A process for producing lignin and volatile compounds from hydrolysis liquor
© The Author(s) 2017
Received: 7 September 2016
Accepted: 9 February 2017
Published: 23 February 2017
Hot water hydrolysis process is commercially applied for treating wood chips prior to pulping or wood pellet production, while it produces hydrolysis liquor as a by-product. Since the hydrolysis liquor is dilute, the production of value-added materials from it would be challenging.
In this study, acidification was proposed as a viable method to extract (1) furfural and acetic acid from hot water hydrolysis liquor and (2) lignin compounds from the liquor. The thermal properties of the precipitates made from the acidification of hydrolysis liquor confirmed the volatile characteristics of precipitates. Membrane dialysis was effective in removing inorganic salts associated with lignin compounds. The purified lignin compounds had a glass transition temperature (Tg) of 180–190 °C, and were thermally stable.
The results confirmed that lignin compounds present in hot water hydrolysis liquor had different characteristics. The acidification of hydrolysis liquor primarily removed the volatile compounds from hydrolysis liquor. Based on these results, a process for producing purified lignin and precipitates of volatile compounds was proposed.
KeywordsAcidification Hydrolysis Lignin Furfural Biorefining
The current low price of pulp products has significantly hampered the overall profitability of the pulping industry. Forest biorefinery has been considered as an option to revisit this industry. In forest biorefinery, energy or biomaterials are produced in addition to pulp products . In a forest biorefining process, cellulose can be produced as dissolving pulp, while lignin and hemicelluloses are converted to other value-added products [1, 2].
Hot water hydrolysis process is commercially used for extracting hemicelluloses from wood chips. It was reported that hydrolysis liquor contains hemicelluloses and some lignin that can be used in the production of value-added products . Hot water hydrolysis process can be carried out prior to pulping process [4, 5] or in wet torrefaction process . In both processes, the hydrolyzed wood chips are transferred to the next steps for producing dissolving pulp or wood pellets, while a large volume of hydrolysis liquor that contains dissolved hemicelluloses and lignin is treated as a waste .
It is well-known that the severity of hydrolysis conditions affects the removal of lignocelluloses from wood chips, as well as the properties of extracted hemicellulose and lignin , which implies that changing the hydrolysis process conditions allows for producing hydrolysis liquor with different properties and chemistries. The first objective of this work was to study the effect of hydrolysis conditions in extracting lignocelluloses from the wood chips.
The hydrolysis liquor can be used as fermentation intermediate for the production of xylitol and ethanol due to the presence of dissolved hemicelluloses in the hydrolysis liquor . However, fermentation inhibitors, such as furfural, acetic acid, and lignin derivatives in the hydrolysis liquor would hamper the efficiency of the fermentation processes [9, 10]. Lignin can also be used as fuel or in the production of phenols, for instance . Presently, hemicellulose and lignin of the hydrolysis liquor cannot be economically utilized in the production of value-added products due to the dilute nature of the hydrolysis liquor. In the past, ultrafiltration was proposed for isolating hemicellulose and lignin from hydrolysis liquor [12, 13], which could be efficient in concentrating hydrolysis liquor. However, filter blockage and fouling should be considered as main operation challenges of this process [14–16]. Adsorption and flocculation can also be viable options for extracting hemicellulose and lignin from hydrolysis liquor, but the need for recovering adsorbents, the high price and/or sensitivity of flocculants to the chemistry of hydrolysis liquor may be major barriers in the implementation of adsorption or flocculation process at an industrial scale . Acidification has been commercialized as LignoBoost and LignoForce technologies for extracting kraft lignin from black liquor of kraft pulping process [18, 19]. Although some research results showed that acidification was efficient in extracting organics from hydrolysis liquor of kraft-based dissolving pulp production process [20–22], it is not clear what components were extracted via acidifying hydrolysis liquor and what properties the extracted components had. Since the literature results on the acidification process are not conclusive, the second objective of this work was to evaluate the effectiveness of acidification in extracting different components from a hydrolysis liquor.
In the present work, spruce wood chips were treated with hot water in a pulping digester and then the hydrolysis liquor was collected and characterized to specify the impact of acidification on the precipitation of organic compounds extracted from wood chips.
Subsequently, the thermal properties of the precipitates were investigated in order to identify the potential end-use applications for the precipitates. The main novelties of this work were as follows:(1) a detailed investigation on the efficiency of acidification in removing different organic components from hydrolysis liquor including volatile compounds and hydrolysis lignin, which would impact the properties of the precipitates and their end-use applications, and (2) the development of a process for producing hydrolysis lignin and precipitates made of volatile compounds.
Industrially produced spruce wood chips (with the moisture content of 37%) were received from a mill located in northern Ontario, Canada. This wood species is commonly used in Finland and Canada for pulp and energy production purposes. Sodium hydroxide pellets, sodium sulfate (analytical grade), sodium sulfite (analytical grade), acetic anhydride, para-hydroxybenzoic acid, 2-chloro-4,4,5,5-tetramethyl-1,2,3-dioxaphospholane, 3-(trimethylsilyl) propionic-2,2,3,3-d4 acid sodium salt (TSP), chromium(III) acetylacetonate, deuteriochloroform (CDCl3), anhydrous pyridine, hydrochloric acid (37%, reagent grade), and sulfuric acid (98 wt%) were received from Sigma Aldrich company. Cellulose acetate membrane dialysis with a molecular cut-off of 1000 g/mol was obtained from Wako Chemicals, Japan.
Hot water hydrolysis treatment
In this set of experiments, 300 g of wood chips was placed in a 2 L pulping digester, Greenwood, TX. The impact of liquid to solid (L/S) ratio in the autohydrolysis of softwood was studied in the past [23, 24]. Leppanen et al. conducted the autohydrolysis of Norway spruce with L/S ratio 15/1 . In current work, due to the small size of the pulping digester (2 L), the L/S ratio of 15/1 generated hydrolysis liquor with undetectable organic compounds (as it would result in a small quantity of wood in the digester). Therefore, a liquid to wood ratio of 8 (on a dried basis) was selected in this analysis with adding deionized water to the digester. The heating rate of the hydrolysis treatment was adjusted to 4.5 °C/min when the temperature of the digester was below 100 °C and to 2.5 °C/min when the temperature of the digester increased above 100 °C. The liquor in the digester was circulated at the flow rate of 6 L/min. Furthermore, autohydrolysis was successfully applied to spruce wood chips in the temperature range of 100–240 °C and time of 100 min [24, 25]. Song et al. reported a significant lignin isolation in the temperature range of 160–180 °C [24, 26]. In the current work, the hydrolysis treatment was conducted at 170, 180, or 190 °C for 15 or 45 min, where the pH of hydrolysis liquor after the hydrolysis treatment (i.e., after experiment at room temperature) was 3.2–3.6.
Chemical composition analysis
In this set of experiments, spruce wood chips were dried and then ground to a size smaller than 1 mm and then kept in a desiccator prior to analysis. In order to measure the hemicellulose and cellulose contents, the NREL method was applied to the ground wood particles . The Klason lignin method was used to determine the contents of acid-soluble and acid-insoluble lignin of the ground wood particles (T 222 om-98 and UM 250). To determine the total content of extractives in spruce wood chips, they were treated with acetone/water (95/5 v/v) in Glas-Col Combo Mantle extraction apparatus for 6 h. The final content of the extractives was determined using a gravimetric method.
The concentrations of polysugars and monosugars in the hydrolysis liquor and soda liquor were determined using ion chromatography, Dionex, ICS 5000, Thermofisher Scientific, equipped with CarboPac™ SA10 column and an electrochemical detector (ED) (Dionex-300, Dionex Corporation, Canada). Deionized water and KOH Eluent Generator (EGC 500 KOH, ThermoScientific) were used to generate an eluent of 1.00 mM of KOH at a flow rate of 1.2 mL/min. The column temperature was set at 30 °C. The monosugar concentration in the liquors was measured without pretreating the liquors but after adjusting pH of the liquors to 7. The hydrolysis and soda liquors were acid-hydrolyzed under the conditions of 4% sulfuric acid at 121 °C for 1 h in an oil bath (Hakke S45, Instruments, Inc., Portsmouth, N.H., USA) based on the method described in the literature . This acid hydrolysis is widely used for converting oligosugars to monosugars [4, 12]. Afterward, the concentration of monosugars in the hydrolysis liquors was measured as stated above, and it reflected the concentration of total monosugars (after conversion of oligosugars to monosugars) in the hydrolysis and soda liquors. The concentrations of polysugars were determined via subtracting total sugar concentrations from monosugar concentrations.
Lignin, furfural, and acetic acid analyses
The lignin content of the liquors was determined according to TAPPI UM 250 using UV spectrophotometry at 205 nm (GENESYS 10S UV–Vis, Thermo Scientific) .
To measure the contents of furfural and acetic acid, the liquors were first dried. Then 0.4 wt% of 3-(trimethylsilyl) propionic-2,2,3,3-d4 acid sodium salt (TSP) in deuterium oxide (D2O) was prepared. About 40 mg of dried liquor was added to 700 µL of the D2O solution. After mixing the solution, it was transferred to the NMR vials. A proton nuclear magnetic resonance, NMR, Varian Unity Inova 500 MHz spectrometer was used for determining the concentrations of furfural and acetic acid in the hydrolysis and soda liquors according to the previously established method .
Molecular weight analysis of hydrolysis and soda liquors
Samples with a 5 g/L concentration in 0.1 mol/L NaNO3 were prepared from the hydrolysis and soda liquors, and then they were stirred at 300 rpm for 24 h. Then samples were filtered with a 0.2 µm nylon filter (13 mm diameter), and the filtered solutions were used for molecular weight analysis. The molecular weight of the samples was measured using a gel permeation chromatography, Malvern GPCmax VE2001 Module + Viscotek TDA305 with multi-detectors. The columns of PolyAnalytic PAA206 and PAA203 were used in the analysis, and a 0.1 mmol NaNO3 solution was used as solvent and eluent. The flow rate was set at 0.70 mL/min, while the column temperature was 35 °C and poly (ethylene oxide) was used as a standard sample. The UV detector at 280 nm wavelength was used for determining the molecular weight of lignin, and IR detector was used for measuring the molecular weight of polysugars. This method was used for determining the molecular weight of lignin in the past .
Acidification of hydrolysis and soda liquors
Strong sulfuric acid treatment of hydrolysis liquor was followed as a method to separate hydrolysis lignin from hydrolysis liquor. The acidification at a high temperature is commercially used in the LignoForce technology to extract kraft lignin from black liquor . To understand the efficiency of acidification process in isolating lignin from hydrolysis and soda liquors, the liquors were acidified with sulfuric acid (1 mL of 98 wt% in 900 mL liquor) to the pH of 1.5 (Fig. 1). The dilution factor caused by mixing acid with the liquors was considered in determining the concentration of organic compounds in the liquors. Then the mixtures were heated to 80 °C and kept for 15 min at 80 °C. The precipitates formed in hydrolysis and soda liquors were then separated via filtration/centrifugation (4000 rpm for 10 min). The collected samples after centrifugation were analyzed comprehensively. A part of the collected precipitates of soda liquor was dialyzed for 2 days using membrane dialysis, while changing water every 4 h to remove impurity, and the properties of dialyzed samples were assessed.
TGA and DSC analyses of precipitates
The thermal characteristics of the precipitates made from hydrolysis and soda liquors were analyzed using a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). In this set of experiments, 8–12 mg of dried precipitates were loaded in a platinum (Pt) crucible of a thermogravimetric analyzer (TGA)-i1000 series (Instrument Specialist Inc.) and heated isothermally at 100 °C for 10 min to ensure moisture removals. Then the samples were heated to 700 °C under nitrogen (35 mL/min) with an increment rate of 10 °C/min.
Moreover, the thermal behavior of precipitates were investigated using a differential scanning calorimeter (DSC), TA instrument, Q2000, and the standard cell RC mode of DSC was also used for analysis. The samples were treated at 60 °C in an oven for removing moisture, then 8–10 mg of the dried samples were loaded into a Tzero aluminum pan, and analyzed by heat/cool/heat method in a temperature range from 30 to 250 °C at 50 mL/min in nitrogen. The heating and cooling rates were both controlled at 5 °C/min, and the second heating cycle (showed as exotherm up) was chosen for glass transition and melting point analyses.
31P NMR analysis of precipitates
The OH functional groups of the precipitates were analyzed by quantitative phosphorous nuclear magnetic resonance (31P NMR) analysis. This process was carried out following a previously established procedure . The precipitates were dried in a freeze drier overnight and a 36.6 mg sample was added to 500 µL of anhydrous pyridine/chloroform-d (1.6/1.0, v/v) solution. A 50 µL of a pyridine/chloroform-d (1.6/1.0) solution of chromium (III) acetylacetonate (5.6 mg/mL) was then added to the precipitates and the reaction mixture was stirred at room temperature for 10 min. A chloroform/pyridine-d mixture (1/1.6) of cyclohexanol (35 µL, 21.5 mg/mL) was then added as the internal standard. After the addition of cyclohexanol, 100 µL of 2-chloro-4,4,5,5-tetramethyl-1,2,3-dioxaphosphine was added as a phosphorylating agent and stirred for 10 min at room temperature. Upon completion, the reaction mixture was analyzed using an INOVA-500 MHz NMR instrument (Varian, USA).
Results and discussion
Wood chip properties
Properties of hydrolysis and soda liquors at different temperatures and residence times
Soda liquor lignin
The results in Table 2 also show the following: (1) by increasing the temperature at 15 min hydrolysis time, the concentration of acetic acid increased; (2) by increasing the temperature at 45 min hydrolysis time, the concentration of acetic acid decreased; and (3) by extending time of hydrolysis from 15 to 45 min, the acetic acid content of hydrolysis liquor was reduced. It is hypothesized that, at a short hydrolysis time of 15 min, more acetyl groups were cleaved by increasing temperature and thus more acetic acid was formed in the hydrolysis liquor . By extending time, or basically providing more severe hydrolysis conditions, the formed acetic acid might have degraded to other products and hence the concentration of acetic acid was reduced (Table 2).
The molecular weight of the lignin in hydrolysis liquor varied between 21,000 and 24,000 g/mol. It has been found that the molecular weight of milled wood lignin, which was a representative of native lignin for spruce wood , was about 23,500 g/mol .
The results also showed that, by extending time from 15 to 45 min, there was a slight increase in the concentrations of furfural and monosugars, but a minor decrease in the concentrations of polysugars. It can be claimed that the time extension hydrolyzed (i.e., cleaved) polysugars to monosugars, but the monosugars were subsequently converted to furfural . The concentration of lignin was insignificantly changed via time extension, implying that the hydrolysis conditions were not strong for major lignin removal from wood chips .
As discussed earlier, some lignin compounds were generated and precipitated/adsorbed to the digester surface, which were collected via soda liquor treatment. The concentration of soda liquor lignin in soda liquor is also listed in Table 2. No furfural, acetic acid, or sugars were detected in the soda liquor, indicating that these compounds did not adsorb/interact with soda liquor lignin and/or precipitate in the vessel, but were indeed remained in the hydrolysis liquor. It is evident that by increasing the temperature from 170 to 180 °C, more soda liquor lignin was removed from wood chips but the mass of removed soda liquor lignin was slightly reduced at 190 °C. The results in Table 2 show that the molecular weight of soda liquor lignin was around 3000 g/mol. The molecular weight of soda liquor lignin was lower than that of hydrolysis lignin (Table 2) and that of dioxane lignin or acetic acid-hydrolyzed lignin (6000 g/mol) reported elsewhere . The molecular weight of soda liquor lignin was lower at the hydrolysis time of 45 min (compared to 15 min). Generally, by extending time, more lignin can be removed from wood chips. The reduction in molecular weight may suggest that the time extension cleaved a part of LCC intermolecular bonds and degraded some carbohydrates. Consequently, the overall molecular weight of lignin presented in soda liquor was reduced. The reduction in the amount of lignin in soda liquor at 190 °C may provide evidence for this hypothesis.
Acidification of hydrolysis and soda liquors
Properties of acidified hydrolysis liquor and soda liquor
Mono sugara, g/L
Poly sugara, g/L
Hydrolysis lignina, g/L
Acetic acida, g/L
Mw of hydrolysis lignina, g/mol
Mw of poly sugara, g/mol
Soda liquor ligninb, g/L
Functional group associated with precipitates made from the acidification of hydrolysis and soda liquors generated after 45 min of the hydrolysis treatment
Precipitates of hydrolysis liquor (mmol/g)
Precipitates of soda liquor (mmol/g)
Aliphatic hydroxyl (OH), phenolate, and carboxylate groups originally exist in lignin [30, 39], and some free phenolate and aliphatic groups would be formed during hydrolysis process [40, 41]. The formation of C–C bonds would occur in the condensation reaction under acidic conditions and contributed to C–C bonds (Tables 2, 3) [42, 43]. Although Table 4 indicates a decrease in C-5 substitution, other carbon–carbon bonds, such as β-β and β-5 can be formed in the condensation reaction [44, 45]. It was reported that the precipitates of hydrolysis liquor made from steam hydrolysis of mixed hardwood contained 1.88 mmol/g of aliphatic hydroxyl groups, which agrees with that of the present work .
It is also evident in Table 4 that increasing the hydrolysis temperature decreased the number of functional groups in the precipitates. The decrease in the contents of the guaiacyl, phenolate, and carboxylate groups in the precipitates (Table 4) is in agreement with the molecular weight decrease at a high temperature shown in Table 2. A previous study claimed that by increasing the temperature, the degradation of carboxylate groups in spruce wood increased , which is consistent with the degradation of carboxylate groups in this work when the temperature increased from 170 to 190 °C. The results in Table 4 also depict that the precipitates of soda liquor had generally less aliphatic and guaiacyl hydroxyl, but more C5 substituted, carboxylate, and p-hydroxy phenyl groups.
Thermal properties of precipitates from hydrolysis liquor
Thermal properties of unpurified soda liquor lignin
In order to verify if the endothermic peaks in Fig. 5 (i.e., melting temperature) are due to the melting of the inorganic salts in the precipitates, the heat flows of the pure salts were analyzed as functions of the temperature (Additional file 1). Among NaOH, Na2SO3, and Na2SO4, only Na2SO4 showed a peak in the heating curve at approximately 240–250 °C. The melting points of NaOH, Na2SO3, and Na2SO4 were 318, 33.4, and 884 °C, respectively . An earlier study showed that the endothermic peak at about 250 °C was due to the changes in the crystalline structure of Na2SO4 . This confirmed that the peak for Na2SO4 was a consequence of the changes in the structure of Na2SO4 present in soda liquor lignin. Therefore, the results confirmed that the heat flow peaks in Fig. 5 were not generated by the organics of precipitates, but they were created by inorganic compounds (i.e., sodium sulfate) present in the precipitates.
Thermal properties of purified soda liquor lignin
It is worth noting that the mass loss in Fig. 6 (20–40 wt%) is less than the typical mass loss for the pyrolysis of lignin (40–50%). As discussed earlier, to remove inorganic salts in the dialysis process, some of the small molecular weight compounds might have passed through the membrane. Accordingly, the purified precipitates (i.e., purified soda liquor lignin) had a higher molecular weight, and thus showed higher thermal stability (i.e., less mass loss).
The heat flow of purified precipitates was also analyzed as a function of temperature (Additional file 1). A peak in the heat flow was observed at 180–190 °C, which suggested that the structure of precipitates changed its state from a glassy state into a rubbery state. The Tg of lignin depends on the processes by which lignin is produced and on the wood source . It has been reported that Tg of lignin made from acid hydrolysis of softwood was 95 °C, while that of lignin made from steam explosion of softwood was 139 °C . In another report, the Tg of lignin made from hot water hydrolysis of hardwood was 170–180 °C . In this work, increasing the temperature of hydrolysis treatment from 170 to 190 °C increased the Tg from 184 to 192 °C. This is consistent with an earlier study in which a Tg increase by 8 °C was reported for increasing the temperature of hot water treatment of hardwood by 20 °C . Also, heat flow analysis of purified precipitates did not experience any melting point between 200 and 220 °C, which confirms that the melting points in Fig. 4 were indeed due to the presence of inorganic salts in the impure precipitates.
Process development and product applications
Mass of components in treated wood chips, precipitates of acidification of hydrolysis liquor, acidified hydrolysis liquor, acidified soda liquor, and soda liquor lignin (based on 100 g oven dried wood)
Acidified hydrolysis liquor, %a
Precipitates of acidified hydrolysis liquor, %a
Acidified soda liquor, %a
Wood residue, %
Lignin in solution
Afterward, the acidified hydrolysis liquor can be sent to wastewater treatment. It can then be neutralized and further treated via biological treatment processes . In the developed process shown in Fig. 7, the spent acid that is generated in the purification process of lignin can be used as a source of acid for acidification of hydrolysis liquor. This process is similar to LignoForce in that it uses sedimentation/filtration tank to isolate lignin compounds from hydrolysis liquor and it uses acid washing to further purify the lignin compounds.
The thermal analyses confirm that soda liquor lignin had thermally stable characteristics. Therefore, this product can be used in composite production (e.g.. lignin–epoxy resin composites) in which the thermal stability of composite is an advantage . However, more in-depth analysis is required to validate it. In addition, the acidification of hydrolysis liquor made the precipitates that were mainly furfural and acetic acid. These chemicals can be used as platform chemicals for the production of other value-added chemicals, such as plastics, pharmaceutical, and agrochemical industries .
As seen in Table 5, it would be possible to produce 1, 5, and 19 tons of furfural from 1000 tons of wood chips if the procedures for the production of samples 4, 5, and 6 were followed, respectively. Acetic acid would be produced at the rates of 6, 4, and 3 tons if the procedures for the samples 4, 5, and 6 were followed, respectively. It should be stated that this process may not be economical if considered independent as the extraction yield is rather low (Table 5). However, hydrolysis is commercially used as a pretreatment step in the production of dissolving pulp following kraft process and is used for producing wood pellets [4–6]. The proposed process may be economical in these processes, as it may generate additional revenues from a waste resource. However, detailed economic analysis should be conducted to understand the financial feasibility of the proposed process.
Processing temperature and residence time showed major effects on the furfural production, but minor effects on sugars and lignin isolations from treated biomass. Increasing the severity of hydrolysis process led to increases in the concentrations of hydrolysis lignin from 11.6 to 14.3 g/L, monosugars from 3 to 12 g/L, and furfural from 0.3 to 4 g/L. However, the concentration of polysugar was the maximum at 180 °C, and more sever conditions reduced its concentration in hydrolysis liquor. The molecular weight of hydrolysis lignin was approximately 22 kg/mol and was insignificantly changed under different hydrolysis conditions. The acidification of hydrolysis liquor led to the precipitates that contained mainly furfural and acetic acid rather than hydrolysis lignin and sugars. The concentrations of furfural and acetic acid in hydrolysis liquor were significantly decreased (approximately 31–76%), but those of lignin and sugars reduced by less than 13%. The acidification of soda liquor led to precipitation of soda liquor lignin (1% removed from the wood chips) and inorganic impurities. The purified soda liquor lignin showed Tg around 180–190 °C and thermal resistance. Based on these results, a process for producing purified lignin and the precipitates of volatile compounds from hydrolysis liquor was developed.
differential scanning calorimetry
liquid to solid
nuclear magnetic resonance
3-(trimethylsilyl) propionic-2,2,3,3-d4 acid sodium salt
TK was the main author of this work and conducted the majority of analysis using the generated data by others. YZ performed DSC analysis. DT carried out the hydrolysis analysis. WG performed the GPC analysis. JP helped with NMR analysis. LH and ND cosupervised TK in this research at Abo Academi and PF was the lead supervisor of the group on this project at Lakehead University. All authors read and approved the final manuscript.
TK, ND, and LH are associated with laboratory of inorganic chemistry at Abo Academi University in Finland and their research area includes thermal analysis of biomass (e.g. combustion, gasification, and torrefaction). JP is associated with FPInnovations in Canada and her main research interest is the analysis and modification of lignocelluloses. YZ, DT, WG, and PF are researchers at Lakehead University in Canada and their main research areas include the extraction of lignocelluloses from spent liquor and conversion of biomass to value-added products.
This work is part of activities at Biomass Utilization Research Laboratory of Lakehead University and the Johan Gadolin Process Chemistry Center, a Center of Excellence, of Abo Akademi University.
The authors declare that they have no competing interests.
Availability of supporting data
The raw data that are related to this work can be available upon requests from the corresponding author.
The authors would like to thank (1) Early Researcher Award program of the Government of Ontario, (2) Canada Research Chair and Canadian Foundation for Innovation of the Government of Canada, and (3) Graduate School of Chemical Engineering and Kone foundation at Abo Akademi University for supporting this research. These funding sources were used for covering the costs associated with laboratory analysis of this work at Lakehead University in Canada and with covering travel costs of TK to Canada.
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