247
Hydrolysis and Fermentation Technologies for Alcohols
9.4.1.5 ionic liquid Pretreatment
An ionic liquid is a salt composed of anions and cations that are poorly coordinated
and that has a melting point below 100°C. Ionic liquids have been demonstrated as
very efficient solvents for hydrogenation, esterification, nanomaterial synthesis, biocatalysis, and selective extraction of aromatics [28,29]. The first demonstration of
an ionic liquid as a cellulose solvent under relatively mild operating conditions was
reported in 2002 by Swatloski [29]. The treatment used a range of anions and 1-butylmethylimidazolium cations; some ionic liquids were able to completely dissolve
microcrystalline cellulose and cellulose was recovered through the addition of an antisolvent such as water or ethanol. The most effective cellulose solvents were the ionic
liquids that contain chloride anions. An important finding associated with this novel
pretreatment method is that enzymes can more efficiently hydrolyze into glucose, an
amorphous cellulose produced by ionic liquids, than the microcrystalline cellulose
found in lignocellulose naturally [28,30]. More research on this treatment is needed.
9.4.2 hydrolySiS
There are two types of hydrolysis processes for lignocellulose. The old process
that has been practiced for a long time is acid or chemical hydrolysis and the new
and novel process is enzymatic hydrolysis. Here we briefly examine both of these
processes.
9.4.2.1 acid or Chemical hydrolysis
Important parameters in acid or chemical hydrolysis are the surface-to-volume ratio
of particles, acid concentration, temperature, and time. The surface-to-volume
ratio is especially important because it determines the magnitude of yield of glucose.
Smaller particles result in better hydrolysis [31]. An increase in the liquid-to-solid
ratio also gives a faster reaction. However, higher ratio requires larger equipment
and more capital cost. For chemical hydrolysis, a liquid-to-solid ratio of 10/1 seems
to be most suitable [31].
The chemical hydrolysis is carried out by first pulverizing lignocellulose or waste
into a fine particle size. The powdered waste is mixed with aqueous solution of weak
acid (0.2%–10%) at about 180°C–230°C and moderate pressure. The acid solution
converts waste into glucose, but the extent of yield depends on the nature of the
waste (i.e., Kraft paper will give 84%–86% yield, whereas ground refuse will give
38%–53% yield). The yield will increase with temperature. Generally, 0.5% H 2 SO 4
concentration is used.
The Tennessee Valley Authority (TVA) developed a two-stage, low-temperature,
atmospheric pressure process that utilizes the separate unit operations to convert
hemicellulose and cellulose to sugars [32]. An experimental pilot plant was designed
and built in 1984. The process showed a very low level of inhibitor concentration.
The results of this study are briefly summarized as follows:
1. The size of ground corn stover of 2.5 cm was adequate for the hydrolysis of
hemicellulose.
2. The time required for optimum hydrolysis in 10% acid at 100°C was 2 h.
Hydrolysis and Fermentation Technologies for Alcohols
9.4.1.5 ionic liquid Pretreatment
An ionic liquid is a salt composed of anions and cations that are poorly coordinated
and that has a melting point below 100°C. Ionic liquids have been demonstrated as
very efficient solvents for hydrogenation, esterification, nanomaterial synthesis, biocatalysis, and selective extraction of aromatics [28,29]. The first demonstration of
an ionic liquid as a cellulose solvent under relatively mild operating conditions was
reported in 2002 by Swatloski [29]. The treatment used a range of anions and 1-butylmethylimidazolium cations; some ionic liquids were able to completely dissolve
microcrystalline cellulose and cellulose was recovered through the addition of an antisolvent such as water or ethanol. The most effective cellulose solvents were the ionic
liquids that contain chloride anions. An important finding associated with this novel
pretreatment method is that enzymes can more efficiently hydrolyze into glucose, an
amorphous cellulose produced by ionic liquids, than the microcrystalline cellulose
found in lignocellulose naturally [28,30]. More research on this treatment is needed.
9.4.2 hydrolySiS
There are two types of hydrolysis processes for lignocellulose. The old process
that has been practiced for a long time is acid or chemical hydrolysis and the new
and novel process is enzymatic hydrolysis. Here we briefly examine both of these
processes.
9.4.2.1 acid or Chemical hydrolysis
Important parameters in acid or chemical hydrolysis are the surface-to-volume ratio
of particles, acid concentration, temperature, and time. The surface-to-volume
ratio is especially important because it determines the magnitude of yield of glucose.
Smaller particles result in better hydrolysis [31]. An increase in the liquid-to-solid
ratio also gives a faster reaction. However, higher ratio requires larger equipment
and more capital cost. For chemical hydrolysis, a liquid-to-solid ratio of 10/1 seems
to be most suitable [31].
The chemical hydrolysis is carried out by first pulverizing lignocellulose or waste
into a fine particle size. The powdered waste is mixed with aqueous solution of weak
acid (0.2%–10%) at about 180°C–230°C and moderate pressure. The acid solution
converts waste into glucose, but the extent of yield depends on the nature of the
waste (i.e., Kraft paper will give 84%–86% yield, whereas ground refuse will give
38%–53% yield). The yield will increase with temperature. Generally, 0.5% H 2 SO 4
concentration is used.
The Tennessee Valley Authority (TVA) developed a two-stage, low-temperature,
atmospheric pressure process that utilizes the separate unit operations to convert
hemicellulose and cellulose to sugars [32]. An experimental pilot plant was designed
and built in 1984. The process showed a very low level of inhibitor concentration.
The results of this study are briefly summarized as follows:
1. The size of ground corn stover of 2.5 cm was adequate for the hydrolysis of
hemicellulose.
2. The time required for optimum hydrolysis in 10% acid at 100°C was 2 h.