The document summarizes research into degrading lignin using doped catalysts. Lignin is a major component of plant biomass but is difficult to decompose. The research aims to optimize lignin degradation reaction conditions and catalyst types/dopants to produce low molecular weight products. Initial experiments used silica-alumina and zeolite catalysts, with and without copper, zinc, or lithium doping. Qualitative analysis of products found activated silica-alumina at 1g catalyst, 3g lignin, and 100mL water produced minimal solids. Future work will further characterize products and experiment with more catalyst mixtures and doping to improve yields.

1. DEGRADATION OF LIGNIN
USING DOPED CATALYSTS
Garrett Mitchell
Department of Chemistry, University of North Dakota

2. INTRODUCTION

3. What is lignin?
• The second most abundant natural raw materials on earth, by mass
• Also, it is the most abundant aromatic polymer, making it a potentially great
source for producing phenolic compounds
• Plant biomass consists of around 15–30 wt% of lignin
• Lignin is the “glue” of the cell walls that helps the cellulose and hemi-cellulose
stay in a stable structure
• It is very hard to decompose

4. SEM Photos of Lignin

5. http://5e.plantphys.net/image.php?id=130

6. Why choose Lignin?
• For one, there is a lot of it, and so far it has been virtually untapped
• It is a waste product from the paper industry ‘s pulping process that is burned in order to
regain some energy losses, and the recovery boiler is usually a bottleneck in the pulping
plant, making profit from such a material would be very advantageous
• In the future, production of biofuels will also generate a significant amount of lignin, making
it more abundant.
• Since Lignin is a product from biomass, if any chemicals can be produced
from it, they will be sustainable unlike petroleum products, which is good for
the long term

7. Disadvantages of Lignin Degradation
• There are many different types of lignin that depend on a variety of factors,
making it hard for find one specific solution to work will all types
• Type of plant
• Age of plant
• Plant’s conditions
• Separation technique
• Lignin is also very stable and not easily broken down
• Due to the complex nature of lignin, many different side reactions occur, such
crosslinking between degradation products to produce char, which is a larger
molecule than lignin and to be avoided

8. Types of Degradation methods
• Biochemical and biotechnical degradation
• Can be very selective and energy efficient but also can be very costly
• Thermochemical degradation
• Not as selective, but more easily done
• Involves high temperatures and pressures which can also be costly
• Selection of proper solvents and catalysts can help with yields and selectivity, as well as
becoming more cost effective
• The method that this study will be covering

9. Reaction conditions / Aim of the experiment Products / Results References
Liquefaction of lignin in SCW, T > 400 °C oil Funazukuri et al. 1990
Different lignins in supercritical methanol or
ethanol
with different alkaline salts added
stoichiometrically,
T = 290 °C
monomer (c.a. 180 g・mol-1) Miller et al. 1999
Characterisation of lignin derived products in
methanol,
obtained by treating buna wood with SCW
products have more
phenolic hydroxyl groups
than in lignin
Ehara et al. 2000
Decomposition of lignin in SCW with and
without
addition of phenol, T = 673 K
higher water density/ phenol
added →products with
lower molecular weight
Saisu et al. 2003
Base catalysed depolymerisation of lignin in
subcritical
aqueous solutions, catalyst: alkali hydroxides,
T = 300 –
340 °C
alkylated phenols,
alkoxybenzenes,
alkoxyphenols,
hydrocarbons
Shabtai et al. 2003
Gasification of lignin in SCW, catalyst:
Ni/MgO, T = 250 – 400 °C, variation of water
density
carbon dioxide, methane,
hydrogen (yield 78 %)
Sato et al. 2006
Organosolv lignin, SCW, T > Tc, catalyst :
Pd/C, stirred
autoclave
brown and viscous oils
(yield: 70 %) , CO, CO2,
CH4, C2H6
Johnson et al. 1988
Literature Highlights

10. METHOD

11. Two-Phase Project
• The project is separated into two different phases:
1. Optimization based on reaction conditions as well as solvent and catalyst ratios, to be
done with undoped catalysts
2. Optimization based on effects of different catalysts and dopants

12. Materials used
• The type of lignin used was Indulin AT, a kraft lignin
• Catalyst types used were activated silica-alumina and ZSM_5 zeolites of
varying Si/Al ratios
• Both methanol and DI water was used as the solvent, but mostly DI water
• Dopants for the catalyst included the following purchased from Sigma-Aldrich
and used as is:
• Copper(ǁ) Nitrate hemipentahydrate, 98% purity
• Zinc Nitrate Hexahydrate, 98% purity
• Lithium chloride, 99% purity

13. Reaction procedure
• The degradation of lignin was carried out in a Parr pressure reactor. The
reactor was charged at room temperature, then purged with Nitrogen gas 5
times. The reactor was then heated to the reaction temperature. The reaction
was then allowed to run for 30 minutes, then cooled to 50 degrees Celsius at
which the reactor was emptied. The reactor was also cooled if the pressure
became too high.
• Inlet feed and outlet product mixture was weight to determine weight loss
• Once reaction was finished, sample was vaccum filtered and solid sample was
dried then weighed to find mass/liquid fraction

14. Parr Reactor
http://www.webpages.uidaho.edu/niatt/research/project_descriptions/klk768.htm

15. Catalyst Preparation
• Catalyst Activation:
• Silica-Alumina grade 135 was activated by calcination in a muffle furnace for 12 hrs. in a
muffle furnace at 550°C
• More detailed explanation later
• Zeolite Catalysts were pre-activated and used as is
• Catalyst doping:
• For doping the catalyst, dopant was added in order to create a 1wt% metal ion mixture in the doped
catalyst, as well as DI water added with a ratio of 30mL DI water/1g catalyst.
• The mixture was then stirred for ~12 hrs.
• After stirring, the doped catalyst was separated from the water by vacuum-filtration
• After separation, the catalyst was dried at 100°C for 1 hr. then calcined at 500°C for 4 hrs. in a
muffle furnace

16. Analysis Techniques
• Dry solid samples from reaction, as well as initial lignin samples were
evaluated by TGA analysis
• Activated and non-activated silica-alumina were evaluated using FTIR

17. RESULTS AND DISCUSSION

18. TGA analysis

19. TGA analysis cont’d
• Initial TGA analyses show that lignin and its decomposition products undergo
the most mass loss in the region of 250-450 °C
• Can be explained by the complex structure of lignin.
• Analysis shows that the degradation products lose a smaller percentage of
mass in that region
• Those same bonds have already been broken during degradation in reactor under less
severe conditions, showing that the catalyst is effective
• At temperatures higher than 450°C mass loss is not affected by the reaction
• Likely due to the relative non-severity of reaction conditions to TGA analysis.

20. TGA analysis cont’d

21. Product Mixture-Qualitative Analysis
Recombinant Lignin
Char
Liquid Phase

22. Product Mixture-Qualitative Analysis cont’d
• Since we are after the low molecular weight product that are dissolved in the
liquid phase, by visual inspection, optimization of the degradation reaction
can be done by reducing the amount of product recombinant lignin and char
• Also if a different type of particulate is formed, it can be investigated to see if
the products are useful or non using other analysis techniques

23. 10g cat. 20g lignin 300mL DI
Water
Copper(II) doped Silica-Alumina
Too much recombinant lignin,
more aggressive reaction
conditions or a different catalyst
type is needed
1 g cat. 5g lignin 100mL DI
Water
Activated Silica-Alumina catalyst
Too much char formation, less
aggressive reaction conditions or
a different catalyst type is

24. 1g cat. 3g lignin 100mL DI
Water
Activated Silica-Alumina catalyst
Reaction mixture seems to work
pretty well, not much solids
overall
1g cat. 3g lignin 150mL DI
Water
Activated Silica-Alumina catalyst
Interesting light-brown
particulate formed, further
investigation required
?

25. Activation of Silica-Alumina
• Hydrogen
bonded
OH groups
• Al-O-Al
and Al-O-
Si groups

26. Zeolites vs. Silica-Alumina
Weitkamp J, “Zeolites and catalysis” Solid State Ionics, 2000, 175-188

27. CONCLUSION

28. Conclusion
• The addition of a catalyst has had the effect of breaking the bonds usually
required by higher operating conditions, and some optimization has been
done. So far, it seems that a mixture of 1g catalyst and 3g lignin seems like a
good combination and that the amount of solvent does not have a large effect,
at least at the range that we have experimented on.

29. Future Work
• Continued experimentation with reaction mixtures and then on to doping of
catalyst
• Analytical equipment to be used to fully characterize the products
• FTIR
• Continued TGA possibly with DSC
• GC analysis and potentially MS

30. Acknowledgements
• I would like to thank Dr. Seames and Sara Pourjafar for their support and
guidance.
• This material is based upon work supported by the National Science
Foundation Research Experience for Undergraduate under Grant No. CHE
1156584. Any opinions, findings, and conclusions or recommendations
expressed in this material are those of the author(s) and do not necessarily
reflect the views of the National Science Foundation

31. Questions?