1, 3-propylene glycol refining system

Abstract

The utility model relates to a 1, 3-propylene glycol refining system which comprises a light component removal tower and a propylene glycol tower, a raw material pipeline is arranged in the middle of the light component removal tower, and a light component extraction pipe and a desalted water pipeline are arranged at the top; a tower kettle of the light component removal tower is communicated with a feeding hole in the middle of the propylene glycol tower, the tower top of the propylene glycol tower is communicated with a liquid phase hydrogenation unit, a hydrogenated liquid phase outlet is communicated with a product pump, and an outlet of the product pump is respectively communicated with the top of the propylene glycol tower and the feeding hole of the light component removal tower through two independent pipelines; a rectifying section of the propylene glycol tower is provided with a side extraction pipeline which is used for extracting a polyester-grade 1, 3-propylene glycol product; the feeding hole of the light component removal tower is also communicated with an alkali liquor pipe; the feeding hole of the propylene glycol tower is also communicated with a reducing additive pipe; according to the continuous liquid-phase hydrogenation device, alkali liquor neutralization, water azeotropic distillation, reducing additives, liquid-phase hydrogenation and propylene glycol distillation are organically coupled, continuous liquid-phase hydrogenation is carried out on reflux liquid of the propylene glycol tower, the refining effect can be improved from the industrial grade to the polyester grade, the 100% yield is achieved, and meanwhile coking of the propylene glycol tower can be slowed down.

Description

Technical Field

[0001] The utility model belongs to the technical field of chemical production, and particularly relates to a 1,3-propylene glycol refining system, which is used for the refining process of 1,3-propylene glycol obtained by biological method or chemical method. Background Art

[0002] 1,3-Propanediol (PDO) is an important chemical raw material and an important synthetic monomer for polymers such as polyester and polyether. Its most widely used application is as a monomer for preparing a new polyester fiber, polytrimethylene terephthalate (PTT). As a new polyester material, PTT polyester is widely used in decorative materials, textile fibers, clothing, engineering plastics and films due to its softness, good elasticity and stain resistance. It is known as the new polyester fiber of the 21st century. With the increase in the commercial application of PTT, the global market size is expected to continue to grow, thereby driving the demand for PDO, a key monomer. In addition, 1,3-propanediol can also be used to manufacture various plasticizers, emulsifiers and other products, and can be used in many livelihood areas such as food, medicine, and detergents.

[0003] The production technology of PDO is divided into chemical method and biological method. Among them, the chemical method of synthesizing PDO in industrial production mainly includes acrolein hydration hydrogenation method and ethylene oxide carbonylation method, and the biological method is mainly represented by the biological fermentation method developed by DuPont in the United States.

[0004] In addition to requiring a purity of ≥99.9wt%, the ultraviolet absorbance (270nm) and thermal stability of polyester-grade 1,3-propylene glycol are also another important indicator for measuring its quality. The ultraviolet absorbance (270nm) is required to be ≤0.08, and the ultraviolet transmittance (270nm UV value) is converted to ≥84%. The UV value can sensitively reflect the content of characteristic impurities in the propylene glycol product and indirectly reflect the product quality of propylene glycol. A low UV value will affect the technical indicators of polyester fiber such as coloring, strength and color.

[0005] CN201810351371.2 discloses a method for preparing 1,3-propylene glycol by hydration and hydrogenation of acrolein, which uses N-alkyl amino acid to homogeneously catalyze the hydration reaction of acrolein to prepare 3-hydroxypropionaldehyde, and the obtained 3-hydroxypropionaldehyde aqueous solution is directly hydrogenated to prepare PDO; the patent does not mention the technical indicators of the prepared PDO product.

[0006] CN202211511187.2 discloses a method and device for producing 1,3-propylene glycol, which uses propylene as raw material and makes full use of acrylic acid, the main by-product produced in the propylene oxidation reaction, so that it is also used as an intermediate raw material to be converted into PDO through esterification reaction and catalytic hydrogenation reaction; this method has obvious cost advantages, but also does not mention the technical indicators of the prepared PDO product.

[0007] DuPont Namur mentioned the use of hydrogenation to improve the quality of 1,3-propylene glycol in its three patents: hydrogenation of biochemically derived 1,3-propylene glycol (CN100448827C), hydrogenation of chemically derived 1,3-propylene glycol (CN100448826C), and purification of biologically produced 1,3-propylene glycol (CN100478446C). However, the above patents use a variety of combined processes such as filtration, membrane separation, ion exchange, distillation, and hydrogenation, and the process is complicated; in addition, a single hydrogenation method has limited effect on improving the quality of propylene glycol, and although hydrogenation can convert some aldehyde impurities into 1,3-propylene glycol, it will also produce a small amount of impurities such as methanol, ethanol, and water. Therefore, the purification method of pure direct hydrogenation can usually only produce industrial-grade 1,3-propylene glycol products, and cannot meet polyester grade requirements. Summary of the invention

[0008] In order to purify the 1,3-propylene glycol product obtained by biological or chemical methods to reach polyester-grade indicators, while slowing down the coking of the propylene glycol tower, extending the tower washing cycle, and improving the yield of polyester-grade propylene glycol, the utility model provides a 1,3-propylene glycol refining system.

[0009] The technical solution adopted by the utility model is as follows:

[0010] A 1,3-propylene glycol refining system comprises a lightness removal tower C101 and a propylene glycol tower C102, wherein the lightness removal tower C101 and the propylene glycol tower C102 are both vacuum distillation towers; a raw material pipeline is provided in the middle of the lightness removal tower C101 for supplying a raw material crude propylene glycol 1 to be refined; the lightness removal tower C101 is used to purify the crude propylene glycol 1 and remove light components 4 at the top of the tower; the bottom of the lightness removal tower C101 is connected to the bottom of the propylene glycol tower C102; The feed inlet, the top of the propylene glycol tower C102 is connected to the liquid phase hydrogenation unit, which is used to hydrogenate and refine the liquid phase components drawn out and condensed from the top of the propylene glycol tower C102. After the hydrogenated materials are separated by a gas-liquid separator, the hydrogenated liquid phase refluxes to the top of the propylene glycol tower C102; the polyester-grade 1,3-propylene glycol product 6 is extracted from the side line of the distillation section of the propylene glycol tower C102; the heavy component 8 is discharged from the bottom of the propylene glycol tower C102.

[0011] The light components and heavy components mentioned in the present invention refer to components that can be separated from 1,3-propylene glycol after being distilled in the light-removing tower C101 and the propylene glycol tower C102, wherein the stream discharged from the top of the light-removing tower C101 after separation is called the light component, and the component discharged from the bottom of the propylene glycol tower C102 after separation is called the heavy component.

[0012] Similar to the structure of a conventional distillation tower, the top of the lightness removal tower C101 of the utility model is connected to the lightness removal tower condenser E101, the lightness removal tower reflux tank V101 and the lightness removal tower reflux pump P101 in sequence through pipelines; the difference is that the lightness removal tower reflux tank V101 of the utility model is also connected to a desalted water pipeline for inputting desalted water 3 into the lightness removal tower reflux tank V101. The desalted water 3 is mixed with the liquid phase light component and transported through the lightness removal tower reflux pump P101, a part of which is extracted as the light component 4, and the other part is refluxed to the top of the lightness removal tower C101.

[0013] The introduction of desalted water 3 is proposed based on the inventor's discovery that the raw material crude propylene glycol often contains impurities such as aldehydes, and due to the use of vacuum distillation, air often leaks into the light removal tower C101 during actual operation, causing alcohols to be oxidized to aldehydes. By adding desalted water to the reflux tank of the light removal tower and using the method of azeotropic distillation with water, the aldehydes that azeotropize with water are enriched at the top of the tower. As the light components are discharged from the system, this method can significantly reduce the aldehyde content at the bottom of the light removal tower C101, thereby improving the quality of propylene glycol at the bottom of the light removal tower.

[0014] The raw material pipeline of the light-removing tower C101 is also connected with an alkali liquid pipe for inputting alkali liquid 2 into the raw material pipeline, and the alkali liquid 2 is mixed with crude propylene glycol 1 and enters the light-removing tower C101. The bottom of the light-removing tower C101 is also provided with an acid value detection device, and its detection result is used as the basis for the amount of alkali liquid added. The introduction of the alkali liquid 2 can neutralize the acidic components in the crude propylene glycol 1 and effectively control the acid value at the bottom of the light-removing tower C101.

[0015] The bottom of the lightness removal tower C101 is also provided with a lightness removal tower reboiler E102 and a lightness removal tower bottom pump P102, and the lightness removal tower bottom pump P102 is used to transport the bottom material of the lightness removal tower C101 to the feed port of the propylene glycol tower C102. Among them, an additive pipe is also connected to the pipeline between the lightness removal tower bottom pump P102 and the feed port of the propylene glycol tower C102, which is used to supply additives 5 to the propylene glycol tower C102, and the additives 5 are preferably additives with strong reducing properties, and more preferably bisulfite. The introduction of the additive helps to reduce the content of aldehydes in propylene glycol and improve ultraviolet transmittance.

[0016] The top of the propylene glycol tower C102 is connected in sequence to a propylene glycol tower condenser E103, a propylene glycol tower reflux tank V102, and a propylene glycol tower reflux pump P103 through pipelines; the outlet stream of the propylene glycol tower reflux pump P103 is divided into two streams, one of which is sent to a liquid phase hydrogenation unit through a hydrogenation pipeline, and the other stream is returned to the top of the propylene glycol tower C102 through a reflux pipeline; the feed port of the liquid phase hydrogenation unit is also connected to a hydrogen pipe for supplying hydrogen 7 to the liquid phase hydrogenation unit.

[0017] The liquid phase hydrogenation unit comprises a liquid phase hydrogenation reactor R201 and a flash tank V201 connected in series; the liquid phase hydrogenation reactor R201 is preferably a trickle bed reactor, which comprises a catalyst bed and a gas-liquid separation chamber located below the catalyst bed, and the upper and lower parts of the gas-liquid separation chamber are connected to the flash tank V201 via a purge gas pipe with a purge gas control valve and a propylene glycol pipe with a propylene glycol control valve, respectively. In the reactor, hydrogen 7 is a continuous phase, and liquid is a dispersed phase. The gas and liquid phases are separated in the gas-liquid separation chamber at the bottom of the reactor, and the separated gas phase enters the flash tank V201 via the purge gas pipe. The operating pressure of the reactor is controlled by hydrogen feed, and the hydrogen concentration in the reactor is adjusted by the purge gas control valve.

[0018] The top of the flash tank V201 is connected to a purge gas cooler E201 to condense and recover part of the vaporized propylene glycol.

[0019] A product pump P201 is provided at the bottom of the flash tank V201, and the outlet of the product pump P201 is connected to the reflux pipeline of the propylene glycol tower C102 and the raw material pipeline of the light removal tower C101. The propylene glycol after liquid phase hydrogenation is sent to the propylene glycol tower for reflux, and a small part (not more than 10%) is returned to the light removal tower for feeding and recycling treatment, so that a part of the light components generated in the liquid phase hydrogenation process and the refining process of the propylene glycol tower C102 is returned to the light removal tower C101 for separation, and is extracted from the top as a light component 4. This circulation process can effectively prevent the light components from accumulating at the top of the propylene glycol tower C102, thereby ensuring the purity of the side-extracted propylene glycol product 6, and the propylene glycol in the circulation flow can enter the propylene glycol tower C102 for refining again after being treated by the light removal tower C101, thereby achieving a 100% yield of polyester-grade propylene glycol products.

[0020] The distillation section of the propylene glycol tower C102 is connected to a side sampling pipeline, to which a side sampling product cooler E106, a side sampling product buffer tank V103 and a side sampling product pump P105 are sequentially connected for producing a polyester-grade 1,3-propylene glycol product 6.

[0021] After the light component impurities generated during the hydrogenation process are refluxed to the propylene glycol tower C102, they come into contact with the rising air flow in the distillation section during the liquid falling process and undergo heat and mass transfer. After passing through several theoretical plates, this part of the light component is transferred into the gas phase again, thereby reducing the content of light component impurities in the material flow that continues to fall, and ultimately 1,3-propylene glycol with a higher purity than the reflux liquid from the top of the propylene glycol tower can be produced from the side line of the distillation section, i.e., a polyester-grade 1,3-propylene glycol product.

[0022] The utility model also provides a method for refining 1,3-propylene glycol, comprising the following steps:

[0023] 1) Crude propylene glycol 1 from upstream enters the light component removal tower C101, and alkali solution 2 is added to the light component removal tower feed. In the light component removal tower C101, light components and propylene glycol are separated, and the top of the tower is the light component 4 containing a small amount of propylene glycol, and the bottom of the tower is mainly propylene glycol, which is refined in the propylene glycol tower C102.

[0024] 2) Desalted water 3 is added to the reflux tank V101 of the lightness removal tower. The desalted water 3 enters the lightness removal tower C101 with the reflux liquid and azeotropes with the aldehyde substances, thereby promoting the enrichment of the aldehyde substances that are difficult to be clearly separated from propylene glycol to the top of the tower, and then discharged from the system with the light components 4, thereby improving the quality of propylene glycol at the bottom of the lightness removal tower C101.

[0025] In the light-removal tower C101, aldehydes may be obtained from a variety of sources, among which the crude propylene glycol 1 may carry certain aldehydes. In addition, due to the vacuum distillation separation, air may leak into the light-removal tower C101, causing alcohols to be oxidized into aldehydes. In order to reduce the aldehyde content at the bottom of the light-removal tower, water azeotropic distillation is used.

[0026] 3) The reducing additive 5 is added from the feed line of the propylene glycol tower C102. The introduction of the additive 5 can cooperate with the subsequent liquid phase hydrogenation process to significantly reduce the aldehyde content in the propylene glycol and improve the ultraviolet transmittance.

[0027] 4) The top stream of the propylene glycol tower C102 is condensed and pressurized by the propylene glycol tower reflux pump P103, and a portion of it is directly sent to the reflux, and a portion of it is sent to the liquid phase hydrogenation unit.

[0028] 5) A portion of the propylene glycol from the propylene glycol tower reflux pump P103 is mixed with hydrogen 7 in the pipeline mixer and then enters the liquid phase hydrogenation reactor. The gas and liquid phases after the reaction are separated at the bottom of the reactor. The gas phase enters the flash tank V201 through the purge gas pipe, and the liquid phase enters the flash tank V201 through the pipeline at the bottom of the reactor. The operating pressure of the reactor is controlled by the hydrogen feed, and the hydrogen concentration in the reactor is adjusted by the purge gas control valve.

[0029] 6) After the liquid phase in the flash tank V201 is pressurized by the product pump P201, a portion of it is refluxed to the top of the propylene glycol tower C102, and a portion of it is circulated to the feed port of the light removal tower C101.

[0030] 7) The polyester-grade propylene glycol product 6 is side-cut in the distillation section of the propylene glycol tower C102, and the side-cut material flow enters the side-cut product cooler E106 and the side-cut product buffer tank V103 in turn, and is then transported to the outside through the side-cut product pump P105. The propylene glycol tower reboiler E104 uses steam as a heat source, and the tower bottom heavy component 8 is pressurized by the propylene glycol tower bottom pump P104, and then sent to the heavy component cooler E105 for cooling and then sent to the outside.

[0031] In order to reduce the acid value of the propylene glycol product and further improve the quality of the propylene glycol product, the alkali solution 2 is quantitatively added to the feed of crude propylene glycol 1. The alkali solution is NaOH alkali solution, preferably 32wt% NaOH, and the amount of alkali solution added is based on the acid value of the bottom of the light removal tower C101, and the acid value is controlled at 0-2mg / kg.

[0032] The amount of desalted water added to the light fraction removal tower reflux tank V101 is adjusted according to the water content in the light fraction, and the water content in the light fraction is controlled to be between 5wt% and 50wt%.

[0033] The addition amount of the reducing additive 5 is preferably 0 to 200 ppm, and the additive is preferably an additive with strong reducing properties, more preferably bisulfite.

[0034] In order to reduce the coking of the bottom of propylene glycol C102, the propylene glycol tower C102 adopts a negative pressure tower, the tower pressure is controlled at 3-20 kPaA, the bottom temperature is controlled at about 155°C, and the ratio of top reflux to side-drawn propylene glycol is preferably 1.5-3:1.

[0035] The catalyst for the liquid phase hydrogenation is a nickel-based catalyst, and the preferred operating conditions are: reaction temperature of 90-150° C., and reaction pressure of 0.2-1.0 MPaG.

[0036] Most of the propylene glycol at the outlet of the propylene glycol tower reflux pump P103 goes to the liquid phase hydrogenation system, and the proportion is preferably ≥90%.

[0037] In order to lower the bottom temperature and reduce coking in the propylene glycol bottom, the reboilers of the lightness removal tower C101 and the propylene glycol tower C102 preferably use falling film reboilers.

[0038] Compared with the prior art, the main points of the utility model are: firstly, it is proposed to organically couple alkali solution neutralization, water azeotropic distillation, additives, liquid phase hydrogenation and propylene glycol distillation, and the propylene glycol product is not directly subjected to liquid phase hydrogenation, but the propylene glycol tower reflux liquid is subjected to continuous liquid phase hydrogenation, so that the quality of propylene glycol can be improved to reach the polyester grade index (improving ultraviolet transmittance, reducing aldehyde content, improving thermal stability, and reducing acid value), and the propylene glycol tower coking can be slowed down, the tower washing cycle can be extended, and the polyester grade propylene glycol yield can be improved, and the original industrial grade propylene glycol can be converted into polyester grade propylene glycol, which significantly improves the economic benefits of the enterprise. By hydrogenating the reflux liquid at the top of the propylene glycol tower in liquid phase, the light components such as methanol and ethanol produced after the liquid phase hydrogenation can also be discharged through the light fraction discharge system, so as to improve the quality of the side-collected propylene glycol product. In general, the process flow has the advantages of advanced technology, short process flow, low investment, low energy consumption, good economic benefits, etc., and is of great significance to the optimization of the biological or chemical method propylene glycol technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1This is a process flow chart of the 1,3-propylene glycol refining system of the present application;

[0040] In the figure: C101 is a lightness removal tower, E101 is a lightness removal tower condenser, V101 is a lightness removal tower reflux tank, P101 is a lightness removal tower reflux pump, E102 is a lightness removal tower reboiler, P102 is a lightness removal tower kettle pump, C102 is a propylene glycol tower, E103 is a propylene glycol tower condenser, V102 is a propylene glycol tower reflux tank, P103 is a propylene glycol tower reflux pump, E104 is a propylene glycol tower reboiler, P104 is a propylene glycol tower kettle pump, E105 is a heavy component cooler, and E106 is a side sampling Product cooler, V103 is the side-production product buffer tank, P105 is the side-production product pump, P201 is the product pump, R201 is the liquid phase hydrogenation reactor, V201 is the flash tank, E201 is the purge gas cooler, 1 is crude propylene glycol, 2 is alkali solution, 3 is desalted water, 4 is light fraction, 5 is additives, 6 is polyester-grade propylene glycol product, 7 is hydrogen, 8 is propylene glycol heavy component, 9 is purge gas, LS is low-pressure steam, CWS is circulating cooling water supply water, and CWR is circulating cooling water return water. Specific implementation plan

[0041] Example 1

[0042] like Figure 1 This embodiment adopts the refining system of the utility model, and uses the crude propylene glycol 1 produced by the fermentation and crude fractionation unit of the 100,000 tons / year biological propylene glycol project as the refining unit raw material. The output of the polyester-grade propylene glycol product 6 of the project is 12.5 t / h.

[0043] The feed rate of crude propylene glycol 1 to the de-lightening tower C101 is 14t / h, and the propylene glycol content in the crude propylene glycol 1 is 99wt%, and the rest are light and heavy components. The amount of alkali solution added to the feed of the de-lightening tower C101 is 15kg / h, and the alkali solution is a 32wt% NaOH aqueous solution. The amount of desalted water added to the top of the de-lightening tower C101 is 0.1t / h, and the circulation amount of the liquid phase hydrogenation unit returning to the de-lightening tower C101 is 1t / h; the total feed rate of the de-lightening tower C101 is 15t / h.

[0044] The top operating pressure of the lightness removal tower C101 is 10kPaA, the top temperature is 53°C, and the bottom temperature is 161°C.

[0045] The vapor phase from the top of the light components removal tower is sent to the light components removal tower condenser E101 for condensation. The condensed light components are buffered in the light components removal tower reflux tank V101 and then pressurized by the light components removal tower reflux pump P101. Part of it is used as tower reflux and part of it is extracted as light components 4. The flow rate of the extracted light components 4 is 0.5 t / h.

[0046] The feed rate of propylene glycol tower C102 is 14.6 t / h, additive 5 is bisulfite, the addition rate is 100 ppm, equivalent to 1.5 kg / h, the propylene glycol content in the feed is 99.6 wt%, the top operating pressure of propylene glycol tower C102 is 5 kPaA, and the bottom temperature is 153°C.

[0047] The vapor phase from the top of the propylene glycol tower is sent to the propylene glycol tower condenser E103 for condensation. The condensed propylene glycol is buffered in the propylene glycol tower reflux tank V102 and then pressurized by the propylene glycol tower reflux pump P103. The direct reflux flow accounts for 10% and the flow rate is 2.6t / h. The flow rate to the liquid phase hydrogenation system is 23.4t / h.

[0048] The polyester-grade propylene glycol product 6 is side-sampled from the distillation section of the propylene glycol tower C102. The side sample flow successively enters the side sample product cooler E106, the side sample product buffer tank V103 and the side sample product pump P105. The side sample volume is 12.5 t / h.

[0049] The propylene glycol tower reboiler E104 uses 1.0 MPaG saturated steam as the heat source. The heavy component in the tower bottom is pressurized by the propylene glycol tower bottom pump P104 and then sent to the heavy component cooler E105 for cooling and then sent out of the boundary. The heavy component flow rate is 1.1 t / h.

[0050] A portion of the propylene glycol from the propylene glycol tower reflux pump P103 is first mixed with hydrogen 7 in a pipeline mixer and then enters the liquid phase hydrogenation reactor R201. The liquid phase hydrogenation reactor R201 is a trickle bed reactor, hydrogen 7 is a continuous phase, liquid is a dispersed phase, gas and liquid are separated at the bottom of the reactor, the operating pressure of the reactor is controlled by hydrogen feed, and the hydrogen concentration in the reactor is adjusted by the purge gas control valve. The gas phase and liquid phase of the liquid phase hydrogenation reactor are controlled by a regulating valve to go to the flash tank V201, and a purge gas cooler E201 is connected to the top of the flash tank to condense and recover part of the vaporized propylene glycol. Most of the propylene glycol after liquid phase hydrogenation is sent to the propylene glycol tower C102 for reflux, and a small part is returned to the light removal tower C101 for feeding. The flow rate of reflux to the propylene glycol tower C102 is 22.4t / h, and the flow rate of propylene glycol returning to the light removal tower C101 is 1t / h. By continuously hydrogenating the top reflux liquid of the propylene glycol tower C102 through liquid phase hydrogenation, the ultraviolet transmittance of the top propylene glycol can be gradually increased, thereby indirectly improving the quality of the side-recovery propylene glycol product.

[0051] The operating conditions of the liquid phase hydrogenation reactor R201 are 1.0 MPaG and 130°C, and the operating conditions of the flash tank V201 are 0.2 MPaG and 130°C.

[0052] The hydrogen consumption of liquid phase hydrogenation reactor R201 is 46.8Nm 3 / h, equivalent to 2Nm 3Hydrogen / ton of fresh propylene glycol, purge gas flow rate is 28Nm 3 / h, the hydrogen concentration in the reactor is about 95V%.

[0053] Example 2

[0054] Compared with Example 1, this example adopts top extraction of propylene glycol product, and the outlet of the propylene glycol tower reflux pump P103 extracts 12.5t / h of liquid phase hydrogenation, which is then cooled as the final product. The other operating conditions are the same as in Example 1.

[0055] Example 3

[0056] Compared with Example 1, this embodiment only adds alkali solution to the feed of the lightness removal tower C101, the alkali solution addition amount is 15kg / h, and the alkali solution is a 32wt% NaOH aqueous solution. The desalted water is supplemented at the top of the lightness removal tower C101, the feed of the propylene glycol tower C102 is cancelled, the liquid phase hydrogenation of the reflux liquid of the propylene glycol tower C102 is cancelled, and the industrial-grade propylene glycol returned to the lightness removal tower after the liquid phase hydrogenation is cancelled. The industrial-grade propylene glycol is extracted as a by-product, and the external extraction flow rate is 1t / h. The other operating conditions are the same as those in Example 1.

[0057] Example 4

[0058] Compared with Example 1, desalted water is only added to the top of the lightness removal tower C101, and the amount of desalted water added to the top of the tower is 0.1 t / h. The addition of alkali solution to the feed of the lightness removal tower C101 is cancelled, the addition of additives to the feed of the propylene glycol tower C102 is cancelled, the liquid phase hydrogenation unit is cancelled, the reflux liquid of the propylene glycol tower C102 is not subjected to liquid phase hydrogenation, the industrial-grade propylene glycol returned to the lightness removal tower after liquid phase hydrogenation is cancelled, and the industrial-grade propylene glycol is extracted as a by-product, and the external extraction flow rate is 1 t / h. The other operating conditions are the same as those in Example 1.

[0059] Example 5

[0060] Compared with Example 1, only the additive is added to the feed of propylene glycol tower C102, and the additive is bisulfite, and the addition amount is 100ppm, which is equivalent to 1.5kg / h. The addition of alkali solution to the feed of lightness removal tower C101 is cancelled, the supplement of desalted water at the top of lightness removal tower C101 is cancelled, the liquid phase hydrogenation unit is cancelled, the reflux liquid of propylene glycol tower C102 is not subjected to liquid phase hydrogenation, the industrial-grade propylene glycol returned to the lightness removal tower after liquid phase hydrogenation is cancelled, and the industrial-grade propylene glycol is extracted as a by-product, and the external extraction flow rate is 1t / h. The other operating conditions are the same as those in Example 1.

[0061] Example 6

[0062] Compared with Example 1, only the liquid phase hydrogenation unit is retained, and the liquid phase hydrogenation flow rate is 26 t / h. The addition of alkali solution to the feed of the lightness removal tower C101 is cancelled, the supplement of desalted water at the top of the lightness removal tower C101 is cancelled, and the addition of additives to the feed of the propylene glycol tower C102 is cancelled. The other operating conditions are the same as those in Example 1.

[0063] Example 7

[0064] Compared with Implementation 1, the addition of alkali solution to the feed of the lightness removal tower C101 is cancelled, the supplement of desalted water at the top of the lightness removal tower C101 is cancelled, the addition of additives to the feed of the propylene glycol tower C102 is cancelled, the liquid phase hydrogenation is cancelled, the reflux liquid of the propylene glycol tower C102 is not subjected to liquid phase hydrogenation, the industrial-grade propylene glycol returned to the lightness removal tower C101 after liquid phase hydrogenation is cancelled, the industrial-grade propylene glycol is produced as a by-product, and the production flow rate is 1 t / h. The other operating conditions are the same as those in Example 1.

[0065] Example 8

[0066] Compared with Example 1, the addition of alkali solution to the feed of the lightness removal tower C101 is cancelled, the supplement of desalted water at the top of the lightness removal tower C101 is cancelled, the addition of additives to the feed of the propylene glycol tower C102 is cancelled, the liquid phase hydrogenation of the C102 reflux liquid is cancelled, the industrial-grade propylene glycol returned to the lightness removal tower after the liquid phase hydrogenation is cancelled, the industrial-grade propylene glycol is produced as a by-product, and the external production flow rate is 1t / h, the side-produced propylene glycol product is subjected to liquid phase hydrogenation, and the liquid-phase hydrogenated propylene glycol is directly sent as a product after cooling, and the other operating conditions are the same as those in Example 1.

[0067] Table 1 Comparison of propylene glycol product quality

[0068]

Claims

1. A 1,3-propylene glycol refining system, comprising a lightness removal tower (C101) and a propylene glycol tower (C102), characterized in that: The light-removal tower (C101) and the propylene glycol tower (C102) are both vacuum distillation towers; a raw material pipeline is provided in the middle of the light-removal tower (C101), and a light component (4) extraction pipe and a desalted water pipeline are provided at the top, and the desalted water pipeline is used to introduce desalted water into the light-removal tower (C101); the bottom of the light-removal tower (C101) is connected to the feed inlet in the middle of the propylene glycol tower (C102), and the top of the propylene glycol tower (C102) is connected to a liquid phase hydrogenation unit, and the hydrogenation unit of the liquid phase hydrogenation unit is connected to the liquid phase hydrogenation unit. The rear liquid phase outlet is connected to a product pump (P201), and the outlet of the product pump (P201) is respectively connected to the top of the propylene glycol tower (C102) and the feed inlet of the light removal tower (C101) through two independent pipelines; the distillation section of the propylene glycol tower (C102) is provided with a side sampling pipeline for sampling a polyester-grade 1,3-propylene glycol product (6); the feed inlet of the light removal tower (C101) is also connected to an alkali liquid pipe; the feed inlet of the propylene glycol tower (C102) is also connected to a reducing additive pipe.

2. The 1,3-propylene glycol purification system according to claim 1, characterized in that: The top of the light-removal tower (C101) is connected in sequence to a light-removal tower condenser (E101), a light-removal tower reflux tank (V101) and a light-removal tower reflux pump (P101) through pipelines; the desalted water pipeline is connected to the light-removal tower reflux tank (V101); the outlet of the light-removal tower reflux pump (P101) is respectively connected to a light component (4) extraction pipe and the top of the light-removal tower (C101).

3. The 1,3-propylene glycol purification system according to claim 1, characterized in that: The additive introduced into the propylene glycol column (C102) via the reducing additive line is bisulfite.

4. The 1,3-propylene glycol purification system according to claim 2, characterized in that: The top of the propylene glycol tower (C102) is connected in sequence to a propylene glycol tower condenser (E103), a propylene glycol tower reflux tank (V102), and a propylene glycol tower reflux pump (P103) through pipelines; the outlet of the propylene glycol tower reflux pump (P103) is connected to a liquid phase hydrogenation unit through a hydrogenation pipeline, and is connected to the top of the propylene glycol tower (C102) through a reflux pipeline; the feed port of the liquid phase hydrogenation unit is also connected to a hydrogen pipe.

5. The 1,3-propylene glycol purification system according to claim 4, characterized in that: The liquid phase hydrogenation unit comprises a liquid phase hydrogenation reactor (R201) and a flash tank (V201) connected in series; the liquid phase hydrogenation reactor (R201) comprises a catalyst bed and a gas-liquid separation chamber located below the catalyst bed, the upper part and the bottom part of the gas-liquid separation chamber are respectively connected to the flash tank (V201) via a purge gas pipe with a purge gas control valve and a propylene glycol pipe with a propylene glycol control valve; the operating pressure of the liquid phase hydrogenation reactor (R201) is controlled by hydrogen feed, and the hydrogen concentration in the liquid phase hydrogenation reactor (R201) is adjusted by the purge gas control valve; the top of the flash tank (V201) is connected to a purge gas cooler (E201) to condense and recover part of the vaporized propylene glycol.

6. The 1,3-propylene glycol purification system according to claim 5, characterized in that: A product pump (P201) is provided at the bottom of the flash tank (V201), and the outlet of the product pump (P201) is respectively connected to the reflux pipeline of the propylene glycol tower (C102) and the raw material pipeline of the light removal tower (C101).

7. The 1,3-propylene glycol purification system according to claim 6, characterized in that: The distillation section of the propylene glycol tower (C102) is connected to a side sampling pipeline, and the side sampling pipeline is sequentially connected to a side sampling product cooler (E106), a side sampling product buffer tank (V103) and a side sampling product pump (P105) for producing a polyester-grade 1,3-propylene glycol product (6); the catalyst for the liquid phase hydrogenation is a nickel-based catalyst; and the reboilers of the lightness removal tower (C101) and the propylene glycol tower (C102) are falling film reboilers.

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