Method of dewatering pulp

Details Method of dewatering pulp Method of dewatering pulp

2002-06-18

2004-03-16

Chin, Peter (Department: 1731)

Paper making and fiber liberation

Processes of chemical liberation, recovery or purification...

Treatment with particular chemical

C162S077000, C210S728000

Reexamination Certificate

active

06706144

ABSTRACT:

TECHNICAL FIELD
This invention concerns the use of a mixture of nonionic and anionic surfactants to assist in the dewatering of aqueous slurries of cellulosic pulp.
BACKGROUND OF THE INVENTION
Various surfactants have been used to assist in the removal of water from aqueous slurries or mats of fibrous materials. For Example, the use of anionic surfactants to assist in the dewatering of cellulosic papermaking slurries on a fourdrinier or cylinder machine is disclosed in International Patent Application Number PCT/US01/20276. A method of dewatering an aqueous mineral wool slurry on fourdrinier machine assisted by an anionic, nonionic or cationic surfactant is disclosed in U.S. Pat. No. 4,062,721. There exists, however, an ongoing need for improved additives to improve the efficiency and flexibility of the dewatering process, particularly for market pulps, which are prepared at one site and then transported to the papermaking site.
SUMMARY OF THE INVENTION
We have discovered that using a combination of nonionic and anionic surfactants in a process for dewatering aqueous cellulosic slurries results in increased dewatering effectiveness over the use of either surfactant alone.
Accordingly, in its principal aspect, this invention is directed to a method of dewatering an aqueous cellulosic pulp slurry comprising
a) adding to an aqueous slurry of washed cellulosic pulp an effective dewatering amount of a mixture of one or more nonionic surfactants and one or more anionic surfactants; and
b) dewatering the pulp.
Use of nonionic surfactants in combination with anionic surfactants makes the anionic surfactants more efficient as a dewatering aid, allowing the same effectiveness (in terms of consistency improvement) at lower anionic surfactant dose and further provides the ability to achieve effectiveness levels not possible using anionic surfactants alone.
Lowering the anionic surfactant dose also decreases the amount of cationic demand introduced to the mill's water systems.
Finally, the dual surfactant system of this invention allows for greater flexibility in tailoring a dewatering program to a particular machine's dewatering needs regarding performance, runnability, and cost.
DETAILED DESCRIPTION OF THE INVENTION
Definitions of Terms
“Alcohol Alkoxy Sulfate” means an anionic surfactant compound of formula R
2
O(R
3
CH
2
CH
2
O)
x
SO
3
−
M
+
where R
2
is C
8
-C
18
alkyl, R
3
is absent or methylene a from 1 to about 50. The alcohol alkoxy sulfate may be in the salt form where M a counterion such as Na, K, Mg, NH
4
, and the like, or in the acid form where M is H. Representative alcohol alkoxy sulfates include sodium and ammonium lauryl ether sulfate. Alcohol alkoxy sulfates are available from Stepan Company, Northfield, Ill.
“Alcohol Alkoxylate” means a nonionic surfactant compound of formula R
6
O(C
2
H
4
O)
x
(C
3
H
6
O)
y
H where R
6
is C
8
-C
24
alkyl, x is 1-20 and y is 1-20. the alcohol alkoxylate is prepared by reacting a C
8
-C
24
alkyl alcohol, or mixture of C
8
-C
24
alkyl alcohols, both designated herein as R
6
OH, with propylene oxide and optionally ethylene oxide. The ethylene oxide and propylene oxide may be added in random or block fashion. Alcohol alkoxylates are available from Huntsman Corporation, Houston, Tex.
“Alcohol Ethoxylate” means a nonionic surfactant compound or mixture of compounds of formula R
1
O(CH
2
CH
2
O)
n
H where R
1
is C
5
-C
25
alkyl or C
5
-C
25
hydroxyalkyl and n is 1-30. Preferred alcohol ethoxylates are those where R
1
is C
8
-C
18
alkyl or C
8
-C
18
hydroxyalkyl and n is 1-20. Alcohol ethoxylates are available from Union Carbide, Danbury, Conn. under the tradename Tergitol and from Sasol North America Inc., Houston, Tex. under the trade name Alfonic.
“Alcohol Sulfate” means compounds of the formula R
2
OSO
3
M, where R
2
and M are defined herein. Representative alcohol sulfates include sodium dodecyl sulfate, tetradecyl sulfate, ammonium lauryl sulfate, magnesium lauryl sulfate, cetyl sulfate, octyl sulfate, nonyl sulfate, decyl sulfate, 4-undeconal, 7-ethyl-2-methyl-sulfate, sodium salt (Niaproof Anionic Surfactant 4, available from Niacet Corporation, Niagra Falls, N.Y.), and the like.
“Alkoxy” and “alkoxyl” mean an alkyl-O— group wherein alkyl is defined herein. Representative alkoxy groups include methoxyl, ethoxyl, propoxyl, butoxyl, and the like.
“Alkyl” means a monovalent group derived from a straight or branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Representative alkyl groups include methyl, ethyl, n- and iso-propyl, and the like.
“Alkyl phenol ethoxylate” means a nonionic surfactant compound of formula R
5
O(CH
2
CH
2
O)
p
H where R
5
is phenyl, optionally substituted with one or two C
8
-C
12
alkyl groups and p is 1-30 Preferred alkyl phenol ethoxylates are those where where R
5
is phenyl substituted with C
9
alkyl and p is 1-20 Alkyl phenol ethoxylates are available from Rhodia Inc., Cranbury, N.J. under the trade name Igepal.
“Alkylene” means a divalent group derived from a straight or branched chain saturated hydrocarbon by the removal of two hydrogen atoms. Representative alkylene groups include methylene, ethylene, propylene, and the like.
“Aryl” means an aromatic monocyclic or multicyclic ring system of about 6 to about 20 carbon atoms, preferably of about 6 to about 10 carbon atoms. Aryl also includes ring systems where two aryl groups are connected through alkylene, alkenylene or alkynylene groups. The aryl is optionally substituted with one or more alkyl, alkoxy or haloalkyl groups. Representative aryl groups include phenyl, biphenyl, naphthyl, cis- and trans-stilbene, biphenylmethyl, diphenylacetylene, and the like.
“Arylalkyl” means means an aryl group attached to the parent molecular moiety through a C
1
-C
8
alkylene group. C
1
-C
2
alkylene groups are preferred. Representative arylalkyl groups include phenylmethyl, phenylethyl, phenylpropyl, 1-naphthylmethyl, and the like.
“Cellulosic pulp” means a mixture of fibers derived from kraft or sulfite pulping of cellulosic materials such as wood. Representative cellulosic pulps include bleached and unbleached pulps and dissolving pulps. Typical bleached pulps contain about 60 to about 70 percent cellulose, about 30 to about 40 percent hemicellulose and less than about one percent lignin. Unbleached pulps generally contain about 65 to about 75 percent cellulose, about 20 to about 30 percent hemicellulose and up to about 5 percent lignin. Dissolving pulps are about 100 percent cellulose.
“Cycloalkyl” means a non-aromatic mono- or multicyclic ring system of about 5 to about 10 carbon atoms. Preferred ring sizes of rings of the ring system include about 5 to about 6 ring atoms. The cycloalkyl is optionally substituted with one or more substituents selected from alkyl, alkoxy and haloalkyl. Representative cycloalkyl include cyclopentyl, cyclohexyl, cycloheptyl, and the like.
“Dialkyl sulfosuccinate” means an anionic surfactant compound of formula R
9
OOCCH
2
CH(SO
3
M)COOR
10
, where R
9
and R
10
are independently selected from amyl, octyl, 2-ethyl hexyl, isobutyl, tridecyl, or lauryl and M is as defined herein. A representative dialkyl is dioctylsulfosuccinate. Dialkyl sulfosuccinates are commercially available from Cytec Industries, West Patterson, N.J.
“Fatty Acid Ethoxylate” means a nonionic surfactant compound of formula R
7
COO(CH
2
CH
2
O)
r
H where R
7
is C
7
-C
25
alkyl and r is 1-30. Fatty acid ethoxylates are commercially available from Henkel Corporation, Emery Group, Ambler, Pa.
“Hydroxyalkyl” means a C
1
-C
8
alkyl substituted by one to three hydroxyl groups with the proviso that no more than one hydroxy group may be attached to a single carbon atom of the alkyl group. Representative hydroxyalkyl include hydroxyethyl, 2-hydroxypropyl, and the like.
“Market pulp” means chemical paper grade pulps which are typically sold on the open market to non-integrated paper mills (i.e. paper mills not having a pulp mill on-site). Market pulp also includes fluff pulp, which is used in diapers and relat

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