Catalytic reductive fractionation (CRF): effects of acidic/alkaline additives
Tom Renders,a Sander Van den Bosch,a Steven-Friso Koelewijn,a Thijs Vangeel,a Gil van den Bossche,a Wouter Schutyser,a,b,* Bert Sels a,*
a
Center for Surface Chemistry and Catalysis, KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium
b National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
* E-mail: [email protected], [email protected]
Classic biorefinery vs. “Lignin-first”
Classic cascade
Lignin-first cascade
Focus on valorization of carbohydrates, not on lignin
STEP
STEP
1
1
Focus on valorization of native lignin, prior to sugars
Degradation & repolymerization: technical lignins
Prevention of degradation & repolymerization
Recalcitrant substrate, low monomer yields
Reactive substrate, high monomer yields
Low added-value, lignin incineration
$
$
Increased added value from lignin
The CRF-biorefinery
Operating conditions
473 – 523 K
40 – 120 bar
Lignocellulose
e.g. poplar, birch,
pine, switchgrass
Lignin oil
Bio-crude
Separation
dimers +
oligomers
monomers
Pd/C
H2
Catalyst + H2
e.g. Pd/C, Ru/C,
Ni/SiO2
Soluble
carbohydrates
Filtration
Carbohydrate
pulp
Elementary steps
Step 1: Solvolytic extraction
Step 2: Depolymerization
Solvent
e.g. MeOH, EtOH,
iPrOH, EtGly
Process summary: Turning the lignin-first paradigm into reality is enabled by a process termed catalytic reductive fractionation (CRF). Herein, lignin is
solvolytically extracted from the biomass matrix (step 1), followed by instant catalytic depolymerization (hydrogenolysis, step 2). The main products
resulting from this biorefinery are a depolymerized lignin oil and a carbohydrate enriched pulp.
Pitfall: High temperatures (523 K) are required in order to obtain a near complete delignification, which implies a high operating pressure (120 bar).
Possible solution: Catalytic additives (H3PO4, NaOH) could possibly assist the solvolytic lignin extraction (step 1) at milder T (473 K) and P (60 bar).
Research question: What are the effects of acidic (H3PO4) or alkaline (NaOH) additives on the CRF process? Are these effects beneficial?
Effects on lignin
Evaluation
Effects on pulp
40
80
30
60
20
10
0
0,20g
0,10g 2.50
0,05g Neutral
0
1.25
5.00 0,05g
0
H3PO4 H3PO4 H3PO4
NaOH
40
20
20
20
10
0
0,10g
2.50
NaOH
Delignification
(% Klason lignin)
Neutral
0
0,05g H3PO4 0,10g H3PO4 0,20g H3PO4
1.25 2.50 5.00
Cellulose
0,20g Neutraal
5.00
0
NaOH
250°C
60
40
20
0
[NaOH] / g.L-1
Lignin
• Decreased monomer yield
• Increased delignification
Lower monomer selectivity (cfr. gap)
Hampered depolymerization by NaOH
Pulp
• Partial loss of hemicellulose
• Partial loss of cellulose
Degradation of released sugars
Carbohydrate balance (wt%)
Gap
Delignification / %
80
Reference, High T
Monomer yield / %
40
473 K
40
0
[H3PO4] / g.L-1
NaOH
100
0
60
473 K
50
0,05g
1.25
NaOH
80
523 K
NaOH
Neutral
Pulp
• Removal of hemicellulose (alcoholysis)
• Effective preservation of cellulose
Cleaner cellulosic pulp
0
[H3PO4] / g.L-1
Other
30
Lignin
• Increased monomer yield
• Increased delignification
Higher lignin conversion at milder T
Similar outcome as high T reference
Neutraal
250°C
0
523 K
Hemicellulose
NaOH
100
80
60
Reference, High T
473 K
H3PO4
100
Reference, High T
100
Delignification / %
50
Carbohydrate balance (wt%)
H3PO4
Reference, High T
Monomer yield / %
Monomer yield (C-mol%)
H3PO4
40
20
0
[NaOH] / g.L-1
Neutral
0
0,05g NaOH 0,10g NaOH 0,20g NaOH
523 K
(1) Van den Bosch, S.; Schutyser, W.; Sels, B. F. et al. Reductive lignocellulose fractionation into soluble lignin-derived phenolic monomers and dimers and processable carbohydrate pulps. Energy Environ. Sci. 2015, 8, 1748-1763.
(2) Renders, T.; Sels, B. F. et al. Influence of acidic (H3PO4) and alkaline (NaOH) additives on the catalytic reductive fractionation of lignocellulose. ACS Catal. 2016, 2055-2066.
1.25 2.50 5.00
473 K
Neutraal
250°C
0
523 K