CA1295095C - Process for the production of a hemicellulose hydrolysate and special pulp - Google Patents
Process for the production of a hemicellulose hydrolysate and special pulpInfo
- Publication number
- CA1295095C CA1295095C CA000564311A CA564311A CA1295095C CA 1295095 C CA1295095 C CA 1295095C CA 000564311 A CA000564311 A CA 000564311A CA 564311 A CA564311 A CA 564311A CA 1295095 C CA1295095 C CA 1295095C
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- Prior art keywords
- cooking
- prehydrolysis
- wood
- lignin
- carried out
- Prior art date
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- Expired - Lifetime
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C3/00—Pulping cellulose-containing materials
- D21C3/22—Other features of pulping processes
- D21C3/222—Use of compounds accelerating the pulping processes
-
- C—CHEMISTRY; METALLURGY
- C13—SUGAR INDUSTRY
- C13K—SACCHARIDES OBTAINED FROM NATURAL SOURCES OR BY HYDROLYSIS OF NATURALLY OCCURRING DISACCHARIDES, OLIGOSACCHARIDES OR POLYSACCHARIDES
- C13K1/00—Glucose; Glucose-containing syrups
- C13K1/02—Glucose; Glucose-containing syrups obtained by saccharification of cellulosic materials
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Emergency Medicine (AREA)
- General Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Biochemistry (AREA)
- Organic Chemistry (AREA)
- Paper (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
- Medicines Containing Material From Animals Or Micro-Organisms (AREA)
- Amplifiers (AREA)
Abstract
Abstract The invention relates to a process for the pro-duction of a hemicellulose hydrolysate and special pulp through two steps, the first step comprising the prehydrolysis of the material and the second step the dissolving of the lignin contained in the prehydro-lyzed material, According to the process the lignin dissolving is carried out by means of a neutral sul-phite cooking with anthraquinone or a derivative thereof as a catalyst, the pH of the cooking liquor being initially at least 10.
Description
1295~95 A process for the production of a hemicellulose hydro-lysate and special pulp The invention relates to a process for the pro-duction of a hemicellulose hydrolysate and special pulp from a material containing lignocellulose through two steps, the first step comprising the hydrolysis of hemicelluloses into simple sugars and the second step the dissolving of lignin for liberating cellulose fibres.
Traditionally, there are two processes for the production of special pulps having a high content of alpha cellulose, such as dissolving pulp: the far-advanced acidic bisulphite cooking and the prehydroly-sis-sulphate cooking. The former was developed at the beginning o~ khe 20th century and the latter in the 1930's, see e.g. Rydholm, S.E., Pulping Processes, p. 649 to 672, Interscience Publishers, New York, 1968. The basic idea in both processes is to remove as much hemicellulose as possible from cellulose fibres in connection with the delignification so as to obtain a high content of alpha cellulose. This is essential because the various uses of dissolving pulp, for in-stance, do not tolerate short-chained hemicellulose molecules with indefinite structure~ In the sulphite process, the removal of hemicellulose takes place during the cooking simultaneously with the dissolving of lignin. The cooking conditions are highly acidic and the temperature varies from 140 to 150C, whereby the hydrolysis is strong. The result, however r is always a compromise with delignification, and no high content of alpha cellulose is obtained. Another draw-back is the decrease in the degree of polymerization of cellulose and the yield losses, which also limit the hydrolysis ~possibilities. Various improvements 1295~95 have been suggested in traditional sulphite cooking, the use of additional chemicals, for instance. Such additional chemicals, used in addition to the basic chemicals of sulphite cooking, include sulphide, white liquor, and anthraquinone, see e.g. Finnish Patent Specification 67 104 and U.S. Patent Specification 4 213 821. These sulphite cooking variations do not, however, imply hydrolytic conditions.
A separate prehydrolysis step is interesting in the view of the fact that it enables the adjustment of the hydrolysis of hemicelluloses as desired by varying the hydrolysis conditions. In the prehydrolysis-sul-phate process the delignification is not carried out until in a separate second cooking step. The prehydro-lygis i9 aarried out either as a water prehydrolysis or in the presence of a catalyst. Organic acids libe-rated from wood in the water prehydrolysis perform a major part of the process, whereas small amounts of mineral acid or sulphur dioxide, in some cases even sulphite waste liquor, are added to the digester in "assisted" prehydrolysis. It has previously been ne-aessary to effect the lignin dissolving step after the prehydrolysis as sulphate cooking which has several drawbacks. The prehydrolysis-sulphate process has e.g.
the following drawbacks:
- The yield is low because of the strong alka-line reaction conditions which cause splitting of cel-lulose. Thus the wood consumption per one ton of ael-lulose is high.
- The content of residual lignin is rather high because the step for the removal of residual lignin in the sulphate cooking process is extremely non-select-ive. Thus there is a great need of bleaching for com-~plete removal of lignin, and the consumption of chemi-cals is high; further, at least five bleaching steps ' ,,, ., ~ .
' '' 129S6~gS
are required.
- Industrial realization of sulphate cooking is complicated, and the cost of investment very high.
Previously the use of sulphite cooking has not been possible, because it is not possible to dissolve from wood material lignin deactivated in the pre-hydrolysis by means of traditional sulphite cooking processes. It has been regarded as impossible to use a sulphite cooking step (cf. Rydholm above) even though it would have advantages over sulphate cooking.
It has now been found out unexpectedly that ex-cellent results can be ob~ained by effecting the lignin dissolving after the prehydrolysis by an alka-line neukral ~ulphite cooking with anthraquinone or a derivative thereof as a catalyst. Such a cooking is known per se ~rom the prior art (see e.g. U.S. Patent Specification 4 213 821); on the contrary, a com-bination of prehydrolysis and such a cooking has not been set forth previously.
The invention relates to a process for the pro-duction of hemicellulose hydrolysate and special pulp from a material containing lignocellulose through two steps, the first step comprising the prehydrolysis of r the material and the second step dissolving of the lignin contained in the prehydrolyzed material. The process is characterized in that the dissolving of lignin is carried out by means of neutral sulphite cooking with anthraquinone or a derivative thereof as a catalyst, the pH of the cooking liquor being in-; itially at least 10.
Suitable prehydrolyzing agents include e.g.
water, mineral acid, sulphur dioxide, sulphite cooking acid, and sulphite waste liquor. Preferred prehydro-lyzing agents include sulphur oxide, sulphuric acid, and~water.
::: :
: : :
.
12~5CP95 A suitable prehydrolyzing temperakure is 100 to 180C, preferably 155 to 170C, ancl a suitable hydro-lyzing time is 10 to 200 minutes, p:referably 90 to 170 minutes.
The material containing lignocellulose prefer-ably consists of softwood or hardwood.
The cooking step is suitably carried out with a cooking liquor comprising 100 to 400 g of sodium sul-phite/kg of dry wood; lO to 100 g of sodium carbon-ate/one kg of dry wood; sodium hydroxide for rising the pH of the cooking liquor to a value between 10 and 13; and 0.01 to 0.2%, calculated on dry wood, of anthraquinone or a derivative thereof.
The cooking temperature preferably ranges from 160 to 180C, and the cooking time is suitably 100 to 200 minutes after the temperature has risen 0.1 to 2C/min from a temperature varying between room tem-perature and 100C.
It is typical of the prehydrolysis-neutral sul-phite-anthraquinone process (PH-NS-AQ process) that delignification to a low content of residual lignin is easy to carry out while the yield of cellulose fibre, however, remains on an exceptionally high level. Thus it is possible to use strong prehydrolysis conditions (e.g. strong acids, such as H2SO4), whereby the hydro-lysis of hemicelluloses into simple sugars is effi-cient; on the other hand, the alpha cellulose content representing the content of residual hemicellulose in cellulose fibre is high and the content of residual pentosan is;low. Due to these properties the process is particularly suitable for the production of high-qua~lity dissolving pulp, for instance! whereby mono-saccharides are obtained simultaneously.
As to the ~new~process, it was found out that the use of the so called neutral sulphite anthraqui-: :: :
::
lZ95~35 none cooking process effects a partial ionization of the lignin inactivated in the prehydrolysis, the in-itial pH being at least 10, e.g. 11 to 12, and that anthraquinone as an additive in the cooking catalyzes the breaking of nucleophilic beta aryl ether bonds, which at the end results in the liberation of fibres, i.e. a successful cooking. It was further found out that sulphite ions in neutral sulphite cooking react simultaneously and participate in the decomposing of the structure of lignin and above all sulphonate the lignin material and fragments which thus become more hydrophilic and dissolve more easily in the cooking liquor, thus contributing to the formation of a successful cooking and to the continuation thereof to a very low content of residual lignin. In short, the prehydrolysis-neutral sulphite anthraquinone process according to the invention not only gives a result as successful as that of the sulphate process but also provides all the advantages typical of sulphite cooking.
~ The increased yield of the procass according to ; the invention is due to the fact that there does not occur splitting of cellulose to any greater degree r during the neutral sulphite cooking step. In sulphate cooking, on the contrary, the high alkalinity causes alkaline hydrolysis, and the peeling-off reaction in particular results irrevocably in a yield loss. The process according to the invention enables the recov-~ery of~ nearly all of the high molecular weight cellu-lose material originally contained in the wood ma-terial.
In the process-chemical sense, another advan-tage is that pulp which has undergone neutral sulphite anthraquinone cooking is easy to bleach, i.e. the re-sLdual lignin remaining in the fibre after t~e cooking ;
.
lzssass is easy to remove. This is due to the fact that the delignification resembles sulphite cooking; the con-densation of the structure of lignin is insignificant;
and the sulphonation makes lignin more hydrophilic.
Contrary to this, the residual lignin in sulphate cooking is strongly condensated and the content there-of is on a higher level. The xemoval of this kind of residual lignin in bleaching requires five to six bleaching steps and plenty of expensive chlorine di-oxide. The bleaching of pulp obtained by means of the process according to the invention can be carried out by three steps only and the demand of chemicals, too, is lower.
~he process according to the invention has the following advantages:
- The yield of the special pulp to be produced .in connection with the production of sugars is in-creased, which improves the production economy.
- The process after the prehydrolysis is sim-plified, which decreases the cost of investment.
- The easier delignification in the cooking step decreases the need of bleaching, thus improving the production economy and reducing the emission of r chlorinated compounds from the bleaching.
- The oxygen or peroxide step after the cook-ing is extremely efficient as compared with that of the prehydrolysis-sulphate process, whereby the re-covery and economy are improved.
- Small-scale production is economically more interesting because it is possible to operate in con-nection with an existing sodium-based sulphite pulp mill without any appreciable additional investments.
The following examples are illustrative of the invention.
, ' .
~295~95 The following abbreviations are used in the examples:
Steps of the bleachinq Processes O = Oxygen step D = Chlorine dioxide step E = Alkali extraction P = Peroxide step -H = Hypochlorite step C = Chlorination Standards SCAN = Scandinavian standard TAPPI = U.S. standard Example 1 Production of a birch hydrolvsate and special Pulp by means of the PH-NS-AO Process from birch chips Chips and a prehydrolyzing liquor were metered into a chip basket positioned in a 20-litre forced circulation digester. The cover of the digester was closed and the prehydrolysis was carried out according to the temperature program by heating the digsster circulation indirectly by means of steam. After the hydrolysis time had passed, the hydrolysate was re-moved from the digester and recovered. The prehydro-s lyzed chip material contained in the digester was washed in the digester for 5 minutes with warm water, the cover was opened, and the chips were passed into a centrifuge in which excess water was removed. The cen-trifugalized material was weighed and a dry substance sample was taken~for determining the hydrolysis loss.
The prehydrolyzed chip material was returned to the digester, cooking liquor and anthraquinone were added, the cover was closed, and the ~ooking was carried out according to the temperature program. At the end o~ the cooking the cooking liquor was removed rapidly and the~ digester was filled with cold water, : :
~, ~
~LZ95('J~5 whereafter water was allowed to flow for 10 hours for washing the cooked chip material. After the wash the pulp was disintegrated by means of a wet disintegrator for one minute and assorted with a flat screen plate of 0.35 mm. Shives were recovered and weighed dry for determining the shive content. The accepted fraction was passed into the centrifuge for dewatering, homo-genized, and weighed. Laboratory analyses were carried out on this pulp and the pulp was further used in bleaching tests.
Prehydrolyzinq step Wood amount, g of abs. dry chips 2000 Prehydrolyzing agent S2 Amount o~ prehydrolyzing agent, % on dry wood 0.25 Liquor ratio 6:1 Temperature rising time, min 40 Prehydrolysis temperature, C 155 Prehydrolysis time, min 170 Prehydrolysis loss, ~ on wood 26.6 Cookinq step Na2SO3, % on wood as NaOH 22 r Na2CO3, % on wood as NaOH 5 Anthraquinone, % on wood 0.1 Liquor ratio 4.5:1 pH of the cooking liquor 11.3 Rising of the temperature Cimin Cooking temperature, C 175 Cooking time, min 170 Yield, % on wood 39.3 Kappa number 17.2 Shive content, % on wood 0.1 :: :
.
,. . .
1295Cg5 Properties of O D-E-D bleached pulp Final yield, % of wood 36.7 ISO brightness 87.1 Alpha cellulose % 94.2 Viscosity, SCAN dm3/kg 764 Example 2 -.
Production of a birch hydrolysate and special pulp by the PH-NS-AQ process from birch chips The test was carried out as disloced in Example 1.
PrehYdrolYzina step_ Wood amount, g of abs. dry chips 2500 Prehydrolyzing agent S2 ~mount of prehydrolyzing agent, % on dry wood (SO2) 0 25 Liquor ratio 3.5:1 Temperature rising time, min 40 : Prehydrolysis temperature, ~ 155 : PrehydroIysis time, min 170 Cookinq step Na2SO3, % on wood as NaOE 20 Na2CO3, % on wood as NaOH 6 ~ Anthraquinone, % on wood 0.1 : Liquor ratio 4.5:1 ~: : pH of the cooking liquor 11.3 Risîng of the temperature C/min ::Cooking temperature, C 175 Cooking:~time~, min ~ : 170 Yield: ~%;~on~wood~ ~5.7 Kap~a:number 48.1 Shive content, %::on wood ~ 1.35 lz~sass Properties of O-P-H bleached pulp Final yield, % on wood 39.7 ISO brightness 87.1 Alpha cellulose % 91.7 Viscosity, SCAN dm3/kg 530 Example 3 Production of a birch hYdrolysate and s~ecial pulp by the PH-NS-AQ Process from birch chips_ The test was carried out as disclosed in Example 1.
Prehydrolyzinq step Wood amount, g o~ abs. dry chi.ps 2500 Prehydrolyzing agent H2SO~
~mount o~ prehydrolyzing agent, % on dry wood 1.0 Liquor ratio 3.5:1 Temperature rising time, min 40 Prehydrolysis temperature, C 155 Prehydrolysis time, min 90 Prehydrolysis loss, % on wood 25.4 Cookinq step Na2SO3, % on wood as NaOH 22 Na2CO3, % on wood as NaOH 5 Anthraquinone, % on wood 0.1 ~iquor ratio 4.5:I
pH of the cooking liquor 11.3 Rising of the temperature C/min Cooking temperature, C 175 ~ : :Cooking time, min 170 : ~ : : Yield, % on wood 37.0 Kappa number : 24.9 :Shive content, % on wood 0.6 :
1;~95~95 Properties of C-E-D bleached pulp Final yield, % on wood 34.2 ISO brightness 90.0 Alpha cellulose % 94.6 Viscosity, SCAN dm3/kg 730 Properties of O-P-D bleached pulp Final yield, % on wood 34.7 ISO brightness 84.4 Alpha cellulose % 94.5 Viscosity, SCAN dm3/kg 720 Example 4 Production of a pine hydrolysate and special pulp bv the PH-NS-AQ process ~rom pine chiPs The test was carried out as disclosed in Example 1.
Prehydrolyzinq step Wood amount, g of abs. dry wood 2000 Prehydrolyzing agent H2O
Liquor ratio 6~
Temperature rising time, min 45 Prehydrolysis temperature, C 170 Prehydrolysis time, min 15 PrehYdrolYsis loss, % on wood 13.2 .
Cookinq step Na2SO3, ~ on wood as NaOH 22 Na2CO3, %~ on:wood as NaOH 5 Anthraquinone,~% on wood : 0.2:
Liquor ratio : ~ 4.5:1 pH of the cooking liquor 11.3 Rising of~the~temperature C/min Cooking temperature, C 175 :
::~ ; : Cooking time, min : 170 ;:~: : : : :
: ~~:: : : :
:
.
129S~g5 Yield, % on wood 40.3 Xappa number 16.5 Shive content, % on wood 0.4 Properties of O-D-E-D bleached pulp Final yield, % on wood 37.2 ISO brightness 84.2 Viscosity, SCAN dm3/kg 890 Reference examPle It was studied how lignin dissolves in cooking : processes generally in use as compared with the cook-ing step of the process according to the invention when the chips are prehydrolyzed according to the prior art. Sulphate cooking and various modifications o sulphite cooking are processes in general u9e.
In the tests the prehydrolysis/cooking was car-ried out as follows:
Test 1 Sulphur dioxide water prehydrolysis, normal Normal acidic Ca bisulphite cooking step Kappa number 150 Test 2 Sulphur dioxide water prehydrolysis, noxmal : ~ ~ r Normal acidic Ca bisulphite cooking step Kappa number 126 Test 3 Water prehydrolysis, weak ~:~ : : Normal acidic Ca bisulphite cooking step : : : Rappa number 118 ~ :
Test 4 ~ :
: Sulphur dioxide wa~er prehydrolysis, weak : Neutralizing lime milk treatment Acidic Ca bisulphite cooking step with an :ex-tremely~hlgh bound 52 : Kappa number 106 :
1295~9S
Test 5 Sulphur dioxide prehydrolysis Cooking step 1: ammonium neutral sulphite cooking Cooking step 2: sulphur dioxide water acidic sulphite cooking Kappa number 141 Test 6 Sulphur dioxide water prehydrolysis, normal Neutral sulphite-anthraquinone cooking step Kappa number 48 Test 7 Sulphur dioxide water-prehydrolysis, normal Sulphate cooking step, normal Rappa number 14 Lignin concentrations measured from the digest-er during the cooking step by means of a cooking liquor analyzer as a function of the cooking time re-duced to the same scale appear from the attached figure 1. The curves thus illustrate the dîssolving of lignin as measured as an increase in the lignin con-tent of the cooking li~uor. The results show that the cooking step after the prehydrolysis in Tests 1 to 4 does not dissolve lignin:efficiently even though at-tempts have been made to improve these sulphite pro-cesses as much as possible. The dissolving obtained in Test 5 was;better because the prehydrolysis is excep-tional and;not technically reasonable. The content of residual lignin in Test 5`~tthe kappa number exceeding 100) is, however,~technically impossible, the reason-able level being:the kappa number of about 50 (= about lO~ of lignin in cooked pulp).~ In Tests 6 and 7, lignin starts to~ dissoIve:rapidly in the relative cooking time~: of 100, the subsequent step being the :: : :: : :
:
,.~
l~g~9S
~4 main delignification of a successful cooking which is completed by a slow residual delignification towards the end of the cooking. In this way, the kappa level of 40 in Test 5 and the kappa level of 15 in Test 7 were achieved. Accordingly, it is obvious that an efficient removal of lignin from prehydrolyzed chip material takes place in the cooking step of the pro-cess according to the invention such as disclosed in Test 6; thus, it can replace the sulphate cooking used in Test 7.
The tests carried out show that normal tech-nical prehydrolysis conditions inactivate lignin to such an extent that no cooking modification within an acidic or neutral cooking pH range is able to dissolve lignin even though the chip material would be neutral-ized between the prehydrolysis and the cooking. The sulphite cooking step used in the process according to the invention is operative only when the cooking con-ditions and the cooking catalyst are chosen appro-priately.
:
:: :
:
::
:: :
~: ::: ~ :: :
,~
' ' '
Traditionally, there are two processes for the production of special pulps having a high content of alpha cellulose, such as dissolving pulp: the far-advanced acidic bisulphite cooking and the prehydroly-sis-sulphate cooking. The former was developed at the beginning o~ khe 20th century and the latter in the 1930's, see e.g. Rydholm, S.E., Pulping Processes, p. 649 to 672, Interscience Publishers, New York, 1968. The basic idea in both processes is to remove as much hemicellulose as possible from cellulose fibres in connection with the delignification so as to obtain a high content of alpha cellulose. This is essential because the various uses of dissolving pulp, for in-stance, do not tolerate short-chained hemicellulose molecules with indefinite structure~ In the sulphite process, the removal of hemicellulose takes place during the cooking simultaneously with the dissolving of lignin. The cooking conditions are highly acidic and the temperature varies from 140 to 150C, whereby the hydrolysis is strong. The result, however r is always a compromise with delignification, and no high content of alpha cellulose is obtained. Another draw-back is the decrease in the degree of polymerization of cellulose and the yield losses, which also limit the hydrolysis ~possibilities. Various improvements 1295~95 have been suggested in traditional sulphite cooking, the use of additional chemicals, for instance. Such additional chemicals, used in addition to the basic chemicals of sulphite cooking, include sulphide, white liquor, and anthraquinone, see e.g. Finnish Patent Specification 67 104 and U.S. Patent Specification 4 213 821. These sulphite cooking variations do not, however, imply hydrolytic conditions.
A separate prehydrolysis step is interesting in the view of the fact that it enables the adjustment of the hydrolysis of hemicelluloses as desired by varying the hydrolysis conditions. In the prehydrolysis-sul-phate process the delignification is not carried out until in a separate second cooking step. The prehydro-lygis i9 aarried out either as a water prehydrolysis or in the presence of a catalyst. Organic acids libe-rated from wood in the water prehydrolysis perform a major part of the process, whereas small amounts of mineral acid or sulphur dioxide, in some cases even sulphite waste liquor, are added to the digester in "assisted" prehydrolysis. It has previously been ne-aessary to effect the lignin dissolving step after the prehydrolysis as sulphate cooking which has several drawbacks. The prehydrolysis-sulphate process has e.g.
the following drawbacks:
- The yield is low because of the strong alka-line reaction conditions which cause splitting of cel-lulose. Thus the wood consumption per one ton of ael-lulose is high.
- The content of residual lignin is rather high because the step for the removal of residual lignin in the sulphate cooking process is extremely non-select-ive. Thus there is a great need of bleaching for com-~plete removal of lignin, and the consumption of chemi-cals is high; further, at least five bleaching steps ' ,,, ., ~ .
' '' 129S6~gS
are required.
- Industrial realization of sulphate cooking is complicated, and the cost of investment very high.
Previously the use of sulphite cooking has not been possible, because it is not possible to dissolve from wood material lignin deactivated in the pre-hydrolysis by means of traditional sulphite cooking processes. It has been regarded as impossible to use a sulphite cooking step (cf. Rydholm above) even though it would have advantages over sulphate cooking.
It has now been found out unexpectedly that ex-cellent results can be ob~ained by effecting the lignin dissolving after the prehydrolysis by an alka-line neukral ~ulphite cooking with anthraquinone or a derivative thereof as a catalyst. Such a cooking is known per se ~rom the prior art (see e.g. U.S. Patent Specification 4 213 821); on the contrary, a com-bination of prehydrolysis and such a cooking has not been set forth previously.
The invention relates to a process for the pro-duction of hemicellulose hydrolysate and special pulp from a material containing lignocellulose through two steps, the first step comprising the prehydrolysis of r the material and the second step dissolving of the lignin contained in the prehydrolyzed material. The process is characterized in that the dissolving of lignin is carried out by means of neutral sulphite cooking with anthraquinone or a derivative thereof as a catalyst, the pH of the cooking liquor being in-; itially at least 10.
Suitable prehydrolyzing agents include e.g.
water, mineral acid, sulphur dioxide, sulphite cooking acid, and sulphite waste liquor. Preferred prehydro-lyzing agents include sulphur oxide, sulphuric acid, and~water.
::: :
: : :
.
12~5CP95 A suitable prehydrolyzing temperakure is 100 to 180C, preferably 155 to 170C, ancl a suitable hydro-lyzing time is 10 to 200 minutes, p:referably 90 to 170 minutes.
The material containing lignocellulose prefer-ably consists of softwood or hardwood.
The cooking step is suitably carried out with a cooking liquor comprising 100 to 400 g of sodium sul-phite/kg of dry wood; lO to 100 g of sodium carbon-ate/one kg of dry wood; sodium hydroxide for rising the pH of the cooking liquor to a value between 10 and 13; and 0.01 to 0.2%, calculated on dry wood, of anthraquinone or a derivative thereof.
The cooking temperature preferably ranges from 160 to 180C, and the cooking time is suitably 100 to 200 minutes after the temperature has risen 0.1 to 2C/min from a temperature varying between room tem-perature and 100C.
It is typical of the prehydrolysis-neutral sul-phite-anthraquinone process (PH-NS-AQ process) that delignification to a low content of residual lignin is easy to carry out while the yield of cellulose fibre, however, remains on an exceptionally high level. Thus it is possible to use strong prehydrolysis conditions (e.g. strong acids, such as H2SO4), whereby the hydro-lysis of hemicelluloses into simple sugars is effi-cient; on the other hand, the alpha cellulose content representing the content of residual hemicellulose in cellulose fibre is high and the content of residual pentosan is;low. Due to these properties the process is particularly suitable for the production of high-qua~lity dissolving pulp, for instance! whereby mono-saccharides are obtained simultaneously.
As to the ~new~process, it was found out that the use of the so called neutral sulphite anthraqui-: :: :
::
lZ95~35 none cooking process effects a partial ionization of the lignin inactivated in the prehydrolysis, the in-itial pH being at least 10, e.g. 11 to 12, and that anthraquinone as an additive in the cooking catalyzes the breaking of nucleophilic beta aryl ether bonds, which at the end results in the liberation of fibres, i.e. a successful cooking. It was further found out that sulphite ions in neutral sulphite cooking react simultaneously and participate in the decomposing of the structure of lignin and above all sulphonate the lignin material and fragments which thus become more hydrophilic and dissolve more easily in the cooking liquor, thus contributing to the formation of a successful cooking and to the continuation thereof to a very low content of residual lignin. In short, the prehydrolysis-neutral sulphite anthraquinone process according to the invention not only gives a result as successful as that of the sulphate process but also provides all the advantages typical of sulphite cooking.
~ The increased yield of the procass according to ; the invention is due to the fact that there does not occur splitting of cellulose to any greater degree r during the neutral sulphite cooking step. In sulphate cooking, on the contrary, the high alkalinity causes alkaline hydrolysis, and the peeling-off reaction in particular results irrevocably in a yield loss. The process according to the invention enables the recov-~ery of~ nearly all of the high molecular weight cellu-lose material originally contained in the wood ma-terial.
In the process-chemical sense, another advan-tage is that pulp which has undergone neutral sulphite anthraquinone cooking is easy to bleach, i.e. the re-sLdual lignin remaining in the fibre after t~e cooking ;
.
lzssass is easy to remove. This is due to the fact that the delignification resembles sulphite cooking; the con-densation of the structure of lignin is insignificant;
and the sulphonation makes lignin more hydrophilic.
Contrary to this, the residual lignin in sulphate cooking is strongly condensated and the content there-of is on a higher level. The xemoval of this kind of residual lignin in bleaching requires five to six bleaching steps and plenty of expensive chlorine di-oxide. The bleaching of pulp obtained by means of the process according to the invention can be carried out by three steps only and the demand of chemicals, too, is lower.
~he process according to the invention has the following advantages:
- The yield of the special pulp to be produced .in connection with the production of sugars is in-creased, which improves the production economy.
- The process after the prehydrolysis is sim-plified, which decreases the cost of investment.
- The easier delignification in the cooking step decreases the need of bleaching, thus improving the production economy and reducing the emission of r chlorinated compounds from the bleaching.
- The oxygen or peroxide step after the cook-ing is extremely efficient as compared with that of the prehydrolysis-sulphate process, whereby the re-covery and economy are improved.
- Small-scale production is economically more interesting because it is possible to operate in con-nection with an existing sodium-based sulphite pulp mill without any appreciable additional investments.
The following examples are illustrative of the invention.
, ' .
~295~95 The following abbreviations are used in the examples:
Steps of the bleachinq Processes O = Oxygen step D = Chlorine dioxide step E = Alkali extraction P = Peroxide step -H = Hypochlorite step C = Chlorination Standards SCAN = Scandinavian standard TAPPI = U.S. standard Example 1 Production of a birch hydrolvsate and special Pulp by means of the PH-NS-AO Process from birch chips Chips and a prehydrolyzing liquor were metered into a chip basket positioned in a 20-litre forced circulation digester. The cover of the digester was closed and the prehydrolysis was carried out according to the temperature program by heating the digsster circulation indirectly by means of steam. After the hydrolysis time had passed, the hydrolysate was re-moved from the digester and recovered. The prehydro-s lyzed chip material contained in the digester was washed in the digester for 5 minutes with warm water, the cover was opened, and the chips were passed into a centrifuge in which excess water was removed. The cen-trifugalized material was weighed and a dry substance sample was taken~for determining the hydrolysis loss.
The prehydrolyzed chip material was returned to the digester, cooking liquor and anthraquinone were added, the cover was closed, and the ~ooking was carried out according to the temperature program. At the end o~ the cooking the cooking liquor was removed rapidly and the~ digester was filled with cold water, : :
~, ~
~LZ95('J~5 whereafter water was allowed to flow for 10 hours for washing the cooked chip material. After the wash the pulp was disintegrated by means of a wet disintegrator for one minute and assorted with a flat screen plate of 0.35 mm. Shives were recovered and weighed dry for determining the shive content. The accepted fraction was passed into the centrifuge for dewatering, homo-genized, and weighed. Laboratory analyses were carried out on this pulp and the pulp was further used in bleaching tests.
Prehydrolyzinq step Wood amount, g of abs. dry chips 2000 Prehydrolyzing agent S2 Amount o~ prehydrolyzing agent, % on dry wood 0.25 Liquor ratio 6:1 Temperature rising time, min 40 Prehydrolysis temperature, C 155 Prehydrolysis time, min 170 Prehydrolysis loss, ~ on wood 26.6 Cookinq step Na2SO3, % on wood as NaOH 22 r Na2CO3, % on wood as NaOH 5 Anthraquinone, % on wood 0.1 Liquor ratio 4.5:1 pH of the cooking liquor 11.3 Rising of the temperature Cimin Cooking temperature, C 175 Cooking time, min 170 Yield, % on wood 39.3 Kappa number 17.2 Shive content, % on wood 0.1 :: :
.
,. . .
1295Cg5 Properties of O D-E-D bleached pulp Final yield, % of wood 36.7 ISO brightness 87.1 Alpha cellulose % 94.2 Viscosity, SCAN dm3/kg 764 Example 2 -.
Production of a birch hydrolysate and special pulp by the PH-NS-AQ process from birch chips The test was carried out as disloced in Example 1.
PrehYdrolYzina step_ Wood amount, g of abs. dry chips 2500 Prehydrolyzing agent S2 ~mount of prehydrolyzing agent, % on dry wood (SO2) 0 25 Liquor ratio 3.5:1 Temperature rising time, min 40 : Prehydrolysis temperature, ~ 155 : PrehydroIysis time, min 170 Cookinq step Na2SO3, % on wood as NaOE 20 Na2CO3, % on wood as NaOH 6 ~ Anthraquinone, % on wood 0.1 : Liquor ratio 4.5:1 ~: : pH of the cooking liquor 11.3 Risîng of the temperature C/min ::Cooking temperature, C 175 Cooking:~time~, min ~ : 170 Yield: ~%;~on~wood~ ~5.7 Kap~a:number 48.1 Shive content, %::on wood ~ 1.35 lz~sass Properties of O-P-H bleached pulp Final yield, % on wood 39.7 ISO brightness 87.1 Alpha cellulose % 91.7 Viscosity, SCAN dm3/kg 530 Example 3 Production of a birch hYdrolysate and s~ecial pulp by the PH-NS-AQ Process from birch chips_ The test was carried out as disclosed in Example 1.
Prehydrolyzinq step Wood amount, g o~ abs. dry chi.ps 2500 Prehydrolyzing agent H2SO~
~mount o~ prehydrolyzing agent, % on dry wood 1.0 Liquor ratio 3.5:1 Temperature rising time, min 40 Prehydrolysis temperature, C 155 Prehydrolysis time, min 90 Prehydrolysis loss, % on wood 25.4 Cookinq step Na2SO3, % on wood as NaOH 22 Na2CO3, % on wood as NaOH 5 Anthraquinone, % on wood 0.1 ~iquor ratio 4.5:I
pH of the cooking liquor 11.3 Rising of the temperature C/min Cooking temperature, C 175 ~ : :Cooking time, min 170 : ~ : : Yield, % on wood 37.0 Kappa number : 24.9 :Shive content, % on wood 0.6 :
1;~95~95 Properties of C-E-D bleached pulp Final yield, % on wood 34.2 ISO brightness 90.0 Alpha cellulose % 94.6 Viscosity, SCAN dm3/kg 730 Properties of O-P-D bleached pulp Final yield, % on wood 34.7 ISO brightness 84.4 Alpha cellulose % 94.5 Viscosity, SCAN dm3/kg 720 Example 4 Production of a pine hydrolysate and special pulp bv the PH-NS-AQ process ~rom pine chiPs The test was carried out as disclosed in Example 1.
Prehydrolyzinq step Wood amount, g of abs. dry wood 2000 Prehydrolyzing agent H2O
Liquor ratio 6~
Temperature rising time, min 45 Prehydrolysis temperature, C 170 Prehydrolysis time, min 15 PrehYdrolYsis loss, % on wood 13.2 .
Cookinq step Na2SO3, ~ on wood as NaOH 22 Na2CO3, %~ on:wood as NaOH 5 Anthraquinone,~% on wood : 0.2:
Liquor ratio : ~ 4.5:1 pH of the cooking liquor 11.3 Rising of~the~temperature C/min Cooking temperature, C 175 :
::~ ; : Cooking time, min : 170 ;:~: : : : :
: ~~:: : : :
:
.
129S~g5 Yield, % on wood 40.3 Xappa number 16.5 Shive content, % on wood 0.4 Properties of O-D-E-D bleached pulp Final yield, % on wood 37.2 ISO brightness 84.2 Viscosity, SCAN dm3/kg 890 Reference examPle It was studied how lignin dissolves in cooking : processes generally in use as compared with the cook-ing step of the process according to the invention when the chips are prehydrolyzed according to the prior art. Sulphate cooking and various modifications o sulphite cooking are processes in general u9e.
In the tests the prehydrolysis/cooking was car-ried out as follows:
Test 1 Sulphur dioxide water prehydrolysis, normal Normal acidic Ca bisulphite cooking step Kappa number 150 Test 2 Sulphur dioxide water prehydrolysis, noxmal : ~ ~ r Normal acidic Ca bisulphite cooking step Kappa number 126 Test 3 Water prehydrolysis, weak ~:~ : : Normal acidic Ca bisulphite cooking step : : : Rappa number 118 ~ :
Test 4 ~ :
: Sulphur dioxide wa~er prehydrolysis, weak : Neutralizing lime milk treatment Acidic Ca bisulphite cooking step with an :ex-tremely~hlgh bound 52 : Kappa number 106 :
1295~9S
Test 5 Sulphur dioxide prehydrolysis Cooking step 1: ammonium neutral sulphite cooking Cooking step 2: sulphur dioxide water acidic sulphite cooking Kappa number 141 Test 6 Sulphur dioxide water prehydrolysis, normal Neutral sulphite-anthraquinone cooking step Kappa number 48 Test 7 Sulphur dioxide water-prehydrolysis, normal Sulphate cooking step, normal Rappa number 14 Lignin concentrations measured from the digest-er during the cooking step by means of a cooking liquor analyzer as a function of the cooking time re-duced to the same scale appear from the attached figure 1. The curves thus illustrate the dîssolving of lignin as measured as an increase in the lignin con-tent of the cooking li~uor. The results show that the cooking step after the prehydrolysis in Tests 1 to 4 does not dissolve lignin:efficiently even though at-tempts have been made to improve these sulphite pro-cesses as much as possible. The dissolving obtained in Test 5 was;better because the prehydrolysis is excep-tional and;not technically reasonable. The content of residual lignin in Test 5`~tthe kappa number exceeding 100) is, however,~technically impossible, the reason-able level being:the kappa number of about 50 (= about lO~ of lignin in cooked pulp).~ In Tests 6 and 7, lignin starts to~ dissoIve:rapidly in the relative cooking time~: of 100, the subsequent step being the :: : :: : :
:
,.~
l~g~9S
~4 main delignification of a successful cooking which is completed by a slow residual delignification towards the end of the cooking. In this way, the kappa level of 40 in Test 5 and the kappa level of 15 in Test 7 were achieved. Accordingly, it is obvious that an efficient removal of lignin from prehydrolyzed chip material takes place in the cooking step of the pro-cess according to the invention such as disclosed in Test 6; thus, it can replace the sulphate cooking used in Test 7.
The tests carried out show that normal tech-nical prehydrolysis conditions inactivate lignin to such an extent that no cooking modification within an acidic or neutral cooking pH range is able to dissolve lignin even though the chip material would be neutral-ized between the prehydrolysis and the cooking. The sulphite cooking step used in the process according to the invention is operative only when the cooking con-ditions and the cooking catalyst are chosen appro-priately.
:
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Claims (8)
1. A process for the production of a hemicellu-lose hydrolysate and special pulp from a material con-taining lignocellulose through two steps, the first step comprising the prehydrolysis of the material and the second step the dissolving of the lignin contained in the prehydrolyzed material, characterized in that the dissolving of lignin is carried out by means of a neutral sulphite cooking with anthraquinone or a deriv-ative therefo as a catalyst, the pH of the cooking liquor being initially at least 10.
2. A process according to claim 1, characterized in that the material containing lignocellulose is hard-wood.
3. A process according to claim 1, characterized in that the material containing lignocellulose is soft-wood.
4. A process according to claim 1, characterized in that the prehydrolysis is carried out by means of water, sulphur dioxide or sulphuric acid at a tem-perature of 155 to 170°C for 90 to 170 minutes.
5. A process according to claim 2, characterized in that the prehydrolysis is carried out by means of water, sulphur dioxide or sulphuric acid at a tem-perature of 155 to 170°C for 90 to 170 minutes.
6. A process according to claim 3, characterized in that the prehydrolysis is carried out by means of water, sulphur dioxide or sulphuric acid at a tem-perature of 155 to 170°C for 90 to 170 minutes.
7. A process according to claim 1, 2 or 3, char-acterized in that the cooking is carried out by means of a cooking liquor comprising 100 to 400 g of sodium sulphite/kg of dry wood; 10 to 100 g of sodium car-bonate/kg of dry wood; sodium hydroxide for rising the pH of the cooking liquor to a value varying from 10 to 13; and 0.01 to 0.2% (calculated on dry wood) of anthraquinone or a derivative thereof, at a temperature of 160 to 180°C for 100 to 200 minutes after the tem-perature is raised 0.1 to 2°C/min from a temperature varying between room temperature and 100°C.
8. A process according to claim 4, 5 or 6, char-acterized in that the cooking is carried out by means of a cooking liquor comprising 100 to 400 g of sodium sulphite/kg of dry wood; 10 to 100 g of sodium car-bonate/kg of dry wood; sodium hydroxide for rising the pH of the cooking liquor to a value varying from 10 to 13; and 0.01 to 0.2% (calculated on dry wood) of anthraquinone or a derivative thereof, at a temperature of 160 to 180°C for 100 to 200 minutes after the tem-perature is raised 0.1 to 2°C/min from a temperature varying between room temperature and 100°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI871730A FI79564C (en) | 1987-04-21 | 1987-04-21 | FOERFARANDE FOER FRAMSTAELLNING AV HEMICELLULOSAHYDROLYSAT OCH SPECIALMASSA. |
| FI871730 | 1987-04-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1295095C true CA1295095C (en) | 1992-02-04 |
Family
ID=8524351
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000564311A Expired - Lifetime CA1295095C (en) | 1987-04-21 | 1988-04-15 | Process for the production of a hemicellulose hydrolysate and special pulp |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0287960B1 (en) |
| AT (1) | ATE111986T1 (en) |
| BR (1) | BR8801894A (en) |
| CA (1) | CA1295095C (en) |
| DE (1) | DE3851565T2 (en) |
| ES (1) | ES2062995T3 (en) |
| FI (1) | FI79564C (en) |
| RU (1) | RU1799408C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10064131C2 (en) * | 2000-12-22 | 2003-03-27 | Sca Hygiene Prod Gmbh | Fully bleached sulfite pulp, process for its manufacture and products made from it |
| EP2067793B2 (en) * | 2007-11-27 | 2014-05-21 | Innventia AB | Utilization of a wood hydrolysate |
| FI129760B (en) | 2020-07-06 | 2022-08-15 | Amppc Finland Oy | A high yield cooking method |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3532597A (en) * | 1969-03-11 | 1970-10-06 | Uddeholms Ab | Preparation of dissolving pulps from wood by hydrolysis and alkaline sulfite digestion |
| ZA773044B (en) | 1976-06-02 | 1978-04-26 | Australian Paper Manufacturers | Improvements in pulping processes |
| DE2628971A1 (en) * | 1976-06-28 | 1978-01-05 | Waldhof Aschaffenburg Papier | Cellulose and wood sugar prodn. from wood - using a washing stage after pre-hydrolysis, with controlled pH during decomposition |
| CA1216105A (en) * | 1984-04-06 | 1987-01-06 | C-I-L Inc. | Pulping process |
-
1987
- 1987-04-21 FI FI871730A patent/FI79564C/en not_active IP Right Cessation
-
1988
- 1988-04-15 AT AT88106006T patent/ATE111986T1/en active
- 1988-04-15 CA CA000564311A patent/CA1295095C/en not_active Expired - Lifetime
- 1988-04-15 EP EP88106006A patent/EP0287960B1/en not_active Expired - Lifetime
- 1988-04-15 DE DE3851565T patent/DE3851565T2/en not_active Expired - Fee Related
- 1988-04-20 RU SU884355611A patent/RU1799408C/en active
- 1988-04-21 BR BR8801894A patent/BR8801894A/en unknown
- 1988-05-11 ES ES88106006T patent/ES2062995T3/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0287960B1 (en) | 1994-09-21 |
| ES2062995T3 (en) | 1995-01-01 |
| FI79564C (en) | 1990-01-10 |
| RU1799408C (en) | 1993-02-28 |
| EP0287960A3 (en) | 1991-04-17 |
| ATE111986T1 (en) | 1994-10-15 |
| FI79564B (en) | 1989-09-29 |
| FI871730A (en) | 1988-10-22 |
| DE3851565D1 (en) | 1994-10-27 |
| FI871730A0 (en) | 1987-04-21 |
| BR8801894A (en) | 1988-11-22 |
| EP0287960A2 (en) | 1988-10-26 |
| DE3851565T2 (en) | 1995-01-26 |
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