain errors can be caused if the solvent is impure. Thermal analysis is typically performed by heating the trap while a carrier gas is introduced to desorb the adsorbed VOCs into a chromatographic column. The thermal analysis sensitivity is high, the interference of solvent analysis can be avoided, and the application is wide.

In the VOCs preconcentration step of the existing equipment, in order to completely and rapidly vaporize the low-temperature-trapped VOCs into the detection and analysis system, the capture tube of VOCs must be rapidly heated from a low temperature condition to a specified temperature (above 100 ℃). However, when the device is used for thermal analysis, heat is easily transferred from the collecting pipe to the adjacent refrigerating part, the stability of the operation of the refrigerating part is affected, the temperature of the refrigerating part is increased, and unnecessary energy waste is caused.

Disclosure of Invention

In view of the above problems, the present invention aims to provide a pretreatment device for the process of enrichment and desorption of volatile organic compounds, which can regulate and control the distance between a VOCs collection tube and a refrigeration component during the operation of the device, ensure that the hot collection tube affects the temperature of a cold block as little as possible during thermal desorption, and improve the overall energy utilization efficiency of the device; when low-temperature adsorption is carried out, the collecting pipe can be quickly attached to the cold block, the temperature of the collecting pipe is quickly reduced to the designated temperature, and the time for cooling the collecting pipe is saved.

In order to achieve the purpose, the invention adopts the following technical scheme: a pretreatment device for an enrichment and desorption process of volatile organic compounds in the atmosphere mainly comprises the following components: the device comprises a VOCs collecting pipe, a distance regulating and controlling assembly and a heating/refrigerating assembly, wherein the VOCs collecting pipe is a U-shaped pipe for carrying out enrichment and concentration operation on VOCs, the heating/refrigerating assembly comprises a cold block and a heating assembly, and the distance regulating and controlling assembly comprises a fixing piece, a corrugated pipe, a connecting rod, a gas circuit connecting pipe and a gas pump; wherein: the cold block is provided with an arc-shaped groove matched with the VOCs collecting pipe in shape, and the VOCs collecting pipe is placed in the arc-shaped groove during refrigeration; one end of the corrugated pipe is a closed end and is connected with one end of a connecting rod, and the other end of the connecting rod is fixedly connected to the upper part of the VOCs collecting pipe; the other end of the corrugated pipe is fixed on the fixing piece and is communicated with the air pump through an air passage connecting pipe, and the corrugated pipe is extended or shortened under the inflation and deflation action of the air pump to push the VOCs collecting pipe to be far away from the cold block or return to the arc-shaped groove of the cold block; and the heating assembly is connected with the upper part of the U-shaped VOCs collecting pipe, and when the VOCs collecting pipe is far away from the cold block, the VOCs collecting pipe heats the VOCs.

In the pretreatment device, the VOCs collecting pipe is a U-shaped pipe for carrying out enrichment and concentration operation on VOCs, preferably, one side of each of two ends of the U-shaped pipe, which is close to the cold block, is provided with a hole with internal threads respectively, and the hole is used for being in threaded connection with the connecting rod; a temperature sensor is arranged at the bottom of the U-shaped pipe and is used for realizing real-time monitoring of the temperature of the collecting pipe. The VOCs collecting pipe can be made of glass, stainless steel and T-C composite materials.

Among the above-mentioned pretreatment device, the distance regulation and control subassembly includes mounting, bellows, connecting rod, gas circuit connecting pipe and air pump, and wherein the mounting can be fixed on cold piece, and bellows one end is connected on the mounting, and the other end is preferred to pass through fast-assembling clamp fixed connection with the connecting rod. The connecting rod is preferably a polytetrafluoroethylene rod, and the polytetrafluoroethylene rod and the VOCs collecting pipe are fixedly connected through threads. The polytetrafluoroethylene material has excellent heat resistance and cold resistance, can be used for a long time at the temperature of minus 180-260 ℃, is allowed to be used under the conditions of quenching and sudden heating, and is very suitable for the working environment in a cold trap. The thermal conductivity of the polytetrafluoroethylene is between 0.244 and 0.273W/(m.k), while the thermal conductivity of the stainless steel is between 10 and 30W/(m.k) at a temperature of 600 ℃ or lower, which is much smaller than that of the polytetrafluoroethylene. The corrugated pipe can be made of materials such as bronze, brass, stainless steel, Monel alloy and the like. The air path connecting pipe is mainly used for connecting the corrugated pipe and the air pump, and the air pump is used for inflating and deflating the corrugated pipe. The gas circuit is strictly sealed to prevent gas leakage.

Each VOCs trapping pipe can be formed by respectively connecting a set of connecting piece-corrugated pipe-gas circuit connecting pipe-air pump assembly at two ends of a U-shaped pipe, or connecting two ends of the U-shaped pipe with a set of corrugated pipe-gas circuit connecting pipe-air pump assembly through a forked connecting piece, so that linkage of two ends of the U-shaped pipe is realized.

In the pretreatment apparatus, preferably, the heating/cooling unit includes a cooling block, a heating power supply, an electric heating connector, and a plurality of electric wires. The side all around of cold piece can be seted up a plurality of and be used for placing the arc recess of VOCs collection pipe, and for example a square cold piece can all set up the arc recess on four sides, places four VOCs collection pipes, and every VOCs collection pipe is regulated and control through the distance regulation and control subassembly separately. VOCs catches the collection pipe and is fixed in the recess during refrigeration, and with cold piece contact on three directions, the cold volume that volatile organic compounds that enables in catching the collection pipe obtained is more sufficient and even, because the recess shape catches the collection pipe with VOCs and is identical, when VOCs catches the collection pipe and is embedded in the recess, the recess can play the effect that fixed VOCs caught the collection pipe to a certain extent. The electric heating connector is connected to the upper part of the VOCs collecting pipe and is connected to a heating power supply through an electric wire, and when the thermal desorption step is carried out, the heating power supply is started to heat the VOCs collecting pipe.

In the pretreatment device for the volatile organic compound enrichment and desorption process, one end of the corrugated pipe is connected with the connecting rod, and the other end of the corrugated pipe is connected with the air pump, so that the corrugated pipe can be regarded as an air volume element with variable volume. According to the first law of thermodynamics, the energy provided by the outside to the working medium in the control body in unit time is equal to the sum of the change of the internal energy of the working medium in the control body in unit time and external work, so when the corrugated pipe is inflated, the energy is equivalent to the energy injected to the corrugated pipe by the outside, if the gas does not contain water vapor and the inflation time is short, the inflation process can be regarded as an adiabatic inflation process, and the internal energy of the working medium is not changed, so most of the energy is converted into the external work of the corrugated pipe, the gas capacity is correspondingly increased, the radial rigidity of the corrugated pipe is greater than the axial rigidity, the elongation is mainly concentrated in the axial direction, the overall effect is that the corrugated pipe can be elongated when the corrugated pipe is inflated, and similarly, the corrugated pipe evacuated can be contracted.

According to the invention, by utilizing the characteristics that the corrugated pipe can extend when being inflated and can contract when the interior of the corrugated pipe is vacuumized, the corrugated pipe is vacuumized when low-temperature adsorption is carried out, the corrugated pipe contracts to drive the connecting rod, the connecting rod drives the collecting pipe to enable the collecting pipe to be tightly attached to the cold block for refrigeration, heat is directly transferred between the collecting pipe and the cold block in a heat conduction mode, the heat transfer efficiency is high, and volatile organic matters can be converted into a solid state from a gaseous state in the collecting pipe more quickly and efficiently; in the thermal desorption process, the heating circuit is connected, the heating connector starts to heat the collecting pipe, meanwhile, the air pump starts to inflate the corrugated pipe, the internal pressure of the corrugated pipe is greater than the external pressure, therefore, the protruding part can expand under the action of the pressure difference, the corrugated pipe extends, the connecting rod and the collecting pipe are further pushed to move forwards, the separation of the collecting pipe and the cold block is realized, the heat transfer mode between the collecting pipe and the cold block is only convection and heat radiation, and the cold quantity loss of the cold block is reduced. Heating the trap tube at this point will have less effect on the cold block temperature. After reaching the heating temperature, the volatile organic compounds trapped in the trapping pipe are gasified and collected.

Compared with the prior art, the invention has the following advantages:

1. the invention designs a pretreatment device for an enrichment and desorption process of volatile organic compounds in the atmosphere. The distance regulation and control assembly can push the collecting pipe away from the cold block during heating, and the heat transfer mode between the collecting pipe and the cold block is only convection and heat radiation, so that the cold loss of the cold block is reduced, and the energy loss during heating and refrigerating conversion when the collecting pipe is tightly attached to the cold block is avoided; the collecting pipe is tightly attached to the cold block during refrigeration, heat is directly transferred between the collecting pipe and the cold block in a heat conduction mode, heat transfer efficiency is high, and volatile organic compounds can be converted from a gaseous state to a solid state in the collecting pipe more quickly and efficiently. The distance regulation and control assembly improves the energy utilization efficiency of the whole device.

2. The device can reduce the influence of the thermal analysis temperature of the collecting pipe on the temperature of the cold block when the cyclic operation of low-temperature adsorption and high-temperature thermal analysis is continuously carried out by utilizing the characteristics that the corrugated pipe can extend when being inflated and can contract when the interior of the corrugated pipe is vacuumized. The temperature-stabilized cold block allows the temperature of the trap to be lowered more quickly during cryoadsorption, reducing the run time for continuous operation of the device.

3. The invention adopts the polytetrafluoroethylene material to contact with the collecting pipe, the polytetrafluoroethylene material has excellent heat resistance and cold resistance, and the influence on the temperature of the collecting pipe is reduced due to small heat conductivity coefficient and poor heat conductivity.

4. The invention adopts a contact type refrigeration method, the collecting pipe is tightly attached to the cold block, and the cold energy can be directly transmitted to the collecting pipe in a heat transfer mode, so that the collecting pipe is quickly cooled. The collecting pipe is arranged in the groove of the cold block, the contact area of the collecting pipe and the cold block is larger, the cold quantity obtained by the gas in the pipe is more uniform relative to the plane contact, and the collecting pipe can be fixed to a certain extent.

5. The invention has simple structure, small device and easy operation, can simultaneously carry out enrichment analysis operation on a plurality of collecting pipes and can be used for routine detection or field observation.

Drawings

FIG. 1 is a schematic structural view of a distance adjusting and controlling member in the pretreatment apparatus according to the embodiment of the present invention;

FIG. 2 is a schematic view of the heating/cooling assembly of the pretreatment apparatus of the embodiment of the present invention, as viewed from the direction A of FIG. 1;

wherein: 1-cooling; 2-VOCs trapping pipe; 3-a polytetrafluoroethylene rod; 4-a bellows; 5-a fixing piece; 6-gas circuit connecting pipe; 7, clamping a hoop; 8, an air pump; 9-heating power supply; 10-an electrically heated joint; 11-temperature sensor.

Detailed Description

The pretreatment device for enriching and analyzing the VOCs in the atmosphere according to the present invention will be described in detail with reference to the accompanying drawings and the implementation process.

In this embodiment, arc-shaped grooves are formed in the left and right sides of one cold block 1, and a set of pretreatment devices for the enrichment and desorption processes of VOCs in the atmosphere is respectively arranged, as shown in fig. 1, each pretreatment device comprises a VOCs collecting pipe 2, a distance control assembly and a heating/refrigerating assembly. The VOCs collecting pipe 2 is a U-shaped pipe, each end of two U-shaped pipes on the left side and the right side of the cold block 1 is shown in figure 1, the distance regulating and controlling assembly comprises a polytetrafluoroethylene rod 3, a corrugated pipe 4, a fixing piece 5, an air path connecting pipe 6, a clamp 7 and an air pump 8, wherein one end of the corrugated pipe 4 is fixed on the fixing piece 5 and is connected with the air pump 8 through the air path connecting pipe 6, and the other end of the corrugated pipe is a closed end and is connected with the polytetrafluoroethylene rod 3 through the clamp 7; the polytetrafluoroethylene rod 3 is fixed with the VOCs trapping pipe 2 through threaded connection, and the VOCs trapping pipe 2 is prevented from falling. During refrigeration, VOCs catches header 2 and hugs closely in the U type recess of cold piece 1, and air pump 8 carries out the evacuation operation to bellows 4, and bellows 4 shrink drives polytetrafluoroethylene pole 3, and polytetrafluoroethylene pole 3 drives VOCs catches header 2 for VOCs catches header 2 and hugs closely cold piece 1 and refrigerates. After the low-temperature trapping is finished, the device enters a thermal desorption process, the air pump 8 inflates the corrugated pipe 4, and the corrugated pipe 4 can be regarded as a variable-volume air-containing element because one end of the corrugated pipe 4 is connected with the air pump 8 and the other end of the corrugated pipe is closed. When the corrugated pipe 4 is inflated, energy is injected into the corrugated pipe 4 equivalently from the outside, according to the first law of thermodynamics, the energy provided to the system from the outside is equal to the sum of internal energy change of a working medium in the system and external work, if gas does not contain water vapor and the inflation time is short, the inflation process can be regarded as an adiabatic inflation process, and the internal energy of the working medium is regarded as unchanged, so most of the energy is converted into the external work of the corrugated pipe, the gas capacity is correspondingly increased, the radial rigidity of the corrugated pipe is greater than the axial rigidity, the elongation is mainly concentrated in the axial direction, the integral effect is that the corrugated pipe 4 can be elongated when inflated, the polytetrafluoroethylene rod 3 is further pushed to move forwards, and the VOCs collecting pipe 2 is separated from the cold block 1. After the thermal desorption process is finished, if the next low-temperature adsorption operation is performed, the air pump 8 is started to vacuumize the corrugated pipe 4, so that the corrugated pipe 4 is contracted, and the VOCs collecting pipe 2 returns to the groove of the cold block 1 to be refrigerated.

Fig. 2 is a schematic view of the U-shaped tube on the right side of the cold block 1 and its heating/cooling assembly seen from direction a of fig. 1, and as shown in fig. 2, the heating/cooling assembly includes the cold block 1 for cooling and an electric heating joint 10 for heating and a heating power supply 9. Wherein electrical heating connects 10 and connects on VOCs catches header 2 upper portion, and electrical heating connects 10 external heating power 9, catches header 2 when VOCs and is pushed away from cold block 1 after, heating power 9 starts, and electrical heating connects 10 and begins to catch header 2 heating to VOCs. The temperature sensor 11 is arranged at the center of the bottom of the VOCs collecting pipe 2, so that the temperature of the collecting pipe can be monitored in real time.

The invention is used for carrying out the complete low-temperature adsorption and high-temperature thermal desorption processes of the volatile organic compounds for one time as follows:

1) fix polytetrafluoroethylene pole 3 and VOCs collection pipe 2, connect bellows 4 on mounting 5, fix polytetrafluoroethylene pole 3 and 4 one end (blind end) of bellows with clamp 7, link to each other gas circuit connecting pipe 6 and the 4 other ends of bellows, gas circuit connecting pipe 6 connects air pump 8.

2) And (3) opening the refrigeration equipment to refrigerate the cold block 1, and refrigerating the VOCs collecting pipe 2 tightly attached to the cold block 1 immediately.

3) After the temperatures of the cold block 1 and the VOCs collecting pipe 2 reach the specified refrigeration temperature, a low-temperature adsorption step is started, and the phase state of volatile organic compounds is changed from a gaseous state to a solid state and is collected.

4) Entering a volatile organic compound thermal desorption process: heating circuit switch-on, electrical heating connects 10 and begins to catch 2 heats of pipe to VOCs, and 8 starts to aerify 4 bellows of air pump simultaneously, and 4 internal pressure of bellows are greater than external pressure, and the bulge of bellows 4 produces deformation more easily, therefore the bulge can expand under the pressure differential effect, and 4 extensions of bellows, and then promote polytetrafluoroethylene pole 3 and VOCs and catch 2 antedisplacement of pipe, realize VOCs and catch the separation of pipe 2 and cold block 1. Heating the VOCs capture tube 2 again will have less effect on the cold block 1. After the heating temperature is reached, the volatile organic compounds trapped in the VOCs trapping pipe 2 are gasified and collected into a subsequent GC for detection.

5) After the volatile organic compounds are recovered, the heating device stops heating, the air pump 8 carries out vacuumizing operation on the corrugated pipe 4, the corrugated pipe 4 contracts, the VOCs collecting pipe 2 returns to the groove of the cold block 1, and the thermal desorption process is finished.

6) If the enrichment and analysis operations of the volatile organic compounds are to be continued, the next volatile organic compound trapping operation is started from the step 3) after the temperature of the VOCs trapping pipe 2 reaches the preset refrigeration temperature. If the next trapping operation is not needed, the power supply of the heating/refrigerating assembly in the device can be turned off, and the volatile organic compounds enrichment operation is completed.

The present invention has been described in terms of the above embodiments, and variations in the structure, location, and connection of the various elements may be made without departing from the scope of the invention.

Claims

1. A pretreatment device for an enrichment and desorption process of volatile organic compounds in the atmosphere comprises a VOCs collecting pipe, a distance regulation and control assembly and a heating/refrigerating assembly, wherein the VOCs collecting pipe is a U-shaped pipe for carrying out enrichment and concentration operation on VOCs, the heating/refrigerating assembly comprises a cold block and a heating assembly, and the distance regulation and control assembly comprises a fixing piece, a corrugated pipe, a connecting rod, a gas circuit connecting pipe and a gas pump; wherein: the cold block is provided with an arc-shaped groove matched with the VOCs collecting pipe in shape, and the VOCs collecting pipe is placed in the arc-shaped groove during refrigeration; one end of the corrugated pipe is a closed end and is connected with one end of a connecting rod, and the other end of the connecting rod is fixedly connected to the upper part of the VOCs collecting pipe; the other end of the corrugated pipe is fixed on the fixing piece and is communicated with the air pump through an air path connecting pipe; the corrugated pipe is stretched or shortened under the inflation and deflation action of the air pump, and the VOCs collecting pipe is pushed to be far away from the cold block or return to the arc-shaped groove of the cold block; and the heating assembly is connected with the upper part of the U-shaped VOCs collecting pipe, and when the VOCs collecting pipe is far away from the cold block, the VOCs collecting pipe heats the VOCs.

2. The pretreatment apparatus as claimed in claim 1, wherein a hole having an internal thread is formed in each of both ends of the upper portion of the U-shaped pipe adjacent to the side of the cold block for screw-coupling with the connecting rod.

3. The pretreatment apparatus according to claim 1, wherein a temperature sensor is attached to a bottom of the U-shaped tube.

4. The pretreatment apparatus of claim 1, wherein the VOCs capture tube is made of glass, stainless steel, or a T-C composite.

5. The pretreatment apparatus according to claim 1, wherein in the distance adjustment and control unit, the fixing member is fixed to a cold block; the blind end and the connecting rod of bellows pass through fast-assembling clamp fixed connection.

6. The pretreatment apparatus as set forth in claim 1, wherein the connecting rod is a polytetrafluoroethylene rod.

7. The pretreatment apparatus of claim 1, wherein the bellows is made of bronze, brass, stainless steel, or monel.

8. The pretreatment apparatus as set forth in claim 1, wherein each of the VOCs trap pipes is connected to a set of a connector-bellows-gas circuit connection pipe-gas pump assembly at each end of the U-shaped pipe, or is connected to a set of a bellows-gas circuit connection pipe-gas pump assembly at each end of the U-shaped pipe through a bifurcated connector.

9. The pretreatment apparatus of claim 1, wherein the heating/cooling assembly comprises a cold block, a heating power source and an electrical heating connector, and one or more arc-shaped grooves for accommodating the VOCs capture tubes are formed in the side surfaces of the periphery of the cold block; the electric heating joint is connected to the upper part of the VOCs collecting pipe and is connected with a heating power supply through an electric wire, and the heating power supply is started to heat the VOCs collecting pipe.