H2O2-Mediated Kraft Lignin Oxidation with Readily Available Metal

Subscriber access provided by NEW YORK UNIV

Article

H2O2-mediated Kraft lignin oxidation with readily available metal salts: what about the effect of ultrasound? François Napoly, Nathalie Kardos, Ludivine Jean-Gerard, Catherine Goux-Henry, Bruno Andrioletti, and Micheline Draye Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b00595 • Publication Date (Web): 18 May 2015 Downloaded from http://pubs.acs.org on May 23, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

H2O2-mediated Kraft lignin oxidation with readily available metal salts: what about the effect of ultrasound? François Napoly,[a] Nathalie Kardos,[b], Ludivine Jean-Gérard,[a] Catherine Goux-Henry,[a] Bruno Andrioletti[a]* and Micheline Draye,[b]* [a] Institut de Chimie et Biochimie Moléculaire et Supramoléculaire (ICBMS), UMR CNRS 5246, Université Claude Bernard Lyon 1, Bâtiment Curien (CPE) 43 Boulevard du 11 novembre 1918, 69622, Villeurbanne Cedex, France. [email protected] [b] Laboratoire de Chimie Moléculaire et Environnement (LCME), Université Savoie MontBlanc, Campus scientifique, Le Bourget du Lac Cedex 73376, France. [email protected]

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 19

ABSTRACT: The hydrogen peroxide-mediated oxidative depolymerization of Kraft lignin was investigated in the presence of different metal salt catalysts in acetone/water (1/1: V/V) at low temperature. Na2WO4, 2H2O appeared to be the best catalyst yielding four vanillin-based monomers. Using the optimized conditions, monomers were obtained in 0.51 wt% yield from lignin. This result is among the best depolymerization yield obtained from lignin using hydrogen peroxide mediated oxidation. Optimization of the reaction conditions (temperature, catalysts loading, oxidant amount) revealed that the monomer formation is closely related to the cleavage vs recombination of the intermediates. In addition, the use of ultrasound irradiation involves higher oxidative coupling of phenoxy radicals resulting from lignin polymerization.


2

Page 3 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION The diminution of the fossil fuel reserves over the years stimulates more and more investigations in the exploitation of renewable sources of energy and chemical production. Today, the largest source of renewable chemicals is found in plants with the cellulose, hemicellulose and lignin. Lignin is one of the major components of the secondary cellular wall of plants and displays a remarkably complex structure. It is currently primarily used as a low-grade fuel to provide heat in the pulp and paper industry.1 From a chemist point of view, lignin is viewed as the second largest source of organic compounds on earth and the first in terms of aromatics.2 Unfortunately, because of its complexity and amorphous character, lignin is one of the most difficult biopolymer to study and transform into new, high-value organic compounds.2 Lignin is a threedimensional aromatic polymer composed of p-coumaryl (1), coniferyl (2) and sinapyl (3) alcohol monomers (Figure 1).

Figure 1. Precursors of the lignin moiety: p-coumaryl (1), coniferyl (2) and sinapyl (3) alcohols. Kraft lignin is a fragmented and alkaline-soluble lignin produced during the Kraft pulping process.3 Numerous methods including reduction (non oxidative cleavage),4 hydrolysis,5 oxidation6 and pyrolysis7 have been proposed for converting Kraft lignin into value-added low-molecularweight species. One of the mostly used strategies consists in the reduction of lignin via hydrogenation or hydrodeoxygenation for the production of fuels, bio-oils or bulk chemicals


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 19

such as benzene, toluene, xylene (BTX) and phenols. Nevertheless, these methods generally require severe conditions such as high temperatures (> 200°C) and high hydrogen pressure for the production of poorly functionalized monomers.8,9,10 Whereas reductive conditions tend to disrupt and remove lignin functionality to produce little functionalized aromatics, oxidation reactions afford more complex aromatic compounds with additional functionalities. Interestingly, many of these chemicals such as vanillin, guaiacol and syringaldehyde are considered as platform molecules usable for the synthesis of high-value chemicals. Commonly, these catalytic processes involve dioxygen or hydrogen peroxide as oxidant. Results published in the literature show that the use of oxygen allows obtaining aromatic compounds in good to moderate yields using catalyst-free reactions11 or in the presence of readily available metal salts such as manganese dioxide MnO2,12 copper sulfate CuSO4/ferric chloride FeCl3,13 cobalt acetate Co(OAc)2/zirconia acetate Zr(OAc)4) catalyst in acetic acid,14 and palladium on alumina (Pd/Al2O3).15 Unfortunately, using these simple approaches, lignin oxidative depolymerization requires high air or oxygen pressures and relatively high temperatures (>100°C). The use of mild conditions seems only to degrade lignin without monomer formation.16 Surprisingly, only a few papers report the use of hydrogen peroxide in combination with readily available metal salts as catalysts. Indeed the results of such oxidations are generally not as competitive in terms of yields and conversions as those obtained with di-oxygen. Noticeably, Crestini et al. investigated the use of H2O2 with methylrhenium trioxide MeReO3 (MTO) as catalyst in homogeneous17 and heterogeneous18 conditions at 25°C. Despite the interesting results obtained with lignin model compounds, the use of this system on Kraft lignin did not afford monomers but only an oxidized form of lignin. Similar results were obtained when the Fenton’s reagent19 iron sulfate/hydrogen peroxide FeSO4/H2O2 was used on steam pre-treated


4

Page 5 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lignin at 25°C. Borthakur et al.20 obtained vanillin in low yields by oxidation of rice straw with manganese sulfate, potassium bisulfate and cupric chloride as catalysts at 100°C. Lee et al. oxidized Kraft lignin in the absence of catalyst21 at 120°C affording non aromatic compounds such as oxalic, malonic, formic, acetic and succinic acids. Finally, guaiacol, vanillin and other phenolic compounds were observed by Park et al.22 under nearly-supercritical water in the presence of either KOH or H2O2. Recently, the effectiveness of ionic liquids (ILs) as solvents for lignin dissolution and depolymerization has been demonstrated.23,24,25 Thus, 1,3-dimethylimidazolium methylsulfate [MMIM][MeSO4] was used as oxidation reaction medium for the production of vanillin from rubber wood lignin.23 Wasserscheid et al. developed a method for the oxidative depolymerization of lignin in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][CF3SO3] using manganese nitrate Mn(NO3)2 as the catalyst and oxygen as the oxidant.24 More than 63% of lignin could be converted using 2% of catalyst. More recently, a process involving a 1,3dimethylimidazolium dimethylphosphate [MMIM][Me2PO4] based IL and methylisobutylketone (MIBK) under O2 exhibited good performance in the oxidative degradation of lignin.25 Finch et al. reported that the use of ultrasonic activation26 can improve the depolymerization of lignin in hydrogenation processes. Indeed, since 1950 when it was first introduced for polymerization reactions, ultrasonic activation has been used in a wide variety of polymer-based applications27. Actually, ultrasounds are known to enhance some processes28 through a physical phenomenon called cavitation, which is the formation, growth and collapse of bubbles in an elastic liquid. By imploding, these bubbles create locally high pressure (up to 1000 bars) and temperature (up to 5000 K) that lead to high-energy radical mechanisms but also generate some interesting physical effects. Thus, the enhancement of catalyst activity by low frequency


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 19

ultrasonic irradiation (e.g. f = 20 kHz) is due to 1) the improvement of mass transfer between the liquid and the catalyst surface, 2) reduction of particle size, increase of surface area and 3) acceleration of suspended particle motion induced by shock waves and microstreaming. Herein we demonstrate that using the appropriate experimental conditions, it is possible to depolymerize Kraft lignin to valuable monomers. Indeed, in the present study, we report on the oxidation of Kraft lignin by H2O2, in the presence of catalytic amounts of metal salts. We paid a particular attention to the study of the role of each reagent, to optimize the reaction in terms of efficiency and eco-friendliness. In this context, we investigated the use of ionic liquids as solvent and ultrasound as activation method in order to reduce the reaction time and the energy consumption. The novelty of our contribution lies in the unique combination of a metal salt under non-conventional activation conditions, to assist Kraft lignin depolymerization. 2. MATERIALS AND METHODS 2.2 Materials. Kraft lignin, Softwood lignin from resinous wood with low sulfonate content, was provided by FCBA Technical Center (Grenoble, France). Lignin was extracted using the kraft process and was washed by precipitation in acidic medium. Elementary analysis: C 52,2Wt%; H 4,7Wt%; O 31,5Wt%; N 0,1Wt%; S 3,1Wt%; Ashes (1000°C) 1,3Wt%; water 6,2Wt%; Total 99,1Wt%. N-butyl-N-ethylpiperidinium

bis(trifluoromethylsulfonyl)imide

[BEpip][NTf2]

was

synthesized according to a procedure previously decribed,29 Vanillin (99%), acetovanillone (98%), vanillic acid (97+%), guaiacol (99+%), diphenyl ether (99%), iron (III) sulfate (technical), iron (III) nitrate nonahydrate (99+%), manganese (II) sulfate monohydrate (99+%),


6

Page 7 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


bismuth (III) sulfate (99%), bismuth (III) nitrate pentahydrate (98%), tungstic acid (99+%), sodium tungstate dihydrate (99+%), aqueous hydrogen peroxide (35 wt%), 1-methylimidazole (99%) and chlorobutane (99+%) were purchased from Acros organics. 1-butyl-3methylimidazolium chloride [BMIM]Cl was synthesized according to the procedure described in the literature.29 [BMIM]Cl synthesis and characterization is given in SI (Supporting Information). Gas chromatography analyses were performed on an Agilent 6890 GC apparatus coupled with a 5973 MS and equipped with an Optima 5 capillary column (dimethylpolysiloxane 30 m x 0.25 mm x 0.25 µm) from Macherey-Nagel. Ultrasounds were generated by a Digital Sonifier® S-250D from Branson (Pelec = 11W) (Figure 2). A 3 mm diameter tapered microtip probe operating at 20 kHz was used. The acoustic power in water (Pacous.vol = 0.38 W.mL-1) was determined by calorimetry using a procedure described in the literature.30 Experiments were thermostated temperature-controlled with a minichiller cooler. 2.3 Experimental Methods Lignin oxidation under silent conditions: A weighed amount of lignin (about 400 mg), 5 to 10% of catalyst and aqueous hydrogen peroxide (35 wt %) were dissolved in : -

10 mL acetone/water (1/1: V/V) or,

-

10 mL acetone/water (1/1: V/V) + 10 wt% [BMIM]Cl or,

-

10 mL NaOHaq (1.0 M) or,

-

10 mL ethyl acetate or,

-

10 mL ethyl acetate and 10 wt% [BMIM]Cl or

-

10 mL [BEpip]NTf2.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 19

The mixture was stirred for one hour at a regulated temperature and then diluted with 10 mL of brine or with an aqueous solution of HCl (1.0 M for the reaction performed with NaOHaq). The precipitated lignin was filtrated off under vacuum. The solid residue and the aqueous layer were washed with ethyl acetate (3 x 15 mL). The combined organic layers were dried over 3 Å molecular sieves, and filtered. After addition of 20 mg of diphenyl ether (internal standard), the samples were analyzed by GC-MS.

Figure 2. Ultrasonic experimental equipment Lignin oxidation under ultrasonic conditions: A weighed amount of pure lignin (about 400 mg), 5 mol% of catalyst in 10 mL acetone/water (1/1: V/V) or 10 mL aqueous solution of NaOH (1.0 M) or 10 mL ethyl acetate, were introduced in a 25 mL double-envelop glass reactor. After addition of aqueous hydrogen peroxide (35 wt %), the mixture was allowed to stand for one minute and subjected to ultrasound irradiation for one hour at a regulated temperature (45 or 80°C). After dilution with 10 mL of brine or 10 mL of an aqueous solution of HCl (1.0 M for the reaction performed with NaOHaq), the precipitated lignin was filtrated off under vacuum. The solid residue was washed with ethyl acetate (3 x 15 mL) and the aqueous layer was extracted


8

Page 9 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with ethyl acetate (3 x 15 mL). The combined organic phases were dried over 3 Å molecular sieves and filtered. After addition of 20 mg of diphenyl ether (internal standard), the samples were analyzed by GC-MS. 2.4 Analytical methods Four monomers (Vanillin (A), acetovanillone (B), vanillic acid (C) and guaiacol (D) (figure 3) were evidenced by GC-MS analysis after derivatization with N,O-bis(trimethylsilyl) trifluoroacetamide/trimethylchlorosilane BSTFA/TMSC (99/1). For the quantitative analysis of the lignin oxidative depolymerization, 100 µL of BSTFA/TMS (99/1) were added to a solution of 100 µL of the organic layer in 1.0 mL acetone. The mixture was stirred and heated at 50°C for 2 hours, and then analyzed by GC-MS: Injection’s volume: 1.0 µL. GC Program: isothermal temperature of the oven at 60°C, followed by an increase of the temperature by 10°C/min until 340°C finished with an isotherm at 340°C for 10 minutes.

Figure 3. Monomers observed after lignin oxidative depolymerization. The acetylation and function titration of the oxidized lignin chemical functions were performed according to the method described in literature.31,32 Tables listing conditions of lignin oxidation, the mass of monomers determined and their GC-MS maps are given in SI (Supporting Information).


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 19

3. RESULTS AND DISCUSSION 3.2 Catalysts comparison and influence of the conditions. The ability to perform oxidations without the need for a strong oxidant and a toxic catalyst, thus preventing the generation of potentially harmful and/or difficult-to-remove species, represents an attractive goal both for multistep synthesis and large scale reactions. With this premise in mind, we turned our attention to the use of catalysts based on iron, manganese, bismuth and tungsten metal salts. To gain insight in their catalytic activity for lignin depolymerization, seven catalytic systems were monitored: Fe2(SO4)3, Fe(NO3),9H2O, Mn(SO4),H2O, Bi2(SO4)3, Bi(NO3)3,5H2O, H2WO4 and Na2WO4,2H2O. Results concerning the use of these catalysts for oxidation catalysis33,34,35,36 and lignin depolymerization19,20 have been published in the literature. The reaction was performed using 2 equivalents of 30% H2O2 during 1 hour in a mixture of acetone and water (1/1: V/V) which is able to partly dissolve the Kraft lignin even at 25°C (295 mg dissolved in 10 mL). This solvent combination had previously been used in one of our laboratory for the oxidation of lignin model compounds.37 Using these conditions, the catalyzed reactions did not produce higher monomer quantity than the blank (un-catalyzed) one. In addition, the use of salts limited the production of the monomer D, even if the temperature was increased to 45°C. When increasing the temperature to 45°C, Bi2(SO4)3 and tungsten oxides catalysts showed higher activity. The best result was obtained using Na2WO4,2H2O despite the low yield of extraction (2.034 mg i.e. 0.51 wt% yield in lignin depolymerization). Although low, this yield is one of the best yields published in the literature for lignin oxidative depolymerization using H2O2 as oxidant.17,19,20,22 Hydrogen peroxide is a widely used oxidant with high active oxygen content. However it is a rather slow oxidizing agent in the absence of activators. Bicarbonate was shown to activate H2O2


10

Page 11 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for sulfides oxidation38 and alkenes epoxidation. The corresponding BAP (bicarbonate-activated peroxide) oxidation system can be used in a large variety of oxidations where a mild, neutral pH oxidant is required. Hence, we investigated the efficiency of the BAP system for lignin oxidative depolymerization. As described in the literature, a manganese salt (MnSO4) with H2O2 as oxidant39 was selected as catalyst and compared with catalyst-free reaction and Na2WO4,2H2O promoted oxidation. Unexpectedly, the results obtained are lower than those obtained in the absence of sodium bicarbonate NaHCO3. In conclusion, these results show that the system Na2WO4,2H2O/H2O2(aq) at 45°C is the most efficient and it was chosen for further optimizations. 3.3 Optimization of the oxidative depolymerization Optimization of the catalytic system was operated in terms of temperature, amount of oxidant and catalytic charge. Increasing the temperature from 25°C to 45°C resulted in an increase of monomers concentration. On the contrary, a rise of the temperature to 56°C led to a decrease of monomers concentration. A similar decrease was observed when the catalytic charge was lowered to 2.5 mol% and/or 1 mol%. Two hypotheses can be put forward to explain this observation: (1) an increase of the temperature favors the degradation of hydrogen peroxide or (2) induces a faster recombination of the monomers with the bulk lignin. The decrease was even more drastic when the catalytic charge was increased to 10 and 15 mol% as no monomer was observed when 20 mol% of catalysts was used. Finally, the best catalytic charge was 5 mol%. Next, we studied the effect of the amount of oxidant on Kraft lignin depolymerization. The best yield of monomers was obtained with 2 equivalents of H2O2 and


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 19

5mol% of catalyst. With additional amounts of oxidant, the yield of monomers decreases, affording 0.249 mg (0.06 wt%) of extracted compounds when using 4 equivalents of oxidant. Thus, the decrease in monomers production may be ascribed to a potential re-condensation of the monomers with the bulk lignin. Finally, among the possible assumptions, a balance between monomers production and recombination depending on the oxidation conditions should be considered. 3.4 Effect of the solvent media In pursuit of our effort to optimize our experimental conditions, we considered the use of biphasic conditions in order to extract the four monomers from the reactive medium hence preventing recombination. Several studies were devoted to the use of ILs for the oxidative degradation of lignin.25,40 On the basis of their high solubilizing properties, we considered the use of ionic liquids as reaction medium. In addition, we envisioned the use of a mixture ionic liquid/molecular solvent in order to compare the potential benefit of using a biphasic mixture for the separation of the produced monomers. The acetone/water mixture (1/1: V/V) was proven to partially solubilize the lignin. Interestingly, addition of a limited amount of [BMIM]Cl (10 wt%), drastically increases the solubility of the lignin. Based on these observations a series of catalytic tests were carried out in acetone/water (1:1); acetone/water/10 wt% [BMIM]Cl; AcOEt; AcOEt/10 wt% [BMIM]Cl; [BEpip]NTf2; 1M NaOHaq. Using 400 mg of lignin and 2 equiv. of 30% H2O2 with 5 mol% of Na2WO4,2H2O during 1 h, the best results are obtained when acetone /water is used as reaction medium even if the lignin is partially solubilized. Although addition of 10 wt% of [BMIM]Cl increases lignin solubility, it


12

Page 13 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


affords lower yields in monomers. The same phenomenon is observed when AcOEt is used as the molecular solvent. In the hydrophobic ionic liquid, [BEpip]NTf2, less than 0.03 wt% of guaiacol is observed as the only monomer. Finally, in 1M NaOHaq, the solubility of lignin reaches 400 mg/10mL. Despite this enhanced solubility, the total of extracted monomers is comparable to the one observed in acetone/water containing [BMIM]Cl (10 wt%). We then studied the effect of the temperature on the monomers production. To this end, we carried out experiments in 1M NaOH at 45°C, 60°C, 80°C and 100°C and compared the results to those obtained in acetone/water at 45°C. Even if the total amount of monomers slightly increases at a temperature of 80°C in 1M NaOHaq, the best result is still obtained in the mixture acetone/water at 45°C. 3.5 Effect of Ultrasound Parvulescu et al.26 have shown that the use of ultrasound can allow the use of milder experimental conditions for lignin depolymerization under reductive conditions. In addition, our group previously reported improvements in oxidation reactions by using non-conventional activations methods such as ultrasound.28,41 In the present work we have investigated the effect of low frequency ultrasound irradiation for Kraft lignin oxidative depolymerization in three different solvents: acetone/water (V/V: 1/1) and ethyl acetate at 45°C, and 1M NaOHaq at 80°C. Mere 0.29, 0.24 and 0.25 wt% yields respectively were obtained at 20 kHz (Pelec,1 = 11.5 W) whereas 0.51, 0.37 and 0.41 wt% yields respectively were obtained under silent conditions. The use of ultrasound decreases the concentration of the monomers released. M. Tortora et al.42 recently showed that high frequency ultrasound irradiation on Kraft lignin involves three diﬀerent processes: the introduction of carboxylic moieties, lignin fragmentation, and lignin


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 19

polymerization. In addition, it was demonstrated that when ultrasound was used in combination with hydrogen peroxide, lignin samples showed a similar behavior with an eﬀect even more pronounced, due to the stronger oxidative conditions exerted by the hydrogen peroxide: It was proposed that the polymerization of lignin and the oxidation of the lignin backbone are induced by the hydroxyl (OH) and superoxide (HO2) radicals generated during cavitation.43 Based on this observation, the decrease in the amount of monomers produced during the process could be explained by re-combinations of the fragments and lignin polymerization. Aiming at supporting this idea, different experimental conditions were explored. In order to favor emulsification at the expense of radicals production, the experiments were performed using an ultra-turrax® with 2 eq. of oxidant and 5 mol% of catalyst at 45°C in acetone/water (1/1). The use of 4 eq. of oxidant under silent conditions and ultrasound was also compared. When hydroxyl (OH) and superoxide (HO2) radicals are not generated in silent conditions or using an ultra-turrax®, monomers are produced in similar amounts. When the oxidant concentration was raised or when ultrasounds were used, the yields of monomers drastically decreased. This observation tends to confirm the hypothesis that monomers recombine when, H2O2 and even when H2O2 in combination with ultrasound are used. 3.6 Oxidized lignin analysis The

structure

of

lignin

after

oxidation

was

then

examined

using

Fourier transform infrared spectroscopy (FTIR), and the oxidative coupling and polymerization of the lignin was acknowledged by the increase of the C-O-C band at 1030 cm-1.44 Surprisingly, the C=O band of non-conjugated carbonyls (1710 cm-1) did not increase significantly reflecting a modest oxidation of the aliphatic OH of side chains. A quantitative evaluation of carboxylic


14

Page 15 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


acids, phenols and hydroxyl functional groups was then performed according to procedures published in the literature.31,32 The results summarized in Table 1 confirm the low oxidation of aliphatic OH of side chain and a slight increase of carboxylic acid concentrations in silent conditions and even more under ultrasound. Table 1. Structural analysis of the initial lignin and two solid residues in the optimized conditions in silent (1) and ultrasonic activation (2). Total hydroxyl

Total phenol

Aliphatic alcool

Total carboxyl acid

(mmol/g)

(mmol/g)

(mmol/g)

(mmol/g)

Initial kraft lignin

6.65

3.8

2.75

1.67

Solid residue (1)

4.42

1.92

2.52

1.72

Solid residue (2)

4.09

1.68

2.41

1.76

Entry

This observation is explained as under ultrasound, superoxide radical species (HO2) generated during cavitation promotes the formation of phenoxy radicals at the phenolic end units which undergo oxidative coupling with an overall increase in condensed OH confirmed by the decrease in phenolic OH concentration. CONCLUSION This work describes the oxidation of Kraft lignin using H2O2/Na2WO4 which proved to be the most effective system for the generation of vanillin, acetovanillone, vanillic acid and guaiacol. Ultrasound was used to induce stronger oxidative conditions. According to monomers concentration determination, FTIR analysis and chemical functions titration, ultrasound irradiation involves higher oxidative coupling of phenoxy radicals issuing from lignin polymerization.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 19

ASSOCIATED CONTENT Supporting Information. [BMIM]Cl synthesis and characterization, Tables listing lignin oxidative depolymerization in terms of type of catalyst, temperature, charge of catalyst, amount of oxidant, solvent, activation method, Tables listing lignin oxidation conditions and mass of monomers determined, GC chromatogram and MS spectra of the four monomers. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding authors: *(MD) Tel.: +33 479 758 859. Fax.: +33 479 758 674. E-mail: [email protected] *(BA) Tel.: +33 472 426 264. Fax.: +33 472 448 160. E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS F. N. deeply acknowledges the Rhône-Alpes region for financial support. B. A. thanks the French Agence Nationale de la Recherche (ANR) (ANR 12 CDII 45 0001 02 “CHEMLIVAL”) for partial financial support. The authors are grateful to Dr. Denilson Da Silva Perez (FCBAGrenoble) who kindly provided the Kraft lignin.


16

Page 17 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES (1) (2)

(3) (4)

(5) (6) (7) (8) (9) (10)

(11)

(12)

(13) (14)

(15)

(16) (17)

Huber, G. W.; Iborra, S.; Corma, A. Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering. Chem. Rev. 2006, 106, 4044. Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B. M. The Catalytic Valorization of Lignin for the Production of Renewable Chemicals. Chem. Rev. 2010, 110, 3552. Review of New Source Performance Standards for Kraft Pulp Mills. EPA-4503-83-017 U Env. Prot Agency Res. Triangle Park 1983. Son, S.; Toste, F. D. Non-Oxidative Vanadium-Catalyzed C-O Bond Cleavage: Application to Degradation of Lignin Model Compounds. Angew. Chem. Int. Ed. 2010, 49, 3791. Sun, Y.; Cheng, J. Hydrolysis of lignocellulosic materials for ethanol production: a review. Bioresour. Technol. 2002, 83, 1. Fargues, C.; Mathias, Á.; Rodrigues, A. Kinetics of vanillin production from kraft lignin oxidation. Ind. Eng. Chem. Res. 1996, 35, 28. Ben, H.; Ragauskas, A. J. Influence of Si/Al Ratio of ZSM-5 Zeolite on the Properties of Lignin Pyrolysis Products. ACS Sustain. Chem. Eng. 2013, 1, 316. Harris, E. E.; D’Ianni, J.; Adkins, H. Reaction of hardwood lignin with hydrogen. J. Am. Chem. Soc. 1938, 60, 1467. Pepper, J. M.; Lee, Y. W. Lignin and related compounds. I. A comparative study of catalysts for lignin hydrogenolysis. Can. J. Chem. 1969, 47, 723. Yan, N.; Zhao, C.; Dyson, P. J.; Wang, C.; Liu, L.; Kou, Y. Selective Degradation of Wood Lignin over Noble‐Metal Catalysts in a Two‐Step Process. ChemSusChem 2008, 1, 626. Pinto, P. C. R.; Costa, C. E.; Rodrigues, A. E. Oxidation of Lignin from Eucalyptus globulus Pulping Liquors to Produce Syringaldehyde and Vanillin. Ind. Eng. Chem. Res. 2013, 52, 4421. Lequart, C.; Kurek, B.; Debeire, P.; Monties, B. MnO2 and oxalate: an abiotic route for the oxidation of aromatic components in wheat straw. J. Agric. Food Chem. 1998, 46, 3868. Xiang, Q.; Lee, Y. Y. Production of oxychemicals from precipitated hardwood lignin. Appl. Biochem. Biotechnol. 2001, 91, 71. Partenheimer, W. The Aerobic Oxidative Cleavage of Lignin to Produce Hydroxyaromatic Benzaldehydes and Carboxylic Acids via Metal/Bromide Catalysts in Acetic Acid/Water Mixtures. Adv. Synth. Catal. 2009, 351, 456. Sales, F. G.; Maranhão, L. C. A.; Filho, N. M. L.; Abreu, C. A. M. Experimental evaluation and continuous catalytic process for fine aldehyde production from lignin. Chem. Eng. Sci. 2007, 62, 5386. Rahimi, A.; Azarpira, A.; Kim, H.; Ralph, J.; Stahl, S. S. Chemoselective Metal-Free Aerobic Alcohol Oxidation in Lignin. J. Am. Chem. Soc. 2013, 135, 6414. Crestini, C.; Pro, P.; Neri, V.; Saladino, R. Methyltrioxorhenium: a new catalyst for the activation of hydrogen peroxide to the oxidation of lignin and lignin model compounds. Bioorg. Med. Chem. 2005, 13, 2569.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 19

(18) Crestini, C.; Caponi, M. C.; Argyropoulos, D. S.; Saladino, R. Immobilized methyltrioxo rhenium (MTO)/H2O2 systems for the oxidation of lignin and lignin model compounds. Bioorg. Med. Chem. 2006, 14, 5292. (19) Crestini, C.; D’Auria, M. Singlet oxygen in the photodegradation of lignin models. Tetrahedron 1997, 53, 7877. (20) Borthakur, N. Process for the preparation of vanillin from agricultural plant waste by manganese salt catalyzed oxidation employing hydrogen peroxide. World Intellect. Prop. Organ. Pat. 2007, WO 2007/094013 A1. (21) Xiang, Q.; Lee, Y. Y. Oxidative cracking of precipitated hardwood lignin by hydrogen peroxide. Appl. Biochem. Biotechnol. 2000, 84, 153. (22) Kim, H. G.; Park, Y. Manageable Conversion of Lignin to Phenolic Chemicals Using a Microwave Reactor in the Presence of Potassium Hydroxide. Ind. Eng. Chem. Res. 2013, 52, 10059. (23) Shamsuri, A. A.; Abdullah, D. K. A Preliminary Study of Oxidation of Lignin from Rubber Wood to Vanillin in Ionic Liquid Medium. Oxid. Commun. 2013, 35, 767. (24) Stärk, K.; Taccardi, N.; Bösmann, A.; Wasserscheid, P. Oxidative Depolymerization of Lignin in Ionic Liquids. ChemSusChem 2010, 3, 719. (25) Liu, S.; Shi, Z.; Li, L.; Yu, S.; Xie, C.; Song, Z. Process of lignin oxidation in an ionic liquid coupled with separation. RSC Adv. 2013, 3, 5789. (26) Finch, K. B. H.; Richards, R. M.; Richel, A.; Medvedovici, A. V.; Gheorghe, N. G.; Verziu, M.; Coman, S. M.; Parvulescu, V. I. Catalytic hydroprocessing of lignin under thermal and ultrasound conditions. Catal. Today 2012, 196, 3. (27) Wells, T.; Kosa, M.; Ragauskas, A. J. Polymerization of Kraft lignin via ultrasonication for high-molecular-weight applications. Ultrason. Sonochem. 2013, 20, 1464. (28) Chatel, G.; Goux-Henry, C.; Kardos, N.; Suptil, J.; Andrioletti, B.; Draye, M. Ultrasound and ionic liquid: An efficient combination to tune the mechanism of alkenes epoxidation. Ultrason. Sonochem. 2012, 19, 390. (29) Cammarata, L.; Kazarian, S. G.; Salter, P. A.; Welton, T. Molecular states of water in room temperature ionic liquids. Phys. Chem. Chem. Phys. 2001, 3, 5192. (30) Koda, S.; Kimura, T.; Kondo, T.; Mitome, H. A standard method to calibrate sonochemical efficiency of an individual reaction system. Ultrason. Sonochem. 2003, 10, 149. (31) Mansson, P. Quantitative Determination of Phenolic and Total Hydroxyl Groups in Lignins. Holzforschung 1983, 37, 143. (32) El Mansouri, N.-E.; Salvadó, J. Analytical methods for determining functional groups in various technical lignins. Ind. Crops Prod. 2007, 26, 116. (33) Pillai, U. R.; Sahle-Demessie, E.; Namboodiri, V. V.; Varma, R. S. An efficient and ecofriendly oxidation of alkenes using iron nitrate and molecular oxygen. Green Chem. 2002, 4, 495. (34) Leonard, N. M.; Wieland, L. C.; Mohan, R. S. Applications of bismuth (III) compounds in organic synthesis. Tetrahedron 2002, 58 (42), 8373. (35) Hulce, M.; Marks, D. W. Organic-Solvent-Free Phase-Transfer Oxidation of Alcohols Using Hydrogen Peroxide. J. Chem. Educ. 2001, 78, 66–68. (36) Payne, G. B.; Smith, C. W. Reactions of Hydrogen Peroxide. III. Tungstic Acid Catalyzed Hydroxylation of Cyclohexene in Nonaqueous Media. J. Org. Chem. 1957, 22, 1682.


18

Page 19 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37) Napoly, F.; Jean-Gérard, L.; Goux-Henry, C.; Draye, M.; Andrioletti, B. Fe(TAML)Li/(diacetoxyiodo)benzene-Mediated Oxidation of Alcohols: Evidence for Mild and Selective C-O and C-C Oxidative Cleavage in Lignin Model Transformations. Eur. J. Org. Chem. 2014, 2014, 781. (38) Richardson, D. E.; Yao, H.; Frank, K. M.; Bennett, D. A. Equilibria, Kinetics, and Mechanism in the Bicarbonate Activation of Hydrogen Peroxide: Oxidation of Sulfides by Peroxymonocarbonate. J. Am. Chem. Soc. 2000, 122, 1729. (39) Lane, B. S.; Vogt, M.; DeRose, V. J.; Burgess, K. Manganese-Catalyzed Epoxidations of Alkenes in Bicarbonate Solutions. J. Am. Chem. Soc. 2002, 124, 11946. (40) Zakzeski, J.; Bruijnincx, P. C. A.; Weckhuysen, B. M. In situ spectroscopic investigation of the cobalt-catalyzed oxidation of lignin model compounds in ionic liquids. Green Chem. 2011, 13, 671. (41) Chatel, G.; Goux-Henry, C.; Mirabaud, A.; Rossi, T.; Kardos, N.; Andrioletti, B.; Draye, M. H2O2/NaHCO3-mediated enantioselective epoxidation of olefins in NTf2-based ionic liquids and under ultrasound. J. Catal. 2012, 291, 127. (42) Tortora, M.; Cavalieri, F.; Mosesso, P.; Ciaffardini, F.; Melone, F.; Crestini, C. Ultrasound Driven Assembly of Lignin into Microcapsules for Storage and Delivery of Hydrophobic Molecules. Biomacromolecules 2014, 15, 1634. (43) Svitelska, G. .; Gallios, G. .; Zouboulis, A. . Sonochemical decomposition of natural polyphenolic compound (condensed tannin). Chemosphere 2004, 56, 981. (44) El Mansouri, N.-E.; Yuan, Q.; Huang, F. Characterization of alkaline lignins for use in phenol-formaldehyde and epoxy resins. BioResources 2011, 6, 2647.


19

H2O2-Mediated Kraft Lignin Oxidation with Readily Available Metal

Recommend Documents