Journal of Chemical, Biological and Physical Sciences Nitrobenzene

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Apr 27, 2016 - 2Visveswaraya National Institute of Technology, Nagpur, Maharashtra ..... C.H. Hoyt, “Lignin” Kirk-Othmer encyclopedia of chemical technology,.

JCBPS; Section D; May 2016 – July2016, Vol. 6, No.3; 501-513.

E- ISSN: 2249 –1929

Journal of Chemical, Biological and Physical Sciences An International Peer Review E-3 Journal of Sciences Available online at www.jcbsc.org

Section D: Environmental Sciences CODEN (USA): JCBPAT

Research Article

Nitrobenzene Oxidation for Isolation of Value Added Products from Industrial Waste Lignin Nandanwar R.A1, Chaudhari A.R1, Ekhe J.D2 1

Priyadarshini Bhagwati College of Engineering, Nagpur, Maharashtra, India.

2

Visveswaraya National Institute of Technology, Nagpur, Maharashtra, India. Received: 19 April 2016; Revised: 27 April 2016; Accepted: 05 May 2016

Abstract: Among the main components of woody biomass, lignin is the most abundant raw material. Lignin constitutes roughly one third of biomass and is typically burned to produce heat and electricity within paper mills and biorefineries. As well, lignin obtained from pulp and paper industry is a major byproduct which poses an environmental burden. Due to its large availability as a waste with high energy content and presence of highly reactive groups, this industrial waste lignin has a potential for production of wide range of chemicals and materials. Lignin obtained from pulp and paper industry can be utilized through its degradation for production of important value added chemicals. Thus in the present study, industrial waste lignin was subjected to oxidative degradation in alkaline medium using oxidizing agents like nitrobenzene and m-dinitrobenzene. The degradation was carried out using thermal and microwave technique. All degradation products obtained are the low molecular weight compounds which were analyzed through HPLC. The degradation products obtained mainly comprise of vanillin, syringaldehyde, phydroxybenzaldehyde and syringic acid etc. All these low molecular weight compounds have immense industrial applications. It was observed that the extent of degradation was more in case of microwave technique as compared to thermal technique, which has reduced the reaction time and with greater yield of products. Thus in this way the industrial waste lignin can be utilized as a feedstock for value added chemicals. The present study has confirmed the higher efficiency of microwaves for lignin degradation. Keywords: Lignin, oxidative degradation, HPLC, value added products. 501

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INTRODUCTION Today’s increased demand for alternative to fossil carbon based products such as the production of transportation biofuels and bulk ‘green’ chemicals expands the interest and the need to create value added products from biomass. For the preparation of aromatic (bulk) chemicals such as phenol, lignin is the most available and accessible biobased feedstock. Lignin is found in trees and other lignocellulosic plant materials representing 15-25% of their weight and about 40% of the biomass energy content1. Lignocellulosic biomass offers many possibilities as feedstock for the energy sector and also for the chemical industry due to its chemical composition, abundant availability and relative low cost. Lignin is the material to serve as a future aromatic resource for the production of liquid biofuels, biomaterials and green chemicals2-4. Lignin is the waste material obtained from pulp and paper industry in very large quantity. Traditionally, the use of lignin has been as a combustion fuel in pulp mills, component in biomass or additive in cement. However, due to its chemical nature, and in particular the presence of large amount of aromatic structures, lignin may be an attractive raw material for the production of basic aromatic chemicals such as benzene, toluene, xylene and phenol, overall reducing CO2 emissions and the need for fossil resources. Paper industries invariably produce lignin as a recurring waste material in huge quantities and its disposal is a general problem. Several utilization techniques are under investigation but they mostly lack in wholesome utilization aspect. Scientists have worked for the degradation reactions of lignin obtained from industrial waste black liquor because of its polymeric structural features5. Some work has already been undertaken for degradation of lignin and sufficient data is also available. Thermal and oxidative degradation of lignin has been employed to establish the chemical structure of polymeric materials6-8. Degradation of lignin yields many value added chemicals like catechols, monomeric phenols, phenolic aldehydes and acids. Among all of the oxidations, the most illuminating has been the alkaline twoelectron transfer process of nitrobenzene degradation which over the years has become a mainstay of lignin investigators. Nitrobenzene was one of the earliest chemical oxidant used and it produced reasonable quantities of vanillin and syringaldehyde depending on the source of lignin. Lignin material on degradation has a potential to produce various important chemicals to name a few, vanillin, phydroxybenzaldehyde, syringaldehyde, veratraldehyde, acetovanillone, syringic acid etc.9-12. These chemicals have enormous applications in pharmaceuticals, food, dyes and chemical industries. Looking into the polymeric structural features of this naturally occurring material, it appeared quite interesting to undertake the degradation reactions of lignin obtained from industrial waste black liquor. Microwave energy is increasingly utilized by the chemists since decades for various chemical reactions. On account of various advantages of microwave technique such as fast reaction, time saving, energy saving, greater yield in various organic reactions13-17, it was thought appropriate and rational to explore this newer technique for the purpose. The present research work is mainly aimed to explore the potential of industrial waste lignin to produce value added products. As well as emphasis has been given on the use of oxidizing agent nitrobenzene and m-dinitrobenzene for oxidative degradation of lignin isolated from industrial waste black liquor. The oxidative products thus obtained are identified by High Performance Liquid Chromatography (HPLC).

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MATERIAL AND METHODS The black liquor obtained from Simplex Paper Mills, Gondia, Maharashtra, was filtered and then acidified upto pH = 5 using dilute HCl, to precipitate out the soluble lignin. It was then filtered and washed with plenty of distilled water and then it was dried in oven overnight at 800C and weighed. About 5 g of crude lignin was obtained from 100ml of black liquor. The crude alkali lignin was dissolved in minimum quantity of 1,4-dioxane and the dissolved lignin was re-precipitated from water. The residue obtained was in the form of shiny brown crystals. It was dried and weighed. The residue can be referred as pure lignin18-24. Characterization of pure lignin: (a) Proximate and Elemental Analysis of Pure Lignin: Proximate analysis of purified lignin was carried out as per American Standard for testing material method. The % moisture, % volatile matter, % ash and % fixed carbon was calculated. Pure lignin was subjected to elemental analysis to know CHNS content. Elemental Analyzer (Carlo Erba Model 1108) was used for elemental analysis (CHNS/O) of purified lignin. The % of oxygen in the analysis was calculated by difference. (b) FTIR studies of Pure Alkali Lignin: The Infra-Red Spectrum of pure lignin has been recorded by using FTIR-Schimadzu 100 and Perkin Elmer using KBr pellets to hypothesize the functional groups present in lignin. Oxidative degradation of pure lignin by Thermal Technique: (a) Oxidative Degradation of Pure Lignin using Alkaline Nitrobenzene by Thermal Technique: Pure lignin (10g) was dissolved in aqueous sodium hydroxide (1N, 300ml) and to it nitrobenzene (50 ml) was added and mixture was refluxed at boiling temperature for 4 hours. After cooling, the upper layer of nitrobenzene was removed with the help of separating funnel and the remaining traces of organic phase were removed by extraction with benzene. The aqueous alkaline layer was acidified with hydrochloric acid (50%) when undegraded lignin was precipitated out. The acidic suspension of lignin with degraded products was again subjected to complete extraction with chloroform. Evaporation of chloroform yielded a mixture of phenolic compounds. The above mixture (10 mg) was dissolved in pure methanol (100 ml) and the solution was analyzed through HPLC25-27. (b) Oxidative Degradation of Pure Lignin using Alkaline m-dinitrobenzene by Thermal Technique: Pure lignin (10g) was dissolved in aqueous sodium hydroxide (1N, 300ml) and to it m-dinitrobenzene (30g) was added and the contents were refluxed at boiling temp for 4 hours. After cooling the contents, insoluble solid was filtered out and filtrate was thoroughly extracted with benzene to remove all the reduced products of m-dinitrobenzene. The aqueous alkaline layer was acidified with hydrochloric acid (50%) and undegraded lignin was precipitated out. The acidic suspension of lignin along with degraded products was again subjected to complete extraction in chloroform. Evaporation of chloroform yielded a mixture of phenolic compounds. The above mixture (10 mg) was dissolved in pure methanol (100 ml) and the solution was analyzed through HPLC. Oxidative Degradation of Pure Lignin by Microwave Technique: (a) Oxidative Degradation of Pure Lignin using Alkaline Nitrobenzene by Microwave Technique: Pure lignin (10g) was dissolved in aqueous sodium hydroxide (1N, 300 ml) and to it nitrobenzene (50ml) was added. The contents were transferred to a round bottom flask. The flask was properly fitted in the 503

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modified microwave oven28,29 and the contents were irradiated with microwave for 50 mins. at full power by pulse irradiation method applying two water condensers to ensure safe refluxion (see Figure 1). After cooling, the upper layer of nitrobenzene was removed with the help of separating funnel and the remaining traces of organic phase were removed by extraction in benzene. The aqueous alkaline layer was acidified with hydrochloric acid (50%) when undegraded lignin was precipitated out. The acidic suspension of lignin with degraded products was again subjected to complete extractions with chloroform. Evaporation of chloroform yielded a mixture of phenolic compounds, which was subjected to HPLC analysis. (b) Oxidative Degradation of Pure Lignin using alkaline m-dinitrobenzene by Microwave Technique: Pure lignin (10g) was dissolved in aqueous sodium hydroxide (1N, 300ml) and to it m-dinitrobenzene (30g) was added. The contents were transferred to a round bottom flask. The flask was properly fitted in the modified microwave oven and the contents were irradiated with microwave for 50 mins. at full power by pulse irradiation method applying two water condensers to ensure safe refluxion (see Figure 1). After cooling the contents the insoluble solid was filtered out and the filtrate was thoroughly extracted in benzene to remove all the reduced products of m-dinitrobenzene. The aqueous alkaline layer was acidified with hydrochloric acid (50%) when undegraded lignin was precipitated out. The acidic suspension of lignin with degraded products was again subjected to complete extractions in chloroform. Evaporation of chloroform yielded a mixture of phenolic compounds, which was subjected to HPLC analysis. Conditions for HPLC Analysis: Name of the equipment: Schimadzu Class-VP, V6.14SPI; column: C18 Schimpac CLC-OSD (M); 4.6mmX25cm; detector: UV; Wavelength 275 nm; solvent system: Methanol: water: acetic acid; flow rate: 0.1 ml/min. All standards and solvents used were of HPLC grade.

Figure 1: Experimental assembly (Modified Microwave Oven) 504

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RESULTS AND DISCUSSION The industrial black liquor contains the crude lignin. About 5g of crude lignin was obtained from 100ml of black liquor. The crude lignin on purification yielded shiny brown crystals (3.5g) which can be referred as pure solid lignin. Characterization of pure lignin: (a) Proximate and Elemental Analysis of Pure Lignin: The proximate analysis showed 4.20% moisture, 42.68% volatile matter and ash is 9.02%. The % of fixed carbon in pure lignin is 44.10%. The elemental analysis of purified lignin showed 58.9 % of carbon and 8.2 % of hydrogen, 0.1 % of nitrogen and 32.8 % of oxygen. (b) FTIR analysis of Pure Lignin: The spectrum clearly indicated the presence of various functional groups such as hydrogen bonded O-H, aromatic skeletal vibrations due to guaiacyl group, carbonyl stretching- unconjugated ketone and carboxyl group, aromatic C-H in plane deformation and aromatic C-H out of plane etc. The Infra red Spectrum of pure lignin (see Figure 2) is characterized by a broad peak at 3413cm-1 which has been assigned to –OH hydrogen bonded, a sharp peak at 2927cm-1 mainly assigned to methyl and methylene group. A symmetric stretch for CH3 of methoxyl group appeared at 2840 cm-1. A small peak at 1713cm-1 assigned to carbonyl stretching unconjugated ketones and carbonyl groups. Sharp peak at 1604cm-1, 1508cm-1, 1426cm-1 represents aromatic skeletal vibrations. Peaks at 1217cm-1and 1119cm-1 have been assigned to syringyl ring breathing with CO stretching and C-O stretching for secondary alcohols respectively. Peaks at 1035cm-1 represents aromatic C-H in plane deformation and peak at 835cm1 represents aromatic C-H out of plane deformation.

Figure 2: FTIR spectrum of purified lignin Oxidative degradation of lignin using Alkaline nitrobenzene and m-dinitrobenzene (by Thermal and Microwave Technique): Oxidative degradation of pure (alkali) lignin using nitrobenzene and mdinitrobenzene under different reaction conditions (thermal and microwave technique) showed formation 505

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of low molecular weight compounds. Table 1 showed the extent of degradation of lignin achieved during various oxidation processes. The extent of degradation varies with the oxidizing agents used. Table 1: Extent of degradation of lignin achieved during oxidation Processes Sr. No.

1. 2. 3. 4.

Type of oxidative Degradation

Thermal Technique – PhNO2 Thermal Technique – (PhNO2)2 Microwave Technique – PhNO2 Microwave Technique – (PhNO2)2

% of residue available for potential utilization using thermal degradation technique

% of extractible mixture

90.6

8.52

89.8

8.95

86.4

11.6

85.5

13

From Table 1, it is observed that when degradation was carried out in presence of m-dinitrobenzene, more amount of lignin gets degraded to phenolic compounds as compared to nitrobenzene. Beside this the extent of degradation is more in case of microwave technique as compared to the thermal method. The low molecular weight fraction on qualitative and quantitative analysis using HPLC showed the presence of p-hydroxybenzaldehyde, vanillin, syringaldehyde and syringic acid along with few more compounds which were also detected but could not be identified due to unavailability of the standards. Unidentified compounds may include acetovanillon, veratraldehyde, divanillin, vanillic acid etc. The qualitative analysis of degraded lignin was carried out and the peaks obtained were identified by comparison of retention time with individual standard sample’s retention time under the same set condition. Oxidative degradation of pure lignin by Thermal Technique: (a) Oxidative Degradation of Pure Lignin using Alkaline Nitrobenzene by Thermal Technique: The HPLC analysis of low molecular weight fraction obtained by oxidative degradation of pure lignin using alkaline nitrobenzene by thermal technique showed the presence of p-hydroxybenzaldehyde (51.25%) and vanillin (9.81%) on total low molecular weight compound basis. With these two fractions the other fractions obtained are Syringic acid (2.85%) and Syringaldehyde (6.79%). All the above mentioned fractions possess important applications in varied areas. (b) Oxidative Degradation of Pure Lignin using Alkaline m-dinitrobenzene by Thermal Technique: The HPLC analysis of low molecular weight fraction obtained by oxidative degradation of pure lignin using alkaline m-dinitrobenzene showed the presence of p-hydroxybenzaldehyde (44.99%) and vanillin (18.15%) on total low molecular weight compound basis. As mentioned in the degradation of lignin with alkaline nitrobenzene, the degradation with m-dinitrobenzene also shows the presence of Syringic acid (7.31%) and Syringaldehyde (14.76%).

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Figure 3: Chromatogram- Thermal Technique PhNO2

Figure 4: Chromatogram- Thermal Technique ph(NO2)

2

Oxidative degradation of pure lignin by Microwave Technique: (a) Oxidative degradation of pure lignin using Alkaline Nitrobenzene by Microwave Technique: The HPLC analysis of low molecular weight fraction obtained by oxidative degradation of pure lignin using alkaline nitrobenzene by microwave technique. The analysis showed the presence of phydroxybenzaldehyde (61.87%) and vanillin (17.10%) on total low molecular weight compound basis. With these two fractions the other fractions obtained are Syringic acid (1.03%) and Syringaldehyde (19.91%). (b) Oxidative degradation of pure lignin using Alkaline m-dinitrobenzene by Microwave Technique: The HPLC analysis of low molecular weight fraction obtained by oxidative degradation of pure lignin using alkaline m-dinitrobenzene by microwave technique. The analysis showed the presence of phydroxybenzaldehyde (47.99%) and vanillin (22.79%) on total low molecular weight compound basis. With these two fractions the other fractions obtained are Syringic acid (9.35%) and Syringaldehyde (19.84%). 507

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Figure 5: Chromatogram- Microwave PhNO2

Figure 6: Chromatogram- Microwave ph(NO2)2 All the above chromatogram obtained on HPLC analysis of the various fractions, showed clearly the presence of p-hydroxybenzaldehyde, vanillin, syringic acid and syringaldehyde in different amount (%). Various peaks were obtained depending upon their retention time, peak area, the analysis of different compounds under different experimental conditions, is summarized as: Oxidative degradation of pure (alkali) lignin using nitrobenzene and m-dinitrobenzene under different reaction conditions (by thermal and microwave technique) showed formation of low molecular weight compounds. The extent of degradation is more in case of microwave technique as compared to the thermal method. Nitrobenzene / m-dinitrobenzene oxidation of pure lignin shows the alkaline twoelectron transfer process. A tentative reaction scheme showing the formation of p-hydroxybenzaldehyde and vanillin is represented in scheme 1. 508

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Table 2: Comparative yield of lignin degradation products by using different techniques

Quantity injected (µl)

Sample Thermal Technique –PhNO2

10

Thermal Technique – (PhNO2)2

10

Microwave – PhNO2

10

Microwave – (PhNO2)2

10

Retention Time (min)

Assignment

Peak area

% of the detected compound

12.989 19.109 24.107 32.098 12.882 19.204 24.112 31.334 13.112 18.998 23.657 32.072 12.998 18.889 23.756 31.121

Syringic acid Syringaldehyde p-hydroxybenzaldehyde Vanillin Syringic acid Syringaldehyde p-hydroxybenzaldehyde Vanillin Syringic acid Syringaldehyde p-hydroxybenzaldehyde Vanillin Syringic acid Syringaldehyde p-hydroxybenzaldehyde Vanillin

10782 25656 193629 37058 5217 10535 32115 12960 15972 308502 958510 265021 7332 15548 37606 17861

2.85 6.79 51.25 9.81 7.31 14.76 44.99 18.15 1.03 19.91 61.87 17.10 9.35 19.84 47.99 22.79

CH2OH CH CH

HO OCH3 6

CH3 CH

16

H3CO

OH HC O

CHOH CH O CH2OH

Carbohydrate

CHO

15

H3CO OCH3

O

CH2OH CH CH

7

OH Boiling Temp. / NaOH

OH

OCH3 vanillin

NO2 O

CH CH H2C

OCH3

OH

CH2 CH

O

O

CH

CH2OH CH HC OH CHO 12

8

H3CO CH2OH CH O H OHC C CH2OH HC O 9 H3CO

p- hydroxy benzaldehyde

H3CO

Other low molecular weight compounds

O

10

OH C O

Lignin

Scheme 1 509

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The formation of an aldehyde through the oxidative degradation of lignin with the help of alkaline nitrobenzene or m-dinitrobenzene can be best explained by two electron transfer process. e.g. formation of vanillin may be stated as shown in scheme 2. OH

CH3 HC

OH

CH3 HC

CH

CH

CH3

CH3

HC

HC OH

OH OH

O

CH

CH 2e

OCH3

O

OH

CH OH

2e

O

2e OCH3

OCH3 O

O

O

O

Scheme 2 Oxidative degradation of lignin using alkaline nitrobenzene and m-dinitrobenzene by thermal and microwave technique indicates the variation in the % of p-hydroxybenzaldehyde and vanillin. The low molecular weight fractions on quantitative analysis using HPLC showed the presence of phydroxybenzaldehyde (51.25%) and vanillin (9.81%) in the mixture obtained by oxidative degradation of lignin using alkaline nitrobenzene by thermal technique. Similarly, p-hydroxybenzaldehyde (44.99%) and vanillin (18.15%) in the mixture obtained by oxidative degradation of lignin using alkaline mdinitrobenzene by thermal technique, on total low molecular weight compound basis. Whereas, the low molecular weight fractions on quantitative analysis using HPLC showed the presence of phydroxybenzaldehyde (61.87%) and vanillin (17.10%) in the mixture obtained by oxidative degradation of lignin using alkaline nitrobenzene by microwave technique. Similarly, p-hydroxybenzaldehyde (47.99%) and vanillin (22.79%) in the mixture obtained by oxidative degradation of lignin using alkaline m-dinitrobenzene by microwave technique, on total low molecular weight compound basis. The extent of extractable low molecular weight compounds was found to be more on pure lignin basis in case of microwave heating as compared to that of thermal heating. Thermal method showed somewhat less degradation in case of nitrobenzene and m-dinitrobenzene. Microwave method showed about more degradation in case of nitrobenzene and m-dinitrobenzene both. Further, the time required for the oxidative degradation using thermal methods have been greatly reduced. Microwave technique is found to be simpler, faster and more effective as far as overall efficiency is concerned. Even though the microwaves can be used in industries for processing food stuffs, material processing, to break down sludge produced by steel mills and other industries and for the treatment of hazardous materials from weapon components and radioactive waste, rubber tyres and fluorescent bulbs, polymer technology, ceramics, alkane decomposition etc, the present work confirms the known advantages of use of microwaves in several organic reactions, beyond doubt. Particularly in this case the system which involves aqueous solutions, the use of microwave is very safe, convenient, high yielding and fast. The comparative yield of lignin degradation and low molecular weight compound formed by using different techniques are represented in Table 2. Demethoxylation of lignin during the pulping process may lead to the relatively lower formation of vanillin during oxidative degradation. Same may be the reason for the greater yield of p-hydroxybenzaldehyde which has been invariably noticed in all types of degradations. Every time standard solutions of p-hydroxybenzaldehyde, syringic acid, syringaldehyde and 510

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vanillin were first injected to find out the respective retention time and then samples were injected, detected and identified by the corresponding retention time. A slight variation was observed in the retention time of p-hydroxybenzaldehyde, syringic acid, syringaldehyde and vanillin in some of the chromatograms, it is mainly due to the fact that the experiments and analysis were carried out at different interval of time and slight variations in the equipment responses, some variations in the flow rate, UV wavelength etc. HPLC analysis provides the way for qualitative and quantitative analysis of four main compounds which have immense industrial importance. p-hydroxybenzaldehyde is an important intermediate of dyes and polymers and is widely used in cardioactive drug (Hantzsch synthesis), in cynocoumarins and mercapto pyrimidines, an intermediate for antimetabolites, it is also a constituent of antihypertensive dihydropyrimidine drugs (Biginelli synthesis) and vanillin is a useful component in imitation flavouring of vanilla in variety of food materials. Syringaldehyde is used as an antioxidant, preservative and in medicine like Antihyperglycemic (stretozotonic) and syringic acid is used as preservative. CONCLUSION In this study, we have carried out the oxidative degradation of lignin by thermal and microwave technique in order to obtain the value added products. The present research work has also confirmed the higher efficiency of microwave technique for lignin degradation. The various value added industrially important chemicals obtained are syringic acid, Syringaldehyde, vanillin and p-hydroxybenzalddehyde etc. All the products possess immense industrial applications. Thus the utilization of alkali lignin for the formation of low molecular weight compounds was confirmed. Nature of the low molecular weight compounds obtained helps in the elucidation of lignin structure. Thus lignin can be considered as a potential feedstock for the chemical industries. REFERENCES 1. J. E. Holladay, J. J. Bozell, , J.F. White, D. Johnson, Top value added chemicals from biomass, volume II. 2007. 2. J.E.G. Van Dam, B. de Klerk-Engels, P.C. Struik, R. Rabbinge, , Securing renewable resource supplies for changing market demands in a biobased economy, Ind.Crops. Prod. 2005.21(1):129-144. 3. A.J. Ragauskas, C. K.Williams, B. H. Davison, G. Britovsek, J. Cairney, C.A. Eckert, Biotechnology for fuels and chemicals, the twenty ninth Symposium, 2006, T.311(5760):484-489. 4. M. Nagy, M. Kosa, H. Thelianderb, A. Ragauskas, Characterization of CO2 precipitated kraft lignin to promote its utilization, J. Green Chem., 2010, 12, 31-34. 5. F.E. Brauns, D.A. Brauns, The chemistry of lignin (supplement volume), Academic Press, N.Y., London, 1965. 6. Sarkanen, K.V., Ludwig, C.H., Lignin, Wiley Interscience; 1971, 575. 7. Pinherio, Paulo Cesar C., Proc. Braz. Symp. Chem. Lignins, other wood compon. 4th edn 45 (Eng.) Through C.A., 1997, 126:133434 M.

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Corresponding authors: Nandanwar R.A Priyadarshini Bhagwati College of Engineering, Nagpur, Maharashtra, India.

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