Isolation and Purification of Monofunctional Methoxyphenols from

Research Article pubs.acs.org/journal/ascecg

Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Isolation and Purification of Monofunctional Methoxyphenols from Loblolly Pine Biocrude Ofei. D. Mante,* Samuel J. Thompson, Mustapha Soukri, and David C. Dayton

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RTI International, Research Triangle Park, North Carolina 27709, United States ABSTRACT: Methoxyphenols (MPs) are valuable chemicals in liquid intermediates from pyrolysis of lignocellulosic biomass. The use of a single technique to recover a highpurity bioproduct of MPs from pyrolysis liquid is challenging. The purpose of this study is to combine distillation and chromatography techniques in sequence to recover exclusively eugenols and guaiacols as monofunctional MPs in biocrude produced from the pyrolysis of loblolly pine with a nonzeolite alumina catalyst. A biocrude containing 11.0 wt % of the targeted monofunctional MPs was first distilled in two stages to recover an MP-rich fraction with 49.3 wt % concentration of MPs at a recovery efficiency of 86.9%. A chromatography separation using silica gel adsorbent was then used to purify the MP-enriched distillate. A final MP bioproduct with average purity of 87.3−93.1 wt % was achieved. The average efficiency of the chromatography separation step varied between 73.9 and 82.5% depending on the silica particle size used. KEYWORDS: Biomass, Pyrolysis, Biocrude, Methoxyphenol, Separation, Distillation, Chromatography, Bioproduct

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the chemical synthesis of various flavorings, such as vanillin, used in the food, personal care products, detergents, household cleaners, and perfumery products industries. Furthermore, the recovery of MPs from biocrude provides a more straightforward approach compared with synthetic routes using petroleum precursors. For instance, the industrial route to guaiacol from petroleum precursors involves four distinct major steps: (1) benzene is converted to cumene; (2) cumene is oxidized to hydroperoxide; (3) hydroperoxide is decomposed with sulfuric acid to make phenol, which is then hydroxylated with peroxide to catechol; and finally (4) monomethylation of catechol produces guaiacol. The requirement for all of these downstream steps exemplifies why oxygenated compounds, when made from petroleum hydrocarbons, are more expensive and require tedious chemistries. Thus MPs, like other valuable oxygenates, have a niche market and price point that could improve the economics and efficiency of thermochemical biorefineries. Nonetheless, separation of oxygenated chemicals from biocrude is challenging because of the complex composition and reactivity of biocrude. This makes bioprocessing separation steps critical to the economical production of biofuels and bioproducts. In general, the choice of a particular separation technique depends on the chemistry, thermochemical characteristics, and thermodynamic properties of the

INTRODUCTION Liquid intermediates from biomass pyrolysis are inherently rich in functionalized (e.g., COOH, CO, OH, OCH3, COC) oxygenated hydrocarbons, making them a potential source of oxygen containing chemical building blocks. The concentration and type of oxygenated compounds can be controlled by a catalyst and the pyrolysis conditions. The market pull of bioproducts presents an opportunity to develop strategies for the coproduction of high-value biobased chemicals/products alongside biofuels. Therefore, an integrated process could be developed to recover valuable oxygenates from the liquid intermediate before the remaining fraction is used to make advanced biofuel. Such a biorefinery concept presents an opportunity to exploit the oxygen functionality of the compounds in the pyrolysis liquid intermediates for additional revenue generation, as practiced in the petroleum refining industry. The concept departs from the objective to extensively defunctionalize catalytic pyrolysis vapors to produce a hydrocarbon-rich, low-oxygen-content biocrude. Monofunctional methoxyphenols (MPs), like eugenols and guaiacols, are examples of valuable oxygenates present in biocrude from biomass pyrolysis that could be separated out before upgrading to advanced biofuels. The concentration of MPs in biocrude depends on the pyrolysis conditions and feedstock. In catalytic pyrolysis of loblolly pine, up to 10 wt % of eugenols and up to 6.5 wt % of guaiacols have been reported.1,2 The MPs have applications in the flavor and fragrance (F&F), pharmaceutical, essential oil, and polymer industries, as illustrated in Figure 1. For example, in the F&F industry, eugenols and guaiacols are used as intermediates for © XXXX American Chemical Society

Received: September 26, 2018 Revised: November 17, 2018 Published: December 18, 2018 A

DOI: 10.1021/acssuschemeng.8b04948 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering

catechols, and syringol from wood tar. It is worth noting that the work by Amen-Chen et al.12 using LLE after distillation did not achieve exclusive separation of the different classes of phenolics in the wood tar. Adsorption is one of the key techniques used to achieve higher purity products in the low-volume, high-margin chemical markets. Studies show that adsorption is effective for recovering phenolics.19−25 Specifically, adsorption has been used to recover oxygenated aromatic compounds and other phenolic derivatives from lignocellulosic depolymerization liquids.22,26−35 For instance, Chen et al.26 used a modified commercial adsorption resin, Amberlite XAD-4, to separate phenolic compounds from the aqueous phase products of rice straw hydrothermal liquefaction. da Costa Lopes et al.27 employed an adsorptive technique using Amberlite XAD-7 and silica C-18 resins to separate high-value phenolics from a biomass fractionation process assisted by ionic liquids. Forss et al.29 developed a method using a strong cation-exchange resin in sodium form to isolate low-molecular-weight aromatic compounds such as guaiacol, vanillin, acetovanillone, and phydroxybenzaldehyde. Nevertheless, adsorption methods generally have low throughput and require large volumes of solvent; the adsorbents require regeneration, and multiple-equilibrium stages can be difficult to attain in counter-current operation. Therefore, using adsorption for separation requires careful consideration and is not likely to be economical to use as a first step in isolating a compound from a starting feedstock or for crude extracts. Hence, in the pharmaceutical, fine chemical, and natural product industries, column chromatography is exclusively used as a purification step. Consequently, in this work, chromatography was evaluated as a purification step after utilizing distillation to isolate a fraction enriched with the targeted MPs. This approach is consistent with the heuristic of performing the most difficult and expensive separation last. This study provides a first account of recovering a bioproduct from biocrude that consists exclusively of eugenols and guaiacols and is free of other monomeric phenolics.

Figure 1. Potential markets or industries for methoxyphenols utilization.

chemical product of interest.3 The choice of separation technique also depends on the target product purity. Several separation methods have been explored with varying degrees of success, to isolate phenolics from pyrolysis liquids.2,4−18 A review by Kim4 details key techniques including liquid−liquid extraction (LLE), distillation, and adsorption for separation of phenolics. A major problem with each of these separation methods is that they typically isolate phenolics in one bulk fraction, particularly with the use of solvent extraction and distillation techniques. For instance, the common boiling points of most of the chemical components present in pyrolysis liquids limit the exclusive separation of a target compound by distillation. As such, the recovered product contains many kinds of compounds and a broad range of phenolics, including simple phenols (e.g., phenol, cresol, xylenol, and higher alkylphenols) as well as phenolics with different functionalities like hydroxyl (e.g., catechols), methoxy (e.g., guaiacols and eugenols), dimethoxy (sygringol), carbonyl (e.g., acetovanillone, coniferyl aldehyde, guaiacylacetone, and vanillin), and carboxyl (e.g., homovanillic acid). Therefore, to recover a purer stream of a class of phenolics from pyrolysis liquids, several separation steps (isolation, concentration, and purification) need to be employed. For each step, a technique can be selected based on the physicochemical characteristics of the intermediate product. Ultimately, the integration of the multiple processes would have to be effective and result in higher separation efficiency and product purity. The works by Murwanashyaka et al.11 and Amen-Chen et al.12 are among the few studies that employed more than one technique to specifically recover phenolics from pyrolysis oils. Murwanashyaka et al.11 utilized steam distillation to concentrate phenolic compounds from birch-wood-derived vacuum pyrolysis oil, which was further purified by solvent extraction to recover a syringol-rich product. First, a fraction with 21.3 wt % phenolic was obtained; in the second step, the phenolic fraction was distilled into 16 different subfractions. Finally, one of the fractions boiling narrowly between 95 and 100 °C with high syringol concentration was then purified by solvent extraction to obtain a product with 92.3% purity. Amen-Chen et al.12 also used distillation in combination with a five-stage cross-current LLE to recover a phenolic fraction of simple phenols, guaiacols,

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EXPERIMENTAL SECTION

Materials: Biocrude. The biocrude used in the study was produced from loblolly pine feedstock (particle size was 2 mm top size; the average moisture content was 15 wt %) in RTI’s 1-tonne per day (1-TPD) catalytic biomass pyrolysis unit. A commercially available spray-dried, nonzeolite, alumina-based catalyst with a BET surface area of 114.6 m2/g and a mean particle size of ∼70 μm was used. The average catalytic pyrolysis temperature was 477 °C, and the established vapor residence time in the mixing zone was ∼0.5 s. The biomass feed rate was ∼35 kg/h, and the catalytic pyrolysis was performed continuously for 15 h. The biocrude produced was collected in a 5-gallon container and stored at room temperature. Details of the operation of the catalytic pyrolysis in the 1-TPD unit can be found in previously published work.1,36 Table 1 shows the Karl Fischer moisture and carbon, hydrogen, nitrogen, and oxygen (CHNO) contents of the biocrude based on the methods described in the Analytical section. Methods. Distillation. Distillation experiments were performed in a fully automated bench-scale PILODIST laboratory distillation unit

Table 1. Moisture and CHNO Analysis of Biocrude Samples elemental composition (wt %), dry basis

B

sample

moisture (wt %)

C (%)

H (%)

N (%)

O (%)

biocrude

7.25

68.85

6.79

0.16

24.21


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Figure 2. GC−MS chromatogram of loblolly pine biocrude. (PETRODIST 300 CC) with one theoretical stage column. A detailed description of the distillation unit was provided in a previous study.2 The distillation was performed in a 500 mL round-bottomed flask under vacuum (20 kPa) according to the ASTM D-1160 method.37 After each run, the weight distributions of the fractions obtained were determined gravimetrically. Column Chromatography. The purification of the MP-rich distillate fraction boiling between 205 and 280 °C was evaluated by normal-phase chromatographic separation. Silica gel with large (63− 200 μm) and small (40−63 μm) particle sizes was evaluated. The separation was conducted in a 61 cm tall glass column with a 50 mm internal diameter and a 500 mL solvent reservoir. The column was wet-loaded with ∼350 g silica in hexanes and packed under a positive pressure of air. The feed sample size was 50 g, resulting in a feed-toadsorbent ratio of 0.14 (g/g). The column was run under a gradient elution from 100% hexanes to 100% dichloromethane (DCM), with final flushing of 100% MeOH. The chromatographic solvent system employed in this study was found to have the optimal separation efficiency of various components of the MP-rich distillate fraction after screening solvent and mixed-solvent systems (e.g., hexanes, DCM, toluene, ethyl acetate in hexanes, DCM in toluene, etc.) with thin-layer chromatography (TLC) on silica gel plates (silica gel 60, F254, EMD Chemical). The chromatographic separation was run under a positive pressure of air to increase the rate of elution from the silica gel. The progress of the separation was monitored by TLC. The first desorption was done in 100% hexanes (∼1.0 L) to elute the first fraction (A). The second fraction (B) was eluted by increasing the adsorbent polarity using 25% DCM in hexanes (∼3.0 L). This was followed by 100% DCM (2.0 L) to elute a third fraction (C) completely off the column. The remaining components were flushed of the silica gel with methanol (∼2 L). The silica gel was dried with air and heated to regenerate the media. A bioproduct with a high concentration of eugenols and guaiacols was obtained after solvent recovery from fraction B. The solvent and silica can be recycled postseparation. The mass balance of the material subjected to silica gel chromatography and compounds removed via separation is >97%. Analytical. The biocrude was analyzed for CHNO, moisture, and density. Moisture content was measured with a Karl Fischer titrator (V20, Mettler Toledo) according to the ASTM E20338 standard test method for water using Hydranal-composite 5 K reagent. The organic elemental composition (CHONS) was determined with an elemental analyzer (FLASH2000, Thermo Scientific). The oxygen content was determined by the difference. The density was measured with an Anton Paar DMA 35 portable density meter at 23 °C according to ASTM D4052.39 The concentration of MPs was determined by gas chromatography−mass spectrometry (GC−MS). Calibration curves developed with pure forms of eugenol, isoeugenol (Z and E), guaiacol, 4-methylguaiacol, 4-ethylguaiacol, and 4-propylguaiacol were used to quantify MPs in biocrude and the product stream from each separation step. The GC−MS analysis was performed with an Agilent 6890 GC and 5975C MS). An HP-5MS column (30 m × 0.25 mm, 0.25 μm film thickness with 5% phenyl-methyl-polysiloxane as the

stationary phase) was used. The mass concentrations of the targeted MPs (eugenol, isoeugenol (Z and E), guaiacol, 4-methylguaiacol, 4ethylguaiacol, and 4-propylguaiacol) in the starting biocrude, separation feed, and recovered products were used to determine a separation step efficiency, overall separation efficiency, and product purity as defined below. separation step efficiency (wt %) mass of MPs in separation step product = mass of MPs in the separation step feed overall separation efficiency (wt %) mass of MPs in the final recovered product = mass of MPs in the starting biocrude

purity (wt %) =

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mass of MPs in the sample mass of sample

RESULTS AND DISCUSSION Biocrude Sample. The oxygen content of the biocrude was 24.2 wt % on dry basis. The initial concentration of the targeted MPs in the loblolly-pine-derived biocrude was quantified to be 11.0 wt % prior to distillation. Figure 2 shows the GC−MS chromatogram of the biocrude. The distribution of isoeugenol (Z and E), eugenol, 4-propylguaiacol, 4-ethylguaiacol, 4-methylguaiacol, and guaiacol was 4.22, 1.50, 0.9, 1.34, 2.24, and 0.82 wt %, respectively. In general, the biocrude was dominated by oxygenated aromatic compounds. Other phenolics identified but not quantified by GC−MS include simple phenols, benzenediols, 4-hydroxy-3-methoxybenzeneacetic acid, 1,2-dimethoxy-4-n-propylbenzene, 1-(4hydroxy-3-methoxyphenyl)-ethanone, 4-(2-hydroxyethyl)-2methoxyphenol, and 4-hydroxy-3-ethoxybenzaldehyde. The GC peak area of di- and triaromatic hydrocarbons such as 1methyl-7-isopropyl phenanthrene in the biocrude is ∼25% of the total ion chromatogram (TIC). Other major chemical species identified in the biocrude include acetic acid, hydroxyacetone, 5-methyl-furancarboxaldehyde, 2-hydroxy-3methyl-2-cyclopenten-1-one, 1,2-cyclopentanedione, and 2,5dihydro-3,5-dimethyl-2-furanone. Distillation. A multistage distillation was initially performed to simulate an actual distillation column with four trays. The objective was to validate the limitation of distillation in recovering a much purer bioproduct of MPs. The biocrude was first fractionated into a light fraction (IBP-180 °C), an MP-rich fraction (180−300 °C), and a heavy fraction (300−

C


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Figure 3. Illustration of distillation of biocrude to concentrate methoxyphenols in four stages.

Table 2. Distillation Yields parameters

1st stage

2nd stage

3rd stage

4th stage

total feed charge (g) light fraction (wt %) MP-rich fraction (wt %) heavy fraction (wt %) residue/bottoms* (wt %) system loss (wt %, by difference) concentration of eugenols (wt %) concentration of guaiacols (wt %) MP separation efficiency (%)

975.5 11.50 28.30 27.10 22.0 11.1 18.0 16.3 83.4

275.1 6.60 65.79 19.82 5.84* 1.95 21.4 24.0 87.0

180.9 3.15 85.05

153.9 7.22 81.33

10.99* 0.81 16.5 31.0 89.0

7.33* 4.11 22.4 28.4 87.0

Figure 4. GC−MS chromatogram of a methoxyphenol-rich fraction after two stages of distillation.

400 °C). The MP-rich fraction from the first-stage distillation was further distilled in the remaining stages, and the boiling range for the subsequent MP-rich fraction was gradually narrowed through the second-stage to the fourth-stage distillations; thus the final MP-rich cut was collected between 220 and 280 °C. A total of 10 individual distillation experiments were conducted; 6 runs for the first stage, 2 runs for the second stage, and one each for the third stage and fourth stage. After each run, the weight distributions of the cut fractions, the residue formed, and products collected in the cold trap were determined gravimetrically. Figure 3 illustrates the multistage distillation that was performed and shows the amount of MPs in the biocrude and the MP-rich fraction from each distillation stage. The analysis of the MP-rich fraction from the first-stage distillations showed that it contained a total of 34.3 wt % of targeted MPs. The concentration of MPs in the MP-rich fractions collected from the second, third, and fourth stages was 45.4, 47.5, and 50.8 wt

%, respectively. A summary of the yields for each distillation stage is shown in Table 2. The yield of the MP-rich fractions was 28.3, 65.8, 85.1, and 81.3 wt % for the first stage, second stage, third stage, and fourth stage, respectively. The data show that the recovery of the MPs was about 83.4% in the first stage, 87% in the second stage, 89% in the third stage, and 87% in the fourth stage. The overall separation efficiency was low (56%) due to the use of many stages. It is worth pointing out that the use of a narrower boiling point range (220 to 280 °C) in the fourth stage consequently affected the recovery of one of the MPs (guaiacol) that has a boiling point (205 °C) that is outside of the range used. Thus the separation efficiency for the fourth stage was lower based on the total MPs recovered. Importantly, the results show that the subsequent distillation of the first MP-rich fraction did not increase the concentration of MPs. The third and fourth stages, for example, were not useful even though the boiling range was narrowed. The high liquid recovery into the MP-rich fraction D


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ACS Sustainable Chemistry & Engineering for the third and fourth stages indicates a lack of efficient concentration of the MPs. On the basis of the GC−MS data, the MP-rich fractions also had several other compounds that boil within the range of 200−285 °C; these compounds include phenol, alkylphenols (e.g., cresol, xylenols), catechols, and 2-cyclopentenones such as 2-hydroxy-3-methyl-2-cyclopenten-1-one, among others. In terms of peak area %, the simple phenols represented ∼13%, and the cyclopentenones were 10% of the area under the total ion chromatogram. The presence of these compounds with a boiling point similar to the MPs partly explains why the multistage distillation did not increase the final MP concentration. Overall, the results demonstrate the limitation of distillation in the recovery of the targeted MPs from the loblolly pine biocrude; the final distillate product was of 51 wt % purity. A different technique, such as chromatography, could then be used to separate the compounds with a similar boiling range of the targeted MPs. Integration of Distillation and Chromatographic Separation. The biocrude was first distilled in two stages to recover an MP-rich fraction for chromatographic separation. In the first stage, the biocrude was distilled to obtain an MP-rich fraction with a boiling range of 175−310 °C. In the second stage, the MP-rich fraction was distilled into a narrower boiling range of 205−280 °C. The two-stage process resulted in an overall recovery efficiency of 86.9% for the targeted MPs. Figure 4 shows the GC−MS chromatogram of the final MPrich fraction. The concentration of the targeted MPs in the final fraction was 49.3 wt %. The distribution of isoeugenol (Z and E), eugenol, 4-propylguaiacol, 4-ethylguaiacol, 4-methylguaiacol, and guaiacol in the enriched fraction was 17.3, 4.30, 7.7, 6.2, 10.1, and 3.8 wt %, respectively. The concentrated MP fraction was then purified by flash chromatographic separation using silica gel adsorbent of large (63−200 μm) and small (40−63 μm) particle sizes at feed-toadsorbent ratio of 0.14 (g/g). During the course of the method development, it was found that increasing the feed to an adsorbent ratio beyond 0.14 (g/g) notably decreased the achievable separation efficiency for the recovery of the monofunctional MPs. Alternatively, decreasing the feed-toadsorbent ratio below 0.14 (g/g) failed to provide meaningful improvement to the separation efficiency and fraction purities and therefore inherently would only increase the process cost. Four different fractions were separated: fraction-A was eluted from the column with hexanes, fraction-B was eluted with 25% DCM in hexanes, fraction-C was eluted with DCM, and fraction-D was eluted with methanol (fraction-D was highly polar and remained on the baseline of the TLC). The MP fraction was primarily concentrated in the fraction-B that was collected when the MP spot on the TLC was clean of other fractions components (i.e., peaks from these compounds were very minimal). The retention factor (Rf) for the fractions A, B, C, and D was estimated to be 0.81, 0.3, 0.05, and 0.0, respectively, in 50% DCM in hexanes. Table 3 shows the average yields of the different fractions collected from the sets of experiments for both silica particle sizes. The yields for fraction-A, fraction-C, and fraction-D seem to vary with the use of different particle-size distribution of the silica. However, fraction-B, which contained most of the MPs, had comparative yields from both silica adsorbents. An average yield of 41.7 and 43.7 wt % of the bioproduct (fraction B) was obtained from the column with the large-particle-size and small-particle-size silica, respectively. Additionally, an average product purity of 87.3 wt % at an average separation efficiency

Table 3. Chromatographic Separation Yields yield (wt %) products

large-size silica

small-size silica

column fraction A 8.8 ± 0.8 16.7 ± 1.5 column fraction B 41.7 ± 1.4 43.7 ± 1.1 column fraction C 34.7 ± 1.0 19.4 ± 1.4 column fraction D 14.2 ± 0.9 18.9 ± 1.0 Concentration of the Various MPs in Fraction-B (wt %) guaiacol 5.9 ± 1.9 5.5 ± 1.5 4-methylguaiacol 16.8 ± 0.3 18.4 ± 0.5 4-ethylguaiacol 9.7 ± 0.8 12.2 ± 1.1 eugenol 13.1 ± 0.6 14.1 ± 0.4 4-propylguaiacol 6.8 ± 0.6 8.8 ± 1.2 isoeugenol (cis and trans) 32.4 ± 0.4 34.0 ± 1.3 Separation Key Performance Parameters purity (wt %) 87.3 ± 2.5 93.1 ± 1.0 separation efficiency (%) 73.9 ± 3.5 82.5 ± 2.8

of 73.9% was achieved with the large-particle silica. On the contrary, the small-particle-size silica enabled a bioproduct with an average purity of 93.1 wt % to be recovered at a separation efficiency of 82.5%. In general, the larger-sized particles of silica (63−200 μm) allow for increased column flow-through and reduced backpressure than the smaller, more narrow-ranged particle sized silica (40−63 μm). Also, on the basis of the TLC, the overlap of fraction-B with fraction-A and fraction-C was more prominent with the larger-sized silica than with the use of the smaller-sized silica. The overlap is due to the high degree of structural and chemical polarity likeness between the target MPs with simple phenols and other kinds of aromatic oxygenates. It can be inferred from the results that the silica of smaller particle size provided better column retention and consequently resulted in relatively higher resolution between compounds of the MP-enriched distillate. Overall, this explains why the silica with small particle size performed better in terms of separation key parameters (product purity and separation efficiency). The GC−MS chromatograms for column fractions A−D are shown in Figure 5. The analysis shows that fraction-A that was eluted by hexanes mainly consisted of aromatic compounds such as 1-methyl-4-(1-methylethyl)-benzene, 1-methyl-7(propan-2-yl) phenanthrene, and hydroxybenzophenones like 3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]phenyl-methanone. The fraction also contained a small number of unknown compounds that may be dimeric compounds. It is of note that some amount of the targeted MPs was also eluted by hexanes, as shown by the GC−MS chromatogram in Figure 5. In terms of the peak area percentage, the aromatic hydrocarbons, hydroxybenzophenones, and the MPs accounted for 30, 19.0, and 22.9% of the TIC, respectively. A solvent gradient elution process was employed by increasing the polarity of the eluent stepwise from 100% hexanes (fraction-A) to 25% DCM in hexanes (fraction-B, targeted MPs), 100% DCM (fraction-C), and finally 100% methanol (fraction-D). The gradient elution process reduced the fraction retention time and improved the quality of separation. Using a single solvent system for the MP fraction elution reduced the separation efficiency via band broadening of the targeted MP fraction-B into fraction-C (e.g., 100% hexanes as solvent) or reduced the MP fraction-B retention time, promoting coelution into fraction-A (e.g., >30% DCM in E


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Figure 5. GC−MS chromatograms for column fractions A−D.

collected together because their Rf values were about the same (almost zero). However, in terms of polarity, fraction-D is relatively more polar and required methanol to establish desorption. According to the GC−MS analysis, the composition of both fractions was relatively more complex and contained many different oxygenated compounds. In general, the oxygenates other than MPs had functionalities that could be classified as simple phenols, multifunctional phenolics, cyclopentenones, furanones/furfural, pyranones, acids, and anhydrosugars. The simple phenols identified were phenol and

hexane solvent systems or more polar cosolvents with hexanes). As shown by the GC−MS chromatogram in Figure 5, fraction-B primarily contained MPs (∼90 wt %). In the case of the small-particle-size silica, the concentration of isoeugenol (Z and E), eugenol, 4-propylguaiacol, 4-ethylguaiacol, 4methylguaiacol, and guaiacol in fraction-B was 33.9, 7.5, 13.8, 10.9, 18.7, and 7.23 wt %, respectively. The contaminants in fraction-B were to a large extent hydrocarbon (aromatics and aliphatics). The remaining components that desorbed from the column as fractions C and D could have been F


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using the two integrated techniques was between 64.2 and 71.7%. The average purity of the final bioproduct ranged between 87.3 and 93.1 wt %. One of the challenges to overcome is solvent consumption. Further experimental investigations on the impact of the feed concentration of MPs on the key performance parameters of the chromatographic separation would be helpful for process scale-up.

alkylphenols such as 4-(2-propenyl)-phenol, cresol, 4-ethylphenol, and xylenols. The multifunctional phenolics were catechol and derivatives, dihydroxybenzaldehyde, apocynin, and vanillin. The cyclopentanones consisted of both alkyl-(3methyl-2-cyclopenten-1-one) and hydroxy derivatives (2hydroxy-3-methyl-2-cyclopenten-1-one). Examples of the furanones and furfural compounds found in fractions C and D included 2(5H)-furanone, methyl-2(5H)-furanone, and 5methyl-2-furancarboxaldehyde. The acidic compounds were acetic acid, butenoic acid, propanoic acid, and 4-hydroxy-3methoxy-benzeneacetic acid. Anhydrosugars identified include levoglucosan, 2,3-anhydro-D-mannosan, and 2,3-anhydro-Dgalactosan. Fraction-C had simple phenols, MPs, multifunctional phenolics, cyclopentenones, and furanones/furfural that accounted for 19.8, 37.1, 17.9, 6.9, and 10.5% of the TIC area, respectively. Likewise, fraction-D contained MPs, multifunctional phenolics, cyclopentanones, furanones/furfural, pyranones, acids, and anhydrosugars, representing 6.1, 29.0, 28.0, 8.6, 5.3, 11.0, and 3.2% of the TIC area, respectively. The results show that most of the simple phenols, vanillin, apocynin, and furanones were concentrated in fraction-C, whereas more polar oxygenates like catechols, 2-hydroxy-3methyl-2-cyclopenten-1-one, carboxylic acids, and anhydrosugars were concentrated in fraction-D. It is worth pointing out that fraction-C contained a reasonable amount of unrecovered MPs. Overall, the chromatographic technique reported herein enabled exclusive separation of the monofunctional MPs from the other oxygenates (simple phenols, multifunctional phenolics, cyclopentenones, furanones/furfural, pyranones, acids, and anhydrosugars) in the MP-enriched distillate fraction. As shown by other chromatographic separation of bio-oil studies,32−35 the use of single-component eluting solvents with low polarity (e.g., hexanes, cyclohexanes, benzene, ether, and dichloromethane) limits the efficiency in desorbing distinct classes of phenolics into high-purity fractions In contrast, the establishment of Rf of 0.81, 0.3, and 0.05 by the gradient elution process in this study indicates that a much purer monofunctional MP fraction can be efficiently achieved. As shown, the gradient elution approach begins the desorption with hexanes, which only elute MPs that do not fully adsorb to the silica gel. Increasing the solvent polarity with 25% DCM in hexanes promotes near-complete desorption of the MP. This approach enhances the separation efficiency while achieving a high-purity product. The drawback of the gradient elution process is the large volume of solvents used, a total of ∼8 L of organic solvents. This could limit the scale-up and the economic feasibility of the chromatography step. A practical solution would be to use a feed with a higher concentration of the MPs. Thus the fraction from the distillation step may have to be subjected to an enrichment step prior to the chromatographic step. For example, an alkaline extraction step may be used to concentrate the MPrich distillate fraction. The benefits would be higher efficiency, purer product, reduced process time, and solvent consumption.

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AUTHOR INFORMATION

Corresponding Author

*Tel: 919-541-6202. Fax: 919-541-8002. E-mail: omante@rti. org. ORCID

Ofei. D. Mante: 0000-0002-0960-2943 Samuel J. Thompson: 0000-0002-8750-5428 Mustapha Soukri: 0000-0002-8512-8067 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

This work was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office under contract DE-EE-0007730 (Building Blocks from Biocrude: High Value Methoxyphenols).

(1) Dayton, D. C.; Carpenter, J. R.; Kataria, A.; Peters, J. E.; Barbee, D.; Mante, O. D.; Gupta, R. Design and operation of a pilot-scale catalytic biomass pyrolysis unit. Green Chem. 2015, 17 (9), 4680− 4689. (2) Mante, O. D.; Dayton, D. C.; Soukri, M. Production and distillative recovery of valuable lignin-derived products from biocrude. RSC Adv. 2016, 6 (96), 94247−94255. (3) Singh, B.; Kumari, A.; Datta, S. Chapter 6: Separations Technologies for Biobased Product Formation-Opportunities and Challenges. In Commercializing Biobased Products: Opportunities, Challenges, Benefits, and Risks; The Royal Society of Chemistry: 2016; pp 92−131. DOI: 10.1039/9781782622444-00092. (4) Kim, J.-S. Production, separation and applications of phenolicrich bio-oil − A review. Bioresour. Technol. 2015, 178, 90−98. (5) Fu, D.; Farag, S.; Chaouki, J.; Jessop, P. G. Extraction of phenols from lignin microwave-pyrolysis oil using a switchable hydrophilicity solvent. Bioresour. Technol. 2014, 154, 101−108. (6) Zhang, X.-S.; Yang, G.-X.; Jiang, H.; Liu, W.-J.; Ding, H.-S. Mass production of chemicals from biomass-derived oil by directly atmospheric distillation coupled with co-pyrolysis. Sci. Rep. 2013, 3, 1120. (7) Fele Ž ilnik, L.; Jazbinšek, A. Recovery of renewable phenolic fraction from pyrolysis oil. Sep. Purif. Technol. 2012, 86, 157−170. (8) Patel, R. N.; Bandyopadhyay, S.; Ganesh, A. Extraction of cardanol and phenol from bio-oils obtained through vacuum pyrolysis of biomass using supercritical fluid extraction. Energy 2011, 36 (3), 1535−1542. (9) Naik, S.; Goud, V. V.; Rout, P. K.; Dalai, A. K. Supercritical CO2 fractionation of bio-oil produced from wheat−hemlock biomass. Bioresour. Technol. 2010, 101 (19), 7605−7613. (10) Li, J.; Wang, C.; Yang, Z. Production and separation of phenols from biomass-derived bio-petroleum. J. Anal. Appl. Pyrolysis 2010, 89 (2), 218−224. (11) Murwanashyaka, J. N.; Pakdel, H.; Roy, C. Seperation of syringol from birch wood-derived vacuum pyrolysis oil. Sep. Purif. Technol. 2001, 24 (1−2), 155−165. (12) Amen-Chen, C.; Pakdel, H.; Roy, C. Separation of phenols from Eucalyptus wood tar. Biomass Bioenergy 1997, 13 (1−2), 25−37.

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CONCLUSIONS A bioproduct consisting primarily of eugenols and guaiacols was recovered from a biocrude made from catalytic pyrolysis of loblolly pine. The separation process entails distillative isolation of a crude mixture of the MPs from the biocrude, followed by purification with silica gel chromatography. The overall efficiency in recovering the MPs from the biocrude G


Research Article

ACS Sustainable Chemistry & Engineering (13) Mantilla, S. V.; Manrique, A. M.; Gauthier-Maradei, P. Methodology for Extraction of Phenolic Compounds of Bio-oil from Agricultural Biomass Wastes. Waste Biomass Valorization 2015, 6 (3), 371−383. (14) Oasmaa, A.; Kuoppala, E. Fast Pyrolysis of Forestry Residue. 3. Storage Stability of Liquid Fuel. Energy Fuels 2003, 17 (4), 1075− 1084. (15) Oasmaa, A.; Kuoppala, E.; Gust, S.; Solantausta, Y. Fast Pyrolysis of Forestry Residue. 1. Effect of Extractives on Phase Separation of Pyrolysis Liquids. Energy Fuels 2003, 17 (1), 1−12. (16) Oasmaa, A.; Kuoppala, E.; Solantausta, Y. Fast Pyrolysis of Forestry Residue. 2. Physicochemical Composition of Product Liquid. Energy Fuels 2003, 17 (2), 433−443. (17) Sipilä, K.; Kuoppala, E.; Fagernäs, L.; Oasmaa, A. Characterization of biomass-based flash pyrolysis oils. Biomass Bioenergy 1998, 14 (2), 103−113. (18) Wang, S.; Wang, Y.; Cai, Q.; Wang, X.; Jin, H.; Luo, Z. Multistep separation of monophenols and pyrolytic lignins from the waterinsoluble phase of bio-oil. Sep. Purif. Technol. 2014, 122, 248−255. (19) Ahmaruzzaman, M. Adsorption of phenolic compounds on lowcost adsorbents: A review. Adv. Colloid Interface Sci. 2008, 143 (1−2), 48−67. (20) Busca, G.; Berardinelli, S.; Resini, C.; Arrighi, L. Technologies for the removal of phenol from fluid streams: A short review of recent developments. J. Hazard. Mater. 2008, 160 (2−3), 265−288. (21) Caetano, M.; Valderrama, C.; Farran, A.; Cortina, J. L. Phenol removal from aqueous solution by adsorption and ion exchange mechanisms onto polymeric resins. J. Colloid Interface Sci. 2009, 338 (2), 402−409. (22) D’Alvise, N.; Lesueur-Lambert, C.; Fertin, B.; Dhulster, P.; Guillochon, D. Removal of Polyphenols and Recovery of Proteins from Alfalfa White Protein Concentrate by Ultrafiltration and Adsorbent Resin Separations. Sep. Sci. Technol. 2000, 35 (15), 2453−2472. (23) Kujawski, W.; Warszawski, A.; Ratajczak, W.; Porȩbski, T.; Capała, W.; Ostrowska, I. Removal of phenol from wastewater by different separation techniques. Desalination 2004, 163 (1), 287−296. (24) Lin, S.-H.; Juang, R.-S. Adsorption of phenol and its derivatives from water using synthetic resins and low-cost natural adsorbents: A review. J. Environ. Manage. 2009, 90 (3), 1336−1349. (25) Roostaei, N.; Tezel, F. H. Removal of phenol from aqueous solutions by adsorption. J. Environ. Manage. 2004, 70 (2), 157−164. (26) Chen, K.; Lyu, H.; Hao, S.; Luo, G.; Zhang, S.; Chen, J. Separation of phenolic compounds with modified adsorption resin from aqueous phase products of hydrothermal liquefaction of rice straw. Bioresour. Technol. 2015, 182, 160−168. (27) da Costa Lopes, A. M.; Brenner, M.; Falé, P.; Roseiro, L. B.; Bogel-Łukasik, R. Extraction and Purification of Phenolic Compounds from Lignocellulosic Biomass Assisted by Ionic Liquid, Polymeric Resins, and Supercritical CO2. ACS Sustainable Chem. Eng. 2016, 4 (6), 3357−3367. (28) Embree, H. D.; Chen, T.; Payne, G. F. Oxygenated aromatic compounds from renewable resources: motivation, opportunities, and adsorptive separations. Chem. Eng. J. 2001, 84 (2), 133−147. (29) Forss, K. G.; Talka, E. T.; Fremer, K. E. Isolation of vanillin from alkaline oxidized spent sulfite liquor. Ind. Eng. Chem. Prod. Res. Dev. 1986, 25 (1), 103−108. (30) Mardis, K. L.; Glemza, A. J.; Brune, B. J.; Payne, G. F.; Gilson, M. K. Differential Adsorption of Phenol Derivatives onto a Polymeric Sorbent: A Combined Molecular Modeling and Experimental Study. J. Phys. Chem. B 1999, 103 (45), 9879−9887. (31) Schmitt, D.; Regenbrecht, C.; Hartmer, M.; Stecker, F.; Waldvogel, S. R. Highly selective generation of vanillin by anodic degradation of lignin: a combined approach of electrochemistry and product isolation by adsorption. Beilstein J. Org. Chem. 2015, 11, 473− 480. (32) Ba, T.; Chaala, A.; Garcia-Perez, M.; Roy, C. Colloidal Properties of Bio-Oils Obtained by Vacuum Pyrolysis of Softwood Bark. Storage Stability. Energy Fuels 2004, 18 (1), 188−201.

(33) Das, P.; Sreelatha, T.; Ganesh, A. Bio oil from pyrolysis of cashew nut shell-characterisation and related properties. Biomass Bioenergy 2004, 27 (3), 265−275. (34) Rutkowski, P. Influence of zinc chloride addition on the chemical structure of bio-oil obtained during co-pyrolysis of wood/ synthetic polymer blends. Waste Manage. 2009, 29 (12), 2983−2993. (35) Wang, Z.; Lin, W.; Song, W.; Du, L.; Li, Z.; Yao, J. Component fractionation of wood-tar by column chromatography with the packing material of silica gel. Chin. Sci. Bull. 2011, 56 (14), 1434. (36) Mante, O. D.; Dayton, D. C.; Carpenter, J. R.; Wang, K.; Peters, J. E. Pilot-scale catalytic fast pyrolysis of loblolly pine over γAl2O3 catalyst. Fuel 2018, 214, 569−579. (37) ASTM D1160-18, Standard Test Method for Distillation of Petroleum Products at Reduced Pressure; ASTM International: West Conshohocken, PA, 2018. www.astm.org. DOI: 10.1520/D1160-18. (38) ASTM E203-16, Standard Test Method for Water Using Volumetric Karl Fischer Titration; ASTM International: West Conshohocken, PA, 2016. www.astm.org. DOI: 10.1520/E0203-16. (39) ASTM D4052-18, Standard Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density Meter; ASTM International: West Conshohocken, PA, 2018. www.astm.org. DOI: 10.1520/D4052-18.

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