INTRODUCTION
Currently, the task of finding alternative energy
sources that are environmentally safe and economically
affordable is very urgent. Of particular interest are
species of herbaceous plants with a high growth rate,
characterised by high values of the above-ground
vegetative mass growth and having practical application
as an energy source [1].
An example is the genus Miscanthus plants, a
practically inexhaustible source of renewable raw
materials in the field of alternative energy. This is due
not only to the chemical properties of their biomass,
but also to high growth rates and enormous biological
productivity, among other things in a temperate climate,
which together make their use in Russia promising [2].
The main advantages of miscanthus biomass in
comparison with other types of perennial grasses are
associated with its higher productivity, resistance to
adverse environmental conditions, increased lignin
content and, consequently, increased calorific capacity.
In addition, the genus Miscanthus plants can
be used to produce biologically active substances.
Miscanthus extracts include fatty acids, sterols and
other aromatic compounds. The main structures
of phenolic compounds and sterols of the bark and
core of Miscanthus × giganteus include vanilla acid,
para-coumaric acid, vanillin, para-hydroxybenzaldehyde,
syringaldehyde, campesterol, stigmasterol,
β - sitosterol, stigmast-3,5-diene-7-one, stigmast-4-ene-3-
one, stigmast-6-ene-3,5-diol, 7-hydroxy-β-sitosterol and
7-oxo-β-citerol [3].
Currently in the world there is an increase in
cultivation of Miscanthus driven by the characteristic
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Foods and Raw Materials, 2019, vol. 7, no. 2
E-ISSN 2310-9599
ISSN 2308-4057
Research Article DOI: http://doi.org/10.21603/2308-4057-2019-2-403-411
Open Access Available online at http:jfrm.ru
Miscanthus plants processing in fuel, energy,
chemical and microbiological industries
Olga O. Babich1 , Olga V. Krieger1,* , Evgeny G. Chupakhin1 , Oksana V. Kozlova2
1 Immanuel Kant Baltic Federal University, Kaliningrad, Russia
2 Kemerovo State University, Kemerovo, Russia
* e-mail: olgakriger58@mail.ru
Received August 26, 2019; Accepted in revised form September 10, 2019; Published October 21, 2019
Abstract: The increasing shortage of fossil hydrocarbon fuel dictates the need to search for and develop alternative energy sources,
including plant biomass. This paper is devoted to the study of the Miscanthus plants biomass potential and the analysis of technologies
of its processing into products targeted at bioenergy, chemistry, and microbiology. Miscanthus is a promising renewable raw material
to replace wood raw materials for the production of chemical, fuel, energy, and microbiological industries. Miscanthus is characterised
by highly productive (up to 40 tons per one hectare of dry matter) C4-photosynthesis. Dry Miscanthus contains 47.1–49.7% carbon,
5.38–5.92% hydrogen, and 41.4–44.6% oxygen. The mineral composition includes K, Cl, N and S, which influence the processes
occurring during biomass combustion. The total amount of extractives per dry substance lies in the range of 0.3–2.2 % for different
extraction reagents. Miscanthus has optimal properties as an energy source. Miscanthus × giganteus pellets showed the energy
value of about 29 kJ/g. For the bioconversion of plants into bioethanol, it is advisable to carry out simultaneous saccharification and
fermentation, thus reducing the duration of process steps and energy costs. Miscanthus cellulose is of high quality and can be used for
the synthesis of new products. Further research will focus on the selection of rational parameters for processing miscanthus biomass
into products with improved physical and chemical characteristics: bioethanol, pellets, industrial cellulose, bacterial cellulose,
carbohydrate substrate.
Keywords: Miscanthus, bioethanol, cellulose, raw materials, processing
Please cite this article in press as: Babich OO, Krieger OV, Chupakhin EG, Kozlova OV. Miscanthus plants processing in fuel,
energy, chemical, and microbiological industries. Foods and Raw Materials. 2019;7(2):403–411. DOI: http://doi.org/10.21603/2308-
4057-2019-2-403-411.
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Babich O.O. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 403–411
high growth rates and a high degree of its biological
needs compliance with agro-climatic conditions.
The purpose of this review was to analyse the
modern methods of processing Miscanthus plants
for bio-ethanol production, technical and bacterial
cellulose, as well as products for microbiological and
biotechnological industry.
STUDY OBJECTS AND METHODS
The representatives of the genus Miscanthus
(Miscanthus Anderss L.) graminoid family (Poaceae)
were the materials of this research. We analysed
botanical characteristics and geographical distribution
of various studied plants, made chemical composition
analysis, and summarised the main processing methods
according to the sources of scientific literature. These
resulted in the analysis of modern methods of obtaining
products for fuel, energy, chemical and microbiological
industries.
RESULTS AND DISCUSSION
The botanical characteristics and distribution
of the genus Miscanthus plants. The Miscanthus
family includes about 40 species of monocotyledonous
herbaceous perennial, sustainable plants with long
curved linear leaves and small buds that bloom in late
summer or early autumn, and about 20 species of
miscanthus proper (Fig. 1).
In the Russian Far East (Primorsky Krai, Sakhalin
and the Southern Kuril Islands), there are three species
of miscanthus: Miscanthus sinensis, Miscanthus
sacchariflorus and Miscanthus purpurascens. It can
grow in the climatic conditions of Central and Eastern
Europe [4]. In the late 20th century there appeared new
miscanthus genotypes adapted to growth in the Northern
regions, including Russian territories.
For the countries of the European Union (EU) it is
recommended to grow miscanthus in the continental
climate zone and the North Mediterranean, where soil
and climatic resources correspond to the requirements of
the plants [5, 6].
In Europe the plants reach a height of 3–4 m, and
the representatives of tropical and subtropical species
may reach 5 m or more in warm and humid climatic
conditions. In the Central part of Russia, according to
research of scientists of the Russian Timiryazev State
Agrarian University, miscanthus giant reaches the height
of 2 m, in Western Siberia – 2.5 m, and 3.9 m in the
middle Volga region. The stems are upright and resistant
to lodging because of their considerable thickness. It
reaches 6 cm in homeland regions (China, Japan, Russian
Far East, USA East coast); in the Middle Volga regions
plants of 1–4 years of life are 0.8–1.5 cm thick [7, 8].
Miscanthus does not impose high requirements to soil
and can grow well on marginal and low density soils whose
granulometric composition is dominated by sand fractions.
In Ukraine it is cultivated on sod-podzolic type of soils; in
the forest-steppe of Novosibirsk Priobye, Middle Volga and
Moscow region – on gray forest soils [9, 10].
For optimal growth and development plants require
certain thermal and water regimes. Miscanthus seed
germination requires ≥ 20°C soil heating with soil
moisture of 60–80% of full field moisture capacity. To
resume the shoots and the active growing season on
crops of previous years, the temperature of the air must
be in the range of 20–25°C. As shown in the literature,
physiological activity of the studied representatives of
the genus is sharply reduced at temperatures below 6°С.
Optimal temperature for adequate photosynthesis
is considered to be 28–32°С. In Eastern Europe this is
enough to produce sufficiently high yields of biomass [11].
It is known that miscanthus belongs to the C4
plants, characterised by: optimum temperature for
photosynthesis of 30–45°C, 40–80 mg/dm2h CO2
assimilation in full sunlight, more economical water
consumption as compared to C3 plants (twice and more),
high drought and heat resistance, salt tolerance. These
lead to better assimilation activity and, consequently,
biological productivity.
The vast majority of well-known scientific
studies are devoted to the three species of the genus
miscanthus: Miscanthus giganteus, Miscanthus sinensis
and Miscanthus sacchariflorus, which are the most
widespread in Russia and abroad [12].
Chinese miscanthus (M. sinensis) is one of the most
common types of ornamental grasses, named differently
in different countries. For example, ‘Chinese silver
grass’ or ‘magic grass’, sometimes ‘Chinese reeds’. In
nature it is widespread in the Russian Far East up to the
taiga zone, also in China, Korea, Japan. As an adventive
species it occurs in many countries, e.g. USA, Brazil and
African States (Fig. 2) [13].
M. sacchariflorus is a species growing on wet
meadows, forest clearings a Figure 1 Chinese Miscanthus ‘Gracillimus’ nd stony slopes in the
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Primorsky Krai, China, Korea, Japan, and also in the
above-mentioned areas [14].
This also is a perennial long-stem herb up to 2 m
in height. Stems are erect, thick and numerous. Leaves
are rather rigid, linear, flat, long-acuminate, 7–18 mm
wide, up to 60 cm long. Flowers are small, in spikelets
with long, white, silky hairs. Inflorescence is 15–25 cm
long, pinkish-silvery, white, fan-shaped, consisting of
8–20 spiciform branchlets with fruits. It blooms in late
August–September. Flowering often occurs in July [15].
Not demanding to soil fertility.
Giant miscanthus (Miscanthus × giganteus), as
described above, has a C4 photosynthetic path and
provides high productivity of plant biomass. The genome
of this species includes a triple set of chromosomes
that do not divide during meiosis because gametes are
not viable. As a rule, seeds are formed sterile, which
significantly limit reproduction of the species, this is a
barrier to the establishment of new fields.
The rhizome structure of giant miscanthus grows
very slowly and decreases proliferation [16, 17].
Therefore, planting material is produced by cultivation
of mother plantations (Queen cells), pre-multiplying
it in vitro, or by rhizomes by targeted separation from
plants of the previous planting year. This technology
is limited by insufficient amount of seedling material
and the lack of landing equipment [18, 19]. In this
regard, high-quality uniform planting material can
be grown in special nurseries with the use of modern
biotechnologies.
Chemical composition and properties of genus
Miscanthus plants. Analysis of miscanthus chemical
composition biomass allows planning proper use of
species. The three main components of lignocellulosic
materials are: cellulose, hemicellulose and lignin. Their
content in each organ is not equivalent and depends on
the plant’s functional and physiological properties. The
amount of cellulose in the stem, as a rule, is higher than
that in the leaves. Lignin contains three-dimensional
phenylpropyl-based polymer that provides structural
rigidity and integrity, as well as prevents lingocellulose
swelling [20–22].
Table 1 shows the differences in concentration of
these substances in the cell wall in the three species
growing on the territory of European countries, after
3–5 years of cultivation [14].
According to the data presented in the table, the
types of miscanthus giganteus and sacchariflorus
differ insignificantly in pulp content and hemicellulose/
lignin ratio.
Table 2 shows the averages of biochemical
composition of leaves, stems and a whole 4-year-old
plant of Miscanthus varieties [4].
Data analysis indicates that the stem of miscanthus
is the most suitable raw material for obtaining a large
amount of high quality cellulose, as it has lower content
of ash and lignin and a higher yield of the target product.
In the process of turning cellulose into ethanol
such indicators as degree of polymerisation (n) and
its crystallinity are of supreme value. The number of
glucose units that make up one polymer molecule is
called the degree of polymerisation.
X-ray diffraction and solid state 13 CP/MAS
NMR spectroscopy are the two most commonly used
methods of cellulose crystallinity determination. The
crystallinity of cellulose for the species Miscanthus
sinensis was measured by X-ray diffraction. Subject to
the dimensions of the particles, differences in the index
of cellulose crystallinity were revealed (Table 3) [23].
Figure 2 Distribution of Chinese Miscanthus (M. sinensis)
Figure 3 Distribution of M. sacchariflorus
Table 1 Composition of miscanthus species cell walls
Species Cellulose, % Hemicellulose, % Lignin, % H:L ratio
M. × giganteus 50.34–52.13 24.83–25.76 12.02–12.58 2.06–2.05
M. sacchariflorus 49.06–50.18 27.41–28.11 12.10–12.13 2.26–2.30
M. sinensis 43.18–45.52 33.83–33.98 9.69–10.32 3.49–3.29
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It is generally believed that cellulose crystalline
regions are harder to decompose than amorphous
domains, due to the strong intermolecular hydrogen
bonds. For the studied species, the researchers found
that the initial rate of cellulose hydrolysis increased with
decreasing crystallinity [24, 25].
Unlike cellulose, hemicelluloses have lower degree
of polymerisation, typically 50–300; they also have a
branched structure and are amorphous. The predominant
hemicellulose polymer for the miscanthus is the
arabinoxylane, which contains a chain of 1.4-linked
xylonic links. Sugar components in hemicellulose can
participate in the formation of lignin-carbohydrate
complexes (LCC) by covalent linkages between lignin
and carbohydrates.
Despite considerable analytical studies aimed
at the characterisation of the LCC, they still remain
poorly defined, and their biosynthesis pathways require
further study [26]. Distribution, structure and content of
lignin is considered to be one of the important factors
responsible for the recovery of lignocellulosic enzymatic
degradation.
Considering miscanthus as fuel, the values of
specific heat of combustion, mineral composition, ash
content and content of volatile substances were analysed.
The specific heat of combustion parameter is closely
linked to the elemental composition and ash content. For
Miscanthus × giganteus it ranges from 17 to 20 MJ/kg.
Dry raw material contains on average 47.1–49.7%
carbon, 5.38–5.92% hydrogen, and 41.4–44.6% oxygen.
Mineral composition includes the following elements:
K, Cl, N and S, which have an impact on the processes
occurring during biomass combustion [27].
Increased content of K and Cl can reduce the melting
point of ash and cause corrosion. High concentrations of
N and S can lead to increased NOx and SO2 formation
during combustion. Miscanthus mineral concentration
varies depending on the type of plant, place of growth,
time of harvest and even the type of fertilisation. Late
harvest is the preferred fuel due to the lower content
of K, Cl and N. Some studies provide the trace element
composition of the miscanthus: S – 0.7–1.9 g/kg, Ca – 0.5–
1.4 g/kg, Mg – 0.2–0.6 g/kg, P – 0.4–1.1 g/kg [28].
Ash content is an important parameter for fuel.
The indicator represents the mass fraction of noncombustible
residue (calculated as anhydrous weight)
percentage, which results from mineral impurities of
the fuel during its complete combustion. According to
generalised data, miscanthus ash consists of 20–40%
SiO2, 20–25% K2O, 5% P2O5, 5% CaO and 5% MgO.
Its composition depends on the content of silt and clay
in the soil. High ash content leads to the formation of
slag and causes thermal process agglomeration, thereby
lowering combustion efficiency of biomass plant [29].
Biomass high moisture content impedes its
combustion, causing a problem of transportation.
Moreover, in the process of wet fuel combustion, a
large number of volatile side-products are released.
Table 4 shows composition of volatile products, ash
content, and molar internal energy (Ea) of miscanthus.
The parameters presented are influenced by the harvest
period, plant species, and climate [30].
In addition to biofuels production, the Miscanthus
plants can be used for obtaining biologically active
substances. The total amount of extractives based on the
dry substance is redistributed in the range of from 0.3
to 2.2% with different extraction reagents. Also more
than 20 hydroxycinnamic acids and their derivatives
were discovered and described. The interest in these
compounds is justified by the potential of plant phenols
Table 3 Miscanthus cellulose crystallinity according to the
diffraction of X-rays
Particle size, μm Cellulose crystallinity, %
250–355 54.2
150–250 50.7
63–150 41.9
< 63 24.8
Table 2 Chemical composition of the Soranovski plant variety
The organs of the plant Performance (in terms of dry substance, %)
WGF* ash content lignin pentosan cellulose by Kürschner
Whole plant 4.98 ± 0.05 5.87 ± 0.05 22.0 ± 0.5 21.0 ± 0.5 53.1 ± 0.5
Leaf 6.32 ± 0.05 9.23 ± 0.05 23.6 ± 0.5 20.3 ± 0.5 43.3 ± 0.5
Stem 2.68 ± 0.05 2.13 ± 0.05 15.0 ± 0.5 23.0 ± 0.5 55.7 ± 0.5
*WGF – wax glaze fraction
Table 4 Energy characteristic of the genus Miscanthus plants
Species Ash, %* Moisture, % Volatile matter, %* Coke residue, %** Ea, kJ/mol
M. × giganteus 2.7 4.2–4.9 73.6–73.9 19.3–19.8 76.3–76.7
M. sacchariflorus 2.2–2.3 3.8–4.1 73.4–73.6 20.3–20.4 69.0–69.3
M. sinensis 3.0–3.2 4.2–4.4 74.7–74.9 17.7–17.9 64.6–65.7
*dry matter
**dry matter ash-free basis
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in the pharmaceutical industry. They can be used as
antioxidant, antimicrobial, anti-inflammatory, anticancer
biological active substances for manufacturing
drugs to prevent HIV, thrombosis and atherosclerosis,
reduce cholesterol, etc. [31, 32].
Features of processing Miscanthus raw materials
for energy industry products. Miscanthus is the
main energy culture, because it has the most optimal
flow ratio of in/out energy content parameters [33].
Miscanthus as a lignocellulosic biomass with a
low moisture content can be processed into fuel
thermochemically. Figure 4 shows a simplified scheme
of the two main ways of producing chemicals and fuels
from thermal conversion of miscanthus biomass [34].
The first way is gasification, followed by Fischer-
Tropsch synthesis, which requires large-scale
installations. Large-scale installations cannot be adapted
to biomass supply chain without biomass pyrolysis
energy compaction before its long range transport. The
second way is fast pyrolysis or biomass liquefaction,
with the consequent quality biological oils increase in
modified refrigerators [35].
Fast miscanthus pyrolysis was investigated in
a fluidised bed reactor for production of bio-oil
depending on the temperature (350–550°C), particle size
(0.3 mm–1.3 mm), feed rate and gas flow rate. The
highest bio-oil yield of 69.2% was observed at the
temperature of 450°C. With increasing temperature the
amount of oxygenates in bio-oil gradually decreased,
and the amount of water and aromatics increased. The
output of the bio-oil did not depend on particle size or
feed speed. The use of gaseous products as a medium
for fluidisation increased the yield of bio-oil. It was also
shown that partial removal of sodium and potassium
increases the yield of Miscanthus × giganteus volatile
substances due to the formation of semi-coke [36].
Miscanthus gasification study was carried out in
a fluidised layer using olivine as the primary catalyst.
It was shown that miscanthus raw material produces
about 1.1 m3/kg gas containing more than 40% of H2 and
24% CO. Gas outlet and H2 concentration increase with
temperature while the yields of tar, semi-coke, CO, CO2
and CH4 decrease.
Experiments on miscanthus gasification were carried
out in a circulating fluidised bed in the presence of
oxygen, magnesite or olivine as a granular catalyst and
kaolin as the additive to reduce agglomeration of the
layer. Alkaline elements, mainly Na, K and Cl in the
ash of miscanthus lead to agglomeration of the silicarich
material in the fluidised bed. The use of magnesite
as an additive or as a bed material leads to a significant
increase in the hydrogen fraction volume in the gaseous
product. Its maximum volume fraction can reach up
to 40% during the gasification of biological material
with a layer of magnesite. Magnesite has also shown
excellent results in resin content reduction and increase
in hydrogen/carbon dioxide ratio (H2:CO).
Thus, the analysis of scientific literature confirms
the prospects of miscanthus as a source of energy. It can
be briquetted or granulated. Combusted pellets from
raw materials of miscanthus (Miscanthus × giganteus)
demonstrated that the energy value of this product
reaches 29 kJ/g. Meanwhile, low-temperature slow
pyrolysis is energetically more favourable [37].
Features of processing plant biomass to
bioethanol. The use of lignocellulosic biomass as a
source of raw materials for the production of bioethanol
has some complications, lying in its complex structure.
It is established that the necessary preliminary chemical
treatment of raw materials is needed. The process
of raw materials bioconversion into bioethanol may
include both separate hydrolysis and fermentation and
simultaneous saccharification and fermentation, known,
scientifically, as SHF and SSF processes, respectively.
One of the main advantages of SHF is the ability of
enzyme preparations and microorganisms to operate
under their optimal conditions. However, a disadvantage
of stages continuous implementation is excessive length.
For the purposes of optimisation, today the consistent
process is faced with an alternative of SSF.
The advantage of this process is the carryingout
of saccharification and fermentation in one
Figure 4 Simplified scheme of fuel and chemicals production
Miscanthus
biomass
Pyrolysis
Liquid-phase
pretreatment
Gasification
Liquefaction
(> 5 МPа H2)
Fast pyrolysis
Update
Joint
Extracts processing
(chemicals)
The
Fischer-
Tropsch
Process
Crude oil
FT Products
CO, H2
and/or
Fuel
Chemical
substances
CO,
H2
bio-oil
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reactor, shortening time process steps and reduction
in energy consumption. It is also known that in the
simultaneous process with introduction of bioethanol
producers reducing substances begin to escape from
the system, getting used for the synthesis of bioethanol.
Thus, the equilibrium of the cellulose hydrolysis
enzymatic reaction is continuously shifted toward the
formation of reaction products (glucose), achieving
saccharification intensification. However, one of the
drawbacks of the simultaneous method is the difference
in optimum temperatures needed for enzyme activity at
saccharification stage (45–50°C) and for microorganisms
cultivation (28–30°C) [9].
The main bioethanol producer in Russia is the
yeast Saccharomyces cerevisiae, used in ethyl alcohol
production both on food raw materials and hydrolysis
media. In some sources these microorganisms are
considered as bioethanol producers on hydrolysates of
various types obtained from miscanthus raw materials.
For example, the paper by Baibakova shows the
scheme of obtaining ethanol as a result of bioconversion
using Saccharomyces serevisiae RNCIM Y-1693,
isolated from the reactor of Kotlas (Arkhangelsk region)
pulp and paper mill [28]. The peculiarity of the strain
is its resistance to harmful impurities of hydrolysates.
Optimal conditions for the strain are the temperature of
26–28°C and native active acidity of the extract of 4.5–
4.7 pH. Earlier it was shown that this strain is resistant
to lack of nutrients in the medium, products of its
own metabolism and media obtained from cellulosecontaining
raw materials by enzymatic hydrolysis. The
raw material was subjected to preliminary chemical
treatment by alkaline delignification, after which the
products of alkaline delignification were converted into
a solution of monosaccharides by enzymatic hydrolysis.
Further, bioethanol was synthesised on the obtained
media [29].
Another paper provides information that
bioethanol is also obtained by converting the strain
with Saccharomyces cerevisiae Y-1693, but a solution
of nitric acid is used for pretreatment. In this case,
bioethanol yield reached 70.9 % [28, 30, 31].
The use of consortium for enzymatic hydrolysate of
miscanthus cellulose based on Pachysolen tannophilus
and Saccharomyces cerevisiae strains is also described.
The yield of ethanol amount to 44 % for P. Tannophilus
RNCIM Y-1532 producer; to 62.5% for S. сerevisiae
RNCIM Y-1693 of theoretically possible. With the
combined use of cultures, the rate of fermentation
increases by 10% compared to S. cerevisiae RNCIM
Y-1693, but there is no increase in the proportion of
ethanol yield. Joint use of strains was considered
inappropriate [28, 31].
Bioconversion by enzyme preparations in
combination with hydrolysis by dilute nitric acid at
90–96°C or alkaline delignification by 4% sodium
hydroxide solution at 90–96°C is used for pretreatment
of raw materials from miscanthus plants. Preparations
‘Cellolux-A’ (Sibbiopharm Ltd, Berdsk) and ‘Bruzime
BGX’ (Polfa Tarchomin Pharmaceutical Works S. A.,
Poland) are used as cellulolytic enzymes.
‘Cellolux-A’ is positioned in the market as cellulase
for non-starch polysaccharides fermentation, ‘Bruzime
BGX’ – as hemicellulase [38]. As a result of enzymatic
methods of miscanthus raw materials hydrolysis,
bioethanol with a low content of ethers and fusel oils
was obtained. There is no methanol in bioethanol
obtained from miscanthus. However, saccharomycetes
do not ferment pentoses, whose amount in hydrolysates
can be significant (depending on the type of raw material
and the method of hydrolysate obtaining), into ethanol.
Several types of yeast are known to ferment xylose into
ethanol: Pachysolen tannophilus, Candida shehatae,
Candida tropicalis, Pichia stipitis, etc. To select a
bioethanol producer, it is necessary to determine the
specific rate of yeast biomass growth and the rate of
substrate utilisation on synthetic media.
In addition to the use of wild strains, work is
underway to obtain recombinant ones with increased
capacity for bioconversion of raw materials. Thus, the
patent CN 106701605 Huazhong Agricultural University
presents a modified Saccharomyces cerevisiae SF4 yeast
for efficient ethanol fermentation using xylose [32].
Specifics of processing plants into products for
the chemical and microbiological industry. Beside
the process of converting miscanthus raw materials to
produce biofuels, a large amount of research is devoted
to the production of cellulose fibres. Cellulose is widely
used in modern industry, e.g. as a tablet excipient in
pharmaceuticals, for the manufacture of fabrics, paper,
plastics, explosives, etc.
The paper by Gismatulina describes obtaining
cellulose from miscanthus of Soranovski variety
(Miscanthus sinensis Andersson) by the nitrate method
featuring two consecutive stages of processing the
crushed material with diluted solutions of nitric acid,
then sodium hydroxide [33].
The cellulose obtained by the nitrite method is
characterised by high quality: the mass fraction of
α-cellulose is 96.1%, the degree of polymerisation is 970,
the ash content and mass fraction of lignin are 0.11 and
0.65%, respectively, the mass fraction of pentosans is
0.8%. Miscanthus cellulose is similar in quality to cotton
cellulose. With these parameters, it can be successfully
used for the synthesis of cellulose ethers and other
valuable products.
In another paper, miscanthus samples are cellulose
from the leaf and stem of miscanthus obtained separately
by two methods (nitrite and combined) [34]. The nitrite
method consists in cooking raw material in a dilute
solution of nitric acid at atmospheric pressure, followed
by treatment with a dilute solution of sodium hydroxide.
Thus, cellulose obtained from the stem by the nitrite
method has a better quality than that from the leaf. This
is reflected in high values of α-cellulose content (94.4%
vs. 91.7%) and degree of polymerisation (800 vs. 580),
and also low values of noncellulosic compounds mass
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fraction: ash – 0.07% vs. 1.01%, acid-insoluble lignin –
0.45% vs. 1.51%.
Celluloses obtained by the combined method
demonstrate the same regularity: cellulose from the stem
is characterised by higher quality than that from the
leaf. The data show high value of polymerization degree
– 1040 vs. 640 and low noncellulosic compounds mass
fraction: ash – 0.14% vs. 0.75%, acid-insoluble lignin
– 0.88% vs. 4.12%, pentosans – 6.38% vs. 8.53%. The
cellulose obtained by the nitrite method may be suitable
for chemical modifications, including nitration. The
cellulose obtained by the combined method can be used
in paper industry [31].
The use of miscanthus as a medium for bacteria
cultivation can be carried out without the targeted
production of simple sugars for use in the food, feed
and pharmaceutical industries, as well as a substrate for
bacterial growth. Some studies on bacterial celluloses
production present media based on incomplete
miscanthus hydrolysates.
Thus, Gladysheva describes obtaining bacterial
cellulose by bioconversion of Medusomyces gisevii
bacteria on a synthetic nutrient medium, including
sucrose, black tea extract, starch hydrolysate, enzymatic
miscanthus hydrolysate [35]. Cultivation was carried out
in static conditions at 25–29°C for 13 days.
Gismatulina also used miscanthus raw materials
to obtain a nutrient medium for the growth of bacteria
producing bacterial cellulose [36, 37]. Pre-hydrolysis
was carried out with 0.2% solution of nitric acid at 90–
95°C for 1 h. Nitric acid treatment was carried out with
4% nitric acid solution at 90–95°C for 6 h. Washing
was performed successively with 1% sodium hydroxide
solution, and then 1 % nitric acid solution. The resulting
pulp was pressed with a vacuum filter, washed to a
neutral reaction of washing water, dried to a moisture
content of 7–10 %.
The raw material for the experiments was ground
to a particle size of 10–15 mm. It was established that
optimal conditions of the principal and longest stage of
obtaining cellulose by the combined method (alkaline
treatment) are: sodium hydroxide concentration,
4%; temperature, 90–98°C; duration, 6 h. Cellulose
extraction under such conditions allows obtaining
the maximum yield of the target product – 35–40%
with α-cellulose content of 87.0–90.3%, degree of
polymerisation 950–990, residual lignin content of 2.0 to
3.0%, ash content of 0.3–0.4%, and pentosan content of
3.0 to 8.0%.
Cellulose isolated from miscanthus by the combined
method is a promising substrate for enzymatic
hydrolysis, with the degree of its conversion was 91–93%
by weight of the substrate. High quality indicators of the
substrate allow predicting the effectiveness of its use for
the subsequent bacterial cellulose biosynthesis.
Also miscanthus raw materials can provide organic
acids, alcohols and adsorbents. The paper describes
obtaining formic acid from lignocellulose or its major
components, which comprises two successive stages:
– acid-catalysed depolymerisation (polysaccharides
hydrolysis, delignification);
– subsequent monomers (monosaccharides, phenolic
derivatives) oxidation into formic acid. A high yield of
formic acid equal to 45% was obtained [23].
Organosolv method of cooking miscanthus raw
materials can also deliver ferulic, vanilla and paracumaric
acids, sterines, among which the main factions
are β-sitosterol, 7-oxo-β-sitosterol, stigmasterol and
campesterol. However, this method has not become
widespread, as sterol derivates are oxidized during
preliminary treatment with organic solvents.
CONCLUSION
Furthering lignocellulose biomass integrated
processing by chemical and/or biotechnological
methods into a range of competitive products and
energy is a modern and fundamental area of industrial
biotechnology developing in industrial countries.
The conducted botanical properties analysis
of chemical composition and modern methods of
processing miscanthus species biomass proved that
it was a promising renewable wood-substituting raw
material for products of chemical, fuel, energy, and
microbiological industries. Further research will focus
on the selection of rational parameters of processing
miscanthus biomass into valuable products with
improved physical and chemical characteristics, such
as bio-ethanol, pellets, technical cellulose, bacterial
cellulose, and carbohydrate-containing substrate.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
FUNDING
The survey lies within a framework of fundamental
research project No. 19-416-390001 ‘Scientific and
technological foundations of Miscanthus plants biomass
processing into products for the fuel and energy,
chemical and microbiological industry’.

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