A method for removing heavy boiler from a propylene glycol refining process

Abstract

This invention provides a method for removing reboilers during propylene glycol refining, relating to the field of propylene glycol refining technology. This invention splits the material in the bottom of the propylene glycol de-refining tower into a first material stream and a second material stream, and implements differentiated vaporization rate control: by precisely controlling the vaporization rate of the first material stream to be significantly lower than that of the second material stream, the overall residence time of reboilers in the refining system is effectively shortened. This not only significantly inhibits the occurrence of side reactions and improves the product yield of propylene glycol, but also reduces reliance on additional high-energy-consuming post-processing equipment, thus reducing equipment investment costs. Compared with traditional reboiler removal processes, this invention can alleviate the problem of pipeline and equipment blockage caused by reboiler accumulation at the source, and has outstanding advantages of low energy consumption and strong operational stability. While ensuring product quality, it achieves simultaneous improvement in process economy and operational reliability.

Description

Technical Field

[0001] This invention relates to the field of propylene glycol refining technology, and more specifically to a method for removing reboiling substances during the refining process of propylene glycol. Background Technology

[0002] 1,2-Propanediol, a colorless, odorless, and non-toxic chemical raw material, is widely used in the pharmaceutical, cosmetic, and food industries. It is a key raw material for the production of unsaturated polyesters and can also be used as a pharmaceutical solvent, a cosmetic moisturizer, and an ingredient in the food industry.

[0003] Currently, the main method used abroad to produce 1,2-propanediol is the hydration of propylene oxide. This process, in addition to producing the target product, also generates dipropylene glycol, tripropylene glycol, and small amounts of glycols with higher carbon numbers. In China, the mainstream production process is the transesterification of propylene carbonate and methanol. This method can co-produce dimethyl carbonate and typically uses alkali metals such as sodium methoxide as catalysts. In recent years, although the transesterification method has been widely adopted in China, it suffers from incomplete catalyst removal: after the reaction, sodium methoxide needs to be converted to sodium carbonate or sodium bicarbonate and filtered out, but a small amount of catalyst remains in the crude propylene glycol and enters the subsequent refining process. During the refining process, the crude propylene glycol passes through a light-light product removal tower and a heavy-light product removal tower. The residual sodium methoxide accumulates in the bottom of the heavy-light product removal tower, causing the propylene glycol to react further at high temperatures to generate more dipropylene glycol, tripropylene glycol, and high-carbon-number glycols, which are reboilers. These reboilers reduce the material's flowability and increase its viscosity, easily causing blockages in pipelines and pumps.

[0004] The current conventional method involves sending the material containing a large amount of propylene glycol from the bottom of the de-boiling tower to other equipment, such as a high-vacuum evaporator or a scraped evaporator. The recovered propylene glycol is then reintroduced into the refining process, while the reboiled material is further processed to recover dipropylene glycol and other materials. This method leads to an increase in the amount of propylene glycol recycled, higher energy consumption, and increased equipment investment. Furthermore, the prolonged residence time of propylene glycol in the system intensifies the polymerization reaction, further reducing the yield of propylene glycol.

[0005] Therefore, there is an urgent need to develop a separation method that can efficiently remove reboiling from crude propylene glycol in order to improve the economic efficiency of the process and solve the problems of high energy consumption, easy equipment blockage and low product yield in the existing technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention discloses a method for removing reboilers during the refining process of propylene glycol. The method involves splitting the bottom material of the de-refining tower in the transesterification process of propylene glycol refining into a first material stream and a second material stream. The vaporization rates of the two material streams are controlled by heating each stream, ensuring that the vaporization rate of the second material stream is higher than that of the first material stream. Reboiler impurities are removed by sampling the second material stream, thereby reducing the accumulation of reboilers during the propylene glycol refining process and increasing the yield of propylene glycol.

[0007] To achieve the above technical objectives, this invention proposes a method for removing reboilers during the purification of propylene glycol, comprising the following steps: (1) The crude propylene glycol is separated sequentially by passing it through a light product removal tower and a heavy product removal tower; (2) The discharge from the bottom of the de-weighting tower is divided into a first material stream and a second material stream. The first material stream and the second material stream are heated to different gasification rates, and the gasification rate of the second material stream is higher than that of the first material stream. (3) The steam generated by heating the first material stream is returned to the deweighting tower; (4) After heating the second material stream, gas-liquid separation is performed. The resulting gas phase is returned to the de-weighting tower, and the liquid phase is split into a production stream and a circulation stream. The circulation stream is returned to the heating process inlet of the second material stream. Thus, reboilers are removed through gas-liquid separation of the second material stream.

[0008] This invention effectively solves the key technical challenges in the removal of reboilers by controlling the diversion of the bottom material in the de-heavy distillation column during propylene glycol refining and employing differentiated vaporization methods. Specifically, this invention diverts the bottom material (including dipropylene glycol, 1,2-propanediol, sodium bicarbonate, etc.) of the de-heavy distillation column into a first material stream and a second material stream, forming a complementary dual-path processing method: the first material stream primarily bears the heating load of the de-heavy distillation column, providing it with a vaporization heat source and maintaining the distillation cycle; the second material stream is mainly used for the removal and separation of reboilers, achieving specialized division of process functions and improving efficiency.

[0009] The research team of this invention discovered that heavy components generally have high boiling points and high viscosity. Based on this, by adjusting the heating intensity of the two material streams, the vaporization rate of the second material stream is made higher than that of the first material stream. This allows a small amount of vaporizable light components in the heavy components to separate from the heavy components, while the unvaporized heavy components can be discharged as residue, preventing their enrichment and impact on separation efficiency. Furthermore, controlling the vaporization rate of the second material stream to be higher than that of the first material stream allows reboilers to be enriched and removed in the second material stream, thereby significantly reducing the risk of equipment blockage, reducing the residence time and polymerization loss of propylene glycol under high-temperature conditions, and avoiding additional equipment investment and increased energy consumption. Ultimately, while ensuring stable system operation, this significantly improves the product yield and process economy of propylene glycol.

[0010] In a further example of the present invention, the vaporization rate of the first material flow is 5% to 10%, and the vaporization rate of the second material flow is 25% to 50%. It should be noted that the vaporization rate refers to the ratio of the material flow rate after vaporization after heating to the material flow rate before heating.

[0011] In a further example of the present invention, the mass flow rate ratio of the first material flow to the second material flow is (5~20):(1~5).

[0012] In a further example of the invention, the mass ratio of the extracted stream to the circulating stream is (5~15):(1~5).

[0013] In a further example of the present invention, the pressure of the first material stream and / or the second material stream extracted from the deweighting tower is 2~10 kPaA and the temperature is 130~160°C.

[0014] In a further example of the present invention, the first material flow is heated to 135~145°C; And / or, heat the second material stream to 145~155°C.

[0015] In a further example of the present invention, the operating pressure of the gas-liquid separation is 2~10 kPaA, and the controlled temperature is 130~160℃.

[0016] In a further example of the invention, the second material stream is distributed to multiple parallel branch material streams for heating, and each branch material stream, after being heated, performs the gas-liquid separation operation independently or by merging.

[0017] The second material flow of this invention can be divided into multiple (two or more) parallel branch material flows, each heated by two or more heaters. This method is mainly suitable for situations where the heat exchange area and processing capacity of a single heater are limited; using two or more heaters in parallel allows for the sharing of the processing load. Since the heat exchange area of ​​a heater is limited by its shell diameter and tube length, designing a single large-sized device not only presents significant structural design challenges but also presents difficulties in transportation and installation. Therefore, by using a parallel connection, processing capacity can be guaranteed while improving the flexibility of equipment configuration.

[0018] It should be noted that when the second material flow is distributed to two or more parallel branch material flows and heated, the gasification rate of each branch material flow is the same.

[0019] In a further example of the invention, the device used to perform the heating operation is any one of a forced circulation reboiler, a falling film reboiler, or a thermosiphon reboiler.

[0020] The operating pressure of the light-weight removal tower is 20~40 kPaA, and the controlled temperature is 146~163℃. And / or, the operating pressure of the deweight removal tower is 2~10 kPaA, and the controlled temperature is 130~160℃.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention splits the propylene glycol de-removal tower bottom feed into a first feed stream and a second feed stream, and implements differentiated vaporization rate control: by precisely controlling the vaporization rate of the first feed stream to be significantly lower than that of the second feed stream, and collecting reboiler impurities from the second feed stream, it effectively shortens the overall residence time of reboilers in the refining system. This not only significantly inhibits the occurrence of side reactions and improves the product yield of propylene glycol, but also reduces reliance on additional high-energy-consuming post-processing equipment, thus reducing equipment investment costs. Compared with traditional reboiler removal processes, this invention can alleviate the problem of pipeline and equipment blockage caused by reboiler accumulation at the source, and has outstanding advantages of low energy consumption and strong operational stability. While ensuring product quality, it achieves simultaneous improvement in process economy and operational reliability. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of an apparatus structure for a method of removing reboilers in the propylene glycol refining process for implementing the present invention is shown; for the sake of brevity, only the reboiler connection structure of the reboiler tower is shown in the figure; Figure 2 This diagram illustrates a device structure for a method of removing reboilers during the propylene glycol refining process in Examples 1-2 of the present invention; for the sake of brevity, only the reboiler connection structure of the reboiler tower is shown in the diagram. Figure 3 A structural diagram of an apparatus for removing reboilers during the propylene glycol refining process in Example 3 of the present invention is shown; for the sake of brevity, only the reboiler connection structure of the reboiler tower is shown in the diagram.

[0024] The above figures include the following reference numerals: 1-De-weight tower, 2-First reboiler, 3-Second reboiler, 4-Gas-liquid separator, 5-Third reboiler. Detailed Implementation

[0025] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0026] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which this invention pertains.

[0027] A method for removing reboilers during propylene glycol refining includes the following steps: (1) The crude propylene glycol is separated sequentially by passing it through a light product removal tower and a heavy product removal tower 1; (2) The discharge from the bottom of the de-weighting tower 1 is divided into a first material stream and a second material stream. The first material stream and the second material stream are heated to different gasification rates, and the gasification rate of the second material stream is higher than that of the first material stream. (3) The steam generated by heating the first material flow is returned to the deweighting tower 1; (4) After heating the second material stream, gas-liquid separation is performed. The resulting gas phase is returned to the de-heavy tower 1, and the liquid phase is split into a production stream and a circulation stream. The circulation stream is returned to the heating process inlet of the second material stream. Thus, reboilers are removed through gas-liquid separation of the second material stream.

[0028] It should be noted that the equipment used in the method for removing reboilers during the propylene glycol refining process of this invention is not limited; optionally, the connection relationship of the various devices can be as follows: Figure 1 As shown: It includes a light-weight removal tower, a heavy-weight removal tower 1, a first reboiler 2, a second reboiler 3, and a gas-liquid separator 4; The material outlet of the bottom of the deweight removal tower 1 is connected to the liquid phase inlet of the first reboiler 2 and the second reboiler 3; The gas phase outlet of the first reboiler 2 is connected to the return port of the bottom of the de-weighting tower 1; The gas phase outlet of the second reboiler 3 is connected to the inlet of the gas-liquid separator 4, the gas phase outlet of the gas-liquid separator 4 is connected to the return port of the de-weighting tower 1, and the liquid phase outlet is connected to the liquid phase inlet of the second reboiler 3.

[0029] It should be noted that the appendix Figures 1-3 In the diagram, FC stands for control, LS stands for steam, and SC stands for steam condensate.

[0030] It should be noted that, optionally, the bottom material from the de-consolidation tower 1 is split into a first material stream and a second material stream after passing through the bottom circulation pump. Furthermore, the liquid phase after gas-liquid separation by the gas-liquid separator 4 is split into a collected stream and a circulating stream after passing through the collection pump. The circulating stream returns to the heating process inlet of the second material stream. The connection relationship of the equipment can be selected as follows: Figure 2 As shown: It includes a light-weight removal tower, a heavy-weight removal tower 1, a first reboiler 2, a second reboiler 3, and a gas-liquid separator 4. The material outlet of the bottom of the deweight removal tower 1 is connected to the liquid phase inlet of the first reboiler 2 and the second reboiler 3 via the bottom circulation pump. The gas phase outlet of the first reboiler 2 is connected to the return port of the bottom of the de-weighting tower 1; The gas phase outlet of the second reboiler 3 is connected to the inlet of the gas-liquid separator 4, the gas phase outlet of the gas-liquid separator 4 is connected to the return port of the de-weighting tower 1, the liquid phase outlet is connected to the extraction pump, and the outlet of the extraction pump is connected to the liquid phase inlet of the second reboiler 3.

[0031] It should be noted that, optionally, the second material flow is distributed to two or more parallel branch material flows and heated, and the branch material flows merge after heating to jointly perform the gas-liquid separation. The connection relationship of the equipment can be selected as follows: Figure 3 As shown: It includes a light-weight removal tower, a heavy-weight removal tower 1, a first reboiler 2, a second reboiler 3, a third reboiler 5, and a gas-liquid separator 4; The material outlet of the bottom of the deweight removal tower 1 is divided into two branches. The first branch is directly connected to the liquid phase inlet of the first reboiler 2; the second branch is connected to the liquid phase inlets of the second reboiler 3 and the third reboiler 5 arranged in parallel. The gas phase outlet of the first reboiler 2 is connected to the return port of the bottom of the de-weighting tower 1; The gas phase outlets of the second reboiler 3 and the third reboiler 5 merge and are connected to the inlet of the gas-liquid separator 4. The gas phase outlet of the gas-liquid separator 4 is connected to the return port of the de-weighting tower 1, and the liquid phase outlet is connected to the liquid phase inlet of the second reboiler 3 and the third reboiler 5 arranged in parallel.

[0032] It should be noted that the specific source process of the bottom material of the propylene glycol de-heavy tower 1 in the method for removing reboilers during the propylene glycol refining process of the present invention is as follows: Crude propylene glycol (components include methanol, 1,2-propanediol, 1-methoxy-2-propanol, dipropylene glycol, water, sodium bicarbonate, etc.) enters the propylene glycol de-light tower in the propylene glycol refining process. After distillation, the light component (components include methanol, 1,2-propanediol, 1-methoxy-2-propanol, water, etc.) is collected from the top of the de-light tower. The bottom product of the de-light tower (components include 1,2-propanediol, dipropylene glycol, sodium bicarbonate, etc.) enters the propylene glycol de-heavy tower 1. After distillation, qualified 1,2-propanediol is collected from the top of the de-heavy tower 1. The bottom product of the de-heavy tower 1 (components include 1,2-propanediol, dipropylene glycol, sodium bicarbonate, etc.) is the bottom material of the propylene glycol de-heavy tower 1.

[0033] It should be noted that the basic operating parameters (such as pressure and temperature) of the light-weight removal tower and the heavy-weight removal tower 1 in this invention can be conventionally selected and adjusted by those skilled in the art according to the system to be separated and the product requirements, without any particular limitation. For example, the operating pressure of the light-weight removal tower is 20~40 kPaA, and the controlled temperature is 146~163℃; the operating pressure of the heavy-weight removal tower 1 is 2~10 kPaA, and the controlled temperature is 130~160℃. Since the core of this invention lies in the subsequent processing of the material in the bottom of the heavy-weight removal tower 1, the detailed operating parameters of the light-weight removal tower and the heavy-weight removal tower 1 will not be described in detail in subsequent specific embodiments.

[0034] Example 1

[0035] A method for removing reboilers during the purification of propylene glycol, the process flow of which is as follows: Figure 2 As shown, the specific steps include: The total flow rate of the bottom material in propylene glycol deweighting tower 1 is 139,908 kg / h, containing 77.05% dipropylene glycol, 22.78% 1,2-propanediol, and 0.17% sodium bicarbonate. After being pumped by the bottom circulation pump of deweighting tower 1, the material is split into a first material stream and a second material stream. The flow rate of the first material stream is 136,000 kg / h, and the flow rate of the second material stream is 3,908 kg / h. The first material stream enters the first reboiler 2 for heating (the controlled temperature of the first reboiler 2 is 143.6℃, ​​and the pressure is 10 kPaA), with a controlled vaporization rate of 6%. After vaporization in the first reboiler 2, the first material stream returns to propylene glycol deweighting tower 1 to provide heating load. The second material stream enters the second reboiler 3 for heating (the controlled temperature of the second reboiler 3 is 154.1℃, and the pressure is 10 kPaA). The second material stream, heated and vaporized by the second reboiler 3 at a controlled temperature of 154.1℃ and a pressure of 10 kPaA, enters the gas-liquid separator 4 (controlled temperature of the gas-liquid separator 4 is 154.1℃ and pressure is 10 kPaA) for gas-liquid separation, resulting in a gas phase and a liquid phase. The gas phase has a flow rate of 3724 kg / h and a composition of 23.5% 1,2-propanediol and 76.5% dipropylene glycol. The liquid phase has a flow rate of 5284 kg / h and a composition of 6.7% 1,2-propanediol, 89.9% dipropylene glycol, and 3.4% sodium bicarbonate. The gas phase is returned to the propylene glycol deweighting tower 1, and the liquid phase is split into a collector flow and a circulating flow after being pumped out. The collector flow has a flow rate of 184 kg / h, and the circulating flow has a flow rate of 5100 kg / h. The circulating flow is returned to the inlet of the second reboiler 3 for further circulation.

[0036] Analysis of the produced stream using gas chromatography revealed that it primarily contained 1,2-propanediol and dipropylene glycol, with dipropylene glycol accounting for 89.9% of the mass, 1,2-propanediol for 6.7%, and sodium bicarbonate for 3.4%. According to the process definition, all components in the produced stream except 1,2-propanediol (i.e., dipropylene glycol and sodium bicarbonate) were considered reboilers. Therefore, the calculated flow rate of reboilers in the produced stream was 184 kg / h × 93.3% = 171.7 kg / h, and the mass fraction of reboilers in the produced stream was 93.3%.

[0037] Example 2

[0038] A method for removing reboilers during the purification of propylene glycol, the process flow of which is as follows: Figure 2 As shown, the specific steps include: The total flow rate of the bottom material in propylene glycol deweighting tower 1 is 140,743 kg / h, containing 77.22% dipropylene glycol, 22.65% 1,2-propanediol, and 0.13% sodium bicarbonate. After being pumped by the bottom circulation pump of deweighting tower 1, the material is split into a first material stream and a second material stream. The flow rate of the first material stream is 136,000 kg / h, and the flow rate of the second material stream is 4,743 kg / h. The first material stream enters the first reboiler 2 for heating (the controlled temperature of the first reboiler 2 is 144℃, and the pressure is 10 kPaA), with a controlled vaporization rate of 8%. After vaporization in the first reboiler 2, the first material stream returns to propylene glycol deweighting tower 1 to provide heating load. The second material stream enters the second reboiler 3 for heating (the controlled temperature of the second reboiler 3 is 154.2℃, and the pressure is 10 kPaA). The second material stream, heated and vaporized by the second reboiler 3 (PaA), with a controlled vaporization rate of 50%, enters the gas-liquid separator 4 (controlled temperature of 154.2℃ and pressure of 10kPaA) for gas-liquid separation, yielding a gas phase and a liquid phase. The gas phase has a flow rate of 4558 kg / h and a composition of 23.3% 1,2-propanediol and 76.7% dipropylene glycol. The liquid phase has a flow rate of 5285 kg / h and a composition of 6.6% 1,2-propanediol, 89.9% dipropylene glycol, and 3.5% sodium bicarbonate. The gas phase is returned to the propylene glycol deweighting tower 1, while the liquid phase is split into a collector flow and a circulating flow after being pumped out. The collector flow has a flow rate of 185 kg / h, and the circulating flow has a flow rate of 5100 kg / h. The circulating flow is returned to the inlet of the second reboiler 3 for further circulation.

[0039] Analysis of the produced stream using gas chromatography revealed that it primarily contained 1,2-propanediol and dipropylene glycol, with dipropylene glycol comprising 89.9% by mass, 1,2-propanediol 6.6%, and sodium bicarbonate 3.5%. According to the process definition, all components in the produced stream except 1,2-propanediol (i.e., dipropylene glycol and sodium bicarbonate) were considered reboilers. Therefore, the calculated flow rate of reboilers in the produced stream was 185 kg / h × 93.4% = 171.79 kg / h, and the mass fraction of reboilers in the produced stream was 93.4%.

[0040] Example 3

[0041] A method for removing reboilers during the purification of propylene glycol, the process flow of which is as follows: Figure 3 As shown, the specific steps include: The total flow rate of the bottom material in propylene glycol deweighting tower 1 is 279,859 kg / h, containing 21.5% 1,2-propanediol, 78.3% dipropylene glycol, and 0.2% sodium bicarbonate. After being pumped by the bottom circulation pump of deweighting tower 1, the material is split into a first material stream and a second material stream. The flow rate of the first material stream is 272,000 kg / h, and the flow rate of the second material stream is 7,859 kg / h. The first material stream enters the first reboiler 2 for heating (the temperature of the first reboiler 2 is controlled at 144.3℃, and the pressure at 10 kPaA), with a controlled vaporization rate of 6%. After vaporization in the first reboiler 2, the first material stream returns to propylene glycol deweighting tower 1 to provide heating load. The second material stream is split into a third material stream and a fourth material stream, which enter the second reboiler 3 and the third reboiler 5 for heating, respectively. The temperature of the second reboiler 3 is controlled at 154.5℃, the pressure at 10 kPaA, and the vaporization rate is 44%. The temperature, pressure, and vaporization rate control parameters of the third reboiler 5 and the second reboiler 3 are the same. The material stream, heated and vaporized by the second and third reboilers 3 and 5, enters the gas-liquid separator 4 for gas-liquid separation (the controlled temperature of the gas-liquid separator 4 is 154.2℃, and the pressure is 10 kPaA), resulting in a gas phase and a liquid phase. The gas phase flow rate is 7489 kg / h, and the gas phase composition is 22.3% 1,2-propanediol and 77.7% dipropylene glycol. The propylene glycol has a liquid phase flow rate of 10570 kg / h and a liquid phase composition of 6.4% 1,2-propanediol, 90.2% dipropylene glycol, and 3.4% sodium bicarbonate. The gas phase is returned to the propylene glycol deweighting tower 1, and the liquid phase is split into a produced flow and a circulating flow after being pumped out. The produced flow rate is 370 kg / h, and the circulating flow rate is 10200 kg / h. The circulating flow is returned to the inlet of the second reboiler 3 and the third reboiler 5 for further circulation.

[0042] Analysis of the produced stream using gas chromatography revealed that it primarily contained 1,2-propanediol, dipropylene glycol, and sodium bicarbonate. The mass fractions of dipropylene glycol were 90.2%, 1,2-propanediol 6.4%, and sodium bicarbonate 3.4%. According to the process definition, all components in the produced stream except 1,2-propanediol (i.e., dipropylene glycol and sodium bicarbonate) were considered reboilers. Therefore, the calculated flow rate of reboilers in the produced stream was 370 kg / h × 93.6% = 346.32 kg / h, and the mass fraction of reboilers in the produced stream was 93.6%.

[0043] Comparative Example 1

[0044] A method for removing reboilers during the purification of propylene glycol specifically includes the following steps: The total flow rate of the bottom material in propylene glycol deweighting tower 1 is 137,003 kg / h, containing 66.4% dipropylene glycol, 32.9% 1,2-propanediol, and 0.7% sodium bicarbonate. After being pumped by the bottom circulation pump of deweighting tower 1, the material is split into a first material stream and a second material stream. The flow rate of the first material stream is 136,000 kg / h, and the flow rate of the second material stream is 1,003 kg / h. The first material stream enters the first reboiler 2 for heating (the temperature of the first reboiler 2 is controlled at 138.4℃ and the pressure at 10 kPa), with a controlled vaporization rate of 4%. After vaporization in the first reboiler 2, the first material stream returns to propylene glycol deweighting tower 1 to provide heating load. The second material stream enters the second reboiler 3 for heating (the temperature of the second reboiler 3 is controlled at 149.4℃ and the pressure at 10 kPa). A) The vaporization rate is controlled at 20%. The second material stream, after being heated and vaporized in the second reboiler 3, enters the gas-liquid separator 4 (the controlled temperature of the gas-liquid separator 4 is 149.4℃, and the pressure is 10kPaA) for gas-liquid separation, resulting in a gas phase and a liquid phase. The gas phase flow rate is 818 kg / h, and the gas phase composition is 37.65% 1,2-propanediol and 62.35% dipropylene glycol. The liquid phase flow rate is 3985 kg / h, and the composition is 12% 1,2-propanediol, 84.5% dipropylene glycol, and 3.5% sodium bicarbonate. The gas phase is returned to the propylene glycol deweighting tower 1. The liquid phase is split into a collector flow and a circulating flow after being pumped out. The collector flow rate is 185 kg / h, and the circulating flow rate is 3800 kg / h. The circulating flow is returned to the inlet of the second reboiler 3 for further circulation.

[0045] Sampling and analysis of the produced stream, using gas chromatography to determine its composition, revealed that the produced stream mainly contains 1,2-propanediol, dipropylene glycol, and sodium bicarbonate. The mass fraction of dipropylene glycol was 84.5%, 1,2-propanediol 12%, and sodium bicarbonate 3.5%. According to the process definition, the components in the produced stream other than 1,2-propanediol (i.e., dipropylene glycol and sodium bicarbonate) are considered reboilers. Therefore, the calculated flow rate of reboilers in the produced stream is 185 kg / h × 88% = 162.8 kg / h, and the mass fraction of reboilers in the produced stream is 88%.

[0046] Comparative Example 2

[0047] Based on the method for removing reboilers during the propylene glycol refining process of Example 1, this comparative example uses the same conditions except for the first vaporization rate. The specific method is as follows: The total flow rate of the bottom material in propylene glycol deweighting tower 1 is 139,823 kg / h, containing 70.9% dipropylene glycol, 29% 1,2-propanediol, and 0.1% sodium bicarbonate. After being pumped by the bottom circulation pump of deweighting tower 1, the material is split into a first material stream and a second material stream. The flow rate of the first material stream is 136,000 kg / h, and the flow rate of the second material stream is 3,823 kg / h. The first material stream enters the first reboiler 2 for heating (the controlled temperature of the first reboiler 2 is 139.9℃, and the pressure is 10 kPa), with a controlled vaporization rate of 2%. After vaporization in the first reboiler 2, the first material stream returns to propylene glycol deweighting tower 1 to provide heating load. The second material stream enters the second reboiler 3 for heating (the controlled temperature of the second reboiler 3 is 151.9℃, and the pressure is 10 kPa). The second material stream, after being heated and vaporized in the second reboiler 3 (PaA), with a controlled vaporization rate of 44%, enters the gas-liquid separator 4 (controlled temperature of 151.9℃ and pressure of 10kPaA) for gas-liquid separation, yielding a gas phase and a liquid phase. The gas phase has a flow rate of 3637 kg / h and a composition of 30% 1,2-propanediol and 70% dipropylene glycol. The liquid phase has a flow rate of 5285 kg / h and a composition of 9.0% 1,2-propanediol, 87.5% dipropylene glycol, and 3.5% sodium bicarbonate. The gas phase is returned to the propylene glycol deweighting tower 1, and the liquid phase is split into a collector flow and a circulating flow after being pumped out. The collector flow has a flow rate of 185 kg / h, and the circulating flow has a flow rate of 5100 kg / h. The circulating flow is returned to the inlet of the second reboiler 3 for further circulation.

[0048] Analysis of the produced stream using gas chromatography revealed that it primarily contained 1,2-propanediol and dipropylene glycol, with dipropylene glycol comprising 85.5% by mass, 1,2-propanediol 11%, and sodium bicarbonate 3.5%. According to the process definition, all components in the produced stream except 1,2-propanediol (i.e., dipropylene glycol and sodium bicarbonate) were considered reboilers. Therefore, the calculated flow rate of reboilers in the produced stream was 185 kg / h × 89% = 164.65 kg / h, and the mass fraction of reboilers in the produced stream was 89%.

[0049] Comparative analysis of Examples 1 and 2, and Comparative Examples 1 and 2, reveals the crucial role of vaporization rate control in the reboiler removal process. In Examples 1 and 2, the vaporization rates of the second material stream were controlled at relatively high levels of 44% and 50%, respectively, significantly higher than the 6% and 8% vaporization rates of the first material stream. In contrast, Comparative Example 1 set the vaporization rate of the second material stream to 20% and the vaporization rate of the first material stream to 4%, while Comparative Example 2 set the vaporization rate of the second material stream to 44%, but the vaporization rate of the first material stream was only 2%. These examples demonstrate that controlling the vaporization rate of the second material stream to be higher than that of the first material stream, with the first material stream's vaporization rate between 5% and 10% and the second material stream's vaporization rate between 25% and 50%, is a core technical element for achieving efficient reboiler removal, improving system processing capacity, and ensuring long-term stable operation. Vaporization rate control not only ensures sufficient material throughput but also optimizes system circulation stability while maintaining high separation purity, effectively solving problems such as high energy consumption and equipment clogging in existing technologies.

[0050] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions. The specific parameters in this embodiment do not necessarily limit the technical solution, but merely illustrate one specific working condition. For those skilled in the art, various simple improvements and modifications can be made without departing from the concept of the present invention, and all such improvements and modifications should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for removing reboilers during the refining of propylene glycol, characterized in that, Includes the following steps: (1) The crude propylene glycol is separated sequentially by passing it through a light product removal tower and a heavy product removal tower; (2) The discharge from the bottom of the de-weighting tower is divided into a first material stream and a second material stream. The first material stream and the second material stream are heated to different gasification rates, and the gasification rate of the second material stream is higher than that of the first material stream. (3) The steam generated by heating the first material stream is returned to the deweighting tower; (4) After heating the second material stream, gas-liquid separation is performed. The resulting gas phase is returned to the de-weighting tower, and the liquid phase is split into a production stream and a circulation stream. The circulation stream is returned to the heating process inlet of the second material stream. Thus, reboilers are removed through gas-liquid separation of the second material stream.

2. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The gasification rate of the first material flow is 5% to 10%, and the gasification rate of the second material flow is 25% to 50%.

3. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The mass flow rate ratio of the first material flow to the second material flow is (5~20):(1~5).

4. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The mass ratio of the produced flow to the circulating flow is (5~15):(1~5).

5. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The pressure of the first material stream and / or the second material stream extracted from the deweighting tower is 2~10 kPaA, and the temperature is 130~160℃.

6. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The first material flow is heated to 135~145℃; And / or, heat the second material stream to 145~155°C.

7. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The operating pressure for gas-liquid separation is 2~10 kPaA, and the controlled temperature is 130~160℃.

8. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The second material flow is distributed to multiple parallel branch material flows for heating. After heating, each branch material flow performs the gas-liquid separation operation independently or by merging.

9. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The equipment used to perform the heating operation is any one of a forced circulation reboiler, a falling film reboiler, or a thermosiphon reboiler.

10. The method for removing reboilers during the propylene glycol refining process according to claim 1, characterized in that, The operating pressure of the light-weight removal tower is 20~40 kPaA, and the controlled temperature is 146~163℃. And / or, the operating pressure of the deweight removal tower is 2~10 kPaA, and the controlled temperature is 130~160℃.

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