Chemical Reactions on Solid Surfaces - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 456

H þ ð HX n OH $ H þ ð

HX n OH ð aq Þþ aq Þ % aq Þ (9.155)

HX n OH $ H þ ð HX m OH $ H þ ð

aq Þþ H 2 O ð aq Þ / aq Þþ HX s OH ð aq Þ (9.156)

where m n , R- denotes the cellulose and/or lignin bonding connected with the fibers,

and P represents a segment/subunit of hemicellulose or lignin. X n represents an n -xylo-
polymer middle group, i.e. ( e O e C 5 H 8 O 3 e ) n , whereas HX n OH is an n -xylooligomer.
HOAc represents the acetic acid molecule, where Ac

þ s ¼

CH 3 CO.
Eqn (9.153) represents the adsorption of hydrogen ions onto the woody biomass surface,
and Eqn (9.154) represents the surface reaction whereby one xylo-oligomer is cleaved from
the woody biomass. One should note that the actual entity participating in the extraction
reaction/hydrolysis reactions can be either H þ or H 3 O þ . In fact, one may write
H þ þ

¼

H 2 O % H 3 O þ (9.157)

and

H 3 O þ % R-X n OH $ H 3 O ð

ð Þþ Þ (9.158)

R-X n OH s s

R-X n OH $ H 3 O þ ð R-X m OH $ H þ ð s Þ / s Þþ HX s OH ð aq Þ (9.159)

H 3 O þ ð R-POAc $ H 3 O þ ð R-POAc ð s Þþ aq Þ % s Þ (9.160)

R-POAc $ H 3 O þ ð R-POH $ H þ ð s Þ % s Þþ HOAc ð aq Þ (9.161)

HPOAc $ H þ ð R-POAc $ H 3 O þð s Þ % R-OH ð s Þþ aq Þ (9.162)

H 3 O þ ð HX n OH $ H 3 O þ ð HX n OH ð aq Þþ aq Þ % aq Þ (9.163)

HX n OH $ H 3 O þ ð HX m OH $ H þ ð aq Þ / aq Þþ HX s OH ð aq Þ (9.164)

Kinetically, the steps as shown in Eqns (9.146) through (9.164) can represent the extrac-
tion/hydrolysis reactions.
The monomeric sugar can further dehydrate in the presence of proton to dehydrated prod-
ucts such as furfural, humic acid, Levulinic acid, etc.
HX 1 OH $ H þ ð H þ þ and other dehydration products (9.165)

Besides the extraction reaction, the polysaccharides can condense back to the woody
biomass:

aq Þ / H 2 O þ furfural ;

R-X n OH $ H þ ð R-X n þ s OH $ H þ ð s Þþ HX s OH ð aq Þ / s Þþ H 2 O ð aq Þ (9.166)

or

HX s OH $ H þ ð R-X n þ s OH $ H þ ð

ð Þþ Þ / Þþ ð Þ (9.167)

R-X n OH s aq s H 2 O aq

Also, the dehydration polymerization of the xylo-oligomers occurs
HX n OH $ H þ ð HX n þ m OH $ H þ ð aq Þþ HX m OH ð aq Þ / aq Þþ H 2 O ð aq Þ (9.168)