Bio-based surfactants and antioxidants

Abstract

The invention relates to a method for separating substituted guaiacol and / or substituted eugenol of formula (I) from a mixture containing lignin fragments, # imgabs0 # wherein R1 is hydrogen or-OCH3; r2 is a linear chain or branched chain C1-C4 alkyl group, or a linear chain or branched chain C1-C4 hydroxyalkyl group; r3 is hydrogen or Na; the method comprises at least the following steps: a) providing a mixture containing lignin fragments; b) separating the mixture of step a) into a fraction rich in lignin oligomers and a fraction rich in lignin monomers; c) separating a solution comprising a compound of formula (I), wherein R3 is hydrogen, from the lignin monomer-rich fraction of step b) by fractionation; d) adding an aqueous NaOH solution having a pH of 11 or higher to the solution of step c) comprising the compound of formula (I), wherein R3 is a cation; e) separating the compound precipitated in step d); optionally a subsequent step f) dissolving the compound separated in step e) in water and reducing the pH of the aqueous solution to a value below pH 10 using an acid; g) separating the compound of formula (I) from the solution of step f), wherein R3 is hydrogen.

Description

[0001] The present invention relates to a method for isolating compounds from lignin compositions and their use as bio-based surfactants, antioxidants, UV light absorbers and stabilizers.

[0002] Surfactants, antioxidants and stabilizers are a class of chemicals widely used in home care, personal care and agrochemical industries, food, medical and health fields, and material formulations such as polymer materials, fuels, engine oils, paints, inks, adhesives and waxes. In view of its diverse markets and huge demand, it is of great concern that their production does not only rely on fossil-based sources, but also comes from renewable raw materials with short lifespans (especially for surfactants) to minimize global environmental problems. Natural antioxidants and bio-based surfactants are commercially available. Although their performance can be comparable to or exceed fossil-based benchmarks, the production of these chemicals still causes environmental pressure due to inefficient extraction processes or deforestation issues, because they usually require the use of food or raw materials (such as fruit or tropical plant fatty acids).

[0003] WO 2018 / 134427 A1 discloses the use of 4-alkylphenol derivatives (such as 2-methoxy-4-n-propylphenol and 2,6-dimethoxy-4-n-propylphenol) to synthesize alternative bisphenols obtained from the depolymerization of lignin encapsulated in lignocellulosic biomass.

[0004] US2888503 A discloses the use of 2,6-dimethoxy-4-propylphenol as an antiozonant in light-colored rubber to prevent cracking caused by ozone.

[0005] Ren et al. (Green Chemistry 2022) discloses a method for separating 4-propyleugenol and 4-propylguaiacol by extracting monomer-rich oil from lignin oil with a 0.3-0.1 mol / L KOH solution. In the second step, the extract solution is rotary evaporated to partially remove water, thereby increasing the KOH concentration to above 0.5 ml / L. The KOH solution is cooled to precipitate crystals. In addition, Ren et al. disclose a computer simulation experiment, that is, using two distillation units to distill a stream of a 4-propyleugenol-rich solution and a 4-propylguaiacol-rich solution to obtain 4-propyleugenol with a purity of 98.4% and a recovery rate of 94.5%, while all 4-propylguaiacol is recovered at a purity of 67.3%. Due to the difficulty in preparing sufficient raw materials for distillation, no real distillation experiments are disclosed. Ren et al. also disclose that NaOH solution is not suitable for purifying 4-propyleugenol by separating 4-propyleugenol sodium salt.

[0006] The problem underlying the present invention is therefore to provide a method for isolating bio-based compounds having surface active, antioxidant, UV light absorbing and stabilizing properties directly from sustainable sources in a few steps.

[0007] This problem is solved by the method according to claim 1. Further preferred embodiments are the subject matter of the dependent claims.

[0008] The present invention relates to a method for separating substituted guaiacol and / or substituted eugenol of general formula (I) from a mixture containing lignin fragments.

[0009]

[0010] wherein R1 is hydrogen or -OCH3, and

[0011] wherein R2 is a linear or branched C1-C4 alkyl group, or a linear or branched C1-C4 hydroxyalkyl group, and

[0012] wherein R3 is hydrogen or Na, and

[0013] The method comprises at least the following steps: first, providing a mixture containing lignin fragments. In the context of the present invention, the term "mixture" can also be understood as a solution or composition. Second, the mixture of the first step is separated into a fraction rich in lignin oligomers and a fraction rich in lignin monomers. Third, a solution containing a compound of formula (I) (wherein R3 is hydrogen) is separated from the fraction rich in lignin monomers of the second step. Fourth, a NaOH aqueous solution having a pH of more than 11 is added to the solution of the third step to induce precipitation of the compound of formula (I). After precipitation, the solution contains a compound of formula (I), wherein R3 is a cation. In the fifth step, the compound precipitated in the fourth step is separated.

[0014] The method of the present invention comprises the following optional steps six and seven. In the sixth step, the compound separated in the fifth step is dissolved in water, and the pH of the aqueous solution is lowered to a value below pH 10 using an acid. In the seventh step, the compound of formula (I) is separated from the solution of step six, wherein R3 is hydrogen.

[0015] Preferably, the composition comprising lignin fragments is obtained by reductive depolymerization of lignin.

[0016] In a preferred embodiment of the present invention, in a second step, the part rich in lignin oligomers and the part rich in lignin monomers are separated by distillation, at least one film or liquid-liquid extraction using a low-polarity solvent (e.g., diethyl ether). In distillation, light lignin fragments and other small fragments evaporate from solution, and the remainder is recovered as a powder containing heavier lignin fragments (e.g., lignin dimers and oligomers). In membrane separation, small lignin fragments and other small mixture components are ultrafiltered from the large lignin fragments rich in lignin oligomers by size exclusion. In liquid-liquid extraction, the light phase containing lignin monomers and other small fragments is dissolved, and the remainder is rich in heavier fragments such as lignin oligomers.

[0017] In the third step, the separation of the compounds of formula (I) is carried out by fractional distillation. In fractional distillation, the evaporation selectivity is driven by a change in pressure and / or temperature, with the column consisting of stripping and / or rectifying sections.

[0018] Preferably, the pH of the NaOH solution containing the compound of formula (I) in the fourth step is 12 to 13.

[0019] In the fifth step, it is preferred that an emulsion is formed as the pH is lowered. Preferably, the heavier phase of the emulsion comprises lignin monomers, which can be separated by decantation or centrifugation.

[0020] Surprisingly, it was found that the method for isolating substituted guaiacols and / or substituted eugenols of formula (I) can produce these compounds in high yield despite the use of fractional distillation to separate the compounds of formula (I) from the fraction rich in lignin monomers and the use of NaOH solution for precipitation. The method of the present invention is easy to handle, easy to control, and can be scaled up on an industrial scale to produce low-cost and high-quality compounds. In addition, the method of the present invention can achieve continuous production of the compounds to be separated. Another benefit is that, using the method of the present invention, the mixture containing the compounds to be separated does not contain sugars, which greatly facilitates further processing and avoids the formation of humins and other degradation products.

[0021] In a preferred embodiment of the present invention, R1 is hydrogen.

[0022] In another preferred embodiment of the present invention, R1 is -OCH3.

[0023] Preferably, R2 is selected from the group consisting of -(CH2)2-CH3, -(CH2)-CH3, -CH3 and -(CH2)3-OH.

[0024] In a preferred embodiment of the present invention, the compound of formula (I) is selected from the group consisting of:

[0025]

[0026]

[0027]

[0028] In a preferred embodiment of the present invention, the concentration of NaOH in the alkaline aqueous solution is 0.1 to 4 mol / L.

[0029] Preferably, the precipitation is carried out at room temperature.

[0030] In a preferred embodiment of the present invention, the method comprises the following subsequent steps six and seven. In the sixth step, the compound isolated in the fifth step is dissolved in water, and the pH of the aqueous solution is lowered to a value below pH 11 using an acid. In the seventh step, the compound of formula (I) wherein R3 is hydrogen is isolated from the solution of step six.

[0031] The method according to claim 9, wherein in step f) the pH is adjusted to 4 to 7.

[0032] The method according to claim 9 or 10, wherein in step f) the acid is HCl, p-TSA, acetic acid, H3PO4 or H2SO4.

[0033] The present invention also includes compositions comprising a compound of formula (I) as described above.

[0034] The present invention also includes the use of the composition as described above as a surfactant, antioxidant, UV light absorber or stabilizer.

[0035] Preferably, the composition comprises 4-propyleugenol as a surfactant, UV light absorber or stabilizer.

[0036] Preferably, the composition comprises 4-propyleugenol salt as a surfactant, antioxidant, UV light absorber or stabilizer.

[0037] A preferred embodiment of the present invention is the use of 4-propyleugenol or a 4-propyleugenol salt as UV light absorber, for example for coatings of sunglasses or as an ingredient in sunscreens.

[0038] Another preferred embodiment of the present invention is the use of 4-propyleugenol or 4-propyleugenol salts as stabilizers for emulsion stability. These compounds have the same application as surfactants to minimize the coalescence of colliding droplets (e.g. as active pharmaceutical ingredients, foods such as ice cream or milk, and in cosmetics).

[0039] The present invention also includes the use of 4-propyleugenol as a nonionic surfactant.

[0040] The present invention further comprises the use of 4-propyleugenol salt as an ionic surfactant.

[0041] The present invention further comprises the use of 4-propyleugenol and / or a 4-propyleugenol salt as a surfactant.

[0042] Preferably, 4-propyleugenol and 4-propyleugenol salts are used as surfactants in the baking industry, pulp and paper processing, agrochemical formulations, fire protection applications, plumbing, personal care products, cleaning products, petrochemicals, medical and pharmaceutical products such as toothpaste, detergents, cosmetics, paints, adhesives, inks, waxes, laxatives and food.

[0043] The present invention also includes the use of 4-propylguaiacol, 4-propanoleugenol, 4-propanolguaiacol and a combination thereof as an antioxidant.

[0044] The present invention also includes the use of 4-propylguaiacol, 4-propyleugenol and a combination thereof as UV light absorbers.

[0045] The present invention also includes the use of 4-propylguaiacol, 4-propyleugenol and a combination thereof as a stabilizer.

[0046] The present invention also includes compositions comprising at least the surface active components 4-propyleugenol and 4-propyleugenol salts.

[0047] The present invention also includes a composition comprising at least the surface active components 4-propanol eugenol and 4-propanol guaiacol.

[0048] Experimental data

[0049] Separation of lignin monomers and lignin oligomers from lignin oil

[0050] The device consists of 2 flasks (lignin mixture container and fraction collector) connected by a glass bridge. The collector is connected to a vacuum line and cooled with liquid nitrogen. After assembling the device, the system is evacuated by vacuum and the lignin mixture flask is heated to the required temperature according to the fraction number to be collected and stirred using a stirring hot plate. The fractions are collected in sequence by changing the vacuum degree and temperature (fraction 0 at 50°C and 0.7mbar; fraction 1 at 210°C (using a heating rate of 1°C / min starting from 50°C) and 0.2mbar). After all volatiles are removed, the heavier lignin fragments (partial oligomers) are recovered after cooling to room temperature.

[0051] gram start Part 0 Part 1 Some oligomers 4-Methylguaiacol 0 0 1 0 4-Ethylguaiacol 1 0 1 0 4-Propylguaiacol 54 0 59 0 4-Propanolguaiacol 6 0 5 0 4-Methyleugenol 0 0 0 0 4-Ethyleugenol 1 0 2 0 4-Propyleugenol 102 0 111 0 4-Propanol Eugenol 16 0 8 6 Eugenol 1 0 1 0 Isoeugenol 1 0 1 0 Methoxyisoeugenol 9 0 10 0 Butylated Hydroxytoluene 4 0 4 0 Ethanol 2 1 7 0 Ethyl glycolate 82 24 68 0 Glycolic acid 24 0 28 0 Dimer + oligomer + unknown 498 0 0 0 Dimer + unknown 0 5 32 0 Dimer + oligomer 0 0 0 423 total 801 31 339 430

[0052] Table 1

[0053] weight% start Part 0 Part 1 Some oligomers 4-Methylguaiacol 0.0 0.0 0.2 0 4-Ethylguaiacol 0.1 0.0 0.2 0 4-Propylguaiacol 6.7 1.5 17.3 0 4-Propanolguaiacol 0.8 0.0 1.5 0 4-Methyleugenol 0.0 0.0 0.0 0 4-Ethyleugenol 0.2 0.0 0.4 0 4-Propyleugenol 12.7 0.0 32.9 0 4-Propanol Eugenol 2.0 0.0 2.4 1 Eugenol 0.1 0.0 0.3 0 Isoeugenol 0.1 0.0 0.4 0 Methoxyisoeugenol 1.2 0.0 3.0 0 Butylated Hydroxytoluene 0.5 0.3 1.2 0 Ethanol 0.3 4.8 2.2 0 Ethyl glycolate 10.2 75.9 20.1 0 Glycolic acid 2.9 0.0 8.3 0 Dimer + oligomer + unknown 62.0 0.0 0.0 0 Dimer + unknown nd 0.0 9.6 0 Dimer + oligomer nd 0.0 0.0 98.4 total 99.8 82.5 100 99.4

[0054] Table 2

[0055] Purification by fractional distillation

[0056] The apparatus used for fractionation consists of 2 flasks (lignin mixture container and fraction collector), a Vigreux column and a glass bridge. The mixture container is connected to the Vigreux column, which is connected to the glass bridge with a collector at the other end. The collector is connected to a vacuum line and cooled using liquid nitrogen. After assembling the apparatus, the system is evacuated by vacuum and the lignin mixture is heated and stirred using a stirring hot plate. The fractions are collected in sequence by changing the vacuum degree and temperature (F0 at 135°C and 1.0 mbar; F1 at 145°C and 0.7 mbar; F2 at 150°C and 0.6 mbar; F3 at 155°C and 0.4 mbar; Fr is the distillation residue after collecting F3).

[0057] weight% F0 F1 F2 F3 Fr 4-Methylguaiacol 1 0 0 0 0 4-Ethylguaiacol 0 0 0 0 0 4-Propylguaiacol 25 1 0 0 0 4-Propanolguaiacol 0 0 4 5 5 4-Methyleugenol 0 0 0 1 0 4-Ethyleugenol 1 4 1 0 0 4-Propyleugenol 6 73 89 67 7 4-Propanol Eugenol 0 0 0 0 0 Eugenol 2 1 0 0 0 Isoeugenol 5 7 0 0 0 Methoxyisoeugenol 0 3 5 11 43 Butylated Hydroxytoluene 1 0 0 0 0 Ethanol 4 0 0 0 0 Ethyl glycolate 1 0 0 0 0 Glycolic acid 9 0 0 0 0 total 55 89 99 84 56

[0058] Table 3

[0059] Purification by pH-driven precipitation

[0060] The apparatus consists of a dropping funnel, a flask with a magnetic stirring bar, a stirring plate, a Buchner filter and an Erlenmeyer flask with a vacuum interface. The alkali solution is added dropwise to the lignin monomer mixture while stirring. The precipitate is then filtered and dried in a vacuum oven at 50°C and 100 mbar. Optionally, the remaining monomers in the aqueous liquid phase can be neutralized and extracted with ethyl acetate or hexane to recover other monomers.

[0061] weight% start Liquid organic phase Precipitated salt 4-Methylguaiacol 0.2 0.5 0.0 4-Ethylguaiacol 0.2 0.5 0.0 4-Propylguaiacol 17.3 53.1 5.2 4-Propanolguaiacol 1.5 0.2 0.0 4-Methyleugenol 0.0 0.0 0.0 4-Ethyleugenol 0.4 0.4 0.6 4-Propyleugenol 32.9 8.3 93.9 4-Propanol Eugenol 2.4 2.1 1.1 Eugenol 0.3 0.4 0.0 Isoeugenol 0.4 1.1 0.0 Methoxyisoeugenol 3.0 5.6 2.9 Butylated Hydroxytoluene 1.2 0.4 0.2 Ethanol 2.2 0.2 0.0 Ethyl glycolate 20.1 0.0 0.0 Glycolic acid 8.3 0.0 0.0 total 90.4 72.7 103.8

[0062] Table 4

[0063] NMR analysis was performed on the solid obtained by pH driven precipitation using 1 M NaOH and ddH2O as solvents.

[0064] 4-Propyleugenol sodium salt (Ib)

[0065] 1H NMR (400MHz, D2O) δ6.48(s,1H),3.68(s,3H),2.39(t,J=7.6Hz,1H),1.50(h,J=7.4Hz,1H),0.82(t,J=7.4Hz,2H)

[0066] Scale-up data for pH-driven precipitation of 4-propyleugenol salt

[0067] The apparatus consists of a dropping funnel, a flask with a magnetic stirring bar, a stirring plate, a Buchner filter and an Erlenmeyer flask with a vacuum interface. The alkali solution is added dropwise to the lignin monomer mixture while stirring. The precipitate is then filtered and dried in a vacuum oven at 50°C and 100 mbar. Optionally, the remaining monomers in the aqueous liquid phase can be neutralized and extracted with ethyl acetate or hexane to recover other monomers.

[0068] mmol of PS 1g scale in NaOH 25g scale in NaOH 30g scale in KOH Initial mixture 1.7 81.1 112.7 Sediment 1.4 75.8 61.3 PS recovery rate 82.9 93.5 54.4 PS concentration [wt%] 93.9 90.0 97.5

[0069] Table 5: PS = 4-propyleugenol, data based on Figure 2 .

[0070] Testing of 4-propyleugenol as an antioxidant

[0071] The antioxidant activity is evaluated by measuring the ability of the compound to react with a free radical (here 2,2-diphenyl-1-picrylhydrazyl, also known as DPPH). The measurement is based on the color difference of DPPH in solution after adding antioxidants of different compound compositions and is measured by UV / Vis spectrophotometry in the range of 400-700 nm (517 nm is the preferred wavelength). Butylated hydroxytoluene (BHT) and vitamin E are used as reference substances (positive controls), glycerol as a negative control (see Figure 3 and 4 ). At a concentration of 5 μg / mL, the inhibition rate of 4-propyleugenol was 65%, while the inhibition rates of BHT and vitamin E were 32% and 28%, respectively. At a concentration of 10 μg / mL, the inhibition rate of 4-propyleugenol was 84%, while the inhibition rates of BHT and vitamin E were 54% and 61%, respectively. Only at a high concentration of 50 μg / mL did the inhibition rates of 4-propyleugenol, BHT, and vitamin E become similar, at 85%, 85%, and 84%, respectively ( Figure 3 ). This clearly demonstrates the excellent activity of 4-propyleugenol as an antioxidant.

[0072] Testing of 4-propyleugenol as a surfactant

[0073] Surface tension measurements were performed using the pendant drop method with a Krüss EasyDrop standard drop shape analysis system. The measurement uses a water / air interface to determine the surface tension of different compounds at application relevant concentrations (0.1 to 1.0 wt. %).

[0074] sample Compound Concentration [wt%] Water / air interface [nM / m] Comparison none 0.00 72.8 1 POHG+POHS 1.00 44.8 2 P S 1.00 33.8 3 P S 0.50 39.8 4 P S 0.10 45.1 5 PS 1.00 32.3 6 PS 0.50 34.9 7 PS 0.10 48.3 8 NaLAS 0.10 33.0 9 SLS 0.20 35.4 10 SLES 0.02 33.8 11 SDBS 0.01 34.1 12 NPE 0.02 36.0 13 DOSS 0.20 51.0

[0075] Table 6: POHG = 4-propanol guaiacol, POHS = 4-propanol eugenol, PS = 4-propyl eugenol, PSNa = 4-propyl eugenol sodium salt, NaLAS = sodium linear alkylbenzene sulfonate; SLS = sodium dodecyl sulfate, SLES = sodium dodecyl ether sulfate, SDBS = sodium dodecylbenzene sulfonate, NPE = nonylphenol ethoxylate, DOSS = dioctyl sodium sulfosuccinate; see Figure 5 Sample 1 contained 26 wt% POHG, 61 wt% POHS, 3 wt% 4-propyleugenol, 0.6 wt% 4-ethyleugenol, and 0.3 wt% methoxyisoeugenol.

Claims

1. A method for separating substituted guaiacols and / or substituted eugenols of formula (I) from a mixture containing lignin fragments, in R1 is hydrogen or -OCH3; R2 is a linear or branched C1-C4 alkyl group, or a linear or branched C1-C4 hydroxyalkyl group; R3 is hydrogen or Na; The method comprises at least the following steps: a) providing a mixture containing lignin fragments; b) separating the mixture of step a) into a fraction rich in lignin oligomers and a fraction rich in lignin monomers; c) separating by fractional distillation a solution comprising a compound of formula (I), wherein R3 is hydrogen, from the lignin monomer-rich fraction of step b); d) adding an aqueous NaOH solution to the solution of step c) comprising the compound of formula (I) to obtain a pH of at least 11, wherein R3 is Na; e) isolating the compound precipitated in step d); Optional next steps: f) dissolving the compound separated in step e) in water and lowering the pH of the aqueous solution to a value below pH 11 using an acid; g) isolating the compound of formula (I) wherein R3 is hydrogen from the solution of step f).

2. The method according to claim 1, wherein: R1 is hydrogen.

3. The method according to claim 1, wherein: R1 is -OCH3.

4. The method according to claim 2 or 3, wherein: R2 is selected from the group consisting of –(CH2)2-CH3, –(CH2)-CH3, –CH3 and –(CH2)3-OH.

5. The method according to any one of claims 1 to 4, wherein: The concentration of NaOH in the solution of step d) is 0.1 to 4 mol / L.

6. The method according to any one of claims 1 to 5, wherein: The precipitation was carried out at room temperature.

7. The method according to any one of claims 1 to 6, further comprising the following steps: f) dissolving the compound separated in step e) in water and lowering the pH of the aqueous solution to a value below pH 11 using an acid; g) isolating the compound of formula (I) wherein R3 is hydrogen from the solution of step f).

8. The method according to claim 7, wherein: In step f) the pH is adjusted to between 4 and 7.

9. The method according to claim 7 or 8, wherein: In step f) the acid is HCl, p-TSA, acetic acid, H3PO4 or H2SO4.

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