United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/037 Aug. 1987
4>EPA Project Summary
An Evaluation of Pristine
Lignin for Hazardous
Waste Treatment
Daniel J. O'Neil, Christopher J. Newman, E. S. K. Chian, and H. Gao
A feasibility study was conducted to
assess the utilization of lignin, isolated
from a steam-exploded hardwood
(Tulip poplar) with 95% ethanol and
0.1N NaOH, as a potential adsorbent
for hazardous waste treatment. Eight
organic compounds and two heavy
metals were selected to allow compar-
ison of lignin isolates with activated
carbon.
Adsorption kinetic studies, adsorp-
tion size studies, and adsorption iso-
therms based on the Freundlich equa-
tion were completed. The lignin isolates
were extensively characterized using
instrumental and classical wet
techniques.
It was found that the adsorption
capacity of lignin for heavy metals
(chromium and lead) is comparable to
activated carbon, despite a huge diver-
gence in surface area (0.1 ma/g vs.
1000 mVg). The surface area discrep-
ancy and the extensive aromatic sub-
stitution in lignin macromolecule
impeded the achievement of an adsorp-
tion capacity of lignin for polar organic
compounds, which would allow it to
be cost-competitive with activated
carbon, although results with phenol
and, to a lesser degree, naphthalene
indicate significant potential for
achieving competitive capacities. A
recommended plan for surface area and
structural enhancement is presented on
the basis that lignin can be developed
as an effective and low-cost adsorbent
for polar priority pollutants and/or as
an ion-exchange resin for heavy metal
wastewater cleanup.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory,
Cincinnati, OH, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
An innovative process for the capture
and concentration of hazardous waste
compounds, such as heavy metals,
organic acids, ketones, etc., which are
found in aqueous waste streams has
been proposed. The process involves the
use of a "pristine lignin" which Georgia
Tech investigators had demonstrated as
being readily isolated from woody wastes
and raw materials by hydrothermal
treatment and solvent extraction. The
production process (Figure 1) in which
the lignin is produced as a by-product
during production of sugars from the
cellulose fraction of lignicellulose raw
materials (and subsequent conversion to
fuel-grade ethanol) appeared to be
economically feasible. Indeed, the eco-
nomics would be enhanced by a volume
market for the lignin co-product (which,
otherwise would be used principally for
process fuel). All requisite process
equipment for production was commer-
cially available.
Unlike "commercial lignins," the
"pristine lignin" is a clean, tractable,
relatively low-molecular weight polymer
with an expected high degree of organic
functionality, unadultered by adventi-
tious impurities. As such it was consid-
-------
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ered that the pristine lignin could be
employed, in one of three general ways,
with or without chemical modification,
viz.,
1. Adsorption
2. Ion-exchange chromatography and
electron-exchange chromatography
3. Precipitation/Coagulation/
Flocculation
The principal economic merit of treating
hazardous wastes with lignin was fore-
cast to be its low cost, particularly when
compared to adsorbents such as acti-
vated carbon and commercial ion-
exchange resins (see Table 1).
Table 1, Costs of Lignin and Alternatives
Water Treatment Chemical
Cost
Activated carbon $ 1.19/kg
Ion-exchange resins 2.87/kg
Coagulants 0.20/kg
Lignin (fuel value) 0.03/kg
Lignin fas ligniosulfonate) 0.13/kg
The U.S. Environmental Protection
Agency (EPA) estimated that, without
regeneration, carbon adsorption costs as
high as $0.42/1000 gallons for a one-
MGD plant would be incurred, i.e., an
annual cost of $153,000. Since the bulk
density of Filtrasorb 300 and 400 acti-
vated carbon averages 433 kg/cu.m.,
and pristine lignin ranges from 336 kg/
cu.m. (ethanolic) to 606 kg/cu.m. (alka-
line), adsorbent vessels should be sim-
ilarly sized. Therefore, capital costs
should be approximately the same
assuming different levels of comparative
efficiency, it was forecast that lignin
could be competitive with activated
carbon if it demonstrated only 1 /15th the
adsorption capacity of the activated
carbon. (Note: a median cost of $0.08/
kg for lignin was assumed.) This cost
comparison is summarized in Table 2.
If one were to proceed in a similar
-------
Table 2. Comparison of Lignin Costs at
Various Efficiency Levels
Relative to Activated Carbon
Efficiency
Twice as efficient
Equal efficiency
1/2 efficiency
1/4 efficiency
1/10 efficiency
1 /1 5 efficiency
Activated Carbon
Metric Tons
Required
64
128.5
257
514
1285
1928
128.5
Annual
Materials
Cost
$ 5.120
10,280
20,560
41.120
102.800
154,000
153,000
manner to compare lignin with ion-
exchange resins, well-over a 20-fold raw
material cost advantage is possible on
a simple equivalency basis.
"Pristine lignin" is considered to be
exceptionally attractive for several
reasons:
1. Low cost
2. Readily disposable after use by
incineration, pyrolysis/gasifica-
tion, and biological (white rot
fungus) decomposition.
3. Metals readily reclaimable after
treatment with lignin.
4. Biologically resistant.
5. High resistance to degradation/
depolymerization.
6. Naturally abundant in nature;
coniferous woods (28%), rice hulls
(40%), barley straw (16-22%),
bagasse (20%).
7. High rich organic functionality,
e.g , phenolic hydroxyl groups on
the aromatic nuclei. Also, quinonic
groups, carboxylic acid groups,
carbonyl moieties, etc.
8. Cation complexation, i.e., heavy
metal trapping.
9. Organic complexation, e.g., simple
phenols, etc.
10. Oxidation-reduction exchange
potential due to quinone and diphe-
noquinone groups possible, i.e.,
reduced ionic mobility.
11. No need for radical engineering
redesign with this technology.
12. Relatively well established science
and technology base for lignin
modification.
13. Modified versions can range from
aqueous solubility (pH-controlled)
to organic-soluble.
14. Existing, though small, commercial
markets for crude lignin exist.
(Most all lignin by-products of
pulping processes are burned and
most of the heat generated from
the lignin is required to evaporate
the water from the spent liquor.)
15. Crude alkali lignin and lignosulfo-
nate products have been used as
emulsifiers, protective colloids to
stabilize emulsions, in ore flotation,
electrolytic refining, and industrial
wastewater treatment. Sequester-
ing action is used to remove scums
and insoluble salts in hard water.
Lignosulfonates react with chrom-
ates and dichromates to give
strongly insoluble materials.
The focus of this research was to
concentrate on the use of lignin as an
adsorbent and a replacement for acti-
vated carbon. It was expected to atten-
uate heavy metals and organic com-
pounds (especially, polar compounds) in
a mechanism not unlike that of humic
acids in nature. The research centered
on three phases:
1 Isolation of pristine lignin from
steam-exploded wood;
2. characterization, chemically and
physically, of the lignin; and
3. adsorption studies of lignin and
comparison with activated carbon.
A feasibility study to assess the
utilization of lignin, isolated from a
steam-exploded hardwood (Tulip poplar)
with 95% ethanol and 0.1 N NaOH, as a
potential adsorbent for hazardous waste
treatment was conducted. Eight organic
compounds and two heavy metals ions
were selected from the EPA priority
pollutant list for use as model compounds
and to allow comparison of lignin isolates
with activated carbon.
Adsorption kinetic studies, adsorption
size studies, and adsorption isotherms
based on the Freundlich equation were
completed. The lignin isolates were
extensively characterized using IR, UV,
C13 NMR, and PMR spectroscopy, elec-
trochemical functional group analysis
(Van Krevelen diagrams), differential
scanning calorimetry, thermogravimetric
analysis, elemental (C, H, N) analysis, gel
permeation chromatography, and BET
surface area analysis. Carbon adsorption
isotherms were produced for compounds
not reported in the literature.
The adsorption capacity of lignin for
heavy metals (chromium and lead) was
found comparable to activated carbon,
despite a huge divergence in surface area
(0.1 m2/g vs. 1000 mVg). The surface
area discrepancy and the extensive
aromatic substitution in lignin macro-
molecule impeded the achievement of an
adsorption capacity of lignin for polar
organic compounds. This would allow it
to be cost-competitive with activated
carbon, although results with phenol
and, to a lesser degree, naphthalene
indicate significant potential for achiev-
ing competitive capacities. A recom-
mended plan for surface area and
structural enhancement is presented on
the basis that lignin can be developed
as an effective and low-cost adsorbent
for polar priority pollutants and/or as an
ion-exchange resin for heavy metal
wastewater cleanup.
Major Findings
Isolation of Pristine Lignin from
Steam-Exploded Wood
The steam-exploded wood which was
studied extensively in this project was
prepared by the hydrothermal decom-
pression of the hardwood chips of Tulip
poplar (L. tulipfera) at 350 psig and for
a residence time of four minutes. Initial
separation processing of this steam-
exploded wood centered on extracting
the lignin component in "pristine form"
by using 95% ethanol and Soxhlet
extraction, followed by precipitation into
mildly acidified water (pH = 4) and
filtration. The average yield of ethanolic
lignin isolate was 7.5%. The same
feedstock was treated with 0.1N NaOH
in a single-stage batch extraction (extrac-
tion efficiency found to be >99.4%) and
lignin was isolated by precipitation and
filtration. The average yield (n = 19) was
31.9% (Range: 26.2 - 39.4%). The
recovery represents a 4.25-fold increase
in extractable pristine lignin from that of
ethanol.
Alkaline extractions were also con-
ducted on steam-exploded aspen hard-
wood, supplied by Stake Technology
(Canada) Ltd., with the caveat that it was
not representative of their materials
-------
(although reportedly processed under
conditions similar to that of the GIT-
processed Tulip poplar) The average
yield (n = 33) was 25.8%.
Despite variations in workup, both the
ethanolic lignm and alkaline lignin
isolates produced dry particulates of low
surface area. The ethanolic lignin, a light,
free-flowing powder contrasted with the
dark, friable nature of the alkaline isolate,
a state which probably reflects the
discrepancy in typical BET surface area
values, i.e., 30 m2/g for ethanolic isolate
and 0.1 mVg for alkaline isolate. A
significant difference in the molecular
weight analyses for all three isolates was
found (Table 3).
Table 3. Molecular Weight and
Polydispersity of Lignin Isolates
Mw
Mn Mw/Mn
Ethanolic Lignin
(Tulip poplar) 1,379 939 147
Alkaline Lignin
(Tulip poplar) 2,333 859 2 72
Alkaline Lignin
(Aspen)
88,311 2,081 42.4
The alkaline-isolated pristine lignin
from Tulip poplar was chosen for detailed
adsorption studies because of its high
yield (necessary, ultimately, for cost-
effectiveness), the promise of adsorptive
power (functionality) as suggested by its
moderately branched macromolecular
structure, and the view that the problem
of increasing surface area could be
resolved m later studies. (The GPC
results suggest that the hydrothermal
steam treatment process will require
controlled analysis for purposes of
preparing a commercial-grade pristine
lignin adsorbent.) In the absence of any
reported extensive studies of solubility
behavior of lignin, a rather comprehen-
sive survey was accomplished in this
study to prepare a data base for the
establishment of potential alternate
extraction procedures. The findings of
this study are summarized in Figure 2.
Chemical and Physical
Characterization of Pristine
Lignin
The extensive characterization pro-
gram included the following techniques:
21
20
19
18
17
16
15
14
13
12
11
10
S
I
c
10
11
12
13
14
15 16
17 18
Solubility Parameter
Figure 2. Lignin solubility behavior.
Moisture, Ash and Klason Lignin
Elemental Analysis
IR, UV, and NMR Spectroscopy
3.
4.
Thermal Analysis (TGA, DSC, Heat
of Combustion)
5. Electrochemical Functional Group
Analysis
6. Gel Permeation Chromatography
7. Electron Microscopy
8. BET Surface Area Analysis
-------
The results of the characterization
indicate that the alkaline lignin isolate
from Tulip poplar, on which adsorption
studies were focused, were not unrepre-
sentative of the structural features
reported in the literature. The major
exception was that the molecular weight
and molecular weight distribution are
relatively low and narrow, respectively.
C'3 NMR spectra in the literature which
were performed with softwood lignin
showed differences in the aromatic
carbon region, as expected A heavy
functional group (phenolic hydroxyl) and
aromatic substitution pattern (methoxy
and propyl moieties) were found, as
expected. Qumonoid and carbonyl
groups are present.
Thermal analysis showed lignin to be
relatively thermostable in terms of
primary bond integrity, that observation
being subject to the qualification that
crosslinking (and corresponding loss of
functionality, i.e., adsorptive capacity)
may be masked m thermograms. The
higher heating value of lignin isolates
(10,350-10,827 BTU/lb, "as is") indi-
cates that lignin would provide a useful
combustible matrix for hazardous waste
isolation and disposal by incineration
Adsorption Behavior of Pristine
Lignin with Selected Model
Compounds
Kinetic studies on the model com-
pounds established the equilibrium time
required for measurement of adsorption
capacity.
Equilibrium concentrations for the
model compounds leveled off within two
days, undetectable limits being reached
after only one day in the cases of bis(2-
ethylhexylphthalate) and pentachloro-
phenol The time required for achieving
equilibrium was less than 12 hours for
chromium, while lead required 48 hours.
For further adsorption studies, an allow-
ance of four days was made to achieve
equilibrium, particularly since large
particle sizes (30 x 40 mesh) had been
used for the kinetic studies. A preliminary
cumulative adsorptive capacity (total of
seven organic compounds) of 5 g/kg was
estimated for the ethanolic lignin isolate
used m this study. It was also noted that
an increase in adsorption of model
compounds, both organic and inorganic,
was achieved with a higher load of lignin,
suggesting the possibility of rapid satu-
ration of adsorption sites on the surface
of the adsorbent and little penetration
(porosity) of the adsorbent
Adsorption Size studies were con-
ducted on three different particle size
fractions (30 x 40, 40 x 60, and 60 x
100 mesh) of ethanolic lignin and one
of alkaline lignin (60 x 100).
Table 4 shows values for a "cumulative
adsorption capacity" of the lignins, at
each size range, for the organic com-
pounds in the multicomponent solution
(based on the final, equilibrium concen-
tration). The values show that particle
size does influence capacity but to a
lesser extent than would be predicted by
correlation of surface area to reduced
particle diameter. This effect strongly
suggested that the mechanism of adsorp-
tion is confined to surface adsorption
sites which are probably saturated
relatively quickly and, additionally, allow
only partial bonding, i.e., only a fraction
of adsorption sites are available, perhaps
due to steric hindrance arising from a
rapid buildup (deposition) of adsorbed
layers.
It was also noted that the ethanolic
lignin had a "cumulative adsorption
capacity" which was 36% greater than
that of the comparable alkaline lignin (60
x 100 mesh). However, the ethanolic
lignin isolate had a measured surface
area of 30 mVg for the alkaline isolate,
suggesting that the alkaline lignin, if
modified to increase its surface area,
could potentially exceed the adsorption
capacity of the ethanolic isolate. The fact
that significantly higher yields of lignin
are obtained by alkaline extraction
further encouraged the preferential
selection of alkaline-isolated pristine
lignin for development as adsorbents.
The results of the adsorption size
studies with chromium and lead indi-
cated that the alkaline isolate possessed
a significantly higher adsorption capacity
for heavy metals than does the lignin
isolated by the ethanolic extraction
procedure. The results are shown in
Table 5. If one defines the adsorption
ability of a resin by the percentage of
metal ions adsorbed based on initial
concentration, significant values are
obtained for chromium and lead with the
alkaline-isolated lignin (60 x 100 mesh),
viz., 91% and 80%, respectively.
The difference in behavior towards
heavy metals may be due to the ionization
Table 4. Cumulative Adsorption Capacity of Lignin Types and Sizes for a 7-Component
Organic Mixture
Lignin Type
EtOH-Lignin**
Mesh Size
30x40
40x60
60 x 100
Sieve
Opening
(mm)
059-0.42
0.42-0.25
0.25-0 15
Adsorption
Capacity
(g/kg)
3.66
4.43
5.30
NaOH-Lignm*
60 x 100
0.25-0.15
3.90
^Cumulative Adsorption Capacity: based on the sum of the final, equilibrium concentrations
for the seven model organic compounds.
""The surface area of the ethanolic isolate (30 x 40 mesh) is 30 sq m/g. A comparable alkaline
lignin isolate (30 x 40 mesh) is 0.1 sq m/g.
Table 5. Adsorption Capacity and Ability of Lignin Isolates for Heavy Metal Ions
Lignin
Alkaline
(60x1 00 mesh)
Ethanolic
(60x1 00 mesh)
Ion
Chromium
Lead
Chromium
Lead
Adsorption
Capacity
@ Equilibrium
Concentration
(9/kg)
3.60
356
2.04
1.88
Adsorption
Ability
(% Ion Adsorbed)'
91
80
52
42
"Percentage of metal ions adsorbed based on original concentration (CJ: C0= 10 ppm.
5
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of organic functional groups during the
alkaline hydroxide extraction and
exchange of sodium ions for protons with
the carboxylate, phenolate, etc., anion
pairs. Adsorption on alkaline lignin
isolates may be expected to be higher
with heavy metals ions due to an ion-
exchange process which is not a major
factor in ethanolic isolates.
Adsorption Isotherms representative
of four groups of hazardous waste
compounds on alkali-isolated pristine
lignin were determined. The compounds
were representative of acid- and neutral-
extractables (phenol, naphthalene),
pesticides (2,4-dichlorophenoxy acetic
acid), purgeables (trichloroethylene), and
heavy metals (chromium). The experi-
mental data for phenol, naphthalene, and
chromium on pristine lignin were com-
pared to the experimental data reported
by EPA or determined in this study for
the compounds on activated carbon. The
comparisons were based on Freundlich
parameters selected from the adsorption
isotherms of the given model compound
at one arbitrary, but common, equili-
brium value.
Under comparable conditions, the
relative adsorptive capacity of activated
carbon for phenol was 46 g/kg. For
pristine lignin, the relative adsorptive
capacity was 1.6 g/kg. To achieve the
same equilibrium concentration, a load-
ing of adsorbent of 100 mg/l of activated
carbon vs. 3000 rng/l of pristine lignin
would be required Therefore, the "effi-
ciency" of pristine lignin is 1/30th that
of activated carbon or 50% below the
minimal 1/15 target value originally
established as a criterion of cost-
effectiveness. However, the activated
carbon adsorbents have surface areas of
1000 mVg whereas the alkaline-isolated
pristine lignin had a value of only 0.1
mVg.
A similar comparative analysis was
made for naphthalene. The relative
adsorption capacities were 184 g/kg and
1.6 g/kg, for activated carbon and
pristine, respectively. The corresponding
adsorbent loads were 25 mg/l and 3000
mg/l.
For the case of heavy metals, pristine
lignin appears to have significantly more
potential as an adsorbent vis-a-vis
activated carbon. For essentially similar
experimental conditions, the relative
adsorption capacity for chromium on
pristine lignin is 8.7 g/kg vs. 27.8 g/kg
with activated carbon. The adsorbent
doses required to achieve a similar
residual concentration were 1.0 g/l and
0.25 g/l for lignin and carbon,
respectively.
The preferred affinity of pristine lignin
for phenol and chromium (and, to a lesser
extent, naphthalene) among the model
hazardous waste compounds is indica-
tive of a highly polar adsorption process
at the surface of the lignin. Heavy metal
adsorption is probably due in large part
to a cation exchange mechanism. Little,
if any, contribution is made to adsorption
processes by a porous microstructure
which is characteristic of commercial
adsorbents. Indeed, the introduction of
porosity, and concommitant increase of
surface area, is required for pristine
lignin to be used as an adsorbent.
Conclusions
1. If the surface area of pristine lignin
isolates could be substantially
increased, they are potentially
competitive with activated carbon
on a cost-effectiveness basis for
adsorption of polar compounds
among priority pollutants.
2. The adsorption capacity of alkaline-
isolated lignin for heavy metals
(chromium and lead) is approxi-
mately equivalent to that of acti-
vated carbon (9 g/kg vs. 28 g/kg)
despite a huge divergence in sur-
face area (0.1 mVg vs. 1000 m2/
g). The applicability of pristine
lignin for polishing of heavy metal
wastewater is suggested with little
further modification being
required.
3. The adsorption capacities (for
model organic compounds) of spe-
cific lignin isolates, which were
examined in this study, were less
than those of activated carbon and
they failed to achieve the 1 /15th-
to-1/20th value of carbon adsorp-
tion capacity (although phenol
results approached the criterion)
which has been targeted as a
technical and economic break-
even criterion for comparability of
lignin and activated carbon. The
adsorption capacities for phenol
under comparable conditions with
activated carbon and pristine lig-
nin, were 46 g/kg and 1.6 g/kg,
respectively. Corresponding adsor-
bent loads were 100 mg/l and
3000 mg/l, respectively. Naphth-
alene was adsorbed by lignin, but
the disparity was greater. Only
marginal adsorption of trichlo-
roethylene was evident and there
was a general insensitivity
increased adsorbent load for t
purgeable compound.
4. The major impediment to achiev
comparability on technoeconor
grounds by lignin with activa'
carbon is attributed to the inor
nately low values of surface ai
(order of 0.1 mVg for alkalir
isolated lignin). In general, ads
bents used in commercial adso
tion processes exhibit high surfe
area per unit of weight (100-10
mVg).
5. Another significant impediment
the realization of higher adsorpti
potential of lignin appeared to
the state of extensive substituti
of the aromatic nuclei in the mac
molecular structure and a hi
methoxyl group content (vis-a-
phenoxy hydroxyl content). Sin
experiments were conducted w
a single source of steam-explod
wood processed under a fixed ;
of conditions (350 psig, 4 minute
the nature of the lignin in t
starting material was itself fix<
i.e., there was no flexibility
varying or modifying the compo
tion of the lignin isolates whi
were studied, other than in t
fraction of the lignin compone
which was extractable (8% I
ethanolic lignin and 32% for alk
line lignin). If conditions could
optimized during steam-explosh
(autohydrolysis), methoxyl grou
could be "uncapped," mcreasii
phenolic hydroxyl content and/
establishing a higher quinor
character, with the possibility
greater electron delocalizatio
hydrogen bonding, and oth
secondary bonding forces becor
ing operative during adsorption
polar compounds.
6. The surface activity of lignin is
lates, though seriously limited
the available active sites on a ve
limited surface area, did show
preferred affinity for phenol ai
chromium (and to a lesser degre
for naphthalene) which is indie
live of a highly polar adsorptu
mechanism at the surface. Tl
magnitude of such effects shou
be enhanced by the induction
micro- and macro-porosity in tt
lignin isolates.
-------
7. The adsorption kinetics study
revealed relatively rapid equili-
brium of heavy metals by alkaline
lignm suggesting primary bonding
forces at work, probably via a cation
exchange mechanism involving
residual sodium ions and the car-
boxylate or phenolate anions of the
lignm macromolecule. In these
studies, alkaline lignin (60 x 100
mesh) removed 91 % of the original
chromium concentration and 80%
of the lead ion concentration.
Despite a higher surface area,
ethanolic lignin isolates did not
perform as well: 52% and 42% for
chromium and lead removal,
respectively.
8. The adsorption isotherm curves,
developed for the Freundlich iso-
therm equation, were of the S-1
type (Giles classification). The
behavior is explained by the force
of interaction between adsorbed
molecules being significant rela-
tive to that between solute and
adsorbent. Solute molecules tend
to be packed in rows or clusters on
the surface and the condition is
encouraged with water as solvent,
which itself is strongly adsorbed on
a polar absorbent (lignin) and when
the solute is mono-functional (as
with phenol).
9. The experimental evidence in toto
suggests that it would be prema-
ture to conclude that pristine lignin
cannot be developed further to be
a low-cost, efficient adsorbent for
polar organic priority pollutants or
a cost-competitive and effective
ion-exchange resin for heavy metal
hazardous waste treatment. As an
adsorbent, its thermal characteris-
tics (higher heating value of over
11,000 BTU/lb strongly suggest its
disposability thermally. Alterna-
tively, biochemical (fungal) degra-
dation may be used. In both dis-
posal cases, the hazardous wastes
would be concentrated.
Recommendations
Despite the limitations of time and
resources that are associated with
feasibility studies such as this one, there
appears to be ample evidence that lignm,
which is isolatable from steam-exploded
wood, when the latter material is itself
processed to optimize the extractability
quantitatively and qualitatively of the
modified lignin, possesses the potential
of being either a low-cost, high-efficiency
adsorbent for polar compounds which is
competitive with activated carbon or a
precursor for a highly efficient ion-
exchange resin for cleanup of heavy
metal ions.
A Phase II study is recommended with
the objective of producing a steam-
exploded or autohydrolyzed hardwood
under operational conditions, whereby
lignin can be chemically debonded from
the carbohydrate (cellulose and hemicel-
lulose) components of wood so that it is
readily extracted in high yields and in a
chemical form in which deleterious
condensation (lignm-hgnin or lignin-
carbohydrate secondary reactions) is
minimized and in which phenolic
hydroxyl and qumonic content is max-
imized. In addition, the lignm should be
isolated, preferentially, by chemical
process operations that provide a surface
area of 100-1 000 mVg. The surface area
enhancement may be achieved by one
or more of the following techniques1
(a) mild crosslinking associated with
"blowing agents"
(b) controlled sol-gel techniques
(c) spray drying
(d) uniform coating of low-cost inert
supports (with or without subsequent
removal of supports)
(e) optimized solvent-nonsolvent
precipitation systems
In a parallel study, the pristine lignin
isolate would be directly compared to
commercial weak-acid and cation
exchange resins. Also, with modification,
because of the highly aromaticized
structure, derivatives of pristine lignin
representative of the major classes of
ion-exchange resins will be prepared,
since the low cost of the lignin isolate
(e.g., 5-6C/lb for phenol) allows deriv-
atives to be highly cost-competitive with
the expensive commercial synthetic ion-
exchange resins (e.g., $3/kg).
In summary, the following study ele-
ments are proposed:
1. Investigate/identify preferred con-
ditions for steam explosion or
autohydrolysis to produce pre-
ferred chemical structure in the
lignin isolate.
2. Qualitatively characterize lignin
isolates to enhance the basic
chemical structure (a) for preferen-
tial adsorption of polar hazardous
waste compounds, and (b) for facile
modification of the structure to
produce ion-exchange resins
3 Maximize yields of extractable
lignin from steam-processed
hardwoods.
4. Develop a (preferably one-stage)
process for producing high surface-
area (100-1000 mVg) lignin iso-
lates with minimal mitigation of
surface activity.
5. Perform kinetics and adsorption
isotherm studies with selected
model polar compounds drawn
from the EPA list of priority pollu-
tants using both modified lignin
isolates and activated carbon.
6. Prepare chemically modified lignin
derivatives for use and evaluation
as ion-exchange resins for the
cleanup of heavy metal pollutants
(and ions, possibly). Minor modifi-
cations include possibilities of (a)
oxidation to increase acidic, phe-
nolic, quinonic, ketonic, or alde-
hydic content, and (b) increasing
crosslink density/gelation through
thermal-or thermochemical treat-
ments. Major modification involves
chemical substitution, for example,
of the aromatic nuclei or prepara-
tion of strong-base, anion-
exchange resins by chloromethyla-
tion followed by reaction with a
trialkyl amine.
7. Characterize the modified lignm
ion-exchange resins as to their
porosity, surface area, ion capacity,
volume stability, swelling, etc.
8. Prepare a final report on the benef-
its, technical and economic, of
employing lignin as an adsorbent
or as an ion-exchange resin for
hazardous waste treatment.
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Daniel J. O'Neil,. Christopher J. Newman, E. S. K. Chian, and H. Gao are with
Georgia Institute of Technology, Atlanta, GA 30332.
T. David Ferguson is the EPA Project Officer (see below}.
The complete report entitled "An Evaluation of Pristine Lignin for Hazardous
Waste Treatment," (Order No. PB 87-191 664/AS; Cost: $24.95. subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. V'A 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S2-87/037
0000329 PS
U S EWVIR PROTECTION AGENCY
REGION 5 LIBRARY
2§0 S OfARBOR* STREET
CHICAGO IL 60604
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