conversion of lignin to liquid compounds

66 downloads 0 Views 615KB Size Report
5 A pie chart – GCMS analysis of liquid phase for lignin treatment with formic acid and methanol. 300 °C, 5 h, formic acid : methanol 3:4 (70 ml loading). Fig.
5th International Scientific Conference Renewable Energy Sources 2014

May 20-22, 2014 Tatranské Matliare High Tatras, Slovak Republic

CONVERSION OF LIGNIN TO LIQUID COMPOUNDS Kalabová, M., Šutý, Š., Lauko, T., Jablonský, M., Ház, A., Sládková, A., Šurina, I. Institute of Natural and Synthetic Polymers, Department of Wood, Pulp and Paper, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovakia e-mail: [email protected]

Abstract This paper reports a process for converting lignin into value-added chemicals. The thermochemical process is termed solvolysis (alcoholysis) of lignin. The reaction consists of heating the lignin at high temperatures (270 – 300°C) in the air atmosphere. Lignin reacts with hydrogen-donor in the presence of alcohol in a high-pressure reactor. A liquid fraction and a significant amount of the char are the most important products of solvolytic depolymerization reaction. The pressure and temperature behavior of observed process was described. A used method employed in this report was described, and also some important results were noticed. Thermal treatment in the air atmosphere can be a promising conversion of lignin into value-added chemicals. Keywords Lignin, solvolysis, acid, alcohol, value-added chemicals

1

INTRODUCTION

Lignin is a copolymer consisting of the monolignols called p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. The lignin monomers are linked by these cleavages: β-O-4-aryl ether, O-4-aryl ether, 4-O-5-diaryl ether, β-5phenylcoumaran, 5-5-biphenyl and ββ- (Resinol) [1]. The most abundant linkages in a lignin structure are β-O-4 aryl ether bonds. Depolymerization of lignin is achieved by thermochemical process. This process lead to breaking the most important bonds such as β-O-4 aryl ether and 5-5-biphenyl bonds remain untouched. Nowadays, lignin is not used only in combustion process for the heat production. Its structure gives new possibilities for its usage in the future. Lignin appears the new source for chemicals and fuels. Common challenge in the lignin degradation to liquids, containing phenolic compounds, includes the degree of depolymerization and deoxygenation. Lignin depolymerization has been explored within solvolysis and also pyrolysis approach [2]. Solvolytic depolymerization treatment was performed in the presence of hydrogen donors like tetralin [3, 4]. Davoudzadeh et al. [5] used tetralin with phenol as solvent for lignin hydrogenolysis. Hydrogen donating solvents such as 9, 10dihydroanthracene (AnH2) and derivatives [6] were used for lignin depolymerization because it is a stronger hydrogen donor compared to tetralin [7]. Liquefaction of biomass for the production of chemicals by solvolysis was performed in acetone, ethanol or water [8]. Ethanol is appropriate solvent

for biomass because of its good properties and it has a low critical temperature. The idea of lignin degradation leads to usage of the cheap and simple chemicals that can give value-added chemicals [7]. Formic acid and acetic acid can be used as hydrogen donor chemicals. A solvolytic reaction in the presence of some alcohols such as methanol, ethanol and 2-propanol is interesting because of their low cost and less harmful impact on the environment. A molecular elimination of formic acid is occurred by the solvolytic process at high temperatures (Fig.1)

Fig. 1 Formic acid molecular elimination occurs during solvolysis. A main reaction is a solvolytic breaking the β-O-4aryl ether bonds. As a result of this process are guaiacol and Hibbert’s ketones. Then guaiacol reacts with ethanol at high temperatures during deoxygenation process and decomposing formic acid to hydrogen and carbon dioxide. The main products of solvolytic reaction are phenol, 2-methyl phenol, 3-methyl phenol and 2,3 – dimethyl phenol, cresol, catechol and other phenolic derivates. 2

EXPERIMENTAL

Part of this paper describes the solvolytic one-step lignin depolymerization. A closed system stirred

5th International Scientific Conference Renewable Energy Sources 2014

reactor from Parr Instruments was used for all experiments. A reactor was filled with dry lignin powder, acid (formic or acetic) and alcohol (methanol, ethanol or isopropanol) in the different volumes. The lignin was dried for 24 hours at 105 °C before using it in the reactor. The same volumes of different kinds of acid and also different kinds of alcohols were used in all experiments. Then the reactor was closed and heated to 300°C for 5 hours. The used lignin from Swedish company Innventia AB was characterized. The elemental analysis made by Vario Macro Cube was C (65 wt %); N (0.12 wt %); H (5.44 wt %); (1.14 wt %) S and O (28.3 wt %) was calculated by difference [9]. After 5-hour reaction time in reactor was finished, a heater and also the reactor stirring were turn off. A reactor was cooled by the air stream to room temperature. It has never been cooled by cold water because a char amount can arise. An experimental process of conversion lignin to liquid is described on the following picture (Fig. 2).

May 20-22, 2014 Tatranské Matliare High Tatras, Slovak Republic

Tab.1 Six combination of lignin reaction with acid and alcohol. Exp. 1 2 3 4 5 6

SM [g] 13 Lignin 13 Lignin 13 Lignin 13 Lignin 13 Lignin 13 Lignin

acid [ml] 30 HCOOH 30 HCOOH 30 HCOOH 30 CH3COOH 30 CH3COOH 30 CH3COOH

alcohol [ml] 40 MeOH 40 EtOH 40

T [°C] 300

t [h] 5

300

5

300

5

300

5

300

5

300

5

2-PrOH

40 MeOH 40 EtOH 40 2-PrOH

The pressure and temperature behavior of reaction was investigated for all experiments. In a closed reactor was observed an autogenous pressure but the highest value was changed according to the used acid or alcohols. The highest pressure was observed by the lignin reaction with formic acid with all kinds of alcohols. A lignin reaction with acetic acid and all kinds of alcohol wasn’t performed in so high pressure. A formic acid was converted to carbon dioxide and hydrogen during the lignin depolymerisation in a large amount. A temperature course in lignin reaction with formic acid and three kinds of used alcohols is shown on the following picture on the first three positions. On the second three positions is shown a lignin reaction with acetic acid and also three kinds of used alcohols (Fig. 3).

Fig. 2 Lignin to liquid conversion Elemental analysis: A solid product (char) was analysed by elemental analysis by Vario Macro Cube. The elemental composition of char in the CHNS was performed and oxygen amount was calculated by difference. A heat of combustion: Higher heating value of char was determined in a FTT calorimetric bomb used a standard method. GCMS analysis: A liquid samples were analysed by GS/MS analyser. Firstly, samples were filtrated by syringe filters. Before analysis, the filtrated samples must be diluted with an appropriate solvent. 3

RESULTS AND DISCUSSIONS

In an experimental part were performed 6 combinations of lignin reaction with acid and alcohol in one step (Tab.1).

Fig. 3 A temperature course in the same reaction time (5h). Two kinds of acids and three kinds of alcohols were used. A temperature course didn’t depend on used alcohol. It had almost the same temperature progress. It was the same in a case of lignin reaction with acetic acid and also three kinds of used alcohols. A temperature 300 °C was achieved between 75 – 90 minutes of reaction time in both cases. A difference in a pressure course of the

5th International Scientific Conference Renewable Energy Sources 2014 lignin reaction with acid and alcohols is visible. The higher values of pressure were achieved in a case lignin reaction with formic acid and alcohols. A temperature stabilised at the constant values after 75 minutes. The pressure had to be regulated because of limitation of reactor. The max pressure in reactor is limited to 200 bar. If the pressure was 190 bar in a reactor, it was necessary to open a valve and release the congested gas. On the following picture is shown a pressure course in the lignin treatment with acids and alcohols.

May 20-22, 2014 Tatranské Matliare High Tatras, Slovak Republic

Phenolic compounds 5%

Others 4% Alcohols 35%

Acetone (solvent for dilution) 56%

Fig. 6 A pie chart – GCMS analysis of liquid phase for lignin treatment with formic acid and ethanol. 300 °C, 5 h, formic acid : ethanol 3:4 (70 ml loading).

Furans 1%

Fig. 4 A pressure course in the same reaction time (5h). Two kinds of acids and three kinds of alcohols were used. GCMS analysis of the liquid products was carried out by the same conditions. The samples were diluted in a 1:1 ratio in acetone and were analysed. On all of pie charts we can see a part belonging to acetone and also chemicals used for the lignin treatment. All chemicals were taken into account and shown in a pie chart.

Others 15%

Phenolic compounds 22%

Esters 1%

Phenolic compouds 21%

Alcohols 34%

Acetone (solvent for dilution) 25%

Fig. 7 A pie chart – GCMS analysis of liquid phase for lignin treatment with formic acid and isopropanol. 300 °C, 5 h, formic acid : isopropanol 3:4 (70 ml loading).

Phenolic compounds 8%

Furans 1%

Others 19%

Others 19%

Acetone (solvent for dilution) 30%

Alcohols 24% Acetic acid 17% Acetone (solvent for dilution) 37%

Fig. 5 A pie chart – GCMS analysis of liquid phase for lignin treatment with formic acid and methanol. 300 °C, 5 h, formic acid : methanol 3:4 (70 ml loading).

Esters 26%

Fig. 8 A pie chart – GCMS analysis of liquid phase for lignin treatment with acetic acid and methanol. 300 °C, 5 h, acetic acid : methanol 3:4 (70 ml loading).

5th International Scientific Conference Renewable Energy Sources 2014

Others 3%

Ethyl acetate 36%

Alcohols 14% Esters 3%

Acetic acid 16%

Phenolic compounds 6%

Acetone (solvent for dilution) 22%

Fig. 9 A pie chart – GCMS analysis of liquid phase for lignin treatment with acetic acid and ethanol. 300 °C, 5 h, acetic acid : ethanol 3:4 (70 ml loading).

Others 6%

Acetone (solvent for dilution) 21% Esters 7%

Isopropyl acetate 66%

Fig. 10 A pie chart – GCMS analysis of liquid phase for lignin treatment with acetic acid and isopropanol. 300 °C, 5 h, acetic acid : isopropanol 3:4 (70 ml loading). The highest yields of phenolic compounds were achieved during lignin treatment with the formic acid. The treatment with the acetic acid wasn’t so effective. When we don’t take into account solvents and main chemicals used for lignin treatment, the main products are phenolic compounds in a case of formic acid and alcohols. In a case of usage the acetic acid, the main products are esters, ethyl acetate in reaction with ethanol and isopropyl acetate in reaction with isopropanol. 4

CONCLUSIONS

This report investigated the solvolytic depolymerization reaction of lignin. The different amount of phenols and phenols derivates were related to used acid and alcohol. A highest amount of phenolic compounds were investigated in lignin treatment with formic acid and methanol or isopropanol. A solvolytic depolymerisation reaction can be used for lignin conversion to liquids.

May 20-22, 2014 Tatranské Matliare High Tatras, Slovak Republic

5

ACKNOWLEDGEMENTS

This article was created with the support of the Ministry of Education, Science, Research and Sport of the Slovak Republic within the Research and Development Operational Programme for the project "University Science Park of STU Bratislava", ITMS 26240220084, and by the project of National Centre for Research and Application of Renewable Energy Sources, ITMS: 26240120016, and by the project Finalization of Infrastructure of the National Centre for Research and Application of Renewable Energy Sources, ITMS: 26240120028, and by the project Competence centre for new materials, advanced technologies and energetics ITMS: 26240220073, co-funded by the European Regional Development Fund. This publication was supported by the Slovak Research and Development Agency under the contract No. APVV-0850-11, and by the project VEGA 1/0775/13. 6

REFERENCES

[1] Pandey, M. P., Kim, S. Ch.: Lignin Depolymerization and Conversion: A Review of Thermochemical Methods. Chem. Eng. Technol. 2011, 34, No. 1, 29–41 [2] Gasson, J., Forchheim, D., Sutter, T., Hornung, U., Kruse, A., Barth, T.: Modeling the Lignin Degradation Kinetics in an Ethanol/Formic Acid Solvolysis Approach. Part 1. Kinetic Model Development. Ind. Eng. Chem. Res. 2012, 51, 10595−10606. [3] Connors, W. J., Johanson, L. N., Sarkanen, K. V., Winslow, P.: Holzforschung 1980, 34, 29. [4] Vasilakos, N. P., Austgen, D. M., Ind. Eng. Chem. Proc. Des. Dev. 1985, 24, 304. [5] Davoudzadeh, F., Smith, B., Avni, E., Coughlin, R. W.: Holz- forschung 1985, 39, 159. [6] Dorrestijn, E., Kranenburg, M., Poinsot, D., Mulder, P.: Holz-forschung 1999, 53, 611. [7] Kleinert, M., Barth, T.: Phenols from lignins. Chem. Eng. Technol. 2008, 31, No. 5, 736– 745 [8] Liu, Z., Zhang, F-S. (2008) Effects of various solvents on the liquefaction of biomass to produce fuels and chemical feedstocks. Energy Convers. Manage. 49:3498–3504. [9] Škulcová, A., Jablonský, M., Ház, A.: Characterization of isolated lignins. Wood, Pulp and Paper 2014, 12.-13. March 2014, (2014) 357-361. (In Slovak)