Process and device for separating and purifying propylene glycol monomethyl ether by using molecular sieve membrane

Abstract

The invention relates to a process for purifying propylene glycol monomethyl ether through rectification-vapor permeation coupling, and belongs to the technical field of separation. Comprising the following steps: sending a propylene glycol monomethyl ether solution containing water and methanol into a rectifying tower, firstly removing methanol in the solution by using a rectifying device, then sending the solution in a tower kettle into a steam permeation device for steam permeation separation, removing moisture on a membrane permeation side, and intercepting propylene glycol monomethyl ether. Compared with the existing rectification sequence separation technology, the process of adding the third component is omitted, so that the retreatment operation of the third component does not need to be considered, the number of rectification towers is reduced, the experimental energy consumption and the device complexity are reduced, and the economic benefit is improved.

Description

Technical Field

[0001] The invention belongs to the field of hydrocarbon processing, and specifically relates to a separation process for producing propylene glycol methyl ether by coupling a molecular sieve membrane with a HPPO process and an energy consumption analysis method thereof. Background Art

[0002] Propylene oxide is a valuable petrochemical and organic synthesis raw material. Propylene oxide provides an important raw material basis for the automotive manufacturing industry, tobacco industry, construction industry and other industries. In 2020, China's production capacity has exceeded 3 million tons / year; it is expected that by 2025, the propylene oxide production capacity will reach 7 million tons / year.

[0003] At present, the industrial production methods for preparing propylene oxide mainly include the chlorohydrin method, the co-oxidation method, and the hydrogen peroxide direct oxidation method (HPPO). The chlorohydrin method has been banned from new construction since 2015 due to problems such as high water consumption, energy consumption, three wastes, and easy corrosion of equipment. The co-oxidation method has been gradually replaced by the HPPO method due to problems such as long process flow, a wide variety of raw materials, high equipment cost, restricted by-products, and high COD of wastewater. The HPPO method is a new process for producing propylene oxide (PO). The reaction conditions are relatively mild. The main reaction (propylene epoxidation) is carried out under the conditions of about 50°C, 3.0MPa(g) and liquid phase. Methanol is used as solvent, and PO is produced by using catalyst Ti-Si molecular sieve and hydrogen peroxide to oxidize propylene. There is an excess of propylene in the feed, and the unreacted propylene is recovered and recycled; the crude product contains PO, methanol, water and a small amount of propylene glycol, etc. The product separation unit can be divided into three main processes: propylene separation, PO refining and methanol purification. In the process of producing propylene oxide by HPPO, in addition to propylene oxide, the product is also rich in byproducts such as propylene glycol monomethyl ether (PM). Traditional incineration and biochemical treatment are costly, wasteful of resources, and increase the CO2 emission pressure of enterprises; resource utilization of high value-added chemicals in wastewater can significantly improve the economic benefits of HPPO process.

[0004] Traditional separation methods for dehydrating organic solvents mainly include adsorption and distillation. Organic matter is easy to form azeotropes or near-boiling products with water. It is difficult to remove water by using a simple distillation process. Special methods such as azeotropic distillation or extractive distillation will introduce a third component for removing water, which has the disadvantages of complex operation process, high energy consumption and introduction of impurities into the product. In the process of separation and purification of propylene oxide, substances such as methanol in wastewater are easy to remove and recycle, but propylene glycol monomethyl ether forms an azeotrope with water, so it is difficult to achieve efficient separation of the two by ordinary distillation. Summary of the invention

[0005] In order to improve the shortcomings of the existing technology, the present invention provides a distillation and steam permeation coupling process. The process flow is as follows: the propylene glycol methyl ether solution is transported to the heating equipment through a flow pump, preheated to a preset temperature and then sent to the steam permeation membrane assembly to separate the propylene glycol methyl ether from water, then the steam is condensed and sent back to the raw material tank, and the steam separated by the membrane is condensed and collected.

[0006] A separation process of coupled distillation and steam permeation, using steam permeation to separate water and propylene glycol monomethyl ether, comprises the following steps: Step 1: passing the wastewater containing propylene glycol monomethyl ether through a CH3OH separation tower, distilling methanol from the top of the tower, and distilling a mixture of propylene glycol monomethyl ether and water from the bottom of the tower; Step 2: passing the tower bottom material through a steam permeation device to remove moisture by steam permeation separation to obtain propylene glycol monomethyl ether.

[0007] In the step 1, the wastewater containing propylene glycol monomethyl ether contains 30-35% of water, 1-2% of methanol and 65-70% of propylene glycol monomethyl ether.

[0008] In the step 1, the tower bottom is the coupling part between the molecular sieve membrane and the distillation tower.

[0009] In the step 2, the membrane used in the steam permeation device is a combination of one or more molecular sieve membranes.

[0010] In the step 2, the permeate side of the steam permeation device is water, and the retentate side is propylene glycol monomethyl ether.

[0011] In the step 2, the operating pressure is between 0.1 MPa and 0.4 MPa.

[0012] In the step 2, the reflux ratio of the CH3OH separation tower is 1.2-2; the top temperature of the tower is controlled at 60-70°C, and the bottom temperature of the tower is controlled at 115-125°C.

[0013] A separation device of distillation-steam permeation coupling, comprising: Methanol separation tank, used for separating methanol from a mixture of propylene glycol monomethyl ether, methanol and water; Steam permeation unit for dehydrating a mixture of propylene glycol monomethyl ether and water. Beneficial Effects

[0014] Steam permeation has more obvious advantages than distillation in the dehydration of azeotropic and near-boiling organic solvents. The propylene glycol methyl ether solution is first separated under distillation. The concentration of the mixed solution at the top of the tower is 68.4 wt.%, and the azeotropic temperature is 98.4 °C. Subsequently, the mixed steam without condensation is dehydrated by steam permeation to achieve the coupling of distillation and steam permeation. When the water content of the organic solution is high, a steam permeation membrane with better stability is used to separate water and organic matter. After the water content on the raw liquid side is gradually reduced, a steam permeation membrane with better water separation performance is used for dehydration. Different membranes are effectively combined to improve separation efficiency and stability.

[0015] In summary, the present invention has the following advantages: Compared with traditional distillation, the operation is less complicated, the azeotropic equilibrium between propylene glycol methyl ether and water can be broken without adding a third component, and the energy consumption of separation is reduced.

[0016] The separation of propylene glycol methyl ether and water through steam permeation separation technology has the characteristics of simple operation and high separation efficiency, and can effectively reduce the cost of the separation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Schematic diagram of the process for removing water from propylene glycol methyl ether by membrane separation coupling in Example 1; Figure 2 : Comparative Example 1 Schematic diagram of the process for removing water from propylene glycol monomethyl ether by conventional distillation; Explanation of the reference numerals: T1-methanol separation tank; M1-sulfolane mixing tank; T2-azeotropic dehydration tower; T3-sulfolane recovery tower; T4-propylene glycol monomethyl ether purification tower; MEMBRANE-membrane module. DETAILED DESCRIPTION

[0018] In order to make the present invention easier to understand, the present invention will be described in detail below in conjunction with the embodiments and drawings. The embodiments are only for illustration and are not intended to limit the scope of application of the present invention. Example

[0019] according to Figure 1 As shown, this embodiment is used to illustrate the propylene glycol monomethyl ether distillation membrane coupled dehydration process and the energy consumption analysis of the corresponding process. A mixture of CH3OH, PM, and H2O is used to simulate the actual mixed solution components, and the mass fractions of each component are 0.015 (CH3OH); 0.672 (PM); 0.313 (H2O). The total flow rate of the mixture is 0.05 L / h. Figure 1As shown, the raw liquid passes through T1 to separate the component CH3OH, the operating pressure of the methanol separation tank is 0.2MPa, and the reflux ratio of the methanol separation tank is 1.5. Then the mixture of PM and H2O enters the MEMBRANE (NaA molecular sieve membrane) for steam permeation to recover propylene glycol monomethyl ether and remove moisture. The MEMBRANE-membrane component controls the temperature at 50°C, and the permeation pressure of the permeation molecular membrane is 0.01MPa. The energy consumption of the entire distillation-steam permeation process is 1408.39 kw, and 1.4 tons of products are produced per hour. The energy consumption per ton of output is 1001.71 kw / ton. Compared with the traditional distillation process, coupling through membrane separation technology effectively reduces the energy consumption in the process, reduces the difficulty of operation, and improves economic efficiency. Comparative Example 1 according to Figure 2 As shown, this comparative example is used to illustrate the conventional propylene glycol monomethyl ether distillation dehydration process and the energy consumption analysis of the corresponding process. A mixture of CH3OH, PM, and H2O is used to simulate the actual mixed solution components, and the mass fractions of the components are 0.015 (CH3OH); 0.672 (PM); 0.313 (H2O). The total flow rate of the mixture is 0.05 L / h. Figure 1 As shown, the raw liquid passes through T1 to separate the component CH3OH, the operating pressure of the methanol separation tank is 0.2MPa, and the reflux ratio of the methanol separation tank is 1.5. Then the mixture of PM and H2O enters T2 and is mixed with the sulfolane entering from M1 to azeotropically remove water, and the azeotropic control temperature is. The obtained low-water content propylene glycol monomethyl ether solution is transferred to T4 for further purification. Sulfolane flows out from the retentate side using T3 and is recycled, and the reflux ratio is controlled at 1:1.5. The energy consumption of the entire distillation process is 8106375 kw, and 1.291 tons of products are produced per hour, and the energy consumption per ton of output is 6279.43 kw / t.

Claims

1. A separation process of coupled distillation and steam permeation, characterized in that: The method of separating water and propylene glycol monomethyl ether by steam permeation comprises the following steps: Step 1: passing the wastewater containing propylene glycol monomethyl ether through a CH3OH separation tower, distilling methanol from the top of the tower, and distilling a mixture of propylene glycol monomethyl ether and water from the bottom of the tower; Step 2: passing the tower bottom material through a steam permeation device to remove moisture by steam permeation separation to obtain propylene glycol monomethyl ether.

2. The distillation-steam permeation coupling process according to claim 1, characterized in that: In the step 1, the wastewater containing propylene glycol monomethyl ether contains 30-35% of water, 1-2% of methanol and 65-70% of propylene glycol monomethyl ether.

3. The distillation-steam permeation coupling process according to claim 1, characterized in that: In the step 1, the tower bottom is the coupling part between the molecular sieve membrane and the distillation tower.

4. The distillation-steam permeation coupling process according to claim 1, characterized in that: In the step 2, the membrane used in the steam permeation device is a combination of one or several molecular sieve membranes, and the membrane is a combination of one or several of NaA molecular sieve membrane, NaY molecular sieve membrane, zeolite membrane, sodium alginate membrane, and PVA membrane.

5. The distillation-steam permeation coupling process according to claim 1, characterized in that: In the step 2, the permeate side of the steam permeation device is water, and the retentate side is propylene glycol monomethyl ether.

6. The distillation-steam permeation coupling process according to claim 1, characterized in that: In the step 2, the operating pressure is between 0.1 MPa and 0.4 MPa.

7. The distillation-steam permeation coupling process according to claim 1, characterized in that: In the step 2, the reflux ratio of the CH3OH separation tower is 1.2-2; the top temperature of the tower is controlled at 60-70°C, and the bottom temperature of the tower is controlled at 115-125°C.

8. A separation device of coupled distillation and steam permeation, characterized in that: include: Methanol separation tank, used for separating methanol from a mixture of propylene glycol monomethyl ether, methanol and water; Steam permeation unit for dehydrating a mixture of propylene glycol monomethyl ether and water.

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