EP0631009A1 - Procédé pour la récupération et le traitement des fibres de plantes à tige creuse - Google Patents

Procédé pour la récupération et le traitement des fibres de plantes à tige creuse Download PDF

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Publication number
EP0631009A1
EP0631009A1 EP94810361A EP94810361A EP0631009A1 EP 0631009 A1 EP0631009 A1 EP 0631009A1 EP 94810361 A EP94810361 A EP 94810361A EP 94810361 A EP94810361 A EP 94810361A EP 0631009 A1 EP0631009 A1 EP 0631009A1
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Prior art keywords
fibers
core particles
pulp
fibrous
fiber
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EP94810361A
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German (de)
English (en)
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Till Grether
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Individual
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
    • D21B1/00—Fibrous raw materials or their mechanical treatment
    • D21B1/02—Pretreatment of the raw materials by chemical or physical means
    • D21B1/025—Separating pith from fibrous vegetable materials

Definitions

  • the present invention relates to a method for the recovery and processing of fibers from hollow stalk plants and to the use of the fibers obtained by the method.
  • the invention particularly relates to fibers of dicotyledonous plants and more particularly to fibers of kenaf or hemp, their preparation, processing and use.
  • the expression "hollow stalk plant” is intended to encompass all plants which form a hollow, generally rather long stem which is filled with a kind of woody marrow. Examples of such plants are the dicotyledonous plants such as kenaf and hemp, but also elder and some reed species.
  • a dicotyledonous plant has two morphologically distinct regions in its stem, namely the outer bark fraction which contains the bast fibers, and the inner, woody core.
  • the ratio between the stalk components varies according to the different species, the nature of the soil and others, and the outer portion comprises 40 to 10 % while the woody core comprises 60 to 90 % of the whole stalk.
  • kenaf fibers will be taken as a basis for the following description of the invention. However, it is emphasized that the invention is not limited thereto but can be practiced in using all dicotyledonous plants which have an analogous structure.
  • Kenaf (hibiscus cannabinus), an annual dicotyledonous plant, originates probably from Eastern Central Africa and is now cultivated all over the world. In Europe, it grows in a height of until 5 meters and produces a dry biomass substance of about 4 to 30 metric tons per hectare, depending on the growth conditions.
  • the field dried, chopped kenaf stalks are stirred in a pulper at elevated temperature in an alkaline aqueous medium, and the bast fibers are the separated from the pulp on a slit screen fractionator.
  • the separation efficiency is relatively poor, 82 % according to Example 1, and the separation step uses chemicals which present environmental risks and render the method uneconomic.
  • PCT/AU92/00027 published under WO 92/12808, discloses a method and an apparatus for grading fibrous material, exemplified by the separation of kenaf stalk materials into the bark fibers and the core materials.
  • the apparatus comprises two or more hollow bodies rotating about inclined axes, the bodies having baffles for tumbling the fibrous materials and slits for decharging the fines.
  • hollow stalk plants can only be used as a fiber material, for example in the paper making industry, more generally in the fiber sheet industry, without introducing additional, costly processing steps if the core materials have been separated from the bark fibers with an efficiency of at least 90 %, it is the first and major object of the present invention to provide a new method and apparatus for the separation of fibers from such plants which affords the required separation efficiency.
  • the method of the invention comprises pulping a fiber material previously obtained by field drying, chopping, and coarse comminution of the plant stalks and subsequent summary removal of core particles, in warm or hot water, preferably water of at least 50 °C, more preferably of 80 to 85 °C, to a solids concentration of from 4 to 20 % by weight during about 5 to 40 minutes, then separating fine, lightweight fibers, other fines and residual core particles from this pulp, and recovering a fibrous pulp wherein the fibers contain less than 10 % by weight of non-fibrous materials.
  • This separation is preferably achieved in passing the pulp into a hydrocyclone having circumferential, central and intermediate collecting volumes, and recovering the fibrous pulp from said intermediate volume of the hydrocyclone situated between said circumferential and central collecting volumes.
  • This method using said hydrocyclone, affords a separation efficiency of at least 95 %, i.e. that the fibrous pulp flowing out of the new hydrocyclone of the invention contains solids comprising at least 95 % by weight of fibers.
  • the overall yield of fibrous materials can be improved as well as the overall separation efficiency when the fibrous pulp discharged from the intermediate volume of the hydrocyclone is fed into a classifying device where fibre bundles not yet opened in the pulping step, and any residual core particles are separated from the fibers and returned to pulping after a milling treatment.
  • the material in the circumferential volume of the hydrocyclone i. e. a layer adjacent to the inner hydrocyclone wall, comprises compact core particles.
  • This material may be collected, separated from the suspending aqueous phase, then milled and returned into the pulper. During milling, the core particles are opened in yielding fine fibers which will, during the procedure described above, accumulate in the central volume of the hydrocyclone.
  • the central volume in the hydrocyclone comprising fine fibers and other lightweight fines, is discharged therefrom and may be used for papermaking or other purposes, thus improving the overall economics of the method.
  • the object of the invention is also met by a dry separation technique, comprising feeding a dry fiber material previously obtained by field and/or air drying, chopping, and coarse comminution of the plant stalks and subsequent summary removal of the core particles, into a multistage zigzag wind sifter.
  • the overhead output of this device is an air suspension of fibers which have been separated from the core particles with an efficiency of at least 90 %.
  • the fibers thus separated from the core particles can easily be recovered from the supporting air by screens well known to the one skilled in the art. For a number of uses, this purity of the fibers is already sufficient but if not, the fibers may be subjected to the wet separation procedure already described above.
  • Fig. 1 which shows in a schematical manner a general flowsheet of an installation 10 for the separation of kenaf fibers from core material
  • the reference numeral 12 denotes the kenaf feed charged into a pulper vessel 14.
  • the kenaf feed is obtained in the following way:
  • the kenaf plants are preferably harvested by means of a modified corn chaffcutter machine and pre-dried on the field.
  • the leaves are separated from the stalks and left on the field as a natural fertilizer.
  • the stalks are then coarsely comminuted in a suitable shredder or a corn chaffcutter into lengths of about 10 to 20 mm.
  • the stalk shreds are then dried to a water content of about 13 to 15 %, either naturally on the field or in grass drying facilities.
  • the dried kenaf shreds are further processed in a central installation, comprising chopping the shreds or opening same on torsion spring drums, and these materials are then separated in a sieving device such as a turbulence classifier. This step results in an about 70 to 80 % separation of the bast fibers from the core materials which are discarded or separately processed.
  • the fibers which still contain from about 2 to 40 % by weight of core particles constitute the feed 12 (Fig. 1). These fiber materials also contain fiber bundles which were left unopened in the chopping step mentioned above.
  • the pulper vessel 14 is equipped with a stirrer 16, driven through a shaft by the stirrer motor 18. Steam and, if necessary, water can be introduced into the pulper vessel 14 through the conduit 20 and 21, respectively, so that the liquid level will be kept constant.
  • the pulping water in the vessel 14 is maintained at a temperature of from about 50 to about 90 °C, preferably about 80 to about 85 °C.
  • the amount of charged kenaf fibers is such that their concentration in the pulper is maintained between 4 and 20 % by weight, preferably at about 14 % by weight.
  • the dwell time of the kenaf fibers in the pulper is about 10 to 20 minutes.
  • the contents of the vessel 14 is then discharged by line 22 into the storage vessel 24.
  • the kenaf fibers are hydrated and softened, most of the fiber bundles are opened, and also a substantial portion of the core particles are opened to yield additional, fine fibers.
  • the pulp in vessel 24 is then pumped into the tangentially ending input pipe 30 of the hydrocyclone 28 for classification; the operation of the hydrocyclone will be explained below.
  • the fiber suspension entering the hydrocyclone 28 is classified into a fiber fraction which leaves the cyclone through line 32, a heavy core fraction consisting principally of unopened core material in the form of dims or tangles discharged through the line 34, and lightweight, fine fibers and other fines, leaving the hydrocyclone by the line 36.
  • the hydrocyclone 28 thus achieves a separation of the charged suspension into three fractions.
  • the fiber fraction is passed into the vertical separator 38, equipped for example with hole or slot sieves, where remaining fiber bundles are separated from the kenaf fibers.
  • This separator 38 is an optional device since it need not be used if fiber bundles can be tolerated in the final sheet made from the fibers, such as a mulching sheet or low-quality papers.
  • the proportion of fibers in the suspension flowing through line 32 is more than 99 %, about 2 to 3 % thereof being residual fiber bundles.
  • These fiber bundles, separated from the fibers in the separator 38 are fed to a vibration sieve 40 through line 42.
  • the fiber suspension which is free from bundles and any other impurity is passed through line 44 into a deflaker 46, and the deflaked mass is discharged into a reaction vessel 50 through line 48.
  • the fines in line 36 from hydrocyclone 28 can be used together with the finally separated kenaf fibers in paper pulp, particularly if mulch sheets are to be produced. Therefore, they can be charged through line 54 into the reaction vessel 50. When this is not desired, the fines are passed through line 56 to other processing facilities or to disposal.
  • the fiber suspension leaving the separator 38 through line 44 is a suspension of non-classified fibers stemming from the bark portion of the plant. These fibers have a length of about 2 to 13 mm or more. For some special uses of the fibers, it has been found advantageous to further separate these fibers, namely for example into a first, short fiber fraction wherein the fibers have a length of about 2 to 8 mm, which can be used as normal binder fibers in papermaking, and a second, long fiber fraction where the fibers have a length of more than 8 mm; these fibers can be used as so-called armouring fibers.
  • a second hole-and-slit sieve separator (not shown) having a construction similar to separator 38 will be disposed between the first separator 38, shown in Fig. 1, and the deflaker 46. Like separator 38, this second separator has one inlet and two outlets. One outlet is connected to deflaker 46, and the other outlet provides a suspension of either the short fibers or the long fibers, as desired.
  • the core particles separated from the fibers in hydrocyclone 28 are charged through line 34 on the vibration sieve 40 together with the fiber bundles (and, if any, residual core particles) coming through line 42 from separator 38.
  • the vibration sieve 40 On the vibration sieve 40, the solids are separated from the aqueous pulping liquor which is collected in vessel 58 and then returned through line 60 into storage vessel 24.
  • the solids remaining on the sieve 40 are fed to a milling device 62, for example an attrition mill sold by Alpine, Austria, wherein the fiber bundles are opened and the core particles are further comminuted; this comminution yields fine fibers since the core particles are mostly tangles of very fine fibers having a length of about 0.1 to 3 mm.
  • the outlet of the attrition mill 62 is returned through line 64 back to the pulper 14.
  • the fibers coming from deflaker 46 and, optionally, the fines from the hydrocyclone 28 (line 54) are further optionally treated to provide bleached fibers. It has surprisingly been found that, probably due to the aforesaid aqueous treatment and separation steps of the fibers, unusual mild conditions are suffficient for this bleaching treatment, and the same bleaching effect is obtained as a bleaching under more severe conditions of fibers which have not undergone the processing method of this invention.
  • the fiber suspension is slightly diluted to a solids content of about 2.5 to 3.5 % by weight.
  • Sodium hydroxide is added until a concentration of about 1.5 % by weight.
  • the mixture is heated, and after about 20 minutes at 80 to 90 °C, about 3 g of hydrogen peroxide having a concentration of about 25 % are added per kg of the suspension.
  • the warm suspension is kept under stirring a further 15 to 25 minutes in the temperature range mentioned above.
  • the suspension is then neutralized by means of a weak acid, particularly acetic acid, to a pH of about 6.5.
  • the fibers are separated by centrifuging and optionally dried. They can be used, as already mentioned, as reinforcing fibers in paper pulps, optionally further containing recycled waste paper, or for replacing cellulose and recycled paper in paper pulps.
  • the fines leaving the hydrocyclone 28 alternatively through line 56 can easily be separated from the pulping water and can advantageously be used, as such or together with the compact core particles leaving the hydrocyclone through line 34, as organic, biologically degradable and food allowable filler.
  • FIG. 2 which shows a vertical sectional view of the hydrocyclone 28 used in the method of this invention
  • reference numerals 30, 32, 34 and 36 denote the same ports or lines, respectively, as in Fig. 1.
  • the pipe 30 ends, in a known manner, tangentially in the upper portion of the cyclone.
  • the upper and lower outlets 32 and 34, respectively, are known from conventional cyclones.
  • the cyclone of Fig. 2 further comprises an inner, central pipe 37 which extends to about the half of the height of the cyclone 28 and serves for evacuating by means of a pump (not shown) the fines fraction of the fibrous material pulp fed into the cyclone through pipe 30.
  • Fig. 3 shows a horizontal cross-sectional view of the cyclone of Fig. 2 in a plane according to line III-III of Fig. 2.
  • This Figure represents the separating condition of the fiber suspension 66 fed into the cyclone through pipe 30. Due to the centrifugal forces of the helical flow of the suspension, the relatively heavy, unopened core particles 68 accumulate near to the inner wall of the cyclone 28 and are transported by inertial forces downward to the outlet opening 34. The central region of the cyclone 28 is subjected to nearly no turbulence and centrifugal forces; the lightest fibres and other fines 70, stemming from opened core tangles, accumulate in this central space and are evacuated through pipe 37.
  • the most interesting main fibers having a length of about 2 to 13 mm or more, as described above, will occupy the intermediate region between the inner wall of the cyclone and the central region and are discharged from the hydrocyclone 28 through the pipe 32 together with the main stream of the liquid fed into the cyclone.
  • the installation described above operates as a continuous process starting from storage vessel 24.
  • the pulping of the kenaf raw material in vessel 14 is discontinuous, but it would be possible to replace the pulping vessel 14 by a continuous pulper.
  • the object of the invention namely the separation of the compact core particles from a fiber material previously obtained by field drying, chopping, and coarse comminution of hollow stem plant stalks, is also attained in a dry process by passing the comminuted stalks through a vertical zigzag wind sifter or air classifier, known per se in the art and sold by the Alpine Company, Austria.
  • a vertical zigzag wind sifter or air classifier known per se in the art and sold by the Alpine Company, Austria.
  • air is passed from below into the wind sifter, and the fibrous mass to be separated is charged from above into the device.
  • a separation is obtained at all the edges of every angle of the wind sifter tube sections which are disposed according to a zigzag configuration.
  • the fibers are lighter than the core particles and are carried away by and together with the air flow through the separator; they can be collected by suitable screening means known per se from this air flow.
  • the heavier core particles fall down against the air stream and can be collected at the bottom of the air separator.
  • the use of air as a separating medium avoids the still repeating entanglement of core tangles and free fibers which, in the known methods, has impaired the desired separation.
  • the fiber fraction is contaminated by less than about 10 % of core particles.
  • a complete and total separation from the remaining about 10 % of core particles can be obtained in feeding the fiber fraction, obtained from the wind sifter, into the wet separation installation described above.
  • the overall separation efficiency will be at least 99,5 %.
  • the fiber materials processed and obtained by the methods of the invention from hollow stem plants may be used in a multitude of fields. These uses have especially become possible through the method of the invention which guarantees an at least 90 % separation of the compact core particles and, in some cases, of the finest fibers, said separation typically yielding even a nearly 100 % separation efficiency. Examples for such uses which are by far not exhaustive, are the following:

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EP94810361A 1993-06-28 1994-06-20 Procédé pour la récupération et le traitement des fibres de plantes à tige creuse Withdrawn EP0631009A1 (fr)

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CH1921/93 1993-06-28
CH192193 1993-06-28

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EP0631009A1 true EP0631009A1 (fr) 1994-12-28

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CA (1) CA2126716A1 (fr)
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102013114386A1 (de) * 2013-12-18 2015-06-18 Uwe D'Agnone Verfahren zur Aufbereitung von Gras für die Herstellung von Papier, Pappen und Karton
EP3058137B1 (fr) 2013-10-15 2021-03-31 Huhtamaki Molded Fiber Technology B.V. Materiau d'emballage d'aliment en paté moulée de gramen et procede correspondant
WO2023031670A1 (fr) * 2021-09-02 2023-03-09 Topcell Ab Procédé de fabrication d'un isolant particulaire de bourrage et matériau isolant produit selon ledit procédé
CN115889396A (zh) * 2023-01-05 2023-04-04 中国科学院过程工程研究所 一种基于工业化利用的田间农作物秸秆分级方法及装置

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB846232A (en) * 1958-01-14 1960-08-31 Hawailan Dev Company Ltd Improvements in and relating to paper-making pulp
US4106979A (en) * 1977-03-21 1978-08-15 Consorzio Fabocart S.P.A. Preparation of paper pulps from dicotyledonous plants
EP0122769A2 (fr) * 1983-04-15 1984-10-24 WM. R. STEWART & SONS (HACKLEMAKERS) LIMITED Séparation des fibres végétales
US4889591A (en) * 1988-05-27 1989-12-26 Process Evaluation And Development Corporation Crotalaria juncea paper pulps
WO1992012808A1 (fr) * 1991-01-29 1992-08-06 Ankal Pty Limited Procede et appareil de triage de materiau fibreux

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB846232A (en) * 1958-01-14 1960-08-31 Hawailan Dev Company Ltd Improvements in and relating to paper-making pulp
US4106979A (en) * 1977-03-21 1978-08-15 Consorzio Fabocart S.P.A. Preparation of paper pulps from dicotyledonous plants
EP0122769A2 (fr) * 1983-04-15 1984-10-24 WM. R. STEWART & SONS (HACKLEMAKERS) LIMITED Séparation des fibres végétales
US4889591A (en) * 1988-05-27 1989-12-26 Process Evaluation And Development Corporation Crotalaria juncea paper pulps
WO1992012808A1 (fr) * 1991-01-29 1992-08-06 Ankal Pty Limited Procede et appareil de triage de materiau fibreux

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
A.F. KALDOR, C. KARLGREN, AND H. VERWEST: "kenaf - a fast growing fiber source for papermaking", TAPPI JOURNAL, vol. 73, no. 11, November 1990 (1990-11-01), ATLANTA US, XP000163303 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3058137B1 (fr) 2013-10-15 2021-03-31 Huhtamaki Molded Fiber Technology B.V. Materiau d'emballage d'aliment en paté moulée de gramen et procede correspondant
DE102013114386A1 (de) * 2013-12-18 2015-06-18 Uwe D'Agnone Verfahren zur Aufbereitung von Gras für die Herstellung von Papier, Pappen und Karton
WO2023031670A1 (fr) * 2021-09-02 2023-03-09 Topcell Ab Procédé de fabrication d'un isolant particulaire de bourrage et matériau isolant produit selon ledit procédé
CN115889396A (zh) * 2023-01-05 2023-04-04 中国科学院过程工程研究所 一种基于工业化利用的田间农作物秸秆分级方法及装置

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ZA944521B (en) 1995-02-15
CA2126716A1 (fr) 1994-12-29

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