FI62357B - FRAMEWORK FOR FRAMSTAELLNING AV FIBERMASSA - Google Patents

Description

I55F1 M (11) ANNOUNCEMENT1 ¢ 21 $ 1

Jua lJ U 'UTLÄGGN t NGSSKRIFT υ (ie Paten tti m venru: ί ty 10 10 1002 (51, «.VS *" * 21 C ”5/02 SUOMI — FINLAND (21) H * e *« tll »Keim» —PttMtamBknlng 8U5 / 73 (22) Htkemhpdhr · —Amftknlnpd »* 19-03-73 (23) Alkuptlvt — Giklgheudag 19-03-73 (41) Tulkit JulklMlal - Bllvlt offMCttg 26-09-73

rmtmttl- ja rekl * teHh * Hitus |. month .. ™ date.- „DO

Patent · och reglfterstyrelsen '' AmekM utltgd och utl. * Krlft * n publicarad 31 - Oö. 82 (32) (33) (31) Requested utuelkeu * —Begird prtorttat 25-03-72 25.03.72 Japan-Japan (JP) 301ÖU / 72, 30185/72 (71) Japan Pulp & Paper Research Institute, Inc-, Well. 7 ~ 5, Ginza U-chome,

Chuo-ku, Tokyo, Japan-Japan (JP) (72) Hiroshi Matsuura, Tokyo, Kyoichi Oku, Tokyo, Japan-Japan (JP) (7 * 0 Ruska & Co (5U) Method for producing pulp - Förfarande för fraiaställning av fibermassa This invention relates to a process for preparing a pulp by treating a vegetable fiber with ammonia or ammonium hydroxide to soften its structure and then grinding it mechanically at an elevated temperature of 50 to 200 ° C, removing lignin from the ground material by treating it with one or more of the following chlorine-based chemicals: chlorine monoxide, chlorine dioxide, hypochlorite, chlorite or chlorate and alkali which is one of the following: ammonia, ammonium hydroxide, a mixture of ammonia and magnesium hydroxide or a mixture of ammonium hydroxide and magnesium hydroxide, after which chlorine-based chemicals are recovered from the lignin removal effluent.

Pulp production methods can be roughly classified into three categories: 1) mechanical process, where pulp is produced by mechanically grinding wood, 2) chemical process, where the pulp is recovered after treating the wood with suitable chemicals to remove lignin that binds the wood fibers together, and 3) semi-chemical. a method using mild chemical treatment in combination with mechanical treatment. Of these, both chemical and semi-chemical methods include the step of removing lignin from wood chips using various cooking soups. The purpose of this step 2 62357 is to make the lignin in the solid phase of wood chips soluble in the broth by the chemicals in the liquid phase. In other words, lignin is removed from the wood by a solid-liquid reaction. In this context, it is necessary to cause the broth to penetrate evenly into the chips in order to obtain a uniform and high-quality pulp by a uniform lignin removal reaction. In addition, to ensure even penetration of the broth into the chips, a predetermined penetration time is required during which the broth sufficiently penetrates the chips before the broth is heated to a cooking temperature where the lignin removal reaction occurs rapidly. In fact, in industrial applications of the sulfate, sulfite and semi-chemical process, it is common to use a long penetration time ranging from several tens of minutes to several hours. As is known, this considerably reduces the productivity of pulp production. It is easy to remember that the disadvantages of such a long penetration time can be well avoided by using small chips. Nolan (TAPPI, Vol. 40, page 170 (1957), and TAPPI, Vol. 51, page 78 (1968) 1 and Kleinert (TAPPI, Vol. 49, page 53 (1963)) have experimentally confirmed the benefits of small chips and proposed However, fibers obtained from fine chips show a higher rate of mechanical damage, resulting in a decrease in the strength of the fiber mass, as confirmed by several studies by Hartler et al. (Svensk Papperstidn 63: 279 (19601)), so it is not always advantageous to use too much. small chip size only to shorten the penetration time.

Several studies have been conducted on the grinding of wood under heated conditions, including thorough studies by Stone (TAPPI 38: 449 and 452 (19551), Lagergren (Svensk Papperstidn 6 ^ 0: 632 and 664 (1957)) and Pulp and Paper Mag. Can. October 1958, page 217), etc. According to these studies, it has been found that 1) the energy required to grind wood decreases when wood is ground at higher temperatures, 2) when wood is ground at higher temperatures, wood fracture occurs mainly in the interlayer layers that hold the fibers together, and thus the breakage of the fibers themselves is reduced. This results in the interlayers being composed mainly of lignin and becoming softer and easier to peel off at higher temperatures. This is used industrially, e.g. 1) in the thermal crushing treatment of wood in the production of wood fiberboard, and 2) in the thermal fiber treatment in the production of high yield pulp containing a large amount of lignin, e.g. wood chips, chemical pulp functional equipment for the thermal defibering of fibrous plants. For example, the Asplund defibrator is well known. The principle of the Asplund defibrator and the details of its development can be found in an article written by Asplund (Svensk Papperstidn 56: 550 (1953)) 1. to obtain a pulp, etc. However, it is not yet known whether the treatment described above can be used in pretreatment, e.g., grinding of vegetable fiber in the production of a cellulose raw material.

Rather, it is generally believed that the application of such a treatment would greatly reduce the strength of the pulp obtained.

Furthermore, the waste liquor generated in the production of cellulose has so far been discharged as such into the water body. This poses a serious environmental pollution problem due to the chlorine compounds, alkaline compounds, etc. contained in the effluent, so it is highly desirable that the effluent be treated appropriately to render it harmless.

The process according to the present invention is mainly characterized in that ammonia is recovered by adding magnesium hydroxide to the waste liquor before incineration.

The object of the invention is to provide a process for the production of pulp, in which the starting material, e.g. wood or other fibrous plants, is ground, preferably under heated conditions, and then lignin is removed, preferably with chlorine compounds and ammonia, and useful chemical compounds are regenerated.

It is a further object of the invention to provide a method for regenerating chlorine compounds and ammonia from waste liquor removed in the production of pulp.

As a result of studies on the removal of lignin from wood or other vegetable fibers using chlorine compounds and ammonia, the inventors found that when wood or vegetable fibers are ground, preferably under heated conditions, the lignin in the wood or vegetable fibers softens and the fibers are easily detached from the interlayers. and lignin removal is easy and efficient. The inventors also found that when a fibrous material, e.g. wood or vegetable fibers, is treated with an alkaline compound under heated conditions prior to the milling step to such an extent that the fibrous structure, softens, the lignin removal is further improved in an efficient manner. It was further found that when the lignin effluent is concentrated and incinerated, the ammonia contained in the effluent decomposes, making it possible to regenerate the chlorine compound or compounds from the effluent. On the other hand, ammonia can be regenerated from the waste broth by adding magnesium oxide or magnesium hydroxide to the waste broth and treating the broth thus obtained in a suitable manner.

The present invention is based on the above-described finding. According to the invention, there is provided a process in which 1) vegetable fiber is mechanically ground at a temperature, preferably between 50-250 ° C, and lignin is removed from the ground to produce pulp using a chlorine compound and ammonia, or 2) vegetable fiber is treated with an alkaline to swell its fibrous structure. and to soften, the fibrous material is mechanically ground at a temperature, preferably in the range of 50 to 250 ° C, and the lignin is thus removed from the ground material to produce a pulp by means of a chlorine compound and ammonia; 3) in the lignin removal step 1) or 2) the broth formed in the lignite is concentrated and incinerated to decompose the ammonia contained in the waste liquor, and a chlorine compound is regenerated from the waste broth, or 4) magnesium hydroxide is added and

The advantages and details of the invention will become apparent from the following description and the accompanying drawings, in which Figure 1 is a schematic representation of effluent treatment steps for regenerating a chlorine compound from an effluent, and Figures 2 and 3 are schematic representations of effluent treatment steps for regenerating both ammonia and chlorine.

The starting materials used in the production of the pulp according to the present invention may be, for example, various wood, bamboo or other vegetable fiber materials. The starting material is in the form of chips when wood is used, or in the form of chips when other vegetable fiber materials are used. The chips or pieces are heated, preferably to 50-250 ° C, by steam, and then mechanically ground, e.g. with a pressure type refiner, to maintain the temperature. In this connection, the temperature at which the chips or pieces are ground is preferably above 50 ° C. If the temperature is below 50 ° C, more mechanical energy is required for grinding, and thus a large amount of fine or short fibers are produced. If, on the other hand, the temperature is

K

62357 above 250 ° C, the yield of the resulting pulp decreases. According to the experiment carried out by the inventors, very good results are obtained when grinding is carried out at a temperature of 100-200 ° C. This will be explained in more detail later in the following examples. Grinding is usually performed using a pressure type refiner. Since the lignin contained in the starting material softens in the grinding treatment under heated conditions, the lignin between the individual fibers is easily detached from them by the refiner.

In this case, the starting material can be converted into a pulp without damaging the fibers in the next lignin removal step using a chlorine compound and ammonia.

Hand-ground wood or other vegetable fibers are subjected to lignin removal using a chlorine compound and ammonia, as not described above, and bleaching to produce pulp.

The chlorine-based substance used in the present invention may be, for example, chlorine, chlorine monoxide, chlorine dioxide, hypochlorite, chlorite, chlorate, etc. i.e. any known chlorine-based substance used in the production and bleaching of pulp may be used, except magnesium hydroxide may be used in combination with ammonia. with. Magnesium hydroxide has the advantage that it can later be used effectively to recover ammonia from pulp waste liquor.

In order to carry out the lignin removal before grinding more efficiently, the starting material is treated under temporal conditions to such an extent that the internal structure of the starting material swells and softens. That is, the wood chips or pieces of other plant fiber material are contacted with the alkaline phase to soften the internal structure of the chips or pieces, the resulting chips or pieces are ground under heated conditions and the lignin is removed with chlorine compound and ammonia as described above. The advantage of alkali treatment is that since the internal structure of the chips or pieces is softened by alkali treatment before grinding under heated conditions, grinding can be performed more efficiently and hydrolysis of carbohydrates in the starting material is prevented by neutralizing alkaline organic acids at high temperature. In other words, when the starting material is pretreated under temporal conditions to swell and soften the internal structure of the starting material, the damage that can occur during the milling step is reduced, so the quality of the pulp is improved, except for organic taps. 6 62357 from the starting material under milled conditions are neutralized with alkali whereby the hydrolysis of the carbohydrates contained in the starting material is prevented, the time substances used are e.g. sodium hydroxide (NaOH), sodium carbonate (NagCO 2), sodium bicarbonate (NaHCO 3), ammonia (NH 4), ammonium hydroxide (NH 4 OH), magnesium oxide (MgO), magnesium Mg (OH) 2) and magnesium carbonate (MgCO 3). These substances can be used alone or in combination. Ammonia is the most suitable of these because it can be regenerated in subsequent treatment of the waste liquor, as will be described later. The amount of alkaline compound in the alkali treatment before the grinding step is not critical. It should be noted that the alkali treatment should be as fast and mild as possible, as the degree of damage to the fibers contained in the starting material tends to increase during the grinding step due to excessive alkali treatment. In addition, in order to prevent the hydrolysis of the carbohydrates contained in the starting material, it is desirable to adjust the amount of the alkaline compound so that the pH of the treatment solution after grinding is neutral or slightly alkaline.

The following describes the regeneration step of the chlorine compound and / or ammonia from the waste liquor generated in the production of the pulp. According to the present invention, the chlorine compound can be preferably regenerated from the waste liquor by concentrating and incinerating the waste liquor to decompose the ammonia contained therein. The regeneration process will be described with reference to Figure 1. Figure 1 shows a regeneration process of a chlorine compound from a waste liquor according to the present invention, whereby all waste liquor removed from the lignin removal step and / or bleaching step 1 is transferred to a waste liquor concentrator 2 for concentration. The concentrator 2 can be any known apparatus using, for example, the opposite osmotic pressure method, an ion exchange resin, etc., or a conventional evaporator. The concentrated broth is then fed to a burner 3, where 3e is burned. The combustor is, for example, of the ordinary type of regenerator boiler and may be a reactor with a fluidized bed, a thermal cracking furnace, a crude type incinerator or any other type of incinerator. When a wet-type incinerator is used as the combustor 3, the concentrator 2 can be omitted. In the incinerator 3, the organic matter contained in the waste liquor is burned to carbon dioxide and water vapor, and the ammonia decomposes into nitrogen gas and water vapor. The chlorine compound is converted to hydrochloric acid. The Santu gas mixture is then fed to a hydrochloric acid purification plant, where hydrochloric acid gas or hydrochloric acid solution is recovered. Other non-hazardous gases are released into the air. The hydrochloric acid or hydrochloric acid solution thus recovered is then fed to the chlorine dioxide production device 5 to obtain chlorine dioxide. The device 5 is connected to the chlorate electrolyser 6. The sodium chlorate formed in the electrolyser 6 is reacted with hydrochloric acid to obtain a gas mixture containing ClOg and Cl2 as follows:

NaClOj +? HCl - * · C102 + fc Clg + NaCl -f- HgO

The resulting gas mixture may be fed to a lignin removal step or a bleaching step 1 for reuse or may be fed to a chlorine dioxide adsorption apparatus (not shown) to recover chlorine dioxide and chlorine by separation. On the other hand, some or all of the hydrochloric acid gas or hydrochloric acid solution regenerated in the hydrochloric acid purifier 4 · can be fed to the conversion device 7 to convert it to chlorine, e.g. by Deacon method, Shell method or Hoechst-Uhde method. or it can be recovered if necessary.

Furthermore, according to the present invention, ammonia can be regenerated by adding magnesium hydroxide to the waste liquor as shown in Figure 2. All waste liquor from the lignin removal step and / or bleaching step 8 is passed to a steam purifier 9i where magnesium hydroxide is added with stirring while steam is introduced into the mixture. It follows that the ammonium salt of the waste liquor is converted into ammonia gas. The ammonia gas is recovered and reused by feeding the gas to a lignin removal step and / or a bleaching step 8. The steam-treated effluent is fed to the concentrator 10 in the same manner as described in connection with Figure 1, and the concentrated liquor is incinerated in the incinerator 11. In this case, magnesium after purification, is reacted with chlorine in the waste liquor to form magnesium chloride. Magnesium chloride is burned and decomposes into magnesium oxide and hydrochloric acid gas. The hydrochloric acid gas is regenerated in the combustor 11 as shown in Figure 1. The regenerated hydrochloric acid gas is purified and converted to eno and Cl2 or only Olgi. The magnesium foum formed in the combustion is quenched by means of a spray device 12, whereby it is converted into magnesium hydroxide. Magnesium hydroxide is fed to a steam purifier 9 to regenerate ammonia. That is, the ammonia recirculates through the lignin removal step and / or bleaching step 8, the steam cleaning device 9 and the lignin removal device 8, the magnesium coke recirculates through the extinguishing device 12, the steam cleaning device 9, the concentrator 10 and the combustion device 11 to the extinguishing device 12. Magnesium oxide to regenerate ammonia can be used repeatedly without the addition of new magnesium oxide while maximizing ammonia recovery.

Figure 3 schematically shows another embodiment of the invention, a method for regenerating chemicals from a waste liquor when pulp is prepared by treating chips or pieces of vegetable fiber with a chlorine-based material and ammonia and magnesium hydroxide in a lignin removal step and / or a bleaching step. The waste liquor removed from the lignin removal step and / or the bleaching step 13 is passed to a steam purifier 14. Magnesium hydroxide is mixed into the broth while steam is introduced into it. The ammonia gas generated in the scrubber 14 is recycled to the lignin removal step and / or the bleaching step. After steam purification, the waste liquor is concentrated in the concentrator 15 as described in connection with Figure 2. The concentrated broth is then burned in a burner 16 to give magnesium oxide. The resulting magnesium oxide is quenched in a quenching device 17 to give magnesium hydroxide. The magnesium hydroxide thus obtained is reused by returning it to both the lignin removal step and / or the bleaching step 13 and the steam cleaning device 14. The chlorinated hydrochloric acid gas regenerated in the incinerator 16 is treated in the words described in connection with Fig. 1.

As can be seen from the above, the process of the present invention has several advantages because the pulp can be advantageously prepared using relatively mild chemicals, e.g. chlorine compound and ammonia, and because the chemical compounds in the pulp effluent are easily regenerated , which would cause environmental pollution.

The invention is illustrated by the following examples, which are by no means intended to limit the invention.

Example 1

Japanese beech chips were preheated with steam at 50, 100, 150, 200 and 250 ° C for 3 min, and the chips thus heated were then ground with a pressure type refiner to maintain the above temperatures. For comparison, the experiment was performed by grinding the raw materials at room temperature (25 ° C) without evaporation. The six different powdered raw materials thus obtained were subjected to chlorine treatment and ammonia extraction treatment to remove lignin. The chips thus treated with * 62357 were further subjected to sodium hypochlorite treatment, ammonia treatment and chlorine dioxide treatment to obtain a bleached pulp. The treatment conditions for each step are shown in Table 1 and the test results for each bleached pulp are shown in Table 2.

table 1

Chemical Handling- Handling- Starting time- more.ys heat ti- ^ ikaN? A ”, (£ wood la (C °) (min) krus (by weight) _ * <> - *>

First step: 22 25 120 5 chlorine treatment

Second stage: 70 60 10 ammonia treatment

Third stage: x)

Sodium hypochlorite

Fourth stage: 5 70 60 10 ammonia treatment

Fifth step: 1.5 70 240 10 Chlorine dioxide treatment x) Note. The amount of Na hypochlorite added is shown as "available" chlorine.

It can be seen from Table 2 that when the grinding of the chips is performed at higher temperatures, the energy required for grinding is reduced and the strength of the obtained bleached pulp is significantly improved, except for the bleached pulp yield is slightly improved as the grinding temperature increases.

In any case, the total pulp yields are over 60, which demonstrates the excellence of this invention.

Example 2 1 kg (absolute dry weight) of a beech chip similar to Example 1 was immersed for 60 min in 10 l of a 50 g / l sodium hydroxide solution and heated to 60 ° C. The embedded chips were then removed from the solution and excess alkaline solution was removed from the chips. The chips were then heated to 130 ° C with steam and held at this temperature for 3 min. The chips thus heated were ground with a refiner while maintaining the temperature. The required grinding energy was 240 kWh / ton of chips. The yield of ground substances was 10,625,357

Table 2 Sample No r '2 "—ζςι — m — m m

Chip grinding conditions,

Grinding temperature (° C) 25 50 100 150 200 250 IKÄt-g »)« o “« · 280 265

Number of fine fibers' (weight τέ) 18.5 16.8 11.4 4.6 3.1 2.8

Test results

Yield of bleached fiber pulp65.3 65.3 65.2 -64.5 63.2 62.7 (weight- $).

Freedom of unground pulp 270 340 505 680 680 700 (ml)

Brightness of unground pulp 86.0 85.9 86.5 86.8 86.1 85.9 (J> G.3.)

Tear-off times ***) 79 84 9g pleasure 107 110

Fracture length xxx ^ (km) 5.7 6.0 6.7 7.8 7.6 7.5 xx ^ 1. The amount (#) that passed through the 80 mesh screen.

XXX) 2. The tear coefficient and the breaking length were determined by means of sheets of paper formed from a pulp ground to 250 ml of CS-freedom with a ΓΡΙ-mill.

89.6 i> by weight of starting chips. The substances thus ground were subjected to a chlorine treatment (where the amount of chlorine added was 21% w / w) and an ammonia treatment (where the amount of ammonia was 15% by weight) to remove lignin. The material thus treated was further subjected to a sodium hypochlorite treatment (where the available chlorine was contained in 6 wt% ρ), a sodium hydroxide treatment (where the amount of sodium hydroxide added was 4 wt / 6) and a chlorine dioxide treatment (where the amount of chlorine dioxide was 1.2 wt.%). ^) to obtain a bleached fibrous pulp with a brightness of 86.5 GK in a yield of 61.8 i> from the weight of the starting chips, The treatment conditions as the amounts of chemicals added were the same as those used in Example 1. The resulting bleached pulp was ground on an IPI mill to give a CS freedom of 400 ml. The pulp thus ground was made into sheets. The tear coefficient of the obtained sheets was 118 and the breaking length was 8.0 km. The experimental results show that when the chips were pretreated with sodium hydroxide, the energy required to grind the chips was reduced and at the same time the quality of the pulp was improved.

Example 3

It is known that when chlorine dioxide is used together with chlorine in the first chlorination step to bleach cellulose, e.g. sulphate cellulose, a decrease in the viscosity of the pulp can be prevented. This example demonstrates the effect of chlorine dioxide when mixed with chlorine during the chlorination step.

The starting material of the sample 4 'of Example 1 was used as starting material. The material was subjected to a first stage chlorine treatment and a second stage ammonia treatment to remove lignin. The material thus treated was further subjected to a third stage sodium hypochlorite treatment, a fourth stage ammonium hydroxide treatment and a fifth stage chlorine dioxide treatment. In this case, the same conditions as in Example 1 were used, except that the Cl2 / C102 mixture was used in the first step for chlorination in the following six ratios (as available chlorine): 100/0, 90/10, 70/30, 50/50, 30/70 and 0 / 100. The properties of the six types of pulp obtained are shown in Table 3.

Table 3 Sample No. ~ T ~ ~~ 2 ~ 3 4 5 ΊΓ

In the first stage

Cl2 / C102 ratio. 100/0 90/10 70/30 50/50 30/70 0/100 test results

Brightness (/ G.E.) 86.8 87.0 87.6 88.1 80.0 88.9

Yield (w / w) 64.5 64.0 67.8 61.2 60.8 59.6

Degree of polymerization 1420 1600 1690 1810 1870 2210

Bounce factor 110 106 108 112 106 111

Fracture length (km) 7.8, 7.8 8.0 7.7 7.9 7.7 x) 'Note. The tear coefficient and fractional length were determined in a Canadian Standard Freeness of 400 ml (PFI mill).

It can be seen from Table 3 that when chlorine dioxide is mixed with chlorine in the chlorination of the first stage, the brightness of the pulps is improved as well as their degree of polymerization. In terms of strengths, no significant differences can be observed with the pulps treated with different mixing ratios of chlorine and chlorine dioxide.

Example 4 1 kg (oven dry weight) of beech chips were treated to have a moisture content of 50% by weight. Ammonia gas was then allowed to be absorbed into the chips by 12,625,35 in a ratio of 2.5 # of chips from a nice weight kiln to swell the wood chips. After that, the chips were heated to 150 ° C with steam, at which temperature they were ground using a pressure refiner. The yield of the obtained powder material increased to 91.2 # by the weight of the oven-dry chips. The ground material was subjected to a 5-step treatment, i.e. treatment with chlorine-based substance, extraction with ammonia, treatment with chlorine-based substance, extraction with ammonia, treatment with chlorine-based substance, under the treatment conditions shown in Table 4. The result was a bleached fibrous pulp with a brightness of 88.3 # G.E. with a yield of 66.1 # by weight of the original dry pulp.

Table 4 1. 2. 3. 4. 5.

step step step step step C102 NH3 C102 NHj cio2

Addition of chemical, n r,, r.

(# of chip weight) * J 1 Temperature (° C) 50 90 70 90 80

Time (min) 60 10 180 10 180 Consistency of starting material 8 20 10 20 10 (w / w)

Example 5

All effluents were recovered after washing the powdered material at the end of each step in Example 4 (treatment with chlorine-based material, extraction with ammonia, treatment with chlorine-based material, extraction with ammonia, treatment with chlorine-based material). The waste liquors thus recovered were mixed together and the mixture was then divided into two equal parts. One of them underwent the following experiment.

The other portion of the effluent was concentrated using a rotary evaporator to a solids concentration of 60 #. The broth thus concentrated was burned in an incinerator. The combustion gas generated in the incinerator was passed to a reflux condenser equipped with water cooling to condense and recover hydrogen chloride gas and water vapor. The results of the analysis showed that the condensed liquid contained 33.7 g of hydrochloric acid. This meant that about 89% by weight of the chlorine used in the form of chlorine dioxide in the preparation of the pulp in Example 4 was recovered. The hydrochloric acid solution thus obtained was concentrated by repeated distillation and condensation steps to give a 32% hydrochloric acid solution. The concentrated hydrochloric acid solution could be used to generate chlorine dioxide by reacting it with sodium chlorate. Thus, it is apparent that the process of the present invention can regenerate the chlorine-based material required in the manufacture of pulp. The ammonia used in the incineration of the waste liquor decomposed into nitrogen gas and water vapor and could therefore not be regenerated. However, ammonia is released into the air in a harmless form, so nothing is created without a pollution problem.

Example 6

The other part of the waste liquor mixture of Example 5 was mixed with 68 g of magnesium hydroxide (corresponding to the amount of ammonia used in the preparation of the pulp). The mixture was then heated with steam to evaporate ammonia gas. The ammonia gas thus evaporated was cooled and condensed to regenerate aqueous ammonia. The results of the analysis showed that the ammonia solution contained 36.4 g of ammonia. This meant that about 91 weight; the ammonia used to make the pulp was regenerated. The remaining solution was then concentrated and incinerated in the same manner as in Example 5 to give 67.7 g of ash. The results of the analysis showed that the ash contained 97.8% by weight of # MgO and the remainder CaCl2. This ash was then washed with water to dissolve the CaCl 2. An appropriate amount of water was added to the thus washed ash while heating HgO to magnesium hydroxide. The amount of magnesium hydroxide obtained was 67.5 g, which was more than 99% by weight of the magnesium hydroxide used to separate the ammonia.

The hydrochloric acid solution was regenerated by concentrating and incinerating the waste liquor in the same manner as in Example 5. The results of the analysis showed that the solution contained 35.2 g of hydrochloric acid. This showed that 95 # of the weight of chlorine used to make the pulp was regenerated. This hydrochloric acid solution could be used to generate chlorine dioxide in the same manner as in Example 5, or it could be converted to chlorine gas by the Deacon method, the Shell method or the Hoechts-Uhde method, in which case chlorine gas was used to produce the pulp.