Effect of Ionic Liquid Treatment on Pyrolysis Products from Bamboo

Article pubs.acs.org/IECR

Effect of Ionic Liquid Treatment on Pyrolysis Products from Bamboo Nawshad Muhammad,†,* Wissam N. Omar,‡ Zakaria Man,† Mohamad Azmi Bustam,† Sikander Rafiq,† and Yoshimitsu Uemura‡ †

PETRONAS Ionic Liquid Centre and ‡Biofuel Center, Department of Chemical Engineering, Universiti Teknologi PETRONAS, Malaysia ABSTRACT: In the present work 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-butyl-3-methylimidazolium acetate (BmimOAc) ionic liquids have been used for the dissolution of bamboo biomass. After dissolution the treated samples were precipitated by using water. The calorific value, CHNS content, lignin content, and proximate analysis of the untreated and precipitated material were measured. The BmimCl treated sample was found to have a higher value for calorific value, elemental percentage of carbon, and lignin content as well as fixed carbon, compared to the untreated and BmimOAc treated samples. The untreated and ionic liquid treated samples were also characterized by TGA and XRD. Low thermal stability and change in crystalline form from cellulose Type I to Type II have been observed by the dissolution and precipitation treatment. Pyrolysis− gas chromatography/mass spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of the untreated and ionic liquid treated samples of bamboo. The desirable products with respect to bio-oil, such as phenols, furans, alcohols, hydrocarbons, and aromatics are increased, while the undesirable products such as aldehydes and ketones, except for total acids, are decreased for the BmimCl treated sample.

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INTRODUCTION Biomass is the total quantity of plants and animals in a particular area.1 It includes crops, forestry ,and marine products along with organic wastes such as municipal solid waste, sewage, and pulp derived black liquor. It is one of the renewable resources and contributes about 12% of today’s world energy supply.2 Wooden based biomass mainly consists of cellulose, lignin, and hemicelluloses. Cellulose, the main part of wood, constitutes 45−50% wood substance by weight. Hemicelluloses constitute 15−25% of softwood and 15−30% of hardwood by weight. Hemicelluloses of hardwoods and softwoods consist mainly of xylans and glucomannans, respectively. Lignin constitutes 23−33% in softwood and 16−25% in hardwoods. Lignin has an irregular structure and is composed of randomly cross-linked phenylpropanoid units.3,4 In these components of wooden biomass, each one of them was either pyrolyzed or degraded at different rates and by different mechanisms.2,5 The conversion of biomass into other valuable chemicals mainly could be done in two ways: biological (fermentation and anaerobic digestion) and thermochemical (combustion, gasification, and pyrolysis). Pyrolysis is considered to be an emerging technology among the various thermochemical processes for conversion of biomass into liquid oil.6 Fast pyrolysis of biomass is a thermochemical conversion process that occurs in a moderate temperature range from 400 to 600 °C to produce dark brown liquid called bio-oil, decomposed solid called char, and noncondensable gases. Bio-oil recovery from biomass using a fast pyrolysis process is relatively high as compared to other types of treatments as reported in the literature.7 However, the quality of the bio-oil is very poor, whereas it has a very high oxygen content up to 50 wt % and high percentages of acids with pH around 2−3 and aldehydes which make it a very corrosive and unstable liquid fuel.8−10 Table 1 shows the difference in selected properties between a typical bio-oil from © 2012 American Chemical Society

Table 1. Comparison between Physical and Chemical Properties of Bio-Oil and Heavy Fuel Oil11,12 properties

bio-oil

moisture content % elemental analysis C% H% O% N% Ash % calorific value, MJ/kg specific gravity viscosity @ 40 °C (cp) flash point °C

25−40

heavy fuel oil 0.1

55−60 6.2 37.3 0.1 0.1 17−22 1.2 30−100 54

85.8 11 0.4 0.15 42−43 0.98 200 90−180

biomass and the standard heavy fuel oil. Upgrading the bio-oil is a very expensive process that requires the construction of corrosive resistance equipment and storage tanks. It is rather more economical to conduct pretreatment of the biomass or use a catalyst to achieve high quality bio-oil directly from the fast pyrolysis process. The desirable quality of bio-oil should have lower percentage of acids, lower viscosity, and higher content of aromatics. The use of catalyst during fast pyrolysis is considered to be one of the promising methods to enhance bio-oil quality. Hajaligol et al.13 investigated the formation of aromatic hydrocarbons during fast pyrolysis of cellulosic material. Py/ GC-MS technique was used to detect the percentage content of the aromatic products such as benzene, toluene, naphthalene, Received: Revised: Accepted: Published: 2280

July 5, 2011 December 27, 2011 January 5, 2012 January 24, 2012 dx.doi.org/10.1021/ie2014313 | Ind. Eng.Chem. Res. 2012, 51, 2280−2289

Industrial & Engineering Chemistry Research

Article

and anthracene produced between 400 and 600 °C. While above 600 °C, the pyrolysis gas/vapor consists mainly of methane, benzene, and hydrogen. Adam et al.14 investigated the catalytic effects of Al-MCM-41 catalyst on pyrolysis vapors of spruce wood. It was found that the effect of MCM-41 type catalyst on the pyrolysis products of spruce wood seem to be related to the pore size of the catalyst. As an example, pore size enlargement and transition metal incorporation reduce the yield of acetic acid and water among pyrolysis products. It is interesting to note that levoglucosan is completely eliminated, while acetic acid, furfural, and furans become major components among cellulose pyrolysis products over the unmodified Al-MCM-41 catalyst. Bridgeman et al.12 used the Py/GC-MS technique to study the effect of biomass particle size on the yield and distribution of the products in the pyrolysis vapors. They have used the peak area that resulted from the analysis to express the mass fraction of each component. The same approach has been adopted by other researchers to investigate the yields and components in the pyrolysis vapor. Zeolite (HZSM-5 and HY) catalytic effects on pyrolysis vapor of poplar wood, fire wood, cotton straw, and rice husk were investigated.15 In this study, the zeolite catalysts show very good deoxygenating properties, and the hydrocarbons detected after pyrolysis are mainly aromatic compounds. These results were supported by Pattiya et al.,11 where they have investigated a wide range of catalysts such as ZSM-5, Al-MCM-41, and Al-MSU-F, metal oxide (zinc oxide, zirconium(IV) oxide, cerium(IV) oxide, and copper chromite) catalysts, proprietary commercial catalysts (Criterion-534 and alumina-stabilized ceria-MI-575), and natural catalysts (slate, char, and ashes derived from char and biomass). Their study shows that ZSM-5, Criterion-534, and Al-MSU-F catalysts enhanced the formation of aromatic hydrocarbons and phenols while ZSM-5 has the added advantage of good deoxygenation properties. Another study16 has presented the py/GC-MS technique as a way to determine the product distribution for commercial Angelica acutiloba roots. The Py/GC-MS technique was also used by Carlson et al.17 to investigate the potential use of zeolites as bio-oil catalyst. The use of catalyst during fast pyrolysis is considered to be an efficient method for reforming of pyrolysis vapors. However, this method has some limitations; as it reduces the yield of vapors during pyrolysis, it required high energy for its functioning, and it also results in uncontrolled types of reactions. Apart from that, the catalyst is easily deactivated, and its regeneration is a difficult process. Nowadays, ionic liquids are in the focus of the scientific interest for several uses. Their attractive properties include chemical and thermal stability, nonflammability, and immeasurably low vapor pressure, and they are designable solvents.18,19 The ability of ionic liquid to dissolve biomass has been published widely, and some good review articles are available on this topic.20,21 In the present study two ionic liquids, 1butyl-3-methylimidazolium chlorides (BmimCl) and 1-butyl-3methylimidazolium acetate (BmimOAc), were used as a solvent for bamboo biomass dissolution. The effect of ionic liquid for possible upgrading of bio-oil was evaluated. The present study covers the effect of ionic liquid treatment on the properties and pyrolysis behaviors of bamboo biomass.

dried in a vacuum oven for 4 h and the water content was checked. A coulometric Karl Fischer titrator, DL 39 (Mettler Toledo), was used to determine the water content of the ionic liquids, which was found to be less than 1 wt %. Bamboo (Gigantochloa scortechinii) locally known as buluh Semantan was received from the local market, and it was ground into different particle sizes (125 μm to 1 mm). It was dried in an oven at 70 °C for 24 h (moisture content 3 wt % by Mettler Toledo HR Halogen Moisture Analyzer). B. Dissolution and Precipitation of Bamboo Biomass. In a typical example, the 0.25 g (5 wt %) of bamboo powder was added to the 5 g of ionic liquid and heated at 120 °C for 24 h (in the case of BmimOAc it was 18 h) with a stirring speed of 400 rpm. After pretreatment, the dissolved materials were precipitated by pouring the bamboo/IL slurry (containing dissolved materials and ionic liquid) into a beaker containing water. The mixture was stirred at room temperature for 30 min. The precipitate formed was filtered through filtration system using nylon membrane filter paper (0.45 μm). After filtration of precipitate, the ionic liquids were recycled by evaporating the water and the precipitate material was dried in an oven at 70 °C for 24 h and was used for further characterization. C. Elemental Analysis. Elementary (CHNS) analysis was carried out using CHNS-2400 supplied by Perkin-Elmer. Oxygen was calculated by difference. All measurements were repeated in triplicate, and a mean value is reported. D. Calorific Value Determination. The calorific values of samples were measured in duplicate using a bomb calorimeter model C2000 series manufactured by IKA Werke. The average value was calculated, and it represents the high heat value (HHV), which includes the latent heat of the water vapor emitted from the specimen. E. Lignin Determination. The sample of approximately 0.1 g was treated with 2 mL of 72% (v/v) sulfuric acid at room temperature for 2 h, followed by dilute acid (4%) at 121 °C for 1 h (in an autoclave under the saturated vapor pressure). The solution was filtered, and the precipitate was used for determination of acid insoluble lignin gravimetrically. The ash content of the precipitate was determined by heating at 575 °C for 3 h in a furnace, which thereby subtracts the ash content during measurement of acid insoluble lignin.22 F. Proximate Analysis. The moisture content of the samples was analyzed using a moisture analyzer (Mettler Toledo HR Halogen Moisture Analyzer). The ash content was determined by ashing at 575 °C for 3 h in a furnace (ASTM E1534-93). A PerkinElmer Pyris 1 thermogravimetric analyzer was used for determination of volatiles and fixed carbon of samples by heating from 105 to 900 °C at a heating rate of 10 °C/min under nitrogen atmosphere. The fixed carbon was considered as the final weight at 900 °C after correction for ash and moisture content. The volatiles were calculated from the difference between the fixed carbon and the original weight after correction for ash and moisture content. G. Thermal Gravimetric Analysis. A thermal gravimetric analyzer Perkin-Elmer Pyris V-3.81 was used to measure the thermal degradation behavior. The sample placed in an aluminum pan was heated to the prescribed temperature under nitrogen atmosphere at a heating rate of 10 °C/min. H. X-ray Diffraction Analysis. The crystallinity of bamboo powder and regenerated materials were monitored by powder X-ray diffraction (PXRD), using a Bruker D8 Advance horizontal X-ray diffractometer equipped with Cu anode, at room temperature. The samples were scanned within 5.00−

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METHODOLOGY A. Material. The ionic liquids (ILs), that is, BmimCl and BmimOAc, were purchased from Merck. Before using, ILs were 2281

dx.doi.org/10.1021/ie2014313 | Ind. Eng.Chem. Res. 2012, 51, 2280−2289


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Table 2. Results of Calorimetry, Elementary Analyses, Acid Insoluble Lignin wt %, and Mass Balance of the Untreated and Treated Samples of Ionic Liquids elementary analysis (wt %) bamboo

calorific value (HHV; M/kg)

C

H

N

O

acid insoluble lignin wt %

mass balance of recovered materials

untreated sample treated with BmimCl treated with BmimOAc

17.4 18.4 16.7

43.14 45.99 41.26

6.22 5.98 6.27

0.983 1.293 1.14

49.65 46.73 51.33

24.2 28.35 21.18

100% 89% 92.5%

which is considered small and from an industrial point of view is not favorable. However, with the advancement in this field, more cost-effective pretreatment processes can be achieved through synthesis of new ionic liquids with high dissolution capacity as well as improvement in the dissolution and regeneration process. Calorimetry, Elementary, and Acid Insoluble Lignin Analyses. The results of calorimetry, elementary, and acid insoluble lignin analyses for the untreated and treated samples with ionic liquids are listed in Table 2. It is clear that the calorific value of the BmimCl treated sample is high as compared to the untreated bamboo and BmimOAc treated samples. The difference might be due to different interactions of these ionic liquids with bamboo biomass during the dissolution and precipitation process. In the case of elementary analysis the carbon content is also found to be high for the BmimCl treated sample as compared to untreated bamboo and the BmimOAc ionic liquid treated sample. The difference in calorific value and carbon content could be correlated with lignin content of the samples, as the lignin content of the samples increased both calorific value and carbon content is noted to increase. The difference in lignin content of ionic liquid treated samples as compared to the untreated sample might be due to the following reasons. The Cl anion in BmimCl, having small size, would interact more with the carbohydrates part of biomass during dissolution, and it would cause the chemical modification of it; thus, the formation of water-soluble products cannot be precipitated with water, and consequently it will increase the lignin content of the precipitated materials. Similar observation was noted for another Cl based ionic liquid, that is, AmimCl, in another work.24 The pH of BmimOAc (pH = 10) was measured high as compared to BmimCl (pH: 7.6), so during precipitation with water the slurry of the BmimOAc treated sample is slightly alkaline (pH: 8) as compared to the BmimCl treated sample. The lignin has high solubility in alkaline solution, so in the case of the BmimOAc treated sample, some lignin content was dissolved instead of precipitating, which caused the decrease in lignin content of the precipitated sample as shown in Table 2. The proximate analysis shows that the fixed carbon wt % has increased for both ionic liquids, especially in BmimCl treated samples, as shown in Table 3. The increase in the carbon content might be due to more carbonization of regenerated

40.00° 2θ in step mode with a step of 0.01° and a rate of 1° min−1. I. Pyrolysis−GC/MS. Py-GC/MS experiments were carried out in a SHIMADZU PYR-4A pyrolyser (Chemical Data System) interfaced to a gas chromatograph (Shimadzu) coupled to a mass selective detector (Shimadzu) operating in electron impact mode (EI) at 70 eV. The 1−2 mg samples were loaded into a platinum sample bucket. A helium carrier gas was purged from the pyrolysis chamber which was held at 600 °C. The sample holder then dropped into the electrical pyrolysis furnace, and the pyrolysis vapors were carried by low flow rate of helium into the GC capillary column. The temperature of the GC/MS injector was held at 290 °C. The GC separation was carried out in a fused silica capillary column. A temperature program from 40 to 290 °C at 4° min−1 was applied with isotherm periods of 2 min at 40 °C and of 30 min at 290 °C.

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RESULTS AND DISCUSSION Dissolution and Precipitation of Biomass. It has been reported that the dissolution rate of biomass in ionic liquids depends on various factors such as particle size and density of biomass, ionic liquids to biomass ratio, water content in biomass, cooking time and temperature, biomass type, and several others.23,24 In view of these factors, the following experiments were conducted to study their effect in a more specific and quantitative manner. The bamboo powder of small particle size (125 μm) was used, as it has been reported that the increase in dissolution rate of smaller wood particles is likely due to increased surface area. Also more mechanical grinding (breaking down the internal structure) was required to obtain smaller particles; thereby it would facilitate its dissolution in ionic liquid.23 In the same context the ionic liquids with low moisture content (BmimCl and BmimOAc have water content 0.5 and 0.63 wt %, respectively) were used. It has been reported that excess in moisture content above 1 wt % would impair the dissolution capacity of ionic liquid because it would compete for hydrogen bonding with cellulose for the anionic part of the ionic liquid.25 In the present work, a temperature of 120 °C was selected for the dissolution process as it would not only make the dissolution process (providing high energy) of the bamboo biomass in ionic liquid easy but it would also reduce the effect of moisture content on the dissolution process.23 During the dissolution process it has been observed that BmimOAc was quite effective in dissolution as compared to BmimCl. Complete dissolution (more than 97%) was measured around 18 and 24 h for BmimOAc and BmimCl, respectively. The resultant dissolved material was regenerated by pouring the slurry of bamboo/IL into water (which acts as a coagulating agent for wooden material). The yield of regenerated material was 92.5% and 89% for BmimOAc and BmimCl, respectively. The decrease in yield was due to loss of water-soluble materials (water-soluble hemicelluloses, starch, ash, etc.) during the dissolution and regeneration process. In this work, the amount of sample dissolved was 5% with respect to ionic liquid content

Table 3. Proximate Analysis of Untreated and Ionic Liquid Treated Bamboo Sample sample untreated sample treated with BmimCl treated with BmimOAc 2282

moisture, wt %

fixed carbon, wt %

volatile, wt %

ash, wt %

4.4 3.1

10.452 23.05

82.24 68.75

2.9 5.1

3.5

15.04

76.96

4.5



Article

material as compared to the untreated sample during flow of nitrogen gas. Thermal Gravimetric Analysis. From thermal gravimetric analysis, the degradation onset temperature values (Ts) are observed to decrease for both ionic liquid samples as compared to the untreated bamboo biomass as shown in Table 4. A similar trend is also observed for thermal decomposition Table 4. Onset Ts and Decomposition Td Temperatures for Untreated and Ionic Liquid Treated Bamboo Sample property

untreated sample

Ts, °C Td, °C

291 339

treated with BmimCl treated with BmimOAc 245 290

247 287

temperatures values (Td), which were 339 °C, 290 °C, and 287 °C for the untreated bamboo biomass and treated samples with BmimCl and BmimOAc ionic liquids, respectively, as shown in Figure 1b. In this case, the decrease in thermal decomposition temperature may add some advantage in the pyrolysis process, as it can be operated at a lower temperature and this will help in saving of energy. It is seen from Figure 1a that more residues were formed in the case of the BmimCl treated sample which could be attributed to the formation of stable residue as a result of ionic liquid treatment. The formation of stable residue as a result of ionic liquid treatment cannot be explained at the moment. The similar observation was reported by Fort et al.26 while treating pine wood chips with BmimCl ionic liquid. X-rays Diffraction Analysis. The X-ray diffraction patterns for the untreated (A) and the regenerated bamboo biomass from BmimCl (B) and BmimOAc (C) ionic liquids are shown in Figure 2. In spectrum (A) the typical diffraction peaks at 2θ 15.8° and 22.2° of cellulose I as discovered earlier are observed.27 While in spectra (B) and (C) the low intensity diffraction peak is observed at 2θ 20.7° which is attributed to cellulose II. From this shifting and decrease in the intensity of the peak, it is clear that a change in crystallinity of the cellulose has taken place during the dissolution and precipitation of the bamboo biomass from ionic liquids. The range of possible structures for cellulose is presented elsewhere.28,29 During the dissolution process, the ionic liquids rapidly broke the intermolecular and intramolecular hydrogen bonds

Figure 2. Diffractograms of untreated bamboo (A) and regenerated materials from BmimOAc (B) and from BmimCl ionic liquid (C).

within the bamboo biomass structure and destroyed the original crystalline form as indicated by the shift in the peaks observed in spectra (B) and (C). During dissolution the cellulose chains are separated and became random, which are later on are rearranged in some new pattern by adding water. Pyrolysis−GC/MS. Py-GC/MS has been employed to determine the effect of two types of ionic liquids and to determine how far they can modify the pyrolysis product distribution of bamboo biomass. The fast pyrolysis temperature was chosen to be 600 °C. From the chromatograms, the main pyrolytic products detected from the pyrolysis of untreated and ionic liquid treated samples as well as their concentrations (peak area %) are listed in Tables 5−7. These results are in good agreement with the reported pyrolytic products of lignocellulosic materials.30,31 In this study, the main compounds generated in the pyrolysis vapors (listed in Tables 5−7) were classified into 8 groups: phenols, aldehydes, ketones, acids, furans, alcohols, aromatics, and hydrocarbons. The total amount (peak area %) of each group in relation to the main

Figure 1. Thermal decomposition (a) and its derivative (b) profile of untreated bamboo (A) regenerated material from BmimCl (B) and BmimOAc (C) ionic liquids. 2283



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Table 5. Identified Pyrolytic Products from Fast Pyrolysis of the Untreated Bambooa

a

peak no.

area (%)

retention time (min)

1 2 3 4 5 6 7 8 9 10 11

1 1.53 7.55 0.43 1.48 2.27 0.61 7.36 3.27 0.45 1.26

1.671 1.766 1.957 2.154 2.317 2.39 2.48 2.839 3.125 3.468 3.642

12 13 14 15 16 17 18 19 20 21 22 23

0.47 4.5 2.34 2.21 1.24 3.95 2.04 0.8 0.5 2.77 0.57 3.01

4.417 4.602 4.816 4.962 5.119 5.759 6.186 6.393 7.107 7.483 8.381 8.477

24

1.25

8.752

25

2.47

9.297

26 27

0.45 1.4

9.538 9.707

28

2.71

10.038

compound

origin

peak no.


area (%)

C C C C C C C C C C L

29 30 31 32 33 34 35 36 37 38 39

10.291 10.408 10.779 11.195 11.475 12.042 12.278 12.391 12.464 12.553 12.958

1.29 1.6 1.19 0.66 4.31 1.19 14.13 0.65 0.51 0.54 1.65

C L C C C C C C C C

40 41 42 43 44 45 46 47 48 49 50 51

13.171 13.3 13.57 13.671 13.991 14.07 14.159 14.328 14.592 14.845 15.013 15.479

0.53 0.99 0.59 1.87 0.74 0.44 1.14 0.94 0.43 0.86 0.43 1.05

52

15.968

0.44

C

53

16.888

0.67

L L

54 55

17.051 18.455

0.51 0.76

alanine acetaldehyde acetone 2-methyl-1-buten-3-yne hydroxy-acetaldehyde 2,3-butanedione 3-pentanone acetic acid 1-hydroxy-2-propanone 2,3-pentanedione diehtylamino-3benzenesulfonamidopentane pyrrole toluene propanal propanoic acid 3-amino-s-triazole furfural 3-methyl-2-hexanone 1-(acetyloxy)-2-propanone 2-methyl-2-cyclopenten-1-one 1,2-cyclopentanedione 1,4,5-trimethyl-imidazole phenol 2-butyl-2-ethyl-3-methyloxazolidine 2-hydroxy-3-methyl-2-cyclopenten1-one 2-hydroxy-benzaldehyde 2-methyl-phenol 4-methyl-phenol

L

compound

origin

2-methoxy-phenol 2-amino-1-propanol 2-pentenal 2,4-dimethyl-phenol 4-ethyl- phenol 1,2-benzenediol 3-methyl-benzaldehyde 4-(1-methylethyl)-phenol 2,3-anhydro-d-mannosan 1-ethyl-4-methoxy-benzene 3-methoxy-1,2-benzenediol

L C C L L L L L C L L

4-ethyl-2-methoxy-phenol 2-allylphenol 4-(2-propenyl)-phenol 2-methoxy-4-vinylphenol 4-(2-propenyl)-phenol 3-methyl-1,2-benzenediol 2,6-dimethoxy-phenol 4-hydroxy-benzaldehyde 1-cyano-4-(5-hexenyl)benzene vanillin 2-allyl-4-methylphenol 2-methoxy-4-(1-propenyl)phenol 1-(4-hydroxy-3-methoxyphenyl ethanone 2,3,5,6-tetrafluoroanisole

L L L L L L L L L L L L

propanoic acid 2,6-dimethoxy-4-(2-propenyl phenol

C L

C

L

Here C and L represent carbohydrates and lignin, respectively.

untreated bamboo biomass. However, in the case of the BmimOAc treated sample, the amount of ketones is found to be more than that of the untreated sample. The effect of the ionic liquid treatment on the furans content in pyrolysis products is shown in Figure 6. Furans are normally dehydration products of carbohydrates.36,37 It is clear from Figure 6 that furans are high for the BmimCl treated sample as compared to BmimOAc treated sample. However, the furans content of both the ionic liquids treated samples are higher than that of the untreated bamboo biomass. Irrespective of its fuel value, the bio-oil can be a promising renewable resource where these high value furan compounds can be further isolated and used as special chemicals or for petrochemical activities. The effect of the ionic liquid treatment on the alcohols content on pyrolysis products is shown in Figure 7. It is clear that the BmimCl treatment sample generated more alcohols during fast pyrolysis. It has been noted that the main component in alcoholic compounds is methanol (7.58%). Methanol is a desirable component as it improves the quality of bio-oil in terms of stability and reduces the viscosity.38 The quality of bio-oils also depends upon the amount of organic acids. The higher the concentration of acid, the more problems that may occur with the metallic materials as it is corrosive to common metals such as aluminum, mild steel, brass, and so on.39 The effects of ionic liquids treatment on acetic acid contents are shown in Figure 8. As acetic acid

products generated is discussed below. The total peak area for each group is the sum of the peak areas of all the individual components that belongs to the respective group and is shown in Figures 4−10. The effect of the ionic liquid treatment on the phenols content of pyrolysis products is shown in Figure 3. Phenols are known to improve the commercial value of bio-oil especially for the resin or adhesive industry.31 It is clear that the phenols content of BmimCl treated samples is high as compared to untreated and BmimOAc treated samples which might be due to difference in lignin content, as most of the monomeric phenolic compounds and oligomers come from fast pyrolysis of lignin.32,33 Phenols and their derivatives can be easily separated from bio-oil and used in pharamaceutical, food, and paint industries and many other products. So, the increase in phenols content will make bio-oils a new alternative source for the recovery of phenols.34,35 The changes in the amounts of carbonyl compounds due to the ionic liquids treatment were monitored, and the results are shown in Figures 4 and 5. One of the limitations concerning the bio-oil is its low stability. Upon storage, the viscosity and molecular weight increase with time. The presence of carbonyls (aldehydes and ketones) has significant impact on the quality of bio-oil as they are responsible for the aging reactions and cause instability to bio-oils. In this study both carbonyl compounds for the BmimCl treated sample are decreased as compared to 2284



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Table 6. Identified Pyrolytic Products from Fast Pyrolysis of the BmimCl Treated Bamboo Samplea

a

peak no.


area (%)

compound

origin

peak no.


area (%)

1 2 3 4 5 6 7 8 9 10 11 12

1.822 2.008 2.457 2.53 2.749 3.007 3.136 3.26 3.44 3.569 3.698 3.911

7.58 1.97 1.18 0.6 0.19 0.67 0.15 0.15 2.24 1.59 0.63 0.34

C C C C C C L C C C C C

53 54 55 56 57 58 59 60 61 62 63 64

12.115 12.441 12.548 12.654 12.929 13.12 13.21 13.429 13.581 13.738 13.822 14.12

0.69 12.36 0.17 0.92 2.17 0.27 0.25 1.54 0.26 0.42 0.69 1.16

C C L C C C C C C C L C L C C C

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

14.266 14.345 14.586 14.659 14.906 15.035 15.103 15.372 15.529 15.703 15.849 15.934 16.023 16.125 16.226 16.445 16.63

L C

82 83

C

2.53

methanol 2-methyl-pentanal 4-methyl-1-pentene formic acid hydroxy-acetaldehyde 2-butenal benzene acetic acid acetic acid 1-hydroxy-2-propanone 2,5-dimethyl-furan hydroxy-acetic acid, methyl ester 1-methyl-1H-pyrrole pyrrole toluene 1-hydroxy-2-butanone propanoic acid 3-amino-s-triazole 3-ethyl-1H-pyrrole hexame-cyclotrisiloxane furfural 2-cyclopenten-1-one 2-furanmethanol p-xylene diacetate-1,2-ethanediol styrene 2-methyl-2-cyclopenten-1-one butyrolactone 1-methyl-2piperidinemethanol 2-methyl-phenol 5-methyl-2furancarboxaldehyde 5-methyl-2furancarboxaldehyde 3-methyl-2-cyclopenten-1-one 1H-imidazole-2carboxaldhyde1-methyl phenol octamethyl cyclotetrasiloxane 1-methoxy-4-methyl benzene 2-ethyl-1-hexanol 3-methyl,1,2cyclopentanedione 2-methyl-phenol

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

4.203 4.467 4.63 4.86 5.22 5.354 5.439 5.635 5.809 5.944 6.393 6.472 6.55 6.854 7.157 7.387 7.64

1.06 0.68 2.47 0.45 1.22 0.43 0.17 4.07 1.9 0.34 0.42 0.46 0.39 0.77 0.23 0.38 0.31

30 31

8.027 8.168

0.16 0.57

32

8.213

0.19

33 34

8.263 8.477

0.2 0.31

35 36 37 38 39

8.634 8.752 9.156 9.296 9.499

4.21 2.29 0.23 0.19 0.61

40

9.796

41

9.97

0.35

42 43 44 45 46 47 48 49 50 51 52

10.167 10.341 10.622 10.818 11.088 11.273 11.385 11.599 11.728 11.851 11.952

4.52 0.22 0.78 0.87 0.55 3.4 0.22 5.53 0.3 0.84 0.67

compound

origin

2,4,6-trimethyl-phenol 2,3-dihydro-benzofuran 3-methoxy-phenol 2-ethyl-6-methyl phenol 2-propyl-phenol 4-(methylthio)-phenol 2-methyl-phenol 2,3-dihydro-benzofuran p-isopropenylphenol 1-(2-hydroxy-5-methyl ethanone 2-methoxy-4-methyl-phenol 4-(2-propenyl)-phenol

L L L L L L L L L C L L

0.39 0.5 0.51 0.29 0.47 0.36 0.6 0.39 0.66 1.12 0.23 0.23 0.24 0.24 0.24 0.24 0.37

3,4-dimethoxy-phenol 1H-indenol 6-methyl-4-indanol 1-tetradecene 4-ethylcatechol vanillin 2-methyl-6-(2-propenyl)-phenol 3-(4-methylphenyl)-2-propyn-1-ol 2-methoxy-4-(1-propenyl)-phenol 4′-hydroxy-acetophenone 5-hydroxy-3-methyl-1-indanone 1-tridecene 1,2,4-triethyl-benzene 1,4-dimethoxy-2,3-dimethylbenzene 3,4-dimethyl benzaldehyde 4-(1-methylpropyl)-phenol 2,3,2-dimethyl- 3,7-benzofurandiol

L L L C L L L L L C L C L L L L L

16.697 16.871

0.27 0.17

1-(2,4,6-trihydroxyphenyl)-ethanone dodecanoic acid

L C

84

16.961

0.45

1-(3,4-dimethoxy)-ethanone

C

C

85 86

17.388 17.804

0.2 0.38

3-[(phenylmethyl)-2-propenoic acid 2-benzothiazolamine

C L

L L C C

87 88 89 90 91

17.95 18.286 18.511 18.59 18.708

0.28 0.29 0.36 0.2 0.29

3-(2-hydroxyl)-propanoic acid 1-heptadecene 2,6-dimethoxy-phenol benzoic acid, 2-ethylhexyl ester [1,1′-biphenyl]-3-ol

C C L L L

L

92

18.949

0.2

L

4-methyl-benzoic acid

L

93

19.101

0.74

4-methyl-phenol 2-methoxy-phenol 2,5-dimethyl-phenol L-alanine, methyl ester 2-ethyl-phenol 2,4-dimethyl-phenol 2-methylindene 2-ethyl-phenol 2,6-dimethyl-phenol 1-dodecene 2-methoxy-4-methyl phenol

L L L C L L L L L C L

94 95 96 97 98 99 100 101 102 103 104

19.376 19.533 20.117 20.415 20.561 20.942 21.167 21.409 22.807 23.003 26.255

0.24 0.18 0.22 0.22 0.2 0.48 1.78 0.2 0.61 0.5 0.4

1-(4-hydroxy-3,5-dimetho xyphenyl)ethanone 3-(4-hydroxyphenyl)-2-propenoic acid, methyl ester 1-octadecene benzidine pentadecanoic acid 1-nonadecene 2-n-octylfuran hexadecenoic acid, Z-11 n-hexadecanoic acid 1-nonadecene oleic acid octadecanoic acid 6-ethyl-phthalic acid

L C L C C C C C C C C L

Here C and L represent carbohydrates and lignin respectively. 2285



Article

Table 7. Identified Pyrolytic Products from Fast Pyrolysis of the BmimOAc Treated Bamboo Samplea peak no.


area (%)

compound

origin

peak no.


area (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

1.884 2.069 2.535 2.603 2.962 3.075 3.192 3.316 3.473 3.574 3.748 3.878 4.046 4.254 4.327 4.377 4.484 4.669 5.079 5.225 5.382

6.47 4.92 2.17 0.58 0.25 1.4 0.3 0.6 0.85 0.58 0.89 2.92 5.19 1.12 0.25 0.26 0.34 1.41 2.4 2.95 0.58

4-pentenal 2-methyl-pentanal 3-methyl-2-butanone 2-methyl-furan 1,4-cyclohexadiene 2-butenal hydroxy-acetaldehyde 3-penten-2-one 2-hexene 4-ethyl-2,2-dimethyl-hexane 2,5-dimethyl-furan acetic acid 1-hydroxy-2-propanone 2,3-dihydro-3-methyl-furan hydroxy-acetic acid, methyl ester propylene glycol 3,3′-oxybis-cyclopentene toluene cyclopentanone methyl propionate 2,3-dimethyl-pentanal

C C C C C C C C C C C C C C C C C L C C C

53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

11.003 11.048 11.323 11.408 11.52 11.688 11.846 12.014 12.076 12.188 12.306 12.452 12.592 12.688 12.997 13.182 13.261 13.373 13.468 13.53 13.766

0.48 0.3 0.46 1.55 0.95 1.71 0.29 0.31 0.94 0.24 0.36 1.21 0.6 0.37 0.25 0.25 1 0.42 0.23 0.23 0.96

22 23 24 25 26 27 28 29 30 31 32

5.495 5.674 5.899 6.185 6.354 6.511 6.612 6.781 6.887 7.033 7.219

0.45 3.51 2.16 0.38 0.42 0.19 0.49 2.1 0.54 0.27 1.12

2,3,5-trimethyl-furan hexamethyl-cyclotrisiloxane, furfural 2-cyclopenten-1-one ethylbenzene p-xylene 3,5-dimethyl-2-octanone acetic acid, (acetyloxy) styrene diethyl-borinic acid 2-methyl-2-cyclopenten-1-one

C C C L L C C L C C

74 75 76 77 78 79 80 81 82 83 84

13.89 14.17 14.277 14.389 14.659 15.007 15.131 15.395 15.546 15.827 16.164

0.2 0.31 0.57 0.48 0.87 0.23 0.28 0.41 0.71 0.27 0.29

33 34

7.359 7.657

0.38 0.41

2-methyl-2-cyclopenten-1-one 2(5H)-furanone

C C

85 86

16.327 16.45

0.22 0.35

35 36

7.769 8.01

0.48 3.34

2,5-hexanedione 1,2-cyclopentanedione

C C

87 88

16.68 16.894

0.89 0.21

37

8.207

0.45

5-methyl-2-furancarboxaldehyde

C

89

17.264

0.22

38 39

8.342 8.443

0.33 0.66

5-methyl-2-furancarboxaldehyde 3-methyl-2-cyclopenten-1-one

C C

90 91

18.331 18.988

0.2 3.64

40

8.662

1.25

3-methyl-2-cyclohexen-1-one

C

92

19.387

0.34

41 42

8.763 8.819

1.73 0.51

C C

93 94

20.134 20.572

0.44 0.32

43

8.999

0.2

C

95

20.763

0.5

44 45 46 47

9.178 9.336 9.628 9.74

0.34 0.21 1.96 2.01

L C C C

96 97 98 99

20.954 21.173 22.453 22.666

48 49 50 51 52

9.914 9.998 10.346 10.442 10.599

0.19 3.43 2.98 0.65 0.26

octamethyl-cyclotetrasiloxane 2,3-dimethyl-2-cyclopenten-1one 2,4-dihydro-2,5,3H-pyrazol-3one 1-methoxy-4-methyl-benzene 1,3-dimethyl-1-cyclohexene 3-methyl,1,2 cyclopentanedione 2-hydroxy-3-methyl,2cyclopenten-1-one 4-methyl-5H-furan-2-one 2-methyl-phenol 4-methyl-phenol 2-methoxy-phenol 2-methyl-benzofuran

C L L L L

100 101 102 103 104

22.818 23.009

2286

compound

origin

maltol propyl-cyclohexane 2-methylindene 2,4-dimethyl-phenol dihydro-4-methyl-2(3H)-furanone 3-ethyl-phenol 2,4-dimethyl-phenol 2-methoxy-4-methyl-phenol 3,4-dimethyl-phenol 3,4,5-trimethyl-phenol 3,6-dimethyl-1H-indazole 2,3-dihydro-benzofuran 2,6-dimethyl-4H-pyran-4-one 1-ethyl-4-methoxy-benzene 1,2-benzenediol 3-methoxy-1,2-benzenediol 4-isopropylthiophenol 2,3-dihydro-1H-inden-1-one 2-allylphenol 4-methyl-1,2-benzenediol 1-(2-hydroxy-5-methylphenyl)ethanone 4-methyl-1,2-benzenediol 4-(2-propenyl)-phenol 2,6-dimethoxy-phenol 1,3-dihydro 2H-benzimidazol-2-one 2-methyl-5-(1-methyl)-cyclohexanone 2-methoxy-4-(1-propenyl)-phenol 2-methyl-6-(2-propenyl)-phenol 2,5-dimethylhydroquinone 2-methoxy-4-(1-propenyl)-phenol 2-(1-methylpropyl)-phenol 6-methyl-5-(1-methyethyl)-5-hepten3-yn-2-ol 1,5-naphthalenediol 4-hydroxy-3-methoxy-benzoic acid, methyl ester 3-(dimethylamino)-phenol 2,3-dihydro-2,2,4,6-tetramethylbenzofuran 1-(4-hydroxy-3-methoxyph enyl)ethanone m-(3-ethylureido)benzoic acid 1-(4-hydroxy-3,5-dimethoxyphenyl)ethanone 1-(2,4,6-trihydroxy-3-methylphenyl)1-butanone pentadecanoic acid 2-n-octylfuran

C C L L C L L L L L L L C L L L L L L L L

C

0.36 1.93 0.2 0.25

14-methyl-pentadecanoic acid, methyl ester Z-7-hexadecenoic acid n-hexadecanoic acid 8-octadecenoic acid, methyl ester octadecanoic acid, methyl ester

0.72 1.25

6-octadecenoic acid, (Z) octadecanoic acid

C C

L L L L C L L L L L C L L L L L L L L C C

C C C C



Article

Table 7. continued a

Here C and L represent carbohydrates and lignin respectively.

Figure 7. Effects of ionic liquids on the production of alcohols.

Figure 3. Effects of ionic liquids on the production of phenols.

normally comes from the acetyl group of hemicelluloses, it has been observed that acetic acid decreases with ionic liquid

Figure 4. Effects of ionic liquids on the production of aldehydes.

Figure 8. Effects of ionic liquids on the production of acetic acids and total acids.

treatment, especially in the BmimCl treated sample as compared to the untreated sample. However, the total acid contents for all samples are about the same as shown in Figure 8. These preliminary results of ionic liquid pretreatment on acid content will need further investigation to minimize the acidity of pyrolytic vapors. The effect of ionic liquid treatment on benzene derivatives is shown in Figure 9. Benzene derivatives are suggested to improve the heating values of bio-oils. In this study it is shown that the BmimCl treated sample produces more benzene

Figure 5. Effects of ionic liquids on the production of ketones.

Figure 6. Effects of ionic liquids on the production of furans.

Figure 9. Effects of ionic liquids on the production of aromatics. 2287



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derivatives as compared to BmimOAc treated and untreated samples. In addition to the above products, a small amount of hydrocarbons has been detected as shown in Figure 10. The presence of hydrocarbon cannot be ignored as they contribute to the heating values of bio-oils. Figure 10 shows that pyrolysis

REFERENCES

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Figure 10. Effects of ionic liquids on the production of hydrocarbons.

of untreated bamboo biomass generates a small amount of hydrocarbons (0.43 peak area %). However, the hydrocarbon content is increased after treatment with ionic liquids, and the result is more pronounced in the BmimCl treated sample.

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CONCLUSION Two ionic liquids with the same cation but different anions, BmimCl and BmimOAc, were used for dissolution of bamboo biomass. The regenerated material from BmimCl is found to have high carbon content in CHNS analysis, calorific value, and fixed carbon in proximate analysis which can be attributed to high lignin content as compared to the untreated and BmimOAc treated samples. The ionic liquid treatment is observed to decrease the thermal stability of the treated bamboo biomass, and thereby it can be pyrolyzed at lower temperature. During dissolution and precipitation from ionic liquid, change in crystallinity type and decrease in XRD peak intensity of cellulose are observed. The BmimCl treatment increased the phenols, furans, alcohols, hydrocarbons, and aromatics contents in the pyrolytic products. The carbonyl products (aldehydes, ketones) which caused the aging reactions and instability of bio-oils are reduced after treatment with BmimCl. In the case of the BmimOAc treated sample, phenols, alcohols, aromatics, and aldehyde components are decreased while ketones, furans, and hydrocarbons contents are increased as compared to the untreated bamboo. However, none of these ionic liquid treatments decreased the total acids content in the pyrolytic products. As such further investigation is necessary to reduce the acidity of pyrolytic products.

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Article

AUTHOR INFORMATION

Corresponding Author

*Tel.: 006053687702. Fax: 006053687598. E-mail: [email protected].

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ACKNOWLEDGMENTS This work has been supported by PETRONAS Ionic Liquid Center, Department of Chemical Engineering, Universiti Teknologi PETRONAS, Malaysia. 2288



Article

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Effect of Ionic Liquid Treatment on Pyrolysis Products from Bamboo

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