209
11
5 Use in biomaterials.
5 Chemical conversion, either to produce mixtures of useful chemicals or to obtain single
target molecules.
These three areas differ both in their significance
in terms of quantity and in the number of applications as well as in the preservation of the original lignin structure. The relevance of these three
applications of lignin will be discussed in more
detail below in the context of these three aspects.
11.4.1 Use of Lignin as a Dispersing
Agent
By far the most important material application of
lignin is its use as a dispersing agent in the form
of ligninsulfonates, especially in cement, gypsum
and concrete. This property is due to the interfacial activity of lignosulfonates. Up to 50% of the
total lignosulfonates available are used in this
application area. They improve the flow properties of concrete so that it can be processed more
easily. The water content in concrete can also be
reduced, which increases its durability. Furthermore, the use of gypsum can be reduced, thus
reducing costs in the production of concrete.
Further applications are in the admixture to
well-flushing agents in oil production, the addition in the production of printing inks and for
electrolyte solution in lead accumulators.
11.4.2 Use of Lignin in Biomaterials
Lignin itself and also lignosulfonates have good
binding properties and are therefore also used
for the production of pellets. This effect is based
on the fact that lignin and lignosulfonates first
become liquid when heated and simultaneously
pressed and then harden again when cooled
down. This is used, for example, in the production of wood pellets for combustion furnaces:
Wood chips are heated under increased pressure,
whereby the lignin first liquefies and then solidifies again during cooling, thus binding and stabilizing the wood pellets. This process can also be
used to pelletize lignin-free materials by adding
ligninsulfonates. For example, feed pellets, pesticides, fertilizers and charcoal briquettes are
5 In the Acetosolv process, an acetic acid
solution of 93% is used in combination with
HCl of 0.1–0.2%. This process combines the
advantages of organic disintegration with
acidic conditions in a single-stage process
followed by bleaching of the pulp. The pulp
obtained from hardwoods has mechanical
properties which typically range between
those of pulp from the sulfate process and
pulp from the sulfite process. In the Acetosolv process, the free hydroxyl groups of
lignin are partially esterified with acetic acid,
known as lignin acetate. The quantity of HCl
is decisive for the quality of the lignin: A lack
of HCl leads to insufficient degradation of the
structure and thus to a lower yield, whereas
too high concentrations lead to increased
condensation of the lignin and thus to undesired high molecular weights.
11.4 Use of Lignin
By far the largest use of lignin is based on the
comparatively high energy content of about
23 GJ t −1 . The lignin contained in the black liquor from the sulfate process after evaporation,
and drying is therefore an excellent fuel for
maintaining the necessary process temperatures.
It is estimated that up to 98% of the lignin produced worldwide is used to generate energy. This
means that “only” approx. 2% of the lignin is
available for all material applications, which still
corresponds to a quantity of approx. one million
tons per year in view of the amount of wood processed annually.
So far, the material use of lignin has been based
almost exclusively on the use of ligninsulfonates
from the sulfite process. Most of the commercially
available Kraft lignin is also converted into lignosulfonates by sulfonation. Ligninsulfonates are
water-soluble over a wide pH range and are toxicologically and environmentally safe. They are sold
as spray-dried powder or as an aqueous solution
with a solids content of about 50%.
The material applications of ligninsulfonates
can be divided into three large areas:
5 The application of lignosulfonates or their
salts as additives, using their dispersing, complexing and emulsion-stabilizing
properties.
11.3 · Lignin Recovery
11
5 Use in biomaterials.
5 Chemical conversion, either to produce mixtures of useful chemicals or to obtain single
target molecules.
These three areas differ both in their significance
in terms of quantity and in the number of applications as well as in the preservation of the original lignin structure. The relevance of these three
applications of lignin will be discussed in more
detail below in the context of these three aspects.
11.4.1 Use of Lignin as a Dispersing
Agent
By far the most important material application of
lignin is its use as a dispersing agent in the form
of ligninsulfonates, especially in cement, gypsum
and concrete. This property is due to the interfacial activity of lignosulfonates. Up to 50% of the
total lignosulfonates available are used in this
application area. They improve the flow properties of concrete so that it can be processed more
easily. The water content in concrete can also be
reduced, which increases its durability. Furthermore, the use of gypsum can be reduced, thus
reducing costs in the production of concrete.
Further applications are in the admixture to
well-flushing agents in oil production, the addition in the production of printing inks and for
electrolyte solution in lead accumulators.
11.4.2 Use of Lignin in Biomaterials
Lignin itself and also lignosulfonates have good
binding properties and are therefore also used
for the production of pellets. This effect is based
on the fact that lignin and lignosulfonates first
become liquid when heated and simultaneously
pressed and then harden again when cooled
down. This is used, for example, in the production of wood pellets for combustion furnaces:
Wood chips are heated under increased pressure,
whereby the lignin first liquefies and then solidifies again during cooling, thus binding and stabilizing the wood pellets. This process can also be
used to pelletize lignin-free materials by adding
ligninsulfonates. For example, feed pellets, pesticides, fertilizers and charcoal briquettes are
5 In the Acetosolv process, an acetic acid
solution of 93% is used in combination with
HCl of 0.1–0.2%. This process combines the
advantages of organic disintegration with
acidic conditions in a single-stage process
followed by bleaching of the pulp. The pulp
obtained from hardwoods has mechanical
properties which typically range between
those of pulp from the sulfate process and
pulp from the sulfite process. In the Acetosolv process, the free hydroxyl groups of
lignin are partially esterified with acetic acid,
known as lignin acetate. The quantity of HCl
is decisive for the quality of the lignin: A lack
of HCl leads to insufficient degradation of the
structure and thus to a lower yield, whereas
too high concentrations lead to increased
condensation of the lignin and thus to undesired high molecular weights.
11.4 Use of Lignin
By far the largest use of lignin is based on the
comparatively high energy content of about
23 GJ t −1 . The lignin contained in the black liquor from the sulfate process after evaporation,
and drying is therefore an excellent fuel for
maintaining the necessary process temperatures.
It is estimated that up to 98% of the lignin produced worldwide is used to generate energy. This
means that “only” approx. 2% of the lignin is
available for all material applications, which still
corresponds to a quantity of approx. one million
tons per year in view of the amount of wood processed annually.
So far, the material use of lignin has been based
almost exclusively on the use of ligninsulfonates
from the sulfite process. Most of the commercially
available Kraft lignin is also converted into lignosulfonates by sulfonation. Ligninsulfonates are
water-soluble over a wide pH range and are toxicologically and environmentally safe. They are sold
as spray-dried powder or as an aqueous solution
with a solids content of about 50%.
The material applications of ligninsulfonates
can be divided into three large areas:
5 The application of lignosulfonates or their
salts as additives, using their dispersing, complexing and emulsion-stabilizing
properties.
11.3 · Lignin Recovery