Sulfite process
Encyclopedia
The sulfite process produces wood pulp
which is almost pure cellulose
fibers by using various salt
s of sulfurous acid
to extract the lignin
from wood chips in large pressure vessels called digester
s. The salts used in the pulping process are either sulfite
s (SO32−), or bisulfite
s (HSO3−), depending on the pH
. The counter ion
can be sodium
(Na+), calcium
(Ca2+), potassium
(K+), magnesium
(Mg2+) or ammonium
(NH4+).
by F.G. Keller in the 1840s. Chemical processes quickly followed, first with J. Roth's use of sulfurous acid
to treat wood, followed by Benjamin Chew Tilghman
's US patent on the use of calcium bisulfite
, Ca(HSO3)2, to pulp wood in 1867. Almost a decade later in 1874 the first commercial sulfite process|sulfite pulp mill was built in Sweden
. It used magnesium as the counter ion and was based on work by Carl Daniel Ekman
.
By 1900 sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. The competing chemical pulping process, the sulfate or kraft process
was developed by Carl F. Dahl in 1879 and the first kraft mill
started (in Sweden) in 1890. The invention of the recovery boiler
by G.H. Tomlinson in the early 1930s allowed kraft mills to recycle almost all of their pulping chemicals. This, along with the ability of the kraft process to accept a wider variety of types of wood and produce stronger fibers made the kraft process the dominant pulping process starting in the 1940s. Sulfite pulps now account for less than 10% of the total chemical pulp production and the number of sulfite mills continues to decrease.
Magnesium was the standard counter ion until calcium replaced it in the 1950s. Sulfite pulping was the dominant process for making wood pulp until it was surpassed by the kraft process
in the 1940s. Sulfite pulps now account for less than 10% of the total chemical pulp production.
with the correct amount of oxygen
to give sulfur dioxide
, which is then absorbed into water to give sulfurous acid
.
Care must be taken to avoid the formation of sulfur trioxide
since it gives undesired sulfuric acid
when it is dissolved in water.
Sulfuric acid is undesirable since it promotes hydrolysis of cellulose without contributing to delignification.
The cooking liquor is prepared by adding the counter ions as hydroxides or carbonates. The relative amounts of each species present in the liquid depend largely on the relative amounts of sulfurous used. For monovalent (Na+, K+ and NH4+) hydroxides, MOH:
For divalent (Ca2+, Mg2+) carbonates, MCO3:
(266 to 320 °F
), again depending on the chemicals used.
Most of the intermediates involved in delignification in sulfite pulping are resonance-stabilized carbocations formed either by protonation of carbon-carbon double bonds or acidic cleavage of ether bonds which connect many of the constituents of lignin. It is the latter reaction which is responsible for most lignin degradation in the sulfite process. The electrophilic carbocations react with bisulfite ions (HSO3-)to give sulfonates.
The sulfite process does not degrade lignin
to the same extent that the kraft process
does and the lignosulfonates from the sulfite process are useful byproducts.
in the kraft process
). Pulp washers, using countercurrent
flow, remove the spent cooking chemicals and degraded lignin and hemicellulose. The extracted brown liquor is concentrated, in multiple effect evaporators. The concentrated brown liquor can be burned in the recovery boiler
to generate steam and recover the inorganic chemicals for reuse in the pulping process or it can be neutralized to recover the useful byproducts of pulping. Recent developments in Chemrec's
black liquor gasification process, adapting the technology to use in the sulfite pulping process, could make second generation biofuels production an alternative to the conventional recovery boiler technology.
The sulfite process can use calcium
, ammonium
, magnesium
or sodium
as a base.
and there was little incentive to recover the inorganic materials.
and nitrogen oxides when burned.
and sulfur dioxide
, both of which are recovered from the flue gases. Magnesium oxide is recovered in a wet scrubber
to give a slurry of magnesium hydroxide
.
This magnesium hydroxide slurry is then used in another scrubber to absorb sulfur dioxide
from the flue gases producing a magnesium bisulfite solution that is clarified, filtered and used as the pulping liquor.
some of the cellulose, which means that sulfite pulp fibers are not as strong as kraft pulp fibers. The yield
of pulp (based on wood used) is higher than for kraft pulping and sulfite pulp is easier to bleach
.
, especially for specialty papers and as a source of cellulose for non-paper applications. It is used to make fine paper
, tissue
, glassine
. and to add strength to newsprint
.
, cellophane
, cellulose acetate
and methylcellulose
.
Rayon is a reconstituted cellulose fiber used to make many fabrics.
Cellophane is a clear reconstituted cellulose film used in wrapping and windows in envelopes.
Cellulose acetate was used to make flexible films for photographic use, computer tapes and so on and also to make fibers.
Methylcellulose and other cellulose ether derivatives are used in a wide range of everyday products from adhesives to baked goods to pharmaceuticals
.
, which find a wide variety of uses whereas relatively inexpensive agent is needed to make a water dispersion of a water-insoluble material. Lignosulfonates are used in tanning
leather, making concrete
, drilling mud, drywall
and so on.
Oxidation of lignosulfonates was used to produce vanillin
(artificial vanilla), and this process is still used by one supplier (Borregaard
, Norway) while all North American production by this route ceased in the 1990s.
, which can be fermented to produce ethanol
.
Wood pulp
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...
which is almost pure cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
fibers by using various salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s of sulfurous acid
Sulfurous acid
Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
to extract the 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...
from wood chips in large pressure vessels called digester
Digester
A digester is a huge vessel where chemical or biological reactions are carried out. These are used in different types of process industries.Digester may also refer to :* Digester-Processes where digesters are used:* Anaerobic digestion...
s. The salts used in the pulping process are either sulfite
Sulfite
Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...
s (SO32−), or bisulfite
Bisulfite
Bisulfite ion is the ion HSO3−. Salts containing the HSO3− ion are termed bisulfites also known as sulfite lyes...
s (HSO3−), depending on the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
. The counter ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
can be sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
(Na+), calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(Ca2+), potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
(K+), magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(Mg2+) or ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
(NH4+).
History
The use of wood to make pulp for paper began with the development of mechanical pulping in GermanyGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
by F.G. Keller in the 1840s. Chemical processes quickly followed, first with J. Roth's use of sulfurous acid
Sulfurous acid
Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
to treat wood, followed by Benjamin Chew Tilghman
Benjamin Chew Tilghman
Benjamin Chew Tilghman was an American soldier and inventor. He is best known as the inventor of the process of sandblasting.-Early life:...
's US patent on the use of calcium bisulfite
Calcium bisulfite
Calcium bisulfite is an inorganic compound which is the salt of a calcium cation and a bisulfite anion. It may be prepared by reacting lime with an excess of sulfurous acid, essentially a mixture of sulfur dioxide and water. It is a weak reducing agent, as is sulfur dioxide, sulfites, and any...
, Ca(HSO3)2, to pulp wood in 1867. Almost a decade later in 1874 the first commercial sulfite process|sulfite pulp mill was built in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
. It used magnesium as the counter ion and was based on work by Carl Daniel Ekman
Carl Daniel Ekman
Carl Daniel Ekman was a Swedish chemical engineer who invented the form of the sulfite process of wood pulp manufacturing which was first established on a firm commercial basis, helping to replace rags as the main raw material of paper with wood pulp...
.
By 1900 sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. The competing chemical pulping process, the sulfate or kraft process
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
was developed by Carl F. Dahl in 1879 and the first kraft mill
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
started (in Sweden) in 1890. The invention of the recovery boiler
Recovery boiler
Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor, which contains lignin from previously processed wood. The black liquor is burned, generating heat, which is usually used in the process or in making electricity,...
by G.H. Tomlinson in the early 1930s allowed kraft mills to recycle almost all of their pulping chemicals. This, along with the ability of the kraft process to accept a wider variety of types of wood and produce stronger fibers made the kraft process the dominant pulping process starting in the 1940s. Sulfite pulps now account for less than 10% of the total chemical pulp production and the number of sulfite mills continues to decrease.
Magnesium was the standard counter ion until calcium replaced it in the 1950s. Sulfite pulping was the dominant process for making wood pulp until it was surpassed by the kraft process
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
in the 1940s. Sulfite pulps now account for less than 10% of the total chemical pulp production.
Pulping liquor preparation
The pulping liquor for most sulfite mills is made by burning sulfurSulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
with the correct amount of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
to give sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, which is then absorbed into water to give sulfurous acid
Sulfurous acid
Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
.
- S + O2 → SO2
- SO2 + H2O H2SO3
Care must be taken to avoid the formation of sulfur trioxide
Sulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...
since it gives undesired sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
when it is dissolved in water.
- 2 SO2 + O2 → 2SO3
- SO3 + H2O H2SO4
Sulfuric acid is undesirable since it promotes hydrolysis of cellulose without contributing to delignification.
The cooking liquor is prepared by adding the counter ions as hydroxides or carbonates. The relative amounts of each species present in the liquid depend largely on the relative amounts of sulfurous used. For monovalent (Na+, K+ and NH4+) hydroxides, MOH:
- H2SO3 + MOH → MHSO3 + H2O
- MHSO3 + MOH → M2SO3 + H2O
For divalent (Ca2+, Mg2+) carbonates, MCO3:
- MCO3 + 2H2SO3 → M(HSO3)2 + CO2 + H2O
- M(HSO3)2 + MCO3 → 2 MSO3 + CO2 + H2O
Pulping
Sulfite pulping is carried out between pH 1.5 and 5, depending on the counterion to sulfite (bisulfite) and the ratio of base to sulfurous acid. The pulp is in contact with the pulping chemicals for 4 to 14 hours and at temperatures ranging from 130 to 160 °CCelsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
(266 to 320 °F
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
), again depending on the chemicals used.
Most of the intermediates involved in delignification in sulfite pulping are resonance-stabilized carbocations formed either by protonation of carbon-carbon double bonds or acidic cleavage of ether bonds which connect many of the constituents of lignin. It is the latter reaction which is responsible for most lignin degradation in the sulfite process. The electrophilic carbocations react with bisulfite ions (HSO3-)to give sulfonates.
- R-O-R' + H+ → R+ + R'OH
- R+ + HSO3- → R-SO3H
The sulfite process does not degrade 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...
to the same extent that the kraft process
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
does and the lignosulfonates from the sulfite process are useful byproducts.
Chemical recovery
The spent cooking liquor from sulfite pulping is usually called brown liquor, but the terms red liquor, thick liquor and sulfite liquor are also used (compared to black liquorBlack liquor
Black liquor is the spent cooking liquor from the kraft process when digesting pulpwood into paper pulp removing lignin, hemicelluloses and other extractives from the wood to free the cellulose fibers....
in the kraft process
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
). Pulp washers, using countercurrent
Countercurrent exchange
Countercurrent exchange is a mechanism occurring in nature and mimicked in industry and engineering, in which there is a crossover of some property, usually heat or some component, between two flowing bodies flowing in opposite directions to each other. The flowing bodies can be liquids, gases, or...
flow, remove the spent cooking chemicals and degraded lignin and hemicellulose. The extracted brown liquor is concentrated, in multiple effect evaporators. The concentrated brown liquor can be burned in the recovery boiler
Recovery boiler
Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor, which contains lignin from previously processed wood. The black liquor is burned, generating heat, which is usually used in the process or in making electricity,...
to generate steam and recover the inorganic chemicals for reuse in the pulping process or it can be neutralized to recover the useful byproducts of pulping. Recent developments in Chemrec's
Chemrec
Chemrec is a Stockholm, Sweden corporation that develops technology for entrained flow gasification of black liquor and certain types brown liquor for production of biofuels from the resulting syngas....
black liquor gasification process, adapting the technology to use in the sulfite pulping process, could make second generation biofuels production an alternative to the conventional recovery boiler technology.
The sulfite process can use calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
, magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
or sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
as a base.
Calcium-based
The earliest process used calcium, obtained as inexpensive calcium carbonateCalcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
and there was little incentive to recover the inorganic materials.
Ammonia-based
Ammonia-based processes do not allow recovery of the pulping chemicals since ammonia or ammonium salts are oxidized to nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and nitrogen oxides when burned.
Magnesium-based
The recovery process used in magnesium-based sulfite pulping the "Magnefite" process is well developed. The concentrated brown liquor is burned in a recovery boiler, producing magnesium oxideMagnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
and sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, both of which are recovered from the flue gases. Magnesium oxide is recovered in a wet scrubber
Scrubber
Scrubber systems are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. Traditionally, the term "scrubber" has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream...
to give a slurry of magnesium hydroxide
Magnesium hydroxide
Magnesium hydroxide is an inorganic compound with the chemical formula Mg2. As a suspension in water, it is often called milk of magnesia because of its milk-like appearance. The solid mineral form of magnesium hydroxide is known as brucite....
.
- MgO + H2O → Mg(OH)2
This magnesium hydroxide slurry is then used in another scrubber to absorb sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
from the flue gases producing a magnesium bisulfite solution that is clarified, filtered and used as the pulping liquor.
- Mg(OH)2 + 2 SO2 → Mg(HSO3)2
Sodium-based
Sodium-based processes use a recovery system similar to that used in the kraft recovery process, except that there is no "lime cycle".Applications
The sulfite process is acidic and one of the drawbacks is that the acidic conditions hydrolyzeHydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
some of the cellulose, which means that sulfite pulp fibers are not as strong as kraft pulp fibers. The yield
Crop yield
In agriculture, crop yield is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself...
of pulp (based on wood used) is higher than for kraft pulping and sulfite pulp is easier to bleach
Bleaching of wood pulp
Bleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...
.
Commodity
Sulfite pulp remains an important commodityCommodity
In economics, a commodity is the generic term for any marketable item produced to satisfy wants or needs. Economic commodities comprise goods and services....
, especially for specialty papers and as a source of cellulose for non-paper applications. It is used to make fine paper
Coated fine paper
Coated fine paper or woodfree coated paper are mainly produced for offset printing.-Standard coated fine papers:This paper quality is normally used for advertising materials, books, annual reports and high quality catalogs. Grammage ranges from 90–170 g/m2 and ISO brightness between 80–96%. The...
, tissue
Tissue paper
Tissue paper is a lightweight paper or, light crêpe paper. Tissue can be made both from virgin and recycled paper pulp.-Properties:Key properties are: strength, absorbency, basis weight, thickness , brightness, stretch, appearance and comfort....
, glassine
Glassine
Glassine is a very thin and smooth paper that is air and water resistant. It is translucent unless dyes are added to color it or make it opaque...
. and to add strength to newsprint
Newsprint
Newsprint is a low-cost, non-archival paper most commonly used to print newspapers, and other publications and advertising material. It usually has an off-white cast and distinctive feel. It is designed for use in printing presses that employ a long web of paper rather than individual sheets of...
.
Dissolving pulp
A special grade of bleached sulfite pulp is known as dissolving pulp which is the raw material for a wide variety of cellulose derivatives, for example rayonRayon
Rayon is a manufactured regenerated cellulose fiber. Because it is produced from naturally occurring polymers, it is neither a truly synthetic fiber nor a natural fiber; it is a semi-synthetic or artificial fiber. Rayon is known by the names viscose rayon and art silk in the textile industry...
, cellophane
Cellophane
Cellophane is a thin, transparent sheet made of regenerated cellulose. Its low permeability to air, oils, greases, bacteria and water makes it useful for food packaging...
, cellulose acetate
Cellulose acetate
Cellulose acetate , first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters and...
and methylcellulose
Methylcellulose
Methyl cellulose is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold water, forming a clear viscous solution or gel. It is sold under a variety of trade names and is used as a thickener and emulsifier in various food and cosmetic...
.
Rayon is a reconstituted cellulose fiber used to make many fabrics.
Cellophane is a clear reconstituted cellulose film used in wrapping and windows in envelopes.
Cellulose acetate was used to make flexible films for photographic use, computer tapes and so on and also to make fibers.
Methylcellulose and other cellulose ether derivatives are used in a wide range of everyday products from adhesives to baked goods to pharmaceuticals
Medication
A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...
.
Byproducts
Sulfite pulping is generally less destructive than kraft pulping, so there are more usable byproducts.Lignosulfonates
Chief among sulfite process byproducts are lignosulfonatesLignosulfonates
Lignosulfonates, or sulfonated lignin, are water-soluble anionic polyelectrolyte polymers: they are byproducts from the production of wood pulp using sulfite pulping....
, which find a wide variety of uses whereas relatively inexpensive agent is needed to make a water dispersion of a water-insoluble material. Lignosulfonates are used in tanning
Tanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...
leather, making concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
, drilling mud, drywall
Drywall
Drywall, also known as plasterboard, wallboard or gypsum board is a panel made of gypsum plaster pressed between two thick sheets of paper...
and so on.
Oxidation of lignosulfonates was used to produce vanillin
Vanillin
Vanillin is a phenolic aldehyde, an organic compound with the molecular formula C8H8O3. Its functional groups include aldehyde, ether, and phenol. It is the primary component of the extract of the vanilla bean. It is also found in Leptotes bicolor, roasted coffee and the Chinese red pine...
(artificial vanilla), and this process is still used by one supplier (Borregaard
Borregaard
Borregaard is a Norwegian company, established in 1889 in the southeastern town of Sarpsborg in Østfold county. Its main products were traditionally pulp and paper. The company later started producing chemicals based on timber as a raw material...
, Norway) while all North American production by this route ceased in the 1990s.
Other byproducts
Acid hydrolysis of cellulose during sulfite pulping produces monosaccharides, predominantly mannoseMannose
Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose. It is not part of human metabolism, but is a component of microbial cell walls, and is therefore a target of the immune system and also of antibiotics....
, which can be fermented to produce 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...
.
See also
- Kraft processKraft processThe kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
- Pulp millPulp millA pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fibre board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods...
- Wood pulpWood pulpPulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...
- Bleaching of wood pulpBleaching of wood pulpBleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...
- PaperPaperPaper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
- Pulp & Paper chemicals