NZ718115B2 - 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. 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 ing, such as salt/ion deple:ion and/or free sugar depletion, preferably by using dewatering, a slurry comprising 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 cellul_ose or CMC etc. "n micrO':ibrillated cellulose the individua' =ibrils have been partly or totally detached from each other.

Microfibrillated cellulose has a very high water binding ty and it is thus very di icu'L to reduce the water content o_ a slurry comprising 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 ation 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 . These techniques 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 techniques. iorni.:ica ,ion is when irreversible bonds between the Sibers are ‘ormed. When horni:fication has occurred it is not le 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 addition o: chemicals which physica:_ly prevent or modi.iy she jibers in such way chat she "orma ion 0' bonds between ose 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 jibers.

Further there is disclosed by L Jchache et al. in Annals o: the University o:: Craiova, ilectri C ingineering , 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 sing cellulose, such as micrO' ted cellulose 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 ose constituents. Since a filter cake is formed during ring, a higher resistance to dewatering is obtained. At the same time, it is more difficult 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 provide 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 ose and a liquid, -subjecting the slurry to an electric field ng 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 an electric field inducing the g liquid of the slurry to flow, and -separating the washing liquid from the cellulose, thus obtaining a purified cellulose.

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

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

The present invention also provides according to a fourth aspect, use of the cellulose according to the second or the third aspect in a strength additive, a thickener, a ity modifier, a rheology modifier, a cleaning powder, a washing powder, a ent, a foam composition, a barrier, a film, a food product, a ceutical composition, 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 cation, 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 derivatives.

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

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 stimulation of other external sources such as mechanical or l or magnetic field. One example is an ultrasound treatment. The purifying, may also be followed by any one or a combination f of the below methods to further dry the material: AH26(11116350_1) 1) Drying methods by evaporation 2) Freeze drying because of sed solids 3) Adding de-hornification additives can also be used in drying of dewatered material 4) dewatered material may also partially 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 voltage 0: 10- lOO V is used. Increasing the vol cage ,ypically increases the wa:er extraction rate. The al 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 depletion and/or free sugar deple :ion, o: the slurry, preferably when using dewatering. The pressure may be d a.:ter she electric field has been applied and :he dewatering o: the slurry has been started. This is due to tha it may be preferred to increase the dry content 0: the s' urry before pressure is app:_ied. r possibili:y is to have weak dewatering inI_‘4—A _Eie' d simultaneously as mechanica:_ pressure is applied. However, it s 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 ing to the process i, is preferred that the dry content 0. she purified, such as salt/ion depleted and/or free sugar ted, pre:ferably 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 involving dewatering, is ably 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.

Further, aromas may be ed.

The present invention also relates to ce:_lulose, such as microfibrillated cellulose, being purified, such as salt/ion ed and/or free sugar depleted, pre'ferab' y by using dewatering according to the process bed 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 micro:fibrillated cellulose by the aid o:: an e' ectric "le- d no or very d horni-=ication c" the micrO'fibril' ated ce'lu' osic fibers will OCCUK.

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

It is intended throughout the present description that the expression "cellulos e” embraces any type of ce'lulose, such as cellu'ose fibres (cellulose material). The ce"u'ose may also be a microfibrillated ce' 'u'ose (MFC). The ose may be bleached or unbleached. The ce' _u_ ose may also be crystalline cellulose, 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:_ properties), 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 a' pU' p, mechanical pulp, :hermomechanical 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 mixture o:: pine and spruce or a mixture 0: birch and spruce. The al pulps that may be used in the present invention include all types 0: chemical wood— based pulps, such as bleached, ha' f—bleached 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. , bamboo or ).

It is intended hout 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 cellulose, such as microfibril'ated cellulose fibers to an electric field the purification such as salt/ion depletion and/or free sugar depletion, preferab'y by using dewatering can strongly be improved. One theory 0: why it works so well, is that the electric field s 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 ical treatment will do. Pilling the water molecules will make it possible to also remove water molecules being absorbed by the microfibri'lated fibers in a very e "icient way.

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

It has been shown that by purifying, such as salt/ion depletion and/or free sugar depletion, preferab'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 ing 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 ve, a thickener or as a viscosity er. Furthermore, the g y 0: the dewatered microfibrillated cellulose is also very good, i.e. no subStantial decrease in bonding ability is seen.

When it comes to on 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 filtrate. This leads to a decrease in the specific conduc civity o_ the product and a decrease in the conductivity 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 electro—endosmosis. FFF is also one further o—osmosis process. Electro—osmosis is the motion o: l iquid, such as water, induced by an applied potential or electric field across a porous material, capillary tube, membrane, hannel, 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 separated from the cel'u' ose, such as microfibrillated ce"ulose, by removing the liquid. It can ably be done by di""erent " iitering techniques.

The s;urry comprises cellulose, such as ibrillated cellulose, and a liquid. The liquid may be water, a solvent and mixtures 0 di" "erent ts and/or liquids. The solvent 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 ring. The t 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 liquid.

The slurry may a:.80 comprise nanopar':icles, polymers, 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 ring.

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

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

The slurry rmay also as set out above se 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 between 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 r the slurry.

It is however, red to use a slurry comprising high amoun VS O micrO'=ibril'ated cellulose. A slurry comprising microfibrillated cellulose 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 improve the purification, preferably by using dewatering, o: a slurry comprising cellulose, such as microfibril'ated cellulose. "t is preferred to apply the pressure after the dewatering with the e'ectric "ie'd has started, i.e when the solid t ol the s:_urry has sed, rably 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 together with the water and no purification (such as salt/ion depletion and/or free sugar depletion) o: the microfibri'lated cellulose will occur. When the solid content ol the slurry is sed, 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 possible to use, for example a roll nip, belt or "elts "or applying the mechanical pressure to slurry during dewatering.

It is also possible to combine the ent with the electric field with other kind ol en tS in order to se the dewatering. ixamples 0" other treatments s increasing the pressure are acoustic and vacuum based systems.

The dry content 0: the slurry comprising ose, such as microfibrillated cellulose, before purifying, such as salt/ion ion and/or free sugar depletion, preferably by using ring, 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 ibrillated cellulose, is about 5—50% by weight, more preferably above 20% by weight. It is thJS possible to receive a slirry comprising microfibril'ated cellulose with very high dry content in a very energy e "icient way. Even though the dry content is increased the properties or the microfibrillated 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 temperature should preferably be kept below boiling point. sed 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 ed according so she process ol the first aspect above. It has been shown chac by purifying, such as salt/ion deplete and/or free sugar deplete, preferably by using dewatering, 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 properties in a fast and very energy e "icient way compared to the use 0 "or e 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 fibrils may also be longer, for e 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 located 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 od fibers. "t can also be made from microbial S, agricultural fibers, such as wheat straw pulp or other non—wood fiber sources. It can also be produced by bacteria or made from CMC.

Using this electric 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 ment o: the present invention the process according to the first aspec o. the invention may be ed 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 invention 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 modifying ce"ulose fibers. "t wou:_d be possib:_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 e MFC production. It would also be possible to e.g. go from Ca—form to m and vice versa.

According to a "urcher preferred embodimenc of the present invention counter—ion change, which preferably fol'ows after the process steps 0. the first aspect, may be per:formed h a process comprising the ing steps: ]J washing ions away from she pu:_p with o s (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 se the pH to about 9) — preferab' y this may be done by adding NaHCO3 and NaOl into the washing liquid o: the electro—osmosis apparath washing the pulp with distilled wa':er in the electro—osmosis apparatus to remove excess Na—ions.

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 vity 0: the pulp, - LOI improved drying or improved re—dispergativity 0'' - LOI the one’s dried pulp. "n r 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 desirable in ing o: electronic equipment, or when making solar ce' 's or batteries from cellulose, due to purity.

The purified ce' 'ulose according to the second and third aspect can be t 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: — barriers due to ed "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 possible 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 ves 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 current and mass of collected water on time at constant applied voltage 20 V.

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

Figure 4 dis closes time dependencies of the water mass cted during ring 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:_ ess s:eel, which serves as the lower electrode, usually e. 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 contamination were observed.

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

Surprisingly it was thus found that o—osmosis dewatering may be used i:'I - in the beginning (more or less) only electro—osmosis is used - due to dewatering the ity wi '1 increase enough — that mechanical pressure 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 ted 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 tion value.

Example 2 Re:ference MFC (initial MFC) — dry t (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 removing 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: etal 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 contents 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 red 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.

Dewatered MFC (electro—osmosis MFC with acetone)—results given below: Salt/Metal ts 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 — dewatering 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. t ll g 0: water was removed with o—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" disti"ed water was added 3)abou: "0 g 0: water was removed a.netal 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 ion limit) iv. Si 0.076 mg/; 6) distilled water (as reference) a” metal content 0: the water i. Ca 0.079 mg/l ii. K 0(below detection limit) iii. Na w 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 nt to those skilled in the art. However, it shou;d be apparent that such other modifications and variations may be e""ected without 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 sing 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 depleted slurry -subjecting the liquid depleted slurry to a second ation 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 ose.

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

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

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

5. The process according to claim 4 wherein the re 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 pressure 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 on depletion and/or free sugar depletion, is about 1-50% by weight.

8. The process according to any one of the preceding 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 tion is above 30°C and below 100°C.

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

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

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

13. The process according to any one of the ing claims further comprising 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, ing to claim 14 in a strength additive, a thickener, a viscosity modifier, a rheology modifier, a cleaning powder, a washing , a ent, a foam ition, a barrier, a film, a food product, a pharmaceutical composition, a cosmetic product, a paper or board product, a g, 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, or to enhance the reactivity of cellulose in the manufacture of regenerated ose or cellulose derivatives.