Lignosulfonates
Encyclopedia
Lignosulfonates, or sulfonated lignin, (CAS number
8062-15-5) are water-soluble anionic polyelectrolyte
polymer
s: they are byproducts from the production of wood pulp
using sulfite pulping
.
Most delignification in sulfite pulping involves acidic cleavage of ether
bonds, which connect many of the constituents of lignin
. The electrophilic carbocations produced during ether cleavage react with bisulfite ions (HSO3-) to give sulfonates.
The primary site for ether cleavage is the α-carbon (carbon atom attached to the aromatic ring) of the propyl
(linear three carbon) side chain. The following structures do not specify the structure since lignin and its derivatives are complex mixtures: the purpose is to give a general idea of the structure of lignosulfonates. The groups labeled "Q" can be a wide variety of groups found in the structure of lignin. Sulfonation occurs on the side chains, not on the aromatic rings, like in p-toluenesulfonic acid
.
Lignosulfonate have very broad ranges of molecular mass
(they are very polydisperse
). A range of from 1000–140,000 da
has been reported for softwood lignosulfonates with lower values reported for hardwoods.
. Ultrafiltration and ion-exchange can also be used to separate lignosulfonates from the spent pulping liquid. A list of CAS numbers for the various metal salts of lignosulfonate is available.
The single largest use for lignosulfonates is as plasticizers in making concrete
, where they allow concrete to be made with less water (giving stronger concrete) while maintaining the ability of the concrete to flow. Lignosulfonates are also used during the production of cement
, where they act as grinding aids in the cement mill
and as a rawmix
slurry deflocculant (that reduces the viscosity
of the slurry).
Lignosulfonates are also used for the production of plasterboard to reduce the amount of water required to make the stucco
flow and form the layer between two sheets of paper. The reduction in water content allows lower kiln temperatures to dry the plasterboard, saving energy.
The ability of lignosulfonates to reduce the viscosity of mineral slurries is used to advantage in oil drilling mud, where it replaced tannic acid
s from quebracho
(a tropical tree).
Lignosulfonates are used to disperse pesticides, dyes, carbon black
, and other insoluble solids and liquids into water. They are used in tanning
leather
. They are also used to suppress dust on unpaved roads.
Oxidation
of lignosulfonates from softwood
trees produced vanillin
(artificial vanilla flavor).
Dimethyl sulfide
and dimethyl sulfoxide
(an important organic solvent
) are produced from lignosulfonates. The first step involves heating lignosulfonates with sulfides or elemental sulfur
to produce dimethyl sulfide. The methyl groups come from methyl ethers present in the lignin. Oxidation of dimethyl sulfide with nitrogen dioxide
produces dimethyl sulfoxide (DMSO).
CAS registry number
CAS Registry Numbersare unique numerical identifiers assigned by the "Chemical Abstracts Service" toevery chemical described in the...
8062-15-5) are water-soluble anionic polyelectrolyte
Polyelectrolyte
Polyelectrolytes are polymers whose repeating units bear an electrolyte group. These groups will dissociate in aqueous solutions , making the polymers charged. Polyelectrolyte properties are thus similar to both electrolytes and polymers , and are sometimes called polysalts. Like salts, their...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
s: they are byproducts from the production of wood pulp
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:...
using sulfite pulping
Sulfite process
The sulfite process produces wood pulp which is almost pure cellulose fibers by using various salts of sulfurous acid to extract the lignin from wood chips in large pressure vessels called digesters. The salts used in the pulping process are either sulfites , or bisulfites , depending on the pH...
.
Most delignification in sulfite pulping involves acidic cleavage of ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
bonds, which connect many of the constituents of 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...
. The electrophilic carbocations produced during ether cleavage react with bisulfite ions (HSO3-) to give sulfonates.
- R-O-R' + H+ → R+ + R'OH
- R+ + HSO3- → R-SO3H
The primary site for ether cleavage is the α-carbon (carbon atom attached to the aromatic ring) of the propyl
Propyl
In organic chemistry, propyl is a three-carbon alkyl substituent with chemical formula -C3H7. It is the substituent form of the alkane propane...
(linear three carbon) side chain. The following structures do not specify the structure since lignin and its derivatives are complex mixtures: the purpose is to give a general idea of the structure of lignosulfonates. The groups labeled "Q" can be a wide variety of groups found in the structure of lignin. Sulfonation occurs on the side chains, not on the aromatic rings, like in p-toluenesulfonic acid
P-Toluenesulfonic acid
p-Toluenesulfonic acid or tosylic acid is an organic compound with the formula CH3C6H4SO3H. It is a white solid that is soluble in water, alcohols, and other polar organic solvents. The 4-CH3C6H4SO2- group is known as the Tosyl group and is often abbreviated as Ts or Tos...
.
Lignosulfonate have very broad ranges of molecular mass
Molecular mass
The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...
(they are very polydisperse
Polydispersity index
In physical and organic chemistry, the polydispersity index , is a measure of the distribution of molecular mass in a given polymer sample. The PDI calculated is the weight average molecular weight divided by the number average molecular weight. It indicates the distribution of individual...
). A range of from 1000–140,000 da
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
has been reported for softwood lignosulfonates with lower values reported for hardwoods.
Preparation
Lignosulfonates are recovered from the spent pulping liquids (red or brown liquor) from sulfite pulping. The most widely used industrial process is the Howard process, in which 90–95% yields of calcium lignosulfonates (CAS number 904-76-3), are precipitated by adding of excess calcium hydroxideCalcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
. Ultrafiltration and ion-exchange can also be used to separate lignosulfonates from the spent pulping liquid. A list of CAS numbers for the various metal salts of lignosulfonate is available.
Uses
Lignosulfonates have a wide variety of applications.The single largest use for lignosulfonates is as plasticizers in 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...
, where they allow concrete to be made with less water (giving stronger concrete) while maintaining the ability of the concrete to flow. Lignosulfonates are also used during the production of cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
, where they act as grinding aids in the cement mill
Cement mill
A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement...
and as a rawmix
Rawmill
A rawmill is the equipment used to grind raw materials into "rawmix" during the manufacture of cement. Rawmix is then fed to a cement kiln, which transforms it into clinker, which is then ground to make cement in the cement mill...
slurry deflocculant (that reduces the viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of the slurry).
Lignosulfonates are also used for the production of plasterboard to reduce the amount of water required to make the stucco
Stucco
Stucco or render is a material made of an aggregate, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is used as decorative coating for walls and ceilings and as a sculptural and artistic material in architecture...
flow and form the layer between two sheets of paper. The reduction in water content allows lower kiln temperatures to dry the plasterboard, saving energy.
The ability of lignosulfonates to reduce the viscosity of mineral slurries is used to advantage in oil drilling mud, where it replaced tannic acid
Tannic acid
Tannic acid is a specific commercial form of tannin, a type of polyphenol. Its weak acidity is due to the numerous phenol groups in the structure...
s from quebracho
Quebracho tree
Quebracho is a common name in Spanish to describe very hard wood tree species. The etymology of the name derived from quiebrahacha, or quebrar hacha, meaning "axe-breaker".-Species:...
(a tropical tree).
Lignosulfonates are used to disperse pesticides, dyes, carbon black
Carbon black
Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
, and other insoluble solids and liquids into water. They 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
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
. They are also used to suppress dust on unpaved roads.
Oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of lignosulfonates from softwood
Softwood
The term softwood is used to describe wood from trees that are known as gymnosperms.Conifers are an example. It may also be used to describe trees, which tend to be evergreen, notable exceptions being bald cypress and the larches....
trees produced 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 flavor).
Dimethyl sulfide
Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...
and dimethyl sulfoxide
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
(an important organic solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
) are produced from lignosulfonates. The first step involves heating lignosulfonates with sulfides or elemental sulfur
Sulfur
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...
to produce dimethyl sulfide. The methyl groups come from methyl ethers present in the lignin. Oxidation of dimethyl sulfide with nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
produces dimethyl sulfoxide (DMSO).