EP2553165B1 - Methods to reduce metals content of bleached pulp while reducing bleaching cost in a chemical pulping process - Google Patents
Methods to reduce metals content of bleached pulp while reducing bleaching cost in a chemical pulping process Download PDFInfo
- Publication number
- EP2553165B1 EP2553165B1 EP11766310.4A EP11766310A EP2553165B1 EP 2553165 B1 EP2553165 B1 EP 2553165B1 EP 11766310 A EP11766310 A EP 11766310A EP 2553165 B1 EP2553165 B1 EP 2553165B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- urea hydrochloride
- pulping
- oxidizer
- pulp
- bleaching
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 238000000034 method Methods 0.000 title claims description 78
- 230000008569 process Effects 0.000 title claims description 48
- 238000004537 pulping Methods 0.000 title claims description 33
- 239000000126 substance Substances 0.000 title claims description 17
- 229910052751 metal Inorganic materials 0.000 title description 30
- 239000002184 metal Substances 0.000 title description 30
- 150000002739 metals Chemical class 0.000 title description 27
- 238000009895 reductive bleaching Methods 0.000 title 1
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 claims description 54
- VYWQTJWGWLKBQA-UHFFFAOYSA-N [amino(hydroxy)methylidene]azanium;chloride Chemical compound Cl.NC(N)=O VYWQTJWGWLKBQA-UHFFFAOYSA-N 0.000 claims description 44
- 239000004155 Chlorine dioxide Substances 0.000 claims description 27
- 239000007800 oxidant agent Substances 0.000 claims description 23
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 21
- 235000019398 chlorine dioxide Nutrition 0.000 claims description 15
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 8
- 239000001301 oxygen Substances 0.000 claims description 8
- 229910052760 oxygen Inorganic materials 0.000 claims description 8
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 claims description 5
- 230000003247 decreasing effect Effects 0.000 claims description 3
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 29
- 238000004061 bleaching Methods 0.000 description 29
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 17
- 239000012535 impurity Substances 0.000 description 17
- 239000002023 wood Substances 0.000 description 17
- 229920005610 lignin Polymers 0.000 description 13
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- 239000000203 mixture Substances 0.000 description 11
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 10
- 229910052791 calcium Inorganic materials 0.000 description 10
- 239000011575 calcium Substances 0.000 description 10
- 239000000123 paper Substances 0.000 description 10
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 9
- 238000010411 cooking Methods 0.000 description 9
- 229910052742 iron Inorganic materials 0.000 description 8
- 229910052723 transition metal Inorganic materials 0.000 description 7
- XTEGARKTQYYJKE-UHFFFAOYSA-M Chlorate Chemical compound [O-]Cl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-M 0.000 description 6
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 6
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 6
- 239000002655 kraft paper Substances 0.000 description 6
- 238000006722 reduction reaction Methods 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 150000003624 transition metals Chemical class 0.000 description 6
- 238000005406 washing Methods 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 5
- 239000002253 acid Substances 0.000 description 5
- 150000007513 acids Chemical class 0.000 description 5
- 229920002678 cellulose Polymers 0.000 description 5
- 239000001913 cellulose Substances 0.000 description 5
- 238000000605 extraction Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000007254 oxidation reaction Methods 0.000 description 5
- 150000002978 peroxides Chemical class 0.000 description 5
- 239000000377 silicon dioxide Substances 0.000 description 5
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 4
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 4
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 4
- 229920002522 Wood fibre Polymers 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 229910052788 barium Inorganic materials 0.000 description 4
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 4
- 239000007844 bleaching agent Substances 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 230000029087 digestion Effects 0.000 description 4
- 229910052749 magnesium Inorganic materials 0.000 description 4
- 239000011777 magnesium Substances 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 239000011572 manganese Substances 0.000 description 4
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 229910052938 sodium sulfate Inorganic materials 0.000 description 4
- 235000011152 sodium sulphate Nutrition 0.000 description 4
- 239000002025 wood fiber Substances 0.000 description 4
- 229920002488 Hemicellulose Polymers 0.000 description 3
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 3
- 239000000654 additive Substances 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 150000001805 chlorine compounds Chemical class 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 230000001419 dependent effect Effects 0.000 description 3
- -1 lime Chemical compound 0.000 description 3
- 150000002927 oxygen compounds Chemical class 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 239000011734 sodium Substances 0.000 description 3
- 229910052708 sodium Inorganic materials 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 2
- 241000196324 Embryophyta Species 0.000 description 2
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 2
- 235000011941 Tilia x europaea Nutrition 0.000 description 2
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- DIZPMCHEQGEION-UHFFFAOYSA-H aluminium sulfate (anhydrous) Chemical compound [Al+3].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O DIZPMCHEQGEION-UHFFFAOYSA-H 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 238000003339 best practice Methods 0.000 description 2
- 229910000019 calcium carbonate Inorganic materials 0.000 description 2
- 239000004202 carbamide Substances 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 239000011121 hardwood Substances 0.000 description 2
- 230000007062 hydrolysis Effects 0.000 description 2
- 238000006460 hydrolysis reaction Methods 0.000 description 2
- 229910010272 inorganic material Inorganic materials 0.000 description 2
- 239000011147 inorganic material Substances 0.000 description 2
- 239000004571 lime Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 230000014759 maintenance of location Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003002 pH adjusting agent Substances 0.000 description 2
- 229940072033 potash Drugs 0.000 description 2
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Substances [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 2
- 235000015320 potassium carbonate Nutrition 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 229910052979 sodium sulfide Inorganic materials 0.000 description 2
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 2
- 235000000346 sugar Nutrition 0.000 description 2
- 150000008163 sugars Chemical class 0.000 description 2
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- 229920003043 Cellulose fiber Polymers 0.000 description 1
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical class S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 description 1
- 102000004190 Enzymes Human genes 0.000 description 1
- 108090000790 Enzymes Proteins 0.000 description 1
- QPCDCPDFJACHGM-UHFFFAOYSA-N N,N-bis{2-[bis(carboxymethyl)amino]ethyl}glycine Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(=O)O)CCN(CC(O)=O)CC(O)=O QPCDCPDFJACHGM-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 240000005809 Prunus persica Species 0.000 description 1
- 235000006040 Prunus persica var persica Nutrition 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- SSBRSHIQIANGKS-UHFFFAOYSA-N [amino(hydroxy)methylidene]azanium;hydrogen sulfate Chemical compound NC(N)=O.OS(O)(=O)=O SSBRSHIQIANGKS-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- 229940037003 alum Drugs 0.000 description 1
- 150000001412 amines Chemical group 0.000 description 1
- 239000012736 aqueous medium Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 239000000920 calcium hydroxide Substances 0.000 description 1
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 1
- QXDMQSPYEZFLGF-UHFFFAOYSA-L calcium oxalate Chemical compound [Ca+2].[O-]C(=O)C([O-])=O QXDMQSPYEZFLGF-UHFFFAOYSA-L 0.000 description 1
- 239000001506 calcium phosphate Substances 0.000 description 1
- 229910000389 calcium phosphate Inorganic materials 0.000 description 1
- 235000011010 calcium phosphates Nutrition 0.000 description 1
- 239000003518 caustics Substances 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 238000005187 foaming Methods 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 1
- AMWRITDGCCNYAT-UHFFFAOYSA-L manganese oxide Inorganic materials [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 description 1
- PPNAOCWZXJOHFK-UHFFFAOYSA-N manganese(2+);oxygen(2-) Chemical class [O-2].[Mn+2] PPNAOCWZXJOHFK-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 150000002898 organic sulfur compounds Chemical class 0.000 description 1
- 230000020477 pH reduction Effects 0.000 description 1
- 239000011087 paperboard Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000000565 sealant Substances 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 239000000344 soap Substances 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 239000011122 softwood Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- YBBRCQOCSYXUOC-UHFFFAOYSA-N sulfuryl dichloride Chemical compound ClS(Cl)(=O)=O YBBRCQOCSYXUOC-UHFFFAOYSA-N 0.000 description 1
- 230000008961 swelling Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Images
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
- D21H17/03—Non-macromolecular organic compounds
- D21H17/05—Non-macromolecular organic compounds containing elements other than carbon and hydrogen only
- D21H17/11—Halides
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1026—Other features in bleaching processes
- D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
- D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
Definitions
- the majority of corrugated boxes, paper grocery bags, fine papers, and market pulps are produced by a sulfate pulping process known as "Kraft" pulping.
- Kraft pulping wood chips are added to an aqueous medium.
- the liquor in which the wood chips are cooked comprises a mixture of black and white liquor, the black liquor being liquor added back to the cooking vessel, or digester, from a prior batch of wood chips and the white liquor being a freshly prepared alkaline solution as described below.
- Black liquor varies considerably among different mills depending on the white liquor used, the wood employed, and the method of cooking.
- Typical white liquor is a solution of sodium hydroxide, sodium carbonate, sodium sulfate, sodium sulfide and various inorganic materials. White liquor solubilizes the pulp and removes the lignin from the wood fibers as described below.
- the largest part of the organic matter removed from the wood during cooking is combined chemically with sodium hydroxide in the form of sodium salts.
- Some of these compounds are resin soaps which account for the intense foaming properties of black liquor.
- organic sulfur compounds and mercaptans which give the characteristic odor to the sulfate-containing black liquor, and small amounts of sodium sulfate, silica and other impurities such as lime, oxide, alumina, potash, and sodium chloride can be present in the black liquor.
- the reaction conditions present during the cook, or digestion cause lignin, the amorphous polymeric binder found in wood fibers, to be hydrolyzed.
- wood chips are digested only long enough to dissolve sufficient lignin to free the cellulosic wood fibers but maintain sufficient lignin intact to provide added strength to the paper.
- the pulping process attempts to maximize pulp yield, which is defined as the dry weight of pulp produced per unit dry weight of wood consumed.
- Bleaching typically involves contacting the pulp with an oxidizer, such as a chlorine compound, for example, chlorine dioxide, or with an oxygen compound, such as ozone, oxygen, peroxide, or the like.
- an oxidizer such as a chlorine compound, for example, chlorine dioxide
- an oxygen compound such as ozone, oxygen, peroxide, or the like.
- the effectiveness of bleaching is highly pH dependent, The respective pH levels can be adjusted downwards as necessary by adding thereto pH adjusters such as acids or materials that will form acids in aqueous solution, such as sulfur dioxide, sulfuric acid, hydrochloric acid, or the like.
- pH adjusters can form insoluble sulfates, such as calcium sulfate, barium sulfate, and the like which are insoluble and unwashable.
- the metals and other impurities tend to remain associated with the fiber and are not washed out of the stock so that as the pH changes through the remaining processing, they tend to form scales on washer facewires, piping, and other associated equipment.
- pH adjusters can also convert transition metals such as iron and manganese to their highly colored sulfate form, resulting in brightness reversion and the need for additional bleaching to compensate for such brightness reversion. The costs associated with removing scaling and maintaining bleaching can be significant.
- a method of decreasing the amount of oxidizer required by a pulping or papermaking process comprising adding to a process stream or solution of the pulping or papermaking process urea hydrochloride to reduce the amount of oxidizer required by the pulping or papermaking process wherein the oxidizer comprises chlorine dioxide, ozone, oxygen, hydrogen peroxide, or combinations thereof is provided.
- a method of reducing one or more metals, impurities, or combinations thereof from a pulping or papermaking process comprises adding to a process stream or solution containing pulp, metals, impurities, or combinations thereof of the pulping or papermaking process an effective amount of urea hydrochloride to reduce metals, impurities, or combinations thereof from the pulping or papermaking process.
- the present disclosure is directed to methods to reduce scaling and bleaching cost in a chemical pulping process. Also described is a method to remove metals and other impurities from the bleached pulp.
- the methods include utilizing urea hydrochloride in place of and/or in addition to certain pH adjusters in a pulping process
- urea hydrochloride in paper and pulp processing has been previously described in U.S. Patent No. 7,029,553 to Williams et al.
- Williams et al. describes that urea hydrochloride can be used to adjust the pH of a process stream and reduce the amount of sulfuric acid used in a papermaking process.
- Williams et al. also describes that urea hydrochloride forms calcium chloride when it comes into contact with solutions to which calcium hydroxide has been added.
- Williams et al. fails to teach or suggest the removal of metals and/or other impurities from a pulping process.
- Williams et al. fails to recognize that a reduction in oxidizer can be realized by the use of urea hydrochloride.
- the present disclosure overcomes the shortcomings of the prior art in that the methods disclosed herein result in lower processing costs by reducing scaling and bleaching costs.
- the use of urea hydrochloride to remove metals and other impurities from pulp Also described herein is the use of urea hydrochloride to reduce brightness reversion in bleached pulps caused by oxidation of certain metals to their highly colored states.
- urea hydrochloride can minimize the amount of oxidizer used for bleaching.
- the methods of the present disclosure utilize urea hydrochloride in place of and/or in addition to certain pH adjusters in a pulping process, particularly a bleaching process.
- pH adjusters typically include acids or materials that will form acids in aqueous solution, such as sulfur dioxide, sulfuric acid, hydrochloric acid, or the like.
- urea hydrochloride can be used in addition to or as a substitution for any suitable pH adjuster as would be known in the art.
- the urea hydrochloride used in accordance with the present disclosure can be formed from any desired ratio of urea and hydrochloric acid that performs the desired function of metal removal.
- Urea hydrochloride suitable for use in the present invention can be prepared by mixing urea with hydrochloric acid at the desired ratio.
- a suitable method for preparing a 1:1 molar ratio urea hydrochloride salt is described in Example 1 of U.S. Pat. No. 5,672,279 .
- Suitable urea hydrochloride compositions are also commercially available.
- NOVOC A-Cl (Peach State Labs, Inc., Rome, Ga.), which is a 1:1 molar ratio aqueous urea sulfate solution containing 0.25% of a quaternary amine corrosion inhibitor.
- the methods of the present disclosure are described as being used in a Kraft pulping process.
- the present disclosure is not to be so limited. Any of the various equivalent wood cooking processes having the production of paper as its ultimate goal may also be employed. However, the Kraft process is described in more detail as follows.
- suitable trees are harvested, debarked and then chipped into suitable size flakes or chips.
- the wood chips that can be processed into pulp using the chemical pulping process of the present disclosure can be either hardwoods, softwoods or mixtures thereof. Such wood chips are sorted with the small and the large chips being removed. The remaining suitable wood chips are then moved to a digester.
- the digester is a vessel for holding the chips and a digesting composition.
- the digester is sealed and the digester composition is heated to a suitable cook temperature under high pressure. After an allotted cooking time at a particular temperature and pressure in the digester, the digester contents (pulp and black liquor) are transferred to a holding tank. The pulp in the holding tank is transferred to the brown stock washers while the liquid (black liquor formed in the digester) is sent to the black liquor recovery area. The black liquor is evaporated to a high solids content in evaporators.
- the Kraft cook is highly alkaline, usually having a pH of 10 to 14, more particularly 12 to 14.
- a Kappa number corresponds directly to the amount of lignin remaining in the pulp. Generally, the higher the Kappa number, the more lignin present in the pulp and, therefore, the higher the pulp yield.
- the Kappa number generally decreases as the digestion time is increased or the alkalinity of the cooking liquor is increased. The goal in such Kraft papermaking processes is to retain as much lignin as possible in order to enhance strength and to reduce the cost, while maintaining the uniformity of the cook. More uniform cooks result in a decreased percentage of rejects and, thereby, reduce costs for running paper mills.
- Cooking, or digestion, of the pulp may be terminated when the amount of rejects in the pulp is reduced to an acceptable level. Substantial yield and quality advantages are achieved if the wood chips are cooked to a higher lignin content. As a result, an increase in a Kappa number target by the use of thinner chips can result in a substantial cost savings.
- the thickness of chips obtainable on a commercial scale is always variable, A major portion of the total rejects frequently originate from a relatively small fraction of the chips having the greatest thickness. The objective in every pulping process is to achieve a lower percentage of rejects.
- Bleaching results in a whiter, brighter paper.
- Bleaching typically involves contacting the pulp with an oxidizer, such as a chlorine compound, for example, chlorine dioxide, or with an oxygen compound, such as ozone, oxygen, hydrogen peroxide, or the like.
- an oxidizer such as a chlorine compound, for example, chlorine dioxide
- an oxygen compound such as ozone, oxygen, hydrogen peroxide, or the like.
- the effectiveness of bleaching is highly pH dependent. The respective pH levels can be adjusted downwards as necessary by adding thereto pH adjusters as described herein.
- the present inventor has determined that pH adjusters, such as sulfuric acid, convert calcium, barium, and other metals present in the pulp to a sulfate form which is insoluble and unwashable.
- the pH adjusters also convert iron and manganese to their highly colored sulfate form. These materials tend to remain associated with the fiber and are not washed out of the stock, so as pH changes through the remaining process steps, calcium carbonate, calcium sulfate, barium sulfate, and iron and manganese oxides all form scales on washer facewires and in piping or associated equipment. Iron, manganese, copper, and the like, all catalyze the decomposition of the oxidizers and cellulose in the presence of oxygen.
- urea hydrochloride is utilized in place of and/or in addition to the pH adjuster and can remove a significant amount of these metals as well as other impurities, such as silica. Such removal reduces the material available for scaling, or that interfere with bleaching.
- the method of the present description is measurable, consistent, and results in pulp with significantly less metal and/or impurity contaminant. For instance, between about 5% and 75% of one or more of metals or other impurities are removed. In some described cases, between about 25% and 70% of one or more of metals or other impurities are removed while in some described cases, between about 50% and 60% of one or more of metals or other impurities are removed.
- the resulting pulp has a metals content of from about 30 mg/kg to about 200 mg/kg.
- Metals can include aluminum, calcium, barium, magnesium, potassium, sodium, and zinc as well as transition metals (especially manganese, copper, and iron transition metals) or combinations thereof.
- Impurities can include one or more of sodium sulfate, silica, lime, oxide, alumina, potash, sodium chloride or combinations thereof.
- An effective amount of urea hydrochloride is employed in a bleaching step of a chemical pulping process to improve the efficiencies of the chemical pulping processes.
- the effective amount depends on the particular urea hydrochloride employed and other factors including, but not limited to, wood type, the digester composition, the operating conditions of the digester, the mode of addition of the compounds including any additional compounds added, as well as other factors and conditions known to those of ordinary skill in the art.
- UCl urea hydrochloride
- UCl urea hydrochloride
- about 680.4 grams (1.5 lbs.) per ton of UCl was utilized in only one of the ClO 2 stages.
- pH control can be managed by use of sulfuric acid, as is the current practice. Addition of the UCl displaces sulfuric acid within the existing control schemes.
- the amount of oxidizer utilized in the process can be reduced when compared to a traditional chemical pulping process that does not utilize such urea hydrochloride.
- the amount of oxidizer can be reduced by about 10% when compared to traditional processes. In certain embodiments, the amount of oxidizer can be reduced by about 15% and in still other embodiments, the amount of oxidizer can be reduced by about 20%.
- brightness can improve from about 88% to about 90% when compared to traditional processes.
- Hydrochloric acid is known to react with chlorate (ClO 3 ) to form chlorine dioxide (ClO 2 ) in acidic environments.
- Chlorate is normally present in the bleach stage filtrate, so this is presumed to be responsible for some of the immediate reduction in bleaching chemical requirements.
- the amount of oxidizer added is from about 15.9 kg to 27.2 kg (35 to 60 lbs.) per ton ClO 2 , and about 6.8 kg to 9.1 kg (15 to 20 lbs.) per ton H 2 O 2 .
- oxidizer can include chlorine compound, for example, chlorine dioxide, or with an oxygen compound, such as ozone, oxygen, hydrogen peroxide, or the like. The effectiveness of bleaching is highly pH dependent.
- additives can be added to the alkaline aqueous mixture in the extraction stages.
- Typical additives include, but are not limited to, conventional additives known for use in a chemical pulping process.
- UCl was introduced into the first chlorine dioxide bleaching stage, along with the sulfuric acid normally used for bleaching pH chemical control, and chlorine dioxide. This was a mill system utilizing a bleaching sequence of 3 chlorine dioxide stages, with two Extraction/Peroxide stages in between. The test was only 24 hours duration, so the system had not stabilized in the later stages. Also there was an upset in the brown stock washer system that resulted in a 15% higher conductivity.
- Paper mills use the conductivity measurement to indicate the additional load of dissolved but unwashed lignin coming into the system. This would normally result in increased ClO 2 demand in the first stage, but in accordance with the methods of the present disclosure, first stage demand actually dropped by 5% (8.1 kgs/ton to 7.7 kg) (17.8 lbs/ton to 16.9).
- Table III lists results from two trials of a mill demonstration. All “best practices” were used to remove metals, and then a portion of the sulfuric acid was replaced with urea hydrochloride. Best practices included increasing washing, increasing the quantity of sewered water, and reducing pH on the pulp dryer. Final pH was controlled to 2.8 in all cases by adjusting sulfuric acid feed. Calcium content is reduced by about 50-60%, as are the transition metals, sodium, and silica.
- Transition metals are known to speed the decomposition of bleaching chemicals like chlorine dioxide and hydrogen peroxide. Mills often use mixtures of chelants (EDTA, DTPA, and the like) to control these materials. Others use mixtures including magnesium to form a floc with iron and manganese.
- EDTA chelants
- DTPA DTPA
- Others use mixtures including magnesium to form a floc with iron and manganese.
- pH was controlled at 2.8 with the sulfuric acid. Chlorine dioxide usage was reduced by 17% and pulp was brighter at comparable incoming kappa numbers, indicating that significant savings could be realized. Sulfuric acid was reduced as was hydrogen peroxide.
- any ranges of values set forth in this specification are to be construed as written description support for claims reciting any sub-ranges having endpoints which are whole number values within the specified range in question.
- a disclosure in this specification of a range of 1-5 shall be considered to support claims to any of the following sub-ranges: 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.
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Description
- The majority of corrugated boxes, paper grocery bags, fine papers, and market pulps are produced by a sulfate pulping process known as "Kraft" pulping. In the typical Kraft process, wood chips are added to an aqueous medium. In general, the liquor in which the wood chips are cooked comprises a mixture of black and white liquor, the black liquor being liquor added back to the cooking vessel, or digester, from a prior batch of wood chips and the white liquor being a freshly prepared alkaline solution as described below. Black liquor varies considerably among different mills depending on the white liquor used, the wood employed, and the method of cooking. Typical white liquor is a solution of sodium hydroxide, sodium carbonate, sodium sulfate, sodium sulfide and various inorganic materials. White liquor solubilizes the pulp and removes the lignin from the wood fibers as described below.
- The largest part of the organic matter removed from the wood during cooking is combined chemically with sodium hydroxide in the form of sodium salts. Some of these compounds are resin soaps which account for the intense foaming properties of black liquor. In addition, organic sulfur compounds and mercaptans, which give the characteristic odor to the sulfate-containing black liquor, and small amounts of sodium sulfate, silica and other impurities such as lime, oxide, alumina, potash, and sodium chloride can be present in the black liquor.
- Competing reactions are also in play. Calcium in the cooking liquor and in the wood (normally bound to the cellulose, but released upon contact with the alkali) form sticky precipitates with fatty and resin acids, swelling to block flow channels. Excess calcium can form precipitates with lignin, and hemicellulose among others. Such precipitates can present many difficulties in later stages. In high heat transfer areas, calcium cations form tenacious scales, reducing flow and heat transfer. In addition to calcium, certain other metals can catalyze the hydrolysis of wood sugars, hemicellulose, and cellulose, and can interfere in certain oxidation/reduction reactions. Moreover, aluminum, calcium, barium, magnesium, and transition metals (especially manganese, copper, and iron) can interfere with bleaching as well as other processes.
- The reaction conditions present during the cook, or digestion, cause lignin, the amorphous polymeric binder found in wood fibers, to be hydrolyzed. Ideally, wood chips are digested only long enough to dissolve sufficient lignin to free the cellulosic wood fibers but maintain sufficient lignin intact to provide added strength to the paper. The pulping process attempts to maximize pulp yield, which is defined as the dry weight of pulp produced per unit dry weight of wood consumed.
- As the pulping process continues, the rate of cellulose dissolution increases to the point where it exceeds the rate of lignin dissolution. As a result, the pulping process must be stopped and more compounds that more selectively dissolve lignin must be added. This is termed "bleaching," and results in a whiter, brighter paper. Bleaching typically involves contacting the pulp with an oxidizer, such as a chlorine compound, for example, chlorine dioxide, or with an oxygen compound, such as ozone, oxygen, peroxide, or the like. The effectiveness of bleaching is highly pH dependent, The respective pH levels can be adjusted downwards as necessary by adding thereto pH adjusters such as acids or materials that will form acids in aqueous solution, such as sulfur dioxide, sulfuric acid, hydrochloric acid, or the like.
- However, such pH adjusters can form insoluble sulfates, such as calcium sulfate, barium sulfate, and the like which are insoluble and unwashable. The metals and other impurities tend to remain associated with the fiber and are not washed out of the stock so that as the pH changes through the remaining processing, they tend to form scales on washer facewires, piping, and other associated equipment. Furthermore, such pH adjusters can also convert transition metals such as iron and manganese to their highly colored sulfate form, resulting in brightness reversion and the need for additional bleaching to compensate for such brightness reversion. The costs associated with removing scaling and maintaining bleaching can be significant.
- As such, a need exists for a method whereby metals and other impurities can be removed from pulp. It would be particularly beneficial if such a method could reduce brightness reversion in bleached pulps caused by oxidation of certain metals to their highly colored states. It would also be desirable if such method could minimize the amount of oxidizer utilized in a bleaching process.
- In accordance with certain embodiments of the present disclosure, a method of decreasing the amount of oxidizer required by a pulping or papermaking process comprising adding to a process stream or solution of the pulping or papermaking process urea hydrochloride to reduce the amount of oxidizer required by the pulping or papermaking process wherein the oxidizer comprises chlorine dioxide, ozone, oxygen, hydrogen peroxide, or combinations thereof is provided.
- A method of reducing one or more metals, impurities, or combinations thereof from a pulping or papermaking process is also described that comprises adding to a process stream or solution containing pulp, metals, impurities, or combinations thereof of the pulping or papermaking process an effective amount of urea hydrochloride to reduce metals, impurities, or combinations thereof from the pulping or papermaking process.
- Other features and aspects of the present disclosure are discussed in greater detail below.
- Reference now will be made in detail to various embodiments of the disclosure, one or more examples of which are set forth below. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. Features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.
- The present disclosure is directed to methods to reduce scaling and bleaching cost in a chemical pulping process. Also described is a method to remove metals and other impurities from the bleached pulp. The methods include utilizing urea hydrochloride in place of and/or in addition to certain pH adjusters in a pulping process
- The use of urea hydrochloride in paper and pulp processing has been previously described in
U.S. Patent No. 7,029,553 to Williams et al. Williams et al. describes that urea hydrochloride can be used to adjust the pH of a process stream and reduce the amount of sulfuric acid used in a papermaking process. Williams et al. also describes that urea hydrochloride forms calcium chloride when it comes into contact with solutions to which calcium hydroxide has been added. - However, Williams et al. fails to teach or suggest the removal of metals and/or other impurities from a pulping process. In addition, Williams et al. fails to recognize that a reduction in oxidizer can be realized by the use of urea hydrochloride. The present disclosure overcomes the shortcomings of the prior art in that the methods disclosed herein result in lower processing costs by reducing scaling and bleaching costs. Also described herein is the use of urea hydrochloride to remove metals and other impurities from pulp. Also described herein is the use of urea hydrochloride to reduce brightness reversion in bleached pulps caused by oxidation of certain metals to their highly colored states. Furthermore, urea hydrochloride can minimize the amount of oxidizer used for bleaching.
- In accordance with the present description, as digestion proceeds, certain metals and/or other impurities are prevented from adhering to process equipment as scale. Sealants such as calcium carbonate, calcium sulfate, calcium phosphate, calcium oxalate, barium sulfate, and the like, are controlled. Also, other metals are controlled, preventing them from interfering with oxidation/reduction reactions and from catalyzing the hydrolysis of sugars, hemicelluloses, and cellulose. Such metals can be found in the ash of wood chips in sufficient quantity to cause the abovementioned problems.
- The methods of the present disclosure utilize urea hydrochloride in place of and/or in addition to certain pH adjusters in a pulping process, particularly a bleaching process. Such pH adjusters typically include acids or materials that will form acids in aqueous solution, such as sulfur dioxide, sulfuric acid, hydrochloric acid, or the like. However, urea hydrochloride can be used in addition to or as a substitution for any suitable pH adjuster as would be known in the art.
- The urea hydrochloride used in accordance with the present disclosure can be formed from any desired ratio of urea and hydrochloric acid that performs the desired function of metal removal. Urea hydrochloride suitable for use in the present invention can be prepared by mixing urea with hydrochloric acid at the desired ratio. A suitable method for preparing a 1:1 molar ratio urea hydrochloride salt is described in Example 1 of
U.S. Pat. No. 5,672,279 . Suitable urea hydrochloride compositions are also commercially available. One such composition is NOVOC A-Cl (Peach State Labs, Inc., Rome, Ga.), which is a 1:1 molar ratio aqueous urea sulfate solution containing 0.25% of a quaternary amine corrosion inhibitor. - The methods of the present disclosure are described as being used in a Kraft pulping process. The present disclosure, however, is not to be so limited. Any of the various equivalent wood cooking processes having the production of paper as its ultimate goal may also be employed. However, the Kraft process is described in more detail as follows.
- Initially, suitable trees are harvested, debarked and then chipped into suitable size flakes or chips. The wood chips that can be processed into pulp using the chemical pulping process of the present disclosure can be either hardwoods, softwoods or mixtures thereof. Such wood chips are sorted with the small and the large chips being removed. The remaining suitable wood chips are then moved to a digester. The digester is a vessel for holding the chips and a digesting composition.
- In a batch type digester, wood chips and a mixture of "black liquor," the spent liquor from a previous digester cook, and "white liquor," typically a solution of sodium hydroxide, sodium carbonate, sodium sulfate, sodium sulfide and various inorganic materials are pumped into the digester. In the cooking process, lignin, which binds the wood fiber together, is dissolved in the white liquor forming pulp and black liquor.
- The digester is sealed and the digester composition is heated to a suitable cook temperature under high pressure. After an allotted cooking time at a particular temperature and pressure in the digester, the digester contents (pulp and black liquor) are transferred to a holding tank. The pulp in the holding tank is transferred to the brown stock washers while the liquid (black liquor formed in the digester) is sent to the black liquor recovery area. The black liquor is evaporated to a high solids content in evaporators. The Kraft cook is highly alkaline, usually having a pH of 10 to 14, more particularly 12 to 14.
- A Kappa number corresponds directly to the amount of lignin remaining in the pulp. Generally, the higher the Kappa number, the more lignin present in the pulp and, therefore, the higher the pulp yield. The Kappa number generally decreases as the digestion time is increased or the alkalinity of the cooking liquor is increased. The goal in such Kraft papermaking processes is to retain as much lignin as possible in order to enhance strength and to reduce the cost, while maintaining the uniformity of the cook. More uniform cooks result in a decreased percentage of rejects and, thereby, reduce costs for running paper mills.
- Cooking, or digestion, of the pulp may be terminated when the amount of rejects in the pulp is reduced to an acceptable level. Substantial yield and quality advantages are achieved if the wood chips are cooked to a higher lignin content. As a result, an increase in a Kappa number target by the use of thinner chips can result in a substantial cost savings. However, the thickness of chips obtainable on a commercial scale is always variable, A major portion of the total rejects frequently originate from a relatively small fraction of the chips having the greatest thickness. The objective in every pulping process is to achieve a lower percentage of rejects.
- After one or more washing steps, the pulp is subjected to bleaching treatments. Bleaching results in a whiter, brighter paper. Bleaching typically involves contacting the pulp with an oxidizer, such as a chlorine compound, for example, chlorine dioxide, or with an oxygen compound, such as ozone, oxygen, hydrogen peroxide, or the like. The effectiveness of bleaching is highly pH dependent. The respective pH levels can be adjusted downwards as necessary by adding thereto pH adjusters as described herein.
- Since most mills have abandoned bleaching with elemental chlorine, the simplest bleach plants contemplate three stages, most typically chlorine dioxide operating at about
pH 2 to about pH4 for one hour retention time, with washing, followed by caustic extraction where the liquid contains sodium hydroxide, hydrogen peroxide or oxygen, and another washing stage, completed by a second chlorine dioxide stage with washing. Shorthand for this configuration is D-Ep-D. Others will add another Ep-D, to form D-Ep-D-Ep-D. There are many other configurations possible, including acidification and enzyme treatments, and the methods of the present disclosure have application in all of them. - The present inventor has determined that pH adjusters, such as sulfuric acid, convert calcium, barium, and other metals present in the pulp to a sulfate form which is insoluble and unwashable. The pH adjusters also convert iron and manganese to their highly colored sulfate form. These materials tend to remain associated with the fiber and are not washed out of the stock, so as pH changes through the remaining process steps, calcium carbonate, calcium sulfate, barium sulfate, and iron and manganese oxides all form scales on washer facewires and in piping or associated equipment. Iron, manganese, copper, and the like, all catalyze the decomposition of the oxidizers and cellulose in the presence of oxygen.
- In accordance with the present description, urea hydrochloride is utilized in place of and/or in addition to the pH adjuster and can remove a significant amount of these metals as well as other impurities, such as silica. Such removal reduces the material available for scaling, or that interfere with bleaching. The method of the present description is measurable, consistent, and results in pulp with significantly less metal and/or impurity contaminant. For instance, between about 5% and 75% of one or more of metals or other impurities are removed. In some described cases, between about 25% and 70% of one or more of metals or other impurities are removed while in some described cases, between about 50% and 60% of one or more of metals or other impurities are removed. The resulting pulp has a metals content of from about 30 mg/kg to about 200 mg/kg.
- It is assumed that reactions with the chloride ion are stoichiometric, where 2 moles of chloride can react with one mole of the divalent metal to form a soluble salt. However, the laboratory example described herein in Table 1 describes that about 200 ppm of urea hydrochloride removes greater than 200 ppm of calcium, magnesium, manganese, iron, and aluminum with an approximate ratio of 1:1. In addition, about 1200 ppm of sodium is removed, compared with about 600 ppm with H2SO4.
- Metals can include aluminum, calcium, barium, magnesium, potassium, sodium, and zinc as well as transition metals (especially manganese, copper, and iron transition metals) or combinations thereof. Impurities can include one or more of sodium sulfate, silica, lime, oxide, alumina, potash, sodium chloride or combinations thereof.
- An effective amount of urea hydrochloride is employed in a bleaching step of a chemical pulping process to improve the efficiencies of the chemical pulping processes. The effective amount depends on the particular urea hydrochloride employed and other factors including, but not limited to, wood type, the digester composition, the operating conditions of the digester, the mode of addition of the compounds including any additional compounds added, as well as other factors and conditions known to those of ordinary skill in the art.
- For instance, about 453.6 - 1814.4 grams (1-4 lbs.) of urea hydrochloride (UCl) per ton of pulp provides the maximum removal of metals. In certain embodiments of the present disclosure, about 680.4 grams (1.5 lbs.) per ton of UCl was utilized in only one of the ClO2 stages. In the interest of keeping total chemical cost as low as possible, pH control can be managed by use of sulfuric acid, as is the current practice. Addition of the UCl displaces sulfuric acid within the existing control schemes.
- As a result of the urea hydrochloride being added in a bleaching step, the amount of oxidizer utilized in the process can be reduced when compared to a traditional chemical pulping process that does not utilize such urea hydrochloride. The amount of oxidizer can be reduced by about 10% when compared to traditional processes. In certain embodiments, the amount of oxidizer can be reduced by about 15% and in still other embodiments, the amount of oxidizer can be reduced by about 20%. In addition, brightness can improve from about 88% to about 90% when compared to traditional processes.
- Hydrochloric acid is known to react with chlorate (ClO3) to form chlorine dioxide (ClO2) in acidic environments. Chlorate is normally present in the bleach stage filtrate, so this is presumed to be responsible for some of the immediate reduction in bleaching chemical requirements. For instance, the amount of oxidizer added is from about 15.9 kg to 27.2 kg (35 to 60 lbs.) per ton ClO2, and about 6.8 kg to 9.1 kg (15 to 20 lbs.) per ton H2O2. As described above, oxidizer can include chlorine compound, for example, chlorine dioxide, or with an oxygen compound, such as ozone, oxygen, hydrogen peroxide, or the like. The effectiveness of bleaching is highly pH dependent.
- In some embodiments, other additives can be added to the alkaline aqueous mixture in the extraction stages. Typical additives include, but are not limited to, conventional additives known for use in a chemical pulping process.
- Also described are methods of reducing the formation of scaling in the pulp washers, bleach plants, and evaporators. Such methods can remove metals and/or other impurities, thereby improving the bleach chemical efficiency. Also described are methods of reducing brightness reversion in bleached pulps caused by oxidation of certain metals to their highly colored states.
- The following examples are meant to illustrate the disclosure described herein and are not intended to limit the scope of this disclosure.
- Laboratory evaluation using semi-bleached pulp (one stage with ClO2, one alkaline extraction stage EOP was washed with one liter of deionized water; alkaline extraction stage assisted by oxygen and peroxide, an EOP stage). The others were washed with either sulfuric or urea hydrochloride as noted. Samples were analyzed by ICP Spectrometer.
- In the present study, there is a reduction in aluminum, barium, copper, iron, and manganese with 3 pH UCl versus 2 pH H2SO4. The sulfate compounds are substantive to cellulose fiber at low pH (aluminum sulfate or alum is used as a sizing and retention aid in papermaking). As pH drops to 2 with the UCl, calcium continues to reduce. The drop in silica was unexpected, but is likely to be important in making low-ash pulps. The removal of the transition metals was also unexpected, but led to removal of those metals from the pulp to reduce bleaching costs in peroxide stages, and to reduce decomposition of ClO2 in later bleaching stages.
- UCl was introduced into the first chlorine dioxide bleaching stage, along with the sulfuric acid normally used for bleaching pH chemical control, and chlorine dioxide. This was a mill system utilizing a bleaching sequence of 3 chlorine dioxide stages, with two Extraction/Peroxide stages in between. The test was only 24 hours duration, so the system had not stabilized in the later stages. Also there was an upset in the brown stock washer system that resulted in a 15% higher conductivity.
- Paper mills use the conductivity measurement to indicate the additional load of dissolved but unwashed lignin coming into the system. This would normally result in increased ClO2 demand in the first stage, but in accordance with the methods of the present disclosure, first stage demand actually dropped by 5% (8.1 kgs/ton to 7.7 kg) (17.8 lbs/ton to 16.9).
- Final pulp brightness was improved, and would have allowed further chemical cuts. Insofar as pH control, 680.4 grams (1.5 lbs) per ton of the UCl displaced 317.5 grams (0.7 lbs) per ton of H2SO4 despite the increased brownstock conductivity (2.4 kgs/ton to 2.1) (5.3 lbs/ton to 4.6). Brightness improved from 87.8 to 89.2. This brightness measurement is the most common in the United States and is the one described in TAPPI T 452 Brightness of Pulp, Paper and Paperboard (Directional Reflectance at 457 nm).
- Finally, peroxide usage dropped 4.4% (8.3 kgs/ton to 7.9 kg) (18.2 lbs/ton to 17.4).
- The laboratory work is most representative of the final washing stage prior to bleaching. TABLE II illustrates that ClO2, H2O2, and H2SO4 were reduced by 1 kgs/ton, 362.9 grams/ton, and 317.5 grams/ton (2.2 LBS/ton, .8 LBS/ton, and .7 LBS/ton), respectively with the addition of urea hydrochloride. The relative costs on these chemicals are approximately ClO2 ($0.18/kg, $0.40/lb), H2O2 ($0.44) and H2SO4 ($0.37). Using these metrics a cost reduction of $1.49/bleached ton of pulp is calculated.
- TABLE II further shows that bleaching costs were lower and brightness was higher using urea hydrochloride at kappa numbers that are the same or relatively close. The ClO2/kappa and the ClO2/brightness point are all favorable.
- Further, when urea hydrochloride was added the ClO2 was cut in response to the brightness on the front end increasing. This occurred even as the tonnage rate was going up. The ClO2 leveled out and then went up very quickly when the urea hydrochloride was taken out of the system.
- Table III lists results from two trials of a mill demonstration. All "best practices" were used to remove metals, and then a portion of the sulfuric acid was replaced with urea hydrochloride. Best practices included increasing washing, increasing the quantity of sewered water, and reducing pH on the pulp dryer. Final pH was controlled to 2.8 in all cases by adjusting sulfuric acid feed. Calcium content is reduced by about 50-60%, as are the transition metals, sodium, and silica.
- Transition metals are known to speed the decomposition of bleaching chemicals like chlorine dioxide and hydrogen peroxide. Mills often use mixtures of chelants (EDTA, DTPA, and the like) to control these materials. Others use mixtures including magnesium to form a floc with iron and manganese. In another short evaluation in a mill pulping hardwoods, 680.4 grams (1.5 lbs) per ton urea hydrochloride was used to replace a portion of sulfuric acid. pH was controlled at 2.8 with the sulfuric acid. Chlorine dioxide usage was reduced by 17% and pulp was brighter at comparable incoming kappa numbers, indicating that significant savings could be realized. Sulfuric acid was reduced as was hydrogen peroxide.
- In the interests of brevity and conciseness, any ranges of values set forth in this specification are to be construed as written description support for claims reciting any sub-ranges having endpoints which are whole number values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of 1-5 shall be considered to support claims to any of the following sub-ranges: 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.
- These and other modifications and variations to the present disclosure can be practiced by those of ordinary skill in the art, which is more particularly set forth in the appended claims. In
addition, it should be understood that aspects of the various embodiments can be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the disclosure.
Claims (9)
- A method of decreasing the amount of oxidizer required by a pulping or papermaking process comprising adding to a process stream or solution of the pulping or papermaking process urea hydrochloride to reduce the amount of oxidizer required by the pulping or papermaking process wherein the oxidizer comprises chlorine dioxide, ozone, oxygen, hydrogen peroxide, or combinations thereof.
- A method according to claim 1, wherein the oxidizer comprises chlorine dioxide.
- A method according to claim 1, wherein the oxidizer comprises hydrogen peroxide.
- A method according to claim 1, wherein the amount of urea hydrochloride is from 6,8-27,2 kg (15-60 lbs) per ton of oxidizer.
- A method according to claim 2, wherein the amount of urea hydrochloride is from 15,8-27,2 kg (35 - 60 lbs) per ton chlorine dioxide.
- A method according to claim 3, wherein the amount of urea hydrochloride is from 6,8-9,07 kg (15-20 lbs.) per ton of hydrogen peroxide.
- A method according to claim 1, wherein the oxidizer required by the pulping or papermaking process is reduced by at least 10%, when compared to a traditional chemical pulping process that does not utilize urea hydrochloride.
- A method according to claim 1, wherein the oxidizer required by the pulping or papermaking process is reduced by at least 15%, when compared to a traditional chemical pulping process that does not utilize urea hydrochloride.
- A method according to claim 1, wherein the oxidizer required by the pulping or papermaking process is reduced by at least 20%, when compared to a traditional chemical pulping process that does not utilize urea hydrochloride.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US12/751,143 US20110240239A1 (en) | 2010-03-31 | 2010-03-31 | Methods to Reduce Metals Content of Bleached Pulp While Reducing Bleaching Cost in a Chemical Pulping Process |
PCT/US2011/025845 WO2011126613A2 (en) | 2010-03-31 | 2011-02-23 | Methods to reduce metals content of bleached pulp while reducing bleaching cost in a chemical pulping process |
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EP2553165A2 EP2553165A2 (en) | 2013-02-06 |
EP2553165A4 EP2553165A4 (en) | 2016-08-24 |
EP2553165B1 true EP2553165B1 (en) | 2019-03-20 |
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EP11766310.4A Active EP2553165B1 (en) | 2010-03-31 | 2011-02-23 | Methods to reduce metals content of bleached pulp while reducing bleaching cost in a chemical pulping process |
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US (1) | US20110240239A1 (en) |
EP (1) | EP2553165B1 (en) |
BR (1) | BR112012025085B1 (en) |
CA (1) | CA2795150A1 (en) |
ES (1) | ES2726053T3 (en) |
PT (1) | PT2553165T (en) |
WO (1) | WO2011126613A2 (en) |
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US7029553B1 (en) * | 1992-07-24 | 2006-04-18 | Peach State Labs, Inc. | Urea sulfate and urea hydrochloride in paper and pulp processing |
US5672279A (en) * | 1992-07-24 | 1997-09-30 | Peach State Labs, Inc. | Method for using urea hydrochloride |
US5234466A (en) * | 1992-07-24 | 1993-08-10 | Peach State Labs, Inc. | Lowering of the pH of textile processing solutions by adding urea sulfate as a pH adjusting agent |
CA2398329A1 (en) * | 2001-08-20 | 2003-02-20 | Hercules Incorporated | Process for purifying sand |
WO2005045127A1 (en) * | 2003-11-07 | 2005-05-19 | Commonwealth Scientific And Industrial Research Organisation | A method for bleaching lignocellulosic materials |
-
2010
- 2010-03-31 US US12/751,143 patent/US20110240239A1/en not_active Abandoned
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2011
- 2011-02-23 EP EP11766310.4A patent/EP2553165B1/en active Active
- 2011-02-23 BR BR112012025085-0A patent/BR112012025085B1/en active IP Right Grant
- 2011-02-23 PT PT11766310T patent/PT2553165T/en unknown
- 2011-02-23 WO PCT/US2011/025845 patent/WO2011126613A2/en active Application Filing
- 2011-02-23 ES ES11766310T patent/ES2726053T3/en active Active
- 2011-02-23 CA CA2795150A patent/CA2795150A1/en not_active Abandoned
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Also Published As
Publication number | Publication date |
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EP2553165A4 (en) | 2016-08-24 |
WO2011126613A2 (en) | 2011-10-13 |
EP2553165A2 (en) | 2013-02-06 |
WO2011126613A3 (en) | 2012-01-12 |
US20110240239A1 (en) | 2011-10-06 |
BR112012025085B1 (en) | 2020-03-17 |
BR112012025085A2 (en) | 2016-06-21 |
PT2553165T (en) | 2019-05-30 |
CA2795150A1 (en) | 2011-10-13 |
ES2726053T3 (en) | 2019-10-01 |
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