System and method for treating polyurethane solid waste in molten salt

Abstract

The invention provides a system and method for treating polyurethane solid waste in molten salt, and belongs to the field of nitrogenous solid waste treatment. The problem that harmful gas is generated during high-temperature molten salt oxidation of organic solid waste is solved. A system for treating polyurethane solid waste in molten salt comprises a first-stage reaction kettle, a gas outlet end is connected with a second-stage reaction kettle, the first-stage reaction kettle and the second-stage reaction kettle are each provided with a gas heating device used for heating inlet gas, and reaction devices used for heating the molten salt and polyurethane are arranged in the first-stage reaction kettle and the second-stage reaction kettle; the gas component and flow control device is connected with the first-stage reaction kettle through a gas heating device and is used for inputting a certain type of gas into the first-stage reaction kettle at a certain speed; and the electrolysis device is used for applying a certain voltage to the fused salt in the reaction device in the second-stage reaction kettle. The method is mainly used for treating the polyurethane solid waste.

Description

Technical Field

[0001] The present invention belongs to the field of nitrogen-containing solid waste treatment, and particularly relates to a system and method for treating polyurethane solid waste in molten salt. Background Art

[0002] Polyurethane has a wide range of applications, including products such as coatings, adhesives, fabric finishing agents, leather modifiers, polyurethane flexible / rigid foams, elastomers, etc., and is mainly applied in the fields of textiles, construction, aviation, ships, transportation, medicine, electronics, etc. Ordinary pyrolysis methods will produce acidic, toxic, flammable and explosive gases such as NOx, CO, and H2.

[0003] NaOH is beneficial to enhancing the neutralization ability of carbonate molten salt. While pyrolyzing nitrogen-containing polyurethane solid waste, it can effectively prevent the generation of NOx, and it is an effective system suitable for the treatment of nitrogen-containing solid waste. However, when organic solid waste is oxidized in high-temperature molten salt, other hydrocarbon gases, CO, and H2 gases will inevitably be produced, making it difficult to recycle the tail gas. Summary of the Invention

[0004] In view of this, the present invention aims to propose a system and method for treating polyurethane solid waste in molten salt to solve the problem of the generation of harmful gases when organic solid waste is oxidized in high-temperature molten salt.

[0005] To achieve the above object, the present invention adopts the following technical solutions. According to one aspect of the present invention, a system for treating polyurethane solid waste in molten salt is provided, including:

[0006] A primary reaction kettle, one gas outlet end of which is connected to a secondary reaction kettle. Among them, both the primary reaction kettle and the secondary reaction kettle are provided with gas heating devices for heating the incoming gas, and both are internally provided with reaction devices for heating the molten salt and polyurethane.

[0007] A gas composition and flow control device, which is connected to the primary reaction kettle through a gas heating device, and is used to input a certain type of gas into the primary reaction kettle at a certain speed.

[0008] An electrolysis device, which is used to apply a certain voltage to the secondary reaction kettle.

[0009] Furthermore, the molten salt is NaOH-Li2CO3-Na2CO3-K2CO3, and the mass ratio is 3:8:6:6.

[0010] Furthermore, the ratio of the molten salt to polyurethane is 1:1.

[0011] Furthermore, the reaction device is a crucible.

[0012] Further, the system further includes a gas composition analysis device for detecting gas components, and both the first-stage reaction kettle and the second-stage reaction kettle are connected to the gas composition analysis device.

[0013] Further, the gas composition analysis device includes a gas filtration and flow rate detection device, a gas condensation device, an on-line gas mass spectrometer, and a vacuum pump that are connected in sequence.

[0014] According to another aspect of the present invention, there is provided a method for directionally generating CH4 gas using a system for treating polyurethane solid waste in molten salt as described above, including the following steps:

[0015] Fully mix the pre-molten molten salt and polyurethane in a certain proportion and decompose them in the first-stage reaction kettle at a certain temperature for a certain time;

[0016] Pass the reaction tail gas into the molten salt in the second-stage reaction kettle, and apply a certain voltage to react with the tail gas at a certain temperature to generate CH4 gas.

[0017] Further, the decomposition conditions in the first-stage reaction kettle are: decompose at 400 °C for 0.5 h, and the electrolysis conditions in the second-stage reaction kettle are: electrolyze at 2.5 V for 8 h.

[0018] Further, the position where the tail gas is introduced into the second-stage reaction kettle is the bottom of the electrode, and the bottom of the electrode is located in the molten salt at the corresponding position.

[0019] Further, the pre-melting step of the molten salt is to pre-dry each salt at 200 °C for 12 h and pre-melt it at 400 °C for 2 h according to the ratio of NaOH-Li2CO3-Na2CO3-K2CO3 of 3:8:6:6.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The combination of NaOH and basic carbonate molten salt can effectively avoid the generation of NO and NO2 gases;

[0022] 2. Through the method of molten salt electrochemistry, various hydrocarbon gases, CO, and H2 generated by polyurethane are directionally converted into CH4 gas, realizing the absorption of acidic tail gas and the purification and recycling of combustible gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0024] Figure 1Schematic diagram of the structure of a system for treating polyurethane solid waste in molten salt according to the present invention;

[0025] Figure 2 Flow chart of the method according to the present invention;

[0026] Figure 3 XRD pattern of the waste salt after molten salt oxidation according to the present invention;

[0027] Figure 4 Graph of the change of H2 intensity with time before and after using the method according to the present invention;

[0028] Figure 5 Graph of the change of CO intensity with time before and after using the method according to the present invention;

[0029] Figure 6 Graph of the change of CH4 intensity with time before and after using the method according to the present invention.

[0030] Gas composition and flow control device 1; Gas heating device 2; First reaction kettle 3; First crucible 4; Polyurethane 5; Molten salt 6; Electrolysis device 7; Second reaction kettle 8; Second crucible 9; Gas filtration and flow detection device 10; Gas condensation device 11; Gas online mass spectrometer 12; Vacuum pump 13. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0032] It should be noted that the descriptions of directions such as "left", "right", "left side", "right side", "upper part", "lower part", "top", "bottom", etc. in the present invention are all defined based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the structure must be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation to the present invention. In the description of the present invention, "a plurality" means more than two, unless otherwise specifically defined.

[0033] In the description of the present invention, unless otherwise clearly defined and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] Referring to the accompanying drawings to illustrate this embodiment, according to one aspect of the present invention, a system for treating polyurethane solid waste in molten salt is provided, including:

[0035] A primary reactor 3, with a gas outlet end connected to a secondary reactor 8. Among them, both the primary reactor 3 and the secondary reactor 8 are provided with a gas heating device 2 for heating the incoming gas, and both are internally provided with a reaction device for heating the molten salt and polyurethane.

[0036] Both the primary reactor 3 and the secondary reactor 8 can use conventional molten salt reactors. For the gas heating device 2, various methods such as a combustion compensator, a combustion compensator, a heating rod, high-frequency electromagnetism, pyrolysis gas combustion heating, etc. can be selected according to different requirements. The purpose of its setting is to make the temperature of the gas entering the primary reactor 3 and the secondary reactor 8 reach a predetermined value, which can be set according to the actual situation, and no exhaustive list is made here. For the specific connection form between the primary reactor 3 and the secondary reactor 8 and the gas heating device 2, and how the gas composition and flow control device 1 are connected to the gas heating device 2, corresponding reasonable settings are made according to the type of the actually selected gas heating device 2, as long as it can ensure that the gas temperature can reach the predetermined value. The molten salt here is specifically NaOH-Li2CO3-Na2CO3-K2CO3, with a mass ratio of 3:8:6:6. The prepared molten salt and polyurethane are mixed and added to the reaction device in a mass ratio of 1:1. Among them, the reaction device in the primary reactor 3 is the first crucible 4, and the reaction device in the secondary reactor 8 is the second crucible 9. The first crucible 4 and the second crucible 9 have the same structure, and the first crucible 4 and the second crucible 9 are respectively fixed in the corresponding reactors in a manner conducive to the reaction, and the fixing method is reasonably selected according to the actual situation. For the heating method of the crucible in the reactor, an existing method can be selected.

[0037] The gas composition and flow control device 1 is connected to the primary reactor 3 through a gas heating device 2, and is used to input a certain type of gas into the primary reactor 3 at a certain speed. The setting of the gas composition and flow control device 1 is mainly to introduce a predetermined type of gas into the primary reactor 3, the secondary reactor 8, and the system flow path. On the one hand, it is to use the predetermined type of gas to evacuate the gas in the system flow path, ensure the purity of the gas composition in the system flow path, and ensure the progress of the reaction. Secondly, it is to make the gas detection results accurate when comparing the cases with and without applying voltage. Specifically, the gas composition and flow control device 1 is provided with an Ar gas cylinder and an O2 gas cylinder. When outputting gas, the gas flow rates are respectively controlled at 16 mL / min and 64 mL / min. The gas flow rate control can adopt existing control means, such as setting an electric control valve on the gas outlet pipeline of the gas cylinder, and controlling the flow rate by controlling the opening of the electric control valve. Make a reasonable selection according to the actual situation.

[0038] The electrolysis device 7 is used to apply a certain voltage to the molten salt in the reaction device of the secondary reactor 8. The electrolysis device 7 is specifically set with a nickel electrode as the working electrode and an effective current area of 0.1 cm 2 , and the counter electrode is a graphite electrode. The bottom of the electrode is located in the second crucible 9, and the gas inlet position of the secondary reactor 8 is at the bottom of the electrode, which is conducive to the rapid reaction of the gas under the action of voltage to generate the corresponding CH4 gas in a directional manner.

[0039] The system further includes a gas composition analysis device for detecting the gas composition. Both the primary reactor 3 and the secondary reactor 8 are connected to the gas composition analysis device. Specifically, the gas composition analysis device includes a gas filtration and flow rate detection device 10, a gas condensation device 11, a gas online mass spectrometer 12, and a vacuum pump 13 connected in sequence. The gas filtration and flow rate detection device 10 is specifically a flow rate detection device with a filtration function for detecting the gas flow rate. The gas condensation device 11 is used to cool the gas and separate the condensed water from the gas. The gas outlet end is connected to the gas online mass spectrometer 12. Through the gas online mass spectrometer 12, the gas composition can be analyzed and displayed. The vacuum pump 13 is connected to the outlet end of the gas online mass spectrometer 12 and is used to provide power for the movement of the gas. For the specific installation position of the vacuum pump 13, it can be set at any position in the gas composition analysis device flow path according to the actual situation, not limited to being behind the gas online mass spectrometer 12. For the gas filtration and flow rate detection device 10, the gas condensation device 11, the gas online mass spectrometer 12, and the vacuum pump 13, existing equipment can be used, and reasonable selection can be made according to actual needs.

[0040] According to another aspect of the present invention, a method for directionally generating CH4 gas using a system for treating polyurethane solid waste in molten salt as described above is provided, including the following steps:

[0041] Pre-dry each salt at 200 °C for 12 h and pre-melt it at 400 °C for 2 h in the ratio of NaOH-Li2CO3-Na2CO3-K2CO3 being 3:8:6:6. After fully mixing the pre-melted molten salt and polyurethane in a certain ratio, decompose it in the primary reactor 3 at 400 °C for 0.5 h;

[0042] Pass the reaction tail gas into the molten salt of the secondary reactor 8, apply a voltage of 2.5 V to the molten salt at 430 °C, and electrolyze for 8 h to react with the tail gas to generate CH4 gas.

[0043] In this embodiment, the position where the tail gas is introduced into the secondary reactor 8 is the bottom of the electrode, and the bottom of the electrode is located in the molten salt at the corresponding position. This gas introduction method is conducive to the rapid and efficient progress of the reaction and improves the reaction efficiency.

[0044] To verify the effectiveness of applying voltage on the change of gas composition, first, the flow rates of Ar and O2 gases are respectively controlled at 16 mL / min and 64 mL / min through the gas composition and flow control device 1, and the gas filtration and flow detection device 10, gas condensation device 11, gas online mass spectrometer 12, and vacuum pump 13 are turned on. Other gases in the flow path are evacuated by Ar and O2 until the gas composition data of the gas online mass spectrometer 12 is stable.

[0045] The gas introduced into the first-stage reactor 3 is heated by the gas heating device 2 corresponding to the first-stage reactor 3, and the first crucible 4 loaded with polyurethane 5 and molten salt 6 is placed in the first-stage reactor 3. Then, the first-stage reactor 3 is heated to 400 °C and kept warm for 0.5 h, and the tail gas is passed through the gas filtration and flow detection device 10, gas condensation device 11, gas online mass spectrometer 12, and vacuum pump 13 for composition detection. After the reaction, the waste salt in the first crucible 4 is cooled and subjected to XRD detection to obtain the Figure 3 XRD pattern of the waste salt after molten salt oxidation as shown.

[0046] Finally, the tail gas coming out of the first-stage reactor 3 is heated by the gas heating device 2 corresponding to the second-stage reactor 8, and the tail gas is introduced into the molten salt in the second crucible 9 of the second-stage reactor 8. This molten salt is the same as the molten salt in the first crucible 4. At the same time, a constant voltage of 2.5 V is applied to the second-stage reactor for 8 h through the electrolysis device 7, and the reacted gas is passed through the gas filtration and flow detection device 10, gas condensation device 11, gas online mass spectrometer 12, and vacuum pump 13 for composition detection. The gas detection results with and without electrochemical control are compared to obtain the Figures 4 - 6 which respectively show the graphs of the intensity changes of H2, CO, and CH4 with time before and after the molten salt electrochemical method.

[0047] From Figure 3 it can be seen that after the polyurethane is treated by this system, the nitrogen-containing tail gas can be effectively adsorbed as nitrate, indicating that this system can effectively neutralize the nitrogen-containing acidic tail gas and produce nitrate in the carbonate. From Figures 4 - 6It can be seen that there are various gases such as CO, H2, and methane in the gas after molten salt oxidation. After being controlled by the molten salt electrochemistry method, the intensities of CO and H2 gases are significantly reduced, while the CH4 in the gas products is significantly enhanced. It was also found during the experiment that the overall amount of H2 gas increases with time, and as the molten salt electrochemistry control time increases, the reduction effect of the H2 content becomes more obvious. The CO content first increases and then decreases with time. When the molten salt electrochemistry control time is further increased, there will be an intersection point in the CO intensity before and after electrochemistry control. Experiments have proved that when the molten salt electrochemistry control time is less than 1800 s, the content of CO in the tail gas can be effectively reduced. The reason for this result may be that too long electrolysis time may cause the carbonate system itself to decompose to form CO, resulting in an increase in its content. This example proves that the NaOH-Li2CO3-Na2CO3-K2CO3 molten salt system can effectively neutralize the nitrogen-containing tail gas and can combine with the molten salt electrochemistry method to increase the content of CH4 in the tail gas, facilitating the recycling of the tail gas.

[0048] In the above description, the sensors, controllers, control programs, etc. that may be involved are all prior arts and will not be elaborated.

[0049] The embodiments of the present invention disclosed above are only used to help explain the present invention. The embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. According to the content of this specification, many modifications and changes can be made. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the relevant technical field can well understand and utilize the present invention.

Claims

1. A system for treating polyurethane solid waste in molten salt, characterized in that: include: A primary reactor (3), a gas outlet end of which is connected to a secondary reactor (8), wherein the primary reactor (3) and the secondary reactor (8) are both provided with a gas heating device (2) for heating the incoming gas, and are both provided with a reaction device for heating molten salt and polyurethane; The gas composition and flow control device (1) is connected to the primary reaction kettle (3) via a gas heating device (2) and is used to input a certain type of gas into the primary reaction kettle (3) at a certain speed; The electrolysis device (7) is used to apply a certain voltage to the secondary reaction kettle (8).

2. A system for treating polyurethane solid waste in molten salt according to claim 1, characterized in that: The molten salt is NaOH-Li2CO3-Na2CO3-K2CO3, and the mass ratio is 3:8:6:

6.

3. A system for treating polyurethane solid waste in molten salt according to claim 1 or 2, characterized in that: The ratio of the molten salt to the polyurethane is 1:

1.

4. A system for treating polyurethane solid waste in molten salt according to claim 3, characterized in that: The reaction device is a crucible.

5. The system for treating polyurethane solid waste in molten salt according to claim 1, characterized in that: The system also includes a gas component analysis device for detecting gas components, and the primary reaction kettle (3) and the secondary reaction kettle (8) are both connected to the gas component analysis device.

6. A system for treating polyurethane solid waste in molten salt according to claim 5, characterized in that: The gas component analysis device comprises a gas filtering and flow detection device (10), a gas condensation device (11), a gas online mass spectrometer (12) and a vacuum pump (13) which are connected in sequence.

7. A method for directional generation of CH4 gas using a polyurethane solid waste treatment system in molten salt as claimed in claim 1, 2, 4, 5 or 6, characterized in that: The steps include: The pre-melted molten salt and polyurethane are fully mixed in a certain proportion and then decomposed at a certain temperature for a certain time in a primary reactor (3); The tail gas after the reaction is introduced into the molten salt in the secondary reactor (8), and a certain voltage is applied to the molten salt at a certain temperature to react with the tail gas to generate CH4 gas.

8. The method according to claim 7, characterized in that The decomposition conditions in the primary reactor (3) are: decomposition at 400° C. for 0.5 h, and the electrolysis conditions in the secondary reactor (8) are: electrolysis at 2.5 V for 8 h.

9. The method according to claim 7, characterized in that: The position where the tail gas is introduced into the secondary reactor (8) is the bottom of the electrode, and the bottom of the electrode is located in the molten salt at a corresponding position.

10. The method according to claim 7, characterized in that: The pre-melting step of the molten salt is to pre-dry each salt at 200°C for 12 hours and pre-melt it at 400°C for 2 hours in a ratio of NaOH-Li2CO3-Na2CO3-K2CO3 of 3:8:6:6.

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