Abbreviations: BM--biomass, FWB--forest waste biomass,
IRS--infrared spectroscopy, LP--liquid product, TCL--thermochemical
liquefaction, TLC--thin layer chromatography.
Biomass (BM) in its availability, variety, and abundance is a
practically inexhaustible resource of feedstock for energy and chemical
needs. BM is a term for all organic material that stems from plants
(including algae, trees, and crops). The BM resource is also considered
to be a combustible natural high molecular matter, in which the energy
of sunlight is stored in chemical bonds . Coals and oil shales can
also be termed BM, since they are fossilized remains of higher plants
and marine fauna that grew and lived tens and hundreds of millions of
years ago. There are determinations where BM is generally defined as any
hydrocarbon material, mainly consisting of carbon, hydrogen, oxygen, and
nitrogen, sulphur being also present in less proportions . Most often
BM refers to forestry (trees, plants, purposely grown crops) and
biological wastes (agricultural, agro-industrial, and domestic). The
energy enclosed in different ingredients of terrestrial and aquatic
plants as well as in technological and decaying residues of those and in
other renewable resources of biological origin can be released either by
direct use like in combustion or converted by thermochemical or
biochemical upgrading into synthetic liquid and gaseous fuels or higher
value products for the chemical industry. Liquefaction, gasification,
and coking of BM lead to the formation of liquid, gaseous, and solid
products with higher energy density than the original. From that point
of view bioresource can be observed as a promising alternative to both
crude petroleum and fossil fuels.
Chemically, the cell walls of plants contain varying amounts of
three main biopolymers--cellulose, hemicellulose, and lignin--and a
small amount of other extractives. So, the main building blocks in BM
are carbohydrates and the role of lignin is to reinforce the cell walls,
to make them waterproof, and it is deposited in wounds as a barrier to
pathogen ingress [3, 4]. BM energy--the energy stored in plants,
actually, originates from solar energy through the photosynthesis
process. This energy can be recovered by burning BM as a fuel. During
combustion, BM releases heat and carbon dioxide that was absorbed while
the plant was growing, so the use of BM is the reversal of
photosynthesis, carbon dioxide recycling. In contrast to fossil fuels,
utilizing BM energy does not add extra carbon dioxide to the
environment; besides, BM is the only renewable source of carbon and it
can be converted into convenient fuels [5, 6]. BM differs from other
alternative energy resources in that the resource as a feedstock is
varied. Organic material from trees, plants, and crops available
everywhere in its individual multitude and obtained as a whole or
ingredients has been submitted to thermochemical liquefaction (TCL)
using different processes and facilities. Comparison and parallels with
fossil BM using data obtained for kukersite oil shale have been drawn
further here and there.
Usually, BM in large quantities is easily available unsorted and
blended, which influences less direct combustion but more the
liquefaction process. Forest waste biomass (FWB) includes whatever
direct and indirect forest-originating wastes such as logging residues,
brushwood, ingredients of different trees, forestry residues, the
remains of the wood-working industry, and others. Those used in mass or
separately do not generate much differing amounts of ash and air
emissions. At the same time softwood and hardwood, bark and needles,
leaves and cones etc. of individual strains of BM submitted to TCL can
produce quite different yields and compositions of products though the
same liquefaction conditions are used.
WORLD PRACTICE IN BM CONVERSION: RECENT 25 YEARS
Thermal destruction is, indubitably, the main technology used for
BM liquefaction. Numerous methods and facilities are being applied to
upgrade waste BM into products of higher value . Fundamentals
concerning BM thermal destruction and regularities of products formation
have been described [7-9]. Since the early 1980s much attention has been
paid to the BM thermal transformation in Canada, USA, Finland, Sweden,
Italy, Germany, Switzerland, Spain, United Kingdom, France, and Belgium.
The principal results and developments on investigations in these
countries during the period 1983-1990 have been highlighted in [10, 11].
Pyrolysis, thermal destruction without using pressure, any solvent, or
chemical, was the basic process used while wood and peat were the main
materials pyrolysed as BM representatives. Minor attention has been paid
to thermal destruction in pressurized solvents and other BM species.
Pyrolysis of BM yields liquid, gaseous, and solid products. Like in
the case of fossilized high-molecular organic matter the mutual ratio of
these is strongly dependent on pyrolysis conditions. Each of the
products obtained from BM--liquid product (LP, in the literature often
termed also as "bio-liquid", "bio-oil",
"bio-crude", "oil", "tar", "black
liquor"), bio-gas, and charcoal can be regarded as an upgraded one
having higher energetical density and broader use value compared with
the initial feedstock. Varying pyrolysis conditions closer to coking,
gasification, or liquefaction, a desired product of market value in high
yield can be obtained.
The yield and composition of BM conversion products mainly depend
on pyrolysis conditions such as temperature, heating rate, residence
time, and products evacuation conditions from the hot zone (measured as
residence time in the gas phase), particles size, and presence of
additives and less on the composition of BM subjected to pyrolysis
[7-9]. As for feedstock, consisting mainly of holocellulose and lignin,
BM variety is often determined as lignocellulosic matter and both the
yield and the composition of pyrolysis products primarily depends on the
cellulose/hemicellulose/lignin ratio in the pyrolysis feedstock.
Temperature has been considered the main parameter among process
variables determining products distribution between liquid, gaseous, and
solid phases. Pyrolysis of BM, according to the temperature, includes
three principal stages as follows :
(1) below 300[degrees]C--dehydrogenation processes; [H.sub.2]O,
C[O.sub.2], and CO formation; charcoal is the main product;
(2) 300-600[degrees]C--fragmentation reactions, primary tar is the
(3) above 600[degrees]C--depolymerization, cracking, and reforming
reactions of primarily formed products and their reactions with free
radicals; gas is the main product.
It was demonstrated that the residence time, in particular that in
the gas phase, has also a significant effect on the above reactions. So,
the residence times of solid feedstock and gaseous primary products in
the hot zone at pyrolysis temperature as well as condensation velocity
of the vaporized products strongly affect the disproportion regularities
of pyrolysis products between liquid, gaseous, and solid phases. Several
regularities between process variables were fixed. In the temperature
region 450-600[degrees]C preferably charcoal formation was noticed at
lower heating rates while elevated heating rates and a short residence
time in the same temperature region favoured tar yield. Temperatures
higher than 700[degrees]C and a long residence time in the gas phase
favoured tar cracking and gas formation. At a slow heating rate and low
pyrolysis temperature (less than 10[degrees]C/min and below
500[degrees]C, respectively) both the gas and solid state residence
times are long (the former one more than 5 s) favouring solid residue
and liquid formation. The mechanism of BM pyrolysis was described to
occur via several consecutive and parallel stages :
The mechanism of renewable BM pyrolysis bears notable resemblance
to that of fossilized organic matter like kerogen in oil shales.
Estonian kukersite oil shale has been thoroughly investigated during
more than 80 years and the mechanism of its pyrolysis has been accepted
Both the BM and kerogen pyrolysis process begins with the formation
of high-molecular LP. In the case of kerogen the product is known as
thermobitumen and for BM as primary tar. Final products of renewable and
fossil BM pyrolysis--oil, gas, and solid residue--in their majority form
only after thermal decomposition of those primary intermediates. Small
parts of oil and gas are formed simultaneously with intermediates. Both
feeds--organic matter of oil shale and BM--contain a small amount of
extractables (bitumens extracted by conventional solvents). Kukersite
belongs to highly oxygenated caustobioliths while growing BM is extra
highly oxygenated. The oxygen supply in both ones is transferred into
liquid and gaseous aim products. Gas, be it obtained from kukersite
shale or BM pyrolysis, is characterized by a high concentration of
carbon oxides, and in the composition of LPs numerous groups of similar
compounds can be found.
The most promising industrial applications are processes producing
tarry or oily LP for use as fuel oil or for further processing. Numerous
pyrolysis methods and facilities have been applied for BM liquefaction
since 1990 such as slow pyrolysis, low-temperature pyrolysis, vacuum
pyrolysis, entrained-flow pyrolysis, fast pyrolysis, flash pyrolysis,
vortex ablative pyrolysis, mill pyrolysis, fluid-bed pyrolysis,
pyrolysis with partial combustion, and updraft fixed-bed pyrolysis .
Depending on the conditions used the yields of LP obtained on BM feed
varied from 8% to 80%. The highest LP yields from peat and wood, 50-80%,
were obtained by the flash pyrolysis method, first reported by Graham et
al. . Samples of BM were heated up as quickly as possible (usually
within 0.5-5 s up to 400-600[degrees]C) followed by quick evacuation and
condensation of gaseous products (residence time in the gas phase less
than 2 s). It was demonstrated that practically at any temperature
sufficient for BM decomposition a high LP yield can be obtained by
varying solid and gas phase residence times. For instance, at
500-600[degrees]C the residence time in the gas phase must be short to
avoid cracking but long enough for solid matter. Fast pyrolysis
operating with heating rates of 1000-10 000[degrees]C/s and residence
times in the gas phase less than 0.5 s usually results in yielding
valuable gases (lower olefines and other hydrocarbons) when temperatures
from 600 to 1000[degrees]C are used.
Flash pyrolysis LP obtained from wood in high yields has often been
characterized as a dark and fairly viscous (10-55 cP at 70[degrees]C)
tarry liquid, having density around 1.2 g/mL and molar H/C ratio
1.46-1.70. Such LP obtained in yields 50-80% on woody feed by flash
pyrolysis contains 30-50 wt.% oxygen, 15-20 wt.% water, 4-7 wt.% organic
acids, and 10 wt.% char in suspension, water being dissolved in the oily
phase as a constituent of the part that cannot be separated . The
higher the yield of LP, the higher its oxygen concentration.
"Liquid wood" as a reactive mixture is unstable even at room
temperature and has a heating value only about half of that of
conventional light fuel oil. Products of similar composition and in
comparable yields as in flash pyrolysis can be obtained also in vacuum
pyrolysis at slower heating rates. Neither individual nor group
composition of wood-derived tars has been properly characterized, also
several aspects of tar recovery are uncertain. Nevertheless, several
pragmatic conclusions can drawn basing on the results of investigations
on BM liquefaction from the period since 1990:
* BM species, kinds, and ingredients in their global multitude have
been defined similarly as consisting of three main polymers--cellulose,
hemicellulose, and lignin;
* BM has been brought into prominence as an alternative to fossil
fuels for producing petroleum substitutes;
* LP yields from pyrolysis of cellulose, hemicellulose, and lignin
taken singly under different conditions have been reported; as a result,
the LP yield from any lignocellulosic material can be approximately
predicted knowing the concentration and ratio of these components in a
material not pyrolized before;
* the liquefaction potential of BM in pyrolysis units has been
estimated and LP yields as high as up to 80 wt.% from wood and 50 wt.%
from peat have been obtained using, respectively, flash pyrolysis and
the fluidized bed technology;
* LPs from BM pyrolysis have been characterized as rich in oxygen
but containing poor amounts of commercially interesting chemicals.
Therefore BMderived liquids obtained meet hardly fuel oil qualities and
must be upgraded by further processing;
* an impulse has been given to developing solvolytical and
hydrotreating processes with the aim to upgrade and deoxygenate
Thermochemical liquefaction (TCL) and upgrading
Pyrolysis liquids from BM, though obtained in high yields, urgently
need upgrading (deoxygenation) to be used as petroleum substitutes and
directly marketable hydrocarbon fuels [13-15]. For upgrading one- and
multi-stage methods with solvents and chemical agents used have been
developed. One-stage upgrading processes such as liquefaction via
solvolysis, high-pressure liquefaction, catalytic hydroliquefaction,
hydrotreating, steam/water liquefaction, ironcatalysed pressurized
aqueous pyrolysis, thermochemical solvolytic processes at elevated
temperature used to be mainly conducted in autoclave-type reactors.
Multi-stage upgrading processes involved BM decomposition in several
consecutive steps such as pyrolysis, stabilization, and upgrading. As a
typical example a two-step hydrotreating process for the production of
hydrocarbon fuels from BM pyrolysis oils was developed by D. C. Elliot
and co-workers from the Pacific Northwest Laboratories, USA . In the
first stage, a low-temperature catalytic treatment (270[degrees]C, 13.8
MPa, sulphided cobalt-molybdenum on aluminia) was used to convert
unstable pyrolysate into a tar similar to the high-pressure liquefaction
product. This tar was then hydrodeoxygenated and hydrocracked at
elevated temperature by conventional hydrotreating techniques
(400[degrees]C, 13.8 MPa) to produce petrol. Single-step processing of
the pyrolysate in the same conditions, except that temperature was
elevated up to 350[degrees]C, produced only limited quantities of the
hydrocarbon product before the catalytic bed plugged with a coke-like
material. One-stage processes developed were characterized by low
efficiency while technically feasible multi-stage ones were regarded as
too expensive. The higher the efficiency of oxygen removal, the lower
the yield of the liquid upgraded. The yield of upgraded oil from BM,
containing 1-10% of residual oxygen, was usually in the range 15-30% on
the initial feedstock basis.
Since 1990, in particular during the last 10 years, the geography
of investigations dealing with BM liquefaction and the assortment of BM
species used have been significantly widened, emphasis being strongly
displaced from pyrolysis towards thermochemical methods. At present
investigations on BM liquefaction and upgrading are being carried out in
the EU, USA, Canada, Japan, China, Indonesia, Turkey, Azerbaidjan,
Russia, New Zealand, and other countries. Liquid biofuels, such as
wheat, sugar-cane, rapeseed, and sunflower oil are already being used in
some member states of the European Union, for example in Austria,
Belgium, France, Germany, Italy, and Spain . Practically, BM of all
kinds from various geographical areas belonging to different botanical
families of both terrestrial and aquatic origin have been submitted to
TCL to estimate their prospects of yielding energy carriers and upgraded
(hydrocarbon) liquids. BM samples tested include a wide range of
materials, among them forest products (wood residues, branches, shrubs,
sawdust, bark, needles, leaves, cones, etc. from forest cleanings and
logging) and energy crops (short rotation woody crops, herbaceous woody
crops, grasses, starch crops, sugar crops, forage crops, oilseed crops)
as well as wastes (agricultural production wastes, agricultural
processing wastes, urban wood wastes, crop residues), and aquatic plants
and organisms. Forest waste BM is currently not used in the traditional
forest products industries; this concerns both unused wild and residual
materials, including forest residues left after forest harvesting,
residual trees, and shrubs. Presently under-managed woodland is
dominating and therefore forest residues alone account for some 50% of
the total forest BM and are currently left in the forest to rot .
Graminaceous BM (cereal stalks, straw), grasses (weeds, clovers,
alfalfa), starch (maize, wheat, barley), sugars (cane, beet), and other
high moisture herbaceous and aquatic plants (vegetables, sorghum,
cotton, rushes, plankton), animal wastes, and municipal solid wastes
have mainly been submitted to biological degradation via microbic
digestion and fermentation to produce bio-alcohols while those BM wastes
deposited in landfills were demonstrated to be promising for biogas
(methane) in situ production [16-20]. Considering the oxygeneous
character of LPs from BM efforts have been made to convert BM into
dimethyl ether usable as a new ultraclean alternative fuel for diesel
engines [21, 22].
The list of individual samples submitted to TCL is long and
steadily lengthening. Reported data include algae (Betryococcos braunii,
Dunaliellu ferriolecta, Microcystis viridis); oriental beech and spruce,
ailanthus, northern poplar, birch, and oak, reed (Phragmites australis),
tea waste, wheat and rye straw, corncob, olive husk, hazelnut shells,
hazelnut seedcoat, corn stover, tobacco stalk, tobacco leaves, sunflower
stalk, unhusked rice, wastes from oil-palm, cotton, and banana
plantations, Cunninghamia lanceolata, polysaccharides, Verbascum stalk,
cotton plant and cotton gin, proteins, garbage, sugar cane bagasse, pine
and spruce needles, and many others [2, 23-42]. Solvent extraction
methods, mainly using water and H-donating solvents with and without
catalysts or additives, are preferred [43-72]. It was demonstrated that
cellulose material, all other carbohydrates, wood wastes, urban wastes,
sewage sludge, agricultural wastes, etc. can be converted to oil with CO
and [H.sub.2]O for the [H.sub.2]O-gas shift reaction and
[Na.sub.2]C[O.sub.3] as catalyst. In  a liquefaction process in hot
compressed water around 300[degrees]C and 10 MPa using sodium carbonate
as the catalyst, without any reducing gas such as [H.sub.2] and CO, was
developed. Water conversion, as well as several other liquefaction
processes, has the significant merit of not requiring a drying process
for feedstock and those processes can be conducted at high moisture
Water is the most conventional, the cheapest, and an
environmentally safe solvent. Water, in smaller or larger amounts, is
always present in TCL processes of solid fuels, particularly in BM
liquefaction even when absolutely dry feedstock is used, forming in situ
during liquefaction as a result of the decomposition of BM organic
matter. In an aqueous medium with water used as the solvent or
co-solvent, high enough LP yields characterized by a moderate oxygen
content have been obtained. The addition of alkalis (hydroxides,
carbonates, and formates) increases the solvolytical power of water
towards BM, accelerates hydrolysis of high-molecular constituents in BM
at lower temperatures and thermal degradation at higher temperatures. As
a result, higher liquid yields are obtained as compared with those using
only water. That is why BM liquefaction processes using sub- and
supercritical water (the latter often activated by adding additives or
catalysts) are favoured in modern BM processing methods [23, 25, 26, 32,
43-58]. In  water conversion of algae into oil at 300-340[degrees]C
and 20 MPa during 30-60 min with and without [Na.sub.2]C[O.sub.3] as
catalyst was conducted and the oil yield was increased from 28-32 up to
38-40 wt.%. In  18 kinds of Indonesian BM were submitted to
liquefaction in hot compressed water at 300[degrees]C and 10 MPa using
[Na.sub.2]C[O.sub.3] as catalyst and the oil was obtained in the range
of yields 21-36 wt.% on organic basis. In alkali-catalysed aqueous
liquefaction the liquid yields as high as up to 65 wt.% in the
liquefaction of BM wastes or unused BM  and even over 90 wt.% in the
liquefaction of oriental beech, Ailanthus, tea wastes, and hazelnut
seed-coats  are reported. In spite of the high liquefaction
efficiency the LPs obtained were characterized as heavy oils with a very
high oxygen content similar to flash-pyrolysis oils. Such products are
classified into unupgraded ones and have to be submitted to additional
processing. Significantly high liquid yields have been obtained also by
using instead of water other solvents in the supercritical state, such
as alcohols [C.sub.1]-[C.sub.4], acetone, and glycerol [25, 30, 31,
59-64]. As they are strongly influenced by mass transfer from the
solvent into the LP composition, these processes should be regarded as
specific ones. The above-listed solvents often decompose under
supercritical conditions in close contact with bio-organic material and
incorporate chemically via their fragments into the LP composition.
Similarly to water conversion the presence of alkalis contributes to
increasing the liquid yield in BM liquefaction with alcohols and acetone
[25, 30, 31, 60]. As it was mentioned above BM flash and fast pyrolysis
yield LP containing up to 50% of oxygen while the content of oxygen in
those of sub- and supercritical extraction of different BM species is
usually in the range 20-25 wt.%. Even liquids obtained in BM reductive
liquefaction (BM liquefaction and hydrogenation in one stage) using
tetralin and other H-donor solvents can often contain excessive oxygen,
which has to be removed. To compete with petroleum crude, LPs obtained
as synthetic bio-crudes in different processes of pyrolysis, extraction,
and hydroliquefaction badly need oxygen removal, visbreaking, and
stabilization. Hydrodeoxynation is the main process used in BM-derived
LPs upgrading, actually involving all the processes that have been used
in BM upgrading practice in different manner such as catalytically
activated hydropyrolysis, hydroliquefaction, and catalytical
hydrocracking using in situ hydrogenation or hydrogen from outside.
Sometimes common (vapour) cracking or cracking over zeolites has been
used in upgrading leading to redistribution of BM internal hydrogen and
oxygen and disproportion in the transformation of those into desired
products, respectively into liquid and gas composition [13, 14, 64-70].
Two-stage processes involving obtaining primary liquids in as high yield
as possible accompanied by successive catalytic hydrotreatment have been
performed with bi-functional Ni-Mo and dispersed iron catalysts used to
obtain upgraded oils with a low oxygen content (less than 2%) and a
heating value of the same magnitude as that of conventional petroleum
fuels [71, 72]. In BM catalytic hydroliquefaction hydrogen is consumed
mainly in hydrodeoxygenation reactions and Co-Mo or red mud, known as
powerful catalysts in the processing of fossil BM, can be successfully
Chemical composition of BM
BM includes a large variety of different lignocellulosic materials.
Containing small amounts of extractives and mineral matter, the main
organic matter of trees, purposefully grown coppices, crops, grasses,
and wastes from the agricultural and forest industries consists of
polymerized lignin, cellulose, and hemicellulose molecules in different
proportions (see Table 1).
Ultimate analysis data (Table 2) characterize BM representatives as
having an extraordinarily high oxygen concentration (40-50 wt.%) and a
negligible concentration of sulphur and nitrogen (less than 2% usually).
As a result of TCL the macromolecules in the initial BM are
decomposed into fragments of lighter molecules. Depending on TCL
conditions, gaseous, solid, and liquid products in different yields and
of different composition can be obtained.
The gas obtained in BM pyrolysis contains large amounts of CO,
[H.sub.2], and C[H.sub.4] and therefore it can be used as synthesis gas
or fuel gas. BM-derived fuel gas is characterized by the heating value
of 10-20 MJ/[Nm.sup.3], which is lower than that of natural gas (29-38
MJ/[Nm.sup.3]). BM gasification was particularly popular in the 1970s
and several technologies such as Peatgas, Hy-gas, and Hyflex processes,
with mainly peat used, were developed to pilot plant level with the aim
to produce either a rich in [CH.sub.4] substitute to natural gas or low
boiling hydrocarbons (mainly olefines) for further conversion. Naval
process uses wood and its ingredients to obtain olefines and from those
petrol. Of the olefines [C.sub.2]-[C.sub.4] 9-10% was obtained at
750[degrees]C, the ethylene content was 4% on dry wood basis.
Carbon-rich charcoal obtained in pyrolysis has a high heating value
comparable with that of coal coke (~25 MJ/kg), and due to its low
sulphur and nitrogen concentrations its combustion does not generate
poisonous oxides in considerable amounts. Because of its scanty ash
content charcoal can be used as metallurgic coke or in the preparation
of active charcoal. The chemical character of the oxygen containing
functional groups on the char surface revealed that they are
polyfunctional cationites. Thus, charcoals have hydrophilic surfaces and
are suitable for removing metal ions and other pollutants from water
The LP obtained in BM pyrolysis as organic condensable is
oxygeneous and contains a large amount of water and polyfunctional
oxygen compounds and less simple phenols, alcohols, acids, ketones, and
aldehydes. The concentration of hydrocarbons, typical constituents in
natural petroleum and shale oil, is low.
Fragments formed as unstable and reactive can repolymerize into
solvent soluble compounds with appropriate molecular weights. Depending
on the operating conditions, which determine liquefaction severity,
various compounds in different concentrations can be found in the
composition of solvent solubles (see Fig. 1).
Actually, lignin as well as cellulose in different lignocellulosic
materials may have different chemical composition. As is known [84, 85],
the polymerization degree of glucose monomers linked with glucoside
bonds in the cellulose of bark has been estimated as 2800-3300 and that
of xylanes in hemicellulose 150-250. Lignin is an amorphous heterogenic
polymer consisting of propylphenyl monomers connected via C-O-C and C-C
bonds. The lignin in bark composition is more heterogeneous than that in
wood. Of bark lignin 30-50% was found to be similar to that of wood, but
the rest did not dissolve in 72% [H.sub.2]S[O.sub.4] and was
characterized by high contents of carboxyl and low methoxyl groups .
The composition of functional groups in lignin monomers does not vary
only in conformity with the parent system from which lignin is
separated. Bark and wood, needles and leaves, softwood and hardwood,
both coniferous and broadleaf trees between themselves, even individual
species liable to environmental impacts or of different biological age,
can differ in the lignin concentration and composition .
[FIGURE 1 OMITTED]
BM-derived primary liquids like initial BM also contain large
amounts of oxygen but as a result of thorough upgrading most of the
oxygen can be removed (Table 3).
Fuels and other chemicals from BM
Different oxygen-containing chemicals have been separated from LPs
and LP as total product has been successfully used as boiler fuel with
heating value of 25-30 MJ/kg. Chemical fractionation of different LPs
has shown them to be almost exclusively made up of oxygenated compounds.
The aliphatic fraction accounts for < 1 wt.% of the LP only. The
aromatic, phenolic, and aromatic oxygenated compounds and polar
fractions of the LP make up ca 15, 62, and 9 wt.%, respectively .
LPs have typically water contents of 15-35 wt.%, fast pyrolysis
oils are characterized by higher and slow-pyrolysis oils by lower water
contents . Being mostly emulsions LPs do not form separate layers of
water and oil, and the water is a constitutional part of the
single-phase chemical solution. Thus water cannot be removed by
conventional methods like distillation.
Primary LPs generally contain, besides water, considerable amounts
of acetic and formic acids, methanol, furfurylalcohol, levoglucosan,
levoglucosenone, acetone, dihydroxyacetone, hydroxyacetaldehyde,
furfural, acetoine, and phenolic pyrolytic liquid [6, 90, 91]. Using
mild extraction methods groups of compounds such as tannins [92, 93],
sugars , resins and carboxylic acids , waxes , and
flobafenes  can be obtained. The above-listed as well as other
chemicals separated from LPs such as various polyphenols, glyco- and
glycerylaldehydes, esters, and others can be used in the manufacturing
of drugs, odourants, glues, and plasticizers [90, 91].
Investigation of the composition of the functional groups of LPs
showed all types of functionalities to be present: acids, sugars,
alcohols, ketones, aldehydes, phenols and their derivatives, furanes,
lactones, acetates, ethers, but mostly mixed oxygenates. More than 300
compounds have been identified as fragments of the basic polymers of BM,
which make up only 40% to 50% of the identity revealed until now. The
phenolic fraction (often above 50 wt.% of total liquid) consists of
relatively small amounts of phenol, eugenol, cresols, xylenols, and
guaiacols and much larger quantities of alkylated polyphenols (so-called
water insoluble pyrolytic lignin) . Basically, the recovery of pure
compounds from the complex liquid is technically feasible, but
economically still not very attractive because of high costs of the
recovery of chemicals and their low concentration in the liquids.
Production of BM energy is technically feasible but still more
costly than the use of fossil fuels unless associated with disposal or
pollution control [97-101]. Though BM conversion by pyrolysis has many
environmental and economic advantages over fossil fuels, oil shale,
coal, and natural crude production dominate because costs are kept lower
by various means, including government protection. However, the Shell
hydrothermal upgrading (HTU) process offers biocrude production for
about 25 $/bbl oil equivalent . At present the natural crude prices
in the world market surpass 60 $/bbl, so the time has arrived to pay
special attention to renewable resources.
Recently methods based on the utilization of various BM mixtures
including those with coals as feed for thermochemical co-liquefaction
have been developed with the aim to elevate the economic profitability
of BM processing and to lessen the environmental pollution caused by
processing codes [102-105].
One should always remember that the earth's natural BM
replacement represents an energy supply of around 3000 EJ (3 x
[10.sup.21] J) a year, of which under 2% is currently used as fuel. In
2000 the bulk of BM energy was produced from wood and wood wastes (64%),
followed by municipal solid wastes (24%), agricultural wastes (5%), and
landfill gases (5%) .
DEVELOPMENTS ON BM THERMOCHEMICAL CONVERSION IN ESTONIA
Estonia has both fossil and renewable BM resources. Besides
kukersite oil shale, which has been industrially burnt and liquefied for
electricity and shale oil production for more than eighty years already,
the energetic potential of other local resources should be taken into
account. The most abundant resources in Estonia regarded as alterantive
energy sources are Dictyonema argillite, peat, and forest wastes, and
continuously accumulating polymeric wastes (rubber, plastics). In
limited quantities easily cultivable renewables such as an energy crop
(Salix), reed (Phragmites communis), and reed-mace (Typha) are
available. Investigations on BM thermochemical conversion, concentrated
on liquefaction, were initiated in Estonia by the Department of Oil
Shale Technology, Tallinn University of Technology (TUT), in 2001 and
since then are being carried out in parallel to researches on oil shale
liquefaction. Both directions are closely connected as renewable and
fossil BM (lignocellulosic and kerogeneous high-molecular organics) can
be liquefied and analysed by using similar methods and apparatus. All
the above-mentioned materials are under study in Tallinn Oil Shale
Research Laboratory at TUT with various liquefaction methods used. Below
liquefaction of forest-originating materials, which include woody
sawdust, bark, and needles from forestry and wood processing activities
is discussed. Such material is widely available from forest cleanings,
as wood and logging residues, and from wood processing enterprises. Our
investigations serve as basic research, aimed at working out
fundamentals for modifying existing oil shale processing technologies
for effective liquefaction of both fossil and renewable fuels to produce
substitutes to natural crude petroleum.
As it is known, industrial utilization of kukersite oil shale in
Estonia using the present technologies is limited by the EU till 2016.
This means that during the period of transition the environmentally
harmful oil shale processing technologies have to be replaced with
modern ones. That is why intensive investigations are indispensable to
find out the best possible solutions in the following areas:
* varying raw materials as feed for liquefaction;
* working out the fundamentals for co-processing fossil fuels with
renewables (and wastes);
* elevating the proportion of organics in the liquefaction feed and
increasing oil yield;
* increasing the assortment of products and modification of the oil
* decreasing environmental pollution.
Below the results obtained in the liquefaction of coniferous forest
waste biomass (FWB) are presented. This type of BM is the most widely
available BM species in Estonia. Liquefaction was carried out under the
conditions similar to those used in the pyrolysis, hydrogenation, and
thermal dissolution of oil shales. The aim was to obtain initial data
for designing and developing fundamentals of co-liquefaction processes
of domestic fossil and renewable feedstocks.
Processing of forest trees gives various wastes. The root system
makes up 10-40%, stem 55-80%, and crown (branches with leaves or
needles) 5-25% of the mass of a growing tree. Bark forms 10-20% of the
stem or about 10% of the whole tree. The proportion of tree parts is
influenced by its species, age, growing conditions, number of branches,
About a half of the Estonian territory (2.25 million hectares) is
covered with forest. Softwood is up to now preferably used. As a result
of steady and intensive use the share of coniferous trees, pine and
spruce, has decreased from 70% at the beginning of the 20th century to
52% at present. Still, conifers make up more than a half of the total
Samples of FWB from recently felled coniferous trees were
individually ground using the desintegrator technology (Desi-11,
productivity 20 kg/h). As a result particles of 0.04-0.1 mm size were
As examples of unused forest residues the following materials were
selected and individually liquefied: pine (Pinus sylvestris) sawdust and
bark and spruce (Picea abies) sprays (needles with twigs). In practical
applications wood, crushwood, bark, needles, leaves, cones, or other
kinds of FWB are scarcely ever assorted before liquefaction, combustion,
or gasification but are used as a blend the composition of which is
seldom uniform. Liquefaction of BM species separately enables to
elucidate specific and common features and variation limits in
liquefaction as a basis for predicting the behaviour of mixed BM.
All the initial samples, which consisted of pine sawdust, pine
bark, and spruce needles, were practically concentrates of organic
matter, their mineral ash concentration (Ad) being only 0.4-3.5%. The
dry organic matter (100--[A.sub.d]) made up 96.5-99.6 wt.%. The moisture
content ([W.sub.a]) fluctuated between 8 and 9 wt.% depending on storing
conditions. Any BM sample like sawdust can intensively absorb
atmospheric moisture and needs drying before being submitted to
liquefaction. In aqueous liquefaction processes, however, drying is not
necessary as part of technological water can be replaced on account of
the water the sample includes. The C, H, N, and O concentrations of the
initial samples were respectively 50.4-52.2, 6.3-6.5, 0.2-1.1, and
41.0-42.1 wt.%. The molar ratio H/C was 1.45-1.52 and O/C 0.59-0.63.
TCL methods at fixed experimental conditions described in Table 4
were used for the liquefaction of tree ingredients.
[FIGURE 2 OMITTED]
The pressure vs. time diagram in Fig. 2 represents FWB
hydrogenation and water conversion generally. The respective curves for
sawdust, bark, and needles individually differ in the fluctuating
amplitude by [+ or -] 5% only.
Liquid yield obtained in pyrolysis is usually determined as the
weight of condensable volatile matter and that obtained in water
conversion or hydrogenation as the weight of soluble matter in a certain
As LPs are of hydrophilic character and shale oils lipophilic,
their solubility in conventional solvents is different. As is known
, thermobitumen and shale oil formed as a result of its
decomposition are both almost totally soluble in benzene and practically
insoluble in water while the solubility of LPs from BM, on the contrary,
is low in benzene and significant in water. In order to estimate the
liquefaction potential of various materials and the efficiency of
different liquefaction processes, comparable data on liquid yield and
composition should be obtained. That is why the following extraction
schemes, depicted in Figs 3 and 4, were worked out. According to these
schemes the yield of LP was determined as the total weight of solvent
solubles, summarizing respectively the weights of soluble matter in
solvents of different polarity--in water, benzene, and acetone. Basing
on solution principles enables to adequately compare the liquefaction
potential of all kinds of renewable and fossil fuels when semicoking,
water conversion, or hydrogenation are used as TCL methods.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
Chemical composition of water soluble, benzene soluble, and acetone
soluble fractions was investigated using ultimate analysis and
chromatographic and spectroscopic techniques. Ultimate analysis was
performed with an Elementar Vario EL analyzer and infrared spectra were
taken on an Interspec 2020 spectrometer. The chemical group composition
of liquid samples was determined by preparative thin-layer
chromatography (TLC). Plates of 24 x 24 cm coated with a 2 mm silica gel
(60 [micro]m) layer were used. Samples (500 mg) were analysed with
n-hexane as the eluent. TLC fractions were analysed by gas
chromatography using Chrom-5 apparatus in packed columns (4% E-301 on
Chromaton N AW HMDS) with temperature programming. Individual
composition of gaseous compounds was also analysed by gas chromatography
in packed columns (molecular sieves, sepharon) under isothermal
Results and discussion
Yields of liquefaction products
The maximum and minimum yields of liquid, gaseous, and solid
products obtained from sawdust, bark, and needles as solvent solubles,
volatiles, and insoluble non-volatile residue by using semicoking, water
conversion, and hydrogenation methods are presented in Table 5.
Table 5 shows that gas formation is the absolutely dominating
process despite which method or feed was used. The proportion of
non-condensable gas and water amounts on average to 50 wt.% among BM TCL
products being slightly less in semicoking with the Fischer assay and
slightly more in autoclavic extraction and hydrogenation, 45-46 and
47-54 wt.%, respectively. The remaining 50% of products consist of
liquid (solubles) and solid (insolubles) matter in weight percentages
ratio of approximately 20 : 30. However, sawdust hydrogenation yielded 8
wt.% for summary LP and bark hydrogenation 41 wt.% for solid residue as
exceptional minimum and maximum values. These values differ considerably
from the rest. Water has often been included into LP composition in
investigations dealing with BM liquefaction. In the destruction practice
of fossil fuels, on the contrary, water is seldom included into the
liquid balance. We added water to gas yield wittingly, because oxygen is
released as a result of intensive deoxygenation via both gas and water.
As Table 5 reveals the weight proportions of gaseous, liquid, and solid
conversion products of BM are rather similar although quite different
methods, process variables, and feed composition were used.
As a rule, minimum and maximum yields of liquid fractions and
summary LP in Table 5 were fixed when pine sawdust or spruce needles as
feedstock were individually liquefied. Pine bark showed values between
the maximum and minimum but very seldom close to these. In catalytical
hydrogenation and water conversion needles gave the highest and sawdust
the lowest liquid yield, but in semicoking just vice versa. These
regularities can be of great importance in industrial-scale TCL of mixed
woody materials such as logging-cuts and woodworking remnants,
containing wood, bark, needles, and other tree-derived BM species in
different, often in occasional quantities. Basing on the data in Table 5
one can deduce that for keeping LP in specification limits and to avoid
large deviations in the liquid yield, any proportion of bark can be used
in the blend but the quantities of wood and needles should be equal to
roughly compensate for the minimizing influence of the former and the
maximizing influence of the latter. Thus, the ratio 50 : 20 : 30
describes the disproportion regularity between the gas, liquid, and
solid phases of FWB converted in this work at conditions optimum for oil
shales. This regularity is approximately valid for individual FWB but
much better when wood, bark, and needles are blended.
Comparison with the results obtained in kukersite oil shale TCL
 with the same methods and under equal conditions reveals that in
BM TCL considerably lower yields of liquid and higher yields of gas were
obtained. Obviously, the conditions used as optimum ones for kukersite
are too severe for BM. Possibilities of achieving high yields of
oxygen-rich LP from BM demonstrated before were not of interest in our
strivings. As it was stated before, the present work aims at obtaining
liquids as partially upgraded already, characterized by a moderate
oxygen content like shale oil.
Table 5 demonstrates that the lowest yields of total solubles were
obtained in hydrogenation using molecular hydrogen. The result belongs
to the predicted ones because in the case of long-term hydrogenation
deeper deoxygenation occurs involving further decomposition and gas
formation from the liquid formed. In water conversion the water probably
has some preserving effect avoiding perceivable decomposition of the
liquid once formed and, also, equilibrium between reaction products is
achieved earlier than after 4 h. Semicoking differs from other processes
used by continuous evacuation of gaseous and liquid products in the
vapour phase and their rapid condensation.
The chemical composition of TCL products depends on the composition
of the initial BM sample submitted to liquefaction and on the conditions
of TCL. Opportunities to modify the chemical composition of TCL products
by altering TCL conditions were studied.
The elemental composition of sawdust, bark, and needles under study
in this work as initial feedstocks of BM was very similar. In Table 6
the elemental composition of LPs from pine bark with averaged C, H, and
O concentrations is presented.
As can be seen the LP obtained in bark hydrogenation and kukersite
semicoking oil are rather similar.
The composition of functional groups of solvent soluble matter was
investigated using infrared spectroscopic (IRS) methods. Infrared
spectra of different LP fractions are presented in Fig. 5. The spectra
of TCL products soluble in water, benzene, and acetone are clearly
distinguishable. Visible absorptions are quantitatively rather than
qualitatively distinguished and differences in the composition of
spectra depend more on the method used than on the initial material
Various oxygen functionalities occurring in abundance are the most
characteristic in the composition of LP fractions. According to the
absorptions at 1034, 1078, 1118-1123, 1154, 1200, 1223-1229, 1265-1278,
1648-1652, 1675-1685, 1696-1702, 3016, 3050-3069, and in the region
3324-3416 [cm.sup.-1] one can find C-O, O-H, C-O-H, C-O-C, C=O, C-C-O,
S=O and also N-H, C-N, C-N-C, and C-S groups surviving not only
thermolytical but also chemical attacks of protons and supercritical
water. Formation of intermolecular hydrogen bonds between polar
compounds such as ethers, ketones, or amides, preferable
multi-substituted nature of derivatives, and abundance of oxygen
functionalities cause shifts of absorption bands of certain functional
groups, overshadowing and covering up broad absorptions with those in
minority and often complicate identification. Absorptions typical of
methyl, methylene, and methyne groups in alkyl chains appear at
3000-2800, 1400-1300, and at around 725 [cm.sup.-1]. As it was expected,
long alkyl chains (~ 725 [cm.sup.-1]) are practically absent from the
composition of the acetone soluble fraction. Absorptions at 2960, 2872,
1460, and 1380 [cm.sup.-1] caused by C[H.sub.3]- groups in different
positions as well as those at 2930, 2860, and 790-720 [cm.sup.-1]
(-C[H.sub.2]- groups) are considerable. The most of methylene and
methyne groups are bounded into different ring structures such as cyclic
hydrocarbons and aromatic compounds. Absorption in the region 3010-3070
[cm.sup.-1] refers to the presence of =C-H groups. The absorption in
815-960 [cm.sup.-1] belongs to vinyl and terminal methylene groups in
unsaturated compounds. In the same regions also aromatic C-H absorbtions
(3020, 3050, 860, 815, 760 [cm.sup.-1]) are visible. Benzene nucleus
manifests itself at 1600 and 1500-1515 [cm.sup.-1].
[FIGURE 5 OMITTED]
Absorptions at 1170 and 1145 [cm.sup.-1] typical of isopropyl
groups derived from lignin decomposition are more visible in semicoking
liquids, while mono-, sesqui-, and polyterpenes manifest themselves at
2800-3000 and 800-840 [cm.sup.-1] conspicuously in bark- and
needle-derived liquids. Mono- and triterpenes such as 2-pinene,
limonene, and suberine can be expected to be present. It is known that
fossilized isoprenoids can survive severe processing conditions. In
pyrolytical transformations of oil shales at inert and even at reductive
conditions isoprenoids [C.sub.19]-[C.sub.21] are even dominating over
respective n-alkanes in the composition of liquids obtained [109-111].
Cyclic hydrocarbons and their derivatives manifest themselves by
adsorption at around 3040 and 1462-1452 [cm.sup.-1], more or less
intensively, in all fractions.
Note that the use of severe thermal destruction contributing to the
supercritical or chemical agents leading to the formation of products
changed beyond recognition not mild depolymerization resulting in the
formation of recognizable links of the original polymers in parent
lignocellulosic matter (such as sugars and other carbohydrates from
holocellulose, phenylpropanes from lignin, and others) in this work was
intentional. Severe processing variables caused large-scale but not
exhaustive deoxygenation and cracking of the initial BM. This was
inevitably accompanied also by undesired secondary reactions between
primary products. That is why among the intentionally obtained oily
products polymeric remnats survived, and oligosaccharidic fragments and
various re-structured and distorted derivatives exist. LPs, in
particular woody ones, are known as very unstable and internally
reactive even at ambient temperature. So, during TCL, isolation, and
storage in contact with air oxygen the final composition of solvent
solubles submitted to analysis can be affected by a series of concurrent
and consecutive secondary reactions such as dehydrogenation,
condensation, denaturation, oxidation, sedimentation, re-polymerization,
coagulation, resin formation, and other spontaneous alterations and
interactions. In spite of being submitted to large destruction and
transformations, the initial matter of BM manifests itself in infrared
spectra by oxygeneous and cyclic character. Though oxygen-containing
compounds are re-distributed into all fractions, Fig. 5 demonstrates
that hydroxyl functionalities were mainly separated by polar solvents
(especially mighthy absorptions at 3300-3500 [cm.sup.-1] in water
solubles) while -C=O containing compounds with the absorption maximum
between 1648 and 1702 [cm.sup.-1] are considerably soluble in benzene. A
spectrum of benzene solubles is clearly recognizable by a low hydroxyl
concentration and amplified aliphatic, aromatic, and cyclic
hydrocarbonaceous functionalities (especially in the regions 720
[cm.sup.-1] (long alkyl chains), 1462-1452 [cm.sup.-1] (cyclic
structures), and 1515, 1600, and 1450 [cm.sup.-1] (complex referring to
skeleton vibrations of benzene nuclei)). The compounds present in
solvent solubles can be expected to include compounds of varied
molecular weight, besides low-molecular oily products and monomers also
polyfunctionalized compounds, oligomeric derivatives, and polymeric
remnants being present.
As to the chemical composition of the solvent soluble fractions, we
can suppose the following. Water solubles are represented by polar
hydrophilic compounds, probably of different alcohols, carboxylic acids,
aldehydes, sugars, phenols, and other oxygeneous compounds. As it was
mentioned above, lower oxygeneous homologues such as methanol, formic
and acetic acids, formaldehyde and acetaldehyde, acetone, and several
simple ketoaldehydes were formed in abundance as a result of pyrolytical
decomposition of BM in inert media, including semicoking. In water
conversion and hydrogenation under the conditions used in this work
those compounds were not rapidly evacuated from the hot reaction zone.
Being in close contact with other decomposition fragments and influenced
by high temperature and pressure for a long time they can initiate
different reactions, including chemical incorporation, reductive
decomposition, synthesis gas reactions and others. Lipophilic oily
compounds such as hydrocarbons, water insoluble phenols, as well as
asphalthenes are concentrated into benzene solubles. The group
composition of these was determined later. Acetone soluble matter is
presented by polar hydrophobic compounds and hetero-atomic structures
insoluble in nonpolar solvents. This fraction, closer to solid than to
liquid, probably consists of large polyfunctionalized fragments of the
initial macromolecules not decomposed entirely. Due to their low
volatility and poor solubility in conventional solvents, these fragments
cannot be analysed by chromatographic methods. Meier et al. 
demonstrated that the acetone soluble part of the thermochemical
decomposition products of lignocellulosic materials consists mainly of
lignin-derived ones while the cellulosic part yields mainly water
solubles. However, by C, H, and O concentrations the acetone extract
manifests itself as an in-between water and benzene soluble, but it
contains significantly more N and S than both these.
In the infrared spectra absorptions belonging not only to -C-N,
-C=N, -C-S, -N-H, and -C=S but also to functional groups such as P-H,
P=S, -S=O, P-O-aromatic (or aliphatic) radical, -N-CS, -N-CS=N, N-N=O,
and C-N=O can be found. As heteroatoms other than oxygen are
concentrated into the composition of acetone solubles, the presence of
pyrrolic, pyranic, sulphoxidic, metallorganic, letcitinic and other
phospholipidic, tioketonic, tioalcoholic, tioureatic, amidic, and many
other fragments containing one or more heteroatoms in the form of
remnants, substitutes, derivation or recombination products in this
fraction is probable. Often absorption bands for some radicals and of
those containing substitutes differ only slightly. For example, the
characteristic absorption of the phenyl group in organic compounds and
that of linked to different elements in the periodical system are close.
Most metal-phenylic compounds have absorption bands in the spectrum
region 1050-1120 [cm.sup.-1] and these are visible in acetone solubles
in Fig. 5.
On the basis of the above observations acetone solubles can be
qualified as nonaliphatic polar hydrophobic polyfunctionalized
heteroatomic compounds of different origin. Having a sufficient reserve
of hydrogen, acetone solubles can give an additional amount of both
water and benzene solubles in further decomposition.
Specifying water solubles as chemicals and acetone solubles as
transition compounds, the goal of our investigations includes maximizing
the yield of benzene solubles and minimizing that of acetone solubles.
Our interest was limited to obtaining liquid petroleum-like oily
products and phenols. Other products obtained were regarded as
by-products. Only such limitation can create a basis to futher
developing processes of co-liquefaction of Estonian oil shale and BM to
obtain chemically modified syncrude and valuable phenolic compounds.
Investigating the composition of the monophenolic compounds in slow
pyrolysis oil of Siberian larch at different temperatures Chuprova &
Levin  found that the proportion of the most valuable
dihydroxyphenols among other ones was highest at 500[degrees]C. In the
presence of high-pressurized solvents or gases the temperature can be
lowered in the range from 350 (beginning of kukersite kerogen
bituminization) to 450[degrees]C (thermobitumen decomposition).
The group composition of benzene soluble compounds separated by TLC
is presented in Table 7. The yields of respective compounds were limited
by minimum and maximum yields obtained in the TCL of sawdust, bark, and
In benzene fractions high polar compounds prevail. Their proportion
in all hydrogenized fractions is practically equal to that of neutral
oxygen ones. Outstandingly high contents of polar compounds were
registered in the composition of semicoking as well as water conversion
benzene soluble extracts, respectively 58-77 and 64-71 wt.%, while that
in hydrogenate was only 22-34 wt.%. Neutral oxygen compounds are another
dominating class of compounds. Their percentage is considerably lower
than that of high polar compounds but never lower than that of any
hydrocarbonaceous fractions obtained. The concentration of the most
valuable constituents of motor fuels--aromatic, alicyclic, and aliphatic
hydrocarbons--is variable depending on both the method and the feedstock
used. Though Table 7 includes a benzene fraction poor in hydrocarbons
(2% in the semicoking of pine sawdust), other experiments yielded
sometimes more hydrocarbons. The higher the content of hydrocarbons, the
closer the product to natural petroleum. Hydrogenates stand out as
having a particularly high concentration of hydrocarbons. Table 7 shows
that the total yield of hydrocarbons was 34-39 wt.% (sawdust and
needles), but in bark hydrogenation it amounted even to 54 wt.%.
Compared with kukersite shale oil the hydrogenates obtained are
characterized by a similar group composition and, in some cases, even by
a higher hydrocarbon content. It is obvious that the primary extracts
obtained as only partially deoxygenated and not totally decomposed
urgently need additional deoxygenation and decomposition as secondary
upgrading (hydrogenation). Co-upgrading of LP derived from BM with shale
oil or with any heavy fraction of shale oil can open up new prospects.
Individual composition of hydrocarbons
The individual composition of TLC hydrocarbon fractions was
analysed by gas chromatography. Chromatograms of non-aromatic
hydrocarbons are presented in Fig. 6. It is obvious that the outstanding
peaks in all chromatograms belong to n-alkanes [C.sub.14]-[C.sub.26],
those of alicyclic hydrocarbons being suppressed. Semicoking yields
considerable amounts of n-alkenes, their concentration is close to the
adjacent saturated homologues (chromatogram (a) in Fig. 6). The
chromatogram of non-aromatic hydrocarbons obtained in semicoking is the
most representative of the composition of different types of
hydrocarbons. Smaller peaks visible belong to isomeric and cyclic
alkanes and alkenes, terpenes, and steroids.
Among aromatic compounds lower benzene alkylsubstituted
derivatives, naphthalene, methyl- and dimethylnaphthalenes, diphenyl,
acenaphthene, fluorene, phenanthrene, and anthracene were identified.
Although there are lines of peaks among aromatic compounds, we
could not identify several peaks in high concentration. These may belong
to different derivatives of mono- and bicyclic aromatic hydrocarbons,
but also to alicyclic compounds. In  it is demonstrated that in
group composition determination with TLC homologous series of alicyclic
and aromatic-alicyclic (hybrid) compounds were identified between
aliphatic and polycyclic aromatic hydrocarbons. In any case, these
compounds were separated as hydrocarbonaceous ones. The benzene solubles
from different hydrogenation and water conversion experiments are quite
comparable with kukersite retort oil containing in several cases even
more hydrocarbons, their content amounting to 50-54 wt.% of the total
extract. Similarities in the group composition and differences in the
individual compounds in groups make it attractive to develop processes
of co-upgrading bio- and shale oils to modify and improve compounded oil
Gas, which made up about a half in the yield of autoclavic
processing and one fifth in semicoking of BM, was submitted to further
chromatographic analysis to determine its composition.
The main gaseous compound formed was carbon dioxide, its share
being as high as 60-75% of the total gas amount in both water conversion
and semicoking (Table 8). Hydrogenation gas, which contains large
amounts of unreacted hydrogen, was characterized by a lower carbon
dioxide content (27-49 vol.%). Still, the share of carbon dioxide in
BM-derived gas was close to the values obtained by other methods.
Semicoking yielded a considerable amount of carbon mono-oxide
(especially from bark and needles). The methane percentage was high
enough (6-13 vol.% in hydrogenation and even 23 vol.% in the case water
conversion of needles), that of other gaseous hydrocarbons was
significantly lower. The share of residual hydrogen after hydrogenation
(23%) showed that as compared with other feedstocks bark consumed more
[FIGURE 6 OMITTED]
Biomass, a diversified resource in its colossal majority
permanently regenerated directly or indirectly by plant growth, is
generally of lignocellulosic nature. Unused BM and remainders of BM used
as material or food accumulate as natural and processing wastes. The
cost of such feedstocks often does not surpass transportation costs.
Processes such as mining, flotation, drying, or assorting are usually
not necessary in BM procurement and further combustion or liquefaction.
Hence, availability, productivity, renewability, sustainability, and
similarity in main building blocks are the important factors making the
use of BM as a feedstock attractive.
BM as a feedstock can be successfully used for the production of
synthetic liquid fuels similar to conventional petroleum fuels and
non-petroleum chemicals. BM contains negligible amounts of sulphur and
nitrogen and has a low ash content. Compared with fossil fuels, BM
generates far less harmful air emissions and its use will considerably
reduce the amount of solid waste sent to landfills.
Conversion processing of BM leads to the formation of fuels with a
higher energy density than the original. Oxygen-containing chemicals can
be separated as well. Pyrolysis, hydrogenation, and sub- or
supercritical extraction are the methods often used in BM thermal and
thermochemical liquefaction. Operating at temperatures within
300-550[degrees]C with and without hydrogen, with water and other
solvents and catalyst additions LPs can be obtained in various yields
and chemical compositions. Both BM and liquids derived from it are
characterized by as high as up to 50 wt.% oxygen content. Due to large
amounts of oxygenated compounds present, the BM-derived liquids have a
polar nature and do not mix readily with hydrocarbons but they do mix
with water and other polar solvents. This is one of the specific
features of BM-derived liquids compared with those originating from
fossil fuels. Pyrolysis yields considerable amounts of a highly
oxygenated liquid, which can be used as light and heavy fuel oil as well
as refinery feed as the excessive oxygen can be removed via
hydroprocessing. As a result of effective reductive deoxygenation the
yield of upgraded LP decreases proportionally with the decreasing oxygen
concentration, which can be diminished to the level meeting
transportation fuel specifications.
Investigations initiated in Estonia focus on working out the
fundamentals of individual and co-processing of BM and oil shales on the
basis of not only the existing industrial facilities but also on those
that have to be introduced to modify the oil shale industry in Estonia
keeping space with scientific progress. The technologies applied allow
obtaining LPs close to shale-derived syncrude quality.
It is obvious that deoxygenation, a strongly desired process,
occurred intensively in spite of which TCL process or feedstock under
investigation was used though the oxygen concentration was reduced
insufficiently--only by half. To further reduce the oxygen amount to
achieve the concentration comparable with that in kukersite shale oil
(6-10 wt.%) and to enhance hydrocarbon yield, upgrading in a second
stage seems unavoidable.
The yields of LPs obtained in this work seem to be small compared
with those obtained in flash pyrolysis. Actually considerably more
deoxygenated liquids were obtained in this work and theoretically
calculated hydrocarbonaceous potential of BM initially containing 40-50
wt.% oxygen, after its removal as CO2 (totally deoxygenated liquid), is
less than 30-35 wt.%--due to other cracking and coke formation
processes, 20-25% can be attainable. Total deoxygenation is hardly ever
achieved. Further investigations are being carried out to obtain the
above-mentioned level and product, which could be characterized as being
in between nonconventional petroleum and natural crude.
Additional hydrocracking to upgrade BM-derived liquids alone and
together with shale oil heavy fractions are also on the agenda.
Received 19 May 2005
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Table 1. Some kinds of BM and their
Type and reference number cellulose
Wood  43 22
Softwood  40-44 24-29
Hardwood  43-48 27-35
Pine (Pinus sylvestris) 45 20
wood (a) 
Pine wood  52 No data
Spruce wood  43 26
Spruce (Picea abies) wood (a)  41 26
Birch (Betula pendula) wood (a)  38 37
Poplar wood  44 30
Scots pine (a)  50 21
Scandinavian and Baltic 20-30 15-20
softwood bark (b) 
Pine (Pinus pinaster) bark (a)  24 15
Pine bark (a)  34 16
Pine (Pinus halepensis) needles  24 No data
Mullein (Verbascum) stalk  50.3 17.6
Common reed (Phragmites 43.3 15.5
Wheat straw  28.8 39.1
Corncob  52 32
Hazelnut shell  25.9 29.9
Corn stover  51.2 30.7
Tobacco leaf  36.3 34.4
Lignin Solvent extractables,
Type and reference number solvent used
Wood  36 No data
Softwood  26-33 1-5 (not specified)
Hardwood  16-24 2-8 (not specified)
Pine (Pinus sylvestris) 28 6 (not specified)
wood (a) 
Pine wood  28 0.6 (water)
Spruce wood  29 1.6 (acetone)
Spruce (Picea abies) wood (a)  29 3 (not specified)
Birch (Betula pendula) wood (a)  20 4 (not specified)
Poplar wood  21 2.4 (acetone)
Scots pine (a)  26 2.7 (hot water)
Scandinavian and Baltic 25 5
softwood bark (b) 
Pine (Pinus pinaster) bark (a)  44 (c) 17 (dichloromethane,
Pine bark (a)  34 14 (not specified)
Pine (Pinus halepensis) needles  18 21 (ethanol, toluene)
Mullein (Verbascum) stalk  31.4 0.7 (petroleum ether)
Common reed (Phragmites 27.1 No data
Wheat straw  18.6 8.0 (alcohol-benzene)
Corncob  15 1.3 (acetone)
Hazelnut shell  42.5 4.2 (acetone-water)
Corn stover  14.4 1.9 (diethyl ether)
Tobacco leaf  12.1 10.0 (dichloromethane)
(a) Ash and moisture included. (b) Tannin concentration 10-15%
included. (c) Other polyphenols included.
Table 2. Ultimate analysis of various kinds of forest BM
Type and reference number C H
Wood (c)  52 6.3
Wood  48-50 6.0-6.5
Pine (Pinus pinaster) wood  52.5 5.2
Poplar wood  50.1 6.0
Spruce wood  52.1 6.1
Spruce wood  49.9 6.2
Pine branches ([empty set] 47.9 6.2
> 0.5 cm) 
Pine branches ([empty set] 45.4 6.8
< 0.5 cm) (c) 
Blended forestry wastes (spruce 51.1 5.9
80%, pine 10%, birch 10%) 
Blended forestry wastes (spruce 51.4 6.0
86%, pine 9%, birch 5%) 
Pine sawdust, bark free  51.0 6.2
Variation limits 45.4-52.5 5.2-6.8
Pine bark (c)  55.9 5.3
Pine (Pinus brutia) bark  50.2 5.4
Pine bark  55.9 5.5
Japanese red pine bark (c)  46.9 5.3
Bark waste  51-56 6.0-8.5
Variation limits 46.9-56 5.3-8.5
Pine needles (c) (Pinus pinaster) 46.9 6.7
Cellulose  43.7 6.4
Spruce holocellulose  47.1 6.0
Birch holocellulose  45.4 6.0
Birch Willstatter lignin  61.3 5.8
Spruce lignin  66.7 5.9
Lignin  63.9 5.8
Xylan (c)  43.5 6.2
Rye straw (c)  45.5 6.5
Wheat straw (c)  45.5 5.1
Corncob (c)  49.0 5.4
Hazelnut shell (c)  52.9 5.6
Corn stover (c)  49.5 5.4
Tobacco leaf (c)  43.0 4.5
Type and reference number N+S O (b)
Wood (c)  0.4 40.5
Wood  0.5-2.3 38-42
Pine (Pinus pinaster) wood  0.8 41.5
Poplar wood  0.5 43.4
Spruce wood  0.3 41.5
Spruce wood  43.9
Pine branches ([empty set] 0.3 45.6
> 0.5 cm) 
Pine branches ([empty set] 0.3 47.4
< 0.5 cm) (c) 
Blended forestry wastes (spruce 0.5 42.5
80%, pine 10%, birch 10%) 
Blended forestry wastes (spruce 0.5 42.1
86%, pine 9%, birch 5%) 
Pine sawdust, bark free  0.1 42.7
Variation limits 0.1-2.3 38-47.4
Pine bark (c)  0.4 37.1
Pine (Pinus brutia) bark  0.4 44.0
Pine bark  38.6
Japanese red pine bark (c)  46.0
Bark waste  0.3-0.8 24-40
Variation limits 0.3-0.8 24-46.0
Pine needles (c) (Pinus pinaster) 1.9 44.6
Cellulose  49.9
Spruce holocellulose  46.9
Birch holocellulose  48.6
Birch Willstatter lignin  32.9
Spruce lignin  27.4
Lignin  30.3
Xylan (c)  49.9
Rye straw (c)  1.9 42.0
Wheat straw (c)  1.8 34.1
Corncob (c)  0.4 44.6
Hazelnut shell (c)  1.4 40.1
Corn stover (c)  0.6 41.8
Tobacco leaf (c)  0.5 35.8
Molar ratio (a)
Type and reference number H/C O/C
Wood (c)  1.45 0.58
Wood  1.44-1.63 0.57-0.66
Pine (Pinus pinaster) wood  1.2 0.6
Poplar wood  1.4 0.7
Spruce wood  1.4 0.6
Spruce wood  1.5 0.7
Pine branches ([empty set] 1.6 0.7
> 0.5 cm) 
Pine branches ([empty set] 1.8 0.8
< 0.5 cm) (c) 
Blended forestry wastes (spruce 1.4 0.6
80%, pine 10%, birch 10%) 
Blended forestry wastes (spruce 1.4 0.6
86%, pine 9%, birch 5%) 
Pine sawdust, bark free  1.5 0.6
Variation limits 1.19-1.80 0.57-0.78
Pine bark (c)  1.14 0.50
Pine (Pinus brutia) bark  1.29 0.66
Pine bark  1.18 0.52
Japanese red pine bark (c)  1.36 0.74
Bark waste  1.41-1.82 0.32-0.59
Variation limits 1.14-1.82 0.32-0.74
Pine needles (c) (Pinus pinaster) 1.71 0.71
Cellulose  1.76 0.86
Spruce holocellulose  1.53 0.75
Birch holocellulose  1.59 0.80
Birch Willstatter lignin  1.13 0.40
Spruce lignin  1.06 0.31
Lignin  1.09 0.35
Xylan (c)  1.71 0.86
Rye straw (c)  1.71 0.69
Wheat straw (c)  1.34 0.56
Corncob (c)  1.32 0.68
Hazelnut shell (c)  1.27 0.57
Corn stover (c)  1.31 0.63
Tobacco leaf (c)  1.25 0.62
(a) Calculated by the authors.
(b) Often calculated by difference.
(c) Ash content reserved.
Table 3. Ultimate analysis of liquids
Wood- or bark-derived liquids C H
Wood fast pyrolysis oil  55.3-63.5 5.2-7.0
Acacia slow pyrolysis 58.8 6.9
Eycalyptus slow pyrolysis 63.9 7.8
Sawdust fast pyrolysis 60.4 6.9
Sawdust fast pyrolysis oil 87.7 8.9
Oaken BM solvolytical 82.2 9.3
lique-faction oil fraction
liquefaction oil followed
by catalytical upgrading
Heavy fraction 84.9 8.3
Light fraction 86.2 8.1
Upgraded oil 86.9 9.8
Bark-derived slow pyrolysis
Bio-oil from barks 63.9 7.6
(Pinus brutia Ten.) 
Bio-oil from pine bark  63.3 7.2
Wood- or bark-derived liquids N+S O (by
Wood fast pyrolysis oil  0.07-0.44 29.1-39.4
Acacia slow pyrolysis 0.6 33.7
Eycalyptus slow pyrolysis 0.6 27.7
Sawdust fast pyrolysis 0.9 31.8
Sawdust fast pyrolysis oil 0.4 3
Oaken BM solvolytical 5.9 2.6
lique-faction oil fraction
liquefaction oil followed
by catalytical upgrading
Heavy fraction 0.7b 6.1
Light fraction 1.7b 4
Upgraded oil 0.9b 2.4
Bark-derived slow pyrolysis
Bio-oil from barks 0.1 28.4
(Pinus brutia Ten.) 
Bio-oil from pine bark  0.8 28.7
Wood- or bark-derived liquids H/C O/C
Wood fast pyrolysis oil  1.12-1.32 0.34-0.53
Acacia slow pyrolysis 1.41 0.43
Eycalyptus slow pyrolysis 1.46 0.32
Sawdust fast pyrolysis 1.37 0.39
Sawdust fast pyrolysis oil 1.22 0.03
Oaken BM solvolytical 1.36 0.02
lique-faction oil fraction
liquefaction oil followed
by catalytical upgrading
Heavy fraction 1.17 0.05
Light fraction 1.13 0.04
Upgraded oil 1.35 0.04
Bark-derived slow pyrolysis
Bio-oil from barks 1.43 0.33
(Pinus brutia Ten.) 
Bio-oil from pine bark  1.36 0.34
(a) Calculated by the authors.
(b) (N + S) by difference.
Table 4. Operating conditions
Method Reactor Temperature, Duration,
Semicoking Fischer assay Up to 525 1.5
Water Autoclave 380 4
Hydro- Autoclave 4
Method Pressure, MPa
Initial Working Residual
Water 0.1 Up to 40 0.1-1
Hydro- 6.5 Up to 40 Up to 6.5
Method Weight, g
Water 60 180/-
Hydro- 60 -/6
Table 5. Yield of liquefaction products, wt.% (dry basis)
Semicoking Water Catalytical
Water 8-16 6-9 1-2
Benzene solubles 7-9 6-16 5-18
Acetone solubles 1-2 3-4 2-5
Summary LP, oil as 16-26 16-27 8-22
Gas + reaction water 45-46 47-52 47-54
Solid residue 29-39 26-32 32-41
Table 6. Ultimate analysis of oils obtained from pine bark by
using different TCL methods
Object/Method Concentration, wt.%
C H N O (a) S
LP/Semicoking 67.7 7.8 0.6 23.8 0.1
LP/Water 73.2 7.6 0.5 18.5 0.2
LP/Catalytical 81.5 8.5 0.5 9.4 0.1
Kukersite semi- 81-84 9.5-10.5 0.1-0.2 6-8 0.6-0.8
Object/Method Molar ratio
H/C N/C O/C S/C
LP/Semicoking 1.38 0.008 0.23 0.0005
LP/Water 1.25 0.006 0.19 0.001
LP/Catalytical 1.25 0.005 0.09 0.0005
Kukersite semi- 1.47 0.002 0.07 0.004
(a) By difference.
Table 7. Group composition of benzene soluble compounds
TLC fraction separated Yield, wt.%
High polar compounds 58-77 64-71
(oxygeneous, other hetero-
atomics, and asphalthenes)
Neutral oxygen compounds 9-36 13-17
Polycyclic aromatic hydrocarbons 3-6 8
Monocyclic aromatic hydrocarbons 1-4 3
Non-aromatic hydrocarbons 2-9 4-8
TLC fraction separated Yield, wt.%
hydrogenation semicoking 
High polar compounds 22-34 23
(oxygeneous, other hetero-
atomics, and asphalthenes)
Neutral oxygen compounds 25-32 34
Polycyclic aromatic hydrocarbons 16-25 17
Monocyclic aromatic hydrocarbons 3-5 8
Non-aromatic hydrocarbons 8-24 18
Table 8. Gas composition
Concentration in total gas, vol.%
Gas identified Semicoking Water conversion Catalytical
Carbon dioxide 62-74 57-75 27-49
Carbon oxide 15-26 1-5 0-1
Hydrogen 1-2 1-4 32-44
Hydrogen sulphide 0-1 1-2 1-2
Methane 5-8 11-23 6-13
Alkanes C2-C4 1-3 9-12 6-16
Alkenes C2-C4 0-2 0-1 0