Continuous hydrolysis and water washing apparatus for trifluoropropylmethyldichlorosilane

Abstract

The utility model relates to a continuous hydrolysis and washing device of trifluoropropyl methyl dichlorosilane, belongs to the organic silicon monomer post -treatment equipment technical field, the device includes the continuous hydrolysis and the phase separation system, washing and phase separation system and waste gas treatment system that communicate in proper order, the utility model discloses the combination structure of stirrer and venturi mixer in hydrolysis kettle and washing kettle, greatly strengthened the mass transfer and mixing efficiency of liquid liquid two phases, the automatic control loop that is constituted with the outlet tee control valve of spectroscopic analysis appearance and export is set up in hydrolysis and each level phase separation jar discharge, realized real -time accurate monitoring and intelligent control to oil -water interface, and the continuous, stable, efficient phase separation is guaranteed, the utility model solves the problem of low efficiency, extensive control, quality unstable of traditional intermittent process, is applicable to the large -scale, continuous, clean production of high -quality fluorine silicon monomer hydrolyzate.

Description

Technical Field

[0001] This utility model relates to the technical field of fine chemicals and post-processing equipment for organosilicon monomers. Specifically, it relates to an apparatus for the continuous hydrolysis, separation and washing of trifluoropropylmethyldichlorosilane to produce high-purity trifluoropropylmethyldichlorosilane hydrolysate. Background Technology

[0002] Trifluoropropylmethyldichlorosilane is a key monomer in the synthesis of high-performance fluorosilicone polymers such as fluorosilicone rubber and fluorosilicone oil. As a crucial step in its downstream processing, the hydrolysis reaction of this monomer is essential. Its hydrolysate is a direct raw material for preparing various fluorosilicone intermediates, such as trifluoropropylmethylcyclotrisiloxane (D3F), and its purity and quality directly affect the performance of the final polymer.

[0003] Regarding the hydrolysis of trifluoropropylmethyldichlorosilane, numerous existing technologies have been reported, both in terms of the hydrolysis process and the equipment involved. For example, CN101875726A mentions a method for preparing polyorganosiloxanes by hydrolyzing dimethyldichlorosilane, but does not address the issue of continuous industrial separation of the organic phase and the dilute acid phase; CN101817505A mentions a method for directly obtaining gaseous hydrogen chloride by hydrolyzing dimethyldichlorosilane, but the combined separator using a plate column cannot visually observe the separation state of the two phases, thus failing to efficiently remove hydrochloric acid from the siloxane; CN104058370A mentions a method for adsorbing siloxanes with resin during the hydrolysis of dimethyldichlorosilane, but industrial scale-up has not been achieved; CN210385810U mentions a method for pyrolyzing dimethyldichlorosilane hydrolysates, but does not guarantee the removal of hydrochloric acid from the siloxanes after hydrolysis, posing a risk of damaging downstream pyrolyzed polymers. While other methods for the continuous hydrolysis of chlorosilanes have been explored in the industry, they generally suffer from problems such as batch operation, severe equipment corrosion, complex processes, or poor adaptability to specific monomers. More importantly, these methods have failed to fundamentally solve the core challenges of low mass transfer efficiency between liquid and liquid phases and accurate, continuous monitoring and control of the phase interface.

[0004] Therefore, developing a continuous hydrolysis and washing device for trifluoropropylmethyldichlorosilane that can achieve efficient mixing, precise separation, continuous and stable operation, and significantly improve product quality and production efficiency has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of the above-mentioned state of the prior art, the purpose of this utility model is to overcome the shortcomings of existing intermittent hydrolysis devices, such as low production efficiency, uneven mass and heat transfer, poor phase separation control accuracy, and large product quality fluctuations, and to provide a trifluoropropylmethyldichlorosilane continuous hydrolysis and washing device with reasonable structural design that can achieve enhanced mixing and precise phase separation.

[0006] The present invention adopts the following technical solution:

[0007] The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus includes a continuous hydrolysis and phase separation system and a washing and phase separation system. The continuous hydrolysis and phase separation system includes a hydrolysis kettle, a hydrolysis separator, and a hydrochloric acid storage tank. The washing and phase separation system includes a washing kettle, a washing separator, and a hydrolyzed product tank. The outlet of the hydrolysis kettle is connected to the inlet of the hydrolysis separator via a hydrolysis circulation pump. The outlet of the hydrolysis separator is equipped with a spectrometer electrically connected to a three-way control valve to form an automatic level control loop. The spectrometer is connected to the inlets of the hydrochloric acid storage tank and the washing kettle via the three-way control valve. The outlet of the washing kettle is connected to the inlet of the washing separator via a washing circulation pump. The outlet of the washing separator is equipped with a spectrometer electrically connected to a three-way control valve to form an automatic level control loop. The spectrometer is connected to the inlets of the hydrolysis kettle and the hydrolyzed product tank via the three-way control valve.

[0008] According to this utility model, preferably, a water washing kettle, a water washing separator, and a spectrometer electrically connected to a three-way control valve to form an automatic liquid level control loop constitute a water washing and phase separation unit. The water washing and phase separation system includes at least two water washing and phase separation units connected in series.

[0009] According to this utility model, preferably, both the hydrolysis vessel and the washing vessel are equipped with a stirring device and a Venturi mixer, and the material is fed through the Venturi mixer.

[0010] According to this utility model, preferably, the inlet of the hydrolysis reactor is connected to the hydrolysis raw material storage tank, and the hydrolysis circulation pump is also connected to the inlet of the hydrolysis reactor through the hydrolysis reactor cooler to form a circulation loop.

[0011] According to this utility model, preferably, the outlet of the hydrochloric acid storage tank is also connected to the inlet of the hydrolysis separator via an organic phase feeding pump to form a circulation loop; more preferably, the outlet of the hydrochloric acid storage tank is also connected to a hydrochloric acid delivery pump.

[0012] According to this utility model, preferably, the outlet of the hydrolysate finished product tank is connected to a hydrolysate feeding pump.

[0013] According to the present invention, preferably, the trifluoropropylmethyldichlorosilane continuous hydrolysis and washing device further includes a waste gas treatment system. The waste gas treatment system includes an alkaline tank and an alkaline absorption tower. The hydrolysis kettle, hydrolysis separator, and hydrochloric acid storage tank are all connected to the alkaline tank. The alkaline tank is connected to the upper part of the alkaline absorption tower through a circulating pump. The top of the alkaline absorption tower is connected to the waste gas treatment device through an induced draft fan.

[0014] More preferably, at least two alkali tanks are provided and connected in series; more preferably, the inlet of the alkali tank is connected to a Venturi mixer and fed through the Venturi mixer, and the alkali tank is also connected to the inlet of the alkali tank through a circulating pump.

[0015] The beneficial effects of this utility model are as follows:

[0016] 1. Achieve efficient continuous production: By integrating multiple unit operations such as hydrolysis, phase separation, and water washing into a continuous unit, the traditional intermittent operation mode is changed, which greatly improves equipment utilization and production efficiency.

[0017] 2. Precise and intelligent phase separation, stable and reliable operation: Utilizing a closed-loop control circuit of a spectral imaging analyzer and a three-way control valve, real-time, precise, and automatic monitoring and control of the liquid-liquid phase interface is achieved. This design intelligently responds to interface changes caused by feed fluctuations, completely avoiding human error, ensuring that the organic phase product is free of acid and the aqueous phase is free of entrained products, significantly improving product purity and yield, and minimizing subsequent washing load.

[0018] 3. Enhanced mass and heat transfer for improved product quality: A combination of a Venturi mixer and mechanical stirring can be introduced into the hydrolysis reactor, creating extremely vigorous mixing conditions. This ensures thorough mixing of the reactants, accelerating the reaction rate and preventing localized overheating through efficient heat dispersion. This results in hydrolysate products with a narrower molecular weight distribution and more uniform quality. Furthermore, a combination of a Venturi mixer and mechanical stirring can be introduced into the washing reactor, creating extremely vigorous mixing conditions. This ensures instantaneous and thorough contact between the reactants and washing water, accelerating the washing process and effectively removing residual hydrochloric acid from the hydrolysate.

[0019] 4. Resource recycling and environmental protection: A two-stage series washing process can be adopted to realize the cascade utilization of washing water, including secondary fresh water → primary reuse → hydrolysis reuse, which greatly reduces the consumption of fresh water and wastewater discharge. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the main structure of this utility model.

[0021] The components include: 1. Hydrolysis raw material storage tank; 2. Hydrolysis reactor cooler; 3. First Venturi mixer; 4. Hydrolysis reactor; 5. Hydrolysis circulating pump; 6. Hydrolysis separator; 7. First spectrometer; 8. Hydrochloric acid temporary storage tank; 9. Organic phase feed pump; 10. Hydrochloric acid transfer pump; 11. First-stage water washing separator; 12. Second spectrometer; 13. Second Venturi mixer; 14. First-stage water washing reactor; 15. First-stage water washing circulating pump; 16. Third Venturi mixer; 17. Second-stage water washing reactor; 18. Second-stage water washing circulating pump; 19. Second-stage water washing separator; 20. Third spectrometer; 21. Hydrolyzed product tank; 22. Hydrolyzed product feed pump; 23. First-stage alkali tank; 24. Fourth Venturi mixer; 25. First-stage circulating pump; 26. Second-stage alkali tank; 27. Alkali absorption tower; 28. Second-stage circulating pump; 29. ​​Exhaust fan. Detailed Implementation

[0022] This utility model discloses a continuous hydrolysis and washing device for trifluoropropylmethyldichlorosilane, comprising a continuous hydrolysis and phase separation system and a washing and phase separation system connected sequentially by pipelines. In a preferred embodiment, it also includes a waste gas treatment system. All specific equipment is conventional and existing equipment in the chemical industry.

[0023] The spectrometer used in this invention is an online analytical instrument based on near-infrared spectroscopy or visible light imaging principles. It can distinguish the differences in transmittance and specific spectral characteristics between the organic and aqueous phases in real time, thereby accurately identifying and tracking the phase interface position. Existing equipment, such as the spectrometer model HS-iSJ16L1D050A1H1S3F1D1V1E1C1T000 available from Nantong Haishi Optoelectronics Co., Ltd., with a signal output of 4-20mA + video output, TCP / IP communication, and 485 communication, is electrically connected to a three-way control valve to form an automatic liquid level control loop. The three-way control valve switches according to the different analytical results of the spectrometer for the aqueous and organic phases. The three-way control valve is also a conventional existing device, such as the L-type pneumatic three-way valve available from Wuxi Guangming Anticorrosion Valve Factory.

[0024] The Venturi mixer used in this invention is also an existing device, such as the adjustable Venturi injector reported in CN208373371U. The motive fluid inlet of the Venturi mixer is connected to the feed line of the corresponding device, its suction port is connected to the corresponding aqueous phase pipeline, and its outlet leads to the interior of the corresponding device. The Venturi mixer utilizes high-speed flowing material as the motive fluid to draw in hydrolysate, achieving uniform mixing at the microscale in a very short time, greatly enhancing mass transfer and the reaction / washing process.

[0025] In a preferred embodiment of this invention, both the hydrolysis separator 6 and the washing separator are vertical tanks with internal rectifiers to facilitate rapid and stable stratification of the two phases. The top of the hydrolysis vessel 4 is provided with an air vent, and the washing vessel can be connected to a tap water pipeline for water replenishment.

[0026] In a preferred embodiment, the trifluoropropylmethyldichlorosilane continuous hydrolysis and washing device can also be equipped with a DCS automatic control system for centralized control of the start, stop, and interlocking of each feed pump, agitator, and automatic valve, and for receiving and processing signals from the spectrometer to achieve fully automated continuous operation. The spectrometer performs real-time detection of the interface in the continuous liquid separation process and provides the detection results to the DCS system in 4-20mA format. The video output function enables real-time remote video monitoring of the interface. The DCS system then controls the three-way control valve to switch according to the detection results, thereby achieving automated closed-loop control of the continuous liquid separation process. This reduces the need for manual observation via sight glasses and manual valve control, improving production safety and the level of process automation. The DCS system model that can be used in this invention is, for example, MACSV 6.5.4 CHINESE, available from Hangzhou Hollysys Automation Co., Ltd. The control program can be selected from existing programs or written by those skilled in the art according to different needs. Connecting to a DCS (Distributed Control System) can improve automation and safety, reduce manual intervention, lower labor intensity, and also prevent operators from directly contacting corrosive chemicals (such as hydrochloric acid and hydrogen chloride gas), thus improving production safety.

[0027] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the implementation of the present invention is not limited thereto.

[0028] Example 1

[0029] like Figure 1 As shown, a continuous hydrolysis and washing device for trifluoropropylmethyldichlorosilane includes a continuous hydrolysis and phase separation system and a washing and phase separation system. The continuous hydrolysis and phase separation system includes a hydrolysis kettle 4, a hydrolysis separating tank 6, and a hydrochloric acid temporary storage tank 8. The washing and phase separation system includes a washing kettle, a washing separating tank, and a hydrolyzed product tank 21. The outlet of the hydrolysis kettle 4 is connected to the inlet of the hydrolysis separating tank 6 via a hydrolysis circulation pump 5. The outlet of the hydrolysis separating tank 6 is equipped with a spectrometer electrically connected to a three-way control valve to form an automatic liquid level control loop. The spectrometer is connected to the inlets of the hydrochloric acid temporary storage tank 8 and the washing kettle via the three-way control valve. The outlet of the washing kettle is connected to the inlet of the washing separating tank via a washing circulation pump. The outlet of the washing separating tank is equipped with a spectrometer electrically connected to a three-way control valve to form an automatic liquid level control loop. The spectrometer is connected to the inlets of the hydrolysis kettle 4 and the hydrolyzed product tank 21 via the three-way control valve.

[0030] Example 2

[0031] As described in Example 1, the difference is:

[0032] A water washing kettle, a water washing separator, and a spectrometer electrically connected to a three-way control valve to form an automatic liquid level control loop constitute a water washing and phase separation unit. The water washing and phase separation system includes two water washing and phase separation units connected in series.

[0033] That is, the water washing and phase separation system includes a primary water washing tank 14, a primary water washing separator 11, a secondary water washing tank 17, and a secondary water washing separator 19. The outlet of the primary water washing tank 14 is connected to the inlet of the primary water washing separator 11 through a primary water washing circulation pump 15. The outlet of the primary water washing separator 11 is equipped with a second spectrometer 12, which is electrically connected to a three-way control valve and forms an automatic liquid level control loop. The second spectrometer 12 is connected to the inlets of the hydrolysis tank 4 and the secondary water washing tank 17 through a three-way control valve. The outlet of the secondary water washing tank 17 is connected to the inlet of the secondary water washing separator 19 through a secondary water washing circulation pump 18. The outlet of the secondary water washing separator 19 is equipped with a third spectrometer 20, which is electrically connected to a three-way control valve and forms an automatic liquid level control loop. The third spectrometer 20 is connected to the inlets of the primary water washing tank 14 and the hydrolysate finished product tank 21 through a three-way control valve.

[0034] Example 3

[0035] As described in Example 2, the difference is:

[0036] Both the hydrolysis vessel 4 and the washing vessel are equipped with a stirring device and a Venturi mixer, and the feed is fed through the Venturi mixer.

[0037] Specifically: the hydrolysis reactor 4 is equipped with a first Venturi mixer 3, the primary washing reactor 14 is equipped with a second Venturi mixer 13, and the secondary washing reactor 17 is equipped with a third Venturi mixer 16. All three reactors—hydrolysis reactor 4, primary washing reactor 14, and secondary washing reactor 17—are equipped with stirring devices. The outlet of the primary washing reactor 14 is connected to the inlet of the first Venturi mixer 3 via a primary washing circulation pump 15, and the outlet of the secondary washing reactor 17 is connected to the inlet of the third Venturi mixer 16 via a secondary washing circulation pump 18.

[0038] Example 4

[0039] As described in Example 3, the difference is:

[0040] The inlet of the hydrolysis reactor 4 is connected to the hydrolysis raw material storage tank 1, and the hydrolysis circulation pump 5 is also connected to the inlet of the hydrolysis reactor 4 through the hydrolysis reactor cooler 2 to form a circulation loop.

[0041] The outlet of the hydrochloric acid storage tank 8 is also connected to the inlet of the hydrolysis separation tank 6 via the organic phase feeding pump 9 to form a circulation loop; the outlet of the hydrochloric acid storage tank 8 is also connected to the hydrochloric acid transfer pump 10, and the outlet of the hydrolysate finished product tank 21 is connected to the hydrolysate feeding pump 22.

[0042] Example 5

[0043] As described in Example 4, the difference is:

[0044] The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing device also includes a waste gas treatment system, which includes an alkali tank and an alkali absorption tower 27. The hydrolysis kettle 4, the hydrolysis separator 6, and the hydrochloric acid temporary storage tank 8 are all connected to the alkali tank. The alkali tank is connected to the upper part of the alkali absorption tower 27 through a circulating pump. The top of the alkali absorption tower 27 is connected to the waste gas treatment device through an induced draft fan 29.

[0045] Example 6

[0046] As described in Example 5, the difference is:

[0047] There are two alkali solution tanks connected in series.

[0048] Specifically, the alkali solution tanks include a primary alkali solution tank 23 and a secondary alkali solution tank 26, which are connected in series. The inlet of the primary alkali solution tank 23 is also equipped with a fourth Venturi mixer 24. The outlet of the primary alkali solution tank 23 is connected to the inlet of the fourth Venturi mixer 24 via a primary circulation pump 25. The outlet of the secondary alkali solution tank 26 is connected to the upper part of the alkali absorption tower 27 via a secondary circulation pump 28. The gas outlets of the hydrolysis reactor 4, the hydrolysis separator 6, and the hydrochloric acid temporary storage tank 8 are all connected to the inlet of the primary alkali solution tank 23.

[0049] The material flow direction and operation process of a preferred embodiment of this utility model are as follows:

[0050] 1. Continuous Hydrolysis and Phase Separation: Trifluoropropylmethyldichlorosilane feedstock enters the first Venturi mixer 3 of the hydrolysis reactor 4 from the feedstock storage tank 1. Process water (tap water for initial start-up, recycled water from the primary washing separator 11 during normal operation) and silane monomer undergo instantaneous and vigorous mixing and emulsification in the throat of the first Venturi mixer 3 before entering the hydrolysis reactor 4. A stirrer in the hydrolysis reactor 4 further maintains system mixing. The hydrolysis reaction proceeds rapidly, and excess gas can be recycled or extracted. The resulting mixture is continuously pumped into the hydrolysis separator 6. A first spectrometer on the outlet pipe of the hydrolysis separator 6 monitors the interface in real time and ensures a continuous and stable flow of the upper hydrochloric acid phase to the hydrochloric acid storage tank 8 by controlling the switching of the three-way control valve, while the lower organic phase (crude hydrolysis product) is continuously and smoothly sent to the primary washing reactor 14. The hydrochloric acid in the hydrochloric acid storage tank 8 is removed by the hydrochloric acid transfer pump 10.

[0051] 2. Washing and Phase Separation: The organic phase from the hydrolysis section enters the primary washing tank 14. Reclaimed water from the secondary washing separator 19 is efficiently mixed with the organic phase and washed via the second Venturi mixer 13 to neutralize hydrochloric acid. The washed mixture then enters the primary washing separator 11. Under the control of the second spectrometer 12 and a three-way control valve, the upper washing wastewater (acidic) is precisely separated and entirely returned to the hydrolysis tank 4 as reaction water, achieving resource recovery. The lower organic phase enters the secondary washing tank 17. In the secondary washing tank 17, the organic phase and fresh tap water undergo final washing via the third Venturi mixer 16. After washing, the organic phase enters the secondary washing separator 19. Under the control of the third spectrometer 20 and a three-way control valve, the upper washing water (nearly neutral) is separated and entirely sent to the primary washing tank 14 as primary washing water, achieving cascade utilization. After final phase separation, the lower layer of completely neutral and pure trifluoropropylmethyldichlorosilane hydrolysate is continuously fed into the hydrolysate finished product tank 21 for storage and use in subsequent processes.

[0052] 3. Waste gas treatment: The acidic gas from the hydrolysis kettle 4, hydrolysis separator 6, and hydrochloric acid storage tank 8 is transferred to the primary alkali tank 23 for neutralization and absorption, and then enters the secondary alkali tank 26 for absorption. The alkali is pumped into the alkali absorption tower 27 by the secondary circulation pump 28 for further absorption. Finally, the waste gas enters the waste gas treatment device for treatment.

[0053] This invention achieves an upgrade in hydrolysate production from intermittent to continuous, from extensive to precise, and from high consumption to energy saving through the core design of "enhanced mixing (Venturi + stirring) + intelligent phase separation (spectral analysis + closed-loop control) + multi-stage washing". It has significant advantages such as stable product quality, high production efficiency, and low resource consumption.

Claims

1. A continuous hydrolysis and washing apparatus for trifluoropropylmethyldichlorosilane, characterized in that, The device includes a continuous hydrolysis and phase separation system and a water washing and phase separation system. The continuous hydrolysis and phase separation system includes a hydrolysis kettle (4), a hydrolysis separator (6), and a hydrochloric acid storage tank (8). The water washing and phase separation system includes a water washing kettle, a water washing separator, and a hydrolyzed product tank (21). The outlet of the hydrolysis kettle (4) is connected to the inlet of the hydrolysis separator (6) through a hydrolysis circulation pump (5). The outlet of the hydrolysis separator (6) is equipped with a spectrometer that is electrically connected to a three-way control valve and forms an automatic liquid level control loop. The spectrometer is connected to the inlet of the hydrochloric acid storage tank (8) and the water washing kettle through the three-way control valve. The outlet of the water washing kettle is connected to the inlet of the water washing separator through a water washing circulation pump. The outlet of the water washing separator is equipped with a spectrometer that is electrically connected to a three-way control valve and forms an automatic liquid level control loop. The spectrometer is connected to the inlet of the hydrolysis kettle (4) and the hydrolyzed product tank (21) through the three-way control valve.

2. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 1, characterized in that, A water washing kettle, a water washing separator, and a spectrometer electrically connected to a three-way control valve to form an automatic liquid level control loop constitute a water washing and phase separation unit. The water washing and phase separation system includes at least two water washing and phase separation units connected in series.

3. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 1 or 2, characterized in that, Both the hydrolysis vessel (4) and the washing vessel are equipped with a stirring device and a Venturi mixer, and the feed is fed through the Venturi mixer.

4. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 3, characterized in that, The inlet of the hydrolysis reactor (4) is connected to the hydrolysis raw material storage tank (1), and the hydrolysis circulation pump (5) is also connected to the inlet of the hydrolysis reactor (4) through the hydrolysis reactor cooler (2) to form a circulation loop.

5. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 4, characterized in that, The outlet of the hydrochloric acid storage tank (8) is also connected to the inlet of the hydrolysis separator (6) via an organic phase feed pump (9) to form a circulation loop; the outlet of the hydrochloric acid storage tank (8) is also connected to a hydrochloric acid transfer pump (10).

6. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 5, characterized in that, The outlet of the hydrolysate finished product tank (21) is connected to the hydrolysate feeding pump (22).

7. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to any one of claims 4-6, characterized in that, The trifluoropropylmethyldichlorosilane continuous hydrolysis washing device also includes a waste gas treatment system, which includes an alkali tank and an alkali absorption tower (27). The hydrolysis kettle (4), the hydrolysis separator (6), and the hydrochloric acid storage tank (8) are all connected to the alkali tank. The alkali tank is connected to the upper part of the alkali absorption tower (27) through a circulating pump. The top of the alkali absorption tower (27) is connected to the waste gas treatment device through an induced draft fan (29).

8. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 7, characterized in that, There are at least two alkali tanks connected in series.

9. The trifluoropropylmethyldichlorosilane continuous hydrolysis and washing apparatus according to claim 8, characterized in that, The inlet of the alkali tank is connected to a Venturi mixer and fed through the Venturi mixer. The alkali tank is also connected to the inlet of the alkali tank via a circulating pump.

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