Coupling of ionic liquid treatment and membrane filtration for recovery of lignin from lignocellulosic biomass Gayatri Gogoi, Swapnali Hazarika ⇑ Chemical Engineering Group, Engineering Science and Technology Division, CSIR-NEIST, Jorhat 785006, Assam, India Academy of Scientific and Innovative Research, CSIR-NEIST Campus, India article info Article history: Received 28 February 2016 Received in revised form 10 September 2016 Accepted 14 September 2016 Available online 17 September 2016 Keywords: Lignocellulosic biomass Ionic liquid Pretreatment Cellulosel Lignin Membrane abstract The work demonstrates the pretreatment of lignocellulosic biomass (Rice straw) in imidazolium based ionic liquids. Three different imidazolium based ionic liquids, 1-ethyl-3-methyl–imidazolium acetate, 1-methyl-3-octylimidazolium chloride and 1-butyl-3-methyl-imidazolium tetrafluoroborate were used to dissolve the lignocelluloses of rice straw and the dissolution process was optimised under several con- ditions viz. time, temperature and particle size of biomass. The dissolution process was investigated by characterizing the biomass before and after treatment by FTIR, XRD, SEM and Zeta Potential analysis. From the pretreated lignocelluloses, cellulose and lignin were separated using chemical methods. On the basis of investigations, the role of ionic liquids on dissolution of lignocelluloses and effect of different imidazolium based ionic liquids for the regeneration of cellulose and lignin were discussed. After the sep- aration process ionic liquid was recovered using nano filtration membrane and was reused for further study. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Biomass provides alternative and renewable energy resources for sustainable production of organic fuels and chemicals. Further- more lignocellulosic biomass from agricultural residues, forestry wastes, waste paper and crops which is a renewable, relatively carbon-neutral source of energy has come under intense research scrutiny due to its potential use as a starting material for bioprod- ucts from biofuels to specialty chemicals [1–3]. In this study rice straw (Oryza sativa) collected from the North East India, one of the hotspots of biodiversity of the world was considered as the lignocellulosic biomass for processing and recovery of value added product by greener approach. Various pretreatment options are defined in literature such as dilute acid, concentrated acid, and organosolvent pretreatment. However this study emphasizes the potential of certain ionic liquids as pretreatment solvents for ligno- cellulosic biomass. Lignocellulosic biomass contains 30–50% cellulose, a glucose polymer; 10–40% hemicelluloses, a sugar heteropolymer and 5–30% lignin, a non-fermentable phenyl propene unit plus lesser amounts of minerals, oils, soluble sugars, and other components [4,5]. The dense network of intramolecular/intermolecular hydrogen bonds in cellulose, branched hetero polysaccharides of hemicelluloses with shorter chain lengths and three dimensional amorphous lignin provides a complex network in lignocellulosic biomass [6–8]. Because of this, new and efficient solvents and process technologies are needed to break the complex network of lignocellulosic biomass. Ionic liquid serves as a new class of designer solvents that can dissolve a large number of biomacro- molecules such as cellulose, lignin, silk fibroin, and starch with high efficiency [9–11]. As an environment friendly material, the applications of ionic liquids have been extensively reported as solvent to facilitate green applications in reactions and separations due to their unique ben- eficial properties usually negligible vapour pressure, low flamma- bility, high thermal stability over a wide range of temperatures and tuneable properties such as hydrophobicity, polarity and sol- vent power [12–16]. Due to the IL’s solvent power, their use in the development of alternative methods for the extraction and pro- cessing of carbohydrates and other compounds from lignocellu- losic biomass was recently explored intensively [17,18]. In this study pretreatment of lignocellulosic biomass with ionic liquid was carried out to alter the structure of lignocellulosic biomass by breaking the lignin seal and disrupting the crystalline structure of cellulose. A typical deconstruction sequence for lignocelluloses is: size reduction to chips and pretreatment that solubilises the http://dx.doi.org/10.1016/j.seppur.2016.09.019 1383-5866/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Chemical Engineering Group, Engineering Science and Technology Division, CSIR-NEIST, Jorhat 785006, Assam, India. E-mail address: [email protected](S. Hazarika). Separation and Purification Technology 173 (2017) 113–120 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Transcript
Separation and Purification Technology 173 (2017) 113–120
The work demonstrates the pretreatment of lignocellulosic biomass (Rice straw) in imidazolium basedionic liquids. Three different imidazolium based ionic liquids, 1-ethyl-3-methyl–imidazolium acetate,1-methyl-3-octylimidazolium chloride and 1-butyl-3-methyl-imidazolium tetrafluoroborate were usedto dissolve the lignocelluloses of rice straw and the dissolution process was optimised under several con-ditions viz. time, temperature and particle size of biomass. The dissolution process was investigated bycharacterizing the biomass before and after treatment by FTIR, XRD, SEM and Zeta Potential analysis.From the pretreated lignocelluloses, cellulose and lignin were separated using chemical methods. Onthe basis of investigations, the role of ionic liquids on dissolution of lignocelluloses and effect of differentimidazolium based ionic liquids for the regeneration of cellulose and lignin were discussed. After the sep-aration process ionic liquid was recovered using nano filtration membrane and was reused for furtherstudy.
� 2016 Elsevier B.V. All rights reserved.
1. Introduction
Biomass provides alternative and renewable energy resourcesfor sustainable production of organic fuels and chemicals. Further-more lignocellulosic biomass from agricultural residues, forestrywastes, waste paper and crops which is a renewable, relativelycarbon-neutral source of energy has come under intense researchscrutiny due to its potential use as a starting material for bioprod-ucts from biofuels to specialty chemicals [1–3]. In this study ricestraw (Oryza sativa) collected from the North East India, one ofthe hotspots of biodiversity of the world was considered as thelignocellulosic biomass for processing and recovery of value addedproduct by greener approach. Various pretreatment options aredefined in literature such as dilute acid, concentrated acid, andorganosolvent pretreatment. However this study emphasizes thepotential of certain ionic liquids as pretreatment solvents for ligno-cellulosic biomass.
Lignocellulosic biomass contains �30–50% cellulose, a glucosepolymer; 10–40% hemicelluloses, a sugar heteropolymer and�5–30% lignin, a non-fermentable phenyl propene unit plus lesseramounts of minerals, oils, soluble sugars, and other components
[4,5]. The dense network of intramolecular/intermolecularhydrogen bonds in cellulose, branched hetero polysaccharides ofhemicelluloses with shorter chain lengths and three dimensionalamorphous lignin provides a complex network in lignocellulosicbiomass [6–8]. Because of this, new and efficient solvents andprocess technologies are needed to break the complex network oflignocellulosic biomass. Ionic liquid serves as a new class ofdesigner solvents that can dissolve a large number of biomacro-molecules such as cellulose, lignin, silk fibroin, and starch withhigh efficiency [9–11].
As an environment friendly material, the applications of ionicliquids have been extensively reported as solvent to facilitate greenapplications in reactions and separations due to their unique ben-eficial properties usually negligible vapour pressure, low flamma-bility, high thermal stability over a wide range of temperaturesand tuneable properties such as hydrophobicity, polarity and sol-vent power [12–16]. Due to the IL’s solvent power, their use inthe development of alternative methods for the extraction and pro-cessing of carbohydrates and other compounds from lignocellu-losic biomass was recently explored intensively [17,18]. In thisstudy pretreatment of lignocellulosic biomass with ionic liquidwas carried out to alter the structure of lignocellulosic biomassby breaking the lignin seal and disrupting the crystalline structureof cellulose. A typical deconstruction sequence for lignocellulosesis: size reduction to chips and pretreatment that solubilises the
Fig. 1. Schematic representation of the pre-treatment of biomass using ILs andfurther regeneration and fractionation into cellulose, hemicelluloses and lignin.
114 G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120
hemicelluloses and alters/removes lignin and cellulose [19]. Togain a greater insight into ionic liquid pretreatment, the effect ofionic liquids with different anionic groups on the structuralchanges of rice straw was investigated. Various ionic liquids suchas 1-methyl-3-octyl imidazolium chloride, 1-ethyl-3-methyl-imidazolium acetate, 1-butyl-3-methyl-imidazolium tetrafluorob-orate have been applied as solvents in pretreatment step.
Since ionic liquids are very expensive than the conventional sol-vents hence recycling and reuse of the ionic liquids is a crucial fac-tor for the economic efficiency of the extraction process. Thus inour study recovery of ionic liquids has been studied using nano fil-tration membrane.
2. Experimental
2.1. Materials
The lignocellulosic feedstock used in this study was rice straw(Oryza Sativa) collected from the Jorhat district of Assam, India.The biomass was washed, air-dried and then finely groundedwith a grinder and sieved (150 lm, 300 lm, 450 lm) beforeuse. The prepared grounded rice straw samples were then storedin plastic bags at room temperature. The ionic liquids 1-methyl-3-octylimidazolium chloride, 1-ethyl-3-methylimidazolium acetateand 1-butyl-3-methyl imidazolium tertrafluoroborate werepurchased from Sigma-Aldrich (USA) and were used withoutfurther purification. The standard lignin was purchased fromTCI, Japan. The commercial polyamide thin film compositemembranes (FilmTec NF 270-400) viable for operation at pH3–10 and temperature up to 45 �C were used for the recoveryof ionic liquids.
2.2. Dissolution of rice straw
0.2 g of the rice straw was taken for each experiment and 5 mLionic liquid was added to each sample and stirred using a homog-enizer with a constant speed of 400 rpm at different temperatures.The samples were collected every one hour interval of time and fil-tered and analysed by UV visible spectrophotometer. The UVabsorption peak for lignin was noted at 280 nm. After dissolutionof the biomass in ionic liquid percentage of biomass dissolvedwas calculated according to the equation:
Diss ¼ 1�Mund
Mo
� �� 100
where Mund ?Mass of undissolved residue recovered.Mo?Mass of original biomass.Diss? Dissolution %.
2.3. Lignocellulose recovery
Once the lignocellulose has been pretreated, it needs to berecovered and further processed. The first step is to separatethe three major components-cellulose, hemicelluloses and lignin.Two prominent stages appear in separating the components.Firstly cellulose is precipitated by adding an organic solvent(acetone)-water mixture (1:1). As the cellulose is precipitatedthe lignin remains in the solution. After evaporating off theorganic solvent lignin can be recovered. Since acidificationreduces the basicity of the ionic liquids which in turn lowersthe lignin solubility, thus 0.1 N H2SO4 was added to the lignincontaining IL solution to increase the amount of lignin recovery[20,11,15]. The typical process for the separation of lignocellu-loses with ionic liquids is represented schematically as shownin Fig. 1.
2.4. Recovery and recycle of ionic liquid
Due to high cost of ionic liquid it is important to recover theused IL from its aqueous mixture after recovery of lignin. Nano fil-tration, a pressure driven membrane process was carried out forrecovery of ionic liquid in a standard experimental set up asdescribed in our published work [21] in which a two compartmentmembrane cell was used for the study. Volume of each compart-ment of the cell was 150 mL. The commercial polyamide thin filmcomposite membrane was placed between the compartments withsilicone-rubber packing and the cell was connected with a reser-voir of 500 mL. The solution of dissolved lignocelluloses in ionicliquid was stirred continuously and circulated by peristaltic pumpthat was connected to the reservoir applying a pressure 5 bar andflow rate 20 mL/min. Permeate flux was calculated by using theequation given as,
J ¼ VDCADt
where V is the volume of permeate at time t, DC is the concentra-tion variation in the corresponding aqueous solution at the timeinterval Dt, A is the area of the membrane. Rejection of the mem-brane is given as,
R% ¼ Cf � Cp
Cf� 100
where Cf is the concentration in feed and Cp is the concentration inpermeate.
2.5. Analytical methods
Samples were analysed by UV–Visible Spectrophotometer(Thermo Scientific, EVOLUTION 201), IR (PERKIN Elmer System2000), XRD (JDX-11P-3A, JEOL, Japan), surface morphology wasstudied by a scanning electron microscope (LEO 1427VP, UK), zetapotential and isoelectric point were determined by ElectrokineticAnalyzer [Anton-Paar SurPASS].
3. Results and discussion
3.1. Dissolution of lignocelluloses
After ten hours of ionic liquid treatment the lignocelluloses con-tent is high in the solution as is evident from the change in colour
Fig. 2. Photographs showing the colour intensity of the ionic liquid [EMIM]OAc and the ionic liquid treated rice straw after a successive interval of 1 h for 10 h.
Fig. 3. Chemical structures of the ionic liquids.
G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120 115
of ionic liquid shown in Fig. 2 which is a qualitative study. Disso-lution of lignocelluloses in ionic liquid are known to be dependenton the ionic liquid, as well as on several conditions inherent to pre-treatment, such as temperature, time, and particle size of biomass.Major effects of these parameters in the biomass pretreatment aredescribed in the following sections, which contribute for a betterunderstanding of pretreatment of lignocellulosic biomass withionic liquids.
3.2. Influence of IL ions in the biomass dissolution
Because of the complex matrix of lignocelluloses, new andefficient solvents and process technologies are needed for dissolu-tion and further separation of lignoclluloses. Several studies shownthat imidazolium based ionic liquids could effectively dissolvelignocellulosic components [14,22]. Theoretical modelling hasshown that cations based on imidazole are particularly well suitedfor dissolving lignin since the cation can favourably interact witharomatic phenyl rings of lignin [23]. In our study, three imida-zolium based ionic liquids viz. 1-butyl-3-methyl-imidazoliumtetrafluoroborate, 1-ethyl-3-methyl–imidazolium acetate,1-methyl-3-octylimidazolium chloride shown in Fig. 3 are usedfor dissolution of rice straw at atmospheric pressure and elevatedtemperature (50–150 �C). On treating the rice straw with 1-butyl-3-methyl-imidazolium tetrafluoroborate at temperature range of50–150 �C, no significant change in dissolution was observed.However the chloride and acetate based ionic liquid (1-ethyl-3-methyl–imidazolium acetate, 1-methyl-3-octylimidazolium chlo-ride) resulted a significant dissolution as is evident from thechange in colour intensity shown in Fig. 2. It has been shown thathydrogen bond basicity of the anion of the ionic liquid plays crucialrole in dissolving lignocelluloses.
The viscosity and the melting point of ILs also play an importantrole in the dissolution of lignocelluloses because it can effect themixing and mass transfer of lignocelluloses and IL itself. Studiesshowed that the low viscosity ILs undergoes for rapid extractionof cellulose and other carbohydrates due to the higher mobility
of the ions [11,15]. However, in our case, among the three ILs, acet-ate based ionic liquids with medium viscosity shows good abilityfor pretreatment of lignocelluloses. This observation perhapsexplained from the lowest melting point of the acetate based IL(>30�) whereas other ILs have melting point range from 285 to402 �C as shown in the Table 1. This is due to the reason that ILhaving low melting point facilitates the better dissolution ofbiomass.
The effect of selected ionic liquids on the dissolution of ricestraw and subsequent regeneration of cellulose and precipitation
Table 1Properties of ionic liquids.
IL Melting point Viscosity Molecular weight Density Flash point Partition coefficient Refractive index
116 G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120
of lignin was investigated and it was concluded that among theseionic liquids, 1-ethyl-3-methyl–imidazolium acetate is more effi-cient for dissolution of lignin than the others.
3.3. Cellulose regeneration and recovery of lignin
From the study the amount of cellulose regenerated on dissolu-tion with the ionic liquids were found to be 29%, 34% and 46%respectively from 1-butyl-3-methyl-imidazolium tetrafluorobo-rate, 1-methyl-3-octylimidazolium chloride and 1-ethyl-3-methyl–imidazolium acetate. Thus 1-ethyl-3-methyl–imidazolium acet-ate serves as the efficient solvent for the pretreatment of the ligno-celluloses. Dissolution mechanism of cellulose in ILs is based onthe capability of anions of ILs to effectively break the extensiveintra- and inter-molecular hydrogen bonding network in cellulose.Dissolution of rice straw is influenced by the interaction betweenanion of the ionic liquid and hydroxyl group of the cellulose [24–26]. Anion of the ionic liquid acts as the hydrogen bond acceptorin dissolution where it interacts specifically with the hydroxyl pro-tons of the cellulosic materials and facilitates the formation ofhydrogen bonds between cellulose and ionic liquid [27,28]. Ionicliquids with a strong hydrogen bond basicity are effective in weak-ening the hydrogen-bonding network of the polymer chains.Among the three selected ionic liquids, the acetate based IL hashigher hydrogen bond basicity due to which [EMIM]OAc is moreeffective for cellulose dissolution. Fig. 4 shows one of the proposedmechanism of cellulose dissolution in ionic liquids [29,30].
After dissolution process, the reaction mixture was appeareddark brown in colour which is imparted by the dissolved ligninof the lignocellulosic matrix [9,11,24]. As with dissolution of cellu-lose, imidazolium cations of the ILs also plays role in the dissolu-tion of lignin due to the g-g interactions between the cations andthe aromatic rings (polyphenolic structure) of lignin [23,31]. Onthe basis of the results from the screening experiments, weselected IL [EMIM]OAc for the extraction of lignin from rice straw.Lignin extractability of the IL was recorded by UV absorption cali-brated at 280 nm. The lignin extracted during pretreatment withionic liquid was recovered by acid precipitation and was found tobe 43%. Among the three selected ionic liquids 1-ethyl-3-methyl–imidazolium acetate was found to be more efficient for extractionand recovery of lignin from the rice straw.
3.4. Temperature effect
The dissolution kinetics of rice straw in IL was studied over awide range of temperatures (50–150 �C) which is shown in Fig. 5
Cellulose
OH+ [EMIM]+OAc
O
H
[EMIM]+
AcO- O [EMIM]+
H
-OAc
Cellulose
Cellulose
OH
HO
Cellulose
Fig. 4. Dissolution mechanism of cellulose in 1-ethyl-3-methyl imidazoliumacetate.
(a). The increase of temperature accelerates swelling and dissolu-tion rates of lignocelluloses in ionic liquids which is due to desta-bilisation effect of temperature on the hydrogen bonds in thestructure of cellulose and lignin [32,33]. On decreasing tempera-ture longer times are required for an efficient swelling and dissolu-tion of lignocelluloses.
3.5. Reaction time effect
To investigate the effect of reaction time on dissolution, bio-mass (rice straw) dissolution at 150 �C was conducted for five dif-ferent residence times viz. 4 h, 6 h, 8 h, 10 h and 12 h and theextent of dissolution of the biomass was measured for each timewhich is shown in Fig. 5(b). Long pre-treatment times werereported to favour lignin extraction. As the pretreatment timeincreases the diffusion of ionic liquid into the biomass is improvedand increases the dissolution and extraction of lignin from biomass[20].
3.6. Particle size of biomass
Particle size is one of the crucial factor which directly impactson the contact and diffusion of ionic liquid into the lignocellulosicmaterial and thus the solubilisation of lignocellulosic biomass. Itwas found that the solubility of finely milled biomass is higherthan that of coarser material. Thus smaller the particle size of thebiomass the greater is the solubilisation of lignocellulosic biomassas shown in Fig. 5(c).
3.7. Structural characterization
3.7.1. FT-IRIn order to see the effects of ionic liquid pretreatment, studies
on the chemical and structural characteristics of the ionic liquidtreated rice straw and untreated rice straw are essential. Ionicliquid treated rice straws have altered chemical and structuralcharacteristics compared to the untreated rice straw. Table 2gives the group frequencies of absorbtion bands assigned withthe lignocellulosic components. The changes in the structuralcharacteristics of the untreated rice straw and the celluloseregenerated from the different ionic liquids can be observedfrom the FTIR spectra as shown in Fig. 6. The untreated ricestraw gives characteristic absorbances at 800–950 cm�1,1035 cm�1, 1368 cm�1, 1457 cm�1, 1638 cm�1, 2913 cm�1,3000–4000 cm�1 that are assigned with characteristic groups oflignocellulosic components as shown in Table 2. IR spectra ofall the regenerated cellulose from the three ionic liquids givesabsorbances at 800 cm�1, 1040 cm�1, 1368 cm�1, 1638 cm�1,2913 cm�1 and 3000–4000 cm�1 indicating assignments withCAH deformation, CAO asymmetric stretching vibration in cellu-lose, hemicelluloses and aryl group of lignin, symmetric CAHbending in cellulose and CAH stretching in cellulose respectively.On comparing the characteristics of the IR spectra of untreatedrice straw and the regenerated celluloses of different IL treatedrice straw it has been established that cellulose regeneratedfrom [EMIM]OAc treated rice straw gives more intensed absor-bance peaks at the assigned bands compared to the other twoILs which indicates the highest dissolution and regeneration of
(b)(a)
(c)
20 40 60 80 100 120 140 1600
20
40
60
80
100
Temperature (°C)
% D
isso
lved
bio
mss
0 2 4 6 8 10 12 140
20
40
60
80
% D
isso
lved
bio
mas
s
Time (hr)
0 100 200 300 400 50020
40
60
80
100
% D
isso
lved
bio
mas
s
Particle size (micron)
Fig. 5. Effect of (a) temperature, (b) time and (c) particle size of biomass on the dissolution of rice straw with ionic liquid [EMIM]OAc.
Table 2Group frequencies of absorption bands of lignocellulosic rice straw.
Group frequency(wavenumber, cm�1)
Origin Assignment
800–950 CAH CAH deformation�1035 CAO CAO asymmetric stretching vibration in
cellulose, hemicelluloses and aryl OH groupof lignin
�1368 CAH Symmetric CAH bending in cellulose�1457 CAH Asymmetric bending of CH3 and methoxy
(AOCH3) groups present in lignin�1509 C@C Vibration in aromatic ring of lignin�1638 OAH OAH bending vibration of adsorbed water
molecule�1733 C@O Stretching vibration in acetyl group of
hemicelluloses�2913 CAH CAH stretching in cellulose rich material2995–4000 OAH Free and hydrogen bonded OAH stretching
Fig. 6. FTIR spectra of (a) untreated rice straw and cellulose regenerated from theionic liquids, (b) [EMIM]OAc, (c) [BMIM]TFB, and (d) [MOIM]Cl.
G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120 117
cellulose in [EMIM]OAc. The IR spectra of the lignin extractedfrom IL [EMIM]OAc treated rice straw and the commercial ligninshows a quite resemblance in their structural characteristics asshown in Fig. 7. Both the spectra gives characteristic absorbanceat 1035 cm�1 which gives the assignment for aryl OH group oflignin while absorbance at 1457 cm�1 assigns the asymmetricbending of CH3 and AOCH3 groups present in lignin. A sharpabsorbance peak at 1510 cm�1 shows the C@C vibration in thearomatic ring of lignin and a broad peak at 3450 cm�1 assignsthe free and hydrogen bonded OAH stretching in lignin. ThusFTIR spectra of the lignin extracted from the [EMIM]OAc treatedrice straw interpretates the higher dissolution capacity of theionic liquid for the extraction of lignin from the rice straw. Thissuggest that [EMIM]OAc effectively dissolves both cellulose andlignin of the biomass.
3.7.2. XRD characterizationThe crystallinity of the rice straw was analysed by XRD by
determining the crystallinity index. The crystallinity index is themeasure of the relative degree of crystallinity which can be deter-mined by XRD using relationship,
CrI ¼ Icr � IamIcr
� 100
where Icr is the maximum intensity of crystalline region and Iam isthe maximum intensity of the amorphous region. As shown in
4000 3500 3000 2500 2000 1500 1000 500
10
20
30
40
50
Wavenumber (cm-1)
(a) Extracted lignin (b) Commercial lignin
(a)
(b)
%T
Fig. 7. FTIR spectra of (a) recovered lignin and (b) commercial lignin.
1-Ethyl-3-methyl imidazolium acetate based regeneratedcellulose
14
118 G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120
Fig. 8 occurrence of a sharper peak at 2h = 24.5� gives lower crys-tallinity of the regenerated cellulose after treatment with ionic liq-uid compared with the untreated rice straw. The lower crystallinityindex of the regenerated cellulose is due to the presence of higheramount of amorphous cellulose.
From Table 3 it was observed that the crystallinity index of theregenerated cellulose of 1-ethyl-3-methyl imidazolium acetatetreated rice straw was lowest (14%) followed by 1-butyl-3-methyl-imidazolium tetrafluoro borate and 1-methyl-3-octyl imi-dazolium chloride (29.8% and 31.45% respectively). A significantdifference in the crystallinity index of the regenerated celluloseon treatment with different IL shows the different ability of theILs to dissolve the cellulose. The acetate based IL disrupts the cel-lulose crystallinity of the rice straw more effectively.
Fig. 9. SEM images of (a) untreated rice straw and rice straw after treating with (b) 1-ethyl-3-methyl-imidazolium acetate, (c) 1-methyl-3-octyl imidazolium chloride, and (d)1-butyl-3-methyl-imidazolium tetrafluoroborate.
-4 -2 0 2 4 6-60-50-40-30-20-10
0102030405060
Zeta
pot
entia
l (m
V)
pH-4 -2 0 2 4 6
-60-50-40-30-20-10
0102030405060
Zet
a po
tent
ial (
mV
)
pH
(a) (b)
Fig. 10. pH dependence of zeta potential for (a) rice straw; (b) IL treated rice straw.
G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120 119
3.7.3. SEM analysisThe SEM analysis of biomass before and after treatment demon-
strates that surface structure disruption of the rice straw occurs onpretreatment with ionic liquids as shown in Fig. 9 which shows thesignificant changes in the morphology of biomass after treatmentwith ionic liquids. The untreated rice straw shows an even andsmooth surface while the morphology of the rice straw after treat-ment shows a disordered and a loose surface. The disruption of thepretreated rice straw is due to the swelling of the lignocellulosicmatrix caused by the solvating action of liquid [20].
porous structures with high swelling propensity. Fig. 10(a) and (b) shows the pH dependence of the apparent zeta potentialfor rice straw before and after IL treatment. The isoelectric point,where zeta potential is zero, for untreated rice straw and IL treatedrice straw corresponds to pH 1.11 and 2.001 which indicates thedifferent surface chemistry of treated and untreated lignocellulosicbiomass. The negative zeta potential at a higher pH reflects theenhanced swelling capacity of the IL treated rice straw thatincreases the accessability of functional groups located at the innersurface of the biomass [34].
3.7.5. Recovery of ionic liquid by nano filtrationAfter separation of cellulose and lignin from the ionic liquid
treated lignocellulosic mixture, ionic liquid is recovered from themixture using nano filtration membrane. Fig. 11 shows the time
Fig. 11. Plot of time versus flux and % rejection of nano filtration of ionic liquid.
versus flux and % rejection plot from which it is observed thatabout 95% rejection of IL is recovered using NF membrane.
4. Conclusion
From this study it has been demonstrated that ionic liquid canbe used for the pretreatment of lignocellulosic biomass for theextraction and separation of the lignocellulosic components.Hydrogen bonding and P-P interactions between the complexstructure of the lignocelluloses and IL effectively plays role in thedissolution process. Among the three selected ionic liquids 1-Butyl-3-Methyl-imidazolium tetrafluoroborate, 1-Ethyl-3-Methyl–imidazolium acetate and 1-Methyl-3-Octylimidazolium chloride,1-Ethyl-3-Methyl–imidazolium acetate serves as the best solventdue to its certain physicochemical properties such as lower viscos-ity and melting point and higher hydrogen bonding basicity. Ligninwas recovered by chemical method and after its recovery IL wasrecovered by using nano filtration membrane.
Acknowledgement
Authors acknowledge CSIR New Delhi for financial support andDirector, CSIR NEIST for his keen interest on this work.
References
[1] J.H. Clark, Green chemistry for the second generation biorefinery sustainablechemical manufacturing based on biomass, J. Chem. Technol. Biotechnol. 82(2007) 603–609.
[2] Y.H.P. Zhang, Reviving the carbohydrate economy via multiproductlignocellulose biorefineries, J. Ind. Microbiol. Biotechnol. 35 (2008) 367–375.
[3] A.J. Ragauskas, C.K. William, B.H. Davisonm, G. Britovsek, J. Cairney, C.A. EckertJr., W.J. Frederick, J.P. Hallett, D.J. Leak, C.L. Liotta, J.R. Mielenz, R. Murphy, R.Templer, T. Tschaplinski, The path forward for biofuels and biomaterials,Science 311 (2006) 484–489.
[4] P. McKendry, Energy production from biomass (part1): overview of biomass,Bioresour. Technol. 83 (2002) 37–46.
[6] A. Brandt, J. Grasvik, J.P. Hallett, T. Welton, Deconstruction of lignocellulosicbiomass with ionic liquids, Green Chem. 15 (2013) 550–583.
[7] C. Mai, U. Kues, H. Militz, Biotechnology in the wood industry, Appl. Microbiol.Biotechnol. 63 (2004) 477–494.
[8] D.N.S. Hon, N. Shiraishi, Wood and Cellulosic Chemistry, second ed., M. DekkarInc., New York, 1991, p. 1020.
[9] Q. Li, Y.C. He, M. Xian, G. Jun, X. Xu, J.M. Yang, L.Z. Li, Improving enzymatichydrolysis of wheat straw using ionic liquid 1-ethyl-3-methyl imidazoliumdiethyl phosphate pretreatment, Bioresour. Technol. 100 (2009) 3570–3575.
[10] R. Arora, C. Manisseri, C. Li, Markus D. Ong, H.V. Scheller, K. Vogel, B.A.Simmons, S. Singh, Monitoring and analyzing process streams towardsunderstanding ionic liquid pretreatment of switchgrass (Panicum virgatumL.), Bioenergy Resor. 3 (2010) 134–145.
120 G. Gogoi, S. Hazarika / Separation and Purification Technology 173 (2017) 113–120
[11] N. Sun, M. Rahman, Y. Qin, M.L. Maxim, H. Rodriguez, R.D. Rogers, Completedissolution and partial delignification of wood in the ionic liquid 1-ethyl-3-methylimidazolium acetate, Green Chem. 11 (2009) 646–655.
[13] S.H. Lee, T.V. Doherty, R.J. Linhardt, J.S. Dordick, Ionic liquid mediated selectiveextraction of lignin from wood leading to enhanced enzymatic cellulosehydrolysis, Biotechnol. Bioeng. 102 (2009) 1368–1376.
[14] H. Zhang, J. Wu, J. Zhang, J.S. He, 1-Allyl-3-methylimidazolium chloride roomtemperature ionic liquid: a new and powerful non-derivatizing solvent for thecellulose, Macromolecules 38 (2005) 8272–8277.
[15] D.A. Fort, R.C. Remsing, R.P. Swatloski, P. Moyna, G. Moyna, R.D. Rogers, Canionic liquids dissolve wood? Processing and analysis of lignocellulosicmaterials with 1-n-butyl-3-methylimidazolium chloride, Green Chem. 9(2007) 63–69.
[16] H. Olivier-Bourbigou, L. Magna, D. Morvan, Ionic liquids and catalysis: recentprogress from knowledge to applications, Appl. Catal. A 373 (2010) 1–56.
[17] A. Pinkert, K.N. Marsh, S.S. Pong, M.P. Staiger, Ionic liquids and their interactionwith cellulose, Chem. Rev. 109 (2009) 6712–6728.
[18] S.A. Forsyth, J.M. Pringle, D.R. Mac Farlane, Ionic liquids- an overview, Aust. J.Chem. 57 (2004) 113–119.
[19] N. Mosier, C. Wyman, B. Dale, R. Elander, Y.Y. Lee, M. Holtzapple, M. Ladisch,Bioresour. Technol. 96 (2005) 673–686.
[20] A. Brandt, J.P. Hallett, D.J. Leak, R.J. Murphy, T. Welton, The effect of the ionicliquid anion in the pretreatment of pine wood chips, Green Chem. 12 (2010)672–679.
[21] S. Hazarika, N.N. Dutta, P.G. Rao, Dissolution of lignocelluloses in ionic liquidsand its recovery by nanofiltration membrane, Sep. Purif. Technol. 97 (2012)123–129.
[22] J. Vitz, T. Erdmenger, C. Haensch, U.S. Schubert, Extended dissolution studies ofcellulose in imidazolium based ionic liquids, Green Chem. 11 (2009) 417–424.
[23] B.G. Janesko, Modelling interactions between lignocellulose and ionic liquidsusing DFT-D, Phys. Chem. Chem. Phys. 13 (2011) 11393–11401.
[24] H. Zhao, C.L. Jones, G.A. Baker, S. Xia, O. Olubajo, V.N. Person, Regeneratingcellulose from ionic liquids for an accelerated enzymatic hydrolysis, J.Biotechnol. 139 (2009) 47–54.
[25] A.P. Dadi, S. Varanasi, C.A. Schall, Enhancement of cellulose saccharificationkinetics using an ionic liquid pretreatment step, Biotechnol. Bioeng. 95 (2006)904–910.
[26] B. Kosan, C. Michels, F. Meister, Dissolution and forming of cellulose with ionicliquids, Cellulose 15 (2008) 59–66.
[27] S.H. Ha, N.L. Mai, G. An, Y.M. Koo, Microwave assisted pretreatment ofcellulose in ionic liquid for accelerated enzymatic hydrolysis, Bioresour.Technol. 102 (2011) 1214–1219.
[28] R.C. Remsing, R.P. Swatloski, R.D. Rogers, G. Moyna, Mechanism of cellulosedissolution in the ionic liquid 1-n-butyl-3-methylimidazolium chloride: a C13and Cl35/37 NMR relaxation study on model systems, Chem. Commun. 12(2006) 1271–1273.
[29] L. Feng, Z.I. Chen, Research progress on dissolution and functional modificationof cellulose in ionic liquids, J. Molec. Liq. 142 (2008) 1–5.
[31] I. Kilpelainen, H. Xie, A. King, M. Granstrom, S. Heikkinen, D.S. Argyropoulos,Dissolution of wood in ionic liquids, J. Agri. Food Chem. 55 (2007) 9142–9148.
[32] M. Zavrel, D. Bross, M. Funke, J. Buchs, A.C. Spiess, High-throughput screeningfor ionic liquids dissolving (ligno-) cellulose, Bioresour. Technol. 100 (2009)2580–2587.
[33] X. Wang, H. Li, Y. Cao, Q. Tang, Cellulose extraction from wood chip in an ionicliquid 1-allyl-3-methylimidazolium chloride (AmimCl), Bioresour. Technol.102 (2011) 7959–7965.
[34] A. Baltazar-Y-Jimenez, A. Bismarck, Surface modification of lignocellulosicfibres in atmospheric air pressure plasma, Green Chem. 9 (2007) 1057–1066.
