JPS6253497A - Pulping method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to the processing of lerulose-based materials and more particularly to improvements in the ligninization and/or bleaching of chemical pulps.

BACKGROUND OF THE INVENTION Bleaching is a continuation of a cooking process in which lignin-based substances and colored substances remaining in chemical pulp are selectively removed with as little deterioration as possible of the pulp. Bleaching of pulp has become highly advanced, involving multi-step procedures. Bleaching of chemical pulp was accomplished in several stages that together constituted a bleaching sequence.

Each stage consists of phases beginning with the addition and reaction of chemicals and pulp and ending with washing of the pulp. There are many process variables within each stage that are determined by the type of reaction desired at that particular stage and the operating conditions for that stage. These variables include: % of chemical added and consumed, chemical concentration, consistency, temperature, time and pH.

The delignifying and whitening effect of air or oxygen on chemical cellulosic pulps in alkaline media has been known for a long time. The currently widely used method is to pre-prepare the pulp with an alkali (usually 2.0-3.0% N on an absolutely dry basis).
a0H) and high concentration (
25-30%). The pulp is then fluffed) and exposed to oxygen at a pressure of 0.6-0.8 HPa at 80 DEG-165 DEG C. for a reaction time of up to 30 minutes.

Developments in oxygen delignification at low (4-5%) and intermediate (10-15%) concentrations have been reported and since they avoid the pressurization step required to obtain higher concentrations of 25-30%. be interested. Pulp is 80-1
Reaction time up to 6 hours at a temperature of 65 °C 0.5-1
．． 4) Exposure to 4 Pa oxygen pressure. Typically, these oxygen treatments displace half of the chlorine required in the normal chlorination step, increasing the kappa number from an initial value of 30-35 for softwood pulps to about 15-17 and hardening. For wood pulp it is reduced from 12-18 to 6-9. These delignification steps reduce pulp viscosity (
approximately 30-40%). The above method requires 0, 6-0,
The use of a high pressure vessel is necessary to equalize the oxygen pressure of 8 HPa.

In 1970, oxygen became recognized as useful in conventional caustic extraction steps. Thus, the oxygen in the catchment during the extraction stage made it possible to reduce the kappa number and thus the required temperature of the chlorine dioxide or hypochlorous acid in the later stages, referred to herein as the oxidative extraction stage. This B-opening prompted rapid acceptance of the oxidative extraction step on an industrial scale, and the process has progressed considerably since then. If the mill had an upflow extraction column that could provide some pressure in the form of a hydrostatic head, then the only improvements required to existing bleach plants would be an inlet static mixer or a high A shear type mixer was installed. If the mill had a downflow column, the desired effect would be a high shear mixer followed by an upflow prehold (IIpflOW) directed to the top of the column.
pre-retention) may be obtained by placing a tube. The conditions for carrying out the oxidative extraction stage are as follows: pulp concentration 9-14%
, temperature 50-80°C, holding time 3-60 minutes, NaOH charge 2-4 m on pulp bone-dry basis, oxygen pressure at least 0.14 MPa0.
tional 5ulrimue Pu1pina Co
Kruger and Suss (Niru) in the Minutes pages 143-148
aer and 5uss) teach that oxygen and peroxide treatment of softwood sulfite pulp can provide a 2 point whiteness increase compared to peroxide treatment alone. In their method they teach that the oxygen pressure must be 0.38 Pa and that peroxide silicate stabilization is required. They also teach OP treatment of sulphite pulp without further treatment in other processing steps. Krueger and Sass recently published a paper on the oxidative extraction of alkaline peroxides on sulfite pulp only after treatment with acidic nitrogen (i.e., N-EOP). Das Papier, 38, Jahrgang Head 11.
1984. pp. 529-534.

A sequential sequence consisting of an oxygen treatment followed by a peroxide treatment is described in U.S. Pat. No. 4,459,174 to Papageorges et al.
It is known to use tial 5equence).

The use of alkaline hydrogen peroxide as a delignification and whitening agent for unbleached kraft and sulfite pulps is also known. The optimum conditions for the use of alkaline hydrogen peroxide on softwood are reported as follows:
-20%, holding time 2 hours, temperature 80-100℃, Na
2.5% for OH charged pulp and pulp, bone dry (
(oven-dry) base, 1% hydrogen peroxide. By applying these conditions, it is possible to reduce the kappa number from an initial value of 30 to about 18 for softwood kraft pulp.

The use of peroxide in the first alkaline extraction step, first reported in 1946 and subsequently in other papers, has been successfully implemented in some mills to decolorize pulp. This treatment alleviates the common loss in whiteness during conventional extraction steps.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improvement in a process for the delignification/bleaching of chemical pulps in which the pulp is treated with an oxygen-containing gas without the need for a heavily pressurized vessel.

It is a further object of the present invention to provide an improvement in the delignification/bleaching of chemical pulps in which the pulp is delignified while minimizing pulp deterioration.

The above stated objectives are achieved in the present invention by the use of two improvements in the pulp delignification/bleaching process. The first and most important improvement exposes the washed pulp from the chemical kettle to the simultaneous reaction of an alkali compound, an alkali compound, and an oxygen-containing gas under certain preferred processing conditions.

Surprisingly, this simultaneous reaction makes it possible to delignify and brighten the pulp at low operating pressures while minimizing its deterioration. Minimal modifications to existing blunt equipment are required so that the new process can be implemented economically and commercially.

A second improvement involves treatment of the washed and chlorinated pulp, which consists of exposing the pulp to the simultaneous reactions of peroxide compounds, alkali compounds and oxygen-containing gases under the desired processing conditions.

The two improvements of the invention can also be combined for even greater effect. In this case, the pulp is first delignified using the first modification shown above, and then the washed pulp is treated with a chlorination step (by C, C/D or D/C), where C is chlorine alone. C/D refers to the chlorination stage in which 5 to 30% of the total active chlorine is committed by chlorine dioxide, and D/C refers to the chlorination stage in which 5 to 30% of the total active chlorine
% of the total active chlorine is replaced by chlorine dioxide. Subsequently, the washed chlorinated pulp is subjected to a second treatment stage as described above.

The present invention is applicable to any chemical cellulosic pulp (i.e. kraft, soda or sulfite) and is applicable to both softwood or hardwood pulps and/or other pulps such as bagasse or hemp. It can be used for various types of fibrous non-wood lignocellulosic materials.

To describe the invention in more detail, the first feature of the invention is that in the delignification/bleaching step, the lignin-containing, chemically digested and washed pulp is prepared from 0.5% to 4%
% alkali compounds, 0.1 to 2% alkali compounds and 0.4 to 0.6% oxygen gas at pressures from 0°01 to 0.4 MPa,
5% and 25% for a time between 1 and 120 minutes at a temperature between 40-95 °C, in the presence of a catalyst that prevents the reduction of viscosity.
An improvement is provided consisting of simultaneous processing steps at pulp concentrations between % and %. All measurements mentioned in this application are weighted on a bone dry pulp base.

In a second aspect of the invention, an improvement in the process for brightening pulp treated according to the first aspect above and subsequently treated and washed with a chlorine-containing compound comprises: 0.
between 50 and 90 °C with a gas containing 5% to 4% alkali compounds, 0.1 to 1% alkali compounds, and 0.1 to 3% oxygen at 0.1 to 0.4 MPa. An improvement is provided consisting of simultaneous treatment at a concentration of between 5% and 25% for a time of between 3 and 120 minutes at a temperature of .

In a third aspect of the invention, the washed and chlorinated pulp is treated with 0.5% to 4% alkaline compounds, 0.1%
alkaline compounds from up to 1%, and from 0.1 to Q,
from simultaneous treatment with a gas containing from 0.1 to 3% oxygen at 4 MPa at a concentration between 5% and 25% for a time between 3 and 120 minutes at a temperature between 50-90°C. An improvement in the delignification/bleaching process is provided.

An acid treatment or washing step can be carried out to remove any black liquor from the pulp before the delignification step and after the delignification step a washing step is utilized to remove the reaction products. .

The compounds utilized in the improvements of the present invention can be selected from those well known in the art. Thus, for example, alkaline compounds may include the customary hydrogen and inorganic peroxides such as sodium or benzoyl peroxide, tert-butyl peroxide, etc.
Organic peroxides such as hydroperoxides and peracetic acid can be included.

Commonly used alkaline compounds include sodium hydroxide, sodium carbonate, calcium carbonate, magnesium carbonate,
Contains magnesium hydroxide, etc.

In a preferred embodiment of the first aspect of the invention, an alkaline compound, preferably sodium hydroxide, is utilized in a charge range of 1.0 to 3.5% by weight of the bone-dry pulp. The alkaline compound is preferably 0.5 to 1.8% by weight
and oxygen is charged between 0.5 and 2.2% by weight. A preferred catalyst is magnesium sulfate, which can be charged in amounts ranging from 0.1 to 1% by weight. Oxygen is 0.
at a pressure between 1 and 0.3 HPa, preferably between 3 and 30
Deployed and maintained for times in the range of minutes. The preferred temperature, total time and pulp concentration range are 70-95°C, respectively.
, 3-60 minutes and 9-15%. The pt+ at the end of the process will normally be between 9.5 and 12.

Following ligninization, conventional washing steps are applied to remove reaction products.

In a preferred embodiment of the second aspect of the invention, the alkaline compound, preferably sodium hydroxide, is utilized in a charge range of 2 to 3.5% by weight of bone dry pulp. The alkaline compound is preferably between 0.2 and 0.7Iiffi% and the oxygen is between 0.4 and 0.6% by weight.
Charged at a pressure between 1 and Q, 3 HPa. Preferred processing conditions are: concentration between 8 and 20%, time between 3 and 30 minutes and temperature between 60 and 90°C. As in the first aspect of the invention, viscosity protecting catalysts such as magnesium ions can be advantageously used in amounts between 0.1 and 1.0% by weight.

As an example of the first treatment, the kappa number is 26.6 and 0.
An unbleached kraft pulp from softwood pulp having a 5% cucne viscosity of 26.3111 Pa was used in manuring experiments to test the alkaline delignification treatment. The results are shown in Table 1 and summarized in Figures 1 and 2. In each of Examples 1 to 5, samples of the pulp were removed at time intervals of 15.30 and 120 minutes, washed, and the kappa number and viscosity determined.

Example 1 Treatment with NaOH 2 A portion of unbleached pulp was treated with a solution containing 2.5% NaOH on an OD (bone dry) basis and mixed at a concentration of 10% and a temperature of 80°C. did.

2.5% of unbleached pulp on OD basis
N a O + - 1, 1% H2O2 and 0.5% MgS
It was treated with a solution containing O4 and mixed at a concentration of 10% and a temperature of 80°C.

Example 3 A portion of the unbleached pulp treated with Na0l-1 and oxygen at an oxygen pressure of 14 HPa was 2.5% based on ○D based on the pulp.
of NaOH and 0.5% MgSO4, then gaseous oxygen was added and mixed at a concentration of 10% and a temperature of 80° C. and an oxygen pressure of 0.14 MPa was maintained.

2.5% of unbleached pulp on OD basis
of NaOH1 and 0.5% MgSO4 and mixed at a concentration of 10% and a temperature of 80 °C and maintained at an oxygen pressure of 0.50 HPa.

The effects of different alkaline delignification treatments on kappa number and viscosity are shown in Table 1 and Figures 1 and 2. Fixed 2.5% NaOH charge, concentration 10%,
At a temperature of 80°, a mixing strength of 30 rpm, and a reaction time of 3Q minutes, NaOH alone, H2O2 and NaOH, Na01
Treatment with oxygen at -1 and 0.14 MPa and NaOH and Q, oxygen at 50 HPa reduced the kappa number by 14.24.38 and 45%, respectively. Increasing the retention time from 30 minutes to 120 minutes did not substantially reduce the kappa number further. As long as M g++ ions were used as protection, the viscosity decreased by 30% from the initial value during the 30 minute reaction.

N a OH, H202 and R element (oxygen pressure 0°1
Unexpected results were obtained when (at 4 MPa) were mixed into the unbleached pulp in a one-time process. Table 1 and 1
The results in Figure 2 are as follows: using the following charging chemicals, the pulp concentration was 10%, the reaction temperature was 80°C for 15 minutes, the kappa number was 15.0 (44% reduction), and the 0.5% citric viscosity was 2.
Charging chemicals ffi expressed in % of the pulp on a 20D basis showing that a delignified pulp up to 1.1 mPa was obtained: Na0) - 1,2,5%: HO, 1,0%
; Mg5O, 0.5%.

As can be seen from the examples above, and as shown in Figures 1 and 2, the process of the present invention improves the degree of pulp delignification as measured by the kappa number. at the same time,
There is also less pulp deterioration as measured by viscosity.

Thus, significantly, hydrogen peroxide and oxygen at low pressures give better results than oxygen delignification at higher pressures without hydrogen peroxide.

In a second aspect of the invention, an alkali/peroxide/oxygen treatment was used with semi-delignified pulp. This pulp was delignified in conventional manner or as taught herein.

Prior to the current treatment (hereinafter referred to as the EPO stage or X stage), the pulp is usually subjected to a chlorine or chlorine dioxide treatment.

The present invention is conveniently carried out using an oxygen-containing gas which is placed immediately prior to either a reflux group or a reflux hold tube before entering the down column with the lignocellulose-containing material and the alkali and peroxide compounds. mixed in a heated mixer.

As in the case of the first processing step, the compounds used in the practice of the invention are selected from those well known to those skilled in the art. Thus, for example, it will include inorganic peroxides such as hydrogen or sodium peroxide and organic peroxides such as benzoyl peroxide and tert,-butyl hydroperoxide used in the extraction step.

Typically the alkali will be sodium hydroxide, sodium carbonate or magnesium carbonate.

The preferred range of treatment for carrying out the third feature of the present invention is to add an alkali compound to bone-dried pulp from 0.2 to 0.7f.
up to E1%, using between 2 and 3.5% by weight of hydroxide compounds and between 0.4 and 0.6% by weight of oxygen.

The oxygen pressure is preferably maintained between 0.05 and 0°15 MPa and the process variables are between 40°C and 90°C.
The reaction time is from 3 to 30 minutes with a temperature range between 8% and 20%.

An example of the above process is given below.

The sample with a viscosity of 39 mPa was divided into three samples. One sample of the unbleached sample was chlorinated with chlorine alone under the conditions shown in Table 1.

Example 7 A second sample was chlorinated with a mixture of chlorine and chlorine dioxide, but the chlorine dioxide replaced 7% of the chlorine charge.

Example 8 A third sample of pulp was chlorinated sequentially with chlorine dioxide and chlorine. Chlorine dioxide accounts for 40% of the total chlorine charge.
was replaced.

After washing, each sample from Examples 1.2 and 3 was re-divided into 6 parts; one part was extracted with sodium hydroxide; another part was extracted with sodium hydroxide decachlorite - (EH) Another portion was extracted with sodium hydroxide and peroxide.
EP) Another part was extracted with sodium hydroxide + oxygen - (EO
) Another part was extracted with sodium hydroxide deca peroxide deca oxygen (EOP) or
Extracted with oxygen (EHO) The experimental conditions and results are shown in Table 3.

Alkaline hydroxide, peroxide and oxygen improved the degree of delignification as measured by the kappa number in each group of different chlorination treatments. The whiteness of pulps subjected to peroxide-oxidative extraction treatment was substantially higher than those subjected to other oxidative extractions.

The chlorination step was followed by sodium hydroxide, peroxide and oxygen as a pre-delignification step and a peroxide oxidation extraction step (each referred to as (EPO) or X step). .

Example 9 Kappa number 26.6.0.5% citric viscosity 26.3n+P
10% by simultaneous treatment of softwood kraft pulp of a in the presence of hydrogen peroxide, sodium hydroxide, magnesium sulfate, and oxygen at a pressure of 0.14 MPa.
X delignification step. The conditions are listed in Table 3.

After washing the chlorinated pulp, the pulp was divided into three parts and extracted in the following manner under the conditions described in Tables ■ and ■.One part was extracted with sodium hydroxide. E; Another portion was extracted with sodium hydroxide and oxygen (
EO): The third portion was extracted with sodium hydroxide, hydrogen peroxide and oxygen -X.

Each extracted pulp was washed and kappa number, viscosity J
5 and whiteness were measured. The results are listed in Table ■. X
The whiteness of the C/DX-treated pulp reached 77.5% ■SO, which was about 20 points higher than the XC/D(EO)-treated pulp.

Each sample of extracted pulp was then divided into four equal parts and each portion was treated with a different charge of chlorine dioxide using the conditions listed in Table 1. The whiteness obtained for each sample is shown in Table 1 along with the viscosity. XC/DXD-processing excellence is D
It is shown that 91.3% ISO brightness was obtained using 0.40% chlorine dioxide (bone dry basis) in the step, whereas XC/DED and XC/D(EO)D
The whiteness was 88.0 and 89.0, respectively.
It was 8% ISO. When the amount of chlorine dioxide charged to the pulp was increased to 0.60% in the D stage, the maximum whiteness of the pulp was 92% after the XC/DXD-treatment.
o, which is XC/DED and XC
/D This is a value that could not be achieved even with high chlorine dioxide charging in the D stage of continuous processing of (EO)D.

Examples 10 and 11 These examples demonstrate the use of the (EPO) bleaching step in the QC/D (EPO)Dfi white sequence for softwood and hardwood kraft pulps, respectively. ○C/DX
The results of oxygen delignification without peroxide in the I) sequence are shown in Tables 1V and 7, respectively. This sequence produced a bleached pulp with good brightness, but a poorer viscosity than that following XC/DXD bleaching.

The X delignification step is preferred because it allows for lower oxygen pressures while also reducing the time required.

Corner C'J OO Masha's -n-0 5 0 0 0? The above embodiments and examples are for illustration only, and any changes and improvements thereto are for illustrative purposes only. It will be understood that other modifications may be made without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

Figure 1 is a graph illustrating various alkaline delignification methods plotted in terms of Kappa number of pulp versus time, and Figure 2 is a graph plotting the alkaline delignification method of Figure 1 in terms of viscosity versus time. It is. Agent Akira Asamura's drawing - -(1..., no change in content) U 2 =
ENG = "Temporary leap -K = = = = = Te Ding p Procedural amendment (method) Month 77, Showa Otsu 1

Claims (12)

[Claims] (1) A pulping process in which cellulosic material is subjected to chemical cooking, in which the cooked wood pulp is treated with (a) from 0.5 to 4% by weight of an alkaline compound; (b) from 0.1 to 2% by weight Oxygen compound; (c) 0.01 to 0.4M
0.4 to 6% by weight oxygen gas at a partial pressure of up to Pa; and (d) a viscosity-protecting catalyst, and this treatment is
Characterized by a process carried out at a temperature of up to 5°C, for a time of between 1 minute and 120 minutes, at a pulp concentration of between 5% and 25% (all gravimetric measurements are based on bone dry pulp) pulping method. (2) A method according to claim 1, characterized in that the viscosity protection catalyst is magnesium ion present between 0.1 and 1.0% by weight. (3) A method according to claim 1, characterized in that the cellulosic material is selected from the group consisting of softwood and hardwood. (4) the alkali compound is selected from the group consisting of sodium hydroxide, sodium carbonate, calcium carbonate and magnesium carbonate, and the peroxide compound is hydrogen peroxide, sodium peroxide, benzoyl peroxide, tert. Process according to claim 1, characterized in that it is selected from the group consisting of -butyl hydro-peroxide and peracetic acid. (5) A pulp whitening method comprising semi-delignification of pulp, treatment of the semi-delignified pulp with a chlorine-containing compound, and subsequent washing of the chlorinated pulp, which has been washed and chlorinated. The pulp is treated with (a) from 0.5 to 4% by weight of an alkali compound (b)
from 0.1 to 1% by weight of a peroxygen compound; and (c) from 0.1 to 3% by weight of an oxygen-containing gas at a pressure between 0.1 and 0.4 MPa; (d) a viscosity protection catalyst; Simultaneously, the treatment was carried out at 50°C.
to 90° C. for a period of from 3 to 120 minutes at a pulp concentration of between 5% and 25% (
A method characterized by a process in which all gravimetric measurements are based on bone dry pulp. (6) A method according to claim (5), characterized in that the viscosity protection catalyst is magnesium ion present between 0.1 and 1.0% by weight. (7) the alkaline compound is selected from the group consisting of sodium hydroxide, sodium carbonate, calcium carbonate and magnesium carbonate, and the peroxide compound is hydrogen peroxide,
Sodium peroxide, benzoyl peroxide, tert. Process according to claim 1, characterized in that it is selected from the group consisting of -butyl hydro-peroxide and peracetic acid. (8) In a chemical cellulosic pulping process in which the pulp is subjected to chemical cooking: A) the cooked wood pulp is treated with (i) from 0.5 to 4% by weight of an alkali compound; (ii) from 0.1 to 2% by weight; peroxygen compounds up to; (i
ii) 0.4 at partial pressures from 0.01 to 0.4 MPa
and (iv) a viscosity-protecting catalyst;
B) delignification carried out at pulp concentrations between 5% and 25% (all measurements are based on bone-dry pulp) for times between 1 and 120 minutes at concentrations between up to treating the pulp with a chlorine-containing compound; C) washing the chlorinated pulp; and D) treating the washed and chlorinated pulp with (i) from 0.5 to 4% by weight of an alkali compound; (ii) ) 0.1 to 1% by weight peroxygen compound; and (iii) 0.1 to 3% by weight oxygen-containing gas at a pressure between 0.1 and 0.4 MPa; and (iv) viscosity protection. Simultaneously treated with a catalyst, and this treatment is carried out at temperatures from 50°C to 90°C.
carried out at a pulp concentration between 5% and 25% for a time between 3 and 120 minutes at a temperature between Method. (9) the alkali compound in steps A and D is selected from the group consisting of sodium hydroxide, sodium carbonate, calcium carbonate and magnesium carbonate, and the peroxide compound is hydrogen peroxide, sodium peroxide, benzoyl peroxide, tert. ．． 9. A method according to claim 8, characterized in that the viscosity protectant is selected from the group consisting of -butyl hydro-peroxide and peracetic acid; 10. The method of claim 1, wherein the pulp is subjected to a chemical cooking selected from the group consisting of kraft, soda and sulfite cooking. 11. The method of claim 5, wherein the pulp is subjected to a chemical cooking selected from the group consisting of kraft, soda and sulfite cooking. 12. The method of claim 8, wherein the pulp is subjected to a chemical cooking selected from the group consisting of kraft, soda and sulfite cooking.