Soda pulping is a chemical process for making

wood pulp Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. Mixed with water and other chemical or plant-based additives, pulp is the major raw mate ...

with sodium hydroxide as the cooking chemical. In the ''Soda-AQ'' process,

anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoan ...

(AQ) may be used as a pulping additive to decrease the carbohydrate degradation. The soda process gives pulp with lower tear strength than other chemical pulping processes ( sulfite process and kraft process), but has still limited use for easily-pulped materials like straw and some hardwoods.

History

A precursor to the soda pulping process was the paper making process developed by Matthias Koops in 1801 which involved washing wood shavings in limewater, adding soda crystals and then boiling the mixture. Soda pulping was one of the first chemical pulping methods and was invented in 1851 by Burgess (United States) and Watts (England). In France in 1852 Coupier and Mellier patented a soda process based on a 1851 invention the patent of which preceded that of Watt and Burgess, which was filed in 1854. The first mill was started in 1866 in the USA. In 1865 they patented a method for recovery of the cooking liquors by incineration of the spent liquor. Many of the early soda mills converted to kraft mills once it was discovered.

Production

Around 5%-10% of

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distrib ...

production worldwide is produced from

agricultural crops A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponics ...

, valuing agricultural paper production at between $5 billion and $10 billion. The most notable of these agricultural crops are wheat straw and

bagasse Bagasse ( ) is the dry pulpy fibrous material that remains after crushing sugarcane or sorghum stalks to extract their juice. It is used as a biofuel for the production of heat, energy, and electricity, and in the manufacture of pulp and building ...

. Using agricultural crops rather than wood has the added advantage of reducing deforestation. Due to the ease with which bagasse can be chemically pulped, bagasse requires less bleaching chemicals than wood pulp to achieve a bright, white sheet of paper. Most chemical bagasse pulp mills concentrate the spent reaction chemicals and combust them to power the paper-mills and to recover the reaction chemicals.

As solution for silicate scaling

Many

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns a ...

es,

bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...

and some tropical hardwoods contain much silicates that may cause

sodium aluminum silicate Sodium aluminosilicate refers to compounds which contain sodium, aluminium, silicon and oxygen, and which may also contain water. These include synthetic amorphous sodium aluminosilicate, a few naturally occurring minerals and synthetic zeolites. ...

scales. Moderate amounts of silicates can be controlled with purging lime mud or lime kiln ash. Silicate removal from

green liquor Green liquor is the dissolved smelt of sodium carbonate, sodium sulfide and other compounds from the recovery boiler in the kraft process. The liquor's eponymous green colour arises from the presence of colloidal iron sulfide. The green liquor ...

in a soda mill can be achieved by lowering the pH of the liquor with CO₂-containing flue gases from the lime kiln or other sources. No commercial silicate removal system is available for the kraft process, but it can handle the small amounts of silicates from northern woods..

References

{{Paper Papermaking Pulp and paper industry Industrial processes Chemical processes

History

Production

As solution for silicate scaling

See also

References