Removal of stickies in the recycling of paper and paperboard

Abstract

Removal of stickies from waste paper and paperboard is obtained with the use of a modified kaolin-based stickies removal composition. The modified kaolin-based stickies removal composition is produced by modifying the kaolin clay, separating the modified kaolin clay from the non-reactive kaolin clay, and then adding a nonionic surfactant to the modified kaolin-based particles. Removal of stickies is improved by the use of this modified kaolin-based stickies removal composition during the recycling of the waste paper and paperboard.

Claims

1. A method of removing stickies particles from waste paperboard, the method comprising: forming a pulp of waste paperboard product; adding a composition comprising a nonionic surfactant and a modified kaolin-based stickies removal component to said pulp to form a mixture; and subjecting said mixture to a stickies removal operation, wherein said stickies removal operation is selected from the group comprising centrifugation or screening; wherein said nonionic surfactant is selected from a group comprising polyethylene glycol esters, polypropylene glycol esters or blends thereof.

2. The method of claim 1, wherein said stickies removal operation comprises centrifugation.

3. The method of claim 1, wherein said stickies removal operation comprises screening.

4. The method of claim 1, wherein said stickies removal operation does not include flotation.

5. The method of claim 1, wherein said mixture comprises said composition in a concentration of from 0.2 to 20 pounds of composition per dry ton of waste paperboard in said pulp.

6. The method of claim 5, wherein said mixture comprises said composition in a concentration of 1-2 pounds of composition per dry ton of waste paperboard in said pulp.

7. The method of claim 1, wherein said modified kaolin-based stickies removal component is produced by a process which comprises: forming a slurry of dispersed kaolin clay particles; treating the dispersed kaolin clay particles with a modifying reagent; and separating the modified kaolin-based particles from the non-reactive kaolin-based particles.

8. The method of claim 7, wherein the modifying reagent is selected from a group comprising a fatty acid, hydroxamate, sulfonate, amine, siloxane, silane, sulfhydryl, or blends thereof.

9. The method of claim 1, wherein said pulp is formed by a process comprising: shredding said waste paperboard product to form a shredded waste product; and mixing said shredded waste product with hot tap water.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention provides a stickies removal composition which comprises a modified kaolin-based component and a surfactant.

(2) In accordance with the present invention, the kaolin clay particles are first dispersed into a slurry form and then mixed with a surface modifying agent to modify the surface of the kaolin clay particles.

(3) The surface modifying agents that may be used to prepare the modified kaolin-based component include (but are not limited to) hydroxamates, fatty acids, sulfonates, amines, siloxanes, silanes, sulfhydryl, and blends of such agents. The modified kaolin-based particles are then concentrated and separated from the non-reactive kaolin-based particles.

(4) Methods of separating the modified particles include flotation and selective flocculation. In the case of flotation, the modified particles are transferred to a flotation cell and floated. The modified kaolin-based particles after separation from the non-reactive kaolin-based material are then mixed with a surfactant to produce a modified kaolin-based composition that can be used as a stickies removal agent for improving the removal of stickies during the various operations of the paper recycling process.

(5) Crude kaolin clay generally contains kaolinite and other related hydrated aluminum silicate minerals as well as quartz, mica, titanium dioxide and iron oxide minerals.

(6) In a preferred embodiment, to produce the modified kaolin-based component of this invention, the starting crude kaolin clay is initially dispersed by blunging the clay with water in the presence of a dispersant at dosages ranging from about 1 to about 25 pounds per ton of dry solids. Effective dispersants include sodium silicate, sodium metasilicate, sodium hexametaphosphate, and sodium polyacrylate. The preferred dispersant for this invention is sodium silicate using dosages ranging from about 2 to about 16 pounds per ton of dry clay. The pH is adjusted to a range of about 5 to about 11, preferably about 7 to about 10, using a pH modifier such as sodium hydroxide, sodium carbonate or ammonium hydroxide.

(7) The dispersed kaolin clay slurry is then mixed with a surface modifying reagent such as alkyl hydroxamate, fatty acid, siloxane, silane, or a combination of such reagents. The amount of surface modifying reagent added to the dispersed kaolin slurry must be sufficient to surface modify the crude kaolin clay. The surface modifying reagents used are in the range of about 0.2 to about 10 pounds per ton of dry clay, preferably about 0.5 to about 5 pounds per ton.

(8) After mixing with the surface modifying reagent, the kaolin slurry is then transferred to a froth flotation cell and, if necessary, diluted to a pulp density preferably within the range of about 15% to about 45% solids by weight. The operation of the froth flotation machine is conducted in conventional fashion. After an appropriate period of operation, the surface modified kaolin clay particles are concentrated in the froth phase and collected.

(9) In the production of the modified kaolin-based particles for the present invention, the froth flotation process can be conducted either in a mechanical or pneumatic machine. A typical pneumatic machine that can be used is a flotation column, while a typical mechanical machine is an impeller driven flotation machine. The modified material in this invention can also be produced by flotation through the use of other flotation processes such as dissolved air flotation, induced air flotation, bulk oil flotation, skin flotation or table flotation.

(10) During the flotation process, the mineral components of kaolin that are reactive to the modifying reagents will be separated from the non-reactive mineral components of kaolin. Note that only the reactive mineral components of kaolin that have been modified by the modifying reagents are used to produce the modified kaolin-based component of this invention.

(11) The hydroxamate agent used in the present invention is a hydroxamate compound, or a mixture of such compounds, having the general formula:

(12) ##STR00001##
in which R is an alkyl, aryl or alkylaryl group having 4 to 28 carbon atoms, and M is hydrogen, an alkali metal or an alkaline earth metal.

(13) Examples of suitable R groups include butyl, hexyl, octyl, dodecyl, lauryl, 2-ethylhexyl, oleyl, eicosyl, phenyl, tolyl, naphtyl and hexylphenyl.

(14) Examples of suitable alkali metals are lithium, sodium and potassium.

(15) Examples of suitable alkaline earth metals are magnesium, calcium and barium.

(16) In this invention, the fatty acid used has the general formula:

(17) ##STR00002##
in which R′ is an alkyl, aryl or alkylaryl group having 1 to 26 carbon atoms, and M′ is hydrogen, an alkali metal or an alkaline earth metal.

(18) Examples of suitable R′ groups include methyl, ethyl, butyl, octyl, lauryl, 2-ethylhexyl, oleyl, eicoseyl, phenyl, naphtyl and hexylphenyl.

(19) Examples of suitable alkali metals are lithium, sodium and potassium.

(20) Examples of suitable alkaline earth metals are magnesium, calcium and barium.

(21) The siloxanes used in the present invention are organosilane compounds containing a silicon to carbon bond. Examples of suitable siloxanes include hexamethyldisiloxane, hexamethylytrisiloxane, disiloxane, vinylbeptamethyltrisiloxane, octamethyltrisiloxane, tetramethyldisiloxane, tetravinyldimethyldisiloxane, polydimethylsiloxanes, polymethylhydrosiloxanes, polyethylhydrosiloxanes and polymethylalkylsiloxanes.

(22) The silanes used in the present invention are inorganic compounds with the general formula:
Si.sub.n—H.sub.2n+2

(23) Examples of suitable silanes are methyltriethoxysilane, octyldimethylchlorosilane, methyltris(methoxyethoxy)silane, octyltrichlorosilane, and phenyltrimethoxysilane.

(24) A nonionic surfactant is then blended with the modified kaolin-based particles to produce the modified kaolin-based composition for removing stickies of this invention. The nonionic surfactants used in this invention can be any of those which is known in the industry for similar applications. Examples of suitable surfactants are fatty acid ethoxylates, fatty alcohol ethoxylates, castor oil ethoxylates, polyethylene glycol esters, and polypropylene glycol esters.

(25) The inventive composition comprising the modified kaolin-based particles, produced as described herein, and a nonionic surfactant may then be used in contaminant removal methods known in the art of waste paper and waste paperboard processing, including centrifugation, flotation, deinking, washing, screening/fine screening, etc. In these methods, the inventive composition is added to a pulp or slurry comprising waste paper or paperboard including but not limited to old newspaper (ONP), old magazine (OMG), mixed office waste (MOW), sorted white ledger (SWL), sorted office paper (SOP), and old corrugated carton (OCC). Typically, the waste paper/paperboard slurry is formed from mixing waste paper/paperboard materials with a liquid comprising water and sometimes additional chemicals to assist in breakdown of the starting waste product. The waste paper pulp may further be heated and/or chopped to further aid in the breakdown of the raw waste material. The inventive composition described herein may be added with the liquid to form the pulp/slurry (or may be incorporated therein) or may be added after any of the operations described herein, i.e. slurry formation, chopping, and/or heating. The waste paper pulp and inventive composition mixture may then be subjected to any of the known means of stickies removal described herein, namely centrifugation, flotation, washing, deinking, screening/fine screening, or the like, but is preferably subject to a centrifugation process to remove the stickies which now have a higher specific gravity due to their bond with the inventive kaolin composition described herein. In other preferred embodiments, the waste paper pulp and inventive composition mixture is subjected to a screening operation where stickies are removed due to their larger size owing to their bond with the inventive kaolin composition described herein. Also as noted above, the inventive composition has a particular advantage in the washing process of contaminant removal, in that the inventive composition does not generate excessive foam during the washing process, and so in other preferred embodiments, the waste paper pulp and inventive composition mixture is subjected to a washing process.

(26) The inventive composition described herein may be used in a concentration of roughly 0.2 to 20 pounds of composition per dry ton of waste paper/paperboard starting product, but is preferably used in a concentration of 1-5 pounds per dry ton of waste paper/paperboard starting product, and most preferably used in a concentration of 1-2 pounds per dry ton of waste paper/paperboard starting product.

(27) The present invention is further illustrated by the following examples which are illustrative of certain embodiments designed to teach those of ordinary skill in this art how to practice this invention and to represent the best mode contemplated for carrying out this invention.

Example 1

(28) A sample of kaolin clay from Washington County, Ga. was modified and the modified kaolin-based material is then separated from the non-reactive kaolin-based material using the following procedure.

(29) 2000 dry grams of a crude kaolin clay sample were blunged using a high speed mixer. Blunging of the clay was conducted at 62% solids using 7 pounds sodium silicate per ton of dry clay and 1.5 pounds sodium hydroxide per ton of dry clay. The dispersed kaolin clay was then modified with the following reagents: 1 pound alkyl hydroxamate per ton of dry clay, 1 pound tall oil per ton of dry clay and 0.5 pound calcium chloride per ton of dry clay as activator for tall oil. The treated material was diluted to 25% solids with water and then transferred to a Denver D-12 flotation cell. The slurry was then floated to separate the modified mineral components in kaolin from the non-reactive mineral components in the kaolin clay. The modified kaolin-based material was then collected in the froth phase. This material was then dewatered to remove some of the water present in the collected slurry.

(30) The modified kaolin-based material produced in Example 1 is used as the modified kaolin-based stickies removal component, which is then blended with a nonionic surfactant to produce the modified kaolin-based stickies removal agent composition of this invention.

(31) Table 1 shows the differences in the properties of the starting kaolin clay, the non-reactive kaolin-based material, the modified kaolin-based stickies removal component and the modified kaolin-based stickies removal composition. As shown, the modified kaolin-based stickies removal component and the modified kaolin-based stickies removal composition are different from the kaolin clay starting material and the non-reactive kaolin-based material in particle size distribution and chemical composition. The modified kaolin-based stickies removal component and modified kaolin-based stickies removal composition have a coarser particle size distribution with fewer particles finer than 2 microns compared to the starting kaolin clay and the non-reactive kaolin-based material. The chemical composition of the modified kaolin-based stickies removal component and modified kaolin-based stickies removal composition as analyzed by X-ray fluorescence have lower amounts of aluminum and silicon oxides but higher amounts of titanium and iron oxides compared to the starting kaolin clay and non-reactive material.

(32) In addition, due to the blunging of the crude kaolin clay in the presence of a dispersant such as sodium silicate and its pH adjusted to about pH 5 to 11 with a pH modifier such as sodium hydroxide, the resulting modified kaolin-based stickies removal component and modified kaolin-based stickies removal composition are different because the dispersants have modified the surface property of kaolin which now has the dispersant adsorbed on its surface. The crude kaolin clay does not naturally have these adsorbed dispersant chemicals on its surface. In addition, the modified kaolin-based stickies removal component and modified kaolin-based stickies removal composition contain the modifying reagents such as alkyl hydroxamate on their surfaces (see Table 1). These differences allow the modified kaolin-based stickies removal composition to be effective in removing stickies from waste paper and paperboard.

(33) TABLE-US-00001 TABLE 1 Alkyl Particle Size Distribution, % Hydroxamate Passing XRF Chemical Analysis Material Content, ppm 2 μm 1 μm 0.5 μm 0.2 μm Al.sub.2O.sub.3 SiO.sub.2 TiO.sub.2 Fe.sub.2O.sub.3 Si/Al Ratio Kaolin Clay 0 59 45 29 15 37.8 44.7 1.6 0.4 1 Non-Reactive 0 61 48 32 14 38.8 45.6 0.3 0.3 1 Kaolin-Based Material Modified 63 15 6 4 — 28.3 31.1 26.4 0.9 0.93 Kaolin-Based Stickies Removal Component Modified 42 15 6 4 — 28.3 31.1 26.4 0.9 0.93 Kaolin-Based Stickies Removal Composition

Example 2

(34) The fine screening test procedure used in this work is as follows:

(35) 300 gm of old corrugated cardboard (OCC) was shredded and then mixed with hot tap water to 5% solids. The kaolin clay used as the starting material in Example 1 is added here at the rate of 1 pound of kaolin clay per dry ton of OCC. The sample was pulped for 10 minutes in a laboratory pulper. After pulping, the sample was diluted to 1% solids and screened using a fine screen having slots of 0.006″. After screening, the refuse containing the stickies was collected and the amount of stickies removed by fine screening was measured. For the stickies measurement, the stickies were separated from the fiber using a Pulmac Masterscreen and then quantified using the Transparency Film Lamination method. The Pulmac Sticky Scan 200 was used for the quantification of the stickies amount through image analysis. The results are given in Table 2.

(36) In other embodiments, the raw recycled paper product may be shredded and mixed with tap water to a different percentage of solids than that used herein for OCC. The percentage solids may be dictated by the application, and could be anywhere from 2 to 25% solids depending on the starting product.

Example 3

(37) The fine screening test procedure used in Example 2 was repeated on an OCC sample. In Example 3, 1 pound of the non-reactive kaolin-based material produced in Example 1 per dry ton of OCC was used instead. The results of the laboratory screening test are presented in Table 2.

Example 4

(38) Another fine screening test was conducted using the same fine screening test procedures used in Example 2 on an OCC sample. For this test (Example 4), 1 pound of the modified kaolin-based stickies removal component produced in Example 1 per dry ton of OCC was used instead. Table 2 shows the results of the laboratory screening test.

Example 5

(39) The procedure used for the laboratory fine screening test used in Example 2 was repeated using 1 pound of the modified kaolin-based stickies removal composition, including the herein described modified kaolin-based stickies removal component with the addition of a nonionic surfactant, produced in Example 1, per dry ton of OCC. The results of the screening test are presented in Table 2.

(40) As shown, the starting kaolin clay material, the non-reactive kaolin-based material produced from the kaolin clay in Example 1 and the modified kaolin-based stickies removal component produced in Example 1 did not remove any stickies. When the nonionic surfactant was added to the modified kaolin-based stickies removal component to produce the modified kaolin-based stickies removal composition, the use of this composition resulted in significant stickies removal.

(41) TABLE-US-00002 TABLE 2 Amount of Material Used Stickies Removed, as Stickies Removal Reagent ppm Kaolin Clay 0 Non-Reactive Kaolin-Based Material 0 Modified Kaolin-Based Stickies 0 Removal Component Modified Kaolin-Based Stickies 36 Removal Composition

(42) This invention has been described in detail with particular reference to certain embodiments, but variations and modifications can be made without departing from the spirit and scope of the invention as defined in the following claims.