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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• This invention relates to a method for replacing one or more of the conventional chlorine bleaching steps of kraft pulp by the use of tertiary butyl hydroperoxide as a brightening agent in aqueous alkaline medium such as aqueous sodium hydroxide or sodium carbonate.
• Prior art Kraft brown stock as obtained from the pulping process, requires extensive treatment with chlorine and chlorine-compounds in order to obtain a bleached and brightened pulp.
• the first stage normally consists of treating with chlorine and the second stage, which follows, is an extraction with aqueous sodium hydroxide, these stages being designated C and E, respectively.
• the pulp is treated with hypochlorite, the H stage; the final brightness is obtained by treating with chlorine dioxide, the D stage.
• CEHD gives kraft pulps having a GE. brightness of 86 to 87.
• numerous five stage processes have also been designed and used, for example, CEHHD, CEHDH, CEHED, CHDED and CEDED, wherein the letters refer to the same stages as described in the four stage sequence.
• hypochlorite stage causes some damage to the cellulose with consequent loss in strength and color stability, thus sequences were developed which obviate the use of hypochlorite entirely by the substitution of chlorine dioxide, i.e. additional D stages, but these also were more expensive.
• Chlorine and chlorine dioxide are highly toxic and hazardous compounds, chlorine dioxide being highly explosive. All contact with the skin or with their vapors by employees using them must be avoided and this requires expensive and special precautions; and in addition, since they are so highly corrosive, special and expensive stainless steels must be employed in the equipment. Chlorine dioxide, in particular, is difiicult to handle since gas phases containing more than 10 percent ClO must be avoided and since water solubility is only 0.3 percent constant control and metering must be employed.
• the method of the present invention obviates all of these difiiculties.
• the present method completely avoids the pollution problems associated with the prior art method which fact is of exceedingly great importance since the public and many governmental agencies are now greatly concerned With these types of pollution and are requiring either stringent curbing or their entire elimination.
• the cost of the reagents for the instant process is either no greater or less than the chemical cost of the prior art chlorine bleaching compounds, and thus it is not as necessary to employ exactly optimum amounts of such reagents.
• critical amounts are not required to avoid color reversion as with the prior art processes. If an excess is used, it can be recovered and recycled.
• the method of the instant invention provides brightness increase comparable to that of the prior art methods without delignification so that there is no pulp yield loss.
• the present invention is completely flexible, that is it can be substituted for any one or all of the prior art stages, and thus is particularly suitable for replacing chlorine dioxide and obviating of the necessity of using two or more chlorine dioxide stages to replace hypochlorite and obtain final maximum brightness.
• the tertiary butyl hydroperoxide requires only ordinary precautions in handling, is highly stable having none of the hazardous and toxic characteristics of chlorine or chlorine dioxide. Likewise, it is not as corrosive and ordinary stainless steels can be used in fabricating the equipment.
• kraft pulps either as obtained in the form of the brown stock from the pulping stage of manufacture, or as obtained from any of the stages of conventional bleaching are treated with a mixture of tertiary butyl hydroperoxide and an alkaline compound such as sodium hydroxide or sodium carbonate in aqueous solution to provide a brightened pulp having a GE. brightness equal to or greater than that obtained by the conventional prior art methods which have been described.
• the invention is applicable to both hard wood and soft wood types of pulps, and in a particular important embodiment of the invention, the alkaline tertiary butyl hydroperoxide treatment is used to replace conventional chlorine dioxide treatment.
• the method of this invention is applicable either to kraft pulp made from hard woods (angiosperms) or soft woods (gymnosperms).
• the method of this invention can be employed with kraft pulp as it is obtained directly from the pulping processes in the form of brown stock or after any one of the conventional bleaching stages, such as the chlorination stage (C), after the chlorination and extraction stages (CE), or after the hypochlorite stage (CEH).
• the brightening method of this invention replaces the chlorine dioxide or D stage of the kraft process. This constitutes a particularly preferred embodiment of the invention.
• the method of this invention is also particularly applicable in replacing the two chlorine dioxide stages and extraction stage.
• the method can be carried out on pulps having the consistency, normally associated with kraft pulps, i.e. those ranging from 12 to percent, or lower or higher. Consistency refers to the weight percent of dry pulp in the bleaching or brightening liquor. Ordinarily, the consistency is based on air dired pulp weight, however, in the data in this application consistency is based on oven dried pulp weight.
• the brightening method of this invention can be carried out at temperatures in the range of from ambient temperatures, 20 to C., or below, to temperatures of 100 C. Temperatures in the range of from 70 C. to 85 C. are preferred in order to provide a shorter reaction time without reaching the temperature at which the hydroperoxide starts to decompose and vaporize, thereby reducing its effectiveness. Since the brightening reaction is dependent upon the temperature it may take up to two weeks at room temperature to obtain the same degree of brightening that can be obtained from as little as 15 minutes at 85 to 100 C. In general, at the preferred temperature range of from 70 C. to 85 C. times in the range of from 3 hours at the lower limit to /2 hour at the upper are preferred.
• the brightening step is ordinarily carried out at atmospheric pressures although pressures above atmospheric, for example, up to 50 p.s.i.g. may be used if desired or subsatmospheric pressures may be used, for example, a few pounds below atmospheric pressure.
• the weight percent based on the dry pulp of tertairy butyl hydroperoxide in the brightening liquor can range from about 0.5 to 50, however, from 20 to 40 weight percent based on the dry pulp is a more preferred range for both hard and soft wood pulps and when applied to brown stock or after the chlorination or chlorination and extraction stages.
• weight percent based on the dry pulp of tertiary butyl hydroperoxide in the brightening liquor is suflicient and some improvement is obtained even with from 0.5 to 2.5
• the brightening liquor can have a concentration of from about 5 to 20 weight percent tertiary butyl hydroperoxide although this is a matter of convenience and higher or lower concentrations can be employed.
• alkaline compound employed depends upon the quantity of tertiary butyl hydroperoxide employed and also upon the pH desired. In general, sufficient alkaline compound, i.e. sodium hydroxide or sodium carbonate should be used such that the pH ranges from 8 to 10.5 with a preferred range being from about 9 to 10.5.
• the method of this invention can also be carried out in more than one stage, for example, the pulp can be treated in a first stage and the brightening solution is drained from the pulp. The pulp is then treated with the solution to which tertiary butyl hydroperoxide and the alkaline compound have been added to bring the solution to the desired concentration.
• the addition of the water and brightening mixture also is useful in maintaining the desired consistency of the pulp.
• the handsheets were made in conventional manner by transferring the pulp to a Buchner funnel provided with a filter paper. The brightening solution was removed by suction and the pulp washed with several volumes of Water to assure complete removal of the solution. The Wet handsheet was oven dried at 100 C. under vacuum.
• EXAMPLE III A run was carried out in which the same pulps employed in Example I were treated in two successive stages for 6 hours at 50 C. in each stage charging 8.1 percent tertiary butyl hydroperoxide and 3.6 percent sodium hydroxide to each stage. The first treating solution was merely drained from the pulp between the stages. Thus.
• EXAMPLE V A series of runs were carried out wherein the brightening solution recovered from a previous run was fortified with additional tertiary butyl hydroperoxide and sodium hydroxide for treatment of an additional quantity of pulp in order to show that a recycle operation could be suitably employed by the method of the instant invention.
• a method for the brightening of kraft pulp which comprises contacting the pulp with an aqueous solution consisting essentially of tertiary butyl hydroperoxide and sodium hydroxide or sodium carbonate to provide a pH of between 8 and 10.5, said contacting being at a temperature in the range of from 20 C. to 100 C.
• aqueous solution contains from 0.5 to 50 weight percent of tertiary butyl hydroperoxide based on the weight of the dry pulp.

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

Applications Claiming Priority (1)

Publications (1)

Family

ID=22107940

Family Applications (1)

Country Status (10)

Cited By (2)

• 1970
  • 1970-09-15 US US72491A patent/US3707438A/en not_active Expired - Lifetime
• 1971
  • 1971-08-25 CA CA121,346A patent/CA951856A/en not_active Expired
  • 1971-08-26 GB GB4017271A patent/GB1318131A/en not_active Expired
  • 1971-09-07 BE BE772260A patent/BE772260A/fr unknown
  • 1971-09-07 FR FR7132272A patent/FR2107366A5/fr not_active Expired
  • 1971-09-09 DE DE19712145212 patent/DE2145212A1/de active Pending
  • 1971-09-10 ES ES394982A patent/ES394982A1/es not_active Expired
  • 1971-09-10 BR BR5955/71A patent/BR7105955D0/pt unknown
  • 1971-09-10 IT IT52813/71A patent/IT939406B/it active
  • 1971-09-13 NL NL7112585A patent/NL7112585A/xx unknown

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