CA1232109A - Pulping process - Google Patents

Abstract

Abstract of the Disclosure The invention is concerned with an improved pulping process for producing high yield pulps from woody lignocellulosic material wherein the ligno-cellulosic material is treated with a pulping chemi-cal and mechanically defibrated. The improvement comprises pre-treating the lignocellulosic material by impregnating same with a water-miscible loweralkanol-amine and ammonium hydroxide so as to cause softening of lignin in the material and to promote fiber sepa-ration. As a result, pulping chemical and refining energy consumption as well as vapor and liquid effluent pollution are significantly reduced.

Description

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Bac~qround of the Invention The present invention relates to the pro-diction of high yield pulps from wood or other woody lignocellulosic materials, such as chips, shavings and sawdust. More particularly, the invention is directed to a pulping process of the type wherein such lingo-cellulosic material is treated with pulping chemicals and the treated material it subjected to a mechanical defihration.
Various processes exist for production of chemimechanical and semi chemical pulps from wood using pulping chemicals such as Noah, Nazi, Nays, Nikko, and Nazi. These processes produce pulp with properties which limit the use of these pulps for low quality and low price products such as corrugating medium, packaging grade, newsprint furnish, etc.. Due to a limited fiber separation in pulping, high refining energy requirements are typical for those processes. Furthermore, processes such as the chemimechanical pulping process (CUP) and neutral sulfite semi chemical pulping process (NSSC) use sulphur-containing chemicals in pulping and thus en-counter problems related to air and water pollution and corrosion due to the presence of organic sulfur compounds in the process vapors and water effluents.
In the pulping process disclosed in US.
patent No 4,116,75~, for example, wood chips are first sulfonated to a high degree of sulfonation so as to produce a softening of the lignin in the wood sufficient to permit the wood chips to be readily defibrated into individual fibers by customary mechanical I

means. This high level ox sulfonation which is about owe of the maximum level of sulfonation that can be achieved on wood is obtained by cooking the wood chips in an aqueous solution containing a mixture sulfite and bisulfite in high concentrations. Since the attain-mint of the high levels of sulfonation required by such a pulping process involves the use of relatively high concentrations of cooping chemicals as well as of relatively heavy applications of cooking liquor on the wood, it becomes necessary for economic cons-donations to recycle the unrequited sulfite from the cooked chips.
Summary of the Invention It is an object of this invention to imp prove conventional pulping processes using standard pulping chemicals in a manner such as to reduce pulping chemical and refining energy consumption as well as vapor and liquid effluent pollution.
In accordance with the present invention, there is thus provided in a pulping process for pro-during high yield pulps from woody lignocellulosic material wherein the lignocellulosic material is treated with a pulping chemical and mechanically doff-brazed, the improvement comprising pretreating the lignocellulosic material by impregnating same with a water-miscible loweralkanolamine and ammonium hydroxide so as to cause softening of lignin in the material and to promote fiber separation, thereby reducing pulping chemical and refining energy consumption as well as vapor and liquid effluent pollution.

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Examples of suitable loweralkanolamines include water-miscible al~anolamines, such as moo-ethanol amine, diethanolamine, triethanolamine, moo-isopropanolamine, diisopropanolamine and triisopro-panolamine, monoethanolamine being preferred. Mixtures of these amine can of course also be used.
The pretreatment step can be carried out using an aqueous solution or water vapor containing the amine and ammonium hydroxide. Thus, the lignocellulosic mate-fiat such as wood chips can first be treated by atoms-phonic soaking or under heat and pressure conditions in an aqueous solution or water vapor containing the amine or a mixture o-E various amine and ammonium hydroxide to impregnate the wood chips. The amine penetrate into the fiber structure of the wood and react mainly with the lignin contained therein. This reaction causes partial depolymerization of the lignin, for example to an extent of about 1.5 to 5.0%, mainly between fiber elements in middle lamely where about 70% lignin is located, such -that softening of the Lenin occurs, which in turn promotes good fiber separation without damage to the cellulosic fibers. Amine are markedly hydroscopic and the moisture inherent in the wood, particularly green wood which generally contains more than 50% moisture, causes the amine to readily penetrate into the fiber structure of the wood. Ire amount of amine penetrating the fiber structure can be controlled by varying for example the impregnation time, temperature, pressure, amine concentration in the soul-lion or vapor, etc...

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The amine adsorption usually varies with various wood species. The amount of amine required for lignin softening depends on the end product requirements and the chemical and mechanical treatments after the impregnation stage. The required amine amount is preferably comprised between 1.5 and 10.0%
by weight, based on dry wood.
The impregnation can be effected according to a batch or continuous-type operation, using con-ventional equipment such as tanks, batch digesters,etc.. In a continuous-type operation, use can be made of an impregnation vessel which includes an inclined screw conveyor and serves as both pro-treatment vessel and drainer to drain excess pro-treatment liquor. An atmospheric impregnation stage, on the other hand, can be designed to serve also as a chip washer to remove sand, dirt, rocks and the like.
It should also be noted that the impregnation need not be done at the pulp mill site, but can be done elsewhere.
According to the invention, the pretreatment of the lignocellulosic material with a loweralkanolamine is carried out in the presence of ammonium hydroxide.
Indeed, it has been found that when carrying out the amine impregnation in the presence of ammonium hydroxide, the physical properties of the pulp are improved, particularly the Breaking Length and Burst Index values.
The combined use of a loweralkanolamine and ammonium hydroxide in the pretreatment step further has a favor-able effect on the Concord and Ring Crush values as wells on the burley Air Resistance, the pulp yield is also Lo improved. Accordingly, the use of ammonium hydroxide together with a loweralkanolamine makes it possible to tailor the properties of the pulp coming -from the pulp-in chemical treatment stage much more than with the loweralkanolamine alone. The loweralkanolamine and ammonium hydroxide are preferably used in a volume ratio ranging from about 1:2.5 to about 1:0.5.
After the impregnation stage, the impregnated chips are cooked or otherwise treated with conventional pulping chemicals, prior to being mechanically de-vibrated in a defibrator or refiner. It should be noted that the pulping chemical treatment and mechanical de-vibration of chemimechanical pulps can also be effected simultaneously by-adding the pulping chemicals to the refiner feed, in this case, no cooking is required.
Listed hereinbelow are examples of pulping chemicals which may be used to treat the amine impregnated chips:
a) Nazi (chemithermomechanical and chemimechanical pulping processes, b) Nazi awoke pi = 6-9 (neutral sulfite semi-chemical pulping process), c) Noah (soda process), d) Noah -I Nazi (chemimechanical process), e) Nazi, pi = 2-6 (chemimechanical and chemical processes), f) standard sulfate (Raft) pulping liquor containing as active pulping chemicals mainly Noah Nays, and small amounts of other soda chemicals such as Nazi, Nikko, Nazi and Nazi 3 have much effect on the actual pulping reaction, I

g) standard green pulping liquor obtained from a Raft pulping process and containing mainly Nikko Nazi and a small amount ox Nazi, h) standard neutral sulfite pulping liquor containing Nazi + Nikko or Nikko, optionally with Noah (neutral sulfite semi chemical process);
i) standard alkaline sulfite pulping liquor containing Nazi + Noah or Nays, pi = 10~;
j) Mg(HSO3)2, pi = 4.5-6.0 (paper pulp process).
It should be noted that all of the above treatment processes, except the Raft process (f), pro-dupe about 75-95% yield pulps With respect to the Croft process, the pretreatment of the inversion enables the Raft pulp yield to be increased from 45-55% to approximately 55-65%. For eXistillg Raft mills, this would mean lower wood requirements and the possibility to increase the mill capacity without pro-bless associated with chemical recovery which usually constitutes a limitation in a pulping process.
The above pulping chemicals can be prepared by conventional processes or purchased as such and mixed at the mill site. Following are some examples how this can be obtained:
- Should a pulp mill using the process of the invention on site have an existing Raft mill, the chemical treatment with Nikko, Nays, Nazi (plus small amount of Noah as buffer, if required) can simply be done by using the green liquor from the Raft pulping process;
- Nazi and Noah can be purchased-and mixed with water at the mill site without requirements for a ~32~3~

complex chemical preparation system, - Nazi can be purchased or prepared from Noah and S02, S02 can be purchased in liquid form or can be generated by burning Selfware, - Nazi can also be generated from soda ash (Nikko) and S02 at the mill site by standard processes.
It should also be noted that any of these pulping liquors can be buffered with aye, Noah or S02 to provide more alkalinity or make the cooking liquor more acidic depending on the requirements.
As already mentioned, due to the pretreat-mint according to the invention which causes lignin softening and promotes good fiber separation as well as more uniform and faster penetration of chemicals, further treatment with pulping chemicals is required to a lesser extent than in conventional pulping pro-cusses without such pretreatment step. The standard pulping chemical requirements in conventional pulping processes compared with the chemical pulping require-mints in the improved pulping processes of the invention with pretreatment are reported by way of example in Table 1 lo .. _ . . Jo . . .

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The Selfware consumption in the process of the invention (also water and air pollution from Selfware) is reduced in about the same ratio as the chemical consumption is reduced.
The invention thus provides an improved and versatile pulping process for producing various grades of high yield pulps from hardwoods, mixtures of hardwoods, softwoods, straws and annual plants.
As explained above, improved lignin softening and fiber separation is obtained by impregnating wood chips or the like with lower alkanolamines such as monoethanolamine in the presence ox ammonium hydroxide before the chips are cooked or otherwise treated with conventional pulping chemicals. As a result, refining power requirements of the pretreated pulps are lower than those of conventional pulps. vower amounts of conventional pulping chemicals are required for pulping, less Selfware is used in pulping decreasing equipment corrosion, water effluent pollution as well as air pollution from pulp mills. Process condensates and vapors contain less organic Selfware compounds than those of standard processes. Condensates and vapor containing amine are not toxic and harmfully indeed, amine are not toxic at all and the pretreatment of the invention does not provide any pollution.
The process of the invention can be used for new mills producing various grades of high yield pulps (~0-95% yield) with better physical properties and greater versatility than with those processes using standard pulping chemicals only. For existing pulp _ g I

mills using processes such as the thermomechanical, chemimechanical, chemithermomechanical, neutral sulk file semi chemical pulping processes and soda process, the process of the invention enables the physical properties of these pulps to be improved, and is more versatile and easily adaptable for changes in market demands. The amine pretreatment can be easily adapted to existing mills.
Due to the impregnation of the wood chips with amine and the resulting softening of the lignin, as explained above, further treatment with convent tonal pulping chemicals is required to lesser extent than in conventional processes to produce various grades of pulp. It is important to keep Selfware con-tent to minimum to minimize water and air pollution of a pulp mill. The process of the invention does not require as much Selfware or sodium containing chemicals as standard processes. The exact type of pulping chemicals and amounts required depend of course on the wood species used as starting material and the desired properties of the end product. As only a small portion of these chemicals are required in the process of the invention, the requirements for ox-pensive chemical recovery system for Selfware is mini-mixed and the pollution load of Selfware in water effluent and process vapors is minimized.
Brief D Croatian of the Drawings Further features and advantages of the present invention will become more readily apparent from the following description of a pulping process embodying the invention, as well as from working examples thereon, with reference to appended drawings, in which:
Figure 1 is a block flow diagram of a pulping process according to the invention, Figures PA, 2B and 2C are diagrams showing -the variations in pulp properties of spruce chips -treated in accordance with Example 2, and Figure 3 is a diagram similar to that of Lo Fig. PA showing the variations in pulp properties of aspen chips treated in accordance with Example 3.
Description of Preferred Embodiments Referring first to Fig. 1, green wood chips are fed through line 10 to an impregnation vessel 12 containing an aqueous solution of a lower-alkanolamine such as monoethanolamine and ammonium hydroxide which serve to pretreat the chips so as to soften the lignin therein. Make-up solution of the amine and ammonium hydroxide is fed via line 14 and the pretreatment liquor it heated with steam fed through line 16. Sand, dirt, rocks and the like are removed from the vessel via line 18. When the pretreatment is carried out under pressure, vent gases can be directed -to a heat recovery unit via line 19.
After impregnation, the chips are passed to a conventional drainer 20 which may include a screen or perorated bottom conveyor so as to drain away excess pretreatment liquor, and are then optionally fed to a conventional press 22 such as a screw press, disc press, drum press or the like to remove more pretreatment liquor from the chips and to obtain chips having a high I

oven-dry wood content. The spent liquor removed from the drainer 20 and optional press 22 it recycled via line 24 to the impregnation vessel 12 to recover chemicals, water and heat.
After pressing, the impregnated chips are fed to a cooking vessel 26 for treatment with con-ventional pulping chemicals supplied from the comma-eel preparation unit 28 via the fed line 30. Steam is admitted via line 32 to heat -the pulping liquor and chips. The pulping chemical treatment can be carried out under atmospheric or pressure conditions.
The impregnated and cooked chips are thereafter fed via line 34 to a conventional refiner 36 so as to be subjected to mechanical defibration. Before being mechanically defibrated, the chips may optionally be fed to a press I to remove excess pulping liquor which is sent via line 40 to the weak liquor storage tank 42.
In an alternative embodiment suitable for the production of chemimechanical pulps, a portion (for example 25%) of impregnated but uncooked chips may be fed from the press 22 via line I directly to the refiner 36 into which pulping chemicals may be charged via line 46. Thus, by varying the proportions of impregnated uncooked chips and of impregnated cooked chips fed to the refiner 36, van-out grades of pulp can be produced to meet the desired physical properties of the pulps. This provides a great flexibility to produce various pulp grades which cannot be done with conventional processes.

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After the first refining stage 36, the pulp slurry is fed to a press or washer unit 48 into which water is admitted via line 50. The spent pulping liquor and washing water recovered from the unit I are sent via line 52 to the weak liquor storage tank 42, to save chemicals and water and to minimize water effluent load from the mill The weak liquor contained in the tank 42 is recycled via line 54 to the chemical preparation unit 28 into which make-up pulping chemicals may be fed through line 56, or a portion thereof may be sent to a comma-eel recovery unit via line 58.
After the pressing or washing stage 48, the pulp is fed to a second refiner 58 to achieve the desired -freeness. The pulp is thereafter sub-jetted to a screening and cleaning treatment in the unit 60 to produce an end product having the desired physical properties, which is discharged via line 62.
As it is apparent, the invention provides an extremely versatile pulping process The following non-limiting examples further illustrate this invention.

-In the manufacture o-f chemimechanical, comma-thermomechanical and corrugating medium type pulps, wood chips are impregnated in an aqueous solution con-twining an alkanolamine and ammonium hydroxide and hazing a temperature of 180-205F from 15 to 90 minutes and are then cooked with conventional pulping chemicals under controlled temperature and pressure conditions.

The amine concentration in the impregnation liquor which varies depending on the impregnation conditions such as time temperature, liquor to wood ratio, type of wood, etc. is generally comprised between 30 and 100 g/l, whereas the ratio of amine : ammonium hydroxide generally ranges from 1:2.5 to 1:0.5. The cooking -temperature for corrugating medium type pulps is usually 330-355F, for 12-25 minutes, at saturated steam pressure when a continuous digester is used.
The treatment (cooking) conditions for chemimechanical type pulps vary, but the temperature is usually apt proximately off at saturated steam pressure and the cooking time can vary from a few minutes to 60 minutes. An exception is cold soda CUP pulp which could require several hours treatment (soaking) at the room temperature of 80-100F.
The impregnation can be carried out under pressure and heat conditions for pulp grades which require higher physical properties. For example, the impregnation can be done at temperatures of 245~300F, under saturated steam pressure for a time period of 15-30 minutes prior to cooking with a Raft pulping liquor. Vent gases from the amine treatment vessel can be directed to a heat recovery system to recover heat and chemicals. Raft cooking is carried out at temperatures of 330-345F under saturated steam pressure, and the cooking time is approximately 60-90 minutes, total cover to cover time being 3.5-4 0 hours when batch digesters are used. The following is a typical cooking cycle for _ 14 -~32~

a Raft batch digester:
Item Unit Amount Cooking Cycle - Chip and liquor filling and cover on min. 40 - Time to temperature min. 90 - Time at temperature min. 60 - Relief min. 15 - Blowing min. 20 10 Total cover to cover time min. 225 Liquor to wood ratio when cooked in an aqueous solution of chemicals is usually 3.5-4.5 to 1. This means that the cooking vessel contains 3.5-~0 times more cooking liquor, including wood moisture, than dry wood.
EXAMPLE 2 - Spruce Cooks Moisture content of green chips: 34%
Amount of green chips per treatment: 2,3 kg Amount of water per treatment: 18.9 1 20 Amount of monoethanolamine per treatment: 40 ml Amount of ammonium hydroxide - varied as indicated hereinbelow, Number ox treatments: Four (4) - So, So, So and S10.
All cooks were heated with steam under atmospheric conditions for 5 minutes and were cooked for approximately 60 minutes at the cooking tempera-lure of 300-320F. In all cooks, the cooking liquor was circulated by a pump and the liquor indirectly heated by steam.
The pretreatment was carried out using monoethanolamine and ammonium hydroxide in the _ 15 -~32~

following amounts:

Treatment No. Monoethanol- Ammonium amine (ml) Hydroxide (ml) So 40 20 So 40 0 So 40 I

The treated chips were then refined and tested for paper properties at approximately 300 SHOWOFF.
The test results are reported in Table 2 and shown in Figs PA, 2B and 2C.

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En o ox us lo -- 17 _ As it is apparent for these results, by selecting the appropriate amounts of pretreatment chemicals, one can tailor the pulp properties to suit any requirements.
In this respect, the Burst Index is an important specification value for liner board grade classification whereas the Tear Index is an important value in box performance Concord and Ring Crush values are important classification for stiffeners of packaging grades such as corrugating medium and liner boards.
The Gurney Air Resistance figures, on the other hand, are indicative of the detouring kirk-teristics of the pulp. the lower the figure, the better the paper machine operation.
EXAMPLE 3 - Aspen Cooks Moisture content of green chips: 20% approx.
Amount of green chips per treatment: 2,3 kg Amount of water per treatment: 4.0 1 Amount of monoethanolamine per treatment: 25 ml Amount of ammonium hydroxide - varied as indicated hereinbelow.
umber of treatments: Three (3) - AS, AS and AS.
All cooks were heated with direct steam and held at 270-300F for 20 minutes and blown down, Jo circulating pump was used.
The pro treatment was carried out using monoethanolamine and ammonium hydroxide in the following amounts:

_ 18 _ I

_ . . . . _ . . .. _ _ Treatment No. Monoethanol- Ammonium amine my Hydroxide (ml) AS 25 _ .

The treated chips were then refined and tested for paper properties at 300 SHOWOFF. The test results are reported in Table 3 and shown in Fig. 3.

Treatment Tear index Breaking Burst Index No. mum go Length (km) (kPa-m2/g) .~. .-AS 2.52 3.2 1.90 AS 4.00 2~3 One AS 4.30 2~6 1.06 EXPEL 4 - Southern Pine Cook .
The standard Raft cook was modified my starting with 10 minutes pre-s-teaming followed by impregnation of the chips with a solution containing monoethanolamine and ammonium hydroxide in a ratio (volume) of 1:1.5. After impregnation, -the chips were cooked with standard Raft chemicals using approxi-mutely 10.5% active alkali on OLD. wood expressed as aye. Sulfidity was approximately 30%. Ire cook-in was carried out according to the following pro-seedier:

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time to temperature: 90 min.
- time at temperature: 60 mint - cooking temperature: 168C
- liquor to wood ratio: 4:1 The results obtained are reported in Table 4 and are compared with those obtainable in a standard Raft process (without pretreatment with a lower-alkanolamine/ammonium hydroxide mixture).

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Modified Raft Standard Raft . . . . . . __, Burst Index Pam go 7.4 6.26 Tear Index (my m go OWE 17.4 Breaking Length Kim 8~35 8~1 Yield (%) 57.4 54-55 Kappa Jo. 126 90 Active alkali as Noah on ED wood I%) 1OJ 5 14-15 . .
As can be seen from this example, the pulp yield is also improved.

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Claims (24)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a pulping process for producing high yield pulps from woody lignocellulosic material wherein said lignocellulosic material is treated with a pulping chemical and mechanically defibrated, the improvement comprising pre-treating said lignocellulosic material by impregnating same with a water-miscible lowerlakanol-amine and ammonium hydroxide so as to cause softening of lignin in said material and to promote fiber separa-tion, thereby reducing pulping chemical and refining energy consumption as well as vapor and liquid effluent pollution.

2. A process as claimed in claim 1, wherein said loweralkanolamine is an alkanolamine selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanola-mine, triisopropanolamine and mixtures thereof.

3. A process as claimed in claim 2, wherein said loweralkanolamine is monoethanolamine or monoisopropanol-amine, or a mixture thereof.

4. A process as claimed in claim 2, wherein said loweralkanolamine is monoethanolamine.

5. A process as claimed in claim 2, wherein said pre-treatment is carried out using an aqueous solution or water vapor containing said loweralkanolamine and ammonium hydroxide.

6. A process as claimed in claim 5, wherein said pre-treatment is carried under heat and pressure condi-tions.

7. A process as claimed in claims 1, 2 or 4, wherein said pre-treatment is carried on a continuous basis in an impregnation vessel which includes an inclined screw conveyor and serves as both pre-treatment vessel and drainer to drain excess pre-treatment liquor.

8. A process as claimed in claims 1, 2 or 4, wherein said lignocellulosic material is impregnated with an amount of loweralkanolamine comprised between 1.5 and 10.0% by weight, based on dry wood.

9. A process as claimed in claims 1, 2 or 4, wherein said loweralkanolamine and ammonium hydroxide are used in a volume ratio ranging from about 1:2.5 to about 1:0.5.

10. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises sodium sulfite.

11. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises a mixture of sodium sulfite and sodium carbonate.

12. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises sodium hydroxide.

13. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises a mixture of sodium hydroxide and sodium sulfite.

14. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises sodium bi-sulfite.

15. A process as claimed in claim 1, wherein said pulping chemical comprises a sulfate Kraft pulping liquor containing sodium hydroxide and sodium sulfide.

16. A process as claimed in claim 15, wherein the loweralkanolamine used in said pre-treatment is mono-ethanolamine.

17. A process as claimed in claim 16, wherein the monoethanolamine and ammonium hydroxide are used in a volume ratio of about 1:1.5.

18. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises a green pulping liquor obtained from a Kraft pulping process and con-taining sodium carbonate, sodium sulfide and sodium sulfate.

19. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises a neutral sulfite pulping liquor containing sodium sulfite in admixture with sodium carbonate or sodium bicarbonate.

20. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises an alkaline sulfite pulping liquor containing sodium sulfite in admixture with sodium hydroxide or sodium sulfide.

21. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical comprises magnesium bi-sulfite.

22. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical is buffered with sulfur dioxide.

23. A process as claimed in claims 1, 2 or 4, wherein said pulping chemical is buffered with sodium oxide.

24. A pulping process for producing a high yield pulp from woody lignocellulosic material compris-ing pre-treating said lignocellulosic material by impregnating same with a loweralkanolamine in the presence of ammonium hydroxide, prior to contact with said pulping chemical, in amounts sufficient to improve the dewatering characteristics of the high yield pulp and to cause softening of lignin in said material and to promote fiber separation, adding a pulping chemical to the impregnated material and mechanically defibrat-ing the material, said pretreatment reducing pulping chemical and refining energy consumption as well as vapor and liquid effluent pollution.