FI123113B - Procedure for the manufacture of mechanical pulp and the use of mechanical pulp - Google Patents

Description

METHOD FOR MECHANICAL MASS MANUFACTURE AND USE OF MECHANICAL MASS

The present invention relates to a method for treating mechanical pulp and to the use of mechanical pulp.

Resin is a harmful substance in the manufacture of mechanical pulp. When the raw material is six, the resin content is relatively low, so it is unlikely that the resin will cause uncontrollable problems. However, if the raw material is 10 pines containing more pitch than six (about three times as much), during the treatment of the resinous raw material, pitch or pitch and fibers will accumulate on surfaces, such as a paper machine or printing press, and subsequent adverse effects are expected. Therefore, in order to use pine as a fiber wood, the resin must be reduced or eliminated or converted to less harmful ingredients.

The above-mentioned objects can be achieved by the process according to the invention, the features of which are according to claim 1.

20 Pulp is treated with ozone to remove, reduce or modify pitch. Resin is one of the first components of the pulp with which ozone reacts. However, ozone also tends to react with lignin, and as a result, chromophoric compounds are released into the process water. As a result, the brightness of the pulp diminishes and cannot be completely restored to the post-25 subsequent bleaching stage using either dithionite or ß peroxide.

By the process of the invention, it is possible to reduce, eliminate or 'resin the resin by treating the pulp with ozone so that the optical properties can be restored at a later bleaching stage. In practice, you can

CL

it may be necessary to reduce the pitch of the pine so that its pitch Jg after ozonation corresponds to that of the spruce.

LO

C/O

In the process of the invention, the starting raw material consists of supports that have been ground in a pressure groundwood (PGW) or groundwood (GW) process. The logs are coniferous species, preferably pine (Pinus 2 sylvestris) or southern pine (Pinus genus, several species). Pine is a very resinous material, which has been problematic in the use of the massage because the resin portion of the material is harmful in the process. Pine has been used as a mixture with spruce in pulp (GW) or pressure pulp (PWG) pulp. The pine content of the pulp 5 may be, for example, 20-60% by weight, or the pulp may be wholly pine. In general, the present process is useful when the pitch of the wood raw material is greater than 0.8 wt.%, And more useful when the pitch is greater than 2.0 wt.%. However, there is nothing to prevent the process from being used with raw materials having a pitch of 0.8 wt.% Or less, but the benefits of these materials may be less.

In the process of the invention, the resin-containing mechanical pulp is introduced into the process along with the process water flow. The mass is ozonated at a consistency of 0.5-4%. The pulp is ozonized by injecting ozone into the pulp-15 stream prior to a container such as a pulp container. The resinous mass is ozonated at a temperature above 70 * 0, usually 80-87 °, preferably 80-85 °. In order to achieve the above temperature range, it is usually necessary to reduce the temperature of the circulation water, since the normal temperature is about 95Ό.

20 The ozonation process produces acidic by-products, such as organic acids, which lower the pH. Thus, ozonation occurs at a pH below 4 if no means of raising the pH has been used. However, there is no need to raise the pH, since it has been found that if the pH rises above 4, it causes the mass to darken. Thus, a natural drop in pH will result in favorable pulping conditions if the dose of ozone is maintained at a level less than 1 g / l g decomposable pitch. Preferably, the mass is ozonated in more than one step ™; for example, two consecutive steps may be obtained

CD

9 results in a better result than just one step. In practice, there may be two 'sequential tanks, preceded by spraying devices leading to process ozone. Before the first tank the pH may be 3.4 and before the second tank

CL

The pH may preferably range from 3.2 to 3.4. Ozone reacts almost S immediately with pitch, resulting in ozone in the gas leaving the process

LO

§ there are no significant amounts left or none at all.

o C \ 1 3

The total amount of ozone in several stages of the series is equal to or less than 1 g of ozone / g of decomposable pitch, preferably 0.6-0.8 g of 03/1 g of pitch. The amount of resin is a theoretical amount calculated using estimates that spruce contains 0.8 wt% of resin and pine contains 2.4 wt% of resin, i.e. one ton of spruce theoretically contains 8,000 g of resin and one ton of pine contains theoretically 24,000 g of resin. The practical aim is to reduce the pitch content of pine so that it is at the same level as that of spruce. Generally, spruce resin does not affect pulp or paper making processes. 10 Ozone overdose should be avoided because ozone, as mentioned above, tends to react with lignin, resulting in darkening of process water and pulp.

It is possible to lower the temperature of the grinding circulation water by supplying circulation water with lower temperature to the circulation water. The replacement water may be, for example, circulating water coming from a paper machine, which may be downstream after grinding. In addition to lowering the temperature, the replacement water is cleaner than the abrasive circulating water, and thus the relative amount of chromophoric compounds in the circulating water is reduced and the mass darkening due to the effect of the process water is reduced. The replacement water can be introduced into a filtrate basin where it is mixed with the circulation water. Excess circulating water is drained out of the process. Heat is recovered from the water by means of heat exchangers.

After ozonation, the pH of the pulp is adjusted to the pH of the bleaching step. The pulp is then bleached, for example, with dithionite or peroxide. A typical pH range for dithionite bleaching of ozonated pulp is 4.7-5.3

O

™ and peroxide bleaching typically have a pH of about 10.5. Therefore, the level to which the pH

CD

o is adjusted before bleaching, depends on the subsequent bleaching process. Suitable pH adjusting agents include sodium hydroxide (NaOH), sodium bicarbonate ≤ 30 (Na 2 CO 3), magnesium hydroxide Mg (OH) 2), calcium hydroxide (Ca (OH) 2) or

CL

mixtures thereof, o

LO

C/O

LO

According to one embodiment of the invention, the aforementioned preferred temperature range S 80, or 85 ^ may be wider and / or higher (for example, temperatures of up to 35 95 ° C are possible), but replacement water is required to purify circulating water.

4

The resulting pulp is used in the papermaking process to make mechanical pulp containing paper grades such as machine-finished specialty (MFS) papers for promotional materials, direct mail, magazines, newspaper supplements and newsprint, newsprint or superscript, weight coated wood-based lightweight printing paper). Papermaking fibers of such grades may consist entirely of mechanical pulp fibers. It is possible that the mechanical pulp in the paper-10 consists entirely of ozone pine, but it is also possible that only a small amount of the mechanical pulp is pine and is derived from the process. For example, an ozonated pine or pressure piston can be used in admixture with thermomechanical (TMP) fir or chemical pulp. Typical compositions of blends of the above grades of paper may be:

Paper Type Pressure Grinder TMP (w-%) Chemical Filler (w-%) __ (w-%) ___ pulp (w-%) __

Newspapers- 40-50 50-60 0 0-10 paper_____

Supercalant 50-25 25 lined paper_____ LWC, bottom 55-35 10 paper_____

CM

δ, Example.

CD

9 20 'Eight tests were conducted on an industrial scale. Estimates were used that six contains 0.8 wt% resin and pine contains 2.4 wt% resin, and based on these 0 estimates, the required amount of ozone was calculated. The objective was that the resin content of the ozonated mass S should not exceed 0.8 wt%. The results of Table 25 are shown in Table 1.

O

cg 5

Table 1. Calculations for Industrial Scale Experiments.

Experiment Pine-Middle-earth-Removed- Removed- Ozone pressure resin resin resin amount in wax mass (w-%) (kg / tonne (kg / kg resin) (w-%)) ______ J__50__T60__080__OOO__1.29 _2__20__1J2__0. 81 _3__20__L12__032__020__0.40 _4__33__T33__053__028__0.75 _5__33__T33__053__028__0.70 _6__33__T33__053__028__1.49 _7__50__T60__080__OOO__1.03 at the end of the year the 8th grade was the highest, the 8th grade was the same as the 8th grade. -% of inorganic filler The paper obtained did not leave any resin layers on the roll surfaces.

The invention will now be described with reference to the drawing which shows a diagram of the ozone treatment process.

CM

Figure 1 shows a diagram of the ozone treatment process. Mechanical mass

CM

is rubbed in the defibrator into mechanical ° 15 pulp from logs, preferably pine logs. There may be multiple defibrillators in parallel. The mechanical pulp slurry is fed into a buffer tank 1, from where it is pumped by pumps 2 through a mass transfer tube | tone 3.

o

LO

g The slurry is led through the mass transfer pipeline 3 to the pressure boost pump 20 into the wood 4 which increases the pressure of the slurry. Injection nozzle 5 feeds ozone-oxygen ™ mixture to slurry from ozone generating system 8. The ozone generating system 8 (indicated by dashed lines) comprises an ozone generator 9, pumps 6 10 and heat exchangers 11. Mixers 6 mix the ozone-oxygen mixture with the slurry. As can be seen in Figure 1, the pumps 4, injection nozzles 5 and mixers 6 may be parallel. The ozonated slurry is introduced into the first pulp container 7. In the first pulp container, the ozone reacts with the resin in the pulp 5 in the first ozonation step to reduce, remove or transform the resin.

After the first ozonation step, essentially the same process step is repeated in the second ozonation step. Injector nozzle 13 feeds ozone-10 oxygen mixture to slurry from ozone-forming system 8. Mixers 14 mix ozone-oxygen mixture to slurry. The pumps 12, injection nozzles 13 and mixers 14 may be parallel. The ozonated slurry is introduced into the second pulp container 15. In the second pulp container 15, the ozone reacts with the pitch in the pulp in the second ozonation step such that the remaining pitch after the first α-15 sonication step is reduced, eliminated or converted.

Once the pulp has been treated with ozone, the ozone is introduced into the ozone depleting section 16 (marked with dashed lines). The ozone is converted to oxygen and removed from the process.

The pulp is led from the second pulp container 15 to the bleaching step (not shown). Before bleaching, the pulp is treated with a base such that it has a pH suitable for the next step. Suitable bases may be sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3), magnesium hydroxide Mg (OH) 2), calcium hydroxide (Ca (OH) 2) or mixtures thereof.

25

It will be apparent to one skilled in the art that the process diagram may be different from ™ shown in Figure 1, but will still operate according to the basic principle of <X> 9 described herein.

C/O

X

cc

CL

O

m co m co o o c \ j

Claims (10)

7 A process for treating a mechanical pulp, which process comprises introducing a resinous mechanical pulp into a process with a stream of process water 5, ozonizing the resinous pulp at a temperature of 80-87 °, preferably 80-85 ° C, and a consistency of 0.5- 4%, and at a pH less than 4, the pulp after the ozonation process is adjusted to the pH required in the bleach and bleached. Process according to Claim 1, characterized in that the resinous mass is ozonated in more than one step, preferably two steps. Method according to claim 1 or 2, characterized in that the amount of ozone is not more than 1 g / l g of decomposable pitch calculated on the basis of the theoretical pitch. 20 Process according to Claim 2, characterized in that the resinous mass is ozonated before two successive mass containers. A method according to any one of the preceding claims, characterized in that part of the process water stream is replaced by water which is cleaner than the process water stream after the ozonation of the pulp but before the bleaching of the pulp ™. A method according to claim 5, characterized in that part of the process water flow is replaced by circulating water from the paper machine. Q_O Process according to one of the preceding claims, characterized in that the pulp is bleached with dithionite or peroxide. o C \ J Use of pulp according to any one of the preceding claims in papermaking. 8 Use according to claim 8, characterized in that the pulp is at least partially pine. Use according to claim 8, characterized in that the pulp is pine. C \ J δ c \ j i CD O CD X cc CL O m co m co o o c \ j 9