NZ718115A - Process for treating cellulose and cellulose treated according to the process - Google Patents

Abstract

Process for purifying a slurry comprising cellulose by salt/ion depletion and/or free sugar depletion. The process comprises the following steps of providing a slurry comprising cellulose and liquid, subjecting the slurry to a first application of an electric field inducing the liquid of the slurry to flow, separating the liquid from the cellulose thus obtaining a liquid depleted slurry, adding a washing liquid to the liquid depleted slurry, subjecting the liquid depleted slurry to a second application of an electric field inducing the washing liquid of the slurry to flow and separating the washing liquid from the cellulose, thus obtaining a purified cellulose.

Description

Process for treating cellulose and cellulose treated according to the process.

Field of invention The present inven:ion relates to a process for purifying, such as salt/ion deple:ion and/or free sugar depletion, ably by using ring, a slurry sing cellulose, such as micro:fibrillated cellulose, by subjecting the slurry to an electric field.

Background Microfibril' ated cellulose (MFC), which also is known as nanocellulose, is a material_ typically made from wood cellulose fibers. "t can a:_so be riade from microbial sources, agricultural fibers, dissolved _ose or CMC etc. "n micrO':ibrillated cellulose the individua' micrO'=ibrils have been partly or y detached from each other.

Microfibrillated cellulose has a very high water binding capacity and it is thus very di icu'L to reduce the water content o_ a slurry sing microfibriila:ed cellulose and accordingly it is thus di icu'L so puri fy. {igh water content ol a slurry comprising microfibri"a:ed cellulose also prevents usage or MFC in many di "erenL application where MFC with high solids would be required.

Today there exist several di""erenL meLhods :0 remove water from a slurry comprising cellulose, such as microfibrillated cellulose. "v is "or example possible to use di ereno drying techniques. ixamp'es o di "erenL drying techniques are; freeze drying, spray drying and supercritical drying. These ques are however quite energy demanding and thus not so cosL e "icient to use in large scale processes. Also, ication, or superhornLfication, 0: the fibrillated cellulose fibers often tends to occur when water is removed with di "erent drying ques. iorni.:ica ,ion is when irreversible bonds between the Sibers are ‘ormed. When horni:fication has occurred it is not possible jor the jibers to expand and swell in wa':er and :he origina:_ water bonding capaci VY o. the jibers is :hus lOS' The horni :l cation may be prevented by on o: chemicals which physica:_ly prevent or modi.iy she jibers in such way chat she "orma ion 0' bonds between cellulose Sibers are limited or prevented. CA120863Z_A describes a process to re—disperse dried micrO':ibril'ated ce' 'ulose by addition o: additives that will preven the "ibrils :rom bonding to each other and thus also preven:s horni-=ication o the .

Further there is disclosed by L Jchache et al. in Annals o: the University o:: Craiova, ilectri C ingineering series, No. 32, 2008; ISSN 1842—4805 dewatering o: p le and paper waste sludge.

Mechanica: treatments in order :0 remove water :rom a slurry comprising cel:_ulose, such as micro: ibrillated cellulose can also be used. However, they are normally no very success:ul due to the small fiber size and size distribu':ion 0 the micrO'=ibri'lated cellulose. Moreover, l tracion O'— a slurry comprising cellulose, such as micrO' ibri"ated ose is di "icult due to the dense web formed by the s:_urry. Furthermore, the bonds between the micro:fibrilla:ed ce' lulose :ibers are also quite strong and this will also make mechanica:_ dewatering less e'"icient.

The ine""iciency or 'imitations in drying in e.g. pressurized dewatering wi'l "ur cher give problems with the removal of ions of cellulose constituents. Since a filter cake is formed during dewatering, a higher resistance to dewatering is ed. At the same time, it is more ult to remove e.g. ions or other ved species since these might be accumulated in the filter cake. Therefore, the obtained dewatered filter cake of MFC might in fact contain the initial amount of ions or even substantial higher amount of ions.

When using a normal drying method, the ions and residual chemicals will remain in the concentrated fiber suspensions and finally in the dried MFC or cellulose sample.

Object of the Invention It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or to at least e a useful alternative.

Summary of Invention According to a first aspect of the present invention, there is provided a process for purifying by salt/ion depletion and/or free sugar depletion a slurry comprising cellulose, wherein the process comprises the following steps: -providing a slurry comprising cellulose and a liquid, cting the slurry to an electric field inducing the liquid of the slurry to flow, -separating the liquid from the cellulose thus obtaining a liquid depleted slurry, -adding a washing liquid to the liquid depleted slurry, -subjecting the liquid depleted slurry to an electric field inducing the washing liquid of the slurry to flow, and -separating the g liquid from the cellulose, thus ing a purified cellulose.

AH26(11116350_1) The present invention also es ing to a second aspect, a cellulose purified according to the first .

The present invention also provides according to a third aspect, cellulose obtained by the process according to the first aspect.

The present invention also provides ing to a fourth aspect, use of the cellulose ing to the second or the third aspect in a strength additive, a thickener, a viscosity modifier, a gy modifier, a cleaning powder, a washing powder, a detergent, a foam composition, a barrier, a film, a food product, a pharmaceutical ition, a cosmetic product, a paper or board product, a coating, a hygiene/absorbent product, an emulsion/dispersing agent, a drilling mud, a composite material, in water purification, in a filter, in a solar cell, in a battery, in an electronic circuit (which may be flexible, printed or coated), or to enhance the reactivity of cellulose in the manufacture of regenerated cellulose or cellulose tives.

Preferably, the use of an electric field improves purifying such as salt/ion depletion and/or free sugar (carbohydrate) depletion, preferably by using dewatering, of a slurry sing cellulose, such as microfibrillated ose.

The purifying, such as salt/ion depletion and/or free sugar depletion, may preferably be done using dewatering by using electro-osmosis (or capillary electrophoresis). This dewatering may also additionally also involve ation of other external sources such as mechanical or optical or magnetic field. One example is an ultrasound treatment. The purifying, may also be followed by any one or a combination thereof of the below methods to further dry the material: AH26(11116350_1) 1) Drying methods by evaporation 2) Freeze drying because of increased solids 3) Adding de-hornification additives can also be used in drying of dewatered material 4) dewatered material may also lly be dried further to obtain material which behaves like solid particles and thus more easily used in commercial applications while still easily mixed AH26(11116350_1) and dispersed to other components (individual fibers are essentially maintained) or easily used as such. "t is pre'ferred that an elec ,ric field with a e 0: 10- lOO V is used. Increasing the vol cage ,ypically increases the wa:er tion rate. The optirial val ie is when the current in censi cy o_ the generated electric field and the voltage gradien': are at maximum ble levels.

Pressure and/or heat may also be applied to the slurry in order to further improve the puri fying, such as salt/ion ion and/or free sugar deple :ion, o: the slurry, preferably when using dewatering. The pressure may be applied a.:ter she electric field has been applied and :he dewatering o: the slurry has been d. This is due to tha it may be preferred to se the dry content 0: the s' urry before pressure is app:_ied. Another possibili:y is to have weak dewatering inI_‘4—A _Eie' d simultaneously as mechanica:_ pressure is applied. However, it depends o: course on the dry content 0: the slurry being treated.

The pressure applied is pre:ferably a mechanica: pressure, such as compression by the use 0 "or example a roll nip or felts.

The dry content 0: the slurry comprising cellulose, such as ibrillated cellulose, be'fore puri':ying, such as salt/ion deple:ion and/or free sugar dep:_etion, preferably by using dewa':ering is preferably about "—10% by weight. After she trea:ment according to the process i, is preferred that the dry content 0. she purified, such as salt/ion depleted and/or free sugar dep:_eted, rably by using dewatering, slurry comprising cellulose, such as micro:fibrillated cellulose, is about 5—50% by weight.

The temperature 0: the slurry during purifying, preferably ing dewatering, is preferably above 30°C and preferably below 100°C.

The slurry may also comprise nanoparticles (such as absorbents), salt and/or surfactants which are s:imulated by the electric field and improves the liquid flow. "n this way the purifying, salt/ion deple':ion and/or free sugar depletion, pre ferably involving dewatering, 0: the slurry is increased. r, aromas may be depleted.

The present invention also relates to ce:_lulose, such as microfibrillated cellulose, being purified, such as salt/ion depleted and/or free sugar depleted, pre'ferab' y by using dewatering according to the process described above. It has been shown that by purifying, such as salt/ion dep:_etion and/or free sugar depletion, preferably by using dewatering, a slurry comprising cellulose, such as fibrillated cellulose by the aid o:: an e' ectric "le- d no or very limited horni-=ication c" the micrO'fibril' ated ce'lu' osic fibers will OCCUK.

Detailed description of the invention The present inven:ion relates to a process for ing, such as on depletion and/or free sugar depletion, pre ferably by using dewatering a slurry comprising cellulose, such as micro fibril' ated cellulose. Due to the teristics I) fibrilla':ed ce' lulose fibers, e.g. its size, size distribution and fiber bonds, it is normally very di""iculc to purify, such as on deplete and/or free sugar deplete, a slurry comprising mi crofibri'lated cellulose by using dewatering.

It is intended throughout the present description that the expression "cellulos e” embraces any type of ce'lulose, such as cellu'ose fibres (cellulose al). The ce"u'ose may also be a microfibrillated ce' 'u'ose (MFC). The cellulose may be bleached or unbleached. The ce' _u_ ose may also be crystalline ose, MCC (microcrystallinic cellu' ose; has high purity need due to its potential use in pharriaceutical compositions or other medical uses), ENC, NCC (nanocrystal' inic cellulose; may be used in electrical applications and has magnetica:_ ties), CNC, CMC (carboxymethylated cellulose) or synthetic polymer fibers and fibers made from disso' ving pulp. The ce' 'ulose may be present in she "orm O" a pulp, which may be chemica' pU' p, ical pulp, mechanical pulp or chemi(thermo)mechanical pulp (CMP or CTM?). Said chemica' pulp is preferably a sulphite pulp or a Kraft pulp.

The pulp may consist 0'' pulp from hardwood, softwood or both types. The pulp may e.g. contain a e o:: pine and spruce or a mixture 0: birch and spruce. The chemical pulps that may be used in the present invention include all types 0: chemical wood— based pulps, such as bleached, ha' ched and unbleached sulphite, kra ft and soda pulps, and mixtures o: these. The pulp may be 0: dissolved type. The pulp may also comprise textile fibers. The pulp may also come from agriculture (e.g. po:ato, bamboo or carrot).

It is intended throughout the present description that the expression ":free sugar” embraces not only sugars in monomeric forms but also smaller polymers. lt embraces also free carbohydrates.

It has been shown that by subjecting a slurry comprising ose, such as microfibril'ated cellulose fibers to an electric field the cation such as salt/ion depletion and/or free sugar depletion, preferab'y by using dewatering can ly be improved. One theory 0: why it works so well, is that the electric field induces the liquids o: the slurry to flow and thus pU' 's the water molecules away from she microfibri"ated ce' 'ulose fibers instead 0: pushing the microfibri"aced fibers as a mechanical treatment will do. Pilling the water molecules will make it possible to also remove water les being absorbed by the microfibri'lated fibers in a very e "icient way.

It is thus very easy to purify the cellulose fibers 0" the slurry.

It has been shown that by purifying, such as on depletion and/or free sugar depletion, ab'y by Jsing dewatering, a slurry comprising cellulose, such as microfibrillated cellulose, by subjecting the slurry to an electric field, no substantial hornification c" the microfibri"aced fibers will occur. It is thus possible for the microfibri"ated cellulose obtained according to the process or the first aspect to swell when the micro:fibrillated cellulose is in contact wi':h water again. This is 0" great importance when the microfibrillated cellulose for example is used as a Strength additive, a ner or as a viscosity modifier. Furthermore, the bonding ability 0: the red microfibrillated cellulose is also very good, i.e. no subStantial decrease in bonding ability is seen.

When it comes to salt/ion deple :ion this e "ect may be due to she fact thaw she voltage gradient induces a migration of the di""erent i ons wish the te. This leads to a decrease in the specific conduc civity o_ the product and a decrease in the tivity o: the sample.

Preferred embodiments of she first aspect 0: the invention are apparen , from the dependent claims and the s iject matter thereo is "urther set out below.

The dewatering is preferably done by the use 0: electro— osmosis. fl4n ec:ro—osmotic flow is 0 ften abbreviated EOF which is synonymous with electro—osmosis or o—endosmosis. FFF is also one further electro—osmosis process. Electro—osmosis is the motion o: l iquid, such as water, d by an applied potential or electric field across a porous material, capillary tube, membrane, microchannel, or any other uid conduit. The voltage generated by the electric field is pre'ferably between lO—lOO V.

The liquid containing ion/salt and or free sugars of the slurry are ted from the cel'u' ose, such as microfibrillated ce"ulose, by removing the liquid. It can preferably be done by di""erent " iitering techniques.

The s;urry comprises ose, such as microfibrillated cellulose, and a . The liquid may be water, a solvent and mixtures 0 di" "erent solvents and/or liquids. The t may be an alcohol, such as isopropanol, polyethylene glycol, glycol or ethanol. It can also be an acid or base. Solvents, such as isopropano; , can change the surface tension o: the slurry and this will promote dewatering. The solvent may also be a solvent having at least one ketone group, and this may preferably be acetone. "t is a' so possible that the liquid is an ionic .

The slurry may a:.80 comprise nanopar':icles, rs, pigments, salts and/or surfactants which are s:imulated by the electric field and will ir1prove the liquid migration and movement, i.e. she flow, in the electric field and thus also the dewatering.

According to a further preferred embodiment o: the presen ion the washing liquid is water and/or an organic solven .

The organic solvent is preferably acetone. In case drying is desirable as a —up 0: the process according to the firs aspect as set out earlier, water (most pre:ferred distilled water) is preferred as washing liquid in case 0: the ose being MFC, NCC, NFC or other cellulose deriva':ive in a more e "icient way (solvents should there be avoided) to avoid hornification.

The slurry rmay also as set out above comprise fibers 0' regular length. It is also possible that the slurry comprises __I' 'ers, such as nanoclays, polymeric based absorbents, PCC, Kaolin or calcium carbonate. The amounts 0' microfibrillated ce' 'ulose in the slurry may be n 20—90% by weight, :he amount 0 - regular sized fibers such as kra:ft, hardwood and/or softwood fibers may be lO—80% by weight. larger amounts or __|' lers and longer fibers are present in the slurry it is possible to achieve a s:_urry with very high dry content by using the dewa':ering process according to the invention. A dry content o: up to 90% by weight is possib:_e to achieve since the present 0 long fibers and/or fillers wi 'l make it easier to dewater the It is however, preferred to use a slurry comprising high amoun VS O micrO'=ibril'ated cellulose. A slurry comprising microfibrillated ose in an amount 0: 80—lOO% by weight, or 80—90% by weight, is often preferred. "n many cases it is preferred that the slurry comprises 100% O" microfibrillated cellulose, i.e. no fibers 0" longer size is present. The amount 0' microfibrillated cellulose depends on the end use 0: the microfibrillated ce'lu'ose.

It may also be advantageous to subject the slurry to increased pressure in combination with the e'ectric field. "t has been shown that the combination 0" electric "ield and pressure will ly e the purification, preferably by using dewatering, o: a slurry comprising cellulose, such as microfibril'ated cellulose. "t is red to apply the pressure after the dewatering with the e'ectric "ie'd has started, i.e when the solid content ol the s:_urry has increased, pre:ferably to about 4% by weight. the solid content ol the slurry is too low when the pressure is applied, the microfibrillated cellu:_ose is pressed through the openings o: the dewatering device er with the water and no purification (such as salt/ion depletion and/or free sugar ion) o: the microfibri'lated cellulose will occur. When the solid content ol the slurry is increased, the viscosity is also increased and it is possible to apply pressure to the slurry and be able to increase the dewatering I) the slurry.

The pressure is preferab— y a mechanical pressure being applied in any possible way. It le to use, for example a roll nip, belt or "elts "or applying the mechanical re to slurry during dewatering.

It is also possible to combine the ent with the ic field with other kind ol treatmen tS in order to increase the dewatering. ixamples 0" other treatments besides increasing the pressure are acoustic and vacuum based systems.

The dry content 0: the slurry comprising cellulose, such as microfibrillated cellulose, before ing, such as salt/ion depletion and/or free sugar depletion, preferably by using dewatering, is about l—50% by weight. It may also have about 1— % by weight or about l—lO% by weight.

After the treatmenc according to the process ol the first aspect it is preferred that the dry content 0: the dewatered slurry comprising cellulose, such as microfibrillated cellulose, is about 5—50% by weight, more preferably above 20% by weight. It is thJS possible to receive a slirry comprising microfibril'ated ose with very high dry content in a very energy e "icient way. Even though the dry content is increased the properties or the ibrillated cellulose after dilution 0" water is maintained, e.g. the water swelling properties and strength.

The temperature 0: the slurry may be below 30°C before dewatering and increased during the ring process but Kept at a temperature below 100°C. However, lower temperatures, for example room temperatures are also possible. The ature should preferably be kept below boiling point. Increased temperature may improve the dewatering. This is due to that that the viscosity 0: water is decreased.

The present invention also relates to cellulose, such as microfibrillated cellulose, being purified according so she process ol the first aspect above. It has been shown chac by ing, such as salt/ion deplete and/or free sugar deplete, preferably by using ring, a slurry comprising ce'lu'ose, such as microfibri'lated cellulose, by the aid 0: an ic fie'd, no or very limited hornification O" the microfibri'lated cellu'osic fibers wi 'l OCCUK. It is thus possible to produce a microfibril'a:ed cellulose with improved ties in a fast and very energy e t way compared to the use 0 "or example drying techniques.

A microfibri' lated cellulose fiber is normally very thin (~20 nm) and :he length is o:ften between 100 nm to 10 um.

However, the micro:fibrils may also be longer, for example between L0—200 um, bu: _lengths even 2000 um can be found d Je to wide length dis:ribution. Fibers that has been fibri' la:ed and which have microfibri 's on the surface and ibri' S that are separated and d in a water phase 0 " a slurry are included in the definition MFC. Furthermore, whisgers are also included in the definition MFC.

The microfibrillated cellulose is typically made from wood ce'lulose fibers, it is possible to use both hardwood and softwood fibers. "t can also be made from microbial SOUYCGS, ltural fibers, such as wheat straw pulp or other non—wood fiber s. It can also be produced by bacteria or made from CMC.

Using this ic field set out in the first aspect o: the invention, in addition also reduces the number 0: bacteria as their cell walls will blow up. The process 0. the first aspect, as it removes ions, also removes ions and wa':er also from microbes. This means cha this ion removal and water removal will kill/antimicrobial e EC According to a further pre'ferred embodiment o: the present invention the process according to the first aspec o. the invention may be followed by one or more modi:fication steps, such as a counter—ion change as set out below.

According to a further pre'ferred embodiment o_ she present ion the cellu:_ose according to the second and the third aspec may further be processed by using ion exchange e.g. as disclosed in WOQOO9' 96’06 which disc:_oses a method for ing ce"ulose fibers. "t wou:_d be :_e to change cellulose to di "erent counter—ion IOrms to get e.g. CMC adsorbed/absorbed inco fibres. Thus it wou:_d e.g. be possible to have a sodium CO inter ion modi:fication to enhance MFC production. It would also be possible to e.g. go from Ca—form to Na—form and vice versa.

According to a "urcher red embodimenc of the t invention counter—ion change, which preferably fol'ows after the process steps 0. the first aspect, may be per:formed through a process comprising the following steps: ]J washing ions away from she pu:_p with electro osmosis (until she filtrate conductivi:y is :_ow enough) — optionally followed by addition 0' liquid, pre':erably distil' ed wafer, 2) washing the “clean” pu:_p with a sodium carbonate such as NaHCO3 and a basic agent , such as NaOH (to increase the pH to about 9) — preferab' y this may be done by adding NaHCO3 and NaOl into the washing liquid o: the o—osmosis apparath washing the pulp with distilled wa':er in the electro—osmosis apparatus to remove excess s.

Changing o: the counter—ions as set out above could be desirable in several applications; to make pu:_p more homogenous for chemical reactions, for enabling di "erent chemical reactions, - LOI improved reactivity 0: the pulp, - LOI improved drying or improved pergativity 0'' - LOI the one’s dried pulp. "n barrier applica':ions, which may be multi—layered, as set out in the fourth aspecc O_ the presen: invention the use of the cellulose according to the second and third aspect may be especially ble in ing o: electronic equipment, or when making solar ce' 's or batteries from ose, due to purity.

The purified ce' 'ulose according to the second and third aspect can be present as low metal pulps. As such they may be use ul "or low conductivity paper (due to di—electrical prop rti s), nzym tr atm nts o: pulps or as pulp for chemical modifications.

The purified cellulose according to the second and third aspect in the form 0" micro*ibrillated cellulose may be especially useful in the __O' lowing applications/uses: — rs due to improved "ilm "orming properties — washing powders due to ved Cafi removal (absorbs/adsorps) or in other similar applications where hard wa':er is a problem — cleaning drinking water as it is le to achieve improved heavy metal removal from drinking waters (this is still a large problem in some areas 0:: word) — by oxidation and di "erent additives one can improve metal absorption properties — metal absorbents which are biodegradable Preferred features 0'' each aspect o: the invention are as for each 0: the other aspects mutatis mutandis. The prior art documents mentioned herein are incorpora ced to the fullest extent permitted by law. The invention is further described in :he following examples, :ogether wich she appended figures, the only purpose 0: which is :o illustrace she invention and are in no way intended to limit the scope o. she invention in any way.

Figures Figure 1 disc:_oses the dewatering setup scheme (left) and cathode plate with holes.

Figure 2 disc:_oses dependencies of t and mass of collected water on time at constant d voltage 20 V.

Figure 3 disc:_oses dewatering of 'ow tivity MFC.

Figure 4 dis closes time dependencies of the water mass cted during dewatering 0:5 low conductivity MFC at di""erent vo:_tages are ted.

Examples 1.Experimental set-up For investigation 0: MFC dispersion dewatering an experimental setup was assembled, scheme 0: which is on Fig. 1.

It consiscs o a plastic pipe with interna' diameter 46 mm, fitted in:0 a stainless steel funne'. At the lower end 0. she pipe there is a plate with holes, a:_so made 0:_ stainless s:eel, which serves as the lower electrode, usually cathode. A paper __|' ter is placed on the plate, the MFC dispersion is loaded onto she filter. On top or the MFC column there is one more paper __|' ter, a fter this the upper electrode (anode) is placed.

The best results were achieved with platinum electrode — no process changes due to the electrode corrosion or ination were observed.

The setup 0; Fig. l constituted a cell with MFC investigated; DC voltage was applied inco it jrom the current . The water, emerging jrom she junnel was assembled into beaker, which was situated on top of a balance; the mass or the water ex d from MFC was registered during experiments. The experiments y were carried out in two modes: with a voltage U constant or with current i constant.

Dependencies of current and mass of collec:ed water on time at constant applied voltage 20 V is disclosed in Figure 2. An increase of re increase both 2 causes an or current and ent 0' co'lected water.

Surprisingly it was thus found that electro—osmosis dewatering may be used i:'I - in the beginning (more or less) only electro—osmosis is used - due to dewatering the viscosity wi '1 increase enough — that mechanical re may be applied (as reflected in Fig. 2) Figure 3 discloses dewatering of low conductivity MFC.

Figure 4 disc:_oses time dependencies of the water mass collected during dewatering of low conductivity MFC at di "erent voltages are presented. The voltage increase causes an increase o: dewatering speed (initial slope) and process saturation value.

Example 2 Re:ference MFC (initial MFC) — dry content (LR) 1.7% Sa Lt/Metal contents based on dry matter; Al 9.5 mg/g Fe L6 mg/g Ca L200 mg/kg Cu 5.5 mg/kg K 310 mg/kg g 210 mg/kg L.l mg/kg L400 mg/kg L.6 mg/kg ?b L.l mg/kg Si 76 mg/kg Zn 5.9 mg/kg Dewatering procedure 1 - only ng water; A paper 1 oer was places on cathode then MFC and then a second paper 1 oer. A Ler chis the anode was laid on she top 0. :his. The pressure (o: weigh 0 L anode) was 750 kPa. After shor time (2 min) an additional weight was added (pressure to 2400 ?a). The voltage during dewa':ering was 100V and time 640s. ?rocedure was repeated 3 times and pressure was increased (last time 4.6* 10A5 Pa).

Dewatered MFC (electro—osmosis MFC)—results are given below: Salt/Metal contents based on dry matter 30.5% Al 8.5 mg/kg Fe ll mg/kg Ca 30 mg/kg Cu 0.69 mg/kg K 85 mg/kg g 5.7 mg/kg n 0.24 mg/kg Va 12 mg/kg Vi 0.68 mg/kg ?b <0.4 mg/kg Si L3 mg/kg Zn ;.5 mg/kg Example 3 Reference MFC (initial MFC) — dry content (IR) 1.7% Salt/Metal ts based on dry matter; A1 9.5 mg/g Fe L6 mg/g Ca L200 mg/kg Cu 5.5 mg/kg K 310 mg/kg g 210 mg/kg n L.l mg/kg Va L400 mg/kg Vi L.6 mg/kg ?b L.l mg/kg Si 76 mg/kg Zn 5.9 mg/kg Dewatering procedure 2 — removing water and washing with acetone MFC was dewatered 5 min (as in procedure 1 above i.e. ixample 9). Aster this the current was switched o and acetone was added (about the same amount as water was removed in previous step). A:fter this dewatering was started and continued about 10 min. red MFC (electro—osmosis MFC with acetone)—results given below: Salt/Metal contents based on dry matter 23.5% Al 4.6 mg/kg Fe L0 mg/kg Ca L0 mg/kg Cu 0.68 mg/kg K 40 mg/kg g 7.; mg/kg n 0.;3 mg/kg Va 14 mg/kg Vi 0.50 mg/kg ?b <0.4 mg/kg Si L3 mg/kg Zn ;.5 mg/kg Example 4 — Temperature test Using the same set up as out above, temperature tests were performed.

Temperature 90 — 95 °C — ring in 60s = about L6 g water Temperature 21 °C — dewatering in 60s = about L3.5 g water Accordingly it was beneficial to use higher temperature to improve dewatering. Thus the energy needed for dewatering is much lower at elevated temperatures. ixamp'e 5 A further trial was done where even more ions (especially Ca2+ ions) were removed.

In the start the total amount was 20 g 0: wet MFC. l)about ll g 0: water was removed with electro—osmosis a.netal content 0: the water i. Ca 14 mg/l ii. K 2.7 mg/l iii. Na 26 mg/l iv. Si 1.3 mg/l 2) about "0 g 0" ed water was added 3)abou: "0 g 0: water was d l content 0: the water i. Ca 8 mg/l ii. K 0.56 mg/l iii. Na 0.78 mg/l iv. Si 0.22 mg/l 4)abou: 10 g o" discil'ed water was added )abou: 9 g 0: water was removed a” metal contenc o_ the water i. Ca 7.4 mg/l ii. K 0.56 mg/l iii. Na 0 mg/l (below detection limit) iv. Si 0.076 mg/; 6) distilled water (as reference) a” metal t 0: the water i. Ca 0.079 mg/l ii. K 0(below detection limit) iii. Na 0(below detection limit) iv. Si 0(below detection limit) "n view o: the above detailed description o: the present invention, Other modifications and variations will become apparent to those skilled in the art. However, it shou;d be apparent that such other modifications and variations may be e""ected t departing from the spirit and scope or the invention.

I

Claims (15)

WE CLAIM:

1. Process for purifying by salt/ion depletion and/or free sugar depletion, a slurry comprising cellulose, wherein the process comprises the following steps: -providing a slurry comprising cellulose and liquid, -subjecting the slurry to a first application of an electric field inducing the liquid of the slurry to flow, -separating the liquid from the cellulose thus obtaining a liquid depleted slurry, -adding a washing liquid to the liquid ed slurry -subjecting the liquid depleted slurry to a second application of an electric field inducing the washing liquid of the slurry to flow and -separating the g liquid from the cellulose, thus obtaining a purified cellulose.

2. The s according to claim 1 wherein the liquid separation is done by electroosmosis.

3. The process according to any one of the preceding claims wherein the electric field has a e of 10-100 V.

4. The process ing to any one of the preceding claims wherein pressure also is applied to separate the liquid from the ose.

5. The process according to claim 4 wherein the pressure is applied after the electric field has been applied and the liquid separation has started.

6. The process according to any one of claims 4-5 wherein the re is a mechanical pressure.

7. The process according to any one of the preceding claims wherein the dry content of the slurry comprising cellulose, before liquid separation, and/or salt/ion depletion and/or free sugar ion, is about 1-50% by weight.

8. The process according to any one of the ing claims wherein the dry content of the liquid depleted slurry comprising cellulose, is about 5-50% by weight. AH26(13619370_1):KEH

9. The process according to any one of the preceding claims wherein the temperature of the slurry during liquid separation is above 30°C and below 100°C.

10. The process according to any one of the preceding claims wherein the slurry comprises nanoparticles, absorbents, salt, free sugars and/or surfactants which are stimulated by the electric field.

11. The s according to any one of the ing claims wherein the washing liquid is water and/or an organic solvent.

12. The process according to any one of the preceding claims, n the cellulose is microfibrillated cellulose.

13. The s according to any one of the preceding claims further sing a counterion change and/or one or more further washing steps.

14. Cellulose, obtained by the process according to any one of claims 1-12.

15. Use of a cellulose, according to claim 14 in a strength additive, a thickener, a viscosity modifier, a rheology modifier, a cleaning , a washing powder, a detergent, a foam composition, a barrier, a film, a food product, a pharmaceutical composition, a ic product, a paper or board product, a coating, a e/absorbent product, an emulsion/dispersing agent, a ng mud, a composite material , in water purification, in a filter, in a solar cell, in a battery, in an electronic circuit, or to enhance the reactivity of cellulose in the manufacture of regenerated cellulose or cellulose derivatives.