Lignin sulfonate

Structural formula
Example of a lignosulfonate structure
General
Surname	Lignin sulfonate
CAS number	8062-15-5
Monomers / partial structures	Cumaryl alcohol , coniferyl alcohol , sinapyl alcohol
PubChem	24712
Type of polymer	Biopolymer , copolymer
Brief description	light to dark brown color
properties
Physical state	firmly
solubility	soluble in water
safety instructions
GHS labeling of hazardous substances no classification available H and P phrases H: see above P: see above
Toxicological data	> 5000 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Lignosulfonates or lignosulfonates are the salts of ligninsulfonic acid , a water-soluble , anionic , polyelectrolytic , branched polymer . They are by-products in the manufacture of pulp using the sulphite process . Technical lignosulfonates also always contain a mixture of organic and inorganic substances.

Manufacturing

Lignin sulfonates are formed during the chemical digestion of lignin , a chemically not precisely defined biopolymer , which, in the sulfite process , is reacted with salts of sulphurous acid . During the digestion, chemical bonds in the hydrophobic lignin structure are broken and the resulting fragments are converted into a water-soluble form by the addition of sulfonate groups.

Lignin degradation usually takes place through acidic cleavage of the ether bridges that connect the monomer components in the lignin with one another. The electrophilic carbocation that is formed during the ether cleavage then reacts with the bisulfite ion (HSO ₃ ^- ) to form a sulfonic acid group.

R-O-R '+ H ⁺ → R ⁺ + R'OH

R ⁺ + HSO ₃ ^- → R-SO ₃ H

The preferred site for ether cleavage is the α-carbon atom (in the immediate vicinity of the aromatic ring) of the propyl side chain (3 linear carbon atoms). Since the lignin has a very complex structure, the following figure only shows a simplified section of the molecular structure. The groups R ¹ and R ² can correspond to a large number of other structural elements that can be found in lignin. The sulfonation always takes place on the side chain (formation of benzylsulfonic acid groups through the Holmberg digestion) and not, as in the case of p -toluenesulfonic acid , on the aromatic ring.

Depending on the digestion process, a mixture of calcium, magnesium, sodium or ammonium lignin sulfonate with hemicelluloses , sugars, sugar acids , organic acids and inorganic salts is obtained as raw lignin sulphonate ( raw liquor , formerly also called sulphite waste liquor ) . In the acidic calcium bisulfite process, the hemicelluloses from the fiber are partially converted into soluble sugars , which means that the proportion of organic by-products in the raw liquor is significantly higher. On the other hand, the content of inorganic salt is lower, as this precipitates as calcium sulfate ( gypsum ).

Depending on the planned use, this raw liquor is processed through further steps:

• Sediments are removed by filtration or centrifugation .
• Sugars can either be converted into alcohol ( hexoses ) or fodder yeast ( pentoses ) through fermentation, or they can be converted into sugar acids through chemical processes .
• Hemicelluloses and low molecular weight lignosulfonates can be removed by ultrafiltration.
• the cation in the calcium lignosulfonate can be replaced by other metal ions such as potassium, sodium, iron, chromium, manganese, cobalt, etc. by chemical reprecipitation.
• The lignin structure can also be changed by further chemical modifications (sulfonation, desulfonation, carboxylation, oxidation, polymerization, depolymerization).

Lignosulfonates are commercially available as a powder (after spray drying ) or as concentrated solutions with a solids content of 45–55%.

properties

Lignosulfonates are very polydisperse ; that is, they have a very broad molar mass distribution of 1,000–400,000 atomic masses . Lignosulfonates from softwood (conifers) usually have a significantly higher molar mass than ligninsulfonates from hardwood (deciduous trees), but the (mean and maximum) molar mass also depends on the manufacturing process. They dissolve easily in water over a wide pH range (1–14), but are poorly or not at all soluble in most organic solvents. The higher the molar mass, the more hydrophobic the individual particles are. As a powder, lignosulfonates are light to dark brown.

Lignosulfonates are classified as almost non-toxic with an LD ₅₀ value of> 5 g / kg.

use

application areas

• The largest area of ​​application for lignosulfonates is as wetting and dispersing agents with around 68% . The dispersing property is closely related to the ability of the lignosulfonate molecule to adsorb on particle surfaces. The adsorption is influenced by factors such as molar mass , surface charge of the molecule and the particle surface, as well as solution parameters (such as salt concentration, pH value, etc.). With their negatively charged sulfonate groups, they preferentially bind to positively charged mineral surfaces and thus generate electrostatic repulsion between particles. In addition, due to their particle size, they generate steric repulsion, which is significantly stronger than the electrostatic repulsion. As a dispersing agent, lignosulfonates help to drastically reduce the viscosity of suspensions or to significantly increase the solids content with the same viscosity.
• Due to their good adhesive properties, lignosulfonates are used as organic binders for a wide variety of applications. In this case, whole sugary , i.e. H. non-fermented, lignosulfonates are used, which have even better adhesive properties.
• In addition to these two main applications, lignosulfonates are used as a raw material for the production of various chemicals.

In 2006, over 1 million tons of lignosulfonates were consumed worldwide. The following table gives an overview of the areas of application:

property	application	description
disperse	Concrete plasticizer superplasticizer	Plasticization of concrete for better workability - for the mechanism of action, see p. u.
	Grinding aid	Reduction of energy consumption when grinding cement .
	Plasterboard	Reduction of water and therefore energy consumption in the manufacture of plasterboard.
	brick	Reduction of water and therefore energy consumption in brick production.
	Textile paints	Lignosulfonates are used as dye dispersants when dyeing textiles.
	Oil field applications	In oil and gas wells, lignosulfonates are used in drilling and solidifying the borehole.
	Pesticides	Pelleting and dispersing of pesticides.
	Printing inks	Lignosulphonates are used to remove carbon black for printing inks, e.g. B. to prepare for inkjet printer colors.
	Emulsion stabilization	Improvement of the stability of asphalt, wax emulsions or cosmetics
	Lead accumulators	Lignosulfonates help to increase the surface area at the negative pole of the accumulator and thereby extend its service life. They also improve the cold start properties.
	Complexing agents	Lignosulfonates can be used as cleaning agents due to their dispersing and complexing properties.
tie	Corrugated cardboard	In the manufacture of corrugated board lignosulfonates to the stability and strength of the are added to the shaft to increase.
	Refractories	Lignosulfonates are used as binders in the manufacture of refractory masses and in mold construction in foundry technology.
	Pellets	Production of coal briquettes and egg coals, pelleting of metal ores, production of animal feed and fertilizers
	Dust binding	Reduction of dust formation on unpaved roads.
	Chipboard	Due to the phenolic structure of the lignin sulfonate, some of the phenol-formaldehyde resin can be replaced by lignin or lignin sulfonate. The use for gluing solid wood has also been proven.
other	Vanillin	Production of nature-identical vanillin.
	DMS / DMSO	Raw material for the production of chemical substances.
	Ethanol / feed yeast	Fermentation of the pentoses and hexoses by yeast.
	to tan	Additive to improve the tanning process in the manufacture of leather .
	Phenolic resins	Ligninsulfonates can be used in phenolic resins to replace part of the synthetic resin with the renewable raw material lignin.
	fertilizer	for soil improvement

Concrete liquefier / superplasticizer

By far the most important application for lignosulfonates (around 38%) is its use in concrete liquefiers or superplasticizers , i.e. in concrete admixtures that allow it

• to increase the flowability of the concrete , making it easier to process and compact
• to reduce the water content ( w / c value ), which increases the durability / service life of the concrete
• to reduce the cement content, whereby the manufacturing costs can be reduced

Mechanism of action: The lignosulphonate molecules adsorb on the cement surface and disperse (ie separate) the cement particles. As a result, the water that is trapped between the agglomerated cement particles is released and the mixture liquefies. In the first step, the larger (ie more hydrophobic ) molecules will preferentially adsorb. The lignosulfonate molecules mainly bind to the C ₃ A and C ₄ AF phases of the cement, while the C ₃ S and C ₂ S phases are little or not occupied. The hydrate phases formed during the reaction of water and cement will on the one hand overgrow the lignosulphonate molecules, but can in turn be occupied by other ligninsulphonate molecules.

Due to the mechanism of action described and the large number of functional groups in the lignosulfonate molecule, these show, in contrast to synthetic raw materials, a very wide range of compatibility and good effectiveness with various cements.

Sugar and hemicelluloses present in the raw material, but also the lignin sulfonate itself, can lead to a delay (delayed development of strength) in the cement. Lignosulfonates with a particularly high molar mass result in less delay and greater effectiveness, so that they can also be used successfully in self-compacting concrete .

Starting material for the production of other substances

By oxidizing lignosulfonates from softwood , vanillin (vanilla flavor) and its derivatives can be obtained.

Dimethyl sulfide and dimethyl sulfoxide , important organic solvents , can be produced from lignosulfonates. The first step involves the formation of dimethyl sulfide (DMS), which is produced when lignosulfonates are heated with sulfides or elemental sulfur . The methyl group comes from methyl ethers that are present in lignin. Oxidation of the dimethyl sulfide with nitrogen dioxide then gives dimethyl sulfoxide (DMSO).

The sugars contained in the raw lignin sulfonate can be converted by fermentation with yeast. The hexoses , which are mainly found in softwood, are converted into ethanol through alcoholic fermentation . The fermentation of pentoses does not produce alcohol, but CO ₂ , but the conditions can be chosen so that the yeasts multiply to produce fodder yeast.

Further

Lignosulfonates are used as grinding aids in the manufacture of cement . Today they are mainly used to increase the throughput of the cement mill and to reduce energy consumption. But since they can also increase the solids content of suspension, they were and are used in the historical wet process to increase throughput and reduce energy consumption.

Lignosulphonates are used in the production of plasterboard to reduce the amount of water that is required to liquefy the plaster of paris suspension. This enables a reduction in the oven temperature required to dry the panels, which in turn helps to reduce energy consumption.

In the manufacture of bricks, the dispersing effect of lignosulfonates is used to homogenize the clay mixture. This reduces the risk of cracking both during the drying process and during firing.

The dye pigments are dispersed by lignosulfonates and are better bound to the textile fibers. Ligninsulfonates show particularly good heat resistance.

In oil and gas wells, lignosulfonates are used to reduce the viscosity of the drilling fluid suspension or to increase the solids content and thus the density. Here they replace tannic acid, which is made from quebracho (a tropical wood). Also, deep well cements , which are used to stabilize the borehole prior to production, are liquefied and delayed (i.e., longer working time of the mixed cement) with lignosulfonates.

Lignosulfonates are u. a. used to pellet pesticides such as wetting sulfur and later to disperse them in water . They can also be used to improve the uptake of nutrients through the roots and thus the growth of plants.

In the manufacture of charcoal briquettes and egg coals , small amounts of lignosulfonates are added to increase strength. In animal feed, lignosulphonates combine the individual raw materials - usually powder or dust - to form stable pellets.

Lignosulfonates are used on unpaved roads to reduce dust formation and thus erosion of the subsoil.

Individual evidence

1. ↑ ^{a b c d} Lignin Sulfonate (PDF; 315 kB) from USDA AMS , accessed on April 5, 2014.
2. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
3. ↑ Stuart E. Lebo Jr., Jerry D. Gargulak, Timothy J. McNally: Lignin . In: Kirk-Othmer Encyclopedia of Chemical Technology . doi : 10.1002 / 0471238961.12090714120914.a01.pub2 .
4. ^ E. Sjöström: Wood Chemistry: Fundamentals and Applications. Academic Press, 1993.
5. ↑ Bernd Schäfer: Natural substances in the chemical industry. Spektrum Akademischer Verlag, 2007, ISBN 978-3-8274-1614-8 , pp. 109-110.
6. ↑ ^{a b} Report SRIConsulting: Lignosulfonates, Jan. 2009 .
7. ↑ Expert discussion "Material use of lignin", Berlin, March 10, 2009 ( PDF, 1.29 MB ( Memento of the original from May 5, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original - and archive link according to the instructions and then remove this note. ) 
8. ↑ Patent EP1357892 : Multifunctional additive containing particulate constituents for cosmetic compositions and processes for producing the same. ,
9. ↑ Battery Expanders  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.  
10. ↑ Patent DE69812438T2 : Composition for the production of fuel briquettes. Released January 15, 2004 . ‌
11. ↑ Katrin Ursula Schwarz: Investigations into the use of biogenic lignin adhesives in solid wood bonding. Dissertation . 2004 (online)
12. ↑ Yves F. Houst, Paul Bowen, François Perche, Annika Kauppi, Pascal Borget, Laurent Galmiche, Jean-François Le Meins, Françoise Lafuma, Robert J. Flatt, Irene Schober, Phil FG Banfill, David S. Swift, Bernt O. Myrvold, Berit G. Petersen, Kåre Reknes: Design and Function of Novel Superplasticizers for More Durable High Performance Concrete (Superplast Project). In: Cement and Concrete Research. 38 (10), 2008, pp. 1197-1209; doi: 10.1016 / j.cemconres.2008.04.007 .
13. ^ Self-compacting concrete with lignosulphonate based superplasticizer .
14. ^ Properties of the concrete matrix of self-compacting concrete with lignosulphonate superplasticizer .
15. ↑ Borregaard Ingredients ( Memento of the original from October 4, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
16. ↑ Martin B. Hocking: Vanillin: Synthetic Flavoring from Spent Sulfite Liquor. In: Journal of Chemical Education . 74 (9), 1997, pp. 1055-1059; doi: 10.1021 / ed074p1055 .
17. ↑ Patent DE69514167T2 : grinding aid for cement. ‌
18. ↑ Dye dispersant  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .  Borregaard, 2004.
19. ↑ Patent US4590262 : Low electrolyte lignosulfonate. ‌
20. ↑ Patent DE69426161T2 : Process for the production of granules containing active ingredients. ‌
21. ↑ Patent WO2010127142 : Use of lignosulfonates in suspo-emulsions for producing pesticide compositions. ‌
22. ↑ 7CFR205.601: Synthetic substances allowed for use in organic crop production . (Approval of lignosulfonates for plants in the USA)
23. ↑ 21CFR573.600: Lignin sulfonates . (Approval of lignosulfonates in feed and drinking water in the USA).
24. ^ Karin Edvardsson: Evaluation of Dust Suppressants for Gravel Roads: Methods Development and Efficiency Studies. PhD thesis . Royal Institute of Technology, Stockholm 2010 ( PDF, 2.6 MB ).
25. ^ Karin Oscarsson: Dust suppressants for Nordic gravel roads. Licentiate Thesis, KTH, Stockholm, Sweden 2007 ( PDF, 10.8 MB ).