Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/08—Fractionation of cellulose, e.g. separation of cellulose crystallites
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B16/00—Regeneration of cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
  • C08H8/00—Macromolecular compounds derived from lignocellulosic materials

Definitions

• the invention relates generally to a process for converting cellulose to nanocellulose, and more particularly to such a process requiring little input of mechanical energy.
• US 2012/0158955 discloses a process comprising swelling cellulose with an inorganic or organic swelling agent.
• the swollen cellulose can be converted to nanocellulose in a mechanical comminution process requiring less than 2000 Kw/t.
• WO 2010/106053 A2 discloses a process for hydrolyzing cellulose to
• cellulose is dissolved in an inorganic molten salt, for example a hydrate of zinc chloride.
• Hydrochloric acid is added to the solvent medium to drive hydrolysis to glucose.
• Example 5 of this reference shows that when no hydrochloric acid is added the hydrolysis product is predominantly sorbitol.
• the present invention addresses these problems by providing a process for converting cellulose to nanoceliuiose, said process comprising the steps of:
• Another aspect of the invention comprises nanoceliuiose material obtained by the process.
• Yet another aspect of the invention comprises lignin produced as a byproduct of the process in case a lingo-cellulose feedstock is used.
• FIG 1 SEM picture of dried nanoceliuiose material with partially
• FIG. Nanoceliuiose material shaped as a cellulose thread after
• cellulose refers to a polysaccharide polymer produced by virtually all land-based plants.
• the monomer of cellulose is glucose, which is a sugar molecule containing 6 carbon atoms.
• hemicellulose a co-polymer of C5 and C6 sugars
• lignin a co-polymer of C5 and C6 sugars
• Materials such as wood pulp, a major source of cellulose, typically contains cellulose, hemicellulose and lignin.
• cellulose obtained from the cotton plant is virtually lignin free.
• Cellulose as obtained from plants has a degree of polymerization (DP) anywhere in the range of from 1000 to 10,000.
• nanocellulose refers to cellulose particles
• the present invention provides a process comprising dissolving cellulose and precipitating nanocellulose from the solution, requiring little or no mechanical energy.
• An aspect of the present invention is a process for converting cellulose to nanocellulose, said process comprising the steps of:
• Inorganic molten salts have been disclosed in WO 2010/106053 A2 as being capable of dissolving cellulose. Inorganic molten salts share this property with many organic ionic liquids. Inorganic molten salts offer many important advantages over organic ionic liquids, the most important ones being much lower cost, and far greater temperature stability.
• zinc chloride tetra hydrate ZnCl2.4H2O
• zinc chloride tetra hydrate comprises about 70% zinc chloride and about 30% water.
• water present in a salt hydrate is not free water, but it bound to the salt molecules.
• molten salt medium for example in the form of hydrochloric acid, catalyzes hydrolysis of the dissolved cellulose to glucose.
• hydrolysis still takes place, but the predominant hydrolysis product is sorbitol instead of glucose (see Example 5 and Figure 4 of WO 2010/106053 A2).
• Hydrolysis is undesirable in the process of the present invention, because it lowers the yield of nanocellulose and produces highly soluble by-products that are difficult to remove from the solvent medium.
• inorganic molten salt hydrates contain a small amount of protons, even when no proton source (such as hydrochloric acid) is added.
• the small amount of protons is sufficient to catalyze hydrolysis of dissolved cellulose.
• the process of the invention utilizes an inorganic molten salt solvent medium that is substantially proton-free.
• an inorganic molten salt solvent medium is considered substantially proton -free when less than 5% of cellulose dissolved in the medium is hydrolyzed to glucose.
• the solvent medium may be passed through a column of cation-exchange material, in which protons from the solvent are replaced with alkaline cations, such as lithium, sodium, potassium, calcium, magnesium, and the like. It is desirable to use a cation that does not contaminate the molten salt medium.
• the molten salt is a zinc chloride hydrate
• the preferred cation on the exchange column is Zn 2+ . Solvent media that have been made substantially proton- free by this method may develop new protons over time. For this reason, such solvents should be used in the process within a short time after having been passed through the cation exchange column.
• An alternate method for making an inorganic molten salt solvent medium substantially proton -free is the addition of a proton scavenger.
• the oxide or hydroxide of any metal being a stronger reducing agent than hydrogen can be used as a proton scavenger.
• the skilled person will appreciate that the reduction potential of a metal relative to hydrogen can be readily ascertained by consulting a redox table. Most redox tables set the redox potential of hydrogen at zero, so that the redox potential of any metal in the table is reported relative to that of hydrogen.
• Suitable proton scavengers include the oxides and hydroxides of alkali metals and alkaline earth metals, and the oxides and hydroxides of non- noble transition metals. It is desirable to use the oxide or hydroxide of the corresponding molten salt. For example, if a hydrate of zinc chloride is used as the inorganic molten salt, preferred proton-scavengers are ZnO and Zn(OH) 2 .
• the proton scavenging may proceed via a multi-step reaction.
• the proton-scavenging effect of ZnO in a zinc chloride is believed to comprise the following reaction steps:
• pH meters are available for measuring the pH of an aqueous solution. Such pH meters are typically calibrated against buffer solutions having a known pH value, for example 7 or 4.
• the ionic molten salt solvent media are strongly acidic, but the - log [H + ] value should be very high because of the low value of [H + ].
• ZnO is poorly soluble in the zinc chloride tetra hydrate molten salt.
• a feedstock comprising cellulose is dissolved in the solvent medium.
• the feedstock may consist almost entirely of cellulose, for example cotton I inters or delignified wood pulp. It is also possible to use a lignocellulosic feedstock, such as wood chips or sugar cane bagasse.
• the solution may contain significant amounts of insoluble material, for example lignin. It is desirable to remove undissolved solids, for example by filtration, before carrying out step b.
• step b. dissolved cellulose, having been converted to nanocellulose, is precipitated from the solvent medium by adding an anti-solvent.
• an anti-solvent Any liquid that does not dissolve nanocellulose and that is miscible with the inorganic molten salt medium can be used as an anti-solvent. Examples include water and alcohols having from 1 to 6 carbon atoms, for example tertiary- butyl alcohol (TBA).
• the selection of the anti-solvent has an effect on the yield of nanocellulose product and on its composition. Alcohols precipitate more nanocellulosic product from the solution than does water, resulting in a higher yield. The alcohol precipitate contains more short chain product than does the water precipitate, which may be undesirable for certain applications.
• step c the precipitated nanocellulose is separated from the solvent medium. It has been found that the material can be readily separated from the solvent medium by filtration.
• Nanocellulose prepared by this process has been analysed under a
• SEM scanning electron microscope
• the DP was about 800, as compared to about 3,000 for the cellulose in the feedstock.
• the solvent medium can be readily regenerated after use in the process.
• the main contaminants are the anti-solvent, and reaction products that are soluble in the molten salt/anti-solvent mixture (primarily oligosaccharides).
• the anti-solvent can be removed by evaporation, preferably under reduced pressure. After condensation the anti-solvent is available for reuse.
• Dissolved reaction products can be removed by adsorption, by extraction, or a combination thereof.
• lignin from the feedstock can be recovered by
• the lignin by-product of the process of this invention is of much greater purity.
• the formed solid particulates were removed by centrifugation (5000 - 7000 rpm; 400 ml centrifugation vial). Liquid phase was removed from the centrifugation vial keeping solid residue in it. The vial was filled with distilled water (300 ml), shaken to make a homogeneous suspension and centrifuged again. This procedure was repeated at least 6 times to get ZnC concentration below 100 ppm. After the last washing nanoceiiuiose solids were removed from the centrifugation vial and kept as a water suspension with 10 - 12 wt.% dry solids.
• nanoceiiuiose samples were stored as suspensions in the corresponding coagulant with 10 - 12 wt.% dry solids.
• the obtained nanoceiiuiose particles can be stored as a suspension with higher or lower dry solid content by adding or removing an appropriate coagulant to a desired dry solid content in the suspension.
• nanoceiiuiose was obtained as a dry powder by removing of the remaining coagulant by evaporating, by vacuum drying, by drying under supercritical C02 or by freeze drying.
• Fig.1. shows an example of cellulose dried under
• Nanocellulose was produced in a shaped form as a thread or fiber by spinning out the cellulose/70 % ZnC /F O mixture into an antisolvent, for example acetone.
• the formed thread can be washed by coagulant and dried.
• Fig.2. shows an example of cellulose thread made by spinning out of 8% cellulose/70%ZnCl2/H2O solution into acetone.
• Wood particles of 2-3 mm size were mixed with 70 % ZnC /H O solvents in a stirred tank reactor to form a 5 - 10 wt% content homogeneous mixture.
• the mixture was kept under continuous stirring at 90 °C for 20 min.
• remaining solids mainly lignin
• the remaining liquid was mixed with water reactor to get the ZnCb concentration below 30 wt % and to precipitate nanocellulose as particulates.
• the final mixture was kept under stirring for 30 min, and the formed nanocellulose solid particulates were separated by filtration, washed with distilled water till no ZnCb in the washed liquid, and stored as a water suspension with 10-12 wt. % dry solids or as a dry nanocellulose.
• the cellulose feedstock may be modified by using bagasse, switch grass, or any other abundant cellulose source.
• the antisolvent may be substituted with another alcohol or ketone. Lignin produced as a by-product may be further processed into platform chemicals.

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• Crystallography & Structural Chemistry (AREA)
• Analytical Chemistry (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

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• 2016
  • 2016-09-29 JP JP2018536336A patent/JP6818985B2/ja active Active
  • 2016-09-29 US US15/764,395 patent/US10961324B2/en active Active
  • 2016-09-29 WO PCT/EP2016/073202 patent/WO2017055407A1/en not_active Ceased

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