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{{Infobox technology|Name=Pulping|Category=Conversions|Feedstock=Woody biomass|Product=Pulp}}
<onlyinclude>'''Pulping''' is a process that extracts fibrous material from biomass, most commonly as a precursor for paper making. The process separates the fibrous cellulose and lignin from the other components and impurities in the biomass. Main processes are mechanical, chemical, and a combination of mechanical and chemical pulping in a hybrid pulping process.</onlyinclude> Mechanical pulping relies on physical separation methods without added chemicals. However, water can be added to reduce the damage to the fibres from friction. Chemical pulping uses chemicals to remove the lignin from the pulp, resulting in a higher quality pulp. Hybrid technologies use chemicals to soften the lignin before a physical separation results in a pulp that still contains a substantial amount of the lignin.<ref name=":0">{{Cite web|year=|title=PrintWiki, The Free Encyclopedia of Print|e-pub date=|date accessed=6-9-2021|url=http://printwiki.org/Pulping}}</ref> Finally, biological pulping uses biotechnology for the pulping process<ref name=":1">{{Cite journal|title=A review of the traditional pulping methods and the recent improvements in the pulping processes|year=2021-01-03|author=Drake Mboowa|journal=Biomass Conversion and Biorefinery|doi=10.1007/s13399-020-01243-6}}</ref>.

==Feedstock==
Pulping is performed on feedstock with a high fibre content. Before the pulping process, any material that is low in fibrous material should be removed. For example, wood undergoes debarking before the pulping process. Next, the biomass should be [[Sizing|sized]], for example by [[Sizing#Chipping|chipping]].<ref name=":0" /> The most common feedstock for pulping is woody biomass. Examples of non-woody biomass are sisal, rice straw, cotton linen, sugarcane bagasse, pineapple, and straw.<ref name=":1" />
==Process and technologies==
===Chemical pulping===
The chemicals in chemical pulping allow for a near complete removal of the lignin from the biomass. This results in high quality pulps, which can be used for printing and writing paper. However, the yield of chemical pulping is generally lower than other methods, resulting in more expensive pulps.<ref name=":0" />

==== Dissolving pulp and organosolv ====
Dissolving pulp production entails a hydrolysis step before the pulping process, which is commonly sulfate or sulfite pulping. Most common method is to apply steam to the biomass, which hydrolyses and removes the hemicellulose and dissolves the organic acids. Organosolv methods, where organic solvents are introduced, can be used on biomass types that are not suitable for dissolving pulp technologies.<ref name=":1" />

==== Cold soda pulping ====
Cold soda pulping uses room temperature sodium hydroxide (20 to 30 °C) before a disk refining. The cold soda uses a fast impregnation of the biomass, which reduces the losses in lignin and polyose, resulting in high yields (85 – 92%). It can be combined with the Kraft process to recover the sodium hydroxide. The resulting pulp has a low brightness, but can be bleached with peroxide-hypochlorite.<ref name=":1" />

==== Sulphate pulping (Kraft) ====
The Kraft process is the most common pulping process used globally. It uses the chemicals sodium hydroxide and sodium sulfide at elevated temperatures (155 – 180 °C) and a steam pressure of 800 kPa to break down the lignin in the biomass. The lignin breaks down into hydroxyl and hydrosulfide ions, which dissolve in the liquor. Part of the hemicellulose and cellulose is also broken down by the treatment. The used chemicals are known as black liquor, which contains lignin, hemicellulose and extractives (oils, resins, and terpenes). The chemicals can be recovered and replenished with sodium salt, resulting in a cost-effective process.<ref name=":1" />

==== Sulphite pulping ====
Sulfite pulping is similar to sulfate pulping, where both methods cook the biomass with chemicals to cleave the lignin bonds. In sulfite pulping a bisulfite of ammonium, calcium, magnesium, or sodium is used together with sulfur dioxide. Unlike Kraft pulping, this process is sensitive to extractives, which makes the process unsuitable for hardwood species. Moreover, chemical recovery is nearly impossible. The resulting pulp is brighter, easier to bleach and refine compared to Kraft pulp. <ref name=":1" />

=== Hybrid pulping ===
In hybrid pulping, the lignin is softened by chemicals, such as Sodium Sulfite and alkaline salts, before a mechanical pulping step. This results in stiff fibres which are commonly used in corrugated board, roll cores, and containers.<ref name=":0" />

==== Chemi-thermo-mechanical pulping (CTMP) ====
In chemi-thermo-mechanical pulping, the biomass is pre-treated by steam and chemicals. The steam and chemicals soften the lignin, which reduces the mechanical energy required for the pulping. The pulp is obtained in high yields (85-95%) and has a high strength, suitable for high-grade printing paper.<ref name=":1" />

==== Neutral Sulfite Semi Chemical Pulping (NSSC) ====
The Neutral Sulfite Semi Chemical Pulping (NSSC) technology uses a combination of chemical pulping and refining. First the biomass is impregnated with sodium sulfite at 160 to 190 °C to remove lignin. Anthraquinone can be added to increase the rate of delignification. The sulfite is usually combined with a buffer solution to negate the effect of released organic acids. A second step in the process is a disk refining. Up to 15 to 20% of the lignin remains in the NSSC pulp, which is often used in unbleached products, where strength and stiffness are required.<ref name=":1" />

=== Mechanical pulping ===
Mechanical pulping is inexpensive and results in the highest yields. However, mechanical pulp also results in paper with a large number of imperfections. Technological advances are improving the quality of mechanical pulps, while maintaining the low cost and high yields.<ref name=":0" />

==== Refiner ====

===== Refiner mechanical pulping (RMP) =====
In a refiner mechanical pulping process, the biomass is ground between rotating metal discs or plates. In a first step, the biomass is defibrated into separate individual fibres. In a second step, the fibres are loosened. The RMP pulp is stronger, freer, bulkier, and darker compared to traditional SGW pulp.<ref name=":1" />

===== Thermomechanical pulping (TMP) =====
In this refiner process the biomass is preheated by impregnation of steam under pressure. The high temperature (115-155 °C) softens the lignin and helps in fibre separation. The refining takes place in two steps, the first at elevated pressure and temperature, around the glass transition temperature of lignin (140 °C), the second at atmospheric pressure and temperature. The resulting yields are high (>93%) and the pulp is characterised by its high strength.<ref name=":1" />

==== Groundwood ====

===== Pressure groundwood (PGW) =====
''Information still missing.''

===== Stone groundwood (SGW) =====
Stone groundwood pulping is the oldest mechanical pulping method, where the biomass is pressed against a rotating grindstone. The grindstone breaks apart the biomass into thin fibres and fragments, which are washed away with a water stream. The friction results in an increased temperature, which helps the process. The product stream is scanned to remove the larger particles, then the water is removed to thicken the pulp. The process has high yields (about 95%), because most lignin remains in the product.<ref name=":1" />

===== Thermal groundwood (TGW) =====
''Information still missing.''

=== Biological pulping ===
Biological pulping takes advantage of natural methods to break down fibrous materials. For example, white-rot fungi can be used to soften and remove lignin.<ref name=":1" />

==Product==
The resulting product of the pulping process, called pulp, can be further processed into many paper and board products. Depending on the qualities of the pulp, different products are made. Mechanical pulps, which are low quality pulps, are suitable for low-quality paper, such as newspaper, catalogues, paper towels, tissues, and sanitary papers. High quality pulps from chemical pulping are used for printing and writing paper. Finally, the hybrid pulping processes give pulps with stiff fibres and are commonly used in corrugated board, roll cores, and containers.<ref name=":0" />
==Technology providers==
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===Valmet===
Valmet is a developer and supplier of process technologies, automation and services for the pulp, paper and energy industries. The company has over 200 years of industrial history and was reborn through the demerger of the pulp, paper and power businesses from Metso Group. Valmet offers tailored technology solutions for softwood and hardwood kraft pulp production, as well as various mechanical pulping technologies. 
{{Infobox provider-pulping}}

==Patents==
No patents have been identified yet.
==References==
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[[Category:Primary processing]]