Microwave-Assisted Organosolv Delignification: A Potential Eco

Article Cite This: Ind. Eng. Chem. Res. 2019, 58, 10698−10706

pubs.acs.org/IECR

Microwave-Assisted Organosolv Delignification: A Potential EcoDesigned Process for Scalable Valorization of Agroindustrial Wastes Francisco Avelino,† Francisco Marques,‡ Amanda K. L. Soares,§ Kaś sia T. Silva,∥ Renato C. Leitão,‡ Selma E. Mazzetto,∥ and Diego Lomonaco*,∥ †

Federal Institute of Education, Science and Technology of Ceará, Iguatu, Ceara 63503-790, Brazil Embrapa Agroindustria Tropical, Rua Dra. Sara Mesquita, 2270, Planalto do Pici, Fortaleza, Ceara 60511-110, Brazil § Department of Organic Chemistry, Institute of Chemistry, Federal University of Rio de Janeiro, 21941-909 Rio de Janeiro, Rio de Janeiro, Brazil ∥ Department of Organic and Inorganic Chemistry, Federal University of Ceara, Fortaleza, Ceara 60440-900, Brazil

Downloaded via BUFFALO STATE on July 23, 2019 at 18:13:10 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: The extraction of high-purity technical lignins at large scale, such as organosolv lignin, is still a challenge. The objective of this work was to verify the environmental feasibility of microwave-assisted organosolv delignification (MWAOD) of sugar cane bagasse (SCB) for scalable purposes. MWAOD studies were performed using 90% v/v CH3COOH combined with 2.0% v/v HCl (110 °C for 30 min). The effects of the MWAOD process on the lignin structure were evaluated. The results showed that increasing SCB mass in the microwave reactor causes considerable changes in neither the lignin yield and purity nor in their interunit linkages, monolignol composition, and thermal stability. Moreover, using recycled acetic acid spent liquor resulted in minor differences in the process parameters and lignin structure when compared to reactions with a fresh acid liquor. Therefore, MWAOD presents itself as a promising sustainable process for production of high-quality lignin in large scale with high yields. as the high molecular weight and polydispersity.6 These features can affect the lignin reactivity compromising its use for some applications, especially in polymer chemistry. According to published data from the Food and Agriculture Organization of the United Nations (FAO), the global production of sugar cane in 2016 was 1890 × 106 t, of which Brazil contributed 768 × 106 t, representing 40% of the global production.7 Furthermore, the Brazilian sugar cane harvest in the 2017−2018 season produced 657 × 106 t,8 which generated approximately 152 × 106 t of bagasse. Considering that this bagasse contains about 22% lignin,9 it is estimated that 38 × 106 t of lignin from bagasse can potentially be used as a source of phenols. The lignin derived from the sugar cane bagasse can be extracted using a sulfur-free process, such as organosolv, in which organic solvents (acetic or formic acids), in combination with a mineral acid catalyst are used to extract high-quality lignins (low carbohydrate and ash content and sulfur free

1. INTRODUCTION The continuous concern about environmental pollution has led the scientific community to focus on the development of green materials from renewable sources that can partially or fully replace the petroleum-based compounds. The use of green and sustainable technological pathways to produce biobased materials is still one of the main scientific challenges. The lignocellulosic biomass is a renewable source that is constituted of three main building blocks, such as lignin, cellulose, and hemicellulose, which can be applied to the development of biobased products.1,2 Lignin is a polymer with a complex amorphous structure formed by the random polymerization of three monolignols, such as p-hydroxyphenyl (H), syringyl (S), and guaiacyl (G), through ether and carbon−carbon linkages. Despite its complex structure, lignin offers several possibilities of destinations due to its structure and phenolic composition.3 However, lignin structure depends on the type of biomass and the methods employed in its isolation.4 The most generated technical lignin in the world is Kraft lignin, which is a byproduct from the pulp and paper industry.5 Although it has high availability there are some structural features that limit its application, such as the high sulfur and ash contents, as well © 2019 American Chemical Society

Received: Revised: Accepted: Published: 10698

March 1, 2019 May 28, 2019 May 30, 2019 May 30, 2019 DOI: 10.1021/acs.iecr.9b01168 Ind. Eng. Chem. Res. 2019, 58, 10698−10706

Article

Industrial & Engineering Chemistry Research lignins).3 Despite the organic solvents recycling options, organosolv processes are energy intensive due to the hightemperature and -pressure operating conditions combined with the relatively long reaction times that are necessary to obtain lignins with high yields and purities.10−13 In addition to the high energy demand and the safety risks associated with high-pressure operating conditions, the organosolv process tends to have long processing times, which severely impact lignin productivity. Optimization is required in order to maximize lignin productivity prior to scaling up the process. Therefore, an alternative technology that has been used for biorefinery purposes is microwave irradiation,14−18 which, combined with the organosolv process, promotes faster delignification reaction yielding high-quality lignin, as shown by our previous research.19 During application of microwave irradiation (MWI), the molecular dipoles present in the reaction medium interact with the electric field of MWI, causing their rotation and friction resulting in energy loss due to molecular rotation and heat release by friction making. As a result of microwaving, more effective productive collisions between reactants molecules are expected and yield faster reaction times with comparable or higher lignin yields than those of traditional organosolv processes.20 Moreover, the microwave-assisted organosolv delignification also offers the possibility to perform the extractions under atmospheric pressure and mild conditions, resulting in higher quality lignin with elevated yields than those obtained using the traditional organosolv methodology.19,21 The laboratory-scale microwave reactors allow the utilization of large amounts of starting material, which combined with the mild conditions, atmospheric pressure, and short reaction times would perfectly simulate a scalable process to be considered to be used in pilot plants. This is perfectly possible since larger microwave reactors designed for pilot plant operations are available.22 However, to our knowledge, there are no studies in the literature regarding the combination of the MWI with the organosolv process as a potential method for lignin extraction at large scale. This idea would be very useful for the production of several biobased products that require a large amount of high-quality and sulfur-free lignins,23,24 such as phenolic13,23 and epoxy resins,24−26 polyurethanes,23,27,28 biocomposites,29,30 and biomaterials.31,32 According to the above discussion, the objective of this work was to verify the environmental feasibility of the microwaveassisted organosolv delignification as a potential method for scale-up purposes through the use of recycled solvent. The main process metrics (lignin yield, purity, and chemical structure) while increasing the biomass loading were evaluated in this study. In addition, the effect of acetosolv solution recyclability on lignin features was also studied.

(TAPPI T204 cm-97), alpha-cellulose (TAPPI T203 cm-99), lignin (TAPPI T222 om-2), moisture, ash (TAPPI T211 om01), hemicellulose, and holocellulose.33 The lignocellulosic composition of SCB is described in Table S1. 2.3. Microwave-Assisted Organosolv Delignification Experiments (MWAOD). The microwave-assisted experiments were performed in a StartSYNTH microwave reactor (Milestone, Italy) used in an open-vessel configuration (2.45 GHz). A contactless infrared sensor was used to monitor the temperature, with the maximum power applied being limited to 500 W. The reaction conditions (temperature, time, and catalyst concentration) used in this study were previously optimized by our group.19 The first phase of the study was the evaluation of the MWAOD process scalability, in particular, varying the amount of SCBP. In these experiments, different quantities of SCBP (10, 100, 200, and 300 g) were added to a roundbottom flask containing the acetosolv solution (acetic acid/ water solution (9/1, v/v) and 2.0% v/v HCl) in a fiber per solution proportion of 1:10 (g/mL). The experiments were carried out at mild conditions (110 °C during 30 min) under reflux (atmospheric pressure) and continuous magnetic stirring. The experiments were performed in duplicate. The second phase of the studies included the recyclability of the acetosolv solution. Up to three solvent recycling cycles were evaluated. Therefore, SCBP (100 g) was mixed with recycled acetosolv solution and 2.0% v/v HCl at the same ratio used in the first phase. The experiments were carried out at the same conditions described above (110 °C for 30 min) under magnetic stirring and reflux (atmospheric pressure). The same isolation and purification steps described previously19 were employed in either phase. Then the lignins in dry form were weighted, and their yields were calculated according to eq 1

η=

mLigIsol mLigSCB

(1)

where η is the process yield (%), mLigIsol represents the dry weight of lignin obtained in the MWAOD process (g), while mLigSCB represents the dry weight of lignin in SCB (g) as calculated by Klason lignin (TAPPI standards shown in Table S1). 2.4. Structural Characterization of SCB Lignins. Purity was reported combining the percentages of acid-soluble and acid-insoluble (Klason lignin) lignins values of the SCB lignin samples. Klason lignin was evaluated following a standard procedure (TAPPI T222 om-2) with some modifications,34 and the acid-soluble lignin was evaluated by analyzing the first filtrate obtained in Klason lignin experiments by UV−vis spectrophotometry. Experimental details are available in the Supporting Information. Elemental analyses (CHN content) of SCB lignins were carried out using a PerkinElmer 2400 (Series II CHN-S/O) following standard procedures (Table S2). FTIR analyses were carried out using a PerkinElmer spectrometer (model FT-IR/NIR FRONTIER) in transmission mode using KBr pellets. The spectra were recorded in a wavenumber range from 4000 to 400 cm−1 using a resolution of 4 cm−1 and a number of scans (NS) of 32 measurements. The relative content (RC) of functional groups was determined according to a previous procedure reported in the literature.35

2. EXPERIMENTAL SECTION 2.1. Materials. The following solvents were used without any pretreatments: glacial acetic acid (Synth, Brazil), HCl (37%, Synth, Brazil), THF (HPLC-grade), and DMSO-d6 (99.5%, Sigma). 2.2. Raw Material Pretreatment. The sugar cane bagasse (SCB) was supplied by DIAGEO (Maracanau, Brazil) and processed as previously reported.19 The chemical composition of sugar cane bagasse powder (SCBP) was performed following standard procedures for determination of extractives 10699

DOI: 10.1021/acs.iecr.9b01168 Ind. Eng. Chem. Res. 2019, 58, 10698−10706

Article

Industrial & Engineering Chemistry Research 1

H−13C Heteronuclear single-quantum coherence (1H−13C HSQC) experiments were carried out in a Bruker Avance DPX 300 (operating at 300 and 75 MHz for 1H and 13C nuclei, respectively). Lignin sample (30 mg) was dissolved in 0.5 mL of DMSO-d6, in which the residual solvent peak was used as internal reference (DMSO δH/ δC 2.50/39.5 ppm). Differential scanning calorimetry (DSC) analyses were performed in a Mettler-Toledo (Schwerzenbach, Switzerland) model DSC 823e. Lignin (10 mg) was submitted to an annealing program (from 25 to 90 °C for 10 min and from 90 to 0 °C for 3 min) and then heated from 0 to 250 °C under N2 atmosphere with a flow rate of 50 mL min−1 and a heating rate of 20 °C min−1. Closed Al pans with a lid centrally punctured were employed in this experiment. Thermogravimetric analyses (TGA) were carried out in a Mettler-Toledo (Schwerzenbach, Switzerland) model TGA/ SDTA 851e. Lignin sample (10 mg) was submitted to a temperature program starting from 30 to 900 °C under inert atmosphere (N2, flow rate of 50 mL min−1) at a heating rate of 10 °C min−1. Gel permeation chromatography (GPC) analyses were carried out in a Shimadzu chromatograph (model LC-20AD, Kyoto, Japan) using a setup comprised of two analytical GPC columns (Phenogel 5 μ 50 Å and Phenogel 5 μ 103 Å, 4.6 mm × 300 mm, Phenomenex) connected in series at 40 °C using HPLC-grade THF as mobile phase (flow rate of 0.35 mL min−1). A UV−vis detector (Shimadzu SPD-M20A) at 280 nm was used to monitor the lignin samples. Sample preparation and other experimental details are available in the SI.

the microwave irradiation. Therefore, the polar compounds present in SCB would absorb more energy, favoring cleavage of organic molecules and disruption of complex structures, increasing the accessibility of activated ether/ester bonds in the substrate to the nucleophilic attack of water molecules. A small reduction in the process yield (lignin) was observed for a reaction load of 300 g. On the other hand, the purity of SCB lignins did not suffer significant changes with the increase in the amount of loaded starting material varied in a narrow range, from 77% to 84%, as shown by the One Way ANOVA test with a confidence of 99.5%, which considered the lignin purity values as statistically equal. This shows the high efficiency of the MWAOD process to promote cleavage of lignin−carbohydrate complexes (LCC), yielding high-purity and sulfur-free lignins. However, depending on the lignin application a higher purity level may be required.23 There are two alternatives available to increase the lignin purity: the first one is modification of the concentration of the acetosolv aqueous solution by increasing the amount of water, which probably would favor cleavage of ester bonds in LCC in a greater extension. The second one would be purification of the isolated lignin through some treatments, such as alkaline hydrolysis,36 in order to obtain low residual carbohydrate content. It is important to highlight that most papers regarding MWAOD report experiments performed under high pressure and small amounts of raw material (0.2−2 g).37−40 Other recent studies report the use of harsh conditions even under microwave irradiation and also small amounts of starting material (0.3−10 g).41,42 3.2. Structural Characterization of MWAOD Lignins. 3.2.1. Fourier Transform Infrared Spectroscopy (FTIR). Identification of the characteristic functional groups in the MWAOD lignins as well as any possible chemical modification in their structure resulted from the extractions were monitored by FTIR (Figure 2A). In order to help in the visualization of such modifications, the characteristic bands in the fingerprint region were compared by dividing their areas at a defined wavenumber by the corresponding value of the band at 1513 cm−1,35 yielding the relative content of functional groups (RC) (Figure 2B). The characteristic absorption bands of MWAOD lignins were assigned according to a previous report.43,44 Figure 2A shows bands related to the lignin backbone that were preserved after the extraction process: at 1604 and 1513 cm−1 (CC stretching of the aromatic ring skeleton) and at 1465 and 1424 cm−1 (C−H deformations and aromatic skeletal deformations coupled with C−H plane deformation). According to Figure 2B, the increase in the amount of starting material did not influence the relative content of these groups in the obtained lignins, except for some assigned groups at 1034 cm−1, which were considered statistically different by One Way ANOVA analysis with a confidence of 99.5%. The presence of bands at 1710, 1170, and 1126 cm−1 can be associated with the stretching of CO groups, one of the possible assignments related to lignin−carbohydrate complexes (LCC), whichi is indicative of residual carbohydrates in the lignins, which were not hydrolyzed during extraction. Thus, their intensity and their RC values can be used as an estimate of the efficiency of the extraction process. The RC values were quite similar for all lignins (Figure 2B), which means that the MWAOD process was able to promote

3. RESULTS AND DISCUSSION 3.1. Evaluation of MWAOD Feasibility for Scale-up Purposes. Lignin yield and purity were used to assess the MWAOD process feasibility at different SCB loadings as shown in Figure 1.

Figure 1. Effect of the amount of SCB used in the MWAOD process on the lignin yield and purity.

Figure 1 shows a considerable increase in the lignin yield when the amount of SCB was increased from 10 to 200 g. A statistical analysis (One Way ANOVA) showed that the lignin yield values were statistically different (α = 0.05%). This behavior probably is due to kinetic factors involved in the delignification process, specifically the increase in the amount of reactants (SCB and aqueous acetic acid solution), which probably caused a higher interaction between them and 10700


Article

Industrial & Engineering Chemistry Research

made according to published reports present in the literature.46,47 Figure 3 shows that the aliphatic oxygenated region of SCB lignins was composed of fragments linked by alkyl−aryl ether bonds, namely,, the β-O-4 ones. This behavior was observed by the cross-peaks related to the Cα−Hα and Cγ−Hγ correlations of A and A’ substructures. The main difference between these substructures is the presence of the acyl group in the γ carbon (substituent R), which is resultant of the partial acetylation of the aliphatic hydroxyls, due to the use of acetic acid in the pulping process. In Figure 4 the ratio between the relative contents of A′γ and Aγ is shown, which increased along with the amount of starting material. Figure 5 shows that the monolignol composition of SCB lignins was composed of syringyl (S), guaiacyl (G), and phydroxyphenyl (H) units due to the presence of cross-peaks related to the C2,6−H2,6 (S2,6), C2−H2 (G2), C5−H5 (G5), and C2,6−H2,6 (H2,6) correlations. In addition, there was also the presence of cross-peaks related to the oxidized forms of S, G, and H units, such as the ferulates (FA) and p-coumarates (PCA). Although these substructures are already present in native lignins from grass and cereal lignins,6 due to the oxidizing nature of the organosolv process, more oxidized substructures derived from G and H units, such as ferulic and p-coumaric acids, could be formed. Therefore, the organosolv process could contribute to increase the amount of FA and PCA in SCB lignins. In general, the monolignol constituents of SCB lignins were quite similar to other lignins from the same feedstock reported in the literature.46,47 The presence of a cross-peak related to ferulates (FA) in SCB lignins can be attributed to the presence of residual carbohydrates in their structure, since they act like a bridge between the carbohydrates and the lignin. The latter fact correlates with the existence of absorption bands related to LCC at 1711, 1169, and 1123 cm−1 in the FTIR spectra of SCB lignins. However, as shown in Figure 5, the intensities of the crosspeaks related to FA units are relatively low, which suggests that they were hydrolyzed during the pulping process and separated from lignin in the acid precipitation step. This behavior is in agreement with data reported in Figure 6A, in which low amounts of FA are present in all lignin samples. Another remarkable feature presented in Figure 6A and 6B is the RPM values of SCB lignins and their S/G and H/G ratios, which were very similar to each other. This shows that despite the process scale increase the key lignin structural features did not change significantly. Therefore, these results emphasize the capability of the MWAOD process to yield high-quality lignin with controlled modifications in its structure at larger scale, which is very important considering its potential application in pilot plants and industrial purposes. 3.2.3. Gel Permeation Chromatography (GPC). The efficiency of the MWAOD process regarding the use of different amounts of starting material was also evaluated through the molecular weight distribution curves of SCB lignins (Figure S2). Figure 7 shows the number-average (Mn) and weight-average (Mw) molecular weights for those lignins, and Table S4 summarizes their molecular weight data. Figures S2 and 7 show that SCB lignins had very similar and low polydispersity with Mw values within the range expected for organosolv lignins.6 In addition, Table S4 also shows that Mw and PDI values varied in a narrow range, in which for a

Figure 2. Main FTIR absorption bands of the MWAOD lignins. (A) Fingerprint region of MWAOD lignins, and (B) relative content of the main functional groups in their structure.

cleavage of the ester and ether bonds of LCC, independently of the biomass loading. This can be also confirmed by the lignins purity values (Figure 1), which is an indication that the MWAOD process is efficient to yield high-quality lignin even though at a larger scale. 3.2.2. Nuclear Magnetic Resonance (NMR). Evaluation of the effects of the MWAOD process on SCB lignins structure was studied by the 1H−13C HSQC experiment, which provides information about how the monomers are linked to each other (interunit linkages) as well as their types (monolignol composition). Figures 3 and 4 show the oxygenated aliphatic region (δH/δC 3.0−5.5/50−90) relative to the interunits (RPIL). Figures 5 and 6 show the unsaturated/aromatic regions of SCB lignins and their respective relative proportion of monomers (RPM). The full 1H−13C HSQC spectra of SCB lignins without cut off are shown in the SI (Figure S1). RPIL and RPM values were calculated by integrating the signal areas in the oxygenated aliphatic and aromatic regions following the procedure reported by Rencoret et al. (2013).45 The characteristic signals present in the spectra of SCB lignins are shown in Table S3, and their substructures are shown in Figures 3 and 5. The assignments of the main cross-peaks were 10701


Article


Figure 3. Side chain region of 1H−13C HSQC spectra of SCB lignins: (A) 10, (B), 100, (C) 200, and (D) 300 g.

thermal stability with minor differences between their Tonset values. However, the similarities between the Tmax and CY suggest that the increase in the scale of the process did not compromise the quality of the SCB lignins. This fact also correlates with the Tg values of those lignins, which were very similar as well. These values show that polymeric chains of SCB lignins started to gain molecular mobility in a narrow range of temperature. Then the Tg values show that SCB lignins had similar processability (molecular mobility), which is a very important feature for their further valorization, especially in polymer chemistry. 3.3. Assessment of the Reutilization of Acetic Acid Solution in the MWAOD Experiments. Among several advantages of the organosolv process, one of the most important is the possibility of solvent recycling and reuse in the lignin extraction process. Therefore, it is crucial to verify if the successive reutilization of the solvent generates lignins with yields and purities comparable to those obtained using a fresh organosolv solution. Figure 8A shows the variation of the lignin yield and purity with the number of acetosolv solution reutilizations in which those of fresh acetosolv solution were used as reference (labeled as the point 0 in the graph). Similarly, Figure 8B shows how the Mw and Mn values of SCB lignin varied when the acetosolv solution was successively used in its extraction. The data shown in Figure 8A and 8B are summarized in Table 2. Figure 8A clearly shows that the first acetosolv solution reutilization had a lignin yield comparable to that which used a fresh solution. However, after successive reutilization there was observed a reduction in the lignin yield. This fact probably occurred due to the addition of an aqueous catalyst solution to the recuperated acetic acid, which caused its dilution since it already had remaining water from the solvent recuperation. Therefore, the decrease of acetic acid content in the solution

Figure 4. Relative proportion of interunit linkages of SCB lignins.

higher amount of raw material there was a slight increase in those parameters. Despite this minor difference, the most important feature is that all obtained samples presented similar molecular weights and, considering also their monolignol compositions, similar reactivity. This homogeneity is a very relevant characteristic for the process, since further chemical modifications should be considered regarding specific applications. 3.2.4. Thermal Properties. The thermal stability and processability of SCB lignins were evaluated through TGA and DSC analyses. Table 1 summarizes the thermal data obtained from these analyses, such as onset degradation temperature (Tonset) and maximum degradation temperature (Tmax), char yield (CY), and glass transition temperatures (Tg). Figures S3, S4, and S5 show the TGA, DTG, and DSC curves, respectively. Figures S3, S4, and S5 show all SCB lignins had very similar thermal profiles. It can be seen that those lignins had similar 10702


Article


Figure 5. Aromatic region of 1H−13C HSQC spectra of SCB lignins: (A) 10, (B), 100, (C) 200, and (D) 300 g.

Figure 7. Weight-average (Mw) and number-average (Mn) molecular weights of SCB lignins.

Table 1. Thermal Data of SCB Lignins Obtained from TGA and DSC Analyses SCB loading/parameter

Tonset (°C)

Tmax (°C)

CY (%)

Tg (°C)

10 g 100 g 200 g 300 g

218 214 208 207

371 368 375 368

23.7 26.5 19.1 24.3

141 145 140 137

could hinder the solvation of lignin fragments, diminishing the process yield. In addition, Figure 8A also shows that the second and third reutilizations had very similar lignin yields. This suggests that even considering successive dilutions probably there was reached a certain acetic acid/water proportion in which the ability of acetic acid to solvate lignin fragments attained a limit. However, it is shown in Figure 8A that the purity of lignins obtained using the recuperated acetic acid was considerably

Figure 6. Relative proportion of monomers of SCB lignins.

10703


Article


shown in Figure S8. It is possible to observe from Figures S7 and S8 that after three solvent recycles the structural features of SCB lignins, such as monolignol composition and interunit linkages, are still very similar to those obtained using a fresh solution. Therefore, this suggests that even with slight differences in lignin yield, purity, and Mw values, successive solvent recycles can generate lignins with similar structural features to those obtained using a fresh solution.

4. CONCLUSIONS The present work showed that the microwave-assisted organosolv delignification (MWAOD) process has a great potential to be used for lignin extraction at larger scale, generating high-purity lignin with high yield at atmospheric pressure and mild conditions in a matter of minutes. A deep structural characterization proved that the scaling up of MWAOD process yielded lignins with very similar structural features in which their backbone, interunit linkages, and monolignol composition varied in a very narrow range values. They also had quite similar molecular weight distribution curves, Mw and Mn values, as well as thermal stability (Tonset) and processability (Tg), which are important features for their use in polymer chemistry. Moreover, it was also shown that the MWAOD process can be performed using recycled acetic acid, which affected the lignin yield, purity, and quality. Therefore, the results show that the MWAOD process is an eco-friendly, fast, safe, reliable, and feasible method to be used in pilot plants representing an interesting alternative for extraction of high-quality lignin in large scale for further technological applications.

■

Figure 8. (A) Variation of the lignin yield and purity and (B) Mw and Mn values with the number of acetosolv liquor solution recycles.

Table 2. Variation of the Main Parameters Involved in the Quality of SCB Lignin Using Recycled Acetosolv Solution no. of solvent recycling

lignin yield (%)

0 1 2 3

72.2 76.5 61.5 62.8

lignin purity (%)

Mw (g mol−1)

Mn (g mol−1)

± ± ± ±

2062 1336 1362 1527

1059 580 593 670

74.8 91.7 85.8 93.9

1.03 2.41 1.48 4.02

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.9b01168. Experimental details of the characterization of SCB lignins; additional results (lignocellulosic composition of SCB, HSQC spectra, GPC, TGA and DSC curves of SCB lignins) (PDF)

■

AUTHOR INFORMATION

Corresponding Author

higher than that of lignin extracted using a fresh solution. This probably occurred due to the increase of water content in the acetosolv solution as mentioned before, favoring their nucleophilic attack to the ester linkages present in LCC, yielding lignins with lower carbohydrate content. The behavior observed in Figure 8A can be complemented by that in Figure 8B, in which there was a decrease in the Mw and Mn values when the recuperated acetosolv solution was used several times. This can also be explained by the successive additions of aqueous catalyst solution to acetic acid. In this case, the increase in the water content favored cleavage of ether bonds, since water molecules act as a nucleophile. Moreover, the Mw and Mn values suggest that the decrease of acetic acid content favored the solvation of lower molecular weight fragments, which was also observed by the displacement of their molecular weight distribution curves to lower log MW values (Figure S6). Figure S7 shows the 1H−13C HSQC spectrum of the SCB lignin obtained from the third solvent recycle, while the comparison between the RPM values of SCB lignins obtained by using fresh and recycled (3rd reuse) acetosolv solution is

*E-mail: [email protected]. Phone: +55 85 3366 9019. ORCID

Francisco Avelino: 0000-0001-8608-7618 Diego Lomonaco: 0000-0001-5763-4336 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors acknowledge Brazilian agencies CNPq (409814/ 2016-4 e 407291/2018-0), CAPES, and FUNCAP for financial support and CENAUREMN (Centro Nordestino de Aplicaçaõ da Ressonância Magnética Nuclear at Fortaleza, Brazil) for NMR analyses.

■

REFERENCES

(1) Wang, H.; Pu, Y.; Ragauskas, A.; Yang, B. From Lignin to Valuable Products−strategies, Challenges, and Prospects. Bioresour. Technol. 2019, 271, 449−461. (2) Cao, L.; Yu, I. K. M.; Liu, Y.; Ruan, X.; Tsang, D. C. W.; Hunt, A. J.; Ok, Y. S.; Song, H.; Zhang, S. Lignin Valorization for the

10704


Article

Industrial & Engineering Chemistry Research Production of Renewable Chemicals: State-of-the-Art Review and Future Prospects. Bioresour. Technol. 2018, 269, 465−475. (3) Figueiredo, P.; Lintinen, K.; Hirvonen, J. T.; Kostiainen, M. A.; Santos, H. A. Properties and Chemical Modifications of Lignin: Towards Lignin-Based Nanomaterials for Biomedical Applications. Prog. Mater. Sci. 2018, 93, 233−269. (4) Laurichesse, S.; Avérous, L. Chemical Modification of Lignins: Towards Biobased Polymers. Prog. Polym. Sci. 2014, 39 (7), 1266− 1290. (5) Hu, J.; Zhang, Q.; Lee, D. Kraft Lignin Biorefinery: A Perspective. Bioresour. Technol. 2018, 247, 1181−1183. (6) Constant, S.; Wienk, H. L. J.; Frissen, A. E.; de Peinder, P.; Boelens, R.; van eS, D. S.; Grisel, R. J. H.; Weckhuysen, B. M.; Huijgen, W. J. J.; Gosselink, R. J. A.; et al. New Insights into the Structure and Composition of Technical Lignins: A Comparative Characterisation Study. Green Chem. 2016, 18 (9), 2651−2665. (7) FAOSTAT. Food and Agriculture Organization of the United Nations-Statistics Division; http://www.fao.org/faostat/en/#data/ QC, 2016 (accessed May 12, 2018). (8) CONAB. Companhia Nacional de Abastecimento: Acompanhamento Da Safra Brasileir Cana de Açuć ar; https://www.conab.gov.br/ info-agro/safras/cana/boletim-da-safra-de-cana-de-acucar, 2017 (accessed Dec 6, 2018). (9) Rezende, C. A.; De Lima, M.; Maziero, P.; Deazevedo, E.; Garcia, W.; Polikarpov, I. Chemical and Morphological Characterization of Sugarcane Bagasse Submitted to a Delignification Process for Enhanced Enzymatic Digestibility. Biotechnol. Biofuels 2011, 4 (1), 54. (10) Fernández-Rodríguez, J.; Gordobil, O.; Robles, E.; GonzálezAlriols, M.; Labidi, J. Lignin Valorization from Side-Streams Produced during Agriculture Waste Pulping and TCF Bleaching. J. Cleaner Prod. 2017, 142, 2609−2617. (11) Carvajal, J. C.; Gómez, Á .; Cardona, C. A. Comparison of Lignin Extraction Processes: Economic and Environmental Assessment. Bioresour. Technol. 2016, 214, 468−476. (12) Maniet, G.; Schmetz, Q.; Jacquet, N.; Temmerman, M.; Gofflot, S.; Richel, A. Effect of Steam Explosion Treatment on Chemical Composition and Characteristic of Organosolv Fescue Lignin. Ind. Crops Prod. 2017, 99, 79−85. (13) Pinheiro, F. G. C.; Soares, A. K. L.; Santaella, S. T.; Silva, L. M. A. e; Canuto, K. M.; Caceres, C. A.; Rosa, M. de F.; Feitosa, J. P. de A.; Leitao, R. C. Optimization of the Acetosolv Extraction of Lignin from Sugarcane Bagasse for Phenolic Resin Production. Ind. Crops Prod. 2017, 96, 80−90. (14) Kostas, E. T.; Beneroso, D.; Robinson, J. P. The Application of Microwave Heating in Bioenergy: A Review on the Microwave PreTreatment and Upgrading Technologies for Biomass. Renewable Sustainable Energy Rev. 2017, 77, 12−27. (15) Li, H.; Qu, Y.; Yang, Y.; Chang, S.; Xu, J. Microwave Irradiation − A Green and Efficient Way to Pretreat Biomass. Bioresour. Technol. 2016, 199, 34−41. (16) Hassan, S. S.; Williams, G. A.; Jaiswal, A. K. Emerging Technologies for the Pretreatment of Lignocellulosic Biomass. Bioresour. Technol. 2018, 262 (March), 310−318. (17) Chaturvedi, V.; Verma, P. An Overview of Key Pretreatment Processes Employed for Bioconversion of Lignocellulosic Biomass into Biofuels and Value Added Products. 3 Biotech 2013, 3, 415−431. (18) Merino-Pérez, O.; Martínez-Palou, R.; Labidi, J.; Luque, R. Microwave-Assisted Pretreatment of Lignocellulosic Biomass to Produce Biofuels and Value-Added Products. In Production of Biofuels and Chemicals with Microwave; Fang, Z., Smith, R. L., Qi, X., Eds.; Springer: Berlin, 2015; Vol. 3, pp 197−224. (19) Avelino, F.; Silva, K. T. da; de Souza Filho, M. de S. M. S.; Mazzetto, S. E.; Lomonaco, D. Microwave-Assisted Organosolv Extraction of Coconut Shell Lignin by Brønsted and Lewis Acids Catalysts. J. Cleaner Prod. 2018, 189, 785−796. (20) Kappe, C. O. Controlled Microwave Heating in Modern Organic Synthesis. Angew. Chem., Int. Ed. 2004, 43, 6250−6284.

(21) Avelino, F.; Almeida, S. L.; Duarte, E. B.; Sousa, J. R.; Mazzetto, S. E.; de Souza Filho, M. S. M. Thermal and Mechanical Properties of Coconut Shell Lignin-Based Polyurethanes Synthesized by SolventFree Polymerization. J. Mater. Sci. 2018, 53 (2), 1470. (22) Microwave Chemical Co., L. Microwave Chemical Co., Ltd. http://mwcc.jp/en/company/ (accessed Mar 28, 2018). (23) De Wild, P. J.; Huijgen, W. J. J.; Gosselink, R. J. A. Lignin Pyrolysis for Profitable Lignocellulosic Biorefineries. Biofuels, Bioprod. Biorefin. 2014, 8, 645−657. (24) Gioia, C.; Lo Re, G.; Lawoko, M.; Berglund, L. Tunable Thermosetting Epoxies Based on Fractionated and Well- Characterized Lignins. J. Am. Chem. Soc. 2018, 140, 4054−4061. (25) van de Pas, D. J.; Torr, K. M. Biobased Epoxy Resins from Deconstructed Native Softwood Lignin. Biomacromolecules 2017, 18, 2640−2648. (26) Ferdosian, F.; Yuan, Z.; Anderson, M.; Xu, C. Synthesis of Lignin-Based Epoxy Resins: Optimization of Reaction Parameters Using Response Surface Methodology. RSC Adv. 2014, 4, 31745− 31753. (27) Avelino, F.; Miranda, I. P.; Moreira, T. D.; Becker, H.; Romero, F. B.; Taniguchi, C. A. K.; Mazzetto, S. E.; de Sá Moreira de Souza Filho, M. The Influence of the Structural Features of Lignin-Based Polyurethane Coatings on Ammonium Sulfate Release: Kinetics and Thermodynamics of the Process. J. Coatings Technol. Res. 2019, 16, 449−463. (28) Avelino, F.; Almeida, S. L.; Duarte, E. B.; Sousa, J. R.; Mazzetto, S. E.; De Souza Filho, M. De S. M. Thermal and Mechanical Properties of Coconut Shell Lignin-Based Polyurethanes Synthesized by Solvent-Free Polymerization. J. Mater. Sci. 2018, 53 (2), 1470− 1486. (29) Zhang, Y.; Zhou, S.; Fang, X.; Zhou, X.; Wang, J.; Bai, F.; Peng, S. Renewable and Flexible UV-Blocking Film from Poly(Butylene Succinate) and Lignin. Eur. Polym. J. 2019, 116, 265−274. (30) Dahy, H. Efficient Fabrication of Sustainable Building Products from Annually Generated Non-Wood Cellulosic Fibres and Bioplastics with Improved Flammability Resistance. Waste Biomass Valorization 2019, 10, 1167−1175. (31) Spiridon, I.; Tanase, C. E. Design, Characterization and Preliminary Biological Evaluation of New Lignin-PLA Biocomposites. Int. J. Biol. Macromol. 2018, 114, 855−863. (32) Wang, J.; Tian, L.; Luo, B.; Ramakrishna, S.; Kai, D.; Loh, X. J.; Yang, I. H.; Deen, G. R.; Mo, X. Engineering PCL/Lignin Nanofibers as an Antioxidant Scaffold for the Growth of Neuron and Schwann Cell. Colloids Surf., B 2018, 169, 356−365. (33) Yokoyama, T. Y.; Kadla, J. F.; Chang, H.-M. Microanalytical Method for the Characterization of Fiber Components and Morphology of Woody Plants. J. Agric. Food Chem. 2002, 50, 1040−1044. (34) Technical Association of the Pulp and Paper Industry. AcidInsoluble Lignin in Wood and Pulp. Test Method T222 Om-02; Tappi: GA, 2002. (35) Asoka Panamgama, L.; Peramune, P. R. U. S. K. Coconut Coir Pith Lignin: A Physicochemical and Thermal Characterization. Int. J. Biol. Macromol. 2018, 113, 1149−1157. (36) Abdelkafi, F.; Ammar, H.; Rousseau, B.; Tessier, M.; El Gharbi, R.; Fradet, A. Structural Analysis of Alfa Grass (Stipa Tenacissima L.) Lignin Obtained by Acetic Acid/Formic Acid Delignification. Biomacromolecules 2011, 12 (11), 3895−3902. (37) Li, M. F.; Sun, S. N.; Xu, F.; Sun, R. C. Microwave-Assisted Organic Acid Extraction of Lignin from Bamboo: Structure and Antioxidant Activity Investigation. Food Chem. 2012, 134 (3), 1392− 1398. (38) Monteil-Rivera, F.; Huang, G. H.; Paquet, L.; Deschamps, S.; Beaulieu, C.; Hawari, J. Microwave-Assisted Extraction of Lignin from Triticale Straw: Optimization and Microwave Effects. Bioresour. Technol. 2012, 104, 775−782. (39) Xie, J.; Hse, C. Y.; Shupe, T. F.; Hu, T. Physicochemical Characterization of Lignin Recovered from Microwave-Assisted 10705


Article

Industrial & Engineering Chemistry Research Delignified Lignocellulosic Biomass for Use in Biobased Materials. J. Appl. Polym. Sci. 2015, 132 (40), 1−7. (40) Zhou, L.; Budarin, V.; Fan, J.; Sloan, R.; Macquarrie, D. Efficient Method of Lignin Isolation Using Microwave-Assisted Acidolysis and Characterization of the Residual Lignin. ACS Sustainable Chem. Eng. 2017, 5, 3768−3774. (41) Zheng, A.; Zhao, K.; Sun, J.; Jiang, L.; Zhao, Z.; Huang, Z.; Wei, G.; He, F.; Li, H. Effect of Microwave-Assisted Organosolv Fractionation on the Chemical Structure and Decoupling Pyrolysis Behaviors of Waste Biomass. J. Anal. Appl. Pyrolysis 2018, 131, 120− 127. (42) Hernández, Y. R.; García Serrano, L. A.; Maruri, D. T.; Jiménez Aparicio, A. R.; Camacho Díaz, B. H.; Arenas Ocampo, M. L. Optimization of the Microwave-Assisted Ethanosolv Extraction of Lignocellulosic Compounds from the Bagasse of Agave Angustifolia Haw Using the Response Methodology. J. Agric. Food Chem. 2018, 66 (13), 3533−3540. (43) Faix, O. Classification of Lignins from Different Botanical Origins by FT-IR Spectroscopy. Holzforschung 1991, 45 (s1), 21−28. (44) del Río, J. C.; Gutiérrez, A.; Rodríguez, I. M.; Ibarra, D.; Martínez, Á . T. Composition of Non-Woody Plant Lignins and Cinnamic Acids by Py-GC/MS, Py/TMAH and FT-IR. J. Anal. Appl. Pyrolysis 2007, 79, 39−46. (45) Rencoret, J.; Ralph, J.; Marques, G.; Gutiérrez, A.; Martínez, Á . T.; Del Río, J. C. Structural Characterization of Lignin Isolated from Coconut (Cocos Nucifera) Coir Fibers. J. Agric. Food Chem. 2013, 61, 2434−2445. (46) Reinoso, F. A. M.; Rencoret, J.; Gutiérrez, A.; Milagres, A. M. F.; Del Río, J. C.; Ferraz, A. Fate of P-Hydroxycinnamates and Structural Characteristics of Residual Hemicelluloses and Lignin during Alkaline-Sulfite Chemithermomechanical Pretreatment of Sugarcane Bagasse. Biotechnol. Biofuels 2018, 11 (1), 1−12. (47) Zhao, X.; Wen, J.; Chen, H.; Liu, D. The Fate of Lignin during Atmospheric Acetic Acid Pretreatment of Sugarcane Bagasse and the Impacts on Cellulose Enzymatic Hydrolyzability for Bioethanol Production. Renewable Energy 2018, 128, 200−209.

10706


Microwave-Assisted Organosolv Delignification: A Potential Eco

Recommend Documents