Method for synthesizing high-carbon phenolic resin and extracting ortho-position and para-position alkylphenol

Abstract

The invention relates to a method for synthesizing high-carbon phenolic resin and extracting ortho-position and para-position alkylphenol, which is applied to the technical field of organic synthesis and separation and comprises the following steps: taking phenol or phenol and ortho-cresol-containing mixed phenol as a first component and at least one of various alkylphenols selected from coal chemical industry crude phenol rectification products as a second component, carrying out segmented polymerization reaction with aldehyde and a catalyst; controlling the reaction until the content of meta-position phenol is less than or equal to 1% and the content of free phenol is 5-30%, and steaming out unreacted phenol; carrying out secondary polymerization and solvent extraction on the distillate, and rectifying to obtain a product containing high-purity phenol and a plurality of ortho-position and para-position alkylphenols; and dehydrating the resin phase to obtain the high-carbon-content phenolic resin. According to the method, petrochemical phenol is partially replaced with cheap coal-based phenol, various high-added-value alkylphenols are co-produced while high-performance phenolic resin is synthesized, and high-value utilization of resources and cost reduction and efficiency improvement of the process are achieved.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis and separation technology, and more specifically, to a method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resins. Background Technology

[0002] Phenolic resins, as important polymer materials, are widely used in refractory materials, friction materials, casting, electronic insulation, and other fields. Their traditional production mainly relies on petrochemical phenol, resulting in high raw material costs. Meanwhile, coal chemical processes such as coal gasification, coal coking, and coal pyrolysis produce large amounts of crude phenol, which, after refining, yields various alkylphenols such as cresol, xylenol, and tricresol. However, the market for these coal-based phenols, especially m- and p-cresols and mixed xylenols, is approaching saturation and prices are low, making the search for large-scale, high-value-added utilization a challenge for the industry.

[0003] In the existing technology, although there are reports of using high-purity m-cresol or m-ethylphenol to synthesize special phenolic resins (such as photoresist resins) and producing para-phenol as a byproduct (such as CN118930776A, CN119059885A, CN118930775A), these methods require extremely high purity of raw materials and are only suitable for producing small batches of high-value special resins. They cannot utilize the low-grade mixed phenols produced as a byproduct of large-scale industrial production, and the process flow is difficult to couple with the large-scale production of general phenolic resins.

[0004] Therefore, developing a green integrated process that can utilize inexpensive, complex coal-based mixed phenols as part of the raw materials to produce general-purpose phenolic resins while simultaneously extracting a variety of high-value-added ortho- and para-alkylphenols has significant economic and environmental value. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resins. This method can efficiently convert inexpensive and readily available coal-based mixed phenols into high-value general-purpose phenolic resins and various high-purity ortho- and para-alkylphenols, achieving high-value utilization of resources and cost reduction and efficiency improvement in the process.

[0006] To address the above problems, this invention provides a method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resins, comprising the following steps:

[0007] S1. Segmented polymerization and distillation: The first component, the second component, the aldehyde and the catalyst are mixed and subjected to segmented polymerization reaction. The reaction is controlled until the meta-phenol content is ≤1% and the free phenol content is 5-30%. The distillate containing unreacted phenol is distilled off to obtain phenolic resin reaction solution. The meta-phenol is at least one of m-cresol, m-ethylphenol and m-isopropylphenol.

[0008] S2. Phenolic Extraction and Purification: The distillate obtained in step S1 is subjected to secondary polymerization to reduce the content of meta-phenols and free aldehydes. Then, it is extracted with a non-water-soluble solvent. The separated oil layer is distilled to obtain at least one product. The product contains ortho- and para-alkylphenols. Ortho- and para-alkylphenols include, but are not limited to, one or more of ortho-cresol, 2,6-xylenol, p-cresol, 2,4-xylenol, p-ethylphenol, 2,4,6-trimethylphenol, 2,4-methylethylphenol, 2,3,6-trimethylphenol, and p-isopropylphenol.

[0009] The first component is phenol or a mixture of phenol and o-cresol; the second component is selected from one or more of the following obtained by crude phenol distillation of cresol, 2,6-xylenol, m-p-cresol, 2,4 / 2,5-xylenol, m-p-ethylphenol, 2,4,6-trimethylphenol, 2,4 / 2,5-methylethylphenol, 3,4-xylenol / 2,3,6-trimethylphenol, or m-p-isopropylphenol, obtained through coal coking, coal gasification, or coal pyrolysis tar. Preferably, the composition is: 40-70% cresol and o-p-cresol, 0-8% o-ethylphenol, 5-25% phenol, 10-35% o-cresol, and 0% 2,6-xylenol.5-20%, 2,4 / 2,5-xylenol 0-20%, 2-ethyl-6-cresol 0-5%, o-isopropylphenol 0-5%; 2,6-xylenol, 0-50% (intermediate p-cresol), 0-6% (o-ethylphenol), 0-10% phenol, 0-50% (o-cresol), 50-95% (2,6-xylenol), 0-10% (2,4 / 2,5-xylenol), 0-5% (2-ethyl-6-cresol); m-p-cresol, 70-100% (intermediate p-cresol), 0-12% (o-ethylphenol), 0-15% (o-cresol), 0-15% (2,6-xylenol), 0-15% (2,4 / 2,5-xylenol), 0-15% (2-ethyl-6-cresol), 0-5% (2-ethyl-6-cresol), 0-5% (2-ethyl-6-cresol). 2,4 / 2,5-dimethylphenol 0–10%, o-isopropylphenol 0–5%; 2,4 / 2,5-dimethylphenol; 2,4 / 2,5-dimethylphenol, 0–15% of p-cresol, 0–2% of o-ethylphenol, 70–100% of 2,4 / 2,5-dimethylphenol, 0–10% of 2-ethyl-6-methylphenol, 0–5% of o-isopropylphenol, 0–30% of 2,3-dimethylphenol; 80–100% of 2,3-dimethylphenol / m-p-ethylphenol / 3,5-dimethylphenol in m-p-ethylphenol, 0–30% of 3,5-dimethylphenol, 0–10% of 2,4 / 2,5-methylethylphenol, 0–10% of 2,4 / 2,5-dimethylphenol, 2… 4,6-Trimethylphenol 0–10%, o-isopropylphenol 0–5%; 2,4,6-Trimethylphenol: 10–40% of p-ethylphenol, 2,4,6-Trimethylphenol 50–90%, 3,5-Dimethylphenol 10–30%, 2,4 / 2,5-methylethylphenol 0–30%, 3,4-Dimethylphenol 0–10%; 2,4 / 2,5-methylethylphenol: 60–100% of 2,4 / 2,5-methylethylphenol, 3,5-Dimethylphenol 0–30%, m-p-ethylphenol 0–20%, 3,4-Dimethylphenol 0–30%, 2,3,6-Trimethylphenol 0–10%; 3,4-Dimethylphenol / 2,3,6- Trimethylphenol contains 0-20% 2,4 / 2,5-methylethylphenol, 0-10% 3,5-dimethylphenol, 0-10% m-p-ethylphenol, 30-80% 3,4-dimethylphenol, 5-50% 2,3,6-trimethylphenol, and 0-30% m-p-isopropylphenol; m-p-isopropylphenol contains 80-100% 2,3-methylethylphenol / m-p-isopropylphenol / m-p-propylphenol / 3-ethyl-5-methylphenol, 0-15% 3,4-dimethylphenol, 0-5% 2,3,5-trimethylphenol, 0-5% 2,4 / 2,5-methylethylphenol, 0-10% 2,4,5-trimethylphenol, and 0-5% 2,3,6-trimethylphenol.

[0010] Further, in step S1, the segmented polymerization reaction specifically involves: first reacting all of the first component, part of the second component, part of the aldehyde and catalyst at 80–105°C for 1–4 hours; then adding the remaining aldehyde and the remaining second component dropwise, and continuing the reaction for 1–6 hours.

[0011] In this process, a portion of the second component comprises 0-100% of the total mass of the second component, and a portion of the aldehyde comprises 0-100% of the total mass of the aldehyde. The total mass ratio of the first component to the second component is 0:100 to 100:0 (when the first component is a mixed phenol, phenol or the second component may be omitted; the mixed phenol reacts with aldehydes to synthesize resins, o-cresol, etc.). Preferably, a portion of the second component comprises 30-70% of the total mass of the second component, and a portion of the aldehyde comprises 30-70% of the total mass of the aldehyde. The total mass ratio of the first component to the second component is 50:50 to 80:20.

[0012] Further, in step S1, the aldehyde is an aqueous formaldehyde solution, and its total molar amount is 0.5 to 2.0 times the total molar amount of phenol and all meta-phenols; the mass of the catalyst is 0.1 to 10% of the total mass of the phenolic materials, and the catalyst is at least one of oxalic acid, phosphoric acid or hydrochloric acid.

[0013] Preferably, the aldehyde is an aqueous formaldehyde solution, and its total molar amount is 0.7 to 1.5 times the total molar amount of phenol and all meta-phenols; the mass of the catalyst is 0.5 to 5% of the total mass of the phenolic materials.

[0014] Further, in step S2, the secondary polymerization is as follows: an acidic catalyst is added to the distillate, and the reaction is carried out at 80-105°C for 1-3 hours until the free aldehyde content and meta-phenol content in the reaction solution are ≤0.5% and ≤0.5%.

[0015] Furthermore, the acidic catalyst is hydrochloric acid or oxalic acid.

[0016] Furthermore, in step S2, the non-water-soluble solvent is toluene or methyl isobutyl ether, and its feed mass is 0.5 to 2 times the total feed mass of phenolic materials in step S1.

[0017] Further, the phenolic resin reaction solution obtained in step S1 is dehydrated under vacuum, with the final pressure controlled at -0.09 to -0.1 MPa, and the final temperature raised to 150 to 230°C to obtain a thermoplastic phenolic resin with a free phenol content ≤1%; or the final temperature is raised to 80 to 150°C to obtain a general-purpose phenolic resin with a free phenol content ≤3%.

[0018] Furthermore, in step S2, the distillation includes first removing the solvent, and then carrying out efficient distillation under conditions of pressure of -0.07 to -0.1 MPa and reflux ratio of 5 to 30.

[0019] Furthermore, the residue obtained from distillation is returned as a prepolymer to the polymerization reaction in step S1 for use.

[0020] Furthermore, the composition of the mixed phenols, by mass percentage, is: 50-90% phenol, 10-50% o-cresol, and the balance being at least one of m-p-cresol, 2,6-xylenol, and 2,4 / 2,5-xylenol, with the content of m-p-cresol being 0-40%, the content of 2,6-xylenol being 0-10%, and the content of 2,4 / 2,5-xylenol being 0-5%.

[0021] Furthermore, the product obtained in step S2 also includes high-purity phenol.

[0022] Further, the ortho- and para-alkylphenols obtained in step S2 are a mixture of p-cresol and o-ethylphenol, a mixture of p-ethylphenol and 2,3-dimethylphenol, or a mixture of p-isopropylphenol and p-propylphenol.

[0023] Furthermore, the method also includes using the aqueous layer obtained after secondary polymerization and extraction in step S2 to absorb formaldehyde to prepare a formaldehyde aqueous solution, or sending it out as wastewater.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Significantly reduced raw material costs and comprehensive resource utilization. This invention uses inexpensive coal-based mixed phenols to partially or completely replace expensive petrochemical phenols, greatly reducing the production cost of phenolic resins and opening up new avenues for large-scale, high-value-added applications of phenols byproducts of coal chemical industry.

[0026] 2. Diversified products with high added value. This invention enables the co-production of two high-value products in the same process unit: one is high-carbon-content phenolic resin with excellent performance; the other is a variety of high-purity (usually ≥98%) ortho- and para-alkylphenols (such as ortho-cresol, 2,6-xylenol, p-cresol, p-ethylphenol, 2,4-xylenol, etc.). The price of these phenolic monomers is much higher than that of the raw material mixed phenols, resulting in significant economic benefits.

[0027] 3. Integrated and innovative processes, environmentally friendly. This invention achieves efficient and high-purity recovery of unreacted phenols through an integrated process design of "segmented polymerization to control reaction depth—steam distillation separation—secondary polymerization of distillate for impurity removal—solvent extraction—high-efficiency distillation." Formaldehyde and residual phenols in the wastewater are recycled, and the residue from the distillation kettle is reused as a prepolymer, realizing a closed-loop material cycle and reducing the discharge of waste gas, wastewater, and solid waste.

[0028] 4. Due to the introduction of alkylphenol structural units into the resin molecular chain, the carbon content of the resulting phenolic resin is 3-30% higher than that of pure phenolic resin, and the char residue rate is high. It exhibits superior heat resistance and strength when used as a binder for refractory materials, friction materials, and precursors for carbon materials.

[0029] 5. It has relaxed requirements on the purity of the second component raw materials, and can adapt to coal-based crude phenol distillation products from different sources and with different compositions, thus having strong industrial operability and promotional value. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the method for synthesizing high-carbon phenolic resin and extracting ortho- and para-alkylphenols according to the present invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, all "parts" or "kg" in the embodiments refer to units of mass. Experimental methods in the following embodiments that do not specify specific conditions are generally carried out according to conventional conditions in the art.

[0032] Example 1: Using mixed phenols to co-produce resin, phenol, o-cresol and 2,6-xylenol (without phenol and second component)

[0033] In the polymerization reactor, 8.8 kg of the previous batch of prepolymer, the first component (2000 kg of mixed phenols, including 1432 kg of phenol, 486 kg of o-cresol, and 82 kg of 2,6-xylenol), and 30 kg of oxalic acid were added. The pH of the reaction solution was adjusted to 2.8, and the temperature was raised to 85°C. Aldehyde (1100 kg of 37% formaldehyde aqueous solution) was added dropwise over 2 hours. The temperature was raised to 98°C and maintained for 4 hours. Samples were taken for analysis, and the free phenol content was 24.9%.

[0034] After the reaction was complete, unreacted free phenol and water were distilled off by steam distillation. The distillate was transferred to a reaction vessel, 1 kg of oxalic acid was added, and a secondary polymerization reaction was carried out at 85°C for 2 hours. Then, a non-water-soluble solvent (1000 kg of toluene) was added for extraction, and the oil layer was obtained after separation. After washing the oil layer with water, a phenol-toluene solution was obtained.

[0035] The resin phase after free phenols were distilled off was subjected to vacuum dehydration at 80–85°C and a final pressure of -0.08 MPa. The vacuum was then gradually increased to -0.095 MPa, and the temperature was raised to 210°C for final dehydration and curing, yielding 1403.3 kg of thermoplastic phenolic resin. This resin had a softening point of 119°C, a free phenol content of 0.6%, and a char residue of 76.2%. The condensate collected during dehydration was combined with the aforementioned phenol-toluene solution for further treatment.

[0036] After the combined phenol-containing materials were distilled to remove and toluene was recovered, they underwent high-efficiency vacuum distillation (200 theoretical plates, pressure -0.085 MPa, reflux ratio 20:1) to obtain: 215.2 kg of 99.7% phenol, 289.8 kg of 99.8% o-cresol, and 55.3 kg of 99.5% 2,6-xylenol. The 8.9 kg residue in the distillation vessel was returned as prepolymer for use in the next batch of polymerization reaction.

[0037] Example 2: Co-production of resin and various phenols using phenol, crude 2,6-xylenol and m-p-cresol.

[0038] In the polymerization reactor, 45.8 kg of the previous batch of prepolymer, 1000 kg of the first component (coal-processed phenol, 99.2% purity), 200 kg of the second component crude 2,6-xylenol (containing 35.2 kg of o-cresol, 20.4 kg of p-cresol, 36.9 kg of m-cresol, 0.5 kg of o-ethylphenol, and 107 kg of 2,6-xylenol), 64 kg of oxalic acid, 16 kg of formic acid, and 1200 kg of a 37% formaldehyde aqueous solution were added. The pH of the reaction solution was adjusted to 2.3, and the reaction was pre-reacted at 90°C for 1 hour. Subsequently, the remaining 1000 kg of the 37% formaldehyde aqueous solution and the remaining 800 kg of the second component 2,6-xylenol were added dropwise over 3 hours. After the addition was complete, the reaction was maintained at 98°C for 3 hours. Sampling and analysis showed that the m-cresol content was ≤0.005%, and the free phenol content was 24.1%.

[0039] After the reaction was complete, the temperature was raised for steam distillation to remove unreacted free phenol and water. The distillate was transferred to an extraction vessel, and 2 kg of oxalic acid was added. A secondary polymerization reaction was carried out at 100°C for 1.5 hours. Then, 2000 kg of toluene was added for extraction. The separated oil layer was washed with water to obtain a phenolic toluene solution. This solution was first distilled to recover the toluene, and the remaining material was transferred to a high-efficiency distillation column (250 theoretical plates) for distillation at a pressure of -0.085 MPa and a reflux ratio of 25. The distillate yielded 85.3 kg of 99.7% phenol, 61.9 kg of 99.6% o-cresol, 29.5 kg of 98.3% p-cresol (containing 0.5% o-ethylphenol), and 283.4 kg of 99.3% 2,6-xylenol. The 45.7 kg residue in the distillation vessel (containing 42.1 kg of prepolymer) was returned for use in the next batch of polymerization.

[0040] After the free phenols were distilled off, the resin phase was dehydrated under vacuum and cured at 150°C to obtain 1381.5 kg of phenolic resin. The resin had a softening point of 111°C, a free phenol content of 1.2%, and a char residue of 75.1%.

[0041] Example 3: Co-production of resin using phenol and m-cresol, phenol and p-cresol

[0042] In the polymerization reactor, 11.1 kg of the previous batch of prepolymer, 2000 kg of the first component (coal-processed phenol, 99.2% purity), 500 kg of the second component (m-p-cresol fraction, containing 179.5 kg of p-cresol, 308 kg of m-cresol, 1 kg of o-ethylphenol, 7.7 kg of 2,4-xylenol, and 3.8 kg of 2,5-xylenol), 36 kg of oxalic acid, 9 kg of formic acid, and 1760 kg of a 37% formaldehyde aqueous solution were added. The pH was adjusted to 2.9, and the temperature was raised to 90°C. The remaining second component (500 kg of m-p-cresol fraction) was added dropwise over 3 hours. After the addition was complete, the reaction was maintained at 98°C for 3 hours until the m-cresol content was ≤0.02% and the free phenol content was 28.6%.

[0043] After the reaction was completed, steam distillation was performed. 1.5 kg of oxalic acid was added to the distillate, and after a second polymerization at 95°C for 1.5 hours, it was extracted with 2000 kg of toluene. The oil layer was washed with water, and the condensates from the dehydration stage were combined. Solvent recovery and rectification were then carried out. The final yield was 507.8 kg of 99.8% phenol, 280.6 kg of 99.3% p-cresol, and 12.4 kg of crude 90.3% 2,4-xylenol.

[0044] The resin phase was dehydrated under vacuum and cured at 200℃ to obtain 2371.1 kg of phenolic resin with a softening point of 117℃, a free phenol content of 0.7%, and a char residue rate of 76.1%.

[0045] Example 4: Co-production of resin and 2,4-xylenol using phenol and 2,4 / 2,5-xylenol

[0046] In the polymerization reactor, add 31.7 kg of the previous batch of prepolymer, 1000 kg of the first component (coal-processed phenol), 200 kg of the second component (2,4 / 2,5-xylenol fraction, containing 9.6 parts of p-cresol, 10.6 parts of m-cresol, 18.8 parts of 2,3-xylenol, 17.2 parts of 2-ethyl-6-cresol, 85.6 parts of 2,4-xylenol, 56.2 parts of 2,5-xylenol, and 2 parts of o-isopropylphenol), 737 kg of 37% formaldehyde aqueous solution, 44 kg of oxalic acid, and 36 kg of phosphoric acid. Adjust the pH to 2.1 and react at 80-85℃ for 1 hour. Then raise the temperature to 85-90℃ and add the remaining 1000 kg of 37% formaldehyde aqueous solution and the remaining 800 kg of the second component (2,4 / 2,5-xylenol fraction) dropwise over 3 hours. The reaction was carried out at 98℃ for 3 hours until the total content of meta-phenol (m-cresol, 2,3-xylenol, 2,5-xylenol) was ≤0.28% and the free phenol content was 11.0%.

[0047] After the reaction was completed, the mixture was distilled. The distillate was subjected to secondary polymerization catalyzed by 1 kg of 36% hydrochloric acid, and then extracted with 2000 kg of ethyl acetate. The oil layer was treated and purified by distillation to obtain 10.0 kg of 99.6% p-cresol and 330.4 kg of a mixture of 99.85% 2,4-xylenol / 2-ethyl-6-cresol.

[0048] The resin phase was dehydrated and finally treated at 130℃ to obtain 1956.3 kg of phenolic resin with a softening point of 103℃, 2.8% free phenol, and 74.3% char residue.

[0049] Example 5: Co-production of resin using phenol and m- and p-ethylphenol, and a mixture of phenol and p-ethylphenol

[0050] In a polymerization reactor, 12.6 kg of prepolymer, 2000 kg of the first component (coal-processed phenol), 400 kg of a portion of the second component (m-p-ethylphenol fraction, containing 165 parts p-ethylphenol, 167 parts m-ethylphenol, 38.7 parts 2,3-xylenol, 1.1 parts o-isopropylphenol, 8.2 parts 3,5-xylenol, 1.6 parts 2,4 / 2,5-xylenol, 14.4 parts 2,4-methylethylphenol, and 4 parts 2,5-methylethylphenol), 800 kg of 37% formaldehyde aqueous solution, 32 kg of oxalic acid, and 6 kg of phosphoric acid were added. The pH was adjusted to 2.2, and the temperature was raised to 95°C. The remaining 1000 kg of 37% formaldehyde aqueous solution and the remaining 800 kg of the second component (m-p-ethylphenol fraction) were added dropwise over 2.5 hours. The reaction was maintained at 98°C for 2 hours until the m-ethylphenol content was ≤0.01% and the free phenol content was 22.8%.

[0051] The reaction was followed by distillation. The distillate was subjected to secondary polymerization with 0.8 parts of 36% hydrochloric acid, and then extracted with 2000 kg of methyl isobutyl ketone. The oil layer and subsequent dehydration condensate were combined, and after solvent recovery and distillation, 365.6 kg of 99.9% phenol, 492.1 kg of a 99.8% p-ethylphenol / 2,3-xylenol mixture (including 413.9 kg of p-ethylphenol and 77.3 kg of 2,3-xylenol), and 35.1 kg of a 92.6% 2,4-methylethylphenol fraction were obtained.

[0052] The resin phase was dehydrated under vacuum and cured at 190°C to obtain 2468.3 kg of phenolic resin with a softening point of 120°C, 0.8% free phenol, and 76.5% char residue.

[0053] Example 6: Co-production of resin and 2,4,6-trimethylphenol using phenol and crude 2,4,6-trimethylphenol

[0054] In the polymerization reactor, 22.3 kg of the previous batch of prepolymer, 500 kg of the first component (coal-processed phenol), 500 kg of a portion of the second component (crude 2,4,6-trimethylphenol fraction, containing 43 parts of p-ethylphenol, 51 parts of m-ethylphenol, 91.5 parts of 3,5-xylenol, 22.5 parts of 3,4-xylenol, 255.5 parts of 2,4,6-trimethylphenol, 26 parts of 2,4-methylethylphenol, and 10.5 parts of 2,5-methylethylphenol), 500 kg of 37% formaldehyde aqueous solution, and 15 kg of phosphoric acid were added. The pH was adjusted to 1.8, and after reacting at 90°C for 2 hours, 15 kg of phosphoric acid was added. Simultaneously, the remaining 500 kg of 37% formaldehyde aqueous solution and the remaining 500 kg of the second component (crude 2,4,6-trimethylphenol fraction) were added dropwise over 3 hours. The reaction was carried out at 100℃ for 3 hours until the total content of meta-phenol (m-ethylphenol, 3,5-dimethylphenol, etc.) was ≤0.083% and the free phenol content was 22.4%.

[0055] After the reaction was complete, distillation was performed. 2 kg of 36% hydrochloric acid was added to the distillate, and after a second polymerization at 100°C for 1.5 hours, it was extracted with 1500 kg of toluene. The oil layer was washed with water, the solvent was recovered, and then distilled to separate 42.4 kg of a mixture of p-ethylphenol / 2,4,6-trimethylphenol, 406.8 kg of 99.1% 2,4,6-trimethylphenol, and 79.3 kg of a mixture of 2,4,6-trimethylphenol / 2,4-methylethylphenol.

[0056] The resin phase was dehydrated under vacuum and cured at 200℃ to obtain 1161.5 kg of phenolic resin with a softening point of 120℃, 0.6% free phenol, and 78.2% char residue.

[0057] Example 7: Co-production of resin and 2,4-methylethylphenol using phenol and 2,4-methylethylphenol

[0058] In the polymerization reactor, 73.7 kg of the previous batch of prepolymer, 1000 kg of the first component (coal-processed phenol), 400 kg of a portion of the second component (2,4 / 2,5-methylethylphenol fraction, containing 14.8 parts of p-ethylphenol, 16.8 parts of m-ethylphenol, 38 parts of 3,5-xylenol, 59.2 parts of 3,4-xylenol, 25.2 parts of 2,3,6-trimethylphenol, 171.2 parts of 2,4-methylethylphenol, and 74.8 parts of 2,5-methylethylphenol), 745 kg of 37% formaldehyde aqueous solution, and 10 kg of 36% hydrochloric acid were added. The pH was adjusted to 1.9, and the reaction was carried out at 90°C for 1 hour. Subsequently, the remaining second component (600 kg of 2,4 / 2,5-methylethylphenol fraction) and 1000 kg of 37% formaldehyde aqueous solution were added dropwise over 2 hours. After heating to 98℃, add 20kg of 36% hydrochloric acid and keep the reaction at this temperature for 2 hours until the meta-phenol content is ≤0.01% and the free phenol content is 11.3%.

[0059] The reaction was followed by distillation. 6 kg of 36% hydrochloric acid and a small amount of formaldehyde were added to the distillate, and a secondary polymerization was carried out at 100-105℃ for 1 hour. The mixture was then extracted with 2000 kg of methyl isobutyl ketone. After treatment and rectification, the oil layer yielded 178.7 kg of 99.1% 2,4-methylethylphenol, a mixture of 2,4-methylethylphenol and 2,3,6-trimethylphenol (containing 81.5 kg of 2,4-methylethylphenol and 18.2 kg of 2,3,6-trimethylphenol), and 16.1 kg of 99.2% 2,3,6-trimethylphenol.

[0060] The resin phase was dehydrated and finally treated at 190℃ to obtain 1963.3 kg of phenolic resin with a softening point of 116℃, 0.6% free phenol, and 77.3% char residue.

[0061] Example 8: Co-production of resin and 2,3,6-trimethylphenol using phenol and 3,4-xylenol / 2,3,6-trimethylphenol

[0062] In the polymerization reactor, 31.2 kg of the previous batch of prepolymer, 1000 kg of the first component (coal-derived phenol), 64 kg of oxalic acid, 16 kg of formic acid, and 1700 kg of 37% formaldehyde aqueous solution were added. The pH was adjusted to 2.4, and the reaction was carried out at 90°C for 2 hours. Subsequently, 1000 kg of the second component, 3,4-xylenol / 2,3,6-trimethylphenol fraction (containing 24 parts of p-ethylphenol, 26 parts of m-ethylphenol, 72 parts of 3,5-xylenol, 274 parts of 3,4-xylenol, 481 parts of 2,3,6-trimethylphenol, 55 parts of 2,4-methylethylphenol, 18 parts of 2,5-methylethylphenol, 27 parts of m-isopropylphenol, and 23 parts of p-isopropylphenol), was added. After heating to 98°C, 20 kg of 36% hydrochloric acid was added, and the reaction was continued for 2 hours until the total content of meta-phenol was ≤0.30% and the free phenol content was 13.3%.

[0063] The reaction was followed by distillation. The distillate was subjected to secondary polymerization catalyzed by two portions of 36% hydrochloric acid, and then extracted with 2000 kg of methyl isobutyl ketone. After treatment and rectification, the oil layer yielded 29.1 kg of a mixture of p-ethylphenol and 2,4-methylethylphenol, and 408.1 kg of crude 2,3,6-trimethylphenol (93.7% purity, including 382.3 kg of 2,3,6-trimethylphenol).

[0064] The resin phase was dehydrated and cured at 200℃ to obtain 1814.8 kg of phenolic resin with a softening point of 118℃, 0.5% free phenol, and a char residue rate of 77.1%.

[0065] Example 9: Co-production of resin using phenol and m- and p-isopropylphenol, phenol and p-isopropylphenol

[0066] In the polymerization reactor, add 14.4 kg of the previous batch of prepolymer, 2000 kg of the first component (coal-processed phenol), 800 kg of the second component (m-p-isopropylphenol fraction, containing 35.5 kg of 3,4-xylenol, 2 kg of 2,3,6-trimethylphenol, 252 kg of p-isopropylphenol, 305 kg of m-isopropylphenol, 68 kg of p-propylphenol, 70 kg of m-propylphenol, 6.5 kg of 2,3-methylethylphenol, 16 kg of 3-ethyl-5-methylphenol, 14.5 kg of 2,3,5-trimethylphenol, 1.5 kg of 2,4 / 2,5-methylethylphenol, and 29 kg of 2,4,5-trimethylphenol), 72 kg of oxalic acid, and 2100 kg of a portion of 37% formaldehyde aqueous solution. Adjust the pH to 2.6 and raise the temperature to 90°C. Simultaneously add the remaining second component (800 kg of m-p-isopropylphenol fraction) dropwise over 3 hours. After reacting at 98℃ for 1.5 hours, add 6 kg of 36% hydrochloric acid and continue the reaction for 2 hours until the m-isopropylphenol / m-propylphenol content is ≤0.012% and the free phenol content is 15.2%.

[0067] The reaction was followed by distillation. The distillate was subjected to secondary polymerization with 2 kg of oxalic acid and then extracted with 1700 kg of methyl isobutyl ketone. All phenolic materials were combined, and after solvent recovery and distillation, 242.8 kg of 99.8% phenol, 20.1 kg of 99.2% 3,4-xylenol, 338.2 kg of a 99.1% p-isopropylphenol / p-propylphenol mixture, and 46.5 kg of crude 82.6% 2,4,5-trimethylphenol (which can be purified by crystallization to obtain 25.3 kg of 99.1% 2,4,5-trimethylphenol) were obtained.

[0068] After dehydration, the resin phase was cured under two conditions: one at 120℃ yielded 1603 kg of general-purpose phenolic resin (softening point 102℃, free phenol 1.9%, char residue 74.1%); the other at 200℃ yielded 1527.1 kg of thermoplastic phenolic resin (softening point 122℃, free phenol 0.8%, char residue 77.7%).

[0069] Example 10: Using a variety of mixed phenols to co-produce resins and a variety of high-purity phenols

[0070] In the polymerization reactor, 2000 kg of the first component (coal-derived phenol, 95.2% purity), 1000 kg of mixed phenols (containing 716 kg of phenol and 284 kg of o-cresol), 300 kg of tar-derived m-cresol (containing 132 kg of p-cresol, 139 kg of m-cresol, and 29 kg of o-ethylphenol), and 300 kg of gasified m-ethylphenol (containing 122 kg of p-ethylphenol, 126 kg of m-ethylphenol, 29 kg of 2,3-xylenol, 12 kg of 3,5-xylenol, and 2,4 / 2,5-xylenol) were added. Prepare a mixture of 10 kg of cresol, 1 kg of 2,4 / 2,5-methylethylphenol, 300 parts of m-p-isopropylphenol (containing 13 kg of 3,4-xylenol, 16 kg of 2,3,6-trimethylphenol, 120 kg of p-isopropylphenol, 126 kg of m-isopropylphenol, 2.5 kg of 2,3-methylethylphenol, 10 kg of 3-ethyl-5-cresol, 5.5 kg of 2,3,5-trimethylphenol, 6.5 kg of 2,4 / 2,5-methylethylphenol, and 0.5 kg of 2,4,5-trimethylphenol), 80 kg of oxalic acid, and 10 kg of phosphoric acid. Adjust the pH to 2.8 and raise the temperature to 95°C. Simultaneously add 3250 kg of 37% formaldehyde aqueous solution and the remaining second component mixture (500 kg of mixed phenols, 300 kg of m-p-cresol, 300 kg of m-p-ethylphenol, and 300 kg of m-p-isopropylphenol) over 3 hours. The reaction was carried out at 98℃ for 3 hours until the total content of meta-phenol was ≤0.04% and the content of phenol was 9.85%.

[0071] The reaction was followed by distillation. The distillate was subjected to secondary polymerization catalyzed by 2.5 kg of oxalic acid, and then extracted with 2000 kg of ethyl acetate. The oil layer and dehydrated condensate were combined, and after solvent recovery and distillation, the following were obtained in sequence: 354.1 kg of 99.8% phenol, 384.6 kg of 99.6% o-cresol, 246.8 kg of a mixture of 99.5% p-cresol and o-ethylphenol, 236.1 kg of a mixture of 99.6% p-ethylphenol and 2,3-xylenol, and 202.4 kg of a mixture of 3,4-xylenol and p-isopropylphenol.

[0072] The resin phase was dehydrated under vacuum and cured at 230°C to obtain 4087 kg of phenolic resin with a softening point of 131°C, 0.08% free phenol, and a char residue of 79.3%.

[0073] Example 11: Using phenol and cresol, 2,6-xylenol to co-produce resin, o-cresol and p-cresol and 2,4-xylenol, etc.

[0074] In the polymerization reactor, add 92.2 kg of the previous batch of prepolymer, 150 kg of the first component (coal-processed phenol, 99.2%), 1000 kg of the second component (75 kg of phenol, 122 kg of o-cresol, 315 kg of p-cresol, 358 kg of m-cresol, 58 kg of o-ethylphenol, 23 kg of 2,6-xylenol, 29 kg of 2,4-xylenol, and 20 kg of 2,5-xylenol), 27 kg of oxalic acid (dissolved in 40 parts of hot water), and 500 kg of 37% formaldehyde. Adjust the pH to 2.9, raise the temperature to 90°C, and react for 1.5 hours; then add 12 kg of 36% hydrochloric acid. Simultaneously add 500 kg of 37% formaldehyde aqueous solution and 200 kg of the remaining second component, 2,6-xylenol (35.2 kg of o-cresol, 20.4 kg of p-cresol, 36.9 kg of m-cresol, 0.5 kg of o-ethylphenol, and 107 kg of 2,6-xylenol) dropwise over 2 hours. Incubate the reaction at 98℃ for 4 hours until the 2,5-xylenol content is ≤0.04% and the free phenol content is 24.62%.

[0075] The reaction was followed by distillation. The distillate was subjected to secondary polymerization catalyzed by 2 kg of 36% hydrochloric acid, and then extracted with 1500 kg of toluene. The oil layer and dehydrated condensate were combined, and after solvent recovery and distillation, the following were obtained sequentially: 42.1 kg of 99.5% o-cresol, 52.8 kg of o-cresol / 2,6-xylenol (30.2 kg of o-cresol and 22.6 kg of 2,6-xylenol), 61.5 kg of 99.1% 2,6-xylenol, 195 kg of 2,6-xylenol / p-cresol / o-ethylphenol (25.5 kg of 2,6-xylenol, 140.7 kg of p-cresol and 28.8 kg of o-ethylphenol), and 15.5 kg of 99.6% 2,4-xylenol; the residue of 92.6 kg (containing 89.5 kg of prepolymer) was returned to the first-step polymerization reactor to be used with other phenolic substances for the next batch of phenolic resin synthesis.

[0076] The resin phase was dehydrated under vacuum and cured at 210℃ to obtain 1086.2 kg of phenolic resin with a softening point of 118℃, 0.9% free phenol, and 77.2% char residue.

[0077] Example 12: Using cresol, m- and p-cresol to co-produce resin, o-cresol, 2,4-xylenol, and 2,6-xylenol / p-cresol / o-ethylphenol, etc. (without the first component)

[0078] In the polymerization reactor, add 164.1 kg of the previous batch of prepolymer, 1000 kg of the second component cresol (75 kg of phenol, 122 kg of o-cresol, 315 kg of p-cresol, 358 kg of m-cresol, 58 kg of o-ethylphenol, 23 kg of 2,6-xylenol, 29 kg of 2,4-xylenol, and 20 kg of 2,5-xylenol), 40 kg of oxalic acid (dissolved in 60 kg of hot water), 5 kg of 36% hydrochloric acid, and 1000 kg of 37% formaldehyde. Adjust the pH to 2.2 and heat to 90°C for 1 hour; add 10 kg of 36% hydrochloric acid. Simultaneously add 465 kg of 37% formaldehyde aqueous solution and the remaining 1000 kg of the second component m- and p-cresol (containing 674 kg of p-cresol, 974 kg of m-cresol, 2 kg of o-ethylphenol, 15.4 kg of 2,4-xylenol, and 7.6 kg of 2,5-xylenol) over 2.5 hours. The reaction was carried out at 98℃ for 2 hours until the 2,5-xylenol content was ≤0.03% and the free phenol content was 16.13%.

[0079] The reaction was followed by distillation. The distillate was subjected to secondary polymerization catalyzed by 4 kg of 36% hydrochloric acid, and then extracted with 2000 kg of ethyl acetate. The oil layer and dehydrated condensate were combined, and after solvent recovery and distillation, the following were obtained sequentially: 41.4 kg of 99.6% o-cresol, 21.6 kg of o-cresol / 2,6-xylenol (11.1 kg of o-cresol and 10.5 kg of 2,6-xylenol), 299.6 kg of 2,6-xylenol / p-cresol / o-ethylphenol (6.5 kg of 2,6-xylenol, 265.8 kg of p-cresol and 27.3 kg of o-ethylphenol), and 27.1 kg of 99.7% 2,4-xylenol. The residue of 164.7 kg (containing 161.4 kg of prepolymer) was returned to the first-step polymerization reactor to be used with other phenolic substances for the next batch of phenolic resin synthesis.

[0080] The resin phase was dehydrated under vacuum and cured at 195°C to obtain 2016.2 kg of phenolic resin with a softening point of 120°C, 0.8% free phenol, and 77.6% char residue.

[0081] Example 13: Using 2,4 / 2,5-xylenol to co-produce resin, 2,4-xylenol, etc. (without the first component)

[0082] In the polymerization reactor, 28.6 kg of the previous batch of prepolymer, 1000 kg of the second component (2,4 / 2,5-xylenol extracted from vaporized phenol, containing 13 kg of p-cresol, 22 kg of m-cresol, 36 kg of 2,3-xylenol, 549 kg of 2,4-xylenol, and 380 kg of 2,5-xylenol), and 40 kg of 36% hydrochloric acid were added. The pH was adjusted to 1.8, and the temperature was raised to 85-90℃. Simultaneously, 800 kg of 37% formaldehyde (the total formaldehyde amount was 1.36 times the total molar mass of m-cresol, 2,5-xylenol, and 2,3-xylenol) and 1000 kg of 2,4 / 2,5-xylenol were added dropwise over 2.5 hours. The reaction was maintained at 98℃ for 3 hours until the 2,5-xylenol content was ≤0.39% and the free phenol content was 39.94%.

[0083] The reaction was followed by distillation. The distillate was subjected to secondary polymerization catalyzed by 3.5 kg of 36% hydrochloric acid, and then extracted with 3000 kg of methyl isobutyl ketone. The oil layer and dehydrated condensate were combined, and after solvent recovery and distillation, 892.9 parts of 99.6% 2,4-xylenol were obtained. The residue of 28.2 parts (including 23.1 parts of prepolymer) was returned to the first-step polymerization reactor and used together with the 2,4 / 2,5-xylenol raw material for the next batch of phenolic resin synthesis.

[0084] The resin phase was dehydrated under vacuum and cured at 128°C to obtain 1220.8 kg of phenolic resin with a softening point of 96.3°C, 2.5% free phenol, and 75.0% char residue.

[0085] Comparative Example 1: Synthesis of Traditional Phenolic Resin

[0086] In a reactor, 2000 kg of petrochemical phenol (99.9% purity) and 30 kg of oxalic acid were added. After heating to 90°C, 1535 kg of 37% formaldehyde aqueous solution was added dropwise over 2 hours. The temperature was then raised to 95-100°C and the reaction was carried out for 4 hours. The reaction solution was then divided into two equal portions and added to two dehydration reactors for further dehydration.

[0087] One sample, after distillation and dehydration (final pressure -0.09 to -0.1 MPa, final temperature ≤150℃), yielded 1017 kg of phenolic resin. The resulting resin had a softening point of 85-120℃, a free phenol content of 1%-3%, and a char residue rate of 68-73%. This process only yielded phenolic resin, without the co-production of high-value ortho- and para-alkylphenols.

[0088] One sample, after distillation and dehydration (final pressure -0.09 to -0.1 MPa, final temperature ≤230℃), yielded 969.9 kg of phenolic resin product. The resulting resin had a softening point ≥115℃, a free phenol content ≤1%, and a char residue rate of 73-76%. This process only yielded phenolic resin, without the co-production of high-value ortho- and para-alkylphenols.

[0089] Effect Comparison

[0090] As can be seen from the above embodiments and comparative examples:

[0091] Comparative Example 1 used only expensive petrochemical phenol, resulting in a single product. In contrast, the embodiments of this invention use lower-cost coal-based phenols (mixed phenols, industrial cresol, crude 2,6-xylenol, industrial m-p-cresol, various mixed xylenols such as 2,4 / 2,5-xylenol and m-p-ethylphenol, crude 2,4,6-tricresol and methyl ethylphenol mixtures, m-p-isopropylphenol and other mixed tricresols, etc.) to replace phenol as the raw material. When the first component uses mixed phenols as the raw material, phenol or the second component may not be used. While obtaining high-performance phenolic resin, various high-purity ortho- and para-alkylphenols (such as ortho-cresol, 2,6-xylenol, p-cresol, p-ethylphenol, 2,4-xylenol, etc.) are co-produced. The market value of these co-produced phenols far exceeds the cost of the raw materials they replace, achieving significant economic added value.

[0092] The resin obtained in Comparative Example 1 had the highest char residue of 75.3%. The resins obtained in the embodiments of the present invention generally have high char residues; the char residues in multiple embodiments (such as Examples 6, 8, 9, 10, 11, and 12) are all above 77%, reaching a maximum of 79.3% (Example 10), significantly higher than that of Comparative Example 1. This confirms that the resin synthesized by the method of the present invention has a higher carbon content and is expected to provide better heat resistance and strength when used as a binder for refractory or friction materials.

[0093] This invention utilizes a "distillate secondary polymerization" step to convert residual formaldehyde and meta-phenol in wastewater into reusable prepolymers, thereby reducing the wastewater treatment load. The distillation vessel residue is reused as a prepolymer, achieving internal material recycling, reducing solid waste emissions, and embodying the concept of green chemistry.

[0094] In summary, this invention successfully transforms inexpensive coal-based phenol resources into high-value phenolic resins and high-purity fine chemicals. It not only far surpasses traditional processes in terms of economic benefits but also improves the performance of the main products and achieves greening of the process, thus possessing extremely high industrial application value.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resins, characterized in that, Includes the following steps: S1. Segmented polymerization and distillation: The first component, the second component, the aldehyde and the catalyst are mixed and subjected to segmented polymerization reaction. The reaction is controlled until the meta-phenol content is ≤1% and the free phenol content is 5-30%. The distillate containing unreacted phenol is distilled off to obtain phenolic resin reaction solution. The meta-phenol is at least one of m-cresol, m-ethylphenol and m-isopropylphenol. S2. Phenolic Extraction and Purification: The distillate obtained in step S1 is subjected to secondary polymerization to reduce the content of meta-phenols and free aldehydes. Then, it is extracted with a non-water-soluble solvent. The separated oil layer is distilled to obtain at least one product. The product contains ortho- and para-alkylphenols. The ortho- and para-alkylphenols include, but are not limited to, one or more of o-cresol, 2,6-xylenol, p-cresol, 2,4-xylenol, p-ethylphenol, 2,4,6-trimethylphenol, 2,4-methylethylphenol, 2,3,6-trimethylphenol, and p-isopropylphenol. The first component is phenol or a mixture of phenol and o-cresol; the second component is selected from one or more of the following obtained by crude phenol distillation of cresol, 2,6-xylenol, m-p-cresol, 2,4 / 2,5-xylenol, m-p-ethylphenol, 2,4,6-trimethylphenol, 2,4 / 2,5-methylethylphenol, 3,4-xylenol / 2,3,6-trimethylphenol, or m-p-isopropylphenol obtained by coal coking, coal gasification, or coal pyrolysis tar.

2. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 1, characterized in that, In step S1, the segmented polymerization reaction specifically involves: first reacting all of the first component, part of the second component, part of the aldehyde and catalyst at 80-105°C for 1-4 hours; then adding the remaining aldehyde and the remaining second component dropwise, and continuing the reaction for 1-6 hours. Wherein, the mass of the second component is 0 to 100% of the total mass of the second component, and the mass of the aldehyde is 0 to 100% of the total mass of the aldehyde; the total mass ratio of the first component to the second component is 0:100 to 100:

0.

3. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 2, characterized in that, In step S1, the aldehyde is an aqueous formaldehyde solution, and its total molar amount is 0.5 to 2.0 times the total molar amount of phenol and all meta-phenols; the mass of the catalyst is 0.1 to 10% of the total mass of the phenolic materials, and the catalyst is at least one of oxalic acid, phosphoric acid or hydrochloric acid.

4. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 1, characterized in that, In step S2, the secondary polymerization is as follows: an acidic catalyst is added to the distillate, and the reaction is carried out at 80-105°C for 1-3 hours until the free aldehyde content and meta-phenol content in the reaction solution are ≤0.5% and ≤0.5%; the acidic catalyst is hydrochloric acid or oxalic acid.

5. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 4, characterized in that, In step S2, the non-water-soluble solvent is toluene or methyl isobutyl ether, and its feeding mass is 0.5 to 2 times the total feeding mass of phenolic materials in step S1.

6. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 1, characterized in that, The phenolic resin reaction solution obtained in step S1 is dehydrated under vacuum, with the final pressure controlled at -0.09 to -0.1 MPa and the final temperature raised to 150 to 230°C to obtain a thermoplastic phenolic resin with a free phenol content of ≤1%; or the final temperature is raised to 80 to 150°C to obtain a general-purpose phenolic resin with a free phenol content of ≤3%.

7. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 1, characterized in that, In step S2, the distillation includes first removing the solvent, and then carrying out efficient distillation under conditions of pressure of -0.07 to -0.1 MPa and reflux ratio of 5 to 30; the residue obtained from the distillation is returned to the polymerization reaction in step S1 as a prepolymer.

8. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 1, characterized in that, The composition of the mixed phenols, by mass percentage, is: 50-90% phenol, 10-50% o-cresol, and the balance being at least one of m-p-cresol, 2,6-xylenol, and 2,4 / 2,5-xylenol, wherein the content of m-p-cresol is 0-40%, the content of 2,6-xylenol is 0-10%, and the content of 2,4 / 2,5-xylenol is 0-5%.

9. The method for synthesizing and extracting ortho- and para-alkylphenols from high-carbon phenolic resin according to claim 1, characterized in that, The product obtained in step S2 also includes high-purity phenol.

10. The method for synthesizing and extracting ortho- and para-alkylphenols from a high-carbon phenolic resin according to claim 8, characterized in that, The ortho- and para-alkylphenols obtained in step S2 are a mixture of p-cresol and o-ethylphenol, a mixture of p-ethylphenol and 2,3-dimethylphenol, or a mixture of p-isopropylphenol and p-propylphenol; and the method further includes using the aqueous layer obtained after secondary polymerization and extraction in step S2 to absorb formaldehyde to prepare a formaldehyde aqueous solution, or sending it out as wastewater.

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