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.

Contents lists available atScienceDirect

Carbohydrate Polymers journal homepage:www.elsevier.com/locate/carbpol

ethanolamine and organic acids

Rita de C.M Mirandaa,b, Jaci Vilanova Netaa, Luiz Fernando Romanholo Ferreiraa,c,

Walter Alves Gomes Júniord, Carina Soares do 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

b Uniceuma, Mestrado em Meio Ambiente, Renascença, 65075-120, São Luís, MA, Brazil

c ITP, Instituto de Tecnologia e Pesquisa, Av Murilo Dantas, 300-Prédio do ITP, Farolândia, 49032-490, Aracaju, SE, Brazil

d IFBA, Instituto Federal da Bahia, Campus Salvador, Departamento de Tecnologia em Saúde 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, Federação, 40210-630, Salvador, BA, Brazil

A R T I C L E I N F O

Keywords:

Ionic liquid

Biomass

Pineapple

Lignocellulose

Treatment

A B S T R A C T Pineapplefibre was treated with protic ionic liquids (PILs) and the effects on the structure, composition, and properties of thefibres 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 treatedfibres, promoting exposure of cellulose The results correlated with the crystallinity index, which was greater in the treatedfibres compared with that in the untreated fibres The generated residue from the treatment offibres with PIL (1%, v/v) showed lower levels of toxic compounds, demonstrating the advantages of this treatment over conventional biomass treatments

1 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

pre-treatment and steam explosion), chemical (acid prepre-treatment, 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

ap-propriate 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

pre-ferred, and the most traditionally used is imidazolium acetate due to the

highest solubility of lignin (Zakrzewska, Łukasik, &

Bogel-Łukasik, 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 ofβeOe4 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

https://doi.org/10.1016/j.carbpol.2018.10.112

Received 1 June 2018; Received in revised form 29 October 2018; Accepted 30 October 2018

⁎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)

Available online 31 October 2018

0144-8617/ © 2018 Elsevier Ltd All rights reserved

T

selected ionic liquids are formed by organic acids with small alkyl chain

(acetic, propionic, butyric and pentanoic acid) due to their better

de-lignification capacity; and by amines with different substitutions of the

monoethanolamine hydrogen, producing amines more hydrophilic

(2-hydroxyethyl - diethanolamine) or more hydrophobic (methyl –

me-thyl-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)

2 Material and methods

2.1 Materials

In the present study, 12 PILs were used: 2-hydroxyethylammonium

acetate (2HEAA), hydroxyethylammonium propionate (2HEAPr),

2-hydroxyethylammonium butyrate (2HEAB), 2-2-hydroxyethylammonium

pentanoate (2HEAP), bis(2-hydroxyethyl)ammonium acetate (BHEAA),

bis(2-hydroxyethyl)ammonium propionate (BHEAPr),

bis(2-hydro-xyethyl)ammonium butyrate (BHEAB), bis(2-hydrobis(2-hydro-xyethyl)ammonium

pentanoate (BHEAP), N-methyl-2-hydroxyethylammonium acetate

(m-2HEAA), N-methyl-2-hydroxyethylammonium propionate (m-2HEAPr),

N-methyl-2-hydroxyethylammonium butyrate (m-2HEAB), and

N-me-thyl-2-hydroxyethylammonium pentanoate (m-2HEAP) Their cation

and anion chemical structures are depicted inTable 1

The PILs were synthesized by reacting equimolar amounts of amine

and the respective organic acids, according toAlvarez, Mattedi,

Martin-Pastor, Aznar, and Iglesias (2010) During the course of the

experi-ments, 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

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

2.3 Structural characterization

Amorphous and crystalline regions of the samples were character-ized 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 ac-cording to the empirical model (Eq 1) ofSegal, Creely, Martins, and Anndre Conrad (1959)

I am

(002) ( )

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%

2.4 Ionic liquid treatment The methodology for biomass delignification using PILs was devel-oped 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 1 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 bio-mass was centrifuged to separate the solid (recovered biobio-mass) 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, 5 g of the sample were extracted in two consecutive steps with water and ethanol using 250 mL

of solvent for 2 h After extraction, 300 mg of the samples were hy-drolysed with 3 mL of sulphuric acid at 30 °C for 1 h The reaction mixture was diluted to 4% (by weight) with water and autoclaved at

121 °C for 1 h The liquid was then analysed for its sugar content using ultrafast high-pressure liquid chromatography (UFLC) on a Shimadzu-Prominence 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, 9μm, 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 con-centrations 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 Bio-Rad HPX-87H column at 45 °C The mobile phase was 5 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 spectro-photometry at 280 nm

Total lignin content in the untreated and treated samples was measured by the acetyl bromide method, according toSluiter 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 2 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

Table 1

Chemical structure of designed ionic liquid cations and anions

2-hydroxyethylammonium

Acetate

bis(2-hydroxyethyl)ammonium Propionate

N-methyl-2-hydroxyethylammonium Butyrate

Pentanoate

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 Thefinal

volume adjusted to 2 mL with acetic acid The UV spectra of the

solu-tions 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−1cm−1(standard lignin) according to an established method (Arora

et al., 2010

2.6 Quantification of toxic compounds

Furfural and hydroxymethylfurfural concentrations were analysed

using HPLC equipped with a SPD-M20 A Diode-array detector; the

se-paration was performed using a LiChrospher 100 RP-18 (125 × 4 mm,

5μm) column (Hewlett-Packard), operating at 25 °C, with acetonitrile/

water as an eluent at aflow rate of 0.5 mL min−1

3 Result and discussion

The characterization of pineapplefibres before and after treatment

with protic ionic liquids for delignification is important because the

changes caused by PIL treatment affect the success of potential

appli-cations of PILs for biomass recovery

3.1 Chemical characterization of biomass

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

composi-tions of the untreated and PIL-treated biomass samples are shown in

Table 2

The composition of the lignocellulosic material in the untreated

biomass was 34.6% and 25.4% cellulose and hemicellulose,

respec-tively, and 5.14% total lignin In the untreated biomass, the total lignin

content was significantly lower than the other components of the

lig-nocellulosic portion After treatment with PILs, the quantities of

cel-lulose and hemicelcel-lulose 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 toMohanty, Misra, and Drzal (2001)increases in

cellu-lose and hemicellucellu-lose fractions after treatment results from the

re-moval 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)

ob-served changes in the biomass composition of switchgrass after

treat-ment with PIL 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) Table

H2

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%,

re-spectively This could be explained by the fact that, after treatment with

the ionic liquid, thefibres become more exposed and porous

Brígida, Calado, Gonçalves, and Coelho (2011)treated coconut

fi-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 untreatedfibre 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

morpho-logical 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 inFig 1A–M.Fig 1A shows micrographs of the

untreatedfibres with a preserved structure without pores or pits The

"pits" observed inFigs 1B-M indicate the removal of lignin and

cellu-lose 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

ef-fectiveness of treatments Elongated structures with a fibrous

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 li-quids BHEAA, BHEAPr, BHEAB, and BHEAP Thefibres are well pre-served but show the presence of pits In such treatedfibres, conserved cellulose is observed as rod-shapedfibrous 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 pre-vious treatments, the cellulosefibres do not appear to be preserved, although pits are present Thefibres do not appear to be stretched, and their appearance is not preserved compared with pre-treatment, sug-gesting 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 coconutfibres with sodium hydroxide and observed pits and fibre disorganization.Auxenfans et al (2014) reported a complex fibre organization characterized by a highly fi-brillated morphology in untreated sawdust oak

Treatment with the 12 PILs altered the organization of thefibres 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

Fig 1 Micromorphological aspect of pineapple wastefibre 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)

3.3 Crystal index

The determination of the degree of crystallinity is important to

understand the behaviour of cellulosic materials, because these

mate-rials possess crystalline and amorphous regions Crystallinity

determi-nation 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 inFig 2 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° do 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 inFig 3 The highest CrI was

observed after treatment with the ionic liquid BHEAPr (70%), followed

by the material treated with 2HEAPr (68%) and the ionic liquid BHEAB (66%) According toGeorge 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 byZhang 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 cel-lulosic structure after treatment After treatment of lignocelcel-lulosic 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,

3.4 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 inFig 4 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%, re-spectively) 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 perfor-mances 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 in-terfering with the cellulose content InFig 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, dietha-nolamine, and methylmonoethadietha-nolamine, respectively Considering the entire PIL compound, when thefilaments are under the compound it is more hydrophilic For the larger chains, the hydrophobicity of the alkyl

Fig 2 X-ray diffraction data of untreated biomass, microcrystalline cellulose (MCCa−c), and biomass treated with the protic ionic liquids(d–o)

Fig 3 Crystallinity index of microcrystalline cellulose (MCC), the untreated

biomass, and biomass after protic ionic liquids treatment

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 5shows that 2HEAA had the greatest solubility for

cellulose (5%) According toBrandt et al (2013), lengthening the alkyl

chains of the cation progressively reduces cellulose solubility

The ionic liquid behaviour has been explained byPu, 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- 4

ether bond; while the acidic environment of the IL catalyses the

hy-drolysis 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

hy-drogen-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

cellu-lose 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

de-lignification 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 theβeOe4 bonds of both

guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether

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 andfibre 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 hy-drolysis yield and an increase in the number of alkyl chains increased the yield of enzymatic hydrolysis The performance of the IL diisopro-pylammonium indicated that steric effects do 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 hydro-xymethylfurfural (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 inFig 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%; m-2HEAA - 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 hemi-cellulose decreased as a result of treatment, suggesting the conversion

of carbohydrate monomers to furfurals The production of MF and HMF shown in Fig 5is 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 ex-tract in the cellulose nanofibre was prepared using an environmentally friendly solvent.El-Naggar et al (2018), using microcrystals of cellu-lose 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

4 Conclusion

Treatment of lignocellulosicfibres 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 thisfibre

Fig 4 Cellulose, hemicellulose, and lignin removed from the lignocellulosic material after treatment with the protic ionic liquids

Fig 5 Percentage of intermediate toxic compounds produced during the

treatment of lignocellulosic biomass with protic ionic liquids

when free OH is crucial Small amounts of furfural and

hydro-xymethylfurfural 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

pineapplefibre (crown) to remove lignin using PILs proved effective to

obtaining a support for enzymatic immobilization by preserving the

cellulose Thus the PIL-treatedfibre 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

Declarations of interest

None

Acknowledgments

The authors are gratefulfinancial support from Conselho Nacional

de Desenvolvimento Científico e Tecnológico – CNPq, Fundação de

Amparo a Pesquisa e Inovação Tecnológica do Estado de Sergipe –

FAPITEC, and Coordenação de Aperfeiçoamento de Pessoal de Nível

Superior– CAPES for the scholarship of R.C.M Miranda and Á S Lima

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