Title of Invention

PROCESS OF PRODUCING RAW MATERIAL FOR SYNTHETIC AND OTHER FIBRES FROM HERBACEOUS PLANTS

Abstract

The invention relates to a process of environmentally friendly production of pulp from herbaceous plants or the like by subjecting the plants to formic acid cooking and if desired to bleaching with oxidizing bleaching chemicals. The invention also relates to the use of the resultant pulp especially for the production of viscose fibre and fine paper. In addition, the invention relates to a process of producing viscose fibre and fine paper using pulp as raw material. Furthermore, the invention relates to the viscose fibre and fine paper produced by the process.

Full Text

Process of producing raw material for synthetic and other fibres from herbaceous plants The invention relates to a process of producing pulp from herbaceous plants or the like by-formic acid cooking and if desired by bleaching with oxidizing bleaching chemicals. The pulp produced in this manner is particularly useful in the production of textile yarn, non-woven products, wadding, viscose fibres, other fibres based on modified cellulose, and fine paper. The invention also relates to the use of the resultant pulp in the production of textile yarn, non-woven products, wadding, viscose fibres, other fibres based on modified cellulose, and fine paper. In addition, the invention relates to a process of producing viscose fibre and fine paper using herbaceous plants as raw material. Furthermore, the invention relates to the resultant viscose fibre and fine paper. The production of viscose fibres from herbaceous plants by conventional processes is difficult, since herbaceous plants contain many substances that cause great problems in a viscose process and also impair the quality of the product. In particular, the high ash, extractive, silicate and calcium content of herbaceous plants (2 to 10%) cause problems, since a too high amount of these substances in the pulp deteriorates the f ilterability of the viscose. Problematic are also such trace elements of herbaceous plants that act as catalysts of the viscose process and disturb the stability of the process. In conventional alkaline processes, such as a sulphate process, silicates dissolve during cooking, but they are concentrated during recovery and chemicals must be discharged into a sewer, which causes environmental problems. Because of this, alkaline processes cannot be used in the industrial countries for the production of dissolving pulp and, further, viscose. Another drawback of the alkaline cook is that a major part of the nutrients and metals remain in the pulp during the cook and will cause problems in the process steps that follow, particularly in peroxide bleaching, which is commonly used nowadays. It also used to be a problem that raw material for viscose fibres and for fine paper had to be produced mainly by different processes. It has now been discovered that pulp produced by a process of the present invention can also be successfully used for the production of fine paper. The most important in the production of fine paper are the short fibres of bleached chemical pulp, which give the paper good printing characteristics. Herbaceous plants have thinner and, in many varieties, half shorter fibres than deciduous trees, whereby a suitable fibre ratio meeting the opacity and smoothness requirements of paper is achieved quite naturally without grinding. Fine papers include printing, writing and drawing papers and boards. Most fine papers are printed before their final use. Fine papers are made of wood-free pulp and usually contain less than 10% of mechanical pulp. In the production, primarily birch and pine kraft pulp are used as virgin fibre and groundwood as mechanical pulp. Certain quality requirements are set for fine papers, the most typical of them being high brightness and good archival characteristics. Finnish Patent Application 933,729 teaches a process of producing cellulose from wood and annual plants by cooking with diluted acetic acid under pressure and adding formic acid. The cook is conducted at an elevated temperature of 130 to 190°C with an acetic acid content of 50 to 95% by weight and a formic acid content of less than 40%. Finnish Patent 74,750 teaches a process of producing bleached cellulose pulp from lignin-containing cellulose raw material by processing the raw material with cooking liquor that contains organic peroxo acids. The peroxo acids are produced by adding hydrogen peroxide to organic carboxyl acid, such as formic, acetic, propionic or butyric acid. The cook is conducted at a temperature of about 70 to 90°C. It is followed by bleaching with an alkaline solution that contains hydrogen peroxide. In addition to hardwood and softwood, it is possible to use annual plants, grass, straw and bagasse as raw material. In the present invention, the term "herbaceous plants or the like" refers generally to any non-wood sources of fibre. The primary fibre sources useful in the invention include straw, such as corn straw (rice, wheat, rye, oat, barley); grasses, such as esparto, sabai and lemon grass; reeds, such as papyrus, common reed, sugar-cane or bagasse, and bamboo; bast fibres, such as stems of fibre flax or seed flax, kenaf, jute and hemp; leaf fibres, such as manila hemp and sisal; and seed hairs, such as cotton and cotton linters. Herbaceous plants growing in Finland and useful in the present invention include reed canary grass, timothy, cocksfoot, common melilot, smooth brome, creeping fescue, white melilot, red clover, goat"s rue and medick. In the present invention, the term "herbaceous plants or the like" also includes short-fibred hardwood and juvenile thinning wood. The process of the invention is characterized^ —--■■"" ■ • "" ~"" ~ "" . " s~^"" in that herbaceous plants are subjected to formxc acid cooking and if desired bleaching with oxidizing bleaching chemicals. In a preferred embodiment of the method provided by the invention, herbaceous plants are subjected to two-step cooking, whereby they are cooked with formic acid first at a temperature of above 100°C and then at a temperature of 70 to 90°C using hydrogen peroxide as an additive, after which they are subjected to bleaching with hydrogen peroxide. In the process of the invention, all the above-mentioned non-wood fibre plants can be used as raw material. Herbaceous plants used as raw material, such as common reed, need not be preprocessed e.g. by grinding or by fractionating in order to reduce ash and silicates, but the stems, leaves, knots and spikes of the herbaceous plants can be cooked in the form they are obtained from a chaff cutter during the harvest, i.e. as 5 to 15 cm long pieces of stems and leaves. In previously known processes, however, where silicates cannot be recovered, reeds are preprocessed mechanically e.g. by removing the core of sugar-cane or chemically e.g. by acid hydrolysis or hot-water hydrolysis in order to reduce the problems caused by silicates. This kind of preprocessing wastes biomass, and the short fibres, essential to paper making, are lost, unlike in the process provided by the present invention. Short-fibred hardwood and juvenile, thinning wood, which have a sho"rter fibre length than stemwood, can also be used as raw material in the production of fine paper. The most economic way of using thinning wood is to apply a complete tree system, such as a pulp chip system, whereby clean chips are used for producing special fibres. in a preferred embodiment of the process provided by the invention, herbaceous plants are first supplied to a first cooking step conducted with formic acid at an elevated temperature of above 100°C. The elevated temperature ensures better solubility of organic and inorganic compounds without decomposition of the formic acid or any damage to the fibres. The formic acid solution used in the first step usually has a concentration of 70 to 90%, preferably 80%, and the temperature is preferably 105 to 125°C. The solid matter to liquid ratio in the first cooking step is usually from 1:3 to 1:8, preferably from 1:4 to 1:4.5. From the first cooking step the material to be processed is supplied to a second cooking step, which is conducted at a lower temperature of 70 to 90°C, preferably at about 80°C. Formic acid to which hydrogen peroxide has been added is used as cooking liquor. The concentration of the formic acid solution is 70 to 90%, preferably 80%. The amount of hydrogen peroxide added is typically 1 to 3%. The cooking times in the first and second steps can vary from 15 min to 1.5 h. The other acids formed during the process, i.e. acetic acid, lactic acid, propionic acid and methyl formiate, can be recirculated as mixed acid from cooking liquor regeneration to the second cooking step, in which the acids that are heavier than formic acid form more stable peroxy compounds and add to the effective reaction time of the peroxy acids. Peroxides decompose more slowly and so their use in the cook is more effective, whereby a smaller amount of hydrogen peroxide (1 to 2.5%) is needed than e.g. in the process of the above FI patent 74,75 0, where the amount of hydrogen peroxide is more than; 4%. This has made it possible to reduce the aggressivity of peroxyformic acid and to yield a product of more even quality. Methylformiate, in turn, enhances formation of cellulose formiate, which in turn has a positive effect on the production of viscose fibre. To produce bleached pulp, bleaching is conducted after the cook with oxidizing bleaching chemicals. In a preferred embodiment, a normal 2 to 4 step hydrogen peroxide bleaching process is conducted. The bleaching process may be a normal atmospheric process or a pressurized process. Some of the hydrogen peroxide steps can be replaced with steps where other oxidizing bleaching chemicals, such as oxygen or ozone, are used. The process also comprises appropriate washing steps between the cooking and the bleaching steps. The last pulp wash of the second cooking step is typically conducted under pressure with 115 to 125°C water. Part of the acids formed during the process that are heavier than formic acid can be removed from circulation and used in the production of preservatives for e.g. storage of fodder and corn. Excessive concentration and separate distillation of heavy acids can thus be avoided. The first cooking step can be conducted with the cooking liquor of the second step, the liquor containing 80% formic acid and, in addition, other acids formed during the cook, such as acetic acid, lactic acid, propionic acid and other organic acids as well as acids recirculated from the regeneration. In a preferred embodiment of the process, closed water circulations of the acidic cooking step are kept separate from those of the alkaline bleaching step. The silicates formed in the process are recovered as a separate product, excess sodium is recirculated to the bleaching step and organic compounds to a combustion step. The clean water evaporated during the process is used as washing water. The formic acid released from the pulp in the bleaching step is recovered as sodium formiate and recirculated to the power plant to bond sulphur compounds. In the production of viscose fibre, pulp processed as described in the invention and obtained from the cooking and bleaching steps is mercerized typically for 3 0 to 60 min and sulphurized for 3 0 to 60 min by a normal wood-based viscose process. The formic acid used as a cooking chemical dissolves the nutrients and metals of the plants so that after the washing steps the cellulose is sufficiently free of any components that would impair filterability and catalyzation of viscose. In the alkaline hydrogen peroxide bleaching step that follows the cook, the silicates derived from plants dissolve in the bleaching waters effectively, and so silicates do not cause any problems in the production of viscose, either. Further, any extractives contained in the plants are also removed during the cook and bleaching, and so they do not have a harmful effect on the viscose process and the subsequent production of yarn, either. The formic acid based process provided by the invention has made it possible to utilize the even and narrow molecular weight distribution of the cellulose obtained from short-fibred field plants in the production of strong viscose fibre (2.8 to 3.1 cN/dtex) of even quality. Fibres obtained from reed plants are shorter than wood fibres, and a given volumetric unit can hold 6 or 7 times more such fibres than wood fibres. Because of this, reed plants have a much better liquid / retention capacity than wood fibres. This also affects mercerization. Lye penetrates more slowly into the fibres, and the time needed for the reaction is longer than with wood fibres. With the same mercerization time, plenty of insoluble fibre parts remain, forming slimy layers on viscose filters. Lengthening of the mercerization time and use of a catalyst have produced good quality viscose with a filterability-describing Kw character of less than 100, which is considered sufficiently good for industrial use. In the invention, the high ash, nutrient, metal and extractive content of herbaceous plants can be lowered during the process to a level where it does not impair the viscose process, and the fibre distribution can be rendered such that strong viscose of even quality is obtained. High-quality cellulose is also suited for other products obtained from modified cellulose. They include, for example, CMC and cellulose acetate. In the production of fine paper, the pulp processed as described in the method and obtained from the cooking and bleaching steps is conducted to a fine paper production process, in which a suitable proportion of wood fibre is combined thereto. This means, for example, 3 0 to 50% of fibre from herbaceous plants, the rest being wood fibre. It has been observed that the use of e.g. 5 0% of birch fibre and 50% of fibre obtained from herbaceous plants by the peroxy-formic acid technique of the invention produces fine paper that has better qualities than birch/pine-based fine paper. When wood is used as starting material in the production of products (e.g. fine paper) based on special fibres in accordance with the prior art technique, deciduous trees must be selected and their fibres must be ground separately in order to achieve the desired fibre bonding characteristics and to give the paper sufficient opacity and smoothness. When herbaceous plants, whose fibres are thinner and shorter than those of deciduous trees, are used as raw • material, no separate grinding is needed. Also, short fibres allow more bonds in a paper structure than long fibres. This also enables the use of a larger quantity of a filling agent, which may further improve the surface characteristics of paper and lower the price. The problems arisen in the production of fine paper from non-wood fibres have usually related to e.g. dewatering, runability and retention. The strength, density and rigidity characteristics of the paper produced have also been unacceptable. From the pulp produced by the process of the invention, it has, surprisingly, been possible to produce fine paper with good opacity, high brightness, an even surface, suitable gloss, good light scattering efficiency and high surface strength. All these characteristics are desirable in high-quality colour printing. Electronic colour printing will add interest in such paper. On the other hand, the requirements of new printing techniques and environmental protection will add to the requirements set for colours and inks. Stiffer colours will also set requirements for the surface strength of paper in respect of permanence characteristics of colour and fibres. The new peroxy-formic acid technique has made it possible to show, on a pilot scale, that when 50% of the birch is replaced with short-fibred grass fibre, all central printing characteristics relating to offset four-colour printing are better than with birch/pine-based fine paper. The peroxyformic acid process provided by the invention and the subsequent production of viscose and fine paper can be incorporated into a larger system, a flow chart of which is shown in attached figs. 1 and 2. In fig. 1, raw material 16 (which may be reed canary grass or common reed) is supplied to a first cooking step 1. In the first cooking step, formic acid is used as a cooking chemical, the acid entering the cooking step from a previous cooking step 2 as a reversed formic acid flow 18. From the first cooking step, spent liquor is supplied to regeneration along conduit 19. The pulp flow that has undergone the first cooking step is supplied to the second cooking step 2. In the second cooking step, a reversed flow of formic acid solution 22 supplied from the following step, i.e. from an acid wash 3, is used as a cooking chemical together with hydrogen peroxide, which is obtained as a chemical flow 20. The cellulose that has undergone the second cooking step is supplied as a product flow 21 to the acid wash 3. In the acid wash 3, delignified pulp is washed with formic acid obtained as a distillation flow 23 from the regeneration and partly as a make-up chemical flow 24. The acid wash can comprise several steps according to the need. From the acid wash, a cellulose flow 25 is supplied to a water wash 4. The wash may be pressurized and may comprise several steps according to the need. The water used in the wash is obtained as a condensate along conduit 28. After the wash, the water obtained from the wet wash is supplied to the regeneration along conduit 27. Cellulose 26 is supplied from the wet wash to a first bleaching step 5 and a second bleaching step 6. The alkaline bleaching 5 and 6 of cellulose is conducted with hydrogen peroxide, which is shown as a chemical flow 29. There may be more than one bleaching step, depending on the brightness desired. The bleaching liquor of the first bleaching step 5 is obtained as a reversed flow 32 from the following bleaching steps 6 and supplied to fibre recovery 11 along conduit 30. From" the first bleaching step, cellulose 31 is supplied to the following bleaching steps 6. The last bleaching step uses water obtained from evaporation 13 along conduit 34 as a bleaching liquor together with hydrogen peroxide obtained from chemical flow 29. The last bleaching step produces a bleached cellulose flow 33. The cooking chemicals of the first cooking step are supplied to the cooking chemical regeneration 7 along conduit 19, the water of the wet wash is supplied along conduit 27 and a formic acid solution obtained from hemicellulose concentration 10 is supplied along conduit 38. In the regeneration, the formic acid is distilled and recirculated to the acid wash 3 along conduit 23. Part of the distillate can also be supplied to the first and second cooking steps 1 and 2 to adjust acid concentration. Concentrated spent liquor is supplied along conduit 3 6 to lignin recovery 9. Lignin is precipitated from the spent liquor with water, and the remaining hemicellulose-containing aqueous solution is supplied along conduit 37 to the hemicellulose concentration 10. The concentrated aqueous solution that contains formic acid is recirculated from the hemicellulose concentration 10 to the regeneration 7 along conduit 38. Acid 35 is recovered in the regeneration and supplied to production 8 of an organic preservative. Fibres are recovered from the bleaching liquor in the fibre recovery 11. The bleaching liquor is supplied from the first bleaching step 5 to the fibre recovery 11 along conduit 30. A fibre-containing solution 40 is supplied to a filter press 14. A filtrate 39 of the bleaching waters is supplied to ultra filtration 12. In the ultra filtration, particles that are smaller than fibres are recovered from the water and supplied to the compression step 14 along conduit 41. A filtrate of the ultra filtration is supplied to the evaporation 13, which may comprise several steps, along conduit 42. In the evaporation, silicate-containing water is concentrated and the purified water is recirculated to the last bleaching step along conduit 34. The water concentrated with respect to silicate is supplied to silicate recovery 15 along conduit 43. Silicate is recovered in step 15 by adjusting the pH, which is done by adding formic acid as a chemical flow 44. From the silicate recovery, clean water is supplied along conduit 45 either to the flow 3 9 of water supplied to the ultra filtration or to the flow 32 of bleaching water. In the silicate recovery, silicate is recovered as a separate product 46. Water 47 obtained from the filter press is recirculated to the ultra filtration 12 and organic matter 48 is supplied to combustion. Fig. 2 shows a general flow chart in which common reed and/or reed canary grass and formic acid are supplied to a cooking step that comprises the two cooking steps described above. To the second cooking step is also supplied hydrogen peroxide. The pulp obtained from the cooking step is supplied to bleaching, which is conducted with hydrogen peroxide. The pulp obtained from the bleaching is used for the production of fine paper on the one hand and viscose on the other hand. The general flow chart of fig. 2 also shows regeneration step following the cook, lignin recovery and hemicellulose recovery. From the hemicellulose recovery are obtained sugars and from the lignin recovery is obtained lignin. A power plant utilizing peat and bio waste, and electricity produced by the plant are also indicated in the chart. The closed water circulations of the acidic cooking step are kept separate from those of the alkaline bleaching step. The bleaching waters are processed in a separate closed circulation system, silicates are recovered as a separate product, excess sodium is recirculated to the bleaching and organic compounds to combustion. The evaporated clean water is used as washing water. The formic acid released from the pulp during the bleaching is recovered as sodium formiate, which can be supplied with the organic compounds to the power plant for combustion to bond sulphur compounds. The process is friendly to the environment. The formic acid and hydrogen peroxide used as cooking and bleaching chemicals are biodegradable. The process is based on a closed water circulation system, and the chemicals can be recovered without that silicates or any other compounds would cause any problems. In the process of the invention, the circulation systems of both brown stock waters and bleaching waters can be closed. Such a closed water circulation system is not described in FI patent 74,750 mentioned above. In the process of the invention, where the chemicals do not contain sulphur nor chlorine, the water circulation systems are much easier to close than in a conventional sulphate process, where the closing not only requires removal of foreign matter and evaporation but also separate regeneration of sulphur and sodium. In a peroxyformic acid process, the substances contained in the plants dissolve in the first, acidic cooking step and are not carried back to the process with chemicals. The dissolved compounds move to a hemicellulose fraction, wherein they can be used as fermentation nutrients or, together with the ash produced by the power plant, as recirculated nutrients on the fields. It is only silicates that do not dissolve in the cooking liquor, but 99% of them dissolve in he bleaching step and can be recovered as a separate product. Purified water can be recirculated to the bleaching as washing water. Accordingly the present invention provides a process of production of pulp from herbaceous plants or the like, wherein herbaceous plants are subjected to formic acid cooking and if desired bleaching with oxidizing bleaching chemicals, whereby the formic acid cooking comprises two steps; formic acid cooking is first conducted at a temperature of 105 to 125°C and then at a temperature of 70 to 90°C using 1 to 3% hydrogen peroxide, based o the amount of pulp, as an additive, and whereby the cooking time in the first and second cooking step is 15 min to 1.5 h. The invention will now be described more in detail with reference to embodiments given by way of example in which; Example 1 A pilot scale test was conducted, in which 200 kg of common reed harvested in the spring (moisture content 15%) was cooked at 120°C with 80% formic acid (cooking liquor of the second step) in the first step, and with regenerated 80% formic acid and 2.5% of hydrogen peroxide as an additive (based on the amount of pulp) in the second step. The ratio of common reed to cooking liquor (liquid ratio) was 1:4 .5. The cooking times in the first and second cooking steps were 60 min. The cooked pulp was bleached by an alkaline three-step hydrogen peroxide bleaching process at 80°C. Viscose fibre was produced from the pulp processed in the above manner by mercerizing wet pulp that contained 20% of dry matter for 60 min and by sulphurizing it for 60 min. The characteristic describing the filterability, i.e. filterability constant Kw., was 82. The fibre strength was 3.1 cN/dtex. The filterability constant Kw., was obtained from Kw., = 100000 x [(2-P2/P1) / Pi+ P2), where Pi = amount in grams of viscose drained out in 0 min-20 min, and P2 = amount in grams of viscose drained out in 20 to 60 min. The determination was carried out with an equipment comprising an aperture plate on top of which was placed an abutment ring (diameter 7.9 cm, which left about 49 cm2 of the filter surface free) and filter material (cotton linter plate, manufactured by Procter & Gamble/the Buckeye Cellulose Division; quality 12-FW-4) . The backing fabric was unbleached cotton fabric. The fibre strength was determined by stretching several individual fibres until they broke. The strength was obtained by dividing the power needed to break the fibre by the fibre titre. The titre is expressed as a dtex value, which means the linear density of the fibre, so that a 10 000 m long fibre of 1.0 dtex weighs 1.0 g. Example 2 A pilot scale test was conducted, in which 250 kg of common reed harvested in the spring (moisture, content 15%) was cooked at 105°C with 80% formic acid in the first step, and with 2.5% of hydrogen peroxide (based on the amount of pulp) as an additive in the second step. The liquid ratio and cooking times were ". the same as in example 1. The pulp processed in this manner was bleached by a three-step hydrogen peroxide bleaching process at 80°C. Viscose fibre was produced from the pulp processed in the above manner by mercerizing wet pulp that contained 20% of dry matter for 60 min and by sulphurizing it for 60 min. The filterability constant K„ was 121. The fibre strength was 2.9 cN/dtex. Example 3 A pilot scale test was conducted, in which 200 kg of common reed (moisture content 15%) was cooked at 115°C with 80% formic acid (cooking liquor of the second step) in the first step. The liquid ratio was the same as above. The cooking time was 45 min. In the second cooking step, 2.5% of hydrogen peroxide was used as an additive in the 80% formic acid, and the cooking time was 60 min. The pulp was bleached by a three-step alkaline hydrogen peroxide bleaching process. Fine paper was produced with a fibre ratio of 35% of reed fibre obtained above, 35% of birch fibre and 30% of pine fibre. Four km of 80 cm wide base paper with a grammage of 80 g/m2 was driven with a pilot paper machine. The opacity, bulk, stiffness, smoothness and filler retention were better than with birch/pine-based fine paper used as reference material: the opacity of the base paper produced by.the process of the invention was 89.3% (86.8% with the reference paper), the bulk was 1.20 cm3/g (1.18 cm3/g with the reference paper), the stiffness in the machine direction was 0.554 mNm and in the cross machine direction 0.163 mNm (0.317 mNm and 0.154 mNm with the reference paper), the roughness on the wire side was 215 ml/min and on the upper surface 340 ml/min (340 ml/min and 360 ml/min with the reference paper), and the filler retention was 86.03% (84.87% with the reference paper). The resultant base paper was coated in an amount of 10 g/m2 on both sides and supercalendered. In four-colour offset printing, all major advantages relevant to printing were better than with birch/pine-based fine paper. WE CLAIM: 1. A process of production of pulp from herbaceous plants or the like, wherein herbaceous plants are subjected to formic acid cooking and if desired bleaching with oxidizing bleaching chemicals, whereby the formic acid cooking comprises two steps; formic acid cooking is first conducted at a temperature of 105 to 125°C and then at a temperature of 70 to 90°C using 1 to 3% hydrogen peroxide, based on the amount of pulp, as an additive, and whereby the cooking time in the first and second cooking step is 15 min to 1.5 h. 2. The process as claimed in claim 1, wherein the formic acid cooking is conducted with about 80% formic acid. 3. The process as claimed in any one of the preceding claims, wherein said oxidizing bleaching is conducted with hydrogen peroxide. 4. The process as claimed in claim 2, wherein the second cooking step is conducted at a temperature of 80°C with 80% formic acid, adding 1 to 3% of hydrogen peroxide, based on the amount of pulp. 5. The process as claimed in any one of claims 3 to 4, wherein the hydrogen peroxide bleaching comprises 2 to 4 steps. 6. The process as claimed in any one of the preceding claims, wherein the ratio of solid matter consisting of herbaceous plants to cooking liquor is between 1:3 and 1:8, preferably between 1:4 and 1:4.5 at the beginning of the cook. 7. The process as claimed in any one of the preceding claims wherein the herbaceous plants are common reed. 8. The process as claimed in any one of claims 2 to 4, wherein the first cooking step is conducted using cooking liquor of the second step, the liquor containing 80% formic acid and, in addition, other acids formed during the cook, such as acetic acid, lactic acid, propionic acid and other organic acids as well as acids recirculated from regeneration. 9. The process as claimed in any one of the preceding claims, wherein the closed water circulations of the cooking step are kept separate from those of the bleaching step. 10. The process as claimed in any one of the preceding claims, wherein the silicates formed in the process are recovered as a separate products, and excess sodium is recirculated to the bleaching step and organic compounds to a combustion step. 11. The process as claimed in any one of the preceding claims, wherein the clean water evaporated in the process is used as washing water. 12. The process as claimed in any one of the preceding claims wherein the formic acid released from the pulp in the bleaching step is recovered as sodium formiate and recirculated to the power plant to bond sulphur compounds. 13. A process of producing viscose fibres from herbaceous plants or the like, the process comprising a cooking step, a bleaching step and mercerization of the resultant pulp, wherein the cooking step comprises formic acid cooking in accordance with claim 1 and the bleaching step comprises bleaching with oxidizing bleaching chemicals. 14. The process according to claim 13, wherein the formic acid cook comprises two cooking steps in accordance with claim 2 and that the bleaching comprises bleaching with hydrogen peroxide. 15. A process of producing fine paper from herbaceous plants or the like, the process comprising a cooking step, a bleaching step and production of fine paper from the resultant pulp, wherein the cooking step comprises a formic acid cook in accordance with claim 1 and the bleaching step comprises bleaching with oxidizing bleaching chemicals. 16. The process according to claim 15, wherein the formic acid cook comprises two cooking steps in accordance with claim 2 and the bleaching step comprises bleaching with hydrogen peroxide. 17. A process of production of pulp from herbaceous plants substantially as herein described with reference to the accompanying drawings.

Documents:

73-mas-1997 abstract duplicate.pdf

73-mas-1997 abstract.pdf

73-mas-1997 claims duplicate.pdf

73-mas-1997 claims.pdf

73-mas-1997 correspondence others.pdf

73-mas-1997 correspondence po.pdf

73-mas-1997 description (complete) duplicate.pdf

73-mas-1997 description (complete).pdf

73-mas-1997 drawings duplicate.pdf

73-mas-1997 form-2.pdf

73-mas-1997 form-26.pdf

73-mas-1997 form-4.pdf

73-mas-1997 form-6.pdf

73-mas-1997 petition.pdf