Pineapple crown delignification using low-cost ionic liquid based on ethanolamine and organic acids

Pineapple fibre was treated with protic ionic liquids (PILs) and the effects on the structure, composition, and properties of the fibres were evaluated. Treatment with PILs efficiently exposed the fibre surface, as confirmed by scanning electron microscopy.

Carbohydrate Polymers 206 (2019) 302–308 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Pineapple crown delignification using low-cost ionic liquid based on ethanolamine and organic acids T Rita de C.M Mirandaa,b, Jaci Vilanova Netaa, Luiz Fernando Romanholo Ferreiraa,c, Walter Alves Gomes Júniord, Carina Soares Nascimentod, Edelvio de B Gomesd, ⁎ Silvana Mattedie, Cleide M.F Soaresa,c, Álvaro S Limaa,c, a UNIT, Universidade Tiradentes, Av Murilo Dantas, 300, Farolândia, 49032-490, Aracaju, SE, Brazil Uniceuma, Mestrado em Meio Ambiente, Renascenỗa, 65075-120, São Luís, MA, Brazil c ITP, Instituto de Tecnologia e Pesquisa, Av Murilo Dantas, 300-Prédio ITP, Farolândia, 49032-490, Aracaju, SE, Brazil d IFBA, Instituto Federal da Bahia, Campus Salvador, Departamento de Tecnologia em Sẳde e Biologia, Rua Emídio dos Santos, s/n - Barbalho, 40301-015, Salvador, BA, Brazil e UFBA, Universidade Federal da Bahia, Escola Politécnica, Departamento de Engenharia, Rua Aristides Novis 2, Federaỗóo, 40210-630, Salvador, BA, Brazil b A R T I C LE I N FO A B S T R A C T Keywords: Ionic liquid Biomass Pineapple Lignocellulose Treatment Pineapple fibre was treated with protic ionic liquids (PILs) and the effects on the structure, composition, and properties of the fibres were evaluated Treatment with PILs efficiently exposed the fibre surface, as confirmed by scanning electron microscopy The chemical composition analysis revealed reductions in the lignin and hemicellulose contents in the treated fibres, promoting exposure of cellulose The results correlated with the crystallinity index, which was greater in the treated fibres compared with that in the untreated fibres The generated residue from the treatment of fibres with PIL (1%, v/v) showed lower levels of toxic compounds, demonstrating the advantages of this treatment over conventional biomass treatments Introduction The treatment of lignocellulosic biomass is fundamental in the economy (Tan et al., 2009; Yuan, Xu, & Sun, 2013) and characterized as an expensive step in conversion of biomass The main basic treatment based on physical (mechanical comminution, pyrolysis, steam pretreatment and steam explosion), chemical (acid pretreatment, alkali pretreatment and sufur dioxide), biological (microbial and enzymatic) or hydrid tion, microwave irradiation, ammonia fibre explosion and liquid hot water (Singh, Shukla, Tiwari, & Srivastava, 2014; Fu, Mazza, & Tamaki, 2010) Recently, several studies on the efficiency of delignification of aprotic ionic liquids (AILs) were performed (Brandt, Gräsvik, Halletta, & Welton, 2013; Pinkert, Dagmar, Goeke, Marsh, & Pang, 2011; Sun et al., 2009) Their dissolution properties are responsible for the appropriate choice of the cations and/or anions of AILs, moreover the environmentally friendly properties has also an importante role in this process (Anugwom et al., 2014) The short alkyl chain AILs are preferred, and the most traditionally used is imidazolium acetate due to the highest solubility of lignin (Zakrzewska, Bogel-Łukasik, & BogelŁukasik, 2010) However, there are many drawbacks, such as high ⁎ process temperature (> 100 °C), low efficiency (< 50%), solid waste accumulation, high viscosity recovery difficulties and high cost (Rashid, Kait, Regupathi, & Murugesan, 2016) Alternately, the literature has been working with protic ionic liquids (PILs) because they are cheap and easily synthesized (Achinivu, Howard, Li, Gracz, & Henderson, 2014) PILs are salts formed from acid / base reactions (MacFarlane, Pringle, Johansson, Forsyth, & Forsyth, 2006) at mild temperature (< 100 °C) as an alternative to conventional lignin removal methods (Achinivu et al., 2014) The mechanism of action of LPIs is based on the solubility of lignin In the last decade, the studies focused on the dissolution of biogenic polymers and demonstrated the great potential of PILs (Swatloski, Spear, & Holbrey, 2002) The ability of PILs to solubilize lignin and carbohydrates depends on the fact that these compounds act on the complex of bonds formed by the rupture of the lignocellulosic complex (Singh, Simmons, & Vogel, 2009; Swatloski et al., 2002) The action of PILs on lignin, promoting the cleavage of βeOe4 bonds between 130 and 200 °C (Cox & Ekerdt, 2012, 2013; Jia, Cox, Guo, Zhang, & Ekerdt, 2010; Long, Li, Guo, Wang, & Zhang, 2013) Therefore, this work hypothesized that the PILs could remove the residual lignin from pineapple crown as biomass In this study, the Corresponding author at: UNIT, Universidade Tiradentes, Av Murilo Dantas, 300, Farolândia, 49032-490, Aracaju, SE, Brazil E-mail address: aslima2001@yahoo.com.br (Á.S Lima) https://doi.org/10.1016/j.carbpol.2018.10.112 Received June 2018; Received in revised form 29 October 2018; Accepted 30 October 2018 Available online 31 October 2018 0144-8617/ © 2018 Elsevier Ltd All rights reserved Carbohydrate Polymers 206 (2019) 302–308 R de C.M Miranda et al 2.3 Structural characterization selected ionic liquids are formed by organic acids with small alkyl chain (acetic, propionic, butyric and pentanoic acid) due to their better delignification capacity; and by amines with different substitutions of the monoethanolamine hydrogen, producing amines more hydrophilic (2hydroxyethyl - diethanolamine) or more hydrophobic (methyl – methyl-monoethanolamine) In this way the set of ionic liquids depicts different properties, low toxicity and low cost (Oliveira et al., 2016; Ventura et al., 2012) Amorphous and crystalline regions of the samples were characterized by Energy Dispersive X-ray diffraction spectroscopy (XRD, Shimadzu Corp., model XRD-6000), with a CuK radiation source, a voltage of 40 kV, and a current of 40 mA Scans were taken over a range of 2θ values of 10–90° at a scan rate of 0.05° min−1 The degree of crystallinity was evaluated using the crystallinity index, calculated according to the empirical model (Eq 1) of Segal, Creely, Martins, and Anndre Conrad (1959) Material and methods CrI = 2.1 Materials 2.4 Ionic liquid treatment The methodology for biomass delignification using PILs was developed by Varanasi et al (2012) Biomass (300 mg) was mixed with 9.7 mL of PIL at room temperature The solution was then heated to 100 °C in a water bath for h After the treatment, samples were thoroughly mixed and 35 mL of hot water was added to the sample to precipitate the dissolved biomass The mixture of PIL, water, and biomass was centrifuged to separate the solid (recovered biomass) and liquid (PIL and water) phases The recovered biomass was washed four times with hot water to remove excess PIL 2.5 Chemical characterization Untreated and treated biomass samples were analysed according to the protocols of the National Renewable Energy Laboratory (NREL) (Sluiter et al., 2006, 2012) Before the analysis, g of the sample were extracted in two consecutive steps with water and ethanol using 250 mL of solvent for h After extraction, 300 mg of the samples were hydrolysed with mL of sulphuric acid at 30 °C for h The reaction mixture was diluted to 4% (by weight) with water and autoclaved at 121 °C for h The liquid was then analysed for its sugar content using ultrafast high-pressure liquid chromatography (UFLC) on a ShimadzuProminence liquid chromatograph with a refractive index detector (RID-10 A) The concentrations of monomeric sugars in the soluble fraction were determined using a Supelcogel-Pb column (30 cm × 7.8 mm, μm, equipped with a pre-column) at 85 °C and an elution rate of 0.6 mL min−1, using ultrapure water as the mobile phase The concentrations of sugars derived from the hydrolysis of cellulose and hemicellulose were determined from calibration curves generated using standard solutions (Sluiter et al., 2012) The acetyl groups were determined using high-performance liquid chromatography (HPLC) with the same system as above but with a BioRad HPX-87H column at 45 °C The mobile phase was mM H2SO4, at a flow rate of 0.5 mL min−1 The solids were dried to constant weight at 105 °C and considered insoluble lignin (IL) The soluble lignin (SL) concentration in the filtrate was determined based on UV spectrophotometry at 280 nm Total lignin content in the untreated and treated samples was measured by the acetyl bromide method, according to Sluiter et al (2012), with modifications Pineapple powder (5 mg) was treated with 25 wt% acetyl bromide in glacial acetic acid (0.2 mL) The tubes were sealed and incubated at 50 °C for h with shaking at 500 rpm on a thermomixer After digestion, the solutions were diluted with three volumes of acetic acid (0.6 mL), and then 0.1 mL aliquots were 2.2 Morphological characterization Photomicrographs of the untreated and treated biomass samples were obtained using scanning electron microscopy (SEM) (JEOL model JSM5310) by detecting secondary electrons after depositing the sample on a gold substrate Table Chemical structure of designed ionic liquid cations and anions 2-hydroxyethylammonium Anion Acetate bis(2-hydroxyethyl)ammonium Propionate N-methyl-2-hydroxyethylammonium Butyrate (1) where: CrI = crystallinity index (%); I(002) = diffraction peak intensity of the crystalline material that is close to 2θ = 22°; I(am) = diffraction peak intensity of the amorphous material that is close to 2θ = 18° The values found after the calculation of the crystallinity index are relative values, assuming that the value for microcrystalline cellulose (MCC) is 100% In the present study, 12 PILs were used: 2-hydroxyethylammonium acetate (2HEAA), 2-hydroxyethylammonium propionate (2HEAPr), 2hydroxyethylammonium butyrate (2HEAB), 2-hydroxyethylammonium pentanoate (2HEAP), bis(2-hydroxyethyl)ammonium acetate (BHEAA), bis(2-hydroxyethyl)ammonium propionate (BHEAPr), bis(2-hydroxyethyl)ammonium butyrate (BHEAB), bis(2-hydroxyethyl)ammonium pentanoate (BHEAP), N-methyl-2-hydroxyethylammonium acetate (m2HEAA), N-methyl-2-hydroxyethylammonium propionate (m-2HEAPr), N-methyl-2-hydroxyethylammonium butyrate (m-2HEAB), and N-methyl-2-hydroxyethylammonium pentanoate (m-2HEAP) Their cation and anion chemical structures are depicted in Table The PILs were synthesized by reacting equimolar amounts of amine and the respective organic acids, according to Alvarez, Mattedi, MartinPastor, Aznar, and Iglesias (2010) During the course of the experiments, the purities of the solvents were monitored by their density and speed of sound measurements Pineapple crown samples (Ananas comosus) were used as the raw material, which were obtained from a local market in Aracaju SE, Brazil Pineapple crown were washed, cut, and dried at 60 °C for 48 h The dried biomass was milled through a 32–60 mesh sieve Cation I(002) − I(am) I(002) Pentanoate 303 304 35.7 ± 0.9 26.6 ± 1.3 10.6 ± 0.3 8.9 ± 1.1 3.9 ± 0.1 3.2 ± 0.6 1.34 ± 0.03 21.9 ± 0.6 3.92 ± 0.02 0.09 ± 0.05 89.55 34.9 ± 0.9 29.5 ± 1.3 10.6 ± 0.3 8.9 ± 1.1 5.6 ± 0.1 4.4 ± 0.6 2.04 ± 0.03 21.9 ± 0,6 3.92 ± 0.02 1.09 ± 0.05 91.75 35.8 ± 0.9 26.1 ± 1.3 10.6 ± 0.3 8.9 ± 1.1 3.9 ± 0.1 2.7 ± 0.6 1.12 ± 0.03 21.9 ± 0.6 3.91 ± 0.02 2.09 ± 0.05 90.92 35.9 ± 0.9 30.0 ± 1.3 11.8 ± 0.3 10.6 ± 1.1 4.7 ± 0.1 2.9 ± 0.6 1.14 ± 0.03 19.9 ± 0.6 2.72 ± 0.02 1.29 ± 0.05 91.35 35.6 ± 0.9 30.7 ± 1.3 11.3 ± 0.3 10.9 ± 1.3 3.6 ± 0.1 1.9 ± 0.6 1.24 ± 0.03 17.9 ± 0.6 3.91 ± 0.02 0.09 ± 0.05 92.4 38.6 ± 0.9 33.3 ± 1.3 12.6 ± 0.3 13.9 ± 1.1 4.8 ± 0.1 1.9 ± 0.6 0.91 ± 0.03 18.9 ± 0.6 1.12 ± 0.02 1.09 ± 0.05 91.86 35.6 ± 0.9 29.9 ± 1.3 13.8 ± 0.3 8.9 ± 1.1 4.1 ± 0.1 3.1 ± 0.6 1.32 ± 0.03 19.9 ± 0.6 2.92 ± 0.02 1.22 ± 0.05 90.8 36.6 ± 0.9 32.1 ± 1.3 13.6 ± 0.3 11.9 ± 1.1 4.6 ± 0.1 2.6 ± 0.6 1.25 ± 0.03 17.9 ± 0.6 1.91 ± 0.02 1.09 ± 0.05 90.4 BHEAA 2HEAP 2HEAB 2HEAPr 2HEAA H2O Untreated Samples Constituent Table The chemical characteristics of the untreated biomass and that subjected to treatment with protic ionic liquid BHEAPr Although there are some studies on the solubility of lignin in ionic liquids, little is known about the potential of these compounds to treat biomass Chemical characterizations performed before and after the treatment with the ionic liquid are important to discern what changes occur in the biomass as a result of treatment The chemical compositions of the untreated and PIL-treated biomass samples are shown in Table The composition of the lignocellulosic material in the untreated biomass was 34.6% and 25.4% cellulose and hemicellulose, respectively, and 5.14% total lignin In the untreated biomass, the total lignin content was significantly lower than the other components of the lignocellulosic portion After treatment with PILs, the quantities of cellulose and hemicellulose increased, while amount of lignin decreased Hemicellulosic sugars represented 15.43 ± 1.77% of the raw material, with xylose as the main sugar (67%) The cellulose (as glucose) and lignin content (39.97 ± 0.95% and 17.83 ± 0.05%, respectively) were similar to those in other studies using sunflower (Díaz, Cara, Ruiz, Pérez-Bonilla, & Castro, 2011; Pandey & Pitman, 2004; Ruiz et al., 2013) According to Mohanty, Misra, and Drzal (2001) increases in cellulose and hemicellulose fractions after treatment results from the removal of additional materials such as waxes and plant gums Moreover, there was an increase in the quantity of cellulose in the biomass treated with the 2HEAPr (39.3%) compared with the biomass treated with BHEAPr (38.6%) The amount of hemicellulose in the biomass was higher after treatment with m-BHEAP (34.9%) than after treatment with 2HEAPr Xylose was the predominant sugar in all treated and untreated biomass samples The amount of xylose extracted from the untreated biomass was 21.9%, which decreased in biomass treated with PILs Biomass treated with HEAA showed lowest amount of xylose (12.9%) The concentration of ash and acetyl groups also decreased after PIL treatment Ash and acetyl groups were present at 3.9% and 2.09%, respectively, in the untreated biomass while the concentrations in biomass treated with the BHEAPr was 1.1% and in that treated with IL 2HEAB, BHEAB and m-2-HEAB was about 12.09% Similar to the results of the present study, Singh et al (2009) observed changes in the biomass composition of switchgrass after treatment with PIL 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) 37.9 ± 0.9 27.3 ± 1.3 12.8 ± 0.2 9.1 ± 0.1 4.6 ± 0.1 0.8 ± 0.05 1.14 ± 0.03 15.9 ± 0.6 3.31 ± 0.02 1.09 ± 0.01 86.64 3.1 Chemical characterization of biomass 39.3 ± 0.2 27.0 ± 0.3 11.6 ± 0.3 9.9 ± 1.1 4.6 ± 0.1 0.9 ± 0.6 1.04 ± 0.03 19.9 ± 0.6 1.31 ± 0.02 1.92 ± 0.05 90.47 BHEAB The characterization of pineapple fibres before and after treatment with protic ionic liquids for delignification is important because the changes caused by PIL treatment affect the success of potential applications of PILs for biomass recovery 37.8 ± 0.3 29.0 ± 1.3 10.6 ± 0.3 9.9 ± 0.3 6.6 ± 0.1 3.9 ± 0.2 2.14 ± 0.03 18.9 ± 0.6 1.91 ± 0.02 2.09 ± 0.05 91.84 BHEAP Result and discussion 35.6 ± 0.5 27.7 ± 0.8 14.6 ± 0.5 8.2 ± 0.9 4.6 ± 0.3 0.3 ± 0.02 5.14 ± 0.03 21.9 ± 0.6 3.82 ± 0.04 1.19 ± 0.08 m-2HEAA Furfural and hydroxymethylfurfural concentrations were analysed using HPLC equipped with a SPD-M20 A Diode-array detector; the separation was performed using a LiChrospher 100 RP-18 (125 × mm, μm) column (Hewlett-Packard), operating at 25 °C, with acetonitrile/ water as an eluent at a flow rate of 0.5 mL min−1 34.6 ± 0.9 25.4 ± 1.3 10.6 ± 0.3 8.9 ± 1.1 3.6 ± 0.1 1.9 ± 0.6 5.14 ± 0.03 21.9 ± 0.6 3.91 ± 0.02 2.09 ± 0.05 93.04 2.6 Quantification of toxic compounds Cellulose Hemicellulose Xylose Galactose Arabinose Mannose Total Lignin Extractive Ash Acetyl Group Total m-2HEAPr m-2HEAB m-2HEAP transferred to 15 mL centrifuge tubes and 0.5 mL acetic acid was added The solutions were mixed well and 0.3 M sodium hydroxide (0.3 mL) and 0.5 M hydroxylamine hydrochloride (0.1 mL) were added The final volume adjusted to mL with acetic acid The UV spectra of the solutions were measured against a blank prepared using the same method, excluding the biomass The lignin content was determined with the absorbance at 280 nm and a mass extinction coefficient of 15.02 L g−1 cm−1 (standard lignin) according to an established method (Arora et al., 2010 35.9 ± 0.9 34.9 ± 1.3 12.6 ± 0.3 11.4 ± 1.1 5.6 ± 0.1 4.9 ± 0.6 2.22 ± 0.03 17.9 ± 0.6 2.09 ± 0.02 1.07 ± 0.05 94.08 Carbohydrate Polymers 206 (2019) 302–308 R de C.M Miranda et al Carbohydrate Polymers 206 (2019) 302–308 R de C.M Miranda et al appearance were observed and the exposed pits emphasize the removal of lignin by the PILs In addition, PIL treatment preserved the cellulose structure because of contact with the surface Fig 1F–I shows the profile of fibres after treatment with ionic liquids BHEAA, BHEAPr, BHEAB, and BHEAP The fibres are well preserved but show the presence of pits In such treated fibres, conserved cellulose is observed as rod-shaped fibrous structures, suggesting the presence of pectin Fig 1J–M depicts the profiles of the fibres after treatment with ionic liquids m-2HEAA, m-2HEAPr, m-2HEAB, and m-2HEAP Unlike previous treatments, the cellulose fibres not appear to be preserved, although pits are present The fibres not appear to be stretched, and their appearance is not preserved compared with pre-treatment, suggesting an aggressive treatment compared with the PILs used in Figs 1J–M The damage to the fibre denotes the presence of large amounts of pectin, which may hinder the absorption of the PIL and the removal of lignin for good cellulose exposure Brígida et al (2011) treated coconut fibres with sodium hydroxide and observed pits and fibre disorganization Auxenfans et al (2014) reported a complex fibre organization characterized by a highly fibrillated morphology in untreated sawdust oak Treatment with the 12 PILs altered the organization of the fibres inside the samples, resulting in a more irregular and porous texture Thus, these data suggest a strong change in the organization of primary particles without any noticeable changes in their specific surface area These changes in texture create a large volume available among the primary wood grains and therefore should improve the accessibility of enzymes The authors reported lignin, cellulose and hemicellulose contents of about 27%, 36%, and 37%, respectively, before treatment, while after PIL treatment, the concentrations reached 27%, 34% and 39%, respectively This could be explained by the fact that, after treatment with the ionic liquid, the fibres become more exposed and porous Brígida, Calado, Gonỗalves, and Coelho (2011) treated coconut bres with three different chemicals (NaOCl, NaOCl/NaOH, and H2O2) and cellulose recovery increased to 62.77% when treated with NaOCl/ NaOH, compared with the 45.93% recovered from untreated fibre The authors attributed this to the partial removal of hemicellulose, which was confirmed by the disintegration of the biomass Perez-Pimienta et al (2015) used the NREL methodology to characterize agave bagasse pre-treated with [C2mim]OAc and observed increased cellulose and hemicellulose contents, and decreased lignin contents The same profile was observed for ash, with a higher content in the treated biomass 3.2 Morphological characterization of the biomass Scanning electron microscopy (SEM) was used to reveal morphological differences before and after biomass treatment We evaluated the changes in cell wall morphology after the application of PILs in a similar way to previous microscopic studies (Sun, Li, Xue, Simmons, & Singh, 2013) SEM images of pineapple fibres before and after PIL treatment are shown in Fig 1A–M Fig 1A shows micrographs of the untreated fibres with a preserved structure without pores or pits The "pits" observed in Figs 1B-M indicate the removal of lignin and cellulose exposure (Pereira, Voorwald, Cioffi, & Pereira, 2012) Fig 1B–E depicts SEM images of the fibre treated with the ionic liquids 2HEAA, 2HEAPr, 2HEAB, and 2HEAP, which indicate the effectiveness of treatments Elongated structures with a fibrous Fig Micromorphological aspect of pineapple waste fibre without treatment (A) and after treatment with protic ionic liquids 2HEAA (B), 2HEAPr (C), 2HEAB (D), 2HEAP (E), BHEAA (F), BHEAPr (G), BHEAB (H) and BHEAP (I), m-2HEAA (J), m-2HEAPr (K), m-2HEAB (L), and m-2HEAP (M) 305 Carbohydrate Polymers 206 (2019) 302–308 R de C.M Miranda et al Fig X-ray diffraction data of untreated biomass, microcrystalline cellulose (MCC a−c ), and biomass treated with the protic ionic liquids (d–o) by the material treated with 2HEAPr (68%) and the ionic liquid BHEAB (66%) According to George et al (2015), an increase in the CrI is often indicative of hemicellulose and/or lignin removal Enzinne, Reagan, Guoquing, Hanna, and Wesley (2014) carried out recyclability experiments with cellulose in PILs and confirmed that the recovered cellulose largely maintains its cellulose-I crystal structure because of the low solubility of cellulose in the PILs Similar results were obtained by Zhang et al (2014), who reported an increase in the CrI of switchgrass, corn stove, and rice husk cellulose after treating the biomass with PIL 1-butyl-3-methylimidazolium acetate ([C4mim]OAc) In the present study, we used Energy Dispersive X- Ray diffraction Spectroscopy (XRD) to determine the CrI of the cellulosic structure after treatment After treatment of lignocellulosic biomass of agave bagasse, Perez-Pimienta et al (2015) reported that cellulose I and II became more dissolved and hence more amorphous, reducing the crystallinity, 3.3 Crystal index The determination of the degree of crystallinity is important to understand the behaviour of cellulosic materials, because these materials possess crystalline and amorphous regions Crystallinity determination enables the observation of changes that occur in the structure of the cellulosic material, both in the crystalline and amorphous region (Pereira et al., 2012) X-ray diffraction analysis of untreated cellulose and microcrystalline samples treated with PILs are shown in Fig The samples treated with ionic liquids displayed peaks in the diffractograms in the region 10° ≤ 2θ ≤ 20° and regions 18° ≤ 2θ ≤ 20° These peaks after the treatment with ionic liquids were similar to microcrystalline cellulose as all of them had a peak at 2θ = 22.1° This peak probably indicates the distance between hydrogen-bonded sheets in cellulose I, as reported previously After treatment with PILs, the crystallinity of the samples increased when compared to untreated samples, even though the peaks at approximately 38, 44, 65, and 78° not represent cellulose, and are probably characteristics of lignocellulosic samples, because the profile is different from the MCC sample and similar to that of the untreated sample Diffraction data were used to determine the Crystallinity Index (CrI) using Eq 1, and the results are shown in Fig The highest CrI was observed after treatment with the ionic liquid BHEAPr (70%), followed 3.4 Cellulose, Hemicellulose, lignin, and toxic compounds quantification The cellulose, hemicellulose, and total lignin removed from the lignocellulosic material by treatment with the PILs are shown in Fig PILs were demonstrated to be efficient in the removal of lignin and hemicellulose, while preserving the pulp, and thus have the potential to treat lignocellulosic biomass Among the 12 PILs tested, the highest efficiency was demonstrated by 2HEAPr, (lignin and hemicellulose removals of 92% and 48%, respectively) The PIL m-2HEAPr removed 89% of the lignin, 34% of the hemicellulose, and only 0.9% of the cellulose The PIL BHEAA, removed 83% of the lignin, 33% of the hemicellulose, and 1.2% of the cellulose While 2HEAPr, m-2HEAPr, and BHEAA showed the best performances for delignification, all the other tested PILs showed similar trends when treating lignocellulosic biomass from pineapple crowns All PILs removed almost all the lignin and hemicellulose without interfering with the cellulose content In Fig 4, higher lignin removal was observed for PILs with the propionate anion The calculated octanol-water partition coefficients (log P values) for the cations are −1.32, −1.57, and −0.88 for ethanolamine, diethanolamine, and methylmonoethanolamine, respectively Considering the entire PIL compound, when the filaments are under the compound it is more hydrophilic For the larger chains, the hydrophobicity of the alkyl Fig Crystallinity index of microcrystalline cellulose (MCC), the untreated biomass, and biomass after protic ionic liquids treatment 306 Carbohydrate Polymers 206 (2019) 302–308 R de C.M Miranda et al Fig Cellulose, hemicellulose, and lignin removed from the lignocellulosic material after treatment with the protic ionic liquids reacted with water to produce guaiacol at 150 °C Achinivu et al (2014) developed a lignin extraction method from lignocellulosic biomass using PIL, and observed a positive correlation between xylan solubility in the IL and fibre disruption/penetration Studies have explored the effect of cations on the action of PILs George et al (2015) studied the effect of protic and ionic liquids on saccharification and reported that treatment with diethyl-, triethyl-, and diisopropylammonium ILs resulted in higher saccharification yields and similar performances It appears that the overall trend in that work was that the addition of eOH groups to the cation reduced the hydrolysis yield and an increase in the number of alkyl chains increased the yield of enzymatic hydrolysis The performance of the IL diisopropylammonium indicated that steric effects not play a role in the hydrolysis efficiency, at least for cations with short alkyl chain lengths (n = 2–3) Rocha, Costa, and Aznar (2014) used BHEAA to pretreat sugarcane bagasse for enzymatic hydrolysis, with promising results A problem in current lignocellulosic refineries is that conventional treatments use organic solvents and buffers (basic and acid), during which toxic intermediates are generated, such as hydroxymethylfurfural (HMF) and furfural (MF) In the present study, MF and HMF levels were measured after treatment of the biomass with the PIL to indirectly assess the toxicity of the process As shown in Fig 5, the yields of HMF and MF during treatment of biomass with PILs were low Treatment with the PILs produced the following yields of MF: 2HEAA - 5%; 2HEAP - 4%; BHEAP - 8%; m2HEAA - 1%; m-2HEAPr - 5%; and m-2HEAP - 6% HMF was produced by 2HEAA (2%) and BHEAP (2%) Brandt et al (2011) reported that the concentration of hemicellulose decreased as a result of treatment, suggesting the conversion of carbohydrate monomers to furfurals The production of MF and HMF shown in Fig is expected, as high temperatures were used in the present study (120 °C) Sharaf, Mehrez, and Naggar, (2018) studied the preparation of bee honey extracts using cellulose nanofibres as the immobilizing agent The authors reported eco-friendly methods for extracting honey, stating that they obtained good results using ultrasound, soxhlet, and magnetic stirring for propolis extraction The authors further stated that the extract in the cellulose nanofibre was prepared using an environmentally friendly solvent El-Naggar et al (2018), using microcrystals of cellulose for the elaboration of nanogees with the aim of using them for a heavy grating The authors state that they are more efficient for use as a continuous process Fig Percentage of intermediate toxic compounds produced during the treatment of lignocellulosic biomass with protic ionic liquids chain is predominant Among all the PIL, BHEAPr showed highest lignin solubilisation because of intermediate solubility Cellulose did not seem change when the biomass was treatment with the PILs Fig shows that 2HEAA had the greatest solubility for cellulose (5%) According to Brandt et al (2013), lengthening the alkyl chains of the cation progressively reduces cellulose solubility The ionic liquid behaviour has been explained by Pu, Jiang, and Ragauskas (2007), who showed that lignin is more soluble in the PILs than in AILs because of the higher affinity of lignin for the protic ILs This is the results of the nature of the anion synthesized by proton transfer between an equimolar mixture of a Brønsted acid and Brønsted base Cox and Ekerdt (2012) suggested that acidic ILs are successful at breaking down lignin model compounds by hydrolysing the β-O- ether bond; while the acidic environment of the IL catalyses the hydrolysis reaction The anions have a significant effect on the yield and the observed intermediates Brandt et al (2013) reported that solubility seems to be strongly affected by the choice of anion, although hydrogen-bond basicity does not need to be as high as that for cellulose; some intermediate-chain basic ionic liquids seem to be better solvents for lignin than their basic relatives with more hydrogen-bonds The authors also emphasized that a protic cation failed to solubilise cellulose in many cases because of strong interactions between cations and anions For cellulose solubility, the cation should be based on a strong base and a weak carboxylic acid, such as acetic acid or propionic acid Perez-Pimienta et al (2015) reported that the differences in delignification efficiencies during pretreatment of agave biomass with ionic liquids could be attributed to specific interactions of ionic liquids with biomass factors (cation, anion, temperature, and time), and the extent and degree of recalcitrance of the biomass factors (age, method of harvesting, drying point, and storage conditions) Jia et al (2010) reported that the in process of cleavage of βeOe4 bonds of lignin model, compounds that conserved 70% of the βeOe4 bonds of both guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether Conclusion Treatment of lignocellulosic fibres with ionic liquids was effective to remove lignin and hemicellulose by exposing the cellulose, thereby increasing the surface area of the fibres and providing free hydroxy groups The presence of cellulose increases the potential use of this fibre 307 Carbohydrate Polymers 206 (2019) 302–308 R de C.M Miranda et al when free OH is crucial Small amounts of furfural and hydroxymethylfurfural were produced, demonstrating the low toxicity of PILs The PIL BHEAPr showed the greatest efficacy (90%), maintaining the pulp, as observed in the morphological analysis and the calculation of the crystallization rate One of the objectives of delignification is the removal of lignin present in the cells, to obtain inputs that could be used in industry, such as in biofuels In this context, the treatment of the pineapple fibre (crown) to remove lignin using PILs proved effective to obtaining a support for enzymatic immobilization by preserving the cellulose Thus the PIL-treated fibre could be used in industry for the immobilization of enzymes, among which lipase is used as a catalyst in the transesterification process for the production of bio-diesel MacFarlane, D R., Pringle, J M., Johansson, K M., Forsyth, S A., & Forsyth, M (2006) Lewis base ionic liquids Chemical Communications, 1905–1917 El-Naggar, M E., Radwan, E K., El-Wakeel, S T., Kafafy, H., Gad-Allah, T A., El-Kalliny, A S., et al (2018) Synthesis, characterization and adsorption properties of microcrystalline cellulose based nanogel for dyes and heavy metals removal Biomac https://doi.org/10.1016/j.ijbiomac.2018.02.126 Mohanty, A K., Misra, M., & Drzal, L T (2001) Sustainable bio-composites from renewable resources: Opportunities and challenges in the green materials world Composite Interface, 8, 313–343 Oliveira, M V S., Vidal, B T., Melo, C M., Miranda, R C M., Soares, C M F., Coutinho, J A P., et al (2016) (Eco)toxicity and biodegradability of protic ionic liquids Chemosphere (Oxford), 147, 460–466 Pandey, K K., & Pitman, A J (2004) Examination of the lignin content in s softwood and a hardwood decayed by a brown-rot fungus with the acetyl bromide method and fourier transform infrared spectroscopy Journal of Applied Polymer Chemistry 42, 2340–2346 Pereira, P H F., Voorwald, H C J., Cioffi, M O H., & Pereira, M L C S (2012) Preparaỗóo e caracterizaỗóo de materiais híbridos celulose/NbOPO4·nH2O a partir de celulose branqueada de bagaỗo de cana-de-aỗỳcar Polớmeros, 22, 8895 Perez-Pimienta, A., Lopez-Ortega, M G., Chavez-Carvayar, J.Á., Varanasi, P., Stavila, V., Cheng, G., et al (2015) Characterization of agave bagasse as a function of ionic liquid pretreatment Biomass & Bioenergy, 75, 180–188 Pinkert, A., Dagmar, F., Goeke, D F., Marsh, K N., & Pang, S (2011) Extracting wood lignin without dissolving or degrading cellulose:Investigations on the use of food additive-derived ionic liquids Green Chemistry, 13, 3124–3136 Pu, Y., Jiang, N., & Ragauskas, A J (2007) Ionic Liquid as a green solvent for lignin Journal of Wood Chemistry and Technology, 27, 23–33 Rashid, T., Kait, C F., Regupathi, I., & Murugesan, T (2016) Dissolution of kraft lignin using protic ionic liquid and characterization Industrial Crops and Products, 84, 284–293 Rocha, E G A., Costa, A C., & Aznar, M (2014) Use of protic ionic liquids as biomass pretreatment for lignocellulosic ethanol production Chemical Engineering Transition, 37(397), 402 Ruiz, E., Cara, C., Romero, I., Moya, M., Fernandez-Bolanos, J., & Rodriguez, G (2013) Influence of antioxidant extraction on fermentability of olive biomass hydrolysates Journal of Biotechnology, 150, 144–145 Segal, L., Creely, J J., Martins, A E., Jr., & Anndre Conrad, C M (1959) Empirical method for estimating the degree oficial crystallinity of native cellulose using the XRay diffractometer Textile Research Journal, 29, 786–794 Sharaf, S., Mehrez, E., & Naggar, E (2018) Eco-friendlytechnologyfor preparation, characterization, and promotion of honey bee propolis extract loaded cellulose acetate nanofibers in medical domains Singh, R., Shukla, A., Tiwari, S., & Srivastava, M (2014) A review on delignification of celullosic biomass for enhancement of etanol production potential Renewable and Susteainable Energy Reviews, 32, 713–728 Singh, S., Simmons, B A., & Vogel, K P (2009) Visualization of biomass solubilization and cellulose regeneration during ionic liquid pretreatment of switchgrass Biotechnol and Bioengeenering 104, 68–75 Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templentom, D., et al (2006) National renewable energy laboratory (NREL) 1–14 Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templentom, D., et al (2012) National renewable energy laboratory (NREL) 1–16 Sun, L., Li, C., Xue, Z., Simmons, B A., & Singh, S (2013) Unveiling high-resolution, tissue specific dynamic changes in corn stover duringionic liquid pretreatment RSC Advances, 3, 2017–2027 Sun, N., Rahman, M., Qin, Y., Maxim, M L., Rodríguez, H., & Rogers, R D (2009) Complete dissolution and partial delignification of wood in the ionic liquid 1-ethyl-3methylimidazolium acetate Green Chemistry, 11, 646–655 Swatloski, R P S K., Spear, J D., & Holbrey, R D (2002) Dissolution of cellulose [correction of cellose] with ionic liquids Journal of the American Chemical Society, 124, 4974–4975 Tan, S S Y., MacFarlane, D R., Upfal, J., Edye, L A., Doherty, W O S., Patti, A F., et al (2009) Extraction of lignin from lignocellulose at atmospheric pressure using alkylbenzenesulfonate ionic liquid Green Chemitry, 11, 339–345 Varanasi, P., Singh, P., Arora, R., Adams, P D., Auer, M., Simmons, B., et al (2012) Understanding changes in lignin of Panicum virgatum and Eucalyptus globulus as a function of ionic liquid pretreatment Bioresource Technology, 126, 156–161 Ventura, S P M., de Barros, R L F., Sintra, T., Soares, C M F., Lima, Á S., & Coutinho, J A P (2012) Simple screening method to identify toxic/non-toxic ionic liquids: Agar diffusion test adaptation Ecotoxicology and Environmental Safety, 83, 55–62 Yuan, T Q., Xu, F., & Sun, R C (2013) Characterization of lignin structures and lignin carbohydrate complex (LCC) linkages by quantitative 13C and 2D HSQC NMR spectroscopy Journal of Chemical Technology & Biotechnology, 88, 346–352 Zakrzewska, M E., Bogel-Łukasik, E., & Bogel-Łukasik, R (2010) Solubility of carbohydrates in ionic liquids Energy & Fuels : an American Chemical Society Journal, 24, 737–745 Zhang, J., Wang, Y., Zhang, L., Zhang, R., Liu, G., & Cheng, G (2014) Understanding changes in cellulose crystalline structure of lignocellulosic biomass during ionic liquid pretreatment by XRD Bioresource Technology, 151, 402–405 Declarations of interest None Acknowledgments The authors are grateful financial support from Conselho Nacional de Desenvolvimento Cientớco e Tecnolúgico CNPq, Fundaỗóo de Amparo a Pesquisa e Inovaỗóo Tecnolúgica Estado de Sergipe FAPITEC, and Coordenaỗóo de Aperfeiỗoamento de Pessoal de Nớvel Superior CAPES for the scholarship of R.C.M Miranda and Á S Lima References Achinivu, E C., Howard, R M., Li, G., Gracz, H., & Henderson, W A (2014) Lignin extraction from biomass with protic ionic Green Chemistry, 16, 1114–1119 Alvarez, V H., Mattedi, S., Martin-Pastor, M., Aznar, M., & Iglesias, M (2010) Synthesis and thermophysical properties of two new protic long-chain ionic liquids with the oleate anion Fluid Phase Equilibria, 299, 42–50 Anugwom, I., Eta, V., Virtanen, P., Mäki-Arvela, P., Hedenström, M., Hummel, M., et al (2014) Switchable ionic liquids as delignification solventes for lignocellulosic materials ChemSuschem, 7, 1170–1176 Arora, R., Manisseri, C., Li, C., Ong, M D., Scheller, H V., Vogel, K P., et al (2010) Monitoring and analyzing process streams towards understanding ionic liquid pretreatment of switchgrass (Panicum virgatum L.) Bioenergy Resource, 3, 134–145 Auxenfans, T., Buchoux, S., Larcher, D., Husson, G., Husson, E., & Sarazin, C (2014) Enzymatic saccharification and structural properties of industrial wood sawdust: Recycled ionic liquids pretreatments Energy Conversion and Management, 88, 1094–1113 Brandt, A., Gräsvik, J., Halletta, J P., & Welton, T (2013) Deconstruction of lignocellulosic biomass with ionic liquids Green Chemistry, 1, 550–583 Brandt, A., Ray, M J., To, T Q., Leak, D J., Murphy, R J., & Welton, T (2011) Ionic liquid pretreatment of lignocellulosic biomass with ionic liquid–water mixtures Green Chemistry, 13, 2489–2499 Brígida, A I S., Calado, V M A., Gonỗalves, L R B., & Coelho, M A S (2011) Effect of chemical treatments on properties of green coconut fiber Carbohydrate Polymers, 79, 832–838 Cox, B J., & Ekerdt, J G (2012) Depolymerization of oak wood lignin under mild conditions using the acidic ionic liquid 1-H-3-methylimidazolium chloride as both solvent and catalyst Bioresource Technology, 118, 584–588 Cox, B J., & Ekerdt, J G (2013) Pretreatment of yellow pine in an acidic ionic liquid: Extraction of hemicellulose and lignin to facilitate enzymatic digestion Bioresource Technology, 134, 59–65 Díaz, M J., Cara, C., Ruiz, E., Pérez-Bonilla, M., & Castro, E (2011) Hydrothermal pretreatment and enzymatic hydrolysis of sunflower stalks Fuel, 90, 3225–3229 Enzinne, C A., Reagan, M H., Guoquing, L., Hanna, G., & Wesley, A H (2014) Lignin extration from biomass with protic ionic liquids Green Chemistry, 16, 1114–1119 Fu, D., Mazza, G., & Tamaki, Y (2010) Lignin extraction from straw by ionic liquids and enzymatic hydrolysis of the cellulosic residues Journal of Agriculturs and Food Chemistry, 58, 2915–2922 George, A., Brandt, A., Tran, K., Zahari, S M S N S., Klein-Marcuschamer, D., Sun, N., et al (2015) Design of low-cost ionic liquids for lignocellulosic biomass pretreatment Green Chemistry, 17, 1728–1734 Jia, S., Cox, B J., Guo, X., Zhang, Z C., & Ekerdt, J G (2010) Cleaving the β-O-4 bonds of lignin model compounds in an acidic ionic liquid, 1-H-3-methylimidazolium chloride: An optional strategy for the degradation of lignin ChemSusChem, 3, 1078–1084 Long, J., Li, X., Guo, B., Wang, L., & Zhang, N (2013) Catalytic delignification of sugarcane bagasse in the presence of acidic ionic liquids Catalysis Today, 200, 99–105 308 ... of agave biomass with ionic liquids could be attributed to specific interactions of ionic liquids with biomass factors (cation, anion, temperature, and time), and the extent and degree of recalcitrance... depositing the sample on a gold substrate Table Chemical structure of designed ionic liquid cations and anions 2-hydroxyethylammonium Anion Acetate bis(2-hydroxyethyl)ammonium Propionate N-methyl-2-hydroxyethylammonium... anion The calculated octanol-water partition coefficients (log P values) for the cations are −1.32, −1.57, and −0.88 for ethanolamine, diethanolamine, and methylmonoethanolamine, respectively Considering