Organosolv
Encyclopedia
Organosolv is a pulping technique that uses an organic solvent to solubilise lignin and hemicellulose. It has been considered in the context of both pulp and paper manufacture and biorefining for subsequent conversion of cellulose to fuel ethanol. The process was invented by Theodore Kleinert as an environmentally benign alternative to kraft pulping.
Organosolv has several advantages when compared to other popular methods such as kraft or sulfite pulping. In particular, the ability to obtain relatively high quality lignin
adds value to a process stream otherwise considered as waste. Organosolv solvents are easily recovered by distillation leading to less water pollution and elimination of the odour usually associated with kraft pulping.
to break down by hydrolytic cleavage of alpha aryl-ether links into fragments that are soluble in the solvent system. Solvents used include acetone
, methanol
, ethanol
, butanol
, ethylene glycol
, formic acid
, and acetic acid
. The concentration of solvent in water ranges from 40-80%. Higher boiling solvents have the advantage of a lower process pressure. This is weighed against the more difficult solvent recovery by distillation . Ethanol has been suggested as the preferred solvent due to cost and easy recovery. Although butanol is shown to remove more lignin than other solvents and solvent recovery is simplified due to immiscibility in water, its high cost limits its use.
from ethylene glycol
organosolv pulping can be effected by 3 times dilution with acidified water. The lignin precipitates and forms spherical aggregates ranging from 0.5-2.5µm. Filtration, while time consuming, is then most effective while the mixture is hot (>100°C) . Recovery can be achieved by filtration
or centrifugation
. Due to the hydrophobic nature of organosolv lignin, flotation
of organosolv lignin is effective without the use of the collecting and precipitating agents that are required for flotation of kraft lignin.
The Alcohol Pulping and Recovery (APR) process treats wood in 3 stages, each using increasingly cleaner solvent. The important process parameters are extraction time, temperature, solvent composition and pH. Pilot plant operation has shown that ethanol pulping produces pulp superior to sulphite pulp at a lower cost. Lignin and hemicellulose are recovered in high yields. In 1987 the APR process was renamed the Alcell process. The process uses aqueous ethanol solutions (40-60% v/v) to delignify wood at temperatures from 180-210°C and 2-3.5MPa. Solvent is recovered with flash evaporation, vapour condensation and vacuum stripping.
A demonstration organosolv pulp mill has operated in Mirimichi, New Brunswick, Canada from 1989-1996 using the Alcell process. Repap owned the IP to the process when taken over by hedge funds in 1997. The pilot plant boasted superior environmental performance, excellent bleached pulp, an economically attractive scale of 300tons/day and commercially attractive by-products. It is said that the technology can be used to exploit small regions of hardwood resource that could not support a modern sized kraft mill.
Organosolv has several advantages when compared to other popular methods such as kraft or sulfite pulping. In particular, the ability to obtain relatively high quality lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
adds value to a process stream otherwise considered as waste. Organosolv solvents are easily recovered by distillation leading to less water pollution and elimination of the odour usually associated with kraft pulping.
Solvents
Organosolv pulping involves contacting a lignocellulosic feedstock such as chipped wood with an aqueous organic solvent at temperatures ranging from 140–220°C. This causes ligninLignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
to break down by hydrolytic cleavage of alpha aryl-ether links into fragments that are soluble in the solvent system. Solvents used include acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
, methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, butanol
Butanol
Butanol or butyl alcohol can refer to any of the four isomeric alcohols of formula C4H9OH:*n-Butanol, butan-1-ol, 1-butanol, n-butyl alcohol;*Isobutanol, 2-methylpropan-1-ol, isobutyl alcohol;...
, ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
, formic acid
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
, and acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
. The concentration of solvent in water ranges from 40-80%. Higher boiling solvents have the advantage of a lower process pressure. This is weighed against the more difficult solvent recovery by distillation . Ethanol has been suggested as the preferred solvent due to cost and easy recovery. Although butanol is shown to remove more lignin than other solvents and solvent recovery is simplified due to immiscibility in water, its high cost limits its use.
Organosolv for pulp production
Numerous authors report that pulping with ethanol-water solutions gives a lignin free pulp yield 4-4.5% higher than that of kraft pulp . The commonly used solvents acetone and ethanol have been examined with respect to pulp properties. The pulping of wheat straw with 40% mixtures of acetone or ethanol with water requires 60 minutes at 180°C to give good pulp properties . Organic solvents are almost always used as a mixture with water for process considerations such as reducing the vapour pressure and lowering the pH in order to also solubilise hemicellulose.Organosolv for fuel ethanol production
Recently, due to the popularity of 2nd generation biofuels, the organosolv process has been considered in the context of bioethanol production. Cellulose from the organosolv process is amenable to enzymatic hydrolysis into glucose followed by fermentation to dilute ethanol. The organosolv fractionation of mountain beetle killed lodgepole pine has yielded 97% conversion to glucose. Pan et al. recovered 79% of the lignin using conditions of 170°C, 1.1% w/w H2SO4, 65% v/v ethanol for 60 minutes.Lignin recovery
The recoverey of ligninLignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
from ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
organosolv pulping can be effected by 3 times dilution with acidified water. The lignin precipitates and forms spherical aggregates ranging from 0.5-2.5µm. Filtration, while time consuming, is then most effective while the mixture is hot (>100°C) . Recovery can be achieved by filtration
Filtration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
or centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...
. Due to the hydrophobic nature of organosolv lignin, flotation
Flotation
Flotation involves phenomena related to the relative buoyancy of objects. The term may refer to:* Flotation, any material added to the hull of a watercraft to keep the hull afloat...
of organosolv lignin is effective without the use of the collecting and precipitating agents that are required for flotation of kraft lignin.
Processes
Organocell uses two stage organosolv with roughly 50% methanol solutions. Sodium hydroxide is added in the second stage at a loading of 30% w/w of the dry wood. The lignin from the second stage is isolated by adding phosphoric acid until a pH of 4.0 is reached.The Alcohol Pulping and Recovery (APR) process treats wood in 3 stages, each using increasingly cleaner solvent. The important process parameters are extraction time, temperature, solvent composition and pH. Pilot plant operation has shown that ethanol pulping produces pulp superior to sulphite pulp at a lower cost. Lignin and hemicellulose are recovered in high yields. In 1987 the APR process was renamed the Alcell process. The process uses aqueous ethanol solutions (40-60% v/v) to delignify wood at temperatures from 180-210°C and 2-3.5MPa. Solvent is recovered with flash evaporation, vapour condensation and vacuum stripping.
A demonstration organosolv pulp mill has operated in Mirimichi, New Brunswick, Canada from 1989-1996 using the Alcell process. Repap owned the IP to the process when taken over by hedge funds in 1997. The pilot plant boasted superior environmental performance, excellent bleached pulp, an economically attractive scale of 300tons/day and commercially attractive by-products. It is said that the technology can be used to exploit small regions of hardwood resource that could not support a modern sized kraft mill.