Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Reexamination Certificate
2001-08-08
2003-05-27
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
C162S076000, C162S078000
Reexamination Certificate
active
06569286
ABSTRACT:
This invention relates to a process for the oxygen bleaching of wood or non-wood pulp using an agglomerated bleach activator to react with hydrogen peroxide to form a pulp bleaching solutions. In particular it relates to the formation of a pulp bleaching solution by the reaction of a specially formulated agglomerate of a crystalline powder of Tetraacetyl ethylene diamine, commonly known as TAED, with excess hydrogen peroxide and the use of that bleaching solution to bleach and delignify pulp.
Oxygen based bleaching is used for pulp bleaching bee of its environmental benefits and oxidising power. Hydrogen peroxide is increasingly being used in oxygen based pulp bleaching.
Although hydrogen peroxide has environmental benefits over chlorine based bleaches it suffers from some performance disadvantages which become particularly important when an existing pulp bleaching sequence is being converted to operate with hydrogen peroxide. One problem is that the degree of whiteness may be reduced compared with the use of chlorine dioxide, this may significantly reduce the value of the pulp.
A second problem which may occur when process conditions are changed to optimise bleaching for use of hydrogen peroxide is that the fibre length deteriorates and there is a corresponding loss of strength in paper produced from the pulp. A third potential problem is the poor delignification performance of hydrogen peroxide when used on its own.
It has been suggested that use of a stronger oxygen based bleach will solve these problems. However, whilst use of equilibrium peracetic acid or Caro's acid improves the bleaching and reduces colour reversion it also introduces problems of handling and dosing peracid in the pulp plant. It is proposed in several patent applications to react at least part of the hydrogen peroxide with a bleach activator thereby generating a peroxyacid based oxygen bleaching species in situ which facilitates improved pulp bleaching and delignification whilst avoiding the hazards of transporting preformed peracid or generating peracid by reaction of hydrogen peroxide and carboxylic acid under forcing conditions. In WO9521290 there is described a process in which peracid is produced in siti by reaction of a bleach activator such as tetraacetylethylenediamine and hydrogen peroxide at a pH less than the pK
a
of peracetic acid formed from the reaction of these chemicals. It is stated that in a preferred process the TAED is first dissolved in hot water and then added to the hydrogen peroxide before the reacting mixture is dosed to the pulp. Sequestrant may be added to the pulp before the dosing takes place. It is also stated that conditions must be optimized to ensure that all the TAED is consumed. The chemistry must be carefully controlled to achieve consistent results when using such a powerful bleach as peracetic acid.
In EP456032 there is described a similar pulp bleaching process using alkaline TAED and hydrogen peroxide. Bleaching of the pulp is done in plastic bags and no detail is given of how a scaled up process should be operated.
JP05186989 proposes an alkaline process using a bleach activator such as TAED to give brighter pulp when it is used with oxygen and optionally also with hydrogen peroxide, very few details of the process steps are given and hydrogen peroxide is not used in the examples. It appears that the TAED is mixed as a solid with dry pulp at the start of the bleaching step.
GB2304126 proposes use of TAED activated hydrogen peroxide to delignify pulp. Again the form of the TAED is not specified.
It is conventional in pulp bleaching to use letters to represent stages in a process. Some of the commonly used letters are: C for chlorine, D for chlorine dioxide, Z for ozone, P for peroxide, Pa for peracetic acid, O for oxygen, Q for chelation, and Px for mixed peracids. In this specification the notation P
A
is used for the combined addition of a bleaching solution containing hydrogen peroxide and a peracid formed by reaction of the hydrogen peroxide with an agglomerated bleach activator.
TAED is produced as a fine white crystalline powder. Its main use is as a bleach activator for perborate and percarbonate salts in granulated laundry detergent formulations. TAED is normally used in a laundry detergent formulation which contains a large amount of anionic surfactant. In this environment the main problem facing the skilled person is to keep water away from the TAED during storage. To give increased stability and to prevent segregation due to size differences the TAED is therefore agglomerated using one or more binders. A commonly used binder is Sodium Carboxymethylcellulose. The agglomerate typically contains from 80 to about 90% TAED and the remainder is made up of the binder system and optional disintegration and dispersion aids together with other minor components such as pigments, colorants and sequestrants. Sometimes it is beneficial to utilise a co-binder as specified in EP0764717. TAED has also been proposed to be formed into noodles by extrusion. GB1395006 teaches formation of such noodles using 25% by weight of an anionic surfactant mixture including Sodium Laurylsulphate as the binder. Nonionic surfactants with a melting point greater than 35° C. have also been proposed as binders, they are usually heated during the manufacture e.g. using the spray-melt process of DE 2406455. In practice the remainder of the detergent formulation is critical to the successful dispersion and dissolution of the activator as it provides the necessary pH control and surfactants.
WO9418298 describes a bleaching process where an N-acyl bleach activator is reacted with a source of hydrogen peroxide under acid conditions. The product of this reaction may be used in many bleaching and disinfection applications, including pulp and paper bleaching. The activator and other components may be in the form of particles and these particles may be provided by techniques similar to those used in the laundry detergent industry For instance by spray drying liquid slurries; by granulation techniques using binders, for instance synthetic or natural polymers (or derivatives); or by melt blending followed by extrusion or other techniques. A composite product including a bleach activator may also include other additives, especially heavy metal sequestrants and it may include surfactants to act as wetting agents and inorganic salts to act as a diluent or to increase the rate of disintegration or dissolution of the product. The composite product should also include the source of the hydrogen peroxide as well as the bleach activator when it includes the wetting agent. Only two granulated activator particles are exemplified in this document; both contain carboxymethyl cellulose as a binder and neither is used for pulp bleaching.
WO9725402 proposes the use of bleach activators such as TAED for various applications including pulp bleaching. The preferred form of the TAED is a granule, but no details are given of the composition of the granule.
WO9517497 describes a process for preparing a particulate composition containing a liquid bleach activator, a thickener which is preferred to be a polyhydroxy fatty acid amide surfactant and optional filler and non-amide solubilising surfactants. The optional solubilising surfactants may be anionic especially C
11-13
linear alkylbenzenesulphonates, the optional particulate filler material is selected from a group of materials which includes: sodium acetate, sodium phosphate, sodium acid phosphite and sodium sulphate, however, all the examples use sodium alumino-silicate.
WO9800504 discloses the use of an anionic surfactant as part of the binder system for a bleach activator agglomerate. A wide range of bleach precursors are suggested to be suitable, including TAED. Formulation 4 of Example 1 is a bleach precursor particulate containing 65% TAED, 9.8% sodium linear C
12
alkyl benzenesulphonate (anionic surfactant), 0.3% C
2-4
predominantly linear primary alcohol condensed with an average of 3 moles of ethylene oxide (nonionic surfactant), 0.96% sodium toluene
Chadwick Mark Ardern
Turner Neil Anthony
Williams Jane
Withenshaw John David
Alvo Steve
Warwick International Group Limited
Watts Hoffmann Fisher & Heinke
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