Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications

Definitions

• the present invention refers to an improvement in a process for delignifying lignocellulosic pulp by means of oxygen, and more specifically, to an improvement in a process for delignifying lignocellulosic pulp by means of oxygen with the addition of ethanol.
• bleaching of chemical pulps is carried out mainly by employing chlorine-containing compounds such as molecular chlorine, chlorine dioxide and hypochlorites, thus resulting in a corrosive, chlorine-enriched and hardly recoverable effluent, which has a high degree of environmental deterioration.
• chlorine-containing compounds such as molecular chlorine, chlorine dioxide and hypochlorites
• a bleaching agent exhibiting such properties is oxygen and, in recent years, its use has substantially increased.
• the discharge of effluent from the bleaching plant can be reduced to half, due to the fact that effluent from the oxygen delignifying stage, which does not contain chlorides, is entirely recoverable.
• This delignifying limit is a function of the low selectivity of oxygen as a delignifying agent, which is caused by the presence of free radicals derived from oxygen during reaction, thus reducing the cellulose chain lengths.
• Such a reduction is usually characterized by increased reduction of the pulp viscosity after oxygen delignification. Formation of these free radicals is increased by the presence of certain transition metals found in the pulp, wherein their removal or inactivation enhances the process efficiency.
• magnesium salts have a very positive effect on preventing cellulose chain degradation during treatment with oxygen possibly due to inactivation of transition metals, as well as the combination of magnesium salts with chelating agents, e.g.triethanolamine plus magnesium, is also substantially effective in maintaining the pulp viscosity.
• Chelating agents for example, DTPA, EDTA, HEDTA and NTA, in the absence of magnesium, have shown to be inefficient in maintaining pulp viscosity. Removal of transition metals by treating the pulp with acids or chelating agents prior to delignifying the pulp with oxygen renders good results, but it requires additional installations for the bleaching process.
• the use of other additives, such as tin and manganese salts have relatively succeeded.
• a typical bleaching sequence for removing lignim from lignocellulosic material for example, kraft pulp of conifers or foliage, is (C+D) (E+O) DED, where (C+D) is a chlorine/dioxide stage, (E+O) is is oxygen-reinforced alkaline extraction stage, D is a chlorine dioxide stage and E is a single alkaline extraction stage.
• the main oxidizing components are chlorocompounds which produce dangerous organochloro-compounds in the effluent from the bleaching process, which are measured by calculating TOCl (total organic chlorine) or AOX (absorbable organic halogens).
• the need for chlorine-based compounds to bleach brown chemical pulps, for example, kraft, sulfide and organosolvent, and, consequently, the amount of TOCl and AOX discharged into the effluent from the bleaching is directly proportional to the lignin content of the pulp derived from the baking operation.
• the purpose of subjecting the brown pulp to various treatments prior to the bleaching operation is to reduce lignin content of the lignocellulosic material to the maximum so that, in the subsequent bleaching sequences, the smallest possible amount of chlorine-based compounds is consumed.
• a treatment which has been successfully used in the brown pulp is thus called oxygen delignification which due to the low oxygen selectivity, reduction of the Kappa Number of the pulp (indirect measurement of lignin content in the brown pulp) is generally limited to, e.g. in the case of kraft pulp of foliage, from 40-50% and of kraft pulp of conifers, from 45-50%.
• Increasing environmental pressure against the use of chlorine-based compounds has, however, led to several changes in the convention oxygen delignifying process aiming at obtaining a more significant reduction of the Kappa Number.
• an additive which under certain process conditions, during oxygen delignification of the lignocellulosic material, oxygen is made to act more efficiently, as can be inferred from a higher reduction of lignin content in the lignocellulosic material, i.e. a higher reduction of the Kappa Number, as compared with conventional techniques, without, however, prejudicing the quality of the pulp whose cellulosic chains are preserved from the action of free radicals derived from intermediates of the reaction of oxygen with the pulp and with transition metals.
• the use of the invention renders a pulp which in the subsequent bleaching sequences will need a smaller amount of chloro compound to attain the desired whiteness and, as a function of that, a smaller discharge of TOCl or AOX in the effluent from the bleaching plant and will exhibit a high viscosity, since it will contain long chains of carbohydrates, thus resulting in a product having good resistance properties.
• the employed additives are compatible from the recovery point of view, the use of the invention allows a more closed system in the bleaching plant and the additive can be partially recovered for reuse, which makes the process more economical.
• the additive used is ethanol and its dosage may vary from 1 to 130 weight percent, preferably from 10 to 20%, wherein preferably 20 weight percent is added to the pulp, whose consistency may vary in a range of from 5-30%, preferably in a range of from 8-15%, the characteristic range of a pulp of middle consistency prior to the first bleaching stage, possibly immediately after the brown pulp storage tank, preferably together with alkali, which can be sodium hydroxide, oxidized white liquor and/or non-oxidized white liquor, wherein the pH is adjusted to a range between 7 and 13, more preferably to a range between 11 and 12, the additive-containing pulp being fed to a mixing apparatus to which oxygen is added at a pressure varying from 2-6 kgf/cm2, preferably at a pressure of 4 kgf/cm2, and then the pulp is passed to a pressure reactor where the delignification in the presence of oxygen takes place, at a temperature of from 80-140°C, preferably from 100-120°C, wherein the high temperature range of 120°
• This example illustrates the temperature effect on the efficiency of an industrial process for delignifying, with oxygen, a kraft pulp wherein the experiments were carried out without the use of an additive, with the use of ethanol as an additive and with the use of magnesium as an additive.
• the sample consisted of a kraft pulp of conventional eucalyptus having a consistency of 12%, which, prior to treatment, had a Kappa Number of 16.7, viscosity of 30.8 cP and whiteness of 33.8°Iso.
• the reaction time was 60 minutes, using 15 kg 02/ton of kraft pulp, partial pressure of oxygen equal to 4 kgf/cm2, 20 weight percent of ethanol and 0.5 weight percent of MgSO4.7H20.
• Experimental results are shown in Table 1 as follows:
• This example illustrates the ethanol feedstock effect on the efficiency of industrial oxygen delignification of a kraft pulp in accordance with the present invention.
• the reaction time was 60 minutes, using 15 kg 02/ton of pulp, 02 partial pressure of 4 kgf/cm2 at a temperature of 120°C.
• Experimental results are shown in Table 2 as follows:
• This example illustrates the oxygen partial pressure effect on the industrial oxygen delignification of a kraft pulp in accordance with the present invention.
• the reaction time was 60 minutes, using 15 kg 02/ton of pulp, 2 weight percent of sodium hydroxide, 20 weight percent of MgSO4.7H20 at a temperature of 120°C.
• Table 3 Table 3 as follows:
• This example illustrates the alkali feedstock effect on the efficiency of the oxygen delignification of an industrial kraft pulp in accordance with the present invention in comparison with conventional processes wherein treatment does not involve the use of magnesium as additive.
• the reaction time was 60 minutes, using 15 kg 02/ton of pulp, an 02 partial pressure of 4 kgf/cm2, 20 weight percent of ethanol and 0.5 weight percent of MgSo4.7H20 at a temperature of 120°C.
• Table 4 Experiment results are shown in Table 4 as follows:
• Example 1 the use of ethanol as additive in the lignocellulosic pulp oxygen delignifying process of the present invention, provides an increase in the delignifying efficiency, by means of a higher reduction of the Kappa Number and an increase of the process selectivity allowing the process to be carried out at higher temperatures.
• an increase in the process temperature of from 80-140°C confers a significant increase on the delignifying efficiency to the same alkali feedstock, without, however, causing a significant decrease in the process selectivity.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=4052110

Family Applications (1)

Country Status (3)

Cited By (2)

Families Citing this family (1)

Citations (2)

• 1991
  • 1991-06-14 BR BR9102464A patent/BR9102464A/pt not_active IP Right Cessation
• 1992
  • 1992-06-12 EP EP19920500075 patent/EP0524127B1/de not_active Expired - Lifetime
  • 1992-06-12 MX MX9202832A patent/MX9202832A/es unknown

Patent Citations (2)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events