A method for reducing the hydrolysis chlorine content in toluene diisocyanate

Abstract

The invention discloses a method for reducing the hydrolysis chlorine content in toluene diisocyanate, characterized in that a modified self-heat recovery distillation system is used, the modified self-heat recovery distillation system comprises a material distillation section and a heat recovery section, and specifically comprises the following steps: (1) material distillation section: raw materials are passed into a distillation tower for distillation separation, and after the top steam is condensed by a condenser, a part of it is refluxed into the tower, and the other part is extracted; a part of the tower bottom material enters a reboiler through a circulating pump, and enters the bottom of the modified distillation tower after vaporization, and the other part is extracted; (2) heat recovery section: the circulating working fluid in the system is vaporized after absorbing the heat of the top steam in the condenser, and the temperature and pressure are increased by a compressor, and then enters the reboiler to heat the bottom material, and the circulating working fluid is condensed, and then enters the condenser to absorb heat. The top TDI content is ≥99.90%, the hydrolysis chlorine content is ≤0.0015%, and the distillation energy consumption is greatly reduced and the energy utilization rate is improved, the operating cost is effectively reduced, and the economy is improved.

Description

Technical Field

[0001] The invention relates to a purification process of toluene diisocyanate, in particular to a method for reducing the hydrolysis chlorine content in toluene diisocyanate. Background Art

[0002] Toluene diisocyanate (TDI) is mainly used in organic synthesis, production of foam plastics, coatings and as a chemical reagent, and has broad development prospects. At present, the main method for synthesizing TDI is the phosgene method, which has a mature process and high economic benefits. However, this method will produce chlorine-containing impurities such as carbamoyl chloride, dissolved phosgene, and chlorinated aromatics, resulting in residual chlorinated by-products in the product. The hydrolyzed chlorine content is an important indicator of the quality of TDI products. The high or low hydrolyzed chlorine content not only increases the difficulty of subsequent purification, but also leads to a decrease in reaction activity, a darker product color, and a decrease in performance. Based on the influence of hydrolyzed chlorine on the performance of TDI products, the hydrolyzed chlorine content needs to be reduced during the production process.

[0003] Existing research mainly reduces the hydrolyzed chlorine content in crude TDI by treating raw materials with amines, purifying phosgene, distilling, adsorption and other methods. For industrial production, raw material treatment, process and other conditions are not easy to change. The distillation method can achieve better results in large-scale treatment of products with high TDI content. The hydrolyzed chlorine content can be reduced by improving the distillation efficiency. Therefore, distillation is more suitable for industrial TDI production. Dawson et al. used partial reflux, partial reflux plus fractionation, and complete reflux plus fractionation on crude TDI products in the early stage to decompose some hydrolyzed chlorine in the crude product into HCl gas and isocyanate, thereby reducing the hydrolyzed chlorine content. Marcus Paul et al. first carried out dephosgene treatment to control the phosgene content to less than 2% (by weight), and then removed the solvent and optional reaction residues by distillation to produce crude TDI containing less than 20% (by weight) of solvent. Finally, four product fractions were separated in a dividing wall distillation tower. The obtained TDI mass fraction was 99.5%, and the solvent quality and hydrolyzed chlorine content could be reduced to a lower level.

[0004] Although the distillation method can achieve good results in treating TDI hydrolysis chlorine wastewater, the above research generally has problems such as high energy consumption and low energy utilization. At present, the energy consumed by the distillation process is about 60% of all separation processes, but the energy utilization rate of the distillation process is only about 10%. Summary of the invention

[0005] The purpose of the present invention is to study the distillation process of reducing the hydrolyzed chlorine in TDI by adopting a self-regenerative distillation system, and to design a reasonable distillation tower for reducing the hydrolyzed chlorine content in TDI by optimizing the theoretical plate number, feed position and reflux ratio, so as to further reduce the hydrolyzed chlorine content, so that the TDI content at the top of the tower is ≥99.90% and the hydrolyzed chlorine content is ≤0.0015%.

[0006] Another object of the present invention is to use a self-heated distillation system to reduce the hydrolysis chlorine content in TDI. Only 192kW of electricity consumption is required to maintain the normal operation of the entire TDI degradation and hydrolysis chlorine device, which can reduce the operating cost by 65.06% per year compared with the traditional process.

[0007] The technical solutions adopted to achieve the purpose of the present invention are as follows:

[0008] A method for reducing the hydrolysis chlorine content in toluene diisocyanate, characterized in that a self-heat recovery distillation system is used, wherein the self-heat recovery distillation system includes a material distillation section and a heat recovery section, and specifically includes the following steps:

[0009] (1) Material distillation section: The raw materials are passed into the distillation tower for distillation separation. After the top steam is condensed by the condenser, part of it is returned to the tower, and the other part is extracted; part of the bottom material of the tower enters the reboiler through the circulation pump, and after vaporization, it enters the bottom of the modified distillation tower, and the other part is extracted;

[0010] (2) Heat recovery section: The circulating fluid in the system absorbs the heat of the steam at the top of the tower in the condenser and then vaporizes. The temperature and pressure are increased by the compressor and then enter the reboiler to heat the material at the bottom of the tower. At the same time, the circulating fluid is condensed and then enters the condenser to absorb heat.

[0011] Furthermore, the number of theoretical plates of the distillation tower is 10-40.

[0012] Furthermore, the feed position of the distillation tower is the 5th to 10th tower plates.

[0013] Furthermore, the reflux ratio of the distillation tower is 0.5-1.0.

[0014] Furthermore, the compressor is a twin-screw compressor, and the circulating working fluid is the steam generated in the distillation tower.

[0015] Furthermore, the reboiler is a horizontal tube falling film reboiler.

[0016] Furthermore, a circulating pump is arranged at the bottom of the distillation tower to pump the bottom liquid to the top inlet of the falling film reboiler, vaporize in the reboiler, and enter the bottom of the distillation tower from the bottom of the reboiler.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) By adopting the self-heating distillation system, the TDI content at the top of the tower is ≥99.90%, and the hydrolyzed chlorine content is ≤0.0015%, meeting the requirements for removing the hydrolyzed chlorine in TDI.

[0019] (2) The self-reheating distillation system used in this study greatly reduced the distillation energy consumption and improved the energy utilization rate, effectively reducing the operating cost and improving the economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of the self-regenerative distillation system of Example 1 of the present invention;

[0021] 1-distillation tower, 2-condenser, 3-compressor, 4-reboiler, 5-throttling device, 6-circulation pump;

[0022] Figure 2 The effect of the feed position on the hydrolysis chlorine content at the top of the tower in Example 2 of the present invention;

[0023] Figure 3 The effect of the number of theoretical plates on the hydrolyzed chlorine content at the top of the tower in Example 3 of the present invention;

[0024] Figure 4 The figure shows the effect of the reflux ratio on the hydrolyzed chlorine content at the top of the tower in Example 4 of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 creative work are within the scope of protection of the present invention.

[0026] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0027] All numerical designations, such as pH, temperature, length, flow rate, including ranges, are approximate. It is to be understood, although not always expressly stated, that all numerical designations are preceded by the term "about". It is also to be understood, although not always expressly stated, that the reagents described herein are merely examples and that equivalents thereof are known in the art.

[0028] For ease of explanation, spatial relative terms such as "upper", "lower", "left", "right" and the like are used in the embodiments to illustrate the relationship of one element or feature shown in the figure relative to another element or feature. It should be understood that, in addition to the orientation shown in the figure, the spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figure is inverted, the elements described as being "under" other elements or features will be positioned "on" other elements or features. Therefore, the exemplary term "under" can include both upper and lower orientations. The device can be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used here can be interpreted accordingly.

[0029] Example 1

[0030] A method for reducing the hydrolysis chlorine content in toluene diisocyanate, using a self-heating distillation system (such as Figure 1 ), the self-heat recovery distillation system includes a material distillation section and a heat recovery section, and specifically includes the following steps:

[0031] (1) Material distillation section: The raw materials are fed into the distillation tower through the feed pump for distillation separation. After the vapor at the top of the tower is condensed by the condenser, part of it is returned to the tower, and the other part is extracted; part of the material at the bottom of the tower is fed into the reboiler through the circulation pump, and after vaporization, it enters the bottom of the modified distillation tower, and the other part is extracted;

[0032] (2) Heat recovery section: The circulating fluid in the system absorbs the heat of the steam at the top of the tower in the condenser and then vaporizes. The temperature and pressure are increased by the compressor and then enter the reboiler to heat the material at the bottom of the tower. At the same time, the circulating fluid is condensed and then enters the condenser to absorb heat.

[0033] Optionally, in this embodiment, the raw material contains heavy components such as TDI and hydrolyzed chlorine, the feed temperature is 40°C, the pressure is 600 kPa, and the feed flow rate is 10000 kg / h, of which the TDI flow rate is 9999 kg / h and the TDICL is 1 kg / h.

[0034] Optionally, in this embodiment, the amount of water vapor at the top of the tower is 3011 kg / h, the TDI content is ≥99.90%, and the hydrolyzed chlorine content is ≤0.0015%.

[0035] Optionally, the compressor used in this embodiment is a twin-screw compressor, the circulating working fluid is the steam generated in the distillation tower, the inlet and outlet temperatures of the compressor are 140° C. and 166.3° C., and the inlet and outlet pressures are 360 ​​kPa and 720 kPa, respectively.

[0036] Optionally, the reboiler in this embodiment is a horizontal tube falling film reboiler.

[0037] Optionally, a circulating pump is provided at the bottom of the distillation tower in this embodiment to pump the bottom liquid to the top inlet of the falling film reboiler, vaporize in the reboiler, and enter the bottom of the distillation tower from the bottom of the reboiler.

[0038] Example 2

[0039] Based on the method and system described in Example 1, this example optimizes the feed position.

[0040] Specifically, in this embodiment, the number of theoretical plates is set to 17 and the reflux ratio is set to 2. Figure 2 As shown, the effect of feed position on the hydrolysis chlorine content at the top of the tower was investigated. Figure 2 When the feed position in a is between the 2nd and 4th tower plates, as the number of tower plates at the feed position increases, the hydrolyzed chlorine content at the top of the tower shows a rapid decreasing trend. Compared with the feed position at the 2nd tower plate, when the feed position is at the 4th tower plate, the hydrolyzed chlorine content at the top of the tower is reduced by 85.7%. Further increasing the number of tower plates at the feed position, the decreasing trend of the hydrolyzed chlorine content at the top of the tower is slow. Compared with the feed position at the 4th tower plate, when the feed position is at the 5th tower plate, the hydrolyzed chlorine content at the top of the tower is reduced by 59.1%. This indicates that increasing the number of tower plates at the feed position can effectively reduce the hydrolyzed chlorine content at the top of the tower; Figure 2 As shown in b, starting from the 4th tower plate of the feed position, analysis is performed, from the 4th tower plate to the 8th tower plate, the tower top hydrolysis chlorine content is rapidly reduced, compared with the 4th tower plate of the feed position, when the feed position is the 8th tower plate, the tower top hydrolysis chlorine content is reduced by 97.1%, and now the tower top hydrolysis chlorine content is less than 0.05ppm, and when the feed position tower plate number is 10, the tower top hydrolysis chlorine content is only 0.007ppm, tending to 0, further increasing the feed position tower plate number, the tower top hydrolysis chlorine content changes not obviously. In summary, the feed position is preferably the 8th-15th tower plate, more preferably the 10th tower plate.

[0041] Example 3

[0042] Based on the method and system described in Example 1, this example optimizes the number of theoretical plates.

[0043] Specifically, in this embodiment, the feed position is set to the 10th block, and the reflux ratio is 2. Figure 3 As shown, the influence of the number of theoretical plates on the hydrolysis chlorine content of the tower top was investigated. When the number of theoretical plates is within the range of 5-8, as the number of theoretical plates increases, the hydrolysis chlorine content of the tower top decreases rapidly, and the number of theoretical plates is further increased, and the reduction range of the hydrolysis chlorine of the tower top becomes smaller; When the number of theoretical plates is 10, the hydrolysis chlorine content of the tower top is less than 0.3ppm, and the number of theoretical plates is appropriately increased to 15 blocks, at which time the hydrolysis chlorine content of the tower top is at a low level (0.004ppm), and the number of theoretical plates is continued to be increased, and the change of the hydrolysis chlorine content of the tower top is not obvious, therefore,; Theoretical plates are preferably 10-40 blocks, and the need to consider reducing the reflux ratio is more preferably 15 blocks.

[0044] Example 4

[0045] Based on the method and system described in Example 1, this example optimizes the reflux ratio.

[0046] Specifically, in this embodiment, the feed position is set to the 10th tower plate, and the number of theoretical tower plates is 15. Figure 4 As shown in Figure 2, the effect of reflux ratio on the hydrolysis chlorine content at the top of the tower was investigated. Figure 4 As shown in a, the reflux ratio is in the range of 0.1 to 0.4. As the reflux ratio increases, the hydrolysis chlorine content at the top of the tower decreases rapidly. Compared with the reflux ratio of 0.1, when the reflux ratio is 0.4, the hydrolysis chlorine content at the top of the tower decreases by 95.1%. When the reflux ratio is 0.4, the hydrolysis chlorine content at the top of the tower is 3.9ppm. Figure 4 As shown in Figure b, the further increase of the reflux ratio, the lowering range of the hydrolyzed chlorine at the top of the tower becomes smaller. When the reflux ratio is 1.0, the hydrolyzed chlorine at the top of the tower is 0.004ppm, which tends to 0. Therefore, the reflux ratio is preferably 0.4-4, and is more preferably 1 considering the complexity of the hydrolyzed chlorine and the need to wet the packing.

[0047] Example 5

[0048] Based on the method and system described in Examples 1-4, specifically, the feed position is set to the 10th tray in this embodiment, the number of theoretical trays is 15, the reflux ratio is 1, the feed temperature is 40°C, the pressure is 600kPa, the feed flow rate is 10000kg / h, wherein the TDI flow rate is 9999kg / h, and the TDICL is 1kg / h. After separation by a rectifying tower, the tower top temperature is 146.3°C, the pressure is 4kPa, and the total mass flow rate of the TDI product is 9504kg / hr, the TDI sub-mass flow rate is 9504kg / hr, and the hydrolyzed chlorine trace is obtained. The tower bottom temperature is 156.7°C, the pressure is 6kPa, the total mass flow rate of the TDI product is 496kg / hr, the TDI sub-mass flow rate is 495kg / hr, and the hydrolyzed chlorine trace is 1kg / hr. It shows that there is basically no hydrolyzed chlorine at the top of the tower, and the hydrolyzed chlorine is all in the tower bottom. The required tower top TDI content is ≥99.90%, and the hydrolyzed chlorine content is ≤0.0015%.

[0049] Example 6

[0050] Based on the methods and systems described in Examples 1-5, specifically, this example conducts an economic analysis on the self-regenerative distillation system, the designed feed rate of the distillation tower is 10,000 kg / h, and the amount of water vapor at the top of the tower is 3,011 kg / h. This device can operate at a load of 60-120% of the designed capacity. According to the consumption quota of the self-regenerative distillation system in Table 1, only 192 kW of electricity consumption is required to maintain the normal operation of the entire TDI degradation and hydrolysis chlorine device. According to energy prices: the price of industrial steam is 160 yuan / t, and the price of cooling water is 0.2 yuan / m 3 , electricity price is 0.7 yuan / kWh, and the operating parameters in Table 1, compare the economic efficiency of the self-heat distillation system and traditional distillation. According to GB / T 50441-2007 "Petrochemical Design Energy Consumption Calculation Standard": the energy conversion value of steam (in terms of standard coal) is 103kg / t, circulating water is 0.143kg / t, and electricity is 0.371kg / kW.h. Calculated based on the annual working time of 8000h, the economic comparison between the two is shown in Table 2. After using self-heat distillation technology to reduce the hydrolyzed chlorine in TDI, the operating cost was reduced from 6.144 million yuan to 2.147 million yuan, which can reduce the cost by 65.06% each year, with great social and economic benefits.

[0051] Table 1 Consumption quota of heat recovery distillation system

[0052]

[0053] The calculation process is as follows:

[0054] Traditional distillation operating costs: (steam consumption 4.4t / h, circulating cooling water 320m3 / h):

[0055] Steam consumption:

[0056] 4.4t / h×160 yuan / t×8000h / year=5.632 million yuan / year;

[0057] Circulating water consumption:

[0058] 320m3 / h×0.2 ​​yuan / ton×8000 hours / year=512,000 yuan / year;

[0059] Annual operating cost of traditional distillation:

[0060] 5.632 million yuan + 512,000 yuan = 6.144 million yuan

[0061] Annual operating cost of self-regenerative distillation system:

[0062] Power consumption:

[0063] 192×0.7 yuan / degree×8000 hours / year=1.075 million yuan;

[0064] Circulating water consumption:

[0065] 30m3 / h×0.2 ​​yuan / ton×8000 hours / year=48,000 yuan / year;

[0066] Steam consumption:

[0067] 0.8t / h×160 yuan / ton×8000 hours / year=1.024 million yuan / year;

[0068] Annual operating cost of self-regenerative distillation system:

[0069] 1.075 million yuan + 48,000 yuan + 1.024 million yuan = 2.147 million yuan

[0070] The annual operating cost that can be saved by using the self-heat recovery distillation system is:

[0071] 6.144 million yuan - 2.147 million yuan = 3.997 million yuan, a decrease of 65.06%.

[0072] Table 2 Comparison of economic performance between traditional distillation and self-regenerative distillation system

[0073] index Traditional crafts Self-regenerative distillation process Steam cost / 10,000 yuan 563.2 102.4 Cooling water cost / 10,000 yuan 51.2 4.8 Electricity fee / 10,000 yuan 0 107.5 Total / 10,000 yuan 614.4 214.7

[0074] The present invention proves once again that the large-scale treatment of products with high TDI content by the self-reheating distillation method can achieve better results. By optimizing the optimal feed position, the number of theoretical plates, the reflux ratio, etc., the hydrolysis chlorine content can be further reduced, the quality of TDI can be improved, the energy consumption can be reduced, the energy utilization rate can be improved, and the economy can be improved. Therefore, the present invention is more suitable for industrial application.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing the hydrolysis chlorine content in toluene diisocyanate, characterized in that: Adopting self-heating distillation system, The self-heat recovery distillation system includes a material distillation section and a heat recovery section, and specifically includes the following steps: (1) Material distillation section: The raw materials are passed into the distillation tower for distillation separation. After the top steam is condensed by the condenser, part of it is returned to the tower, and the other part is extracted; part of the bottom material of the tower enters the reboiler through the circulation pump, and after vaporization, it enters the bottom of the modified distillation tower, and the other part is extracted; (2) Heat recovery section: The circulating fluid in the system absorbs the heat of the tower top steam in the condenser and then vaporizes. The temperature and pressure are increased by the compressor and then enter the reboiler to heat the tower bottom material. At the same time, the circulating fluid is condensed and then enters the condenser to absorb heat. The number of theoretical plates of the distillation tower is 10-40; the feed position of the distillation tower is the 8th to 15th plate; the reflux ratio of the distillation tower is 0.5-1.0; The feed temperature of the raw materials is 40° C., the pressure is 600 kPa, and the feed flow rate is 10000 kg / h, of which the TDI flow rate is 9999 kg / h and the TDICL flow rate is 1 kg / h.

2. The method according to claim 1, characterized in that The compressor is a twin-screw compressor, and the circulating working medium is the steam generated in the distillation tower.

3. The method according to claim 1, characterized in that The reboiler is a horizontal tube falling film reboiler.

4. The method according to claim 1, characterized in that: A circulating pump is arranged at the bottom of the distillation tower to pump the bottom liquid of the tower to the top inlet of the reboiler, vaporize in the reboiler, and enter the bottom of the distillation tower from the bottom of the reboiler.

Images