EP0672207A1 - Viscose production process. - Google Patents

Viscose production process.

Info

Publication number
EP0672207A1
EP0672207A1 EP19940900624 EP94900624A EP0672207A1 EP 0672207 A1 EP0672207 A1 EP 0672207A1 EP 19940900624 EP19940900624 EP 19940900624 EP 94900624 A EP94900624 A EP 94900624A EP 0672207 A1 EP0672207 A1 EP 0672207A1
Authority
EP
Grant status
Application
Patent type
Prior art keywords
hsl
temperature
digester
characterized
cooking
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.)
Granted
Application number
EP19940900624
Other languages
German (de)
French (fr)
Other versions
EP0672207B1 (en )
Inventor
Wolfgang Wizani
Andreas Krotscheck
Johann Schuster
Karl Lackner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lenzing AG
Primetals Technologies Austria GmbH
voestalpine AG
Original Assignee
Lenzing AG
Primetals Technologies Austria GmbH
voestalpine AG
Priority date (The priority date 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 date listed.)
Filing date
Publication date

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Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00Pulping cellulose-containing materials
    • D21C3/02Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
    • D21C3/022Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing compounds
    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C1/00Pretreatment of the finely-divided materials before digesting
    • D21C1/02Pretreatment of the finely-divided materials before digesting with water or steam

Abstract

A process is disclosed for producing viscose from lignocelluloses such as those of deciduous trees, coniferous trees or annual plants. The lignocellulose is first processed in a digester with saturated steam to cause the preliminary hydrolisis of hemicelluloses, and is then processed without relaxation with hot black liquor (HSL) from a previous sulfate-cellulose digestion, if required with the admixture of fresh white liquor (WL) to neutralise the resulting acid reaction products, so that a neutralisation liquor (NL) is formed in the digester. After the required amount of alkali for delignification is added as fresh white liquor (WL), if required accompanied by the expulsion of neutralisation liquor (NL) and temperature regulation, digestion is carried out, with or without a temperature gradient. When the desired degree of disaggregation is reached, digestion is stopped by expulsing the hot black liquor (HSL) with cold alkaline washing filtrate (WF), so that the cellulose is at the same time freed from still adhering lignin decomposition products, and the thus obtained cellulose is discharged from the digester at a temperature below 100 DEG C.

Description

A process for producing viscose pulps

The present invention relates to a process for the production of viscose pulp by a steam prehydrolysis sulfate (Kraft) - displacement cooking process.

Viscose pulps are chemical pulps, which loseacetat for the production of rayon, cellophane, carboxymethyl cellulose, nitrocellulose, cellulose, are used textile fibers and special papers. The specific characteristics of viscose pulps are the high purity and high content of alpha cellulose.

Viscose pulps have traction materials a high content of alpha cellulose, a low content of hemicellulose, lignin, ash and expression rate. The removal of the hemicellulose in the pulping process is particularly difficult because the pentosans are nearly as resistant to alkali and acids, such as the loose Cellu¬ itself. The alpha cellulose content is determined by dissolving the cellulose in 18% NaOH. The Alpha cellulose is the part of the cellulose, which is not soluble in 18% NaOH. Beta cellulose of the part of the cellulose is referred to, falling with subsequent dilution of the 18% solution and acidifying aus¬. Gamma cellulose as the part of the strength in the 18% NaOH referred to dissolved substances, the solution does not precipitate on neutralization of Lö¬. As a rough guideline can be considered that the alpha cellulose represents the normally present in the plant cellulose, while the beta cellulose is a measure of the degraded during the chemical pulping cellulose and cellulose Gamma is a measure of the remaining hemicellulose.

Depending on the end product, the requirements on the content Alphacellulose¬ are different. For example Rayon submits Alphacellulo¬ segehalt of 88-91 from. However, viscose pulps that loseacetat to cellulose, Nitrocellullose or other derivatives to be used have ben a much higher alpha content ha¬,, ​​at least one alpha content of 94-98 and less than 1.5% hemicellulose. Nitrocellulose explosives for purposes generally produced from cotton linters, since for this purpose an alpha content of 98% and a hemicellulose content of nearly 0% is required.

Unlike paper pulps, where a high Hemicellulose¬ is content desired for reasons of strength, the hemicelluloses must be removed at Viskose¬ cell materials. When Produk¬ tion of rayon, for instance react Xylane with CS 2 in the Xanto- nierungsreaktion, namely as fast as the cellulose itself, which leads to an increased consumption of CS 2nd Other hemicelluloses react more slowly than the cellulose and then bedin¬ gen difficulty in filtration.

Viscose is seen worldwide primarily produced fitverfahren after Sul¬. In step process the acidic sulfite comes zierungsrate vor¬ namely into question because of its schnel¬ len hydrolysis of hemicellulose and the fairly good Delignifi-. However, it also come in two- or mehrstufi¬ gen processes bisulfite and neutral sulfite used.

In general, the following can be the sulfite say: They are generally carried out as batch cooking, that is discontinuous. The cooking temperature is acidic sulfite in the range of 135 ° C, reindeer at 160 "at Bisulfitverfah- C. The heating of the digestion liquor to the optimum cooking temperature of the pressure of the SO 2 gas rises in the cooker, excess S0 2 is at the appropriate time blown off. The digestion requires a total time of about 6-8 hours.

The key parameters for the determination of the final product quality and yield are the sulfidity of pH and temperature. Also, the nature of the base has an effect, in particular on the rate of diffusion of the digestion chemicals in the wood chips. The decomposition of the hemicelluloses, especially xylans and mannans the occurred, notably by acid hydrolysis glukosidi- shear bonds. The degraded hemicelluloses are with the digestion solution from the pulp. The degraded celluloses (beta celluloses) must be removed by subsequent alkaline treatment. The cellulose in viscose pulps generally has a lower DP than in paper pulp. This is ty due to the time required for the removal of hemicelluloses Acidi-, whereby the cellulose is hydrolytically degraded partially. This lower DP has the consequence that Sulfitviskosezell¬ materials can not be used for application areas with high strength requirements, such as "high tenacity rayon cord".

Step sulphite are not able certain Na¬ delhölzer such as Douglas fir, larch and most Kiefernar¬ th catch up because of the high content of resins. The Harz¬ is particularly in the heartwood area content, therefore a decomposition of Sägeholzabfällen with this method - because it is mostly is sapwood - come into question in some cases. For this reason, two in practice or applied multi-step processes. The first stage is less acidic than the second normally. Thereby, the lignin is sulfonated in the first stage, whereby a Rekondensie- tion of the lignin is prevented in the second stage, are removed in the primarily the hemicelluloses.

The sulfite is carried out with different bases namely calcium, sodium, ammonium and magnesium.

The calcium sulfite process is dying because the Chemika¬ makes difficulties lien recovery. Magnesium sulfite are widely used for the production of viscose pulp because of einfa¬ chen chemical recovery. siumsulfitaufschlußprozessen in multistage magnesium, an acidic pH is applied in the first stage. Otherwise, the digestion conditions in Magne¬ siumsulfitprozeß are largely identical to those of the known calcium sulfite.

By ammonium sulfite faster Durchdrin¬ can supply achieved with the cooking chemicals and da¬ shortened by ziumsulfitverfahren the heating time compared to Kal¬ in certain cases, the chips, but has this Verfah ren a number of serious drawbacks, such as increased corrosion, increased foaming problems in sorting because of the nitrogen and a lesser degree Weiße¬ the pulp. The most widely used in industry Verfah reindeer is the sodium sulfite digestion, which has been used since the 50s. One of these, the Rauma-Repola- process which is operated in Finland since 1,962th It is a three step process and is used for spruce and silicic fernholz. The first step is a bisulfite step at pH 3-4 for the impregnation of the wood chips. The second stage corresponds substantially to a conventional sulfite pulping, added in the SO 2 and the viscosity of the pulp is determined. At the end of the second stage is gassed S0. 2 In the drit¬ th stage, sodium carbonate is added to neutralize the cooking liquor. Depending on the temperature and pH conditions are Viskose¬ pulps with alpha cellulose content of 89-95% was prepared.

The Domsjo process, which has been in operation since 1960, is a zwei¬ stage process er¬ with the high yields of viscose ranges are. In the first stage, with a pH of 4.5 - 6 working, the second stage corresponds to a normal acidic sulfite pulping. The pH of the second stage is adjusted by the addition of 2 -water SO. PH 4.5 in the first stage yields are obtained, which are 2% above that of a single-stage Verfah proceedings at correspondingly low sorting losses. At pH 6, while the yield can by 4-5%, on 29-35% gestei¬ siege be at the expense of a higher Glucomannange- haltes. Corresponding to the higher yield of this process the alpha cellulose content is below the above-described method; it amounts to 83-89% the single-stage process and the two-stage method 85-90%. Higher alpha cellulose content with a corresponding lowering of the yield can be obtained at room temperature with subsequent acid treatment to remove the residual inorganic substances by a post-treatment of the fabric with dilute alkali at elevated temperature or with concentrated alkali.

The sulfate (Kraft) pulping method is not suitable in its usual ein¬-stage design for the production of viscose pulp. Only 84-86% alpha cellulose can be achieved with this embodiment. Extended cooking time or er¬ creased cooking temperatures do not lead to the goal. These require a stronger degradation of the cellulose, due to alkaline hydrolysis of the glucosidic linkages in connection with the so-called "peeling off reaction". Connected to an acid treatment - the so-called pre-hydrolysis - can be produced fabrics with this alkaline digestion process from all the chemical pulp manufacturing raw materials usual quality Viskosezell¬. A number of viscose operate according to this method, wherein as a pretreatment finally aus¬ Wasservorhydrolyse with or without the addition of Fremd¬ acid is applied.

The acidity connected to the reaction temperature are the aus¬ impact key factors of this pretreatment. The addition of Mi¬ neralsäure reduces the time or the temperature derliche erfor¬ for hydrolysis. In the treatment of lignocellulosic materials with non-aqueous media are formed from the acetyl groups of the Hemicellu¬ organic acids, especially acetic acid, whereby the pH without the addition of acids is lowered to a pH of about 3-4. In xylan-rich lignocelluloses, such as hardwoods, the pH due to the high content of acetyl groups may further ken absin¬. Although the addition of mineral acids, especially hydrochloric acid accelerates the hydrolysis reaction, but has serious disadvantages, most particularly with regard to corrosion and Prozeßko¬. The reaction conditions in the prehydrolysis affect the yield and quality of the Viskosezellstoffes and they affect the delignification as well as the removal of further hemicelluloses when recondensation follows er¬ of lignins and of kon¬ condensable reaction products from hemicellulose hydrolysis. This occurs with particularly sharp hydrolysis conditions in prehydrolysis and raw materials with a high lignin content, such as conifers.

Wasservorhydrolyse-Sulfatviskosezellstoffe of conifers kön¬ NEN already before bleaching alpha cellulose contents of 95-96% er¬ rich, although about 3% lignin and 2-3% Xylene are still included. Hardwoods usually contain more than 95% alpha cellulose, 1% lignin and 3-4% xylan. The Xylane are usually achieved by an aftertreatment with cold alkali during bleaching. However, this is a kostenauf¬ agile process step.

The prehydrolysis sulfate process can unlock all major raw materials for the pulp production, achieved much höhe¬ re alpha cellulose contents, a much more uniform Moleku¬ large weight distribution of cellulose and higher DP values. However, a disadvantage compared to sulfite is the gerin¬ gere yield wearing be¬ usually only 28-30% before bleaching.

Some methods that have no indu¬-industrial relevance due to certain drawbacks are hereinafter briefly mentioned:

The Sivola process substantially circuit is followed by a post-cleaning with hot sodium carbonate acidic Sulfitauf¬. For pulps having an alpha cellulose content and a purity comparable with that of the prehydrolysis-Sulfatauf¬ following conditions are required statements: 170 ° C, 1-3 hours digestion time, nat in the alkaline step with Natriumkarbo¬ at a chemical dosage of 150-200 kg / t, to maintain a pH of 9-9.5, must also during the sodium karbonatkochung 0.5-1% S0 2 remain in the pulp in order to achieve a aus¬ reaching bleachability of the substance. The first stage is carried out at 125-135 ° C with a treatment time of 3 hours or more.

The prehydrolysis soda-anthraquinone cooking is indeed longer be¬ known as the sulfate cooking, but nen from verschiede¬ cost and quality reasons could not prevail. The yield is low, the residual lignin content is relatively high, the Rein¬ integrated low and the DP of the alpha cellulose is low. In the nach¬ connected bleach to remove residual amounts of lignin and hemicellulose is 1.7 times more bleaching chemicals, expects ge than chlorine required than in the prehydrolysis sulfate. A further economic disadvantage is the addition of 0.5% of anthraquinone. This chemical causes considerable zu¬ additional cost. In development are organosolv processes for the production of viscose. This examined so far only in the laboratory process could not have substantial advantages in terms of alpha cellulose content and delignification and especially given the economy, the ausschlagge¬ by Rückgewin¬ voltage necessity of the organic solvent is bend influenced, to demonstrate to the usual sulfite and sulfate process.

In summary it can be said that, however, the known methods for the production of viscose pulp have different gra¬ four disadvantages. The prehydrolysis-sulphate process kön¬ NEN unlock all common lignocelluloses, yield hochrei¬ ne celluloses with a high alpha cellulose content, which has a large uniformity in molecular weight and a high DP, however with respect to the sulfite to Nach¬ part of a low yield (28-30 % compared to 30-35%). The production of viscose pulp are substantially determined by the raw material costs and power consumption. Another determining factor in the future friendliness the Umweltverträg¬. In different regions, there are already provisions in respect wastewater values ​​strict Vor¬ such as AOX, BOD, COD. Wäh¬ rend few years ago 6 kg AOX per tonne of pulp from durch¬ were acceptable, it must be assumed in ab¬ foreseeable future that these values ​​must be in the range of 0.5 kg or even zero. The same applies to Luftreinhaltebestimmun- gene. Any contamination, ie not in the alpha cellulose Aus¬ transition material for the subsequent derivatization for the production of fibrous materials, has a substantial influence on Chemika¬ lien consumption, waste water and air pollution.

About the prehydrolysis with steam and subsequent digestion for the production of viscose there are a number wissen¬ schaftlicher investigations, such as IH Parekh, SK and SK Roy Sodani Monlik "Dissolving grade pulps from Eucalyptus (tereticornis) hybrid". The resulting Hydroly¬ be separated in various ways to channel them into recovery and its proven harmful Ein¬ river on the quality of the pulp during subsequent cooking to reduce seprodukte. Because of these difficulties, the detail in the paper by H. Sixta, G. Schild and Th. Baldinger in "The Paper", Issue 9/92, pp 527-541, on "The Wasservorhydrolyse Buchholz" are combined, is this possible methods of pre-hydrolysis of the pulp production technically not applied.

Therefore, process improvements or new process for producing viscose pulp must be limited to quality standard, minde¬ least according Water prehydrolysis kraft pulp at Erhö¬ hung in yield and reduction of energy consumption and Chemikalien¬ connected to an environmental discharge waste water and concentrate exhaust side.

The present invention is based on the task, an energy-saving process for producing Viskosezell¬ material from the usual for paper pulp production Ligno¬ celluloses to develop, which has already been at the boiler outlet a high alpha-cellulose and low lignin content associated with high viscosity and yield values and the an¬ closing processing in washing, screening and bleaching requires less technical effort and less Bleichchemika¬ lien, making the process täts- essential Produktquali- and has cost advantages over conventional methods of viscose pulp.

According to this task, the application of a sulfite process is eliminated. can sulfite, as stated above, unlock only certain lignocelluloses, such as not common woods such as pine, give lower cellulose viscosity because of the er¬ ford variable elevated cooking temperature and acidity of the α-cellulose content achieved after a two-stage cook, not more than 85-90%, and after a Blei¬ che only 95-96%, the yield is only 29-35%, and the Endpro¬ domestic product has not suited a limited application, it is, for example, for "high tenacity rayon cord".

The known Wasservorhydrolyse sulfate processes have next to a still rather low yield of 28-30%, a high of energy required in prehydrolysis and cooking and high Chemikalienver¬ consumption in the bleach for low delignification serious disadvantages be¬ from the water prehydrolysis dingt become. In published in September 1992 work by H. Sixta et al. of a viscose LENZING AG says on this issue:

"The pre-hydrolysis is limited by the occurrence difficult to control side reactions. In addition to the desired hydrolytic fragmentation reactions secondary reactions occur which can affect the long term in pulping and bleaching as a function of temperature and time, the process behavior in prehydrolysis and the subsequent delignification reactions. The main side reaction the dehydration of pentoses FURAL to Furman, is the starting point of unwanted inter- and intramole¬-molecular condensation reactions. This resinous Ver¬ arise compounds that are eliminated by continuation of the reaction from the aqueous phase and can ab¬ store on all available surfaces. the deposition of these substances on Hackschnit¬ zel affect the diffusion-controlled mass transfer. this leads to increased resin deposits on the Phasengrenz¬ layer with the consequence aggravated Delignifizierungsreaktio¬ nen in digestion and lead surface and a possible reduction of yield and purity of the degree of finishing Zell¬ produced materials. Big problems cause these resin deposits by gluing and obstruction on the fly. "

The steam prehydrolysis is not used for large-scale Zellstoffher¬ position, as these stungs- other similar Verkru- and clogging problems resulting in poor product quality. Sixta et al. Write Hiezu in the previously cited Pub¬ lication:

"To reduce the high energy costs associated with the evaporation of the pre-hydrolysates, there has been no lack of attempts, the liquor ratio to pure steam Vorhy¬ drolyse (liquor ratio 1: 1 to 1.5: 1) to reduced. This technologically very simple and elegant process but unfortunately has a very negative effect on the pulp quality. the investigations of Havranek and Gajdos (especially with beech and spruce) that steam prehydrolysis is unique Ur¬ thing for higher kappa values, poorer bleachability, niedri¬ gere alkali resistance and reactivity of pulps applies. Eige¬ ne studies confirm the negative influence of steam prehydrolysis on pulp production. "

The deposition of resinous substances on all available surfaces Oberflä¬ that cause big problems by sticking and clogging during operation and cleaning operations Pro¬ duktionsunterbrechungen have the effect are also known from Furman furalerzeugung by treatment of lignocellulose with steam be¬ known. Again, the poor quality of the cellulose is confirmed after the steam treatment in an acidic medium. The residue of the furfural production (60-70% of the raw material used, be¬ standing essentially of cellulose and lignin) is burned or driven on landfills.

The object of the invention is therefore also associated with the undesirable byproducts problems as well as the serious Nach¬ parts of steam prehydrolysis on final product quality wind to über¬ and to connect the energy and process-technical advantages of this process step with an energy and saving bleichchemikalien-, extended displacement.

Not effective was the obvious removal of disturbing reaction products through, for example, steam or water washing. Rekonden- tion and debris could thus not be avoided, for example; In addition, this intermediate step leading to a large loss of energy.

Surprisingly, it was found that by a schungs- Fach¬ man in this field and due to the extensive research and operating results could not be expected that the above-described complex problems thereby releasing ge and combined with the advantages of an extended Verdrängungsko¬ be chung can, that the reaction products of the pre-hydrolysis are not separated, but that the Vorhydro¬ lysis by pump up of the digester with HSL of a preceding digestion and WL stopped and then supply technology a sulfate displacer connected to extended digestion ( "extended delignification") under specific conditions is performed.

Accordingly, the present invention is a process for producing viscose pulp from lignocelluloses according to a steam prehydrolysis sulfate (Kraft) displacement digestion process, which is characterized in that, after prehydrolysis with saturated steam, the digester with hot black liquor (HSL) of a voran¬ previous cooking process, and filled optionally with the addition of fri¬ shear white liquor (WL), while the hydrolysis products are neutralized, whereby the digester neutralization liquor (NL) is formed, that the in the cooking for delignification amount of alkali required in the form of fresh white liquor (WL) zuge¬ leads is optionally wherein a subset of the NL is displaced, that the digestion takes place with or without temperature gradient, and that the boiling process by displacing the cooking liquor (HSL) with al¬ kalischem washing filtrate (WF) is terminated, whereby the alkalilös¬ Liche lignin of the digested fiber material washed out, and the pulp used for the off carrier is cooled from the digester.

A preferred embodiment of the method in the form of a discontinuous process sequence is shown in FIG. 1 represents darge. However, just as is - with the exception of pre-hydrolysis - a continuous procedure possible or conceivable. In the case of a discontinuous process sequence the Ver¬ is driving in nine steps divided. The steam prehydrolysis and digestion of the chips made in one and the same cher Ko¬ (KO). For the alkalis for neutralizing the Hydrolysepro¬ the steam prehydrolysis-products and for subsequent cooking at least four vessels are required, namely for the hot white liquor (HWL) to establish the required alkalinity of alkalis for neutralization and cooking, ge for the hot Schwarzlau¬ (HSL ) of finished cookings, leach for the of neutralization (NL), the prehydrolysis by absorption of the hydrolysis products of the steam produced from HSL and directly from the NL-a container according heat recovery for Eindampfanläge (EDA) and anschlies- sent to recovery boilers for recovery of chemicals and energy - is guided generation and for the alkaline washing filtrate (WF) from brown stock washing, the HSL displaced from the digester with the end of the cooking process and the stock temperature is cooled to below 100 ° C. At the end of the displacement of HSL by WF resulting warm black liquor (WSL) is guided in a separate tank for heat recovery and subsequent forwarding to the EDA.

Specifically, the process steps of this preferred embodiment of the process run as follows:

1. chips filling:

Chips of usual size and quality are correspondingly fills in the pulp production of conventional technologies, for example, with a Svenson steam packer in the diskontinuier¬ Lich working stove (batch digester) of conventional design ge. For this purpose steam is used, the gierückgewinnung within the Ener¬ is generated from cooking liquor (HSL).

2. prehydrolysis:

Chips and digester are to the desired pre-hydrolysis temperature of 130-200 ° C, preferably 130-190 ° C, preferably 155-175 ° C, heated. These fresh steam from energy recovery and flash steam from the pressure vessel of NL is used, the temperature is only slightly below the ge prehydrolysis is. The heating time is depending on the raw material input moisture, raw material input transition temperature, hydrolysis and steam used for 30 to 120 min. The pre-hydrolysis itself is carried out with steam Satt¬ and lasts depending on the raw material, product quality and Prehydrolysis 15 to 60 min.

Preferably, the prehydrolysate during the hydrolysis is Dampfvor¬ via an external line from the bottom of the digester pumped.

3. Cook compliance with HSL and HWL:

To end the prehydrolysis and neutralization of the hydrolysis products is pumped HSL of a preceding digestion with the required pressure, optionally with Bei¬ mixture of hot white liquor (HWL) into the digester. The digester is hydraulically completely filled with liquor. The required for the neutralization conditions, ie, temperature and pH can be adjusted prior to entering the digester through appropriate conditions of HSL and HWL. Filling a digester increases depending on boiler size and Pumpge¬ speeds 5 to 30 minutes to complete.

The filling of the digester is usually without separation of the losses occurring during the prehydrolysis gaseous and steam-volatile reaction products. Separation, for example, for the recovery of products such as furfural, acetic acid and methanol according to processes of the prior industrial technique without impairing the subsequent Ver¬ method steps for the production of viscose according to the present invention, and without adversely affecting the end product quality possible, but with the problems such as afflicted encrustations and blockages, as with the literature on steam prehydrolysis and from the indu¬-industrial furfural and without addition of Mine¬ ralsäure in the hydrolysis of lignocellulose with steam is known.

4. Neutralization:

For uniform and complete neutralization of all acid reaction products of the prehydrolysis liquor is pumped umge¬ in the digester via an externally arranged pump Wärmetau¬ shaving unit on the upper and lower digester screens. Via the heat exchanger a Tempe¬ may additionally be ratureinstellung.

The pH of the neutralization should be greater than 9, preferably in the range of 11. Once the desired conditions are achieved with respect to Neutralisationsbe¬ pH and temperature, er¬ follows the next process step. In general, the adjustment of the neutralization end conditions requires 5 minutes to the 20th 5. displacing NL with HWL:

In order to remove a partial amount of the neutralized Hydroly¬ prehydrolysis seprodukte and terminating the Kochbe¬ conditions in terms of active alkali and optionally Tem¬ temperature a partial amount of NL by HWL is displaced. The HWL can be supplied to the digester from above or below. In the preferred embodiment of the method of the invention the displacement of vor¬ located top to bottom. In this direction of displacement results in a more uniform process control and better energy economy, because due to the lower density of the urea-water solution as compared to the NL is less mixing of the HWL follows er¬ with NL as at a displacement from below upwards. This effect is even stronger in the cases when the HWL has a higher temperature than the NL.

The size of the NL-subset, the displaced and is passed over the NL- container as interim storage and heat exchanger for transferring heat to process liquors, in particular WL, or for producing hot water for Eindampfanläge (EDA) with subsequent combustion in the recovery boiler, depends on raw material , the final product and the Ein¬ position from the neutralization. The displaced amount can range from zero to 100%. When no displacement of the neutralization with the setting of the conditions for heating and cooking is connected by respective flow and temperature adjustment of HSL and HWL supplied in Process. 3 Displacement of NL is oxygen content only for raw materials with low hemicellulose and Extrakt¬ such as linters or flax eligible. As a rule, one-third is urging ver¬ to two thirds of NL. At high hemicellulose and extract content and extreme demands on the purity of the Endproduk¬ tes it may be advantageous to put to er¬ the total amount of NL. In the displacement of large NL-part narrow, it may be advantageous to apply a combined supply of HWL and HSL to the required for cooking Aktiv¬ amount of alkali in the digester set. 6. heating:

The heating to the desired cooking temperature is accomplished by circulating the liquor through an externally installed Pum¬ pen-heat exchanger unit, the heat from HSL or NL a preceding digestion or live steam is transmitted. The duration of heating can be very different. It may be zero, when einge¬ all the parameters for the start of the cook in the neutralization (process step 4) or in the displacement of NL by HSL (HWL +) represents. The heating may coincide at the other extreme with the cooking time when the Kochan¬ are set initial conditions after neutralization and optionally displacing NL-subsets and the digestion is operated with a rising temperature gradient, in which the boiling process of reaching the maximum temperature is terminated.

7. cooking:

During the cooking the cooking liquor is pumped over the external in¬ stallierte pump heat exchanger unit, wherein the necessary heat is conducted to the heat exchanger via steam zu¬. The cooking temperatures are in the range of 140-185 C C, in conventional types of wood and end products typically between 150 and 170 ° C. Depending on the type of heating and process control the cooking time may take a few minutes to 3 hours.

8. Displacement of HSL with washing filtrate (WF):

The cooking is by displacing the cooking liquor (HSL) terminated with cold alkaline wash filtrate from the brown stock washing, the digested material to below 100 ° C cooled and still adhering lignin and other unwanted soluble Pro¬ Dukten by the alkaline washing process of freed.

The supply of the WF can be done from above or below. Vorzugt according to the method of the present invention, the displacement from the top. Due to the difference in density between the cooking liquor (HSL) and WF the advantages mentioned under process step 5 are particularly pronounced. The displacement of HSL takes place in the HSL vessel until the temperature and hence also the dry substance content of the displaced liquor drops by mixing with WF. This exiting from the digester liquor is called because of their lower temperature warm black liquor (WSL).

9. Displacement of warm black liquor (WSL) wf:

The displacement of the cooking liquor HSL by WF occurs without interruption Un¬. The displaced liquor is, as long as HSL volume measures required for the next cooking and Tempera¬ structure of the displaced liquor from the cooking liquor temperature ent speaks conducted into the HSL vessel. Then, it is switched to Zufüh¬ tion in the WSL or NL- container. The WSL will lead zuge¬ by heat exchange of EDA and liquor recovery.

The displacement is terminated if within the digester has reached a Tem¬ temperature of just below 100 ° C. As a rule, the displacement of the process steps 7 and 8 require about 1.2 times the volume contained in the digester Flüssigkeits¬ quantitative.

10. Kocher emptying:

The emptying of the digester is carried out after the hydrogen generation practiced in the Zell¬ cold blow method (cold blow). Here, the fabric with a wash filtrate is Kon¬ consistency of approximately 5% diluted and either blown or by application of pressure by means of steam or air discharged via a pump. For the inventive method, the fiber-friendly process of evacuating is preferred.

multistage sulfite processes and water Sul¬ fatverfahren - - with the method of the present invention are comparatively to the hitherto known state of the art achieved the following significant advantages:

α-cellulose contents substantially higher than with sulfite and equal to or better than that of the sulphate process. A method purity of the pulp considerably higher than in Sulfit¬ and equal to or better than that of the sulphate process. Strengths and viscosity of the pulp very much higher than with sulfite and at the same α-cellulose and the same purity level higher than that of the sulphate process. Yield of the final product of digestion (before further treatment such as bleaching) and yield of α-cellulose equal to or higher than the sulfate process.

process yield of final product after further treatment with the same α-cellulose content very much higher than the Sulfit¬.

Proportion of α-cellulose in the final product of the digestion (before Wei¬ terbehandlung such as bleach) equal to or higher very much higher than in the process Sulfit¬ than the sulphate process and.

The steam prehydrolysis combined with the Verdrängungstech¬ technology of sulfate cooking allows steam savings over the entire cooking process including ancillary facilities such as the chemical recovery compared to the Was¬ servorhydrolyse sulfate method of about 50-60%, ie bezo¬ gen on the same amount of washed pulp, the same α-cellulose content (ca. 96%) are required only 40-50% of the energy for the process correspondingly to the present invention, which has hitherto been used in the conventional sulfate process.

e present invention is by the following examples and 2 (see Fig. 2 and 3) will be explained.

Claims

- I IP atentanspr ü che:
1. A process for producing viscose pulp from Ligno¬ celluloses according to a steam prehydrolysis sulfate (Kraft) -Verdrän¬ supply cooking process, characterized in that after the Vor¬ hydrolysis with saturated steam of the digester with hot black liquor (HSL) of a preceding digestion as well as optionally with the addition of fresh white liquor (WL) is filled and thereby the Hydroly¬ seprodukte be neutralized, thereby tion liquor in the digester Neutralisa¬ (NL) is formed, that the amount of alkali required delignification in the cooking for the de liquor in the form of fresh Wei߬ (WL) fed is, where appropriate, a partial amount of NL is displaced, that the digestion takes place with or without Temperatur¬ gradient and that the cooking liquor by displacing the Koch¬ (HSL) with alkaline washing filtrate (WF) is terminated wo¬ of by the alkali-soluble lignin rials washed digested Fasermate¬ and the pulp is cooled for discharge from the digester.
2. The method of claim 1, characterized in that the prehydrolysate is circulated during steam via an external line from the bottom of the digester.
3. The method of claim 1-2, characterized in that the HSL is a preceding digestion having a temperature in the digester is filled by the domestic product is optimum for the respective raw material and the desired Endpro¬ steam prehydrolysis which the temperature of prehydrolysis, which, for example, 130 carries ° C to 200 ° C be¬, by up to 50 "C above or below.
4. The method of claim 1-3, characterized in that the HSL is optionally substituted by addition of fresh alkali (WL) is set so that after complete filling of the digester a pH of greater than 9, preferably of 10-12 reached, ,
5. The method of claim 1-4, characterized in that the pH and temperature adjustment of NL by WL admixture of appropriate temperature and alkalinity to HSL and / or temperature raturanpassung the HSL is carried out in the digester before the introduction.
6. The method according to claim 1-5, characterized in that the HSL is supplied on top of the digester.
7. The method according to claim 1-5, characterized in that the HSL is supplied from the bottom of the digester.
8. The method according to claims 1-7, characterized in that the required increase in temperature for the start of heating or cooking and the active alkali by displacing a portion or the total amount of NL by WL, if desired in combination with HSL, is effected.
9. The method of claim 1-8, characterized in that the displacement of NL by WL, if appropriate, carried out in combination with HSL, from top to bottom.
10. The method according to claim 1-8, characterized in that the displacement of NL by WL, if appropriate, carried out in combination with HSL, from bottom to top.
11. The method of claim 1-10, characterized in that the cooking with an amount of active alkali of 18-28% as NaOH on bezo¬ gen absolutely dry lignocellulose, at a temperature of 140-185 ° C and cooking times of 40 to 180 minutes, including heating time he follows.
12. The method according to claim 1-11, characterized in that the cooking with a gradient increasing with the cooking time Temperatur¬ is driven, said adjusted linearly with the cooking time or at the beginning of the cook less strongly than at the end, depending on the raw material and final product of the temperature rise or is cooked after an initial temperature increase at a constant temperature until the end.
13. The method according to claim 1-12, characterized in that the cooking formality by displacement of HSL by WF of such Alka¬ and temperature is stopped, that the alkali-soluble lignins of the digested fiber material do not rückkondensie¬ ren and the temperature of the fiber-friendly cooker emptying below 100 ° C is cooled.
14. The method according to claim 1-13, characterized in that the displacement of HSL by WF is effected from top to bottom.
15. The method according to claim 1-13, characterized in that the displacement of HSL by WF is effected from bottom to top.
EP19940900624 1992-12-02 1993-12-02 Viscose production process Expired - Lifetime EP0672207B1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
AT238292 1992-12-02
AT2382/92 1992-12-02
PCT/AT1993/000183 WO1994012719A1 (en) 1992-12-02 1993-12-02 Viscose production process

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CA (1) CA2150381C (en)
DE (1) DE59304443D1 (en)
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ES2097021T3 (en) 1997-03-16 grant
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CA2150381C (en) 2004-11-02 grant
FI952509D0 (en) grant
RU95113599A (en) 1997-05-27 application
EP0672207B1 (en) 1996-11-06 grant
RU2122055C1 (en) 1998-11-20 grant
FI952509A (en) 1995-05-23 application
FI952509A0 (en) 1995-05-23 application
DE59304443D1 (en) 1996-12-12 grant
US5676795A (en) 1997-10-14 grant
JPH08503744A (en) 1996-04-23 application
WO1994012719A1 (en) 1994-06-09 application
CA2150381A1 (en) 1994-06-09 application

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