Preparation method of ionic liquid gel microspheres and their application as liquid chamber microreactor in oil desulfurization

Abstract

The present invention relates to a method for preparing ionic liquid gel microspheres and their application as liquid chamber microreactors in oil desulfurization. Using mesoporous silica as a supporting skeleton, ionic liquid gel microspheres with ionic liquid as a dispersion medium and a high molecular polymer as a gel network are prepared through a two-step process of solution polymerization and high-temperature vacuum desolventization. Then, a heteropolyacid ion-type catalyst is loaded into the ionic liquid gel microspheres to construct a new type of liquid chamber microreactor, which is applied to catalytic oxidative desulfurization of oil products. A catalytic reaction system is designed and constructed that is carried out inside the ionic liquid gel microspheres. As a microreactor, the ionic liquid gel microspheres not only solve the problem of difficult catalyst recovery, but also their high stability can prevent the leakage and loss of catalyst and ionic liquid during application.

Description

Technical Field

[0001] The present invention relates to a method for desulfurizing oil products using ionic liquid gel microspheres as liquid chamber microreactors. Specifically, the present invention relates to a method for preparing ionic liquid gel microspheres, a new method for loading functional substances inside ionic liquid gel microspheres, and a method for constructing a catalytic reaction system carried out inside ionic liquid gel microspheres. Background Art

[0002] Currently, the construction of microreactors based on micro-nanocomposite materials is mainly based on solid-solid and liquid-liquid composites. Solid materials have physical properties such as a stable skeleton, easy formability, and good mechanical properties, but they often have difficulty in achieving rapid dynamic responses. Furthermore, functional group loading, substrate enrichment, and reactions all occur at the surface interface, resulting in a small capacity. Liquids have physical properties such as smooth interfaces, dynamic responses, and self-repair, but they are difficult to use on their own. The chemical properties of liquids are diverse solutes, easy loading, large capacity, high mass transfer efficiency, and fast reactions, but they have a small specific surface area. In recent years, solid-liquid composite materials have attracted the attention of many scholars as an emerging field of materials. Liquid granulation and solid micro-nanomaterialization can increase the specific surface area of both liquids and solids. Their composite can fully utilize the respective advantages and characteristics of solids and liquids to achieve synergistic effects.

[0003] Based on the induction and summary of the current research status, inspired by the multi-compartment, multi-phase structure and soft matter morphology of cells, and from a bionic perspective, the concept of "liquid chamber microreactor" was proposed, which is defined as a micro-nano solid-liquid composite microreactor with at least one liquid phase in addition to the reaction solvent phase, especially when the liquid phase is divided into compartments, which provides new ideas for the development of high-efficiency composite material microreactors.

[0004] Ionic liquids are organic salts composed of anions and cations. Because they are liquid at room temperature, they are also called "room temperature molten salts". As "green" chemical solvents, ionic liquids can be obtained with different properties and structures by selecting anions and cations with different structures, so they are also called "designable solvents". Ionic liquids have incomparable properties that other solvents cannot match, such as: (1) a wide liquid temperature range, excellent thermal stability and chemical stability, suitable for use in a wide temperature range; (2) low vapor pressure, no evaporation during use and storage, reducing environmental pollution caused by volatilization; (3) excellent solubility, good solubility for many substances, conducive to reactions in a homogeneous phase, and improved reaction efficiency; (4) excellent electrochemical properties, with advantages such as high conductivity, good electrochemical stability, and a wide electrochemical window, making them suitable for use as electrochemical reaction media and electrolytes; (5) ion exchangeability, according to experimental needs, can be given special functionality by introducing corresponding functional groups; (6) non-flammable, low toxicity, recyclable and reusable, and environmentally friendly. These outstanding properties of ionic liquids provide new ideas for the greening and efficiency of many traditional chemical reactions and separation processes.

[0005] Ionic liquid gels, a novel class of solid-liquid composite materials, are fabricated by confining the ionic liquid as a liquid dispersion medium within a solid matrix with a three-dimensional spatial network through the interaction between an ionic liquid and a solid network. Ionic liquid gels not only retain the inherent properties of ionic liquids, but their high plasticity in shape satisfies the demand for specialized materials while also expanding the application range of ionic liquids. The structure, properties, and applications of ionic liquid gels are currently a hot topic in colloid and interface science research and a major focus in soft matter research in recent years. Ionic liquid microgels are ionic liquid gels with sizes between micrometers and nanometers. They can reduce the formation of multiscale structures, allowing the ionic liquid within to exist as ion clusters or ion pairs, resulting in properties superior to those of bulk ionic liquid gels. Currently, there are relatively many reports on bulk ionic liquid gels, while reports on ionic liquid microgels are scarce. Summary of the Invention

[0006] This invention prepares ionic liquid gel microspheres based on mesoporous silica using a two-step process of solution polymerization and high-temperature vacuum desolvation. During the preparation process, a heteropolyacid ion catalyst is loaded into the ionic liquid gel microspheres, creating a novel liquid chamber microreactor that is applied to catalyze the oxidative desulfurization of oil products.

[0007] The technical solution adopted by the present invention is: a method for preparing ionic liquid gel microspheres, comprising the following steps:

[0008] 1) Preparation of mesoporous silica: Cetyltrimethylammonium bromide and urea were dissolved in water, n-hexane and n-butanol were added, and after mixing, tetraethyl silicate was added dropwise. The reaction system was reacted at 80°C for 12 hours, and the reaction product was calcined at 500°C for 6 hours to obtain mesoporous silica;

[0009] 2) Preparation of heteropoly acid ion catalyst: Dissolve the heteropoly acid in distilled water, add the ionic liquid under continuous stirring, and react for 30 minutes to obtain the heteropoly acid ion catalyst;

[0010] 3) Preparation of ionic liquid gel microspheres: The mesoporous silica obtained in step 1), the heteropolyacid ion catalyst obtained in step 2), a polymer monomer, an ionic liquid, and an initiator were added to a solvent, and polymerization was carried out at 80° C. for 12 h. The solvent was then removed under vacuum and high temperature to obtain ionic liquid gel microspheres containing the catalyst.

[0011] Furthermore, in step 2), the heteropoly acid is one of phosphotungstic acid, phosphomolybdic acid, phosphotungstovanadic acid and phosphomolybdic chromic acid.

[0012] Furthermore, the heteropoly acid is phosphotungstic acid.

[0013] Further, in step 2 and step 3), the ionic liquid is at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bistrifluoromethylsulfonyl imide, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium dicyanamide, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-hexyl-3-methylimidazolium dihydrogen phosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium hexafluorophosphate, N-ethylpyridinium tetrafluoroborate and N-ethylpyridinium hexafluorophosphate.

[0014] Furthermore, the ionic liquid is 1-butyl-3-methylimidazolium bromide or 1-butyl-3-methylimidazolium tetrafluoroborate.

[0015] Furthermore, in step 3), the polymer monomer is at least one of methyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate, butyl acrylate, acrylamide, acrylic acid, acrylonitrile, glycidyl methacrylate, ethyl trifluoroacrylate and ethylene glycol methyl ether acrylate.

[0016] Furthermore, the polymer monomer is hydroxyethyl methacrylate.

[0017] Furthermore, in step 3), the initiator is one of potassium persulfate, ammonium persulfate, azobisisobutyronitrile, dibenzoyl peroxide and methyl ethyl ketone peroxide.

[0018] Furthermore, the initiator is azobisisobutyronitrile.

[0019] Furthermore, in step 3), the solvent is one of acetone, ethanol, ethyl acetate, chloroform, dichloromethane, N,N-dimethylformamide, N,N-dimethylacetamide, ether, xylene, cyclohexanone, acetonitrile and carbon tetrachloride.

[0020] Furthermore, the solvent is N,N-dimethylformamide.

[0021] Furthermore, in step 3), the amount of initiator added is 1% to 10% of the mass of the polymer monomers.

[0022] Furthermore, in step 3), the amount of the ionic liquid added is 10% to 50% of the mass of the polymer monomer.

[0023] Furthermore, in step 3), the amount of the heteropolyacid ion catalyst added is 5% to 30% of the mass fraction of the ionic liquid gel microspheres.

[0024] Furthermore, in step 3), the vacuum high temperature is a vacuum degree of 10 -4 Pa~0.1Pa, temperature is 70℃~120℃.

[0025] Furthermore, the vacuum high temperature is a vacuum degree of 0.01 Pa and a temperature of 80°C.

[0026] The ionic liquid gel microspheres provided by the present invention are used as liquid chamber microreactors in oil desulfurization.

[0027] Furthermore, the method is as follows: placing the ionic liquid gel microspheres in a hydrogen peroxide solution, mixing them evenly, allowing the hydrogen peroxide solution to swell into the gel network, and obtaining the ionic liquid gel microspheres containing hydrogen peroxide in the gel network by centrifugation; placing the ionic liquid gel microspheres containing hydrogen peroxide in the gel network in an oil product, and performing a desulfurization reaction at 60°C.

[0028] Furthermore, in the hydrogen peroxide solution, the mass fraction of hydrogen peroxide is 5% to 30%.

[0029] The beneficial effects of the present invention are:

[0030] 1. In the present invention, the rich porous structure of mesoporous silica is conducive to the formation of ionic liquid gel in the pores. The strong interaction between the ionic liquid gel and the pores can weaken the bonding between the ionic liquid gel microspheres, thereby obtaining independent ionic liquid gel microspheres.

[0031] 2. The ionic liquid gel microspheres of the present invention can be used as a novel liquid chamber microreactor for oil desulfurization. The ionic liquid gel microspheres of the present invention can achieve catalytic reactions within the gel, and the catalytic products are also retained in the ionic liquid gel microspheres, thereby achieving oil purification.

[0032] 3. The ionic liquid gel microspheres of the present invention are easy to recycle and store. Their excellent stability can prevent the leakage of the internal catalyst and ionic liquid. They have broad application prospects and provide an effective strategy for constructing efficient microreactors.

[0033] 4. The present invention uses mesoporous silica as a supporting framework to prepare ionic liquid gel microspheres. Through a two-step process of solution polymerization and high-temperature vacuum desolvation, ionic liquid gel microspheres with ionic liquid as the dispersion medium and a high molecular weight polymer as the gel network are prepared. Furthermore, a heteropolyacid ion catalyst is loaded into the ionic liquid gel microspheres to construct a novel liquid chamber microreactor, which is applied to catalyze the oxidative desulfurization of oil products. A catalytic reaction system is designed and constructed within the ionic liquid gel microspheres. As microreactors, the ionic liquid gel microspheres not only solve the problem of difficult catalyst recovery, but also their high stability prevents leakage of the catalyst and ionic liquid during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 (a) and (b) are scanning electron microscope images of the mesoporous silica in Example 1.

[0035] Figure 2 (a) and (b) are scanning electron microscope images of the ionic liquid gel microspheres in Example 1.

[0036] Figure 3 This is the infrared absorption spectrum of the ionic liquid gel microspheres in Example 1.

[0037] Figure 4 This is the particle size distribution diagram of the mesoporous silica and ionic liquid gel microspheres in Example 2.

[0038] Figure 5 This is the desulfurization curve of the ionic liquid gel microspheres in Example 3.

[0039] Figure 6 This is a graph showing the desulfurization cycle performance of the ionic liquid gel microspheres in Example 3. DETAILED DESCRIPTION

[0040] In order to better understand the present invention, the present invention is further described below through examples. It should be understood that the purpose of the following examples is to better explain the content of the present invention, rather than to impose any limitation on the scope of protection of the present invention.

[0041] Example 1

[0042] (1) Ionic liquid gel microspheres, prepared as follows:

[0043] 1. Preparation of mesoporous silica:

[0044] First, 0.5 g of hexadecyltrimethylammonium bromide and 0.3 g of urea were dissolved in 15 mL of water, and then 15 mL of n-hexane and 0.5 mL of n-butanol were added. After mixing evenly, 1.0 g of tetraethyl silicate was added dropwise. The reaction system was reacted at 80 ° C for 12 hours. After the reaction, the mixture was centrifuged and washed several times with anhydrous ethanol and distilled water. The obtained product was calcined at 500 ° C for 6 hours in a muffle furnace to obtain mesoporous silica.

[0045] 2. Preparation of heteropolyacid ion catalyst:

[0046] 4.25 g of phosphotungstic acid was dissolved in 50 mL of distilled water. 1.5 g of 1-butyl-3-methylimidazolium chloride was added under continuous stirring. The mixture was reacted at room temperature for 30 minutes to perform ion exchange and obtain a heteropolyacid ion catalyst.

[0047] 3. Preparation of ionic liquid gel microspheres:

[0048] 0.15 g of mesoporous silica, 0.05 g of heteropolyacid ion catalyst, 0.24 g of hydroxyethyl methacrylate, 0.06 g of 1-butyl-3-methylimidazolium tetrafluoroborate and 0.005 g of dibenzoyl peroxide were added to 30 mL of acetone, and the polymerization reaction was carried out at 80° C. for 12 h. The solvent was then removed at a vacuum temperature of 0.01 Pa and a temperature of 90° C. to obtain ionic liquid gel microspheres containing the catalyst.

[0049] (2) Testing

[0050] like Figure 1 As shown, Figure 1 (a) and (b) are scanning electron microscope photos and transmission electron microscope photos of mesoporous silica. It can be clearly seen from the figures that spherical mesoporous silica has a dandelion-like mesoporous structure with high morphology uniformity and an average particle size of about 200 nm.

[0051] like Figure 2 As shown, Figure 2(a) and (b) are scanning electron microscope photos and transmission electron microscope photos of ionic liquid gel microspheres. It can be clearly seen from the figures that their morphology is a spherical structure with a particle size of about 220nm, and the surface of the mesoporous silica is covered with a layer of gel. The pores have been completely filled with gel, and the original pore structure cannot be seen. This shows that ionic liquid gel microspheres can be prepared by utilizing the pore confinement effect and using mesoporous silica as a support.

[0052] like Figure 3 As shown, Figure 3 This is the infrared absorption spectrum of ionic liquid gel microspheres. The characteristic peaks of mesoporous silica, heteropolyacid catalyst, hydroxyethyl methacrylate and 1-butyl-3-methylimidazolium tetrafluoroborate can be clearly seen in the figure, indicating that the ionic liquid gel microspheres were successfully synthesized. (III) Application of ionic liquid gel microspheres as liquid chamber microreactors in oil desulfurization

[0053] Preparation method of model oil: dissolve 1.05 g of benzothiophene and 1.0 g of internal standard dodecane in 500 mL of n-heptane solution to prepare the model oil.

[0054] Application of ionic liquid gel microspheres in oil desulfurization: 0.2 g of ionic liquid gel microspheres were placed in 3.0 mL of a 15% hydrogen peroxide solution and mixed thoroughly, allowing the hydrogen peroxide solution to swell and enter the gel network. Centrifugation was then performed to obtain ionic liquid gel microspheres containing hydrogen peroxide within the gel network. Subsequently, the ionic liquid gel microspheres containing hydrogen peroxide within the gel network were placed in 5.0 mL of model oil and subjected to a desulfurization reaction at 60°C.

[0055] The sulfide content in the model oil was detected by gas chromatography. The desulfurization rate of the model oil by ionic liquid gel microspheres reached 100% within 4 hours.

[0056] Example 2

[0057] (1) Ionic liquid gel microspheres, prepared as follows:

[0058] 1. Preparation of mesoporous silica: same as Example 1

[0059] 2. Preparation of heteropolyacid ion catalyst:

[0060] 2.65 g of phosphomolybdic acid was dissolved in 50 mL of distilled water. 1.0 g of 1-butyl-3-methylimidazolium tetrafluoroborate was added under continuous stirring. The mixture was reacted at room temperature for 30 min to perform ion exchange and obtain a heteropolyacid ion catalyst.

[0061] 3. Preparation of ionic liquid gel microspheres:

[0062] 0.125 g of mesoporous silica, 0.025 g of heteropolyacid ion catalyst, 0.25 g of methyl methacrylate, 0.1 g of 1-butyl-3-methylimidazolium hexafluorophosphate and 0.0025 g of azobisisobutyronitrile were added to 50 mL of N,N-dimethylformamide, and the mixture was polymerized at 80°C for 12 h. The solvent was then removed at a vacuum temperature of 0.1 Pa and 100°C to obtain ionic liquid gel microspheres containing the catalyst.

[0063] (2) Testing

[0064] like Figure 4 As shown, Figure 4 This is the particle size distribution diagram of mesoporous silica and ionic liquid gel microspheres. It can be seen from the figure that the particle size of the ionic liquid gel microspheres is slightly larger than that of the mesoporous silica, indicating that a layer of ionic liquid gel is formed on the surface of the mesoporous silica.

[0065] (III) Application of ionic liquid gel microspheres as liquid chamber microreactors in oil desulfurization

[0066] Preparation method of model oil: 1.44 g of dibenzothiophene and 1.0 g of internal standard dodecane were dissolved in 500 mL of n-heptane solution to prepare the model oil.

[0067] Application of ionic liquid gel microspheres in oil desulfurization: 0.1 g of ionic liquid gel microspheres were placed in 5.0 mL of a 10% hydrogen peroxide solution and mixed thoroughly, allowing the hydrogen peroxide solution to swell and enter the gel network. Centrifugation was then performed to obtain ionic liquid gel microspheres containing hydrogen peroxide within the gel network. Subsequently, the ionic liquid gel microspheres containing hydrogen peroxide within the gel network were placed in 2.0 mL of model oil and subjected to a desulfurization reaction at 60°C.

[0068] The sulfide content in the model oil was detected by gas chromatography. The desulfurization rate of the model oil by ionic liquid gel microspheres reached 100% within 4.5 hours.

[0069] Example 3

[0070] (1) Ionic liquid gel microspheres, prepared as follows:

[0071] 1. Preparation of mesoporous silica: same as Example 1

[0072] 2. Preparation of heteropolyacid ion catalyst:

[0073] 8.5 g of phosphomolybdic acid was dissolved in 50 mL of distilled water. 2.0 g of 1-butyl-3-methylimidazolium tetrafluoroborate was added under continuous stirring. The mixture was reacted at room temperature for 30 min to perform ion exchange and obtain a heteropolyacid ion catalyst.

[0074] 3. Preparation of ionic liquid gel microspheres:

[0075] 0.1 g of mesoporous silica, 0.1 g of heteropolyacid ion catalyst, 0.2 g of hydroxyethyl methacrylate, 0.1 g of 1-butyl-3-methylimidazolium tetrafluoroborate, and 0.005 g of dibenzoyl peroxide were added to 30 mL of N,N-dimethylacetamide, and the mixture was polymerized at 80°C for 12 h. The solvent was then removed at a vacuum temperature of 80°C and a vacuum degree of 0.01 Pa to obtain ionic liquid gel microspheres containing the catalyst.

[0076] (2) Application of ionic liquid gel microspheres as liquid chamber microreactors in oil desulfurization

[0077] Preparation method of model oil: 0.72 g of dibenzothiophene and 0.25 g of internal standard dodecane were dissolved in 250 mL of n-heptane solution to prepare the model oil.

[0078] Application of ionic liquid gel microspheres in oil desulfurization: 0.1 g of ionic liquid gel microspheres were placed in 1.0 mL of a 30% hydrogen peroxide solution and mixed thoroughly, allowing the hydrogen peroxide solution to swell and enter the gel network. Centrifugation was then performed to obtain ionic liquid gel microspheres containing hydrogen peroxide within the gel network. Subsequently, the ionic liquid gel microspheres containing hydrogen peroxide within the gel network were placed in 1.0 mL of model oil and desulfurized at 60°C. The sulfide content in the model oil was determined by gas chromatography.

[0079] (3) Testing

[0080] like Figure 5 As shown, Figure 5 This is a desulfurization curve of ionic liquid gel microspheres. It can be clearly seen in the figure that the desulfurization rate of the ionic liquid gel microspheres on the model oil reaches 100% within 3 hours.

[0081] like Figure 6 As shown, Figure 6 This is the desulfurization cycle performance diagram of ionic liquid gel microspheres. It can be clearly seen in the figure that even after 6 cycle experiments, the desulfurization rate of ionic liquid gel microspheres within 4 hours is still as high as 96%.

[0082] The results of the examples show that the ionic liquid gel microspheres prepared in the present invention have a complete structure and uniform size. At the same time, as a microreactor, they have a highly efficient synergistic effect of substrate enrichment and catalysis. They are stable during application and easy to recycle and reuse, which makes them have promising application prospects in the field of catalysis.

Claims

1. Preparation method of ionic liquid gel microspheres The application of the prepared ionic liquid gel microspheres as liquid chamber microreactors in oil desulfurization is characterized by: The method is as follows: ionic liquid gel microspheres are placed in a hydrogen peroxide solution, and a liquid chamber microreactor based on the ionic liquid gel microspheres is obtained by centrifugation; the microreactor is placed in oil and a desulfurization reaction is carried out at 60°C; The preparation method of ionic liquid gel microspheres comprises the following steps: 1) Preparation of mesoporous silica: Dissolve hexadecyltrimethylammonium bromide and urea in water, add n-hexane and n-butanol, mix well, and then add tetraethyl silicate dropwise. The reaction system is reacted at 80°C for 12 hours. The reaction product is calcined at 500°C for 6 hours to obtain mesoporous silica. 2) Preparation of heteropoly acid ion catalyst: Dissolve the heteropoly acid in distilled water, add the ionic liquid under continuous stirring, and react for 30 minutes to obtain the heteropoly acid ion catalyst; 3) Preparation of ionic liquid gel microspheres: The mesoporous silica obtained in step 1), the heteropolyacid ion catalyst obtained in step 2), a polymer monomer, an ionic liquid, and an initiator are added to a solvent, and polymerization is carried out at 80° C. for 12 hours. The solvent is then removed under vacuum and at high temperature to obtain ionic liquid gel microspheres containing the catalyst; In step 2), the heteropoly acid is one of phosphotungstic acid, phosphomolybdic acid, phosphotungstovanadic acid and phosphomolybdic chromic acid; In step 2 and step 3), the ionic liquid is at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bistrifluoromethylsulfonyl imide, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium dicyanamide, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-hexyl-3-methylimidazolium dihydrogen phosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium hexafluorophosphate, N-ethylpyridinium tetrafluoroborate, and N-ethylpyridinium hexafluorophosphate; In step 3), the polymer monomer is at least one of methyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate, butyl acrylate, acrylamide, acrylic acid, acrylonitrile, glycidyl methacrylate, ethyl trifluoroacrylate and ethylene glycol methyl ether acrylate; In step 3), the amount of initiator added is 1% to 10% of the mass of the polymer monomer; the amount of ionic liquid added is 10% to 50% of the mass of the polymer monomer; the amount of heteropolyacid ion catalyst added is 5% to 30% of the mass fraction of the ionic liquid gel microspheres; the vacuum high temperature is, the vacuum degree is 10 -4 Pa~0.1Pa, temperature is 70℃~120℃; In the hydrogen peroxide solution, the mass fraction of hydrogen peroxide is 5% to 30%.

2. The use according to claim 1, characterized in that In step 3), the initiator is one of potassium persulfate, ammonium persulfate, azobisisobutyronitrile, dibenzoyl peroxide and methyl ethyl ketone peroxide.

3. The use according to claim 1, characterized in that In step 3), the solvent is one of acetone, ethanol, ethyl acetate, chloroform, dichloromethane, N,N-dimethylformamide, N,N-dimethylacetamide, ether, xylene, cyclohexanone, acetonitrile and carbon tetrachloride.

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