JPH09503028A - Chlorine-free bleaching of chemical pulp including two-step treatment with chelating agents - Google Patents

Abstract

(57) [Summary] A chlorine bleach-free bleaching method of lignocellulose-containing fiber material in the form of chemical pulp, which comprises bleaching pulp with a chelating agent and bleaching with ozone and peroxide, immediately after ozone bleaching. In the second stage chelation stage, the pulp is treated with a chelating agent at a pulp concentration of 1-10% for 1-30 minutes at a temperature of 20-90 ° C. and a pH value of 1.5-5. The pulp thus treated is washed and dewatered to a concentration of 8-40% before peroxide bleaching.

Description

Detailed Description of the Invention Chlorine-free bleaching of chemical pulp including two-step treatment with chelating agents   The present invention does not use chlorine bleach for lignocellulose-containing materials in the form of chemical pulp. About bleaching. More specifically, the present invention ozone bleaches pulp and then Regarding oxide bleaching.   In order to make ozone bleaching of pulp more selective, first, pulp is chelated. Treat with an agent such as DTPA or EDTA. As a result, metal ions are Dissolve from the loop and dehydrate to remove the ions prior to ozone bleaching.   Ozone bleached pulp is partially absorbed by the fibers and partially dissolved in the surrounding liquid. Still contains metal. These metals can be peroxide bleached in the next step Must be removed.   According to conventional practice, treatment with a chelating agent at a pulp concentration of 1-10% -60 minutes at a temperature of 20-70 ° C and a pH value of 2-5. After that, the pulp Dehydrate and bleach with ozone. After ozone bleaching, the pulp is washed and dehydrated, then Perform peroxide bleaching. Alternatively, washed and dehydrated Later, additional treatment with a chelating agent is performed. Treatment with this chelating agent is usually , 60 to 90 ° C. for 30 to 120 minutes. Then, before the peroxide bleaching, Wash and dehydrate the pump again.   The first of the above known methods does not give a satisfactory ISO whiteness, the other method is , Requires additional steps that complicate the process and make it more expensive.   According to the present invention, the method is relatively simple and the high ISO whiteness of pulp is obtained. , These problems are eliminated.   Features of the invention will be apparent from the appended claims.   The present invention will be described in detail below with reference to the accompanying drawings.   FIG. 1 is a flow chart of the method of the present invention.   FIG. 2 is a function of peroxide loading for the known method and the method of the present invention, respectively. It is a figure which shows the whiteness of all.   According to the flow chart of FIG. 1, first the chemical pulp is treated with EDTA or DTPA. In order to do so, feed to the first chelation stage 10. Pulp concentration should be 1-10% No treatment is necessary, and the treatment is carried out for 1 to 60 minutes, preferably 5 to 30 minutes. The temperature is 2 It should be between 0 and 70 ° C, preferably between 20 and 40 ° C and the pH value should be between 2 and 5.   After the first chelation step 10, pulp is removed to remove dissolved metal ions. Are washed and dehydrated, for example in a washing press 11. Pulp from the press is ozone-dried. Send to the ozone stage 12 for white. Immediately after the ozone stage 12, the pulp is concentrated by 1-10%. Dilute once and feed to the second chelation stage 13. At this stage, 1 to 30 minutes The temperature is preferably 20 to 90 ° C, preferably 40 to 80 ° C for 5 to 20 minutes, 1.5 Treat pulp with a chelating agent, preferably DTPA or EDTA, at a pH value of ~ 5 I do. The amount of DTPA or EDTA to be filled is 0.5 kg per ton of pulp. Is preferred.   After this second chelation step 13, in a second washing step 14, a concentration of 8-40% is obtained. Washed and dehydrated until complete, and then the pulp is treated with a peroxide stage for peroxide bleaching. Send to 15.   By this method the pulp can be bleached to a whiteness above 83% ISO.   Figure 2 shows the function of peroxide loaded with various treatments between ozone and peroxide stages. As whiteness is shown.   Curve 1 is ozone bleached pulp washed once, dehydrated and then peroxide bleached Regarding idiomatic usage.   Curve 2 is washed, dehydrated and treated with chelating agents by known methods Ozone bleached pulp peroxide, which had been washed and dehydrated again prior to peroxide bleaching Regarding bleaching.   Curve 3 relates to the method according to the invention.   From FIG. 2 it is seen that the bleaching of the invention (curve 3) is significantly better than the conventional bleaching of curve 1. It is clear that various results are obtained. Furthermore, the bleaching method of the present invention is extremely simple. That the result is substantially equivalent to the bleaching result of curve 3 Is also clear. In the experiment conducted in the mill environment, the last two methods (curve 2 and It has been proved that the difference between 3 and 3) is very small.   The invention is not limited to the embodiments shown, which are within the scope of the inventive concept. Of course, it can be changed.

Claims (1)

[Claims] 1. Chemical pulp treated with pulp chelating agent and bleaching with ozone and peroxide A bleaching method for chlorine-free bleaching of lignocellulosic fiber materials in the form of Immediately after ozone bleaching, in the second stage chelation stage, 1-10% pulp concentration At a temperature of 20 to 90 ° C. and a pH value of 1.5 to 5 for 1 to 30 minutes. The pulp treated with a oxidising agent and treated in this way is A method comprising washing and dehydrating to a concentration of 40%. 2. Using DTPA or EDTA as the chelating agent in the second chelation step, Characterized in that the chelating agent is added in an amount of up to 0.5 kg per ton of pulp The method according to claim 1, wherein 3. Bleaching is performed to a whiteness of more than 83% ISO. Or the method of 2.