DEFOAMER COMPOSITION

Abstract: A pulp mill washing defoamer composition is provided containing a cationically-charged species along with other conventional components. The presence of the cationically-charged species leads to a more efficient washing of the pulp, as well as achieving the required defoaming.

Description: DEFOAMER COMPOSITION FIELD OF INVENTION This invention relates to a defoamer composition for use in pulp washing. BACKGROUND TO THE INVENTION In the formation of wood pulp from which paper is made, one commonly-employed procedure involves chemical treatment of wood chips to dissolve lignin and free the cellulosic fibres from the wood chips in a digestion operation, such as by Kraft process. The resulting slurry of wood fibres in spent digestion chemicals, or black liquor, then is passed to a brown stock washing operation wherein the pulp is washed to remove the black liquor, which contains a variety of sodium salts and lignin. The washed pulp then usually is passed to a bleach plant wherein the pulp is bleached and further purified to provide the desired product. Foaming occurs during such washing and it is conventional to add a defoamer composition to the pulp during such washing. Such composition may be a composition as described in our Canadian Patent No. 1,069,742, the disclosure of which is incorporated herein by reference, comprising a suspension of finely- divided hydrophobic lubricating particles in a suitable carrier liquid. The defoamer composition also may be aqueous based, as described, for example, in our copending Canadian Patent application Serial No. 2,048,823 filed August 8, 1991, the disclosure of which is incorporated herein by reference. SUMMARY OF INVENTION In accordance with the present invention, there is provided an improved defoamer composition which comprises at least one water-soluble cationically- charged species as a component of the composition. The presence of the cationically-charged species results more uniform washing of the pulp and hence m efficient use of the defoamer components during s washing. GENERAL DESCRIPTION OF INVENTION The water-soluble cationically-charged speci employed in the improved defoamer composition of t invention may be selected from a variety of su materials which are capable of forming a solid produ by ionic interaction with lignin in the pulp. T water-soluble cationically-charged species may compri a cationic polymeric material, a cationic surfactant mixture of such species. Preferably, a cationic wate soluble polymer possesses a high charge density so as form the solid product readily and a lower molecul weight, so as to be readily water-soluble while n significantly altering the wash water properties. Examples of such cationic water-soluble polyme may include high molecular weight, cation polyacrylamide with low charge density, low molecul weight, highly charged cationic polyacrylamide, cation starches with low charge density poly(ethleneimines which may be quaternized, and other cationic wate soluble polymers. Other water-soluble polymeric components, such water-soluble non-ionic polymers, also may be present the wash water, if desired, along with the cationicall charged species, such as wash water containing wate soluble cationic polymers and/or cationic surfactant and water-soluble non-ionic polymers. The quantity of the cationically-charged speci required to achieve an improvement in washing efficien is quite small and, to some extent, is determined by t concentration of lignin in the pulp mat and the char on the species. The quantity of such cationicall charged species required to ef ect such improvement m vary widely, for example, from about 0.1 up to about 20 wt% of the defoamer composition. The defoamer composition of the invention further comprises other defoaming components conventionally found in defoamer compositions, for example, a suspension of finely-divided hydrophobic lubricating particles in a suitable carrier liquid, as described in the above-mentioned Canadian Patent 1,069,742. The carrier liquid also acts as the carrier liquid for the cationically-charged species and may be any convenient hydrocarbon oil. The liquid hydrocarbon oil may be any inert liquid aliphatic, alicyclic or aromatic hydrocarbon or mixture thereof. The hydrocarbon should be liquid at room temperature and atmospheric pressure, have a viscosity of from about 30 to about 400 SUS at 100°F and an average of from about 6 to about 25 carbon atoms. The finely-divided hydrophobic lubricating particles may include hydrophobic silica particles, hydrophobic oil-insoluble wax particles, or mixtures of the two. Such hydrophobic silica particles usually are precipitated silica particles which have the surface rendered hydrophobic by the use of an oil or other hydrophobic material, such as, a suitable silicone. The hydrophobic oil-insoluble wax particles usually are waxy fatty acid amide particles, generally those formed by reaction of a polyamine containing at least one alkylene group having from 2 to 6 carbon atoms and a fatty acid having from five to twenty-two carbon atoms excluding the carboxyl group carbon. Among the fatty acids which may be used are hexanoic, decanoic, lauric, palmitic, oleic, stearic, ricinoleic, naphthenic acids obtained as by-products from the refining of petroleum, tall oil acids and tallow fatty acids. Polyamines which may be used include ethyl diamine, butylene diamine, diethylene triami triethylene tetramine, " hexamethylene diami decamethylene diamine, hydroxyethyl ethylene diamine l:3-diamino-2-propanol. Examples of suitable hydrophobic amides methylene bis acrylamide, methylene bis pelargonami ethylene bis capramide, methylene bis laurami methylene bis myristamide, methylene bis palmitami methylene bis stearamide, ethylene-bis-εtearami ethylene bis arachidamide and ethylene bis behenamid It is preferred to use mixtures of hydropho silica particles and hydrophobic amide particles as finely-divided hydrophobic lubricating particles. weight ratio of the components of such mixtures may v widely, such as, from about 1:9 to about 9:1, typica about 1:1. The particle size of the finely-divided partic in the composition may vary widely and is colloidal magnitude. The particle size is generally less th about 20 microns, preferably less than about 10 micron There is usually a range of particle sizes in t composition. The proportions of the components of t composition may vary widely although the content finely-divided hydrophobic particulate materi generally does not exceed about 25% by weight of t composition, and quantities as low as about 1% by weig may be used. Preferably, the hydrophobic particl constitute about 5 to about 15% by weight of t composition. The composition may optionally contain min quantities of other components. One such addition component is a spreading agent which may be one or mo anionic, cationic or non-ionic surfactant. Examples of suitable anionic surfactants are fatty acids containing from about 12 to about 22 carbon atoms, soaps of the fatty acids, alkali metal salts of alkyl-aryl sulfonic acids, sulfated or sulfonated oils and alkali metal salts of short chain petroleum sulfonic acids. Examples of suitable cationic surfactants are salts of long chain primary, secondary or tertiary amines and quaternary salts. Examples of suitable non-ionic surfactants are alkoxylated higher fatty alcohols, alkoxylated alkyl phenols, alkoxylated fatty acid amides, polyethylene glycol esters of long chain fatty acids, sorbitans. Spans and Tweens. The spreading agent assists in the spreading of the carrier in the aqueous slurry and hence in the " distribution and penetration of the lubricating particles into the slurry. The quantity of spreading agent used may vary widely, and is generally less than about 7% by weight of the composition, preferably in the range of about 1 to about 2% by weight of the composition. Another minor component which may be included in the composition is a silicone oil, which may be a polysiloxane, for example, a dimethyl polysiloxane. When present, small quantities of silicone oil of from about 0.1 to about 2% by weight are used, preferably about 0.1 to about 1% by weight. Another minor component which may be present is a colloidal or fumed silica which acts as a thickening agent for the composition. Such silica may be present in quantities up to about 5% by weight, preferably about 0.05 to about 0.5% by weight. An alcohol also may be included in the composition to act as a stabilizer. The alcohols which may be used include short chain aliphatic alcohols, for example, isopropyl alcohol. Quantities of such alcohol may var from about 0.3 up to about 2% by weight and preferabl are in the range of about-0.5 to about 1% by weight. One further minor component which may be present i the composition is a fatty acid ester which functions a a dispersing agent and viscosity cutter. This componen may be any fatty acid ester of a long chain fatty acid, such as, a fatty acid having about 5 to about 22 carbo atoms in the chain, and a lower alcohol, such as one having from 1 to 6 carbon atoms. The fatty acid este may be present in the composition in an amount of about 0.4 to about 2% by weight of the composition, preferably about 0.5 to about 1% by weight. As mentioned above, the quantity of cationically- charged species also may vary widely and may comprise from about 0.1 to about 20 wt% of the defoamer composition. In addition to such oil-based defoamer compositions, the defoamer composition incorporating the cationically-charged species may be aqueous based, as described in the aforementioned Canadian Serial No. 2,048,823. In such compositions, components essential to the composition are hydrophobic silica, silicone oil, liquid hydrocarbon oil, water and emulsifiers. Optional components comprise ethylene bis-stearamide and non- ionic surfactants, along with the cationically-charged species. Such essential components may be present in the following proportions: General Preferred Ranσe Ranσe Hydrophobic silica about 1 to about 10 t% about 2 to about 5 wt% Silicone oil about 10 to about 30 t% about 15 to about 25 t% Water about 20 to about 45 t% about 30 to about 40 wt% Process oil about 20 to about 45 t% about 25 to about 40 t% Emulsifiers about 0.5 to about 3 wt% about 1 to about 2 wt% The hydrophobic silica acts as a defoamer component of the composition. When present, generally in an amount of about 1 to -about 5 wt%, ethylene-bis- stearamide also acts as a defoamer component. The silicone oil may be a polysiloxane, for example, dimethyl polysiloxane. The liquid hydrocarbon oil may be any inert liquid aliphatic, alicyclic or aromatic hydrocarbon or mixture thereof. The liquid hydrocarbon oil generally has a viscosity of about 30 to about 400 SVS at 100°F and an average of about 6 to about 25 carbon atoms. One suitable hydrocarbon oil is hydrocarbon process oil. The emulsifier may comprise one of a wide variety of surfactants; When present, non-ionic surfactants, generally in an amount of about 1 to about 5 wt% may be any of a wide class of synthetic surfactants, such as ethoxylated and/or propoxylated long chain alcohols. The components of the defoamer composition employed herein are admixed together to form a homogenous composition, which is added to the pulp, usually kraft pulp, so as to be present at least during the early stages of washing. The composition is added in amounts sufficient to efficiently treat the pulp. The quantity employed depends on the nature of the pulp to be treated and the components present. Generally, the amount of defoamer composition employed may vary up to about 20 pounds per ton of pulp, typically about 1 to 2 pounds per ton of pulp. The defoamer composition of the invention exhibits improved washing properties as a result of the presence of the cationically-charged species, in providing a more uniform washing of the pulp, which in turn, enables a more efficient use of the defoamer component to be achieved. A lesser quantity of defoamer composition may be employed for the same level of final solids conten of the pulp. EXAMPLE A defoamer composition (Defoamer 540 PE) was prepared, comprising hydrophobic silica, hydrocarbon oil and a polyamide. This defoamer was used on the brown stock washers in a commercial pulp mill- for a four month trial. Tests carried out from time to time during the trial period indicated that efficient defoaming was achieved with a 15% increase in drainage of aqueous material from the pulp, corresponding to an increase of 1.5% of the solids content of the pulp obtained, at an applied quantity of about 40% less than conventionally applied for a conventional defoaming composition, from which the cationically-charged species (i.e. the polyamide) was absent. These results show the significant improvement in washing efficiency achieved by the presence of the cationically-charged species in the defoaming composition. SUMMARY OF DISCLOSURE In summary of this disclosure, the present invention provides a novel defoamer composition with improved washing properties which includes a water- soluble cationically-charged species along with other defoaming components. Modifications are possible within the scope of this invention.

Claims: CLAIMS 1. In a defoamer composition for use in the washing of wood pulp, the improvement which comprises at least one water-soluble cationically-charged species as a component of said composition. 2. The composition of claim 1 wherein said water- soluble cationically-charged species is at least one water-soluble cationic polymer and/or water-soluble cationic surfactant. 3. The composition of claim 2 wherein said water- soluble cationic polymer possesses a high charge density. 4. The composition of claim 1 wherein said water- soluble cationically-charged species is a polyacrylamide or polyamine. 5. The composition of claim 1 wherein said water- soluble cationically-charged species is present in said defoamer composition in an amount of from about 0.1 to about 20 wt%. 6. The composition of any one of claims 1, 2, 3, 4 or , 5 which is oil-based and contains a suspension of finely-divided hydrophobic lubricating particles and a liquid carrier for said particles and said cationically- charged species. 7. The composition of any one of claims 1, 2, 3, 4 or 5 which is water-based and contains hydrophobic silica, silicone oil, liquid hydrocarbon oil, water and emulsifiers along with the cationically-charged species.

Inventors: FLAHERTY EDWIN H, RAO MOHAN A, FLAHERTY, EDWIN, H., RAO, MOHAN, A.
Applicants: DORSET IND CHEMICALS LTD, DORSET INDUSTRIAL CHEMICALS LTD.
Application year: 1992
Main classification: B01D19
IPC codes: B01D19, D21C9