Purification method of crude glycerol

Abstract

The invention relates to a purification method of crude glycerine, which comprises the following steps: sequentially carrying out acidification treatment, oil removal treatment, nanofiltration treatment, resin adsorption and membrane distillation on the crude glycerine to obtain a glycerine product, the oil removal treatment is carried out by adopting an oil removal device comprising an oleophylic filter element and a hydrophilic filter element, rapid separation of fatty acid in the crude glycerine is realized, the method is short in time consumption and high in separation efficiency, and the whole operation process can be carried out under a relatively low temperature condition by combining a resin adsorption process and a membrane distillation process; the method not only effectively reduces energy consumption, but also avoids possible polymerization reaction of glycerol in a high-temperature environment; meanwhile, according to the method, effective separation of salt, methanol and water in the crude glycerol can be achieved without dilution treatment on the high-concentration crude glycerol, then a high-purity glycerol product is prepared, the purity of the high-purity glycerol product can reach 99.0% or above, the requirements for environmental protection and energy conservation are met, and the method is suitable for large-scale industrial production and application.

Description

Technical Field

[0001] This invention relates to the field of crude glycerol refining technology, and to a method for purifying crude glycerol, particularly to a method for purifying crude glycerol, a byproduct of biodiesel and / or oleochemical processes. Background Technology

[0002] In the energy and chemical industries, the biodiesel and oleochemical industries are developing rapidly, and the issues of by-product treatment and resource utilization during production are becoming increasingly prominent. Among these, crude glycerol, a typical by-product of biodiesel production, is produced in considerable quantities, with approximately 0.1 tons of crude glycerol generated for every ton of biodiesel produced. High-purity glycerol is an important chemical raw material, widely used and indispensable in the food, pharmaceutical, cosmetic, and tobacco industries, but its source is scarce. Therefore, recycling crude glycerol, a by-product of biodiesel or oleochemical production, can both reduce biodiesel production costs and increase the source of high-purity glycerol. However, this crude glycerol contains various impurities such as fatty acids, methanol, and salts, making it unsuitable for direct use in industrial applications requiring high glycerol purity. Therefore, it is essential to refine and purify it.

[0003] Currently, industrial methods for purifying crude glycerol to obtain high-purity glycerol include acidification, vacuum distillation, ion exchange, membrane separation, and electrodialysis. For example, CN101538188A discloses a method for refining crude glycerol, a byproduct of biodiesel production. This method uses ion exchange resin to remove anions and cations from the crude glycerol, then removes methanol and water separately by distillation, and finally removes trace colored impurities by decolorization with activated carbon or activated clay to obtain high-purity glycerol. However, this method does not pre-treat the fatty acids in the crude glycerol, requiring the ion exchange process to simultaneously remove salts and fatty acids from the material. This additional load increases the resin regeneration frequency and shortens its service life. Moreover, conventional distillation for removing methanol and water is energy-intensive.

[0004] For example, CN102229521A discloses a process for refining crude glycerol and recovering byproducts. This method obtains high-purity glycerol through crude glycerol dilution, resin adsorption, nanofiltration, resin adsorption, and distillation. However, this method also does not pretreat impurity fatty acids, which increases the difficulty of resin adsorption and requires pre-dilution with water, thus increasing the load on subsequent processing. In addition, the energy consumption is high when removing light component impurities using conventional distillation methods.

[0005] For example, CN105585449A discloses a method for processing glycerol, a byproduct of biodiesel production. This method obtains high-purity glycerol through acidification to remove oils, addition of organic alcohols for desalination, dilution of glycerol with water, electrodialysis for desalination, and distillation. However, the acidification process for removing oils is time-consuming. Furthermore, the introduction of organic alcohols and water increases the load on subsequent processing steps, and conventional distillation methods for removing light component impurities are energy-intensive.

[0006] Therefore, there is an urgent need to develop a method for purifying crude glycerol, especially a method for purifying crude glycerol, a byproduct of biodiesel and / or oleochemicals, that can efficiently separate fatty acids without dilution steps, achieve low-energy production of high-purity glycerol, meet the purity requirements of glycerol for the synthesis of dichloropropanol, and simultaneously separate and recover other components to reduce production costs. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for purifying crude glycerol, which achieves efficient separation of fatty acids from crude glycerol. It eliminates the need for dilution of the crude glycerol, enabling the separation and recovery of various components from high-concentration crude glycerol, thus preparing high-purity glycerol suitable for the synthesis of dichloropropanol and reducing production costs.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for purifying crude glycerol, the purification method comprising the following steps:

[0010] Crude glycerol is subjected to acidification, degreasing, nanofiltration, resin adsorption, and membrane distillation in sequence to obtain the glycerol product.

[0011] The oil removal process is carried out using an oil removal device that includes an oleophilic filter element and a hydrophilic filter element.

[0012] This invention employs an oil removal device including oleophilic and hydrophilic filter elements for oil removal. Utilizing the demulsification and aggregation effects of the oleophilic filter element, fatty acids in crude glycerol are demulsified and aggregated, floating to the top due to their lower density. The aqueous phase is then filtered through the hydrophilic filter element to the nanofiltration process, achieving oil-water phase separation. This pre-separates most of the fatty acids in the crude glycerol within a short time, avoiding the high fatty acid content that would lead to excessive nanofiltration load and blockage of the nanofiltration membrane, hindering purification. Combined with acidification and nanofiltration processes, efficient separation of fatty acids from crude glycerol is achieved. Finally, resin adsorption and membrane distillation processes are used to separate salts, methanol, and water from the crude glycerol, yielding a high-purity glycerol product.

[0013] Compared to conventional acidification, settling, and stratification separation methods for oil removal, this invention employs an oil removal device that includes both oleophilic and hydrophilic filter elements. This improves the removal rate of fatty acids from crude glycerol, significantly shortens the oil removal time, and reduces the post-processing load.

[0014] Compared to conventional distillation methods, this invention uses membrane distillation to separate methanol and water from crude glycerol, which consumes relatively less energy.

[0015] Preferably, the crude glycerol comprises, by weight percentage, 75.0-85.0 wt% glycerol, 2.0-2.5 wt% fatty acids, 3.0-4.5 wt% methanol, 5.5-6.0 wt% salt and 3.0-12.5 wt% water.

[0016] The composition includes: 75.0–85.0 wt% glycerol, for example, 75.0 wt%, 78.0 wt%, 80.0 wt%, 82.0 wt%, or 85.0 wt%; 2.0–2.5 wt% fatty acids, for example, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, or 2.5 wt%; 3.0–4.5 wt% methanol, for example, 3.0 wt%, 3.2 wt%, 3.5 wt%, 3.8 wt%, 4.0 wt%, 4.2 wt%, or 4.5 wt%; 5.5–6.0 wt% salt, for example, 5.5 wt%, 5.6 wt%, 5.7 wt%, 5.8 wt%, 5.9 wt%, or 6.0 wt%; and 3.0–12.5 wt% water, for example, 3.0 wt%, 5.0 wt%, 8 wt%, 9 wt%, 10 ... wt%, 10 wt%, 12.0 wt% or 12.5 wt%, etc.

[0017] Preferably, the crude glycerol is selected from biodiesel production byproducts and / or oleochemical byproducts.

[0018] Preferably, the purification method further includes pretreatment of the crude glycerol before the acidification treatment.

[0019] Preferably, the pretreatment includes filtering the crude glycerol using a filter screen to obtain a first filtrate.

[0020] The purpose of the pretreatment described in this invention is to remove suspended solids from crude glycerol, so as to avoid clogging of the filter element or nanofiltration membrane of the subsequent oil removal device.

[0021] Preferably, the pore size of the filter screen is 0.1~5mm, for example, it can be 0.1mm, 0.5mm, 1.0mm, 3.0mm or 5.0mm.

[0022] Preferably, the acidification treatment includes adjusting the pH of the first filtrate to obtain an acidified solution.

[0023] Preferably, the acidification treatment temperature is 80~90℃, for example, it can be 80℃, 82℃, 85℃, 88℃ or 90℃, etc.

[0024] Preferably, the acid solution used in the acidification treatment includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or phosphoric acid, wherein typical but non-limiting combinations include a combination of hydrochloric acid and sulfuric acid or a combination of hydrochloric acid and phosphoric acid, etc.

[0025] Preferably, the endpoint of the acidification treatment is that the pH of the first filtrate is 5.0 to 6.0, for example, it can be 5.0, 5.2, 5.4, 5.6, 5.8 or 6.0, etc.

[0026] Preferably, the oil removal device includes a housing and a first filter element and a second filter element disposed inside the housing.

[0027] The filter element of the first filter component is an oleophilic filter element.

[0028] Preferably, the oleophilic filter element is a first composite membrane made of para-aramid, polypropylene and polyurethane.

[0029] Preferably, the filter element of the second filter component is a hydrophilic filter element.

[0030] Preferably, the hydrophilic filter element is a second composite membrane prepared by combining para-aramid, polyacrylamide and polyacrylonitrile.

[0031] Preferably, an oil drain port is provided on the upper side of the housing.

[0032] Preferably, the bottom of the housing is provided with an inlet pipe and a drain pipe, and the inlet pipe is connected to the first filter component, and the drain pipe is connected to the second filter component.

[0033] Preferably, the degreasing treatment includes first passing the acidified liquid through the oleophilic filter element to remove oil, and then separating it through the hydrophilic filter element to obtain a second filtrate.

[0034] Preferably, the oleophilic filter element includes a first composite membrane, which includes para-aramid, polypropylene, and polyurethane.

[0035] Preferably, the hydrophilic filter element includes a second composite membrane, which includes para-aramid, polyacrylamide, and polyacrylonitrile.

[0036] Preferably, the nanofiltration process includes performing nanofiltration on the second filtrate using a nanofiltration membrane to obtain a third filtrate.

[0037] The nanofiltration process described in this invention is used to remove residual fatty acids from crude glycerol during the degreasing process.

[0038] Preferably, the nanofiltration membrane used in the nanofiltration process is a composite membrane of para-aramid and polytetrafluoroethylene.

[0039] The present invention further preferably uses a nanofiltration membrane made of para-aramid and polytetrafluoroethylene composite material, which has the characteristics of acid resistance, high strength and long service life, thereby avoiding the need for alkali neutralization before nanofiltration and reducing the post-treatment load.

[0040] Preferably, the average pore size of the nanofiltration membrane is 1.0~2.0 nm, for example, it can be 1.0 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm or 2.0 nm.

[0041] Preferably, the nanofiltration membrane has a molecular weight cutoff of 140~480 Da, for example, it can be 140 Da, 180 Da, 220 Da, 260 Da, 300 Da, 340 Da, 380 Da, 420 Da, 460 Da or 480 Da, etc.

[0042] Preferably, the operating pressure of the nanofiltration process is 5.0~10.0 bar, for example, it can be 5.0 bar, 6.0 bar, 7.0 bar, 8.0 bar, 9.0 bar or 10.0 bar.

[0043] Preferably, the resin adsorption includes passing the third filtrate sequentially through a cation exchange column, an anion exchange column, and a mixed cation and anion exchange column for resin adsorption to obtain a fourth filtrate.

[0044] Preferably, the operating temperature of the cation exchange column, the anion exchange column, and the mixed cation and anion exchange column is independently 20~30℃, for example, 20℃, 22℃, 25℃, 28℃, or 30℃.

[0045] Preferably, the resin in the cation exchange column comprises an acidic cation exchange resin.

[0046] Preferably, the resin in the anion exchange column includes a basic anion exchange resin.

[0047] Preferably, the resin in the mixed cation and anion exchange column includes an acidic cation exchange resin and a basic anion exchange resin.

[0048] Preferably, the acidic cation exchange resin comprises a gel-type strongly acidic styrene-based cation exchange resin. For example, it may be type 732 and / or type 734, etc.

[0049] Preferably, the basic anion exchange resin includes a gel-type strong basic styrene-based anion exchange resin, such as type 201 and / or type 717.

[0050] Preferably, the flow rate of the third filtrate during resin adsorption is 10~30 BV / h, for example, it can be 10 BV / h, 12 BV / h, 15 BV / h, 18 BV / h, 20 BV / h, 22 BV / h, 25 BV / h, 28 BV / h or 30 BV / h, etc.

[0051] Preferably, the membrane distillation includes membrane distillation of the fourth filtrate to obtain a glycerol product.

[0052] The purpose of membrane distillation in this invention is to separate methanol and water from crude glycerol, and to recover and reuse the separated methanol and water.

[0053] Preferably, the membrane used in the membrane distillation has an average thickness of 70~80μm, for example, it can be 70μm, 72μm, 75μm, 78μm or 80μm.

[0054] Preferably, the membrane used in the membrane distillation has an average pore size of 0.1~0.5μm, such as 0.1μm, 0.2μm, 0.3μm, 0.4μm or 0.5μm.

[0055] Preferably, the temperature difference across the membrane during membrane distillation is 20~60℃, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, and preferably 40~60℃.

[0056] Preferably, the purity of the glycerin product is ≥99.0%, for example, it can be 99.0%, 99.2%, 99.4%, 99.6% or 99.8%, etc., preferably ≥99.8%.

[0057] As a further preferred technical solution of the present invention, the purification method includes the following steps:

[0058] (1) Crude glycerol is filtered using a filter screen with a pore size of 0.1~5mm to obtain a first filtrate, which is then acidified at 80~90℃. The acidification process includes adjusting the pH of the first filtrate to 5.0~6.0 to obtain an acidified solution.

[0059] The acid solution includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or phosphoric acid.

[0060] (2) The acidified liquid in step (1) is de-oiled using an oil removal device including an oleophilic filter element and a hydrophilic filter element. The oil removal process includes the acidified liquid being de-oiled by the oleophilic filter element and then separated by the hydrophilic filter element to obtain a second filtrate.

[0061] The oleophilic filter element includes a first composite membrane, which comprises para-aramid, polypropylene, and polyurethane; the hydrophilic filter element includes a second composite membrane, which comprises para-aramid, polyacrylamide, and polyacrylonitrile.

[0062] (3) At a working pressure of 5.0~10.0 bar, the second filtrate in step (2) is subjected to nanofiltration treatment using a nanofiltration membrane. The nanofiltration membrane used in the nanofiltration treatment is made of para-aramid and polytetrafluoroethylene with a pore size of 1.0~2.0 nm to obtain the third filtrate.

[0063] (4) The third filtrate from step (3) is sequentially passed through a cation exchange column, an anion exchange column, and a mixed anion and cation exchange column at a flow rate of 10~30 BV / h to obtain a fourth filtrate;

[0064] The operating temperature of each of the cation exchange column, the anion exchange column, and the mixed cation and anion exchange column is independently 20~30℃;

[0065] (5) The fourth filtrate from step (4) is subjected to membrane distillation. The membrane used in the membrane distillation has a thickness of 70~80μm and a pore size of 0.1~0.5μm. The temperature difference between the two sides of the membrane during the membrane distillation is 20~60℃, and a glycerol product with a purity ≥99.0% is obtained.

[0066] Compared with the prior art, the present invention has at least the following beneficial effects:

[0067] The crude glycerol purification method provided by this invention, compared with the traditional acidification and static oil removal method, uses an oil removal device including oleophilic and hydrophilic filter elements for oil removal, combined with acidification and nanofiltration processes, to achieve rapid separation of fatty acids in crude glycerol. This method is time-saving and highly efficient. By combining resin adsorption and membrane distillation processes, the entire operation is carried out at a lower temperature, effectively reducing energy consumption and avoiding polymerization reactions that may occur in glycerol at high temperatures. It eliminates the need for dilution of high-concentration crude glycerol, allowing for the separation of salt, methanol, and water to obtain a high-purity glycerol product with a preferred purity of over 99.0%, meeting environmental protection and energy-saving requirements and suitable for large-scale industrial production applications. Attached Figure Description

[0068] Figure 1 This is a process flow diagram of the crude glycerol purification method provided in Embodiment 1 of the present invention.

[0069] Figure 2 This is a schematic diagram of the oil removal device used in the crude glycerol purification method provided in Embodiment 1 of the present invention.

[0070] In the diagram: 1. Housing; 2. First filter element; 3. Second filter element; 4. Liquid inlet pipe; 5. Drain pipe; 6. Oil outlet. Detailed Implementation

[0071] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0072] The 732 type resin used in the following examples or comparative examples was produced by Langfang Jinan Resin Co., Ltd., and the 201 type resin was produced by Tianjin Bohong Resin Technology Co., Ltd.

[0073] I. Implementation Examples

[0074] Example 1

[0075] This embodiment provides a method for purifying crude glycerol, wherein the crude glycerol is a byproduct of biodiesel production (10 kg), and its composition and content are shown in Table 1.

[0076] Table 1

[0077]

[0078] The purification method is performed as follows: Figure 1 The process flow shown includes the following steps:

[0079] (1) The crude glycerol was pretreated by using a filter screen with a pore size of 0.1 mm, i.e., the suspended matter was removed by filtration to obtain the first filtrate, and then 32 wt% hydrochloric acid was added at 85°C to acidify the first filtrate to adjust the pH to 5.5, so as to obtain the acidified solution.

[0080] (2) Adopting such Figure 2 The oil removal device shown performs oil removal treatment on the acidified liquid in step (1), that is, the oil removal treatment includes the acidified liquid first passing through the oleophilic filter element for oil removal (demulsification, aggregation, floating on the upper layer and being discharged from the oil outlet), and then passing through the hydrophilic filter element for separation (flowing to the lower layer and being discharged from the drain pipe to enter the nanofiltration process), to obtain the second filtrate;

[0081] like Figure 2As shown, the oil removal device includes a housing 1 and a first filter element 2 and a second filter element 3 disposed inside the housing 1; the filter element of the first filter element 2 is an oleophilic filter element, which is made of a first composite membrane prepared by combining para-aramid, polypropylene and polyurethane (mass ratio of 5:2:1); the filter element of the second filter element 3 is a hydrophilic filter element, which is made of a second composite membrane prepared by combining para-aramid, polyacrylamide and polyacrylonitrile (mass ratio of 5:2:1); an oil drain port 6 is provided on the upper side of the housing 1, and an inlet pipe 4 and a drain pipe 5 are provided on the bottom of the housing 1, with the inlet pipe 4 connected to the first filter element 2 and the drain pipe 5 connected to the second filter element 3;

[0082] (3) At a working pressure of 8.0 bar, the second filtrate in step (2) is subjected to nanofiltration treatment using a nanofiltration membrane. The nanofiltration membrane used in the nanofiltration treatment is a composite membrane of para-aramid and polytetrafluoroethylene (mass ratio of 1:1) with an average pore size of 1.5 nm. The third filtrate is obtained, and the backwashing liquid after backwashing the membrane is returned to the oil removal device.

[0083] (4) The third filtrate from step (3) is sequentially passed through a cation exchange column (resin is type 732 resin), an anion exchange column (resin is type 201 resin) and a mixed anion and cation exchange column (the mass ratio of type 732 resin to type 201 resin is 1:1) at a flow rate of 20 BV / h to perform resin adsorption and obtain the fourth filtrate.

[0084] The operating temperature of the cation exchange column, the anion exchange column, and the mixed cation and anion exchange column is 25°C.

[0085] (5) The fourth filtrate from step (4) is subjected to membrane distillation to separate methanol and water. The membrane used in the membrane distillation has an average thickness of 75 μm and an average pore size of 0.25 μm. The temperature difference between the two sides of the membrane during the membrane distillation is 50 °C, and a glycerol product with a purity of 99.8% is obtained.

[0086] Example 2

[0087] This embodiment provides a method for purifying crude glycerol, wherein the crude glycerol is a by-product of oleochemicals (10 kg), and its composition and content are shown in Table 2.

[0088] Table 2

[0089]

[0090] The purification method includes the following steps:

[0091] (1) The crude glycerol was pretreated by using a filter screen with a pore size of 2.0 mm, i.e., the suspended matter was removed by filtration to obtain the first filtrate, and then 32 wt% hydrochloric acid was added at 80°C to acidify the first filtrate to adjust the pH to 5.0, so as to obtain the acidified solution.

[0092] (2) The same oil removal device as in Example 1 is used to remove oil from the acidified liquid in step (1). That is, the oil removal process includes the acidified liquid first passing through the oleophilic filter element to remove oil (after demulsification and aggregation, it floats to the upper layer and is discharged from the oil outlet), and then passing through the hydrophilic filter element for separation (flowing to the lower layer and being discharged from the drain pipe to enter the nanofiltration process) to obtain the second filtrate.

[0093] (3) At a working pressure of 5.0 bar, the second filtrate in step (2) is subjected to nanofiltration treatment using a nanofiltration membrane. The nanofiltration membrane used in the nanofiltration treatment is a composite membrane of para-aramid and polytetrafluoroethylene (mass ratio of 1:1) with an average pore size of 1.0 nm. The third filtrate is obtained, and the backwashing liquid after backwashing the membrane is returned to the oil removal device.

[0094] (4) The third filtrate from step (3) is sequentially passed through a cation exchange column (resin is type 732 resin), an anion exchange column (resin is type 201 resin) and a mixed anion and cation exchange column (the mass ratio of type 732 resin to type 201 resin is 1:1) at a flow rate of 10 BV / h to perform resin adsorption and obtain the fourth filtrate.

[0095] The operating temperature of the cation exchange column, the anion exchange column, and the mixed cation and anion exchange column is 20°C.

[0096] (5) The fourth filtrate from step (4) is subjected to membrane distillation to separate methanol and water. The membrane used in the membrane distillation has an average thickness of 70 μm and an average pore size of 0.1 μm. The temperature difference between the two sides of the membrane during the membrane distillation is 20 °C, and a glycerol product with a purity of 99.2% is obtained.

[0097] Example 3

[0098] This embodiment provides a method for purifying crude glycerol, wherein the crude glycerol is a byproduct of biodiesel production (10 kg), and its composition and content are shown in Table 3.

[0099] Table 3

[0100]

[0101] The purification method includes the following steps:

[0102] (1) The crude glycerol was pretreated by using a filter screen with a pore size of 5.0 mm, i.e., the suspended matter was removed by filtration to obtain the first filtrate, and then 32 wt% hydrochloric acid was added at 90°C to acidify the first filtrate to adjust the pH to 6.0, so as to obtain the acidified solution.

[0103] (2) The same oil removal device as in Example 1 is used to remove oil from the acidified liquid in step (1). That is, the oil removal process includes the acidified liquid first passing through the oleophilic filter element to remove oil (after demulsification and aggregation, it floats to the upper layer and is discharged from the oil outlet), and then passing through the hydrophilic filter element for separation (flowing to the lower layer and being discharged from the drain pipe to enter the nanofiltration process) to obtain the second filtrate.

[0104] (3) At a working pressure of 10.0 bar, the second filtrate in step (2) is subjected to nanofiltration treatment using a nanofiltration membrane. The nanofiltration membrane used in the nanofiltration treatment is a composite membrane of para-aramid and polytetrafluoroethylene (mass ratio of 1:1) with an average pore size of 2.0 nm. The third filtrate is obtained, and the backwashing liquid after backwashing the membrane is returned to the oil removal device.

[0105] (4) The third filtrate from step (3) is sequentially passed through a cation exchange column (resin is type 732 resin), an anion exchange column (resin is type 201 resin) and a mixed anion and cation exchange column (the mass ratio of type 732 resin to type 201 resin is 1:1) at a flow rate of 30 BV / h to perform resin adsorption and obtain the fourth filtrate.

[0106] The operating temperature of the cation exchange column, the anion exchange column, and the mixed cation and anion exchange column is 30°C.

[0107] (5) The fourth filtrate from step (4) is subjected to membrane distillation to separate methanol and water. The membrane used in the membrane distillation has an average thickness of 80 μm and an average pore size of 0.5 μm. The temperature difference across the membrane during the membrane distillation is 60 °C, resulting in a glycerol product with a purity of 99.6%.

[0108] Examples 4 to 6

[0109] The purification methods for crude glycerol provided in Examples 4 to 6 are based on Example 1, except that step (1) is changed to adjust the pH of the first filtrate. That is, the pH of the first filtrate after acidification is 1.5, 3.5 or 7.5, respectively. The rest are the same as in Example 1.

[0110] Example 7 Example 12

[0111] The purification methods for crude glycerol provided in Examples 7 to 12 are the same as those in Example 1, except that the acidification temperature in step (1) is changed to 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0112] Examples 13-15

[0113] The purification methods for crude glycerol provided in Examples 13 to 15 are the same as those in Example 1, except that the average pore size of the nanofiltration membrane in step (3) is changed to 3.5 nm, 5.5 nm or 7.5 nm respectively.

[0114] Example 16

[0115] This embodiment provides a method for purifying crude glycerol. Except for the flow rate of the third filtrate in step (4) being 8 BV / h, the purification method is the same as in Example 1.

[0116] Example 17

[0117] This embodiment provides a method for purifying crude glycerol. Except for the flow rate of the third filtrate in step (4) being 35 BV / h, the purification method is the same as in Example 1.

[0118] Examples 18 to 21

[0119] The purification methods for crude glycerol provided in Examples 18 to 21 are the same as those in Example 1, except that the temperature difference between the two sides of the membrane distillation in step (5) is changed to 20°C, 30°C, 40°C or 60°C respectively.

[0120] Example 22

[0121] This embodiment provides a method for purifying crude glycerol. Except for the nanofiltration membrane in step (3) being made of polyamide, the purification method is the same as in Example 1.

[0122] II. Comparative Example

[0123] Comparative Example 1

[0124] This comparative example provides a method for purifying crude glycerol. Except for step (2), which does not use an oil removal device for oil removal but instead separates the oil and water after standing and stratification, the purification method is the same as in Example 1.

[0125] III. Tests and Results

[0126] ① Test the fatty acid content in the second filtrate of the purification method provided in Example 1 to Example 12 and Comparative Example 1 in step (2) and calculate the average removal rate of fatty acids by the oil removal treatment (the content of fatty acids in crude glycerol is 2.3wt%, so the original content of fatty acids in crude glycerol is 23000mg / Kg, and the cumulative running time is 1 day). The results are shown in Table 4.

[0127] Table 4

[0128]

[0129] The data in Table 4 shows that: (1) Based on the data from Examples 1 to 3, the crude glycerol purification method provided by the present invention uses an oil removal device including an oleophilic filter element and a hydrophilic filter element for oil removal treatment, combined with acidification treatment and nanofiltration treatment, which improves the removal rate of fatty acids before the nanofiltration process to over 99.2%, reduces the load of the nanofiltration process, and reduces the replacement frequency of the nanofiltration membrane.

[0130] (2) As can be seen from the combined examples 1, 4 to 12 and Comparative Example 1, the present invention further preferably has the endpoint of the acidification treatment as the pH of the first filtrate being 5.0 to 6.0, and further preferably has the acidification treatment temperature being 80 to 90°C. This, combined with the oil removal treatment step using an oil removal device including an oleophilic filter element and a hydrophilic filter element, further improves the removal rate of fatty acids.

[0131] ② The average removal rate of fatty acids after sodium filtration in the purification methods described in Example 1 and Comparative Example 1, as well as the initial membrane flux, the cut-off membrane flux, and the purity of the glycerol product of the corresponding nanofiltration membranes, were tested respectively. The results are shown in Table 5.

[0132] Table 5

[0133]

[0134] As can be seen from the data in Table 5, Comparative Example 1 did not use an oil removal device for oil removal. Instead, it allowed the mixture to stand and separate into layers before directly removing fatty acids via nanofiltration. The nanofiltration membrane's flux decreased by 83.7% after only one day of operation, and the purity of the glycerol product was only 99.4%. This indicates that the oil removal process of this invention, which uses an oil removal device including both oleophilic and hydrophilic filter elements, significantly reduces the fatty acid processing load in the nanofiltration process. Moreover, the flux decrease of the nanofiltration membrane is relatively small after 15 days, and the purity of the glycerol product is as high as 99.8%.

[0135] ③ Test the fatty acid content in the third filtrate described in step (3) of Examples 1, 13 to 15 and 22 above and calculate the average removal rate of fatty acids after nanofiltration treatment in step (3) (based on the fatty acid content in the second filtrate, i.e. 115 mg / Kg, with a running time of 15 days), and test the purity of the obtained glycerol product. The results are shown in Table 6.

[0136] Table 6

[0137]

[0138] As can be seen from the data in Table 6, the nanofiltration membrane used in the nanofiltration process of this invention is further preferably made of para-aramid and polytetrafluoroethylene. The average pore size of the nanofiltration membrane is selected to be 1.0~2.0 nm. The two work synergistically to further improve the removal rate of fatty acids in the nanofiltration process, thereby improving the purity of the obtained glycerol product.

[0139] ④ The purity of the glycerol products obtained by the purification methods described in Examples 1 and 16 to 21 above was tested, and the results are shown in Tables 7 and 8.

[0140] Table 7

[0141]

[0142] As can be seen from the data in Table 7, the present invention further optimizes the flow rate of the third filtrate during resin adsorption to be 10~30 BV / h, which is more conducive to the efficient removal of salt from the crude glycerol, thereby improving the purity of the glycerol product.

[0143] Table 8

[0144]

[0145] As can be seen from the data in Table 8, the present invention further optimizes the temperature difference between the two sides of the membrane during membrane distillation to be 40~60℃, which further ensures the complete removal of methanol and water from the crude glycerol, thereby improving the purity of the glycerol product.

[0146] ⑤ The average removal rate of fatty acids and the initial and final membrane flux of the corresponding nanofiltration membrane after 15 and 30 days of nanofiltration treatment of the second filtrate in the purification method described in Example 1 were tested; and the average removal rate of fatty acids and the initial and final membrane flux of the corresponding nanofiltration membrane after 15 days of nanofiltration treatment of the second filtrate in the purification method described in Example 22 were tested. The results are shown in Table 9.

[0147] Table 9

[0148]

[0149] As can be seen from the data in Table 9, when the nanofiltration membrane is made of a composite membrane of para-aramid and polytetrafluoroethylene, the average removal rate of fatty acids is as high as 94.4% after 15 days and still as high as 91.5% after 30 days. Moreover, the membrane flux of the nanofiltration membrane decreases little after 15 or 30 days. However, when the nanofiltration membrane is made of polyamide, the average removal rate of fatty acids only reaches 87.1% after 15 days of nanofiltration treatment, and the membrane flux decreases by 84.3%. Therefore, it is evident that the present invention further specifically selects the nanofiltration membrane made of a composite membrane of para-aramid and polytetrafluoroethylene, which has a longer service life and further improves the removal rate of fatty acids.

[0150] In summary, the crude glycerol purification method provided by this invention employs a specific oil removal device including oleophilic and hydrophilic filter elements for oil removal. Furthermore, the endpoint pH and temperature of the acidification treatment are optimized. The material and average pore size of the nanofiltration membrane used in the nanofiltration treatment, the flow rate of the third filtrate during resin adsorption, and the temperature difference across the membrane during membrane distillation all work within a specific range to improve the separation efficiency of fatty acids, salts, methanol, and water, thereby increasing the purity of the glycerol product. The preparation method can be carried out at a lower temperature without additional dilution of the glycerol, avoiding glycerol polymerization, reducing energy consumption, and thus lowering purification costs.

[0151] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for purifying crude glycerol, characterized by, The purification method comprises the following steps: The crude glycerol is sequentially subjected to acidification treatment, oil removal treatment, nanofiltration treatment, resin adsorption, and membrane distillation to obtain a glycerol product; The oil removal treatment is performed using an oil removal device comprising an oleophilic filter element and a hydrophilic filter element.

2. The purification method according to claim 1, characterized by, The crude glycerol comprises 75.0-85.0 wt% glycerol, 2.0-2.5 wt% fatty acid, 3.0-4.5 wt% methanol, 5.5-6.0 wt% salt, and 3.0-12.5 wt% water in terms of mass percentage.

3. The purification method according to claim 1 or 2, characterized by, The purification method further comprises pretreating the crude glycerol before the acidification treatment; Preferably, the pretreatment comprises filtering the crude glycerol using a filter screen to obtain a first filtrate; Preferably, the filter screen has a pore size of 0.1-5 mm.

4. The purification method according to claim 3, characterized by, The acidification treatment comprises adjusting the pH of the first filtrate to obtain an acidified liquid; Preferably, the acidification treatment is performed at a temperature of 80-90℃; Preferably, the acid solution used in the acidification treatment comprises any one or a combination of at least two of hydrochloric acid, sulfuric acid, or phosphoric acid; Preferably, the acidification treatment is terminated when the pH of the first filtrate is 5.0-6.

0.

5. The purification method according to claim 4, characterized in that, The oil removal treatment comprises removing oil from the acidified liquid using the oleophilic filter element, and then separating the acidified liquid using the hydrophilic filter element to obtain a second filtrate; Preferably, the oleophilic filter element comprises a first composite membrane comprising para-aramid, polypropylene, and polyamine plastic; Preferably, the hydrophilic filter element comprises a second composite membrane comprising para-aramid, polyacrylamide, and polyacrylonitrile.

6. The purification method according to claim 5, characterized by, The nanofiltration treatment comprises nanofiltrating the second filtrate using a nanofiltration membrane to obtain a third filtrate; Preferably, the nanofiltration membrane is a composite membrane of para-aramid and polytetrafluoroethylene; Preferably, the nanofiltration membrane has an average pore size of 1.0-2.0 nm; Preferably, the nanofiltration treatment is performed at a working pressure of 5.0-10.0 bar.

7. The purification method according to claim 6, characterized by, The resin adsorption comprises sequentially passing the third filtrate into a cation exchange column, an anion exchange column, and an anion-cation mixed exchange column for resin adsorption to obtain a fourth filtrate; Preferably, the cation exchange column, the anion exchange column, and the anion-cation mixed exchange column each independently have an operating temperature of 20-30℃; Preferably, the flow rate of the third filtrate during the resin adsorption is 10-30 BV / h.

8. The purification method according to claim 7, characterized by, The membrane distillation comprises subjecting the fourth filtrate to membrane distillation to obtain a glycerol product; Preferably, the membrane used in the membrane distillation has an average thickness of 70-80 μm; Preferably, the membrane used in the membrane distillation has an average pore size of 0.1-0.5 μm; Preferably, the temperature difference between the two sides of the membrane during the membrane distillation is 20-60℃, preferably 40-60℃.

9. The purification method according to any one of claims 1 to 8, characterized in that, The glycerol product has a purity of ≥99.0%, preferably ≥99.8%.

10. The purification process according to any one of claims 1 to 9, characterized in that, The purification method comprises the following steps: (1) filtering crude glycerol using a filter screen having a pore size of 0.1-5 mm to obtain a first filtrate, and then performing acidification treatment at 80-90℃, wherein the acidification treatment comprises adjusting the pH of the first filtrate to 5.0-6.0 to obtain an acidified liquid; The acid liquor includes any one of hydrochloric acid, sulfuric acid or phosphoric acid or a combination of at least two of them; (2) The acidified liquor in step (1) is subjected to oil removal treatment by using an oil removal device including an oleophilic filter core and a hydrophilic filter core, the oil removal treatment including that the acidified liquor is first subjected to oil removal by the oleophilic filter core and then separated by the hydrophilic filter core to obtain a second filtrate; The oleophilic filter core includes a first composite membrane including para-aramid, polypropylene and polyamine rubber, and the hydrophilic filter core includes a second composite membrane including para-aramid, polyacrylamide and polyacrylonitrile; (3) The second filtrate in step (2) is subjected to nanofiltration treatment under a working pressure of 5.0-10.0 bar by using a nanofiltration membrane, the nanofiltration membrane used in the nanofiltration treatment including para-aramid and polytetrafluoroethylene and having an average pore size of 1.0-2.0 nm to obtain a third filtrate; (4) The third filtrate in step (3) is sequentially introduced into a cation exchange column, an anion exchange column and an anion-cation mixed exchange column at a flow rate of 10-30 BV / h for resin adsorption to obtain a fourth filtrate; The operating temperature of the cation exchange column, the anion exchange column and the anion-cation mixed exchange column is independently 20-30℃; (5) The fourth filtrate in step (4) is subjected to membrane distillation, the membrane used in the membrane distillation having an average thickness of 70-80 μm and an average pore size of 0.1-0.5 μm, and the temperature difference between the two sides of the membrane during the membrane distillation is 20-60℃ to obtain a glycerol product with a purity of ≥99.0%.

Images