CA1088260A - Process for manufacturing a semifinished product from ground vegetable raw material - Google Patents
Process for manufacturing a semifinished product from ground vegetable raw materialInfo
- Publication number
- CA1088260A CA1088260A CA248,896A CA248896A CA1088260A CA 1088260 A CA1088260 A CA 1088260A CA 248896 A CA248896 A CA 248896A CA 1088260 A CA1088260 A CA 1088260A
- Authority
- CA
- Canada
- Prior art keywords
- raw material
- temperature
- digestion
- semifinished product
- hours
- 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.)
- Expired
Links
Landscapes
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to processes for manufactu-rig a semifinished product from ground vegetable raw ma-terial. In accordance with the proposed process, ground stea-med raw material is treated with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material, whereupon the raw material is subjected to digestion under temperature conditions such that the temperature is first raised to about 160°C. for from 0.2 to 3 hours depending on the rate of formation of peroxide compo-unds in the cooking liquor, after which said temperature is maintained to allow said peroxide compounds to get formed, where upon the temperature is reduced to about 80°C. for from 0.1 to 4 hours depending on the rate of decomposition into radicals of the peroxide compounds. The proposed process gives a quality high-strength semifinished product of whiteness 40 percent with a yield of about 60 percent.
The present invention relates to processes for manufactu-rig a semifinished product from ground vegetable raw ma-terial. In accordance with the proposed process, ground stea-med raw material is treated with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material, whereupon the raw material is subjected to digestion under temperature conditions such that the temperature is first raised to about 160°C. for from 0.2 to 3 hours depending on the rate of formation of peroxide compo-unds in the cooking liquor, after which said temperature is maintained to allow said peroxide compounds to get formed, where upon the temperature is reduced to about 80°C. for from 0.1 to 4 hours depending on the rate of decomposition into radicals of the peroxide compounds. The proposed process gives a quality high-strength semifinished product of whiteness 40 percent with a yield of about 60 percent.
Description
~8~Z~O
PROCESS FOR ~IANUF'7~CTURING A SI~MIFINISHED
PI~ODUCT FROM GROUND VEGETABLE RAW MATERI~L
The present invention relates to processes for manufac-turing a semifinished product from ground cellulose-containing raw rnaterial without recourse to sulphides which present a pollution hazard.
The process of this invention can be employed most advantageously in the production of ~ibrous semifinished products ear-marked for the manufacture of various kinds of paper and cardboard, as well as for chemical processing of various vegetable ~ -raw materials, such as chopped straw of annual plants, cereal straw, cane, reed, bagasse, wood shavings, sawdust, and coniferou~
and deciduous chips.
In the manufacture of cellulose semifinished products, the chief task is to transfer lignin and part of hemicellulose from the feedstock into the cooking liquor. The level of hemi-cellulose should be at a minimum in the semifinished product earmariced for chemical processing.
It is currently known in the art to make wide use of various modificationsof the sulphite and sulphate processes for .. . .
manufacturing cellulose semifinished products.
Tllese processes employ sulphur-containing reagents and the organic substances dissolved in the course of cooking are subjected to combustion with a view to recovering the chemicals, :
. ~
108~ 0 polluting the environment, above all, with various sulphides.
The combustion procedure is effected in extremely cumbersome soda-ash recovery boiler units which are prone to explode every now and then. The valuable organic substances dissolved in the course of digestion are utilized merely as low-calorie fuel which is ultimately converted to carbon dioxide.
At many sulphite pulp mills, the waste sulphite liquor is dumped untreated into water reservoirs, causing great economic harm.
For this reason, new processes for manufacturing a semifinished product from cellulose-containing vegetable raw material are badly needed.
So far, a number of processes have been developed for manufacturing a semifinished product from cellulose-containing vegetable raw material by use of oxygen in an alkaline medium constituted by various compounds of alkali metals, (above all, sodium) inter alia, sodium hydroxide, sodium bicarbonate and sodium carbonate. `
The most widespread process is two-stage soda-oxygen pulping (U.S. Patent No. 3,691,008, Cl. D21b) in which digestion ;-is carried out in two steps: at the first step, the ground ~
vegetable feedstock is subjected to soda pulping; while at the -second step, after mechanical defibering, the digestion procedure is effected in the presence of oxygen in an aqueous solution of sodium hydroxide. At the first step, the temperature is main-'' ' ' ' ~ . ' .
1088Z~;O
tained at 140 to 190C. and the sodium hydroxide consumption at 10 to 18 percent of the wood chip weight. At the second step of pulping, the temperature is in the range from 95 to 130C.
and the sodium hydroxide consumption is 5 to 12 percent (in terms of sodium oxide) of the beaten material weight at a partial pressure of oxygen of from 7 to 14 kgf/sq.cm.
There also exists a process wherein at the first stage the ground feedstock material is pulped in a sodium carbonate liquor, after which the partially cooked material is defiberized into fibers of bundles of fibers and pulped in the presence of oxygen in an aqueous solution of sodium carbonate.
Both foregoing processes produce no harmful sulphide emissions and give a semifinished product with a sufficiently high yield and having an adequate whiteness.
However, the two prior art processes have the following disadvantages:
- in the course of soda pulping in the absence of oxygen the phenolic and tarry substances forming from the wood pass into the solution and eventually make their way into the effluent;
- special beating equipment is required for defiber-izing the partially digested raw material into fibers or bundles of fibers, calling for considerable power consumption;
- it is necessary to recover the alkaline reagents used up in the digestion process by burning the organic compounds 108~Z~;0 employed at the first and second steps of the process.
Recoverillg the alkaline reagents involves an extremely sophisticated procedure, requiring special shops fitted with cumbersome and sophisticated equipment. Actually, recovery of chemicals costs more and calls for more sophisticated equipment than the manufacture of semifinished products proper.
There exists a more progressive process for preparing wood pulp (Swedish Patent No. 343,029, Cl. D21c) by processing wood, primarily shavings or chips, which reacts with an alkaline liquor containing sodium bicarbonate and/or carbonate in the presence of oxygen pretreated with an absorbing fluid to eliminate its carbon dioxide component. ~`
Another progressive technique is a process for ~
manufacturing pulp of high whiteness by use of oxygen in an ~-alkaline medium (French Patent No. 2,091,515, Cl. 21c, 3/00).
According to the latter technlque, wood pulp is treated with oxygen in an alkaline medium. The amount of the alkali input in the form of a hydroxide and/or carbonate accounts for about 75 percent of the total quantity of alkali used up in the process, the rest of the alkali being introduced into the process in increasing batches continuously or sequentially in the course of pulping; for the most part, the process is effected at pH from 9.2 to 13Ø
Both foregoing processes dispense with the first stage ~
of cooking in an alkaline medium as well as with preliminary ` `
1088Z~0 mechanical defibering of the partially cooked raw material, both procedures being undesirable, as has been mentioned hereabove.
However, these advantages are offset by the problem o~ recovering the chemicals from the waste liquors, which, far from being simplified, grows in complexity.
Indeed, it takes some 400 kg of alkaline reagent in terms of sodium carbonate to produce a ton of semifinished product.
The organic substances dissolved in the course of digestion at the rate of from 400 to 600 kg get oxidized to a considerable degree in the process of digestion, so that their -~
heat value as a fuel drops several times, while their ash content conversely rises.
Hence, combustion of such concentrated waste liquors is not only disadvantageous from the viewpoint of utilization of the heat of combustion of the dissolved organic substances, but calls for additional fuel consumption. Furthermore, wet combustion of waste liquors requires the use of sophisticated equipment capable of operating at a pressure in the range from 200 to 300 kgf/sq.cm. and a temperature of about 300C.
In view of the above, the greatest promise seems to be held by processes for manufacturing a semifinished product through digestion of raw material by use of oxygen in an alkaline medium constituted by ammonium hydroxide, inter alia, a process ~or cooking bagasse with ammonium hydroxide and oxygen (U.S.
Patent No. 3,274,049, Cl. 162-65).
1088;Z60 In this latter process, bagasse is digested in an aqueous alkaline liquor containing ammonium hydroxide as its sole alkali-forming reagent and having a pH of from 9 to 12.2. The ~ ;
process parameters are as follows: partial pressure of oxygen, from 1.8 to 18 kgf/sq.cm; temperature, from 130 to 150C.;
digestion time, from 30 to 90 minutes; the yield of the semifinished product is at least 40 percent of the feedstock ;~
by weight.
When implementing this process, the waste digestion liquor may be utilized, immediately or after concentration, as an organomineral nitrogenous fertilizer. So, this process of oxygen pulping does not require the recovery of the chemicals.
In one of the exemplary embodiments of the process it is indicated that 3 hours of digestion at a temperature of 150C. -~with an ammonium hydroxide liquor of concentration 5.8 percent and pH 12.2 at a partial pressure of oxygen of 17.3 kgf/sq.cm.
and an overall pressure of 21.09 kgf/sq.cm. gave a semifinished product from spruce sawdust with a yield of 49.4 percent.
However, as follows from the title and the sub]ect of the invention, said process is only applicable for manufactur-.. . .
ing a semifinished product from bagasse which lends itself todigestion far more readily than wood feedstock.
The specifiaation of the earlier mentioned U.S. Patent No. 3,691,008, Cl D21b, likewise points out that the process is inapplicable for pulping wood chips.
Our own research confirms that in said process wood raw '"''."'' ~' ~ ~ " ' . ' ' ~o~ o material can be converted to a very poor-quality semifinished product with a yield of not greater than 50 percent and a white-ness of less than 15 percent.
The poor strength of the semifinished product is confirmed by the low yield and stems from the uncontrolled course of radical reactions of oxidation in the process of pulping.
Thus, the latter known process shows the following disadvantages:
- the semifinished product is obtained with a poor yield and has a low whiteness and a poor mechanical strength;
- the semifinished product cannot be produced from the most widespread kind of raw material, viz. wood;
- it is impossible to control the radi!cal reactions of oxidation in the course of pulping; which determine the yield and quality of the semifinished product.
It is an object of the present invention to obviate the aforementioned disadvantages.
20 , It is an object of the present invention to provide a process for manufacturing a semifinished product from ground vegetable raw material, wherein, thanks to the pretreatment of steamed feedstock and the pulping at successive temperatures within an appropriate temperature range, any cellulose-containing raw material, including wood raw material, could be converted to high-strength quality semifinished of whiteness 40 percent with a yield of about 60 percent. ~ -iO88;~;0 It is an important object of the present invention to provicle a process for manufacturing a semifinished product from grouncl vegetable raw material which would make it possible to control the rate of the pulping procedure lasting not longer than 7 hours.
It is a further object of the invention to provide a ' process wherein the raw material could be comprehensively utilized without need for the combustion of the dissolved organic substances `;
which can be subsequently converted to valuable products, inter alia, protein fodder yeasts and fertilizers. ~ ;
It is yet another object of the invention to provide ;
a process which would emit no pollutants, and not only sulphides, but also phenolic substances and resins formed from wood. ~ `~
Accordingly, there is provided a process for manufactur-ing a semifinished product from ground vegetable raw material by digesting presteamed feedstock in the presence of an oxygen-containing gas under pressure in an aqueous solution of an alkaline reagenl at pH from 5 to 12.5, wherein, in accordance with the invention, the presteamed feedstock is treated with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours ~ ~-but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw materlal in the course of pulping, and the digestion procedure is effected under temperature conditions such that the temperature is first raised to about 160C for from 0.2 to 3 hours depending on the rate of formation of peroxide compounds in the cooking liquor, then said temperature 1088Z~0 is maintained for as long as it takes said peroxide compounds to get formed, whereupon an alkaline reagent is added to the liquor and the temperature is lowered to about 80C. for from 0.1 to 4 hours depending on the rate of decomposition of the peroxide compounds into radicals, after which the cooled stock is maintained at said reduced temperature for from 0.1 to 4 hours, and the process is terminated to yield the desired semifinished product.
These and other objects are attained in a process for manufacturing a semifinished product from ground vegetable raw material by digesting presteamed feedstock in the presence . .
of an oxygen-containing gas under pressure in an aqueous solution of an alkaline reagent at pH from 5 to 12.5, wherein, in accordance with the invention, the pres~eamed feedstock is treated with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material in the course of pulping, and the digestion procedure is effected under temperature conditions such that the temperature is first raised to about 160C. for from 0.2 to 3 hours depend- ~
ing on the rate of formation of peroxide compounds in the cooking .
liquor, then said temperature is maintained for as long as it takes said peroxide compounds to get formed, whereupon an alkaline reagent is added to the liquor and the temperature is reduced to about 80C for from 0.1 to 4 hours depending on the rate of ~08~Z~;0 decomposition of the peroxide compounds into radicals, after which the cooled stock is maintained at said reduced temperature for from 0.1 to 4 hours and the process is terminated to yield the desired semifinished product.
The prolonged exposure of the presteamed raw material to an oxidant ensures improved penetration of the cooking reagent into the bulk of the raw material in the course of ~ `~
digestion as well as preoxidation of the lignin component of the raw material even before the digestion procedure begins.
These two features are instrumental in speeding up the pulping -procedure and raising the quality of the semifinished product.
The temperature variation in the course of digestion ;
allows of controlling the rate of formation and decomposition ;-into radicals ofperoxide compounds, which in turn permits controlling the rate of the digestion procedure, contributing to the ~uality of the semifinished product manufactured therein.
In accordance with the invention, the temperature differential between the upper and lower levels amounts up to ~ ;~
50C. depending on the rate of decomposition of the peroxide compounds. It is thereby possible to control the decomposition of the peroxide compounds in the cooking liquor and, hence, the rate of pulping, with the result that the pulp quality is improved.
In order to minimize the effect of the ions of variable-valency metals, which are always present in the digestion liquor, ~Z60 and always affect the pulp quality, in accordance with the invention, the temperature limits, the dwelling times at said temperature as well as the periods of time needed to attain said temperatures are controlled depending on the level of ions of variable-valency metals.
In accordance with the invention, the oxidant employed for the pretreatment at pH from 4 to 6.4 and a temperature of from 100 to 150C. is oxygen. Such pretreatment results in the preoxidation of the lignin component of the raw materials and enhances the diffusion of oxygen during digestion, which in turn speeds up the digestion procedure, improves the quality of the semifinished product and allows the use of the waste liquor as a fertilizer and a culture medium for growing protein fodder yeasts. ~
In accordance with the invention for the pretreatment of ~ -the presteamed raw material nitric acid is employed as the oxidant at a concentration of 3 to 8% and a temperature of 40 to 100C.
Nitration and oxidation of lignin resulting in its destruction -and partial solution take place during the treatment with nitric -acid. At the same time as a result of hydrolytic effect of nitric acid the solution of a certain amount of hemicellulose takes place. The total amount of the vegetable material dissolved at the stage of nitric acid treatment is up to 20% of the weight of absolutely dry initial raw material.
Partial solution of the vegetable material which takes place at the stage of nitric acid treatment causes the formation of a more porous and permeable structure of the raw material which facilitates the penetration of oxygen and ~
the alkaline reactant during the subsequent oxygen-alkaline ~-digestion. As a result it becomes possible to accelerate the 30 digestion, reduce the temperature of the process and the pressure -of the oxygen-containing gas at the oxygen-alkaline stage of digestion, and to employ a wood raw material in the form of wood chips of conventional size. Partial oxidation and des~ruction ~h -11-~Z60 of lignin taking place during the nitric acid treatment considerably lower the ability of lignin to enter into a condensation reaction with ammonia reducing the possibility of formation of dark-colored ~
compounds which lower the quality of the semi-finished product. ~ -The subsequent digestion with an oxygen-containing gas is conducted at a low oxygen pressure of less than 20 kgf/cm2 and a temperature of up to 130C making it possible to obtain a strong and light semi-finished product from wood chips.
In addition, the easily hydrolyzed fraction of poly-saccharides passing into the solution during the nitric acidtreatment is not subjected to oxidation with oxygen but is removed from the cooking vessel when the cooking liquor is replaced prior to the oxygen-alkaline digestion and thus can be fully utilized for preparing fodder yeast which should increase their yield.
According to the invention, in order that the lignin ~ ;~
oxidized during pretreatment may pass into the solution, -~
an alkaline reagent--an aqueous solution of ammonia, -~ -soda, potash, sodium, hydroxide or gaseous ammonia--is added to the cooking liquor in the course of digestion and cooling.
"` .
- lla -~' ' : ' .
~08t~iO
But it is known that condensation of lignin with ammonia slows down the digestion procedure and adversely affects the quality of the semifinished product.
The passage of the lignin into the cooking liquor considerably reduces its condensation, consequently improving the quality of the semifinished product. The quality of the semifinished product will be raised still more if ammonia is added gradually in batches depending on a specified pH value of the cooking liquor.
Further, since the digestion procedure is effected in two stages the temperature at the first stage being 130 to 160C
and at the second 130 to 80C., it becomes possible to control the decomposition of the peroxide compounds into radicals at ;
both stages of digestion and, hence, the rate of digestion and the quality of the pulp.
Then, owing to the fact that alkaline potassium compounds are added to the cooking liquor at a partial pressure of oxygen of 3 to 20 atm. and pH 7 to 12.5, it is possible for the lignin oxidizes at the first stage of digestion, including that condensed with ammonia nitrogen, to pass into the liquor.
This makes for a high-strength and high-whiteness semifinished product produced at a low partial pressure of oxygen and a relatively low digestion temperature; at the same time, it is possible to utilize the dissolved organic substances to manufacture protein fodder yeasts and organomineral fertilizers containing potassium compounds alongside nitrogen compounds.
It is common knowledge that cellulose macromolecules are likely to undergo destruction, particularly in case the cooking liquor has enhanced alkalinity.
The degradation of cellulose reduces the strength of the semifinished product. So, to prevent or at least minimize the cellulose degradation effect, in accordance with the invention, iO~8Z60 inhibitors are added to the cooking liquor at the second stage of digestion, the inhibitors being constituted by magnesium employed at the rate of from 0.05 to 1.0 percent by weight of the ~
ground raw material (in terms of magnesium). ~ ~`
In order to boost the rate of digestion and raise the quality of the semifinished product, in accordance with the invention, after the pretreatment the raw material is subjected ;
to washing.
Since the pretreated rawmaterial is washed with waste liquor produced in the digestion procedure, the fresh water ~
consumption is reduced and the waste liquor comes to contain a - -higher proportion of dissolved organic substances, making utilization of the waste liquor an easier matter.
Furthermore, since the pretreated raw material subjected to the first~stage of digestion is washed to eliminate the dissolved substances and reduce the consumption of chemicals at the second stage of digestion, the delignification procedure at the second stage of digestion is facilitated which, in its turn, leads to a higher quality of the semifinished product at milder process parameters.
Besides, in accordance with the invention, the pretreated raw material is washed with the waste liquor from the second stage of digestion. This is a factor in reducing the consumption of fresh water for the manufacture of the semifinished product, which also conduces to a higher concentration of dissolved ~ ~-substances in the waste liquor.
Thus, the proposed process produces a strong and light semifinished product in a high yield from any kind of vegetable ; raw material, including wood chips. The process of this invention requires no recovery of the chemicals from the waste liquors and is pollution-free.
The organic substances dissolved in the course of
PROCESS FOR ~IANUF'7~CTURING A SI~MIFINISHED
PI~ODUCT FROM GROUND VEGETABLE RAW MATERI~L
The present invention relates to processes for manufac-turing a semifinished product from ground cellulose-containing raw rnaterial without recourse to sulphides which present a pollution hazard.
The process of this invention can be employed most advantageously in the production of ~ibrous semifinished products ear-marked for the manufacture of various kinds of paper and cardboard, as well as for chemical processing of various vegetable ~ -raw materials, such as chopped straw of annual plants, cereal straw, cane, reed, bagasse, wood shavings, sawdust, and coniferou~
and deciduous chips.
In the manufacture of cellulose semifinished products, the chief task is to transfer lignin and part of hemicellulose from the feedstock into the cooking liquor. The level of hemi-cellulose should be at a minimum in the semifinished product earmariced for chemical processing.
It is currently known in the art to make wide use of various modificationsof the sulphite and sulphate processes for .. . .
manufacturing cellulose semifinished products.
Tllese processes employ sulphur-containing reagents and the organic substances dissolved in the course of cooking are subjected to combustion with a view to recovering the chemicals, :
. ~
108~ 0 polluting the environment, above all, with various sulphides.
The combustion procedure is effected in extremely cumbersome soda-ash recovery boiler units which are prone to explode every now and then. The valuable organic substances dissolved in the course of digestion are utilized merely as low-calorie fuel which is ultimately converted to carbon dioxide.
At many sulphite pulp mills, the waste sulphite liquor is dumped untreated into water reservoirs, causing great economic harm.
For this reason, new processes for manufacturing a semifinished product from cellulose-containing vegetable raw material are badly needed.
So far, a number of processes have been developed for manufacturing a semifinished product from cellulose-containing vegetable raw material by use of oxygen in an alkaline medium constituted by various compounds of alkali metals, (above all, sodium) inter alia, sodium hydroxide, sodium bicarbonate and sodium carbonate. `
The most widespread process is two-stage soda-oxygen pulping (U.S. Patent No. 3,691,008, Cl. D21b) in which digestion ;-is carried out in two steps: at the first step, the ground ~
vegetable feedstock is subjected to soda pulping; while at the -second step, after mechanical defibering, the digestion procedure is effected in the presence of oxygen in an aqueous solution of sodium hydroxide. At the first step, the temperature is main-'' ' ' ' ~ . ' .
1088Z~;O
tained at 140 to 190C. and the sodium hydroxide consumption at 10 to 18 percent of the wood chip weight. At the second step of pulping, the temperature is in the range from 95 to 130C.
and the sodium hydroxide consumption is 5 to 12 percent (in terms of sodium oxide) of the beaten material weight at a partial pressure of oxygen of from 7 to 14 kgf/sq.cm.
There also exists a process wherein at the first stage the ground feedstock material is pulped in a sodium carbonate liquor, after which the partially cooked material is defiberized into fibers of bundles of fibers and pulped in the presence of oxygen in an aqueous solution of sodium carbonate.
Both foregoing processes produce no harmful sulphide emissions and give a semifinished product with a sufficiently high yield and having an adequate whiteness.
However, the two prior art processes have the following disadvantages:
- in the course of soda pulping in the absence of oxygen the phenolic and tarry substances forming from the wood pass into the solution and eventually make their way into the effluent;
- special beating equipment is required for defiber-izing the partially digested raw material into fibers or bundles of fibers, calling for considerable power consumption;
- it is necessary to recover the alkaline reagents used up in the digestion process by burning the organic compounds 108~Z~;0 employed at the first and second steps of the process.
Recoverillg the alkaline reagents involves an extremely sophisticated procedure, requiring special shops fitted with cumbersome and sophisticated equipment. Actually, recovery of chemicals costs more and calls for more sophisticated equipment than the manufacture of semifinished products proper.
There exists a more progressive process for preparing wood pulp (Swedish Patent No. 343,029, Cl. D21c) by processing wood, primarily shavings or chips, which reacts with an alkaline liquor containing sodium bicarbonate and/or carbonate in the presence of oxygen pretreated with an absorbing fluid to eliminate its carbon dioxide component. ~`
Another progressive technique is a process for ~
manufacturing pulp of high whiteness by use of oxygen in an ~-alkaline medium (French Patent No. 2,091,515, Cl. 21c, 3/00).
According to the latter technlque, wood pulp is treated with oxygen in an alkaline medium. The amount of the alkali input in the form of a hydroxide and/or carbonate accounts for about 75 percent of the total quantity of alkali used up in the process, the rest of the alkali being introduced into the process in increasing batches continuously or sequentially in the course of pulping; for the most part, the process is effected at pH from 9.2 to 13Ø
Both foregoing processes dispense with the first stage ~
of cooking in an alkaline medium as well as with preliminary ` `
1088Z~0 mechanical defibering of the partially cooked raw material, both procedures being undesirable, as has been mentioned hereabove.
However, these advantages are offset by the problem o~ recovering the chemicals from the waste liquors, which, far from being simplified, grows in complexity.
Indeed, it takes some 400 kg of alkaline reagent in terms of sodium carbonate to produce a ton of semifinished product.
The organic substances dissolved in the course of digestion at the rate of from 400 to 600 kg get oxidized to a considerable degree in the process of digestion, so that their -~
heat value as a fuel drops several times, while their ash content conversely rises.
Hence, combustion of such concentrated waste liquors is not only disadvantageous from the viewpoint of utilization of the heat of combustion of the dissolved organic substances, but calls for additional fuel consumption. Furthermore, wet combustion of waste liquors requires the use of sophisticated equipment capable of operating at a pressure in the range from 200 to 300 kgf/sq.cm. and a temperature of about 300C.
In view of the above, the greatest promise seems to be held by processes for manufacturing a semifinished product through digestion of raw material by use of oxygen in an alkaline medium constituted by ammonium hydroxide, inter alia, a process ~or cooking bagasse with ammonium hydroxide and oxygen (U.S.
Patent No. 3,274,049, Cl. 162-65).
1088;Z60 In this latter process, bagasse is digested in an aqueous alkaline liquor containing ammonium hydroxide as its sole alkali-forming reagent and having a pH of from 9 to 12.2. The ~ ;
process parameters are as follows: partial pressure of oxygen, from 1.8 to 18 kgf/sq.cm; temperature, from 130 to 150C.;
digestion time, from 30 to 90 minutes; the yield of the semifinished product is at least 40 percent of the feedstock ;~
by weight.
When implementing this process, the waste digestion liquor may be utilized, immediately or after concentration, as an organomineral nitrogenous fertilizer. So, this process of oxygen pulping does not require the recovery of the chemicals.
In one of the exemplary embodiments of the process it is indicated that 3 hours of digestion at a temperature of 150C. -~with an ammonium hydroxide liquor of concentration 5.8 percent and pH 12.2 at a partial pressure of oxygen of 17.3 kgf/sq.cm.
and an overall pressure of 21.09 kgf/sq.cm. gave a semifinished product from spruce sawdust with a yield of 49.4 percent.
However, as follows from the title and the sub]ect of the invention, said process is only applicable for manufactur-.. . .
ing a semifinished product from bagasse which lends itself todigestion far more readily than wood feedstock.
The specifiaation of the earlier mentioned U.S. Patent No. 3,691,008, Cl D21b, likewise points out that the process is inapplicable for pulping wood chips.
Our own research confirms that in said process wood raw '"''."'' ~' ~ ~ " ' . ' ' ~o~ o material can be converted to a very poor-quality semifinished product with a yield of not greater than 50 percent and a white-ness of less than 15 percent.
The poor strength of the semifinished product is confirmed by the low yield and stems from the uncontrolled course of radical reactions of oxidation in the process of pulping.
Thus, the latter known process shows the following disadvantages:
- the semifinished product is obtained with a poor yield and has a low whiteness and a poor mechanical strength;
- the semifinished product cannot be produced from the most widespread kind of raw material, viz. wood;
- it is impossible to control the radi!cal reactions of oxidation in the course of pulping; which determine the yield and quality of the semifinished product.
It is an object of the present invention to obviate the aforementioned disadvantages.
20 , It is an object of the present invention to provide a process for manufacturing a semifinished product from ground vegetable raw material, wherein, thanks to the pretreatment of steamed feedstock and the pulping at successive temperatures within an appropriate temperature range, any cellulose-containing raw material, including wood raw material, could be converted to high-strength quality semifinished of whiteness 40 percent with a yield of about 60 percent. ~ -iO88;~;0 It is an important object of the present invention to provicle a process for manufacturing a semifinished product from grouncl vegetable raw material which would make it possible to control the rate of the pulping procedure lasting not longer than 7 hours.
It is a further object of the invention to provide a ' process wherein the raw material could be comprehensively utilized without need for the combustion of the dissolved organic substances `;
which can be subsequently converted to valuable products, inter alia, protein fodder yeasts and fertilizers. ~ ;
It is yet another object of the invention to provide ;
a process which would emit no pollutants, and not only sulphides, but also phenolic substances and resins formed from wood. ~ `~
Accordingly, there is provided a process for manufactur-ing a semifinished product from ground vegetable raw material by digesting presteamed feedstock in the presence of an oxygen-containing gas under pressure in an aqueous solution of an alkaline reagenl at pH from 5 to 12.5, wherein, in accordance with the invention, the presteamed feedstock is treated with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours ~ ~-but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw materlal in the course of pulping, and the digestion procedure is effected under temperature conditions such that the temperature is first raised to about 160C for from 0.2 to 3 hours depending on the rate of formation of peroxide compounds in the cooking liquor, then said temperature 1088Z~0 is maintained for as long as it takes said peroxide compounds to get formed, whereupon an alkaline reagent is added to the liquor and the temperature is lowered to about 80C. for from 0.1 to 4 hours depending on the rate of decomposition of the peroxide compounds into radicals, after which the cooled stock is maintained at said reduced temperature for from 0.1 to 4 hours, and the process is terminated to yield the desired semifinished product.
These and other objects are attained in a process for manufacturing a semifinished product from ground vegetable raw material by digesting presteamed feedstock in the presence . .
of an oxygen-containing gas under pressure in an aqueous solution of an alkaline reagent at pH from 5 to 12.5, wherein, in accordance with the invention, the pres~eamed feedstock is treated with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material in the course of pulping, and the digestion procedure is effected under temperature conditions such that the temperature is first raised to about 160C. for from 0.2 to 3 hours depend- ~
ing on the rate of formation of peroxide compounds in the cooking .
liquor, then said temperature is maintained for as long as it takes said peroxide compounds to get formed, whereupon an alkaline reagent is added to the liquor and the temperature is reduced to about 80C for from 0.1 to 4 hours depending on the rate of ~08~Z~;0 decomposition of the peroxide compounds into radicals, after which the cooled stock is maintained at said reduced temperature for from 0.1 to 4 hours and the process is terminated to yield the desired semifinished product.
The prolonged exposure of the presteamed raw material to an oxidant ensures improved penetration of the cooking reagent into the bulk of the raw material in the course of ~ `~
digestion as well as preoxidation of the lignin component of the raw material even before the digestion procedure begins.
These two features are instrumental in speeding up the pulping -procedure and raising the quality of the semifinished product.
The temperature variation in the course of digestion ;
allows of controlling the rate of formation and decomposition ;-into radicals ofperoxide compounds, which in turn permits controlling the rate of the digestion procedure, contributing to the ~uality of the semifinished product manufactured therein.
In accordance with the invention, the temperature differential between the upper and lower levels amounts up to ~ ;~
50C. depending on the rate of decomposition of the peroxide compounds. It is thereby possible to control the decomposition of the peroxide compounds in the cooking liquor and, hence, the rate of pulping, with the result that the pulp quality is improved.
In order to minimize the effect of the ions of variable-valency metals, which are always present in the digestion liquor, ~Z60 and always affect the pulp quality, in accordance with the invention, the temperature limits, the dwelling times at said temperature as well as the periods of time needed to attain said temperatures are controlled depending on the level of ions of variable-valency metals.
In accordance with the invention, the oxidant employed for the pretreatment at pH from 4 to 6.4 and a temperature of from 100 to 150C. is oxygen. Such pretreatment results in the preoxidation of the lignin component of the raw materials and enhances the diffusion of oxygen during digestion, which in turn speeds up the digestion procedure, improves the quality of the semifinished product and allows the use of the waste liquor as a fertilizer and a culture medium for growing protein fodder yeasts. ~
In accordance with the invention for the pretreatment of ~ -the presteamed raw material nitric acid is employed as the oxidant at a concentration of 3 to 8% and a temperature of 40 to 100C.
Nitration and oxidation of lignin resulting in its destruction -and partial solution take place during the treatment with nitric -acid. At the same time as a result of hydrolytic effect of nitric acid the solution of a certain amount of hemicellulose takes place. The total amount of the vegetable material dissolved at the stage of nitric acid treatment is up to 20% of the weight of absolutely dry initial raw material.
Partial solution of the vegetable material which takes place at the stage of nitric acid treatment causes the formation of a more porous and permeable structure of the raw material which facilitates the penetration of oxygen and ~
the alkaline reactant during the subsequent oxygen-alkaline ~-digestion. As a result it becomes possible to accelerate the 30 digestion, reduce the temperature of the process and the pressure -of the oxygen-containing gas at the oxygen-alkaline stage of digestion, and to employ a wood raw material in the form of wood chips of conventional size. Partial oxidation and des~ruction ~h -11-~Z60 of lignin taking place during the nitric acid treatment considerably lower the ability of lignin to enter into a condensation reaction with ammonia reducing the possibility of formation of dark-colored ~
compounds which lower the quality of the semi-finished product. ~ -The subsequent digestion with an oxygen-containing gas is conducted at a low oxygen pressure of less than 20 kgf/cm2 and a temperature of up to 130C making it possible to obtain a strong and light semi-finished product from wood chips.
In addition, the easily hydrolyzed fraction of poly-saccharides passing into the solution during the nitric acidtreatment is not subjected to oxidation with oxygen but is removed from the cooking vessel when the cooking liquor is replaced prior to the oxygen-alkaline digestion and thus can be fully utilized for preparing fodder yeast which should increase their yield.
According to the invention, in order that the lignin ~ ;~
oxidized during pretreatment may pass into the solution, -~
an alkaline reagent--an aqueous solution of ammonia, -~ -soda, potash, sodium, hydroxide or gaseous ammonia--is added to the cooking liquor in the course of digestion and cooling.
"` .
- lla -~' ' : ' .
~08t~iO
But it is known that condensation of lignin with ammonia slows down the digestion procedure and adversely affects the quality of the semifinished product.
The passage of the lignin into the cooking liquor considerably reduces its condensation, consequently improving the quality of the semifinished product. The quality of the semifinished product will be raised still more if ammonia is added gradually in batches depending on a specified pH value of the cooking liquor.
Further, since the digestion procedure is effected in two stages the temperature at the first stage being 130 to 160C
and at the second 130 to 80C., it becomes possible to control the decomposition of the peroxide compounds into radicals at ;
both stages of digestion and, hence, the rate of digestion and the quality of the pulp.
Then, owing to the fact that alkaline potassium compounds are added to the cooking liquor at a partial pressure of oxygen of 3 to 20 atm. and pH 7 to 12.5, it is possible for the lignin oxidizes at the first stage of digestion, including that condensed with ammonia nitrogen, to pass into the liquor.
This makes for a high-strength and high-whiteness semifinished product produced at a low partial pressure of oxygen and a relatively low digestion temperature; at the same time, it is possible to utilize the dissolved organic substances to manufacture protein fodder yeasts and organomineral fertilizers containing potassium compounds alongside nitrogen compounds.
It is common knowledge that cellulose macromolecules are likely to undergo destruction, particularly in case the cooking liquor has enhanced alkalinity.
The degradation of cellulose reduces the strength of the semifinished product. So, to prevent or at least minimize the cellulose degradation effect, in accordance with the invention, iO~8Z60 inhibitors are added to the cooking liquor at the second stage of digestion, the inhibitors being constituted by magnesium employed at the rate of from 0.05 to 1.0 percent by weight of the ~
ground raw material (in terms of magnesium). ~ ~`
In order to boost the rate of digestion and raise the quality of the semifinished product, in accordance with the invention, after the pretreatment the raw material is subjected ;
to washing.
Since the pretreated rawmaterial is washed with waste liquor produced in the digestion procedure, the fresh water ~
consumption is reduced and the waste liquor comes to contain a - -higher proportion of dissolved organic substances, making utilization of the waste liquor an easier matter.
Furthermore, since the pretreated raw material subjected to the first~stage of digestion is washed to eliminate the dissolved substances and reduce the consumption of chemicals at the second stage of digestion, the delignification procedure at the second stage of digestion is facilitated which, in its turn, leads to a higher quality of the semifinished product at milder process parameters.
Besides, in accordance with the invention, the pretreated raw material is washed with the waste liquor from the second stage of digestion. This is a factor in reducing the consumption of fresh water for the manufacture of the semifinished product, which also conduces to a higher concentration of dissolved ~ ~-substances in the waste liquor.
Thus, the proposed process produces a strong and light semifinished product in a high yield from any kind of vegetable ; raw material, including wood chips. The process of this invention requires no recovery of the chemicals from the waste liquors and is pollution-free.
The organic substances dissolved in the course of
2~;0 digestion may be converted to valuable products, such as protein fodder yeasts and organomineral fertilizers of prolonged activity.
The novel process of this invention may be regarded as a speeded-up process simulating the natural turnover of substances in nature.
The present invention will be hereinafter illustrated by exemplary embodiments of the proposed process for manufacturing a semifinished product from ground vegetable raw material.
The semifinished product is manufactured as follows.
Ground raw material is steamed with saturated water vapour with a temperature of not higher than 180C. so as to completely eliminate all air trapped in the raw material and heat the raw material to 100 to 120C.
The steamed raw material i5 then treated with an oxidant. Where the oxidant is constituted by an oxygen-containing gas, the treatment at the above-given temperature and a partial pressure of oxygen of up to 40 kgf/sq.cm. lasts a short time, from several seconds to one hour. The treatment succeeds in ensuring penetration of oxygen into the pores of the vegetable fibers and partial oxidation of the lignin component of the raw material.
Should nitric acid be employed as the oxidant, the steamed raw material is admixed with a cooled solution of nitric acid of concentration from 3.0 to 8.0 percent so that the temperature of the mixture lies in the range from 40 to 80C.
The mixture is then maintained at said temperature for from - 30 to 60 minutes at a hydraulic pressure of from 0 to 10 kgf/sq.
cm., after which the excessive fluid is drained off and the wet raw material saturated with nitric acid is steam-heated to a temperature of from 96 to 99C. and maintained at said temperature and a pressure close to the atmospheric level for from 1.0 to 1.5 hours. Where nitric acid is employed as the oxidant, the z~o pretreatment provides for a high degree of lignin oxidation.
The raw material subjected to oxidative pretreatment, is then washed with water or with the waste liquor which i9 formed in the course of digestion in the presence of oxygen in an alkaline medium. The washing with the waste liquor is preferable as providing a new waste liquor with a higher concentration of organic substances which more readily lend themselves to subsequent utilization. This kind of washing is particularly important in cases of pretreatment of the raw material with nitric acid which provides for a higher degree of lignin oxida~ion.
The washing after the oxidative treatment not only cuts down the consumption of the alkaline reagent for the neutralization -~
~ : -of the acid products formed in the course of digestion in an alkaline medium in the presence of oxygen, but at the same time permits eliminating from the vegetable raw material the ever-present microadmixtures of the ions of variable-valency metals, such as copper, iron, chromium, cobalt, vanadium, manganese or nickel.
The compounds of these metals promote the radical -`
reactions of raw material oxidation by speeding up the formation of peroxide compounds and the decomposition of same into radicals.
In their turn, the radical reactions cause cellulose degradation, detracting from the strength of the semifinished product.
An acidic medium - at pH less than 6.5 - in the course of oxidative pretreatment of vegetable raw material promotes the passage of said metal ions into the liquor and their subsequent elimination by washing.
The raw material treated as described hereabove, is subjected to digestion by use of oxygen in an alkaline medium in a digester designed for operation at elevated pressure and providing for effective contact of all reacting phases, viz. the raw material, the cooking liquor and the oxygen-containing gas.
108~Z~O
The di(3ester contents are heated for from 0.2 to 3 hours to the top digestion temperature, but not above 160C. The rate of l~eating and the value of the maximum temperature are selected takin~ into account the rate of formation of peroxide compounds in the cooking liquor, the kind and degree of oxidative pre-treatment of the raw material as well as other factors, such as the kind and degree of comminution of the raw material, the pH value of the cooking liquor, or the type of equipment used.
Then the maximum temperature is maintained for from 0.1 to 5 hours until a specified quantity of peroxide compounds is formed in the cooking liquor.
Then the temperature is lowered for from 0.1 to 4.0 hours down to but not below 80C., and the cooled stock is allowed to stand for from 0.1 to 4.0 hours until a semifinished product is formed.
The duration of the temperature-reduction process and the value of the minimum temperature are set on the basis of the rate of decomposition of the peroxide compounds into radicals.
While the digestion is in progress, the digester is additionally charged with an oxygen-containing gas and an alkaline reagent, e.g., an aqueous solution of ammonia, gaseous ammonia or alkaline compounds of potassium, maintaining the pH of the cooking liquor at a value in the range from S to 12.5.
The waste gas is discharged to reduce the overall pressure in the digester.
Having kept the mixture at the maximum temperature, which constitutes the first stage of digestion, the waste liquor may be withdrawn and replaced by a fresh batch which may contain a different alkaline reagent, e.g. potassium hydroxide, wherèas -~
the reagent employed at the first stage of the process is an aqueous solution of ammonia.
The mixture now containing a different alkaline reagent 108~Z~0 is subjected to the second stage of digestion at a lower temperature, generally in the range from 100 to 130C., at pH
in the range from 7 to 12.5 and at a partial pressure of oxygen of from 3 to 20 kgf/sq.cm. for from 0.1 to 4 hours depending on the pulping degree at the first stage of cooking. At the second stage of digestion, particularly if the raw material has been pretreated with oxygen before the first stage of digestion, cellulose degradation inhibitors are desirably introduced into the process, such as magnesium compounds, e.g. magnesium carbonate which is added at the rate of from 0.05 to 1.0 percent magnesium -by weight of the absolutely dry ground raw material.
Between the first and second steps of the cooking process, the partially pulped raw material may be washed with water or with tne waste liquor from the second stage of digestion. This kind of washing is particularly desirable if the second stage :
of the process employs potassium compounds instead of~alkaline ammonium compounds.
The above-described process may be implemented in both continuous and batchetype digesters.
After cooking, the semifinished product is washed and sent for further processing in keeping with its purpose.
Thus, for instance, it may be subjected to bleaching by use of chlorine- and/or oxygen-containing reagents: chlorine, chlorine dioxide, hypochlorites, oxygen, ozone or peroxide.
When the semifinished product is earmarked for chemical processing, the conditions of the oxidative pretreatment may be changed and the bleaching procedure may use the known hot and cold refining techniques.
The waste cooking liquor and the liquor after the oxidative pretreatment of the raw material are utilized as culture media for growing protein fodder yeasts, and the substances left unutilized by the yeasts are used, after concentration ~08U'~tiO
or as such, as an organomineral fertilizer.
Besides, the waste cooking liquor may be utilized to produce a range of valuable by_products, viz. vanillin, acetovanillone, formic, acetic, propionic, ~utyric and oxalic acids as well as other, substances, including nitrogen-containing organic compounds.
The process of this invention may be further improved through stripping the waste oxygen-containing gas of carbon dioxide and other impurities by the potash method or any other technique with a view to recycling the oxygen thus recovered from the waste gas.
Example 1 10 g of aspen chips measuring 20 x 20 x 0.5 mm are placed in a l-liter autoclave and steamed with saturated water vapour having a temperature of 130C. for 15 minutes so that the excess of vapour, air and condensate are removed from the autoclave.
Then oxygen is pumped into the autoclave until the pressure there-in reaches 32 kgf/sq.cm. and the pretreatment is effected for 5 minutes, following which 400 ml of an aqueous solution of ,~ -ammonia of pH 10.7 )the pH of the solution is determined at room temperature) is pumped into the autoclave and the temperature in the autoclave is raised by use of an electric heater for 1 hour to 160C. In the course of heating and subsequently during the cooking procedure the autoclave is rotated about the horizontal longitudinal axis thereof.
The temperature in the autoclave is maintained at 160C. ' for 30 minutes in order that the level of peroxide compounds ~n the cooking liquor may reach 0.020 percent. (The level of peroxide compounds is determined by the quantity of iodine liberated from potassium iodide in an acidic medium. This method is used to determine the overall level of all peroxide compounds, such as ROOR, ROORl, H2O2 and ROOH, as well as quinones).
.:
108~Zf~0 Tl~en the temperature in the autoclave is reduced within S minutes to 130C., and the mixture in the autoclave is subjected to aftercooking for 4 hours.
After this the autoclave is immersed in a bath with running river water and rapidly cooled. The overpressure relieved, the waste cooking liquor is drained off, and the semifinished product is washed, screened and analyzed.
The semifinished product is obtained with a yield of ;
60.1 percent, including 58.3 percent pulp and 1.8 percent partially cooked chips. The pulp contains 6.2 percent lignin and has a whiteness of 41 percent. The waste liquor of pH 7.2 contains 16.8 percent nitrogen by weight of the dissolved organic substances, including amide nitrogen and strongly fixed nitrogen t4.6 percent). ' The pulp lends itself readily to beating; at a specified beating degree and a 100-g weight of one square metre of the pulp ~ -sheet, it has a breaking length of 9,400 m and a folding strength of 2,300 double folds. ~ , Example 2 10 g of aspen chips are steamed and treated with oxygen in a procedure exactly duplicating that of Example l; an aqueous solution of ammonium hydroxide of pH 10.7 is likewise pumped into the autoclave like in Example 1. But the heating is effected to a maximum temperature of only 150C., the duration of the heating procedure amounting to 1 hour as in Example 1.
The maximum temperature is maintained for 1.5 hours until the peroxide compounds account for 0.024 percent of the cookin~ liquor. Then the temperature in the autoclave is reduced for 15 minutes to 140C. and maintained at said reduced level for another 1.75 hours.
The subsequent operations duplicate those of Example 1.
The cooking gives a semifinished product with a yield .....
.,' ~' ~
~088Z~0 of 61.6 percent, including 61.2 percent pulp and 0.4 percent partially cooked chips. The pulp contains 6.3 percent lignin.
The waste liquor of pH 6.3 contains 17.2 percent nitrogen by weight of the dissolved organic substances.
At the same parameters as in Example 1, the pulp has a breaking length of 8,900 m and a folding strength of 1,530 double folds.
Example 3 In the same way as in Example 1, 10 g of spruce chips measuring 20 x 20 x 0.5 mm are subjected to cooking under the following temperature conditions: heating to a maximum tempera-ture of 150C. for 1 hour, maintaining the maximum temperature of 150C. for 1.25 hours; cooling to 140C. for 15 minutes; and maintaining the temperature of 140C. for 3 hours.
The process results in a semifinished product with a yield of 59.2 percent, including 52.5 percent pulp and 6.7 percent partially cooked chips. The pulp contains 5.6 percent lignin.
The was~e liquor has a pH of 6.2.
Example 4 In this example, the procedure of Example 1 is duplicated except that the feedstock is con.stituted by 20 g of aspen chips and the cooking li~uor in an amount of 400 ml has a pH of 10.92.
The autoclave contents are heated to 140C. for 1 hour and then maintained at said temperature for 5 hours. The semifinished product thus produced is obtained with a yield of 59.4 percent, including 58.9 percent pulp and 0.5 percent partially cooked chips. The pulp contains 6.7 percent lignin. The waste liquor of p~ 6.2 is utilized as a culture medium for growing protein fodder yeasts, 1 ton of the semifinished product producing 80 kg of absolutely dry protein fodder yeasts.
Example 5 10 g of aspen chips measuring 20 x 20 x 0.5 mm are .
~()8b~ i0 steamed and treated with oxygen in an autoclave in a manner des-cribed in Example 1. Then 400 ml of an aqueous solution of ammonium hydroxide of pH 10.67 is added to the feedstock and the mixture is heated to 140C. for 1 hour. Said temperature is maintained for another 4 hours until the level of peroxide compounds in the cooking liquor reaches 0.006 percent, whereupon the autoclave is cooled in a bath with running river water.
After this the pressure in the autoclave is relieved, the waste liquor is drained off, while the partially cooked raw material after the first stage of digestion is washed with water.
Then it is again placed in the autoclave, and the latter is charged with 200 ml of a 0.32-percent solution of potassium hydroxide as well as with a certain quantity of MgCO3 such that the magnesium ions in the solution account for 1 percent by weight of the partially cooked raw material. Then the oxygen pressure in the autoclave is raised to 20 kgf/sq.cm. and the temperature is likewise raised to 120C. for 1 hour. Said temperature is maintained for another 2 hours.
After the second stage of digestion, the autoclave is ~ -cooled in a bath with running water, the pressure is relieved, and the autoclave is opened. The waste liquor after the second stage of digestion is drained off, while the semifinished product is washed and analyzed. The two-stage process yields pulp containing 3.8 percent lignin and free from partially cooked chips; the yield is 62.5 percent and the whiteness is 54 percent.
Example 6 Aspen chips measuring 20 x 20 x 3 mm and containing 20 kg of absolutely dry wood are placed in a 10-liter autoclave, steamed with live steam for 8 minutes and mixed with 9 liters of an aqueous solution of nitric acid af concentration 47 g/lit.
The feedstock is maintained in the acid at a pressure of 3.0 kgf/sq.cm. for 60 minutes at a temperature of from 60 to 65C., .
after which the aqueous solution of nitric acid is drained off, ~
whereas the chips are heated with live steam to 97 to 99C., --maintained at this temperature for 1 hour, and repeatedly washed first with the waste liquor from the subsequent oxygen-alkaline -cooking operation and then with hot water. 91.0 g of wet chips pretreated with nitric acid and containing 30.0 g of the starting ~ -absolutely dry wood, are placed in a rotating l-liter autoclave, the latter is charged with 600 ml of a 1.3-percent potash solution, and the pressure in the autoclave is built up to 15 kgf/
sq.cm. with oxygen. Then the autoclave is heated for 1 hour to 130C. and maintained at said temperature for another hour.
All the subsequent operations to cool the autoclave, relieve the pressure and drain off the waste liquor, as well as wash and screen the semifinished product, duplicate those of Example 1. ~ ~ -The semifinished product is obtained with a yield of 60.2 percent, including 58.5 percent pulp and 1.7 percent - -partially cooked chips. The pulp has a whiteness of 52.4 percent u and contains 3.5 percent lignLn. ;-~
The waste liquor has a pH of 9.2.
Example 7 -91 g of wet aspen chips pretreated in a procedure ~-duplicating that of Example 6, are placed in a rotating l-liter -~
autoclave and the latter is charged with 600 ml of an a~ueous solution of ammonium hydroxide of pH 10.92. The pressure in the autoclave is built up to 15 kgf/sq.cm. by supplying oxygen thereinto, whereupon the autoclave is heated for 1 hour to 130C.
and maintained at this temperature for another 30 minutes until the level of peroxide compounds in the liquor reaches 0.047 percent, after which the temperature is reduced within 5 minutes to 110C. and maintained at said level for another 90 minutes.
The subsequent operations duplicate those eariler described.
The semifinished product thus obtained is produced with a yield ,,:
1088'~0 ' of 61.4 percent and contains no partially cooked chips. The -pulp has a whiteness of 47 percent and contains 3.1 percent lignin.
The pulp lends itself readily to beating; under the above-described standard conditions, it has a breaking length of 8,800 m and a folding strength of 1,800 double folds. The pH
of the waste liquor is 9.2.
Thus, the examples given hereabove corroborate the effectiveness of the proposed process for manufacturing a quality semifinished product with a whiteness in excess of 40 percent from the most difficultly pulpable varieties of wood raw material, including chips.
The waste liquors contain no pollutants, as borne out by their applicability for growing protein fodder yeasts therein (see Example 4).
As for other kinds of vegetable raw materials, such as cereal straw, cane, reed or grass, the semifinished product can be obtained therefrom under process conditions similar to those described in the examples hereabove except that the oxidative -pretreatment required is less intensive and the oxygen-alkaline digestion may be effected at a lower oxygen pressure, at a lower temperature or within a shorter period of time.
.,
The novel process of this invention may be regarded as a speeded-up process simulating the natural turnover of substances in nature.
The present invention will be hereinafter illustrated by exemplary embodiments of the proposed process for manufacturing a semifinished product from ground vegetable raw material.
The semifinished product is manufactured as follows.
Ground raw material is steamed with saturated water vapour with a temperature of not higher than 180C. so as to completely eliminate all air trapped in the raw material and heat the raw material to 100 to 120C.
The steamed raw material i5 then treated with an oxidant. Where the oxidant is constituted by an oxygen-containing gas, the treatment at the above-given temperature and a partial pressure of oxygen of up to 40 kgf/sq.cm. lasts a short time, from several seconds to one hour. The treatment succeeds in ensuring penetration of oxygen into the pores of the vegetable fibers and partial oxidation of the lignin component of the raw material.
Should nitric acid be employed as the oxidant, the steamed raw material is admixed with a cooled solution of nitric acid of concentration from 3.0 to 8.0 percent so that the temperature of the mixture lies in the range from 40 to 80C.
The mixture is then maintained at said temperature for from - 30 to 60 minutes at a hydraulic pressure of from 0 to 10 kgf/sq.
cm., after which the excessive fluid is drained off and the wet raw material saturated with nitric acid is steam-heated to a temperature of from 96 to 99C. and maintained at said temperature and a pressure close to the atmospheric level for from 1.0 to 1.5 hours. Where nitric acid is employed as the oxidant, the z~o pretreatment provides for a high degree of lignin oxidation.
The raw material subjected to oxidative pretreatment, is then washed with water or with the waste liquor which i9 formed in the course of digestion in the presence of oxygen in an alkaline medium. The washing with the waste liquor is preferable as providing a new waste liquor with a higher concentration of organic substances which more readily lend themselves to subsequent utilization. This kind of washing is particularly important in cases of pretreatment of the raw material with nitric acid which provides for a higher degree of lignin oxida~ion.
The washing after the oxidative treatment not only cuts down the consumption of the alkaline reagent for the neutralization -~
~ : -of the acid products formed in the course of digestion in an alkaline medium in the presence of oxygen, but at the same time permits eliminating from the vegetable raw material the ever-present microadmixtures of the ions of variable-valency metals, such as copper, iron, chromium, cobalt, vanadium, manganese or nickel.
The compounds of these metals promote the radical -`
reactions of raw material oxidation by speeding up the formation of peroxide compounds and the decomposition of same into radicals.
In their turn, the radical reactions cause cellulose degradation, detracting from the strength of the semifinished product.
An acidic medium - at pH less than 6.5 - in the course of oxidative pretreatment of vegetable raw material promotes the passage of said metal ions into the liquor and their subsequent elimination by washing.
The raw material treated as described hereabove, is subjected to digestion by use of oxygen in an alkaline medium in a digester designed for operation at elevated pressure and providing for effective contact of all reacting phases, viz. the raw material, the cooking liquor and the oxygen-containing gas.
108~Z~O
The di(3ester contents are heated for from 0.2 to 3 hours to the top digestion temperature, but not above 160C. The rate of l~eating and the value of the maximum temperature are selected takin~ into account the rate of formation of peroxide compounds in the cooking liquor, the kind and degree of oxidative pre-treatment of the raw material as well as other factors, such as the kind and degree of comminution of the raw material, the pH value of the cooking liquor, or the type of equipment used.
Then the maximum temperature is maintained for from 0.1 to 5 hours until a specified quantity of peroxide compounds is formed in the cooking liquor.
Then the temperature is lowered for from 0.1 to 4.0 hours down to but not below 80C., and the cooled stock is allowed to stand for from 0.1 to 4.0 hours until a semifinished product is formed.
The duration of the temperature-reduction process and the value of the minimum temperature are set on the basis of the rate of decomposition of the peroxide compounds into radicals.
While the digestion is in progress, the digester is additionally charged with an oxygen-containing gas and an alkaline reagent, e.g., an aqueous solution of ammonia, gaseous ammonia or alkaline compounds of potassium, maintaining the pH of the cooking liquor at a value in the range from S to 12.5.
The waste gas is discharged to reduce the overall pressure in the digester.
Having kept the mixture at the maximum temperature, which constitutes the first stage of digestion, the waste liquor may be withdrawn and replaced by a fresh batch which may contain a different alkaline reagent, e.g. potassium hydroxide, wherèas -~
the reagent employed at the first stage of the process is an aqueous solution of ammonia.
The mixture now containing a different alkaline reagent 108~Z~0 is subjected to the second stage of digestion at a lower temperature, generally in the range from 100 to 130C., at pH
in the range from 7 to 12.5 and at a partial pressure of oxygen of from 3 to 20 kgf/sq.cm. for from 0.1 to 4 hours depending on the pulping degree at the first stage of cooking. At the second stage of digestion, particularly if the raw material has been pretreated with oxygen before the first stage of digestion, cellulose degradation inhibitors are desirably introduced into the process, such as magnesium compounds, e.g. magnesium carbonate which is added at the rate of from 0.05 to 1.0 percent magnesium -by weight of the absolutely dry ground raw material.
Between the first and second steps of the cooking process, the partially pulped raw material may be washed with water or with tne waste liquor from the second stage of digestion. This kind of washing is particularly desirable if the second stage :
of the process employs potassium compounds instead of~alkaline ammonium compounds.
The above-described process may be implemented in both continuous and batchetype digesters.
After cooking, the semifinished product is washed and sent for further processing in keeping with its purpose.
Thus, for instance, it may be subjected to bleaching by use of chlorine- and/or oxygen-containing reagents: chlorine, chlorine dioxide, hypochlorites, oxygen, ozone or peroxide.
When the semifinished product is earmarked for chemical processing, the conditions of the oxidative pretreatment may be changed and the bleaching procedure may use the known hot and cold refining techniques.
The waste cooking liquor and the liquor after the oxidative pretreatment of the raw material are utilized as culture media for growing protein fodder yeasts, and the substances left unutilized by the yeasts are used, after concentration ~08U'~tiO
or as such, as an organomineral fertilizer.
Besides, the waste cooking liquor may be utilized to produce a range of valuable by_products, viz. vanillin, acetovanillone, formic, acetic, propionic, ~utyric and oxalic acids as well as other, substances, including nitrogen-containing organic compounds.
The process of this invention may be further improved through stripping the waste oxygen-containing gas of carbon dioxide and other impurities by the potash method or any other technique with a view to recycling the oxygen thus recovered from the waste gas.
Example 1 10 g of aspen chips measuring 20 x 20 x 0.5 mm are placed in a l-liter autoclave and steamed with saturated water vapour having a temperature of 130C. for 15 minutes so that the excess of vapour, air and condensate are removed from the autoclave.
Then oxygen is pumped into the autoclave until the pressure there-in reaches 32 kgf/sq.cm. and the pretreatment is effected for 5 minutes, following which 400 ml of an aqueous solution of ,~ -ammonia of pH 10.7 )the pH of the solution is determined at room temperature) is pumped into the autoclave and the temperature in the autoclave is raised by use of an electric heater for 1 hour to 160C. In the course of heating and subsequently during the cooking procedure the autoclave is rotated about the horizontal longitudinal axis thereof.
The temperature in the autoclave is maintained at 160C. ' for 30 minutes in order that the level of peroxide compounds ~n the cooking liquor may reach 0.020 percent. (The level of peroxide compounds is determined by the quantity of iodine liberated from potassium iodide in an acidic medium. This method is used to determine the overall level of all peroxide compounds, such as ROOR, ROORl, H2O2 and ROOH, as well as quinones).
.:
108~Zf~0 Tl~en the temperature in the autoclave is reduced within S minutes to 130C., and the mixture in the autoclave is subjected to aftercooking for 4 hours.
After this the autoclave is immersed in a bath with running river water and rapidly cooled. The overpressure relieved, the waste cooking liquor is drained off, and the semifinished product is washed, screened and analyzed.
The semifinished product is obtained with a yield of ;
60.1 percent, including 58.3 percent pulp and 1.8 percent partially cooked chips. The pulp contains 6.2 percent lignin and has a whiteness of 41 percent. The waste liquor of pH 7.2 contains 16.8 percent nitrogen by weight of the dissolved organic substances, including amide nitrogen and strongly fixed nitrogen t4.6 percent). ' The pulp lends itself readily to beating; at a specified beating degree and a 100-g weight of one square metre of the pulp ~ -sheet, it has a breaking length of 9,400 m and a folding strength of 2,300 double folds. ~ , Example 2 10 g of aspen chips are steamed and treated with oxygen in a procedure exactly duplicating that of Example l; an aqueous solution of ammonium hydroxide of pH 10.7 is likewise pumped into the autoclave like in Example 1. But the heating is effected to a maximum temperature of only 150C., the duration of the heating procedure amounting to 1 hour as in Example 1.
The maximum temperature is maintained for 1.5 hours until the peroxide compounds account for 0.024 percent of the cookin~ liquor. Then the temperature in the autoclave is reduced for 15 minutes to 140C. and maintained at said reduced level for another 1.75 hours.
The subsequent operations duplicate those of Example 1.
The cooking gives a semifinished product with a yield .....
.,' ~' ~
~088Z~0 of 61.6 percent, including 61.2 percent pulp and 0.4 percent partially cooked chips. The pulp contains 6.3 percent lignin.
The waste liquor of pH 6.3 contains 17.2 percent nitrogen by weight of the dissolved organic substances.
At the same parameters as in Example 1, the pulp has a breaking length of 8,900 m and a folding strength of 1,530 double folds.
Example 3 In the same way as in Example 1, 10 g of spruce chips measuring 20 x 20 x 0.5 mm are subjected to cooking under the following temperature conditions: heating to a maximum tempera-ture of 150C. for 1 hour, maintaining the maximum temperature of 150C. for 1.25 hours; cooling to 140C. for 15 minutes; and maintaining the temperature of 140C. for 3 hours.
The process results in a semifinished product with a yield of 59.2 percent, including 52.5 percent pulp and 6.7 percent partially cooked chips. The pulp contains 5.6 percent lignin.
The was~e liquor has a pH of 6.2.
Example 4 In this example, the procedure of Example 1 is duplicated except that the feedstock is con.stituted by 20 g of aspen chips and the cooking li~uor in an amount of 400 ml has a pH of 10.92.
The autoclave contents are heated to 140C. for 1 hour and then maintained at said temperature for 5 hours. The semifinished product thus produced is obtained with a yield of 59.4 percent, including 58.9 percent pulp and 0.5 percent partially cooked chips. The pulp contains 6.7 percent lignin. The waste liquor of p~ 6.2 is utilized as a culture medium for growing protein fodder yeasts, 1 ton of the semifinished product producing 80 kg of absolutely dry protein fodder yeasts.
Example 5 10 g of aspen chips measuring 20 x 20 x 0.5 mm are .
~()8b~ i0 steamed and treated with oxygen in an autoclave in a manner des-cribed in Example 1. Then 400 ml of an aqueous solution of ammonium hydroxide of pH 10.67 is added to the feedstock and the mixture is heated to 140C. for 1 hour. Said temperature is maintained for another 4 hours until the level of peroxide compounds in the cooking liquor reaches 0.006 percent, whereupon the autoclave is cooled in a bath with running river water.
After this the pressure in the autoclave is relieved, the waste liquor is drained off, while the partially cooked raw material after the first stage of digestion is washed with water.
Then it is again placed in the autoclave, and the latter is charged with 200 ml of a 0.32-percent solution of potassium hydroxide as well as with a certain quantity of MgCO3 such that the magnesium ions in the solution account for 1 percent by weight of the partially cooked raw material. Then the oxygen pressure in the autoclave is raised to 20 kgf/sq.cm. and the temperature is likewise raised to 120C. for 1 hour. Said temperature is maintained for another 2 hours.
After the second stage of digestion, the autoclave is ~ -cooled in a bath with running water, the pressure is relieved, and the autoclave is opened. The waste liquor after the second stage of digestion is drained off, while the semifinished product is washed and analyzed. The two-stage process yields pulp containing 3.8 percent lignin and free from partially cooked chips; the yield is 62.5 percent and the whiteness is 54 percent.
Example 6 Aspen chips measuring 20 x 20 x 3 mm and containing 20 kg of absolutely dry wood are placed in a 10-liter autoclave, steamed with live steam for 8 minutes and mixed with 9 liters of an aqueous solution of nitric acid af concentration 47 g/lit.
The feedstock is maintained in the acid at a pressure of 3.0 kgf/sq.cm. for 60 minutes at a temperature of from 60 to 65C., .
after which the aqueous solution of nitric acid is drained off, ~
whereas the chips are heated with live steam to 97 to 99C., --maintained at this temperature for 1 hour, and repeatedly washed first with the waste liquor from the subsequent oxygen-alkaline -cooking operation and then with hot water. 91.0 g of wet chips pretreated with nitric acid and containing 30.0 g of the starting ~ -absolutely dry wood, are placed in a rotating l-liter autoclave, the latter is charged with 600 ml of a 1.3-percent potash solution, and the pressure in the autoclave is built up to 15 kgf/
sq.cm. with oxygen. Then the autoclave is heated for 1 hour to 130C. and maintained at said temperature for another hour.
All the subsequent operations to cool the autoclave, relieve the pressure and drain off the waste liquor, as well as wash and screen the semifinished product, duplicate those of Example 1. ~ ~ -The semifinished product is obtained with a yield of 60.2 percent, including 58.5 percent pulp and 1.7 percent - -partially cooked chips. The pulp has a whiteness of 52.4 percent u and contains 3.5 percent lignLn. ;-~
The waste liquor has a pH of 9.2.
Example 7 -91 g of wet aspen chips pretreated in a procedure ~-duplicating that of Example 6, are placed in a rotating l-liter -~
autoclave and the latter is charged with 600 ml of an a~ueous solution of ammonium hydroxide of pH 10.92. The pressure in the autoclave is built up to 15 kgf/sq.cm. by supplying oxygen thereinto, whereupon the autoclave is heated for 1 hour to 130C.
and maintained at this temperature for another 30 minutes until the level of peroxide compounds in the liquor reaches 0.047 percent, after which the temperature is reduced within 5 minutes to 110C. and maintained at said level for another 90 minutes.
The subsequent operations duplicate those eariler described.
The semifinished product thus obtained is produced with a yield ,,:
1088'~0 ' of 61.4 percent and contains no partially cooked chips. The -pulp has a whiteness of 47 percent and contains 3.1 percent lignin.
The pulp lends itself readily to beating; under the above-described standard conditions, it has a breaking length of 8,800 m and a folding strength of 1,800 double folds. The pH
of the waste liquor is 9.2.
Thus, the examples given hereabove corroborate the effectiveness of the proposed process for manufacturing a quality semifinished product with a whiteness in excess of 40 percent from the most difficultly pulpable varieties of wood raw material, including chips.
The waste liquors contain no pollutants, as borne out by their applicability for growing protein fodder yeasts therein (see Example 4).
As for other kinds of vegetable raw materials, such as cereal straw, cane, reed or grass, the semifinished product can be obtained therefrom under process conditions similar to those described in the examples hereabove except that the oxidative -pretreatment required is less intensive and the oxygen-alkaline digestion may be effected at a lower oxygen pressure, at a lower temperature or within a shorter period of time.
.,
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for manufacturing a semifinished product from ground vegetable raw material, which comprises treating the presteamed ground raw material with an oxidant at pH less then 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material in the digestion; digesting said raw material in a cooking liquor under temperature conditions such that the temperature is first raised to about 160°C. for from 0.2 to 3 hours depending on the rate of formation of peroxide compounds in the cooking liquor; maintaining said latter temperature for a period of time sufficient for said peroxide compounds to be formed; adding an alkaline reagent and reducing the temperature to about 80°C. for from 0.1 to 4 hours depending on the rate of decomposition into radicals of said peroxide compounds; maintaining the cooled stock at said reduced temperature for from 0.1 to 4 hours; and terminating the cooking procedure at said reduced temperature to yield the desired semifinished product.
2. A process as set forth in claim 1, wherein the temperature differential between the upper and lower levels amounts up to 50°C. depending on the rate of decomposition of the peroxide compounds.
3. A process as set forth in claim 1, wherein the upper and lower temperatures, the dwelling times at said temperatures, and, accordingly, the periods of heating and cooling to said temperatures, are all controlled depending on the level of ions of variable-valency metals in the mixture of the cooking liquor and the raw material.
4. A process as set forth in claim 1, wherein the ground raw material is pretreated with oxygen at pH from 4 to 6.5 and a temperature of from 100 to 150°C.
5. A process as set forth in claim 1, wherein the ground raw material is pretreated with nitric acid at a concentration of from 3 to 8% and a temperature of from 40 to 100°C.
6. A process for manufacturing a semifinished product from ground vegetable raw material, which comprises treating the presteamed ground raw material with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material in the digestion; digesting said raw material in a cooking liquor under temperature conditions such that the temperature is first raised to about 160°C. for from 0.2 to 3 hours depending on the rate of formation of peroxide compounds in the cooking liquor; maintaining said temperature for a period of time sufficient to allow said peroxide compounds to be formed, with a aqueous solution of ammonia being introduced to cause the lignin oxidized in the pretreatment to pass into the solution; lowering the temperature to about 80°C. for from 0.1 to 4 hours depending on the rate of decomposition into radicals of said peroxide compounds; maintaining the cooled stock at said reduced temperature for from 0.1 to 4 hours; and terminating the digestion process at said reduced temperature to yield the desired semifinished product.
7. A process for manufacturing a semifinished product from ground vegetable raw material, which comprises treating the presteamed ground raw material with an oxidant at pH less than 6.5 for a period of time not exceeding 5 hours but sufficient to ensure adequate penetration of the cooking reagent into the bulk of the raw material in the digestion; digesting said raw material in the cooking liquor under temperature conditions such that the temperature is first raised to about 160°C. for from 0.2 to 3 hours depending on the rate of formation of peroxide compounds in the cooking liquor; maintaining said temperature for a period of time sufficient for said peroxide compounds to be formed, with ammonia being added to the cooking liquor gradually and in batches depending on a preset pH value of the cooking liquor in order that the lignin oxidized in the pretreatment may pass into the solution; reducing the temperature to about 80°C.
for from 0.1 to 4 hours depending on the rate of decomposition into radicals of said peroxide compounds; maintaining the cooled stock at said reduced temperature for from 0.1 to 4 hours; and terminating the digestion procedure at said reduced temperature to yield the desired semifinished product.
for from 0.1 to 4 hours depending on the rate of decomposition into radicals of said peroxide compounds; maintaining the cooled stock at said reduced temperature for from 0.1 to 4 hours; and terminating the digestion procedure at said reduced temperature to yield the desired semifinished product.
8. A process as set forth in claim 7, wherein the digestion is carried out in two stages, the temperature in the first stage being in the range from 130 to 160°C. and in the second stage in the range from 130 to 80°C.
9. A process as set forth in claim 8, wherein, to remove the oxidized lignin formed at the first stage of digestion, alkaline compounds of potassium are added to the cooking liquor at a partial pressure of oxygen of from 3 to 20 atm. and a pH
of the cooking liquor of from 7 to 12.5.
of the cooking liquor of from 7 to 12.5.
10. A process as set forth in claim 8, wherein at the second stage of digestion inhibitors are added to the cooking liquor to prevent or minimize cellulose degradation.
11. A process as set forth in claim 10, wherein the inhibitors are constituted by magnesium compounds employed at the rate of from 0.05 to 1.0 percent magnesium by weight of the absolutely dry ground raw material.
12. A process as set forth in claim 11, wherein the pretreated raw material is washed to remove the dissolved substances therefrom and reduce the consumption of the alkaline reagent in the digestion.
13. A process as set forth in claim 12, wherein the pretreated raw material is washed with the waste liquor from the digestion.
14. A process as set forth in claim 8, wherein the pretreated raw material is washed after the first stage of digestion to remove the dissolved substances therefrom and reduce the consumption of chemicals at the second stage of digestion.
15. A process as set forth in claim 14, wherein the raw material is washed with the waste liquor from the second stage of digestion.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,896A CA1088260A (en) | 1976-03-26 | 1976-03-26 | Process for manufacturing a semifinished product from ground vegetable raw material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,896A CA1088260A (en) | 1976-03-26 | 1976-03-26 | Process for manufacturing a semifinished product from ground vegetable raw material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088260A true CA1088260A (en) | 1980-10-28 |
Family
ID=4105560
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,896A Expired CA1088260A (en) | 1976-03-26 | 1976-03-26 | Process for manufacturing a semifinished product from ground vegetable raw material |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088260A (en) |
-
1976
- 1976-03-26 CA CA248,896A patent/CA1088260A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US9945073B2 (en) | Methods of producing a paper product | |
| RU2383675C1 (en) | Process of industrial cellulose pulp, native lignin and unicellular protein production, which is carried out in catalytic reactor | |
| US4076579A (en) | Pulping of lignocellulosic material by sequential treatment thereof with nitric oxide and oxygen | |
| WO2006121634A2 (en) | New product and processes from an integrated forest biorefinery | |
| CA1283512C (en) | Sulfite cooking method for the production of cellulose from materials containing lignocellulose with recovery of the cooking chemicals | |
| US3347739A (en) | Continuous sodium sulfide pulping of cellulosic material | |
| NO162733B (en) | PROCEDURE FOR THE PREPARATION OF COOKING FLUID FOR POWER BREAD COOKING AND COOKING FLUID FOR THIS. | |
| US4397712A (en) | Semi-chemical pulping process | |
| US4790905A (en) | Process for the pulping of lignocellulose materials with alkali or alkaline earth metal hydroxide or salt and a solvent | |
| NO140535B (en) | PROCEDURE FOR THE PREPARATION OF CELLULOSE PULP BY CONNECTION WITH THE OXYGEN | |
| US3695994A (en) | Impregnation of wood chips with a cellulose protector followed by a soda-oxygen pulping stage | |
| EP0468016B1 (en) | Process for preparing kraft pulp | |
| US5385641A (en) | Delignification of cellulosic raw materials using acetic acid, nitric acid and ozone | |
| US3046182A (en) | Sulphite pulping process | |
| CA1088260A (en) | Process for manufacturing a semifinished product from ground vegetable raw material | |
| CN112593435B (en) | Method for improving papermaking quality by alkaline pectinase combined with chemical reagent degumming | |
| US4750973A (en) | Process for reducing carbohydrate losses in the sulfate pulping of wood by pretreating the wood with oxygen and nitrogen oxides | |
| US3578553A (en) | Nitrogen dioxide pulping process | |
| US3520773A (en) | Alkaline pulping processes with chemical pretreatment | |
| US4445969A (en) | Process for the delignifying bleaching of cellulose pulp by activating the pulp with NO2 and oxygen | |
| US3969184A (en) | Digestion odor control | |
| CA1186855A (en) | Semi-chemical pulping process | |
| FI62561C (en) | FOERFARANDE FOER FRAMSTAELLNING AV ETT HALVFABRIKAT AV VEGETABILISKT RAOMATERIAL | |
| CA1079009A (en) | Method of treating annual vascular plants containing holocellulose and lignin | |
| SU344749A1 (en) | Method for producing hemicellulose |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |