A low-cost furan resin mother liquor and its preparation method

Abstract

This invention belongs to the field of furan resin production and provides a low-cost method for preparing furan resin mother liquor. Formaldehyde, urea, and a portion of furfuryl alcohol are mixed uniformly, and an alkaline catalyst is added for reaction. Then, a Lewis acid is used for further reaction to obtain component I. Formaldehyde and furfuryl alcohol are mixed uniformly, and an acidic catalyst is used for reaction. After cooling, a silane coupling agent is added to continue the reaction to obtain component II. Components I and II are mixed uniformly, the pH is adjusted to 7-9, polyethylene glycol, diethylene glycol, and urea are added, and the reaction is carried out. After cooling, a formaldehyde removal agent is added, and the mixture is mixed uniformly to obtain the final product. By modifying furfuryl alcohol with formaldehyde, the more formaldehyde is modified onto the furfuryl alcohol, the greater the cost reduction. Simultaneously, the modified furfuryl alcohol itself also possesses a certain strength, which is improved compared to pure furfuryl alcohol. This invention effectively reduces the cost of furan resin.

Description

Technical Field

[0001] This invention belongs to the field of furan resin production technology, specifically relating to a low-cost furan resin mother liquor and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Furan resin is currently the most widely used resin in the foundry industry, serving as a crucial foundational material in industrial casting. Its quality directly impacts the precision, stability, and surface finish of castings. However, its high cost makes it difficult to simultaneously meet market demands for both price and strength. Current methods to reduce the cost of furan resin include adding xylose mother liquor, alcohols, and phenolic resins. While phenolic resins increase strength, the other components have little effect and may even reduce strength in certain environments. Furthermore, phenolic resins can affect resin viscosity during use, impacting on-site performance. To date, the industry has yet to find a method that simultaneously reduces cost and improves the strength of furan resin. Summary of the Invention

[0004] To address the problem of the inability to simultaneously reduce the cost and strength of furan resin, this invention provides a method for preparing low-cost furan resin mother liquor. By modifying furfuryl alcohol with formaldehyde, the more formaldehyde modified on furfuryl alcohol, the greater the cost reduction. At the same time, the modified furfuryl alcohol itself also has a certain strength, which is improved compared to pure furfuryl alcohol. Combined with other additives, the cost of furan resin is reduced while its strength and other properties are improved.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a low-cost method for preparing furan resin mother liquor, comprising:

[0007] Formaldehyde, urea, and a portion of furfuryl alcohol are mixed evenly, an alkaline catalyst is added, the pH value is adjusted to 10-11, the temperature is raised to 85-90℃, and the temperature is maintained for 90-100 minutes; then Lewis acid is used to adjust the pH value to 4-5, the temperature is raised to 95-98℃, and the temperature is maintained for 100-110 minutes to obtain component I.

[0008] Mix formaldehyde and furfuryl alcohol evenly, adjust the pH value to 3-4 using an acidic catalyst, heat to 120-140℃, keep warm for more than 3 hours, cool down, add silane coupling agent and continue to keep warm at 99-103℃ for 60-70 minutes to obtain component II;

[0009] Mix components I and II thoroughly, adjust the pH to 7-9, add polyethylene glycol, diethylene glycol, and urea, keep warm at 85-90℃ for 30-40 minutes, cool down, add formaldehyde removal agent, mix thoroughly, and the product is ready.

[0010] A second aspect of the present invention provides a low-cost furan resin mother liquor, which is composed of component I, component II and additives;

[0011] Component I is composed of the following raw materials in parts by weight: 12-19 parts formaldehyde, 12-18 parts urea, 25-40 parts furfuryl alcohol, 0.5-1.1 parts alkaline catalyst, and 1-2 parts Lewis acid.

[0012] Component II is composed of the following raw materials in parts by weight: 5-9 parts formaldehyde, 20-40 parts furfuryl alcohol, 0.5-0.9 parts silane coupling agent, and 0.6-1.5 parts acidic catalyst;

[0013] The additive is composed of the following raw materials in parts by weight: 7-9 parts diethylene glycol, 9-14 parts polyethylene glycol, 2.5-5 parts urea, and 1-2 parts formaldehyde remover.

[0014] Beneficial effects of the present invention

[0015] (1) The present invention modifies furfuryl alcohol with formaldehyde. The more formaldehyde is modified on furfuryl alcohol, the more the cost is reduced. At the same time, the modified furfuryl alcohol itself also has a certain strength, which is improved compared to the strength of pure furfuryl alcohol.

[0016] (2) In this invention, diethylene glycol has a certain plasticizing effect and also acts as an antifreeze agent, which can increase the stability and strength of the resin. Polyethylene glycol has the functions of emulsifier and stabilizer, which can increase the stability of the resin and allow it to be stored for a longer period of time without separation. Compared with formaldehyde, the combined use of the two effectively improves the strength of the resin. Lewis acid acts as an acidic catalyst in resin synthesis, which can slow down the intensity of the resin reaction, allowing the resin to polymerize slowly during the polymerization process, resulting in a more stable molecular chain, which has a certain effect on increasing the strength of the resin. The formaldehyde remover is ammonia water, and its working principle is that ammonium ions react with formaldehyde to generate hexamethylenetetramine salt, consuming excess formaldehyde and thus being used as a formaldehyde remover.

[0017] (3) The preparation method of the present invention is simple, practical and easy to promote. Detailed Implementation

[0018] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] A method for preparing a low-cost furan resin mother liquor includes the following steps:

[0020] Formaldehyde, urea, and a portion of furfuryl alcohol are mixed evenly, an alkaline catalyst is added, the pH value is adjusted to 10-11, the temperature is raised to 85-90℃, and the temperature is maintained for 90-100 minutes; then Lewis acid is used to adjust the pH value to 4-5, the temperature is raised to 95-98℃, and the temperature is maintained for 100-110 minutes to obtain component I.

[0021] Mix formaldehyde and furfuryl alcohol evenly, adjust the pH value to 3-4 using an acidic catalyst, heat to 120-140℃, keep warm for more than 3 hours, cool down, add silane coupling agent and continue to keep warm at 99-103℃ for 60-70 minutes to obtain component II;

[0022] Mix components I and II thoroughly, adjust the pH to 7-9, add polyethylene glycol, diethylene glycol, and urea, keep warm at 85-90℃ for 30-40 minutes, cool down, add formaldehyde removal agent, mix thoroughly, and the product is ready.

[0023] In some embodiments, the base catalyst is triethanolamine;

[0024] In some embodiments, the Lewis acid is boron trifluoride. Lewis acids act as acidic catalysts in resin synthesis, slowing down the intensity of the resin reaction and allowing the resin to polymerize slowly, resulting in more stable molecular chains and contributing to increased resin strength.

[0025] In some embodiments, the acid catalyst is benzoic acid;

[0026] In some embodiments, the silane coupling agent is silane coupling agent KH-603.

[0027] In some embodiments, the formaldehyde is a formaldehyde solution with a mass concentration of 44% to 46% and solid formaldehyde with a content of 92% to 96%, preferably, the formaldehyde is a formaldehyde solution with a mass concentration of 45% and solid formaldehyde with a content of 93%.

[0028] Among the additives, diethylene glycol has a certain plasticizing effect and also acts as an antifreeze agent, which can increase the stability and strength of the resin.

[0029] Polyethylene glycol acts as an emulsifier and stabilizer, increasing the stability of the resin and allowing it to be stored for a longer period without separation.

[0030] In some embodiments, the formaldehyde remover is ammonia water. The working principle is that ammonium ions react with formaldehyde to generate hexamethylenetetramine salt, which consumes excess formaldehyde and is thus used as a formaldehyde remover.

[0031] This invention also provides a low-cost furan resin, composed of the following raw materials in parts by weight:

[0032] Component I is composed of the following raw materials in parts by weight: 12-19 parts formaldehyde, 12-18 parts urea, 25-40 parts furfuryl alcohol, 0.5-1.1 parts alkaline catalyst, and 1-2 parts Lewis acid.

[0033] Component II is composed of the following raw materials in parts by weight: 5-9 parts formaldehyde, 20-40 parts furfuryl alcohol, 0.5-0.9 parts silane coupling agent, and 0.6-1.5 parts acidic catalyst;

[0034] The additive is composed of the following raw materials in parts by weight: 7-9 parts diethylene glycol, 9-14 parts polyethylene glycol, 2.5-5 parts urea, and 1-2 parts formaldehyde remover.

[0035] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0036] In the following examples, all raw materials are commercially available products. Formaldehyde is a 45% formaldehyde solution and a 93% solid formaldehyde solution. The acid catalyst is benzoic acid. The alkaline catalyst is triethanolamine. The Lewis acid is boron trifluoride. The formaldehyde removal agent is ammonia water with a concentration of approximately 18%, manufactured by Hengchang Shengcheng Ammonia Water Plant.

[0037] Example 1:

[0038] Component I: 12 parts formaldehyde, 12 parts urea, 40 parts furfuryl alcohol, 0.5 parts alkaline catalyst, and 1 part Lewis acid.

[0039] Component II: 9 parts formaldehyde, 40 parts furfuryl alcohol, 0.5 parts silane coupling agent KH-603, and 0.8 parts acidic catalyst.

[0040] Additives: 8 parts diethylene glycol, 12 parts polyethylene glycol, 2.5 parts urea, 1 part formaldehyde remover;

[0041] The preparation includes the following steps:

[0042] Weigh out the raw materials according to the formula of Component I. Add formaldehyde, urea, and a portion of furfuryl alcohol to the reaction vessel. Add a measured amount of alkaline catalyst, adjust the pH to 10.5, raise the temperature to 88℃, and hold for 95 minutes. Then, adjust the pH to approximately 4.5 using Lewis acid, raise the temperature to 96℃, and hold for 105 minutes to obtain Component I.

[0043] Weigh all raw materials according to the formula of Component II. Add formaldehyde and furfuryl alcohol to another reactor, adjust the pH to 3.5 using an acidic catalyst, heat to 130℃, and hold for more than 3 hours. After cooling, add silane coupling agent KH-603 and continue to hold at 101℃ for 65 minutes to obtain Component II.

[0044] Weigh each raw material according to the formulation of the additives, add component I and component II to the reaction vessel in proportion, adjust the pH value to 8, add polyethylene glycol, diethylene glycol, and urea, keep warm at 88℃ for 35 minutes, cool down, add formaldehyde removal agent, stir evenly, and obtain the product.

[0045] Comparative Example 1: A common resin mother liquor with the same furfuryl alcohol content and "identical indicators"; where "same furfuryl alcohol content" refers to the total amount of furfuryl alcohol added to components I and II in Example 1 (a total of 80 parts furfuryl alcohol), produced according to the traditional process (formaldehyde 21 parts, urea 14.5 parts, furfuryl alcohol 80 parts, alkaline catalyst 0.5 parts, acidic catalyst 0.8 parts, diethylene glycol 8 parts, polyethylene glycol 12 parts, formaldehyde removal agent 1 part. Formaldehyde and a portion of urea (urea ratio of 4:1 before and after reaction) are reacted at 90-94°C under alkaline conditions for about 2 hours, then furfuryl alcohol is added and reacted under acidic conditions for 1 hour, then the remaining urea is added and reacted under alkaline conditions for 30 minutes, and other subsequent materials are added).

[0046] Comparative Example 2: The Lewis acid was replaced with maleic anhydride, and the rest was the same as in Example 1.

[0047] Comparative Example 3: Diethylene glycol was replaced with methanol, and the rest was the same as in Example 1.

[0048] Comparative Example 4: Polyethylene glycol was replaced with methanol, and the rest was the same as in Example 1.

[0049] Comparative Example 5: "Same indicators", furfuryl alcohol content is 2% higher than that of Example 1, furfuryl alcohol input is 2%, and other process conditions are the same as those of Comparative Example 1.

[0050] Comparative Example 6: "Same indicators", furfuryl alcohol content is 3% higher than that of Example 1, furfuryl alcohol input is 3%, and other process conditions are the same as those of Comparative Example 1.

[0051] Comparative Example 7: "Same indicators", furfuryl alcohol content is 4% higher than that of Example 1, furfuryl alcohol input is 4%, and other process conditions are the same as those of Comparative Example 1.

[0052] Comparative Example 8: "Same indicators", furfuryl alcohol content is 5% higher than that of Example 1, furfuryl alcohol input is 5%, and other process conditions are the same as those of Comparative Example 1.

[0053] Table 1

[0054]

[0055]

[0056] Note: "Same indicators" means that the nitrogen content, Karl Fischer moisture content, distilled moisture content, and pH value of the finished product are the same.

[0057] Compared with methanol used in normal production processes, the strength of diethylene glycol and polyethylene glycol is significantly higher, and the stability of Example 1 is also longer.

[0058] Comparative Examples 5 to 8 show that the normal production method of furan resin requires an additional amount of furfuryl alcohol to achieve the same strength as Example 1. The strength of the resin is only achieved when the furfuryl alcohol content is 4% higher than that of Example 1. Therefore, this indicates that the furan resin preparation method of the present invention can achieve the strength of normal resin with a 4% reduction in furfuryl alcohol content without affecting its performance. This means that, for furan resin of equivalent strength, Example 1 is 4% cheaper than the price of furfuryl alcohol.

[0059] Example 2:

[0060] Component I: 17 parts formaldehyde, 16 parts urea, 30 parts furfuryl alcohol, 0.7 parts alkaline catalyst, and 1.5 parts Lewis acid.

[0061] Component II: 7 parts formaldehyde, 28 parts furfuryl alcohol, 0.7 parts silane coupling agent KH-603, and 0.6 parts acidic catalyst.

[0062] Additives: 9 parts diethylene glycol, 9 parts polyethylene glycol, 3 parts urea, and 1.2 parts formaldehyde remover.

[0063] The preparation method includes the following steps:

[0064] Weigh out the raw materials according to the formula of Component I. Add formaldehyde, urea, and a portion of furfuryl alcohol to the reaction vessel. Add a measured amount of alkaline catalyst, adjust the pH to 10, raise the temperature to 90℃, and hold for 90 minutes. Then, adjust the pH to approximately 4 using Lewis acid, raise the temperature to 98℃, and hold for 100 minutes to obtain Component I.

[0065] Weigh all raw materials according to the formula of Component II. Add formaldehyde and furfuryl alcohol to another reactor, adjust the pH to 3 using an acidic catalyst, raise the temperature to 120°C, and hold for at least 3 hours. After cooling, add silane coupling agent KH-603 and continue to hold at 99°C for 70 minutes to obtain Component II.

[0066] Weigh each raw material according to the additive formula, add component I and component II to the reaction vessel in proportion, adjust the pH value to 7, add polyethylene glycol, diethylene glycol, and urea, keep warm at 90℃ for 30 minutes, cool down, add formaldehyde removal agent, stir evenly, and obtain the product.

[0067] Comparative Example 9: A common resin mother liquor with the same furfuryl alcohol content (i.e., the sum of furfuryl alcohol inputs of components I and II in Example 2) and "same indicators", with other process conditions the same as Comparative Example 1.

[0068] Comparative Example 10: The Lewis acid was replaced with maleic anhydride, and the rest was the same as in Example 2.

[0069] Comparative Example 11: Diethylene glycol was replaced with methanol, and the rest was the same as in Example 2.

[0070] Comparative Example 12: Polyethylene glycol was replaced with methanol, and the rest was the same as in Example 2.

[0071] Comparative Example 13: "Same indicators", furfuryl alcohol content is 2% higher than that of Example 1, furfuryl alcohol input is 2%, and other process conditions are the same as those of Comparative Example 1.

[0072] Comparative Example 14: "Same indicators", furfuryl alcohol content is 3% higher than that of Example 1, furfuryl alcohol input is 3%, and other process conditions are the same as those of Comparative Example 1.

[0073] Comparative Example 15: "Same indicators", furfuryl alcohol content is 4% higher than that of Example 1, furfuryl alcohol input is 4%, and other process conditions are the same as those of Comparative Example 1.

[0074] Comparative Example 16: "Same indicators", furfuryl alcohol content is 5% higher than that of Example 1, furfuryl alcohol input is 5%, and other process conditions are the same as those of Comparative Example 1.

[0075] Table 2

[0076] serial number Free formaldehyde tensile strength compressive strength Volatile matter Resin stability / day Example 2 0.25 1.365 2.875 27.2 186 Comparative Example 9 0.56 0.973 2.13 20.6 146 Comparative Example 10 0.30 1.196 2.672 26.1 168 Comparative Example 11 0.35 1.286 2.798 26.9 189 Comparative Example 12 0.34 1.211 2.806 27.06 176 Comparative Example 13 0.18 1.05 2.25 22.7 172 Comparative Example 14 0.16 1.23 2.463 25.2 180 Comparative Example 15 0.20 1.385 2.801 26.1 175 Comparative Example 16 0.22 1.48 3.02 27 188

[0077] Note: "Same indicators" means that the nitrogen content, Karl Fischer moisture content, distilled moisture content, and pH value of the finished product are the same.

[0078] As shown in Table 2, compared with methanol used in normal production processes, the strength of products using diethylene glycol and polyethylene glycol is significantly higher.

[0079] As can be seen from Comparative Examples 13 to 16, the normal production method of furan resin requires an additional amount of furfuryl alcohol to achieve the same strength as Example 2. The strength of the resin is only achieved when the furfuryl alcohol content is 4% higher than that of Example 2. Therefore, this indicates that the furan resin preparation method of the present invention can achieve the strength of normal resin with a 4% reduction in furfuryl alcohol content without affecting its performance. This means that, for furan resin of equivalent strength, Example 2 is 4% cheaper than the price of furfuryl alcohol.

[0080] Example 3:

[0081] Component I: 19 parts formaldehyde, 18 parts urea, 25 parts furfuryl alcohol, 1.1 parts alkaline catalyst, and 2 parts Lewis acid.

[0082] Component II: 5 parts formaldehyde, 20 parts furfuryl alcohol, 0.9 parts silane coupling agent KH-603, and 1.5 parts acidic catalyst.

[0083] Additives: 7 parts diethylene glycol, 14 parts polyethylene glycol, 5 parts urea, and 2 parts formaldehyde remover.

[0084] The preparation method includes the following steps:

[0085] Weigh out the raw materials according to the formula of Component I. Add formaldehyde, urea, and a portion of furfuryl alcohol to the reaction vessel. Add a measured amount of alkaline catalyst, adjust the pH to 11, raise the temperature to 85°C, and hold for 100 minutes. Then, adjust the pH to approximately 5 using Lewis acid, raise the temperature to 95°C, and hold for 110 minutes to obtain Component I.

[0086] Weigh all raw materials according to the formula of Component II. Add formaldehyde and furfuryl alcohol to another reactor, adjust the pH to 4 using an acidic catalyst, heat to 140℃, and hold for at least 3 hours. After cooling, add silane coupling agent KH-603 and continue to hold at 103℃ for 60 minutes to obtain Component II.

[0087] Weigh each raw material according to the additive formula, add component I and component II to the reaction vessel in proportion, adjust the pH value to 9, add polyethylene glycol, diethylene glycol, and urea, keep warm at 85℃ for 40 minutes, cool down, add formaldehyde removal agent, stir evenly, and obtain the product.

[0088] Comparative Example 17: A common resin mother liquor with the same furfuryl alcohol content (i.e., the sum of furfuryl alcohol inputs of components I and II in Example 3) and "same indicators", with other process conditions the same as Comparative Example 1.

[0089] Comparative Example 18: The Lewis acid was replaced with maleic anhydride, and the rest was the same as in Example 3.

[0090] Comparative Example 19: Diethylene glycol was replaced with methanol, and the rest was the same as in Example 3.

[0091] Comparative Example 20: Polyethylene glycol was replaced with methanol, and the rest was the same as in Example 3.

[0092] Comparative Example 21: "Same indicators", furfuryl alcohol content is 2% higher than that of Example 1, furfuryl alcohol input is 2%, and other process conditions are the same as those of Comparative Example 1.

[0093] Comparative Example 22: "Same indicators", furfuryl alcohol content is 3% higher than that of Example 1, furfuryl alcohol input is 3%, and other process conditions are the same as those of Comparative Example 1.

[0094] Comparative Example 23: "Same indicators", furfuryl alcohol content is 4% higher than that of Example 1, furfuryl alcohol input is 4%, and other process conditions are the same as those of Comparative Example 1.

[0095] Comparative Example 24: "Same indicators", furfuryl alcohol content is 5% higher than that of Example 1, furfuryl alcohol input is 5%, and other process conditions are the same as those of Comparative Example 1.

[0096] Table 3

[0097]

[0098]

[0099] Note: "Same indicators" means that the nitrogen content, Karl Fischer moisture content, distilled moisture content, and pH value of the finished product are the same.

[0100] By comparing the three types of mother liquor with mother liquor of the same index, the resin of the present invention has significantly higher indexes in all aspects than the resin with the same furfuryl alcohol content. Moreover, as can be seen from Tables 1-3, the furan resin mother liquor of the present invention is superior to the mother liquor with at least 2% more furfuryl alcohol content, thus reducing the price of furfuryl alcohol by at least 2%.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a low-cost furan resin mother liquor, characterized in that, include: Formaldehyde, urea, and a portion of furfuryl alcohol are mixed evenly, an alkaline catalyst is added, the pH value is adjusted to 10-11, the temperature is raised to 85-90℃, and the temperature is maintained for 90-100 minutes; then Lewis acid is used to adjust the pH value to 4-5, the temperature is raised to 95-98℃, and the temperature is maintained for 100-110 minutes to obtain component I. Mix formaldehyde and furfuryl alcohol evenly, adjust the pH to 3-4 using an acidic catalyst, heat to 120-140℃, keep warm for more than 3 hours, cool down, add silane coupling agent and continue to keep warm at 99-103℃ for 60-70 minutes to obtain component II; Mix component I and component II thoroughly, adjust the pH to 7-9, add polyethylene glycol, diethylene glycol, and urea, keep warm at 85-90℃ for 30-40 minutes, cool down, add ammonia water, mix thoroughly, and the product is ready. The Lewis acid is boron trifluoride; the formaldehyde is a 45% (w / w) formaldehyde solution and a 93% (w / w) solid formaldehyde. The amounts of each raw material are as follows: Component I: 12 parts formaldehyde, 12 parts urea, 40 parts furfuryl alcohol, 0.5 parts alkaline catalyst, and 1 part Lewis acid; Component II: 9 parts formaldehyde, 40 parts furfuryl alcohol, 0.5 parts silane coupling agent, and 0.8 parts acidic catalyst; Additives: 8 parts diethylene glycol, 12 parts polyethylene glycol, 2.5 parts urea, and 1 part ammonia. Alternatively, component I: 17 parts formaldehyde, 16 parts urea, 30 parts furfuryl alcohol, 0.7 parts alkaline catalyst, and 1.5 parts Lewis acid; Component II: 7 parts formaldehyde, 28 parts furfuryl alcohol, 0.7 parts silane coupling agent, and 0.6 parts acidic catalyst; Additives: 9 parts diethylene glycol, 9 parts polyethylene glycol, 3 parts urea, 1.2 parts ammonia; Alternatively, component I: 19 parts formaldehyde, 18 parts urea, 25 parts furfuryl alcohol, 1.1 parts alkaline catalyst, and 2 parts Lewis acid; Component II: 5 parts formaldehyde, 20 parts furfuryl alcohol, 0.9 parts silane coupling agent, and 1.5 parts acidic catalyst; Additives: 7 parts diethylene glycol, 14 parts polyethylene glycol, 5 parts urea, and 2 parts ammonia.

2. The method for preparing low-cost furan resin mother liquor as described in claim 1, characterized in that, The alkaline catalyst is triethanolamine.

3. The method for preparing low-cost furan resin mother liquor as described in claim 1, characterized in that, The acidic catalyst is benzoic acid.

4. The method for preparing low-cost furan resin mother liquor as described in claim 1, characterized in that, The silane coupling agent is silane coupling agent KH-603.

5. A low-cost furan resin mother liquor prepared by the method of any one of claims 1-4.

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