KR20010021612A - Use of cationic polyelectrolytes and surfactants in the deinking of wastepaper - Google Patents

Abstract

A method of improving ink removal and fiber recovery in dispersed bubble suspension of waste paper desulfurization filtrate, comprising adding a mixture of an alkoxylated tallow fatty acid surfactant and a cationic polyelectrolyte having an average molecular weight of less than about 2,000,000 to the filtrate Is disclosed.

Description

USE OF CATIONIC POLYELECTROLYTES AND SURFACTANTS IN THE DEINKING OF WASTEPAPER}

Long-distance bubble floating screening has been used to deinterpret paper stocks. By combining the surfactant chemistry and the appropriate bubble size distribution together, the ink particles are selectively fractionated into floating bubbles as rejects, but most papermaking fibers remain as acceptable. Currently, most demux plants use some type of dispersed bubble flotation. By properly devising and performing this method, large amounts of ink can be removed from the paper stock with minimal yield loss. It is generally known that there is a lower limit of the particle size of the ink, and particle sizes smaller than that are inefficient for the deinking method.

Scattered bubble flotation is usually carried out on a slurry of waste paper repulped in water. Surfactant-based suspension aids are mixed with the pulp slurry in the pulp group or added to the pulp slurry before entering the flotation tank. Cationic polyelectrolytes may be added to facilitate removal of the microparticles. Slurries introduced into the defrosting tank of the flotation method include fibers, fiber fines, fillers and ink particles. The slurry generally has a suspended solids content of about 10,000 ppm (or 1%), based on the volume of the total slurry. When the pulp slurry reaches the bottom of the flotation tank, the slurry is mixed with the flow of uncompressed ambient air by an impeller. The air flow enters the stock by the action of the stock flow and the impeller. The impeller distributes the bubbles into the stock. Turbulence is formed inside the flotation tank and has a residence time of 1 to 2 minutes. The diameter of the bubbles varies widely, but most have a diameter of about 500 to 2500 microns. The presence of the surfactant helps the hydrophobic ink particles contact the air / water interface of the bubbles and help them float on the interface. If the slurry concentration is too low (approximately less than 8,000 ppm), a large amount of long fibers will float at the interface, resulting in lower process yield. If the slurry concentration is too high (greater than about 12,000 ppm), the removal rate of the ink is reduced as a fiber network is formed and the ink particles are prevented from moving to the bubble surface.

The pulp stock is discharged from the flotation tank by weir overflow. When the stock is discharged, the bubble rejects are removed from the top, leaving less concentrated ink downstream than that present in the inflow. In the deoiling operation of the waste paper pulp, the floating sorting machine is used in series with anywhere from 2 to 8 units. In this series of units the reject of the "first unit" is often lowered to the second stage to improve fiber recovery. The allowance in the second stage is returned to the first line, where the reject in the second stage becomes more viscous and landfilled or incinerated.

Some methods in the art include the use of cationic polymers to increase the removal rate of fine ink particles during the dispersed bubble flotation process. For example, International Patent Publication No. WO 94/28237, which is incorporated herein by reference, discloses small (<5 μM) hydrophilic (ie, flexographic) ink particles in a dispersed bubble flotation demelting process. The use of cationic polymers with nonionic surfactants to increase the removal rate is disclosed. This treatment material is added to the waste paper pulp slurry. Polyamines and polyethyleneimines have been found to be particularly effective.

Japanese Patent No. 6,257,082 discloses a wide range of cationic, anionic, zwitterionic, and conventional chemicals for use in the bubble flotation deinking methods of "enamel-coated used" and "non-coated used". The use of nonionic low molecular weight and high molecular weight polymers is disclosed.

Some deinking plants rely solely on wash deinking methods to remove ink from waste paper pulp. The cleaning method is particularly effective for removing smaller ink particles. Washing deinking methods generally yield substantially higher yields than bubble flotation deinking methods. It is preferable from an economic point of view that the filtrate resulting from the washing operation is recycled to a subsequent dilution process. To remove the ink in the process, the ink must be removed from the filtrate before recycling the filtrate. Removal of ink from the filtrate is usually performed by dissolved air flotation (DAF). While dispersed bubble flotation is a selective separation method, the DAF method removes all suspended material from the stream and returns clean water. The ink is selectively separated, but it is impossible to leave paper fibers in the filtrate. Thus, yield loss is typically 20-30% of the solids introduced in a demelting plant that has relied primarily on cleaning deinking methods to remove the ink.

The present invention relates to the use of cationic polyelectrolytes and surfactants in the deinking process of waste paper.

The present invention provides a mixture of (a) an alkoxylated tallow fatty acid surfactant, and (b) a cationic polyelectrolyte up to about 20 ppm having an average molecular weight of less than about 2,000,000, or an intrinsic viscosity of less than about 2 dB / g. The present invention relates to a method for simultaneously improving the ink removal efficiency and fiber recovery rate of waste paper deinking filtrate in a dispersed bubble flotation method comprising adding an effective amount to the filtrate after washing the pulp. The method of the present invention effectively removes the ink and also provides a high process yield in the deinking of the paper stock.

The advantage of the present invention over the prior art is that it increases fiber recovery, reduces sludge disposal costs and improves separation of fillers over the prior art.

The process of the present invention is particularly useful for washing deinking processes in which it is desirable to increase the yield of the process without degrading the quality of the final product. The practice of these plants is to send the filtrate of the deodorizer to a dissolved bubble flotation (DAF) unit to remove as much suspended solids as possible (inks, fibers and fillers). In order to entangle the fine solids and remove them from the filtrate, low and high molecular weight polymers are added to the filtrate prior to the DAF unit (liquid drawn from the washing and thickening device containing dispersed fines, inks and fillers). The rejected solids remain as sludge in the DAF unit and are incinerated or landfilled after the viscosity is increased.

The present invention flows some or all of the filtrate of the de-icing washer from a DAF unit into a single dispersed bubble flotation tank. Multiple baths can be used in parallel to increase throughput. Before being introduced into the bubble flotation tank, the filtrate will be treated with a mixture of nonionic suspension aid and cationic polyelectrolyte. By air dispersed with this chemical treatment in the bubble flotation tank, the ink and filler particles float to the top of the bath and are removed as bubble rejects, which are incinerated or buried as the viscosity increases. When treated by the process of the present invention, up to about 70% of the usable fibers remain in the aqueous phase in the filtrate, while the ink and inorganic filler are optionally fractionated into foam rejects. In DAF, almost all fibers will be lost from the process, resulting in lower yields and increased waste disposal costs.

Foamy water or filtrate from weak turbulence washers (ie gravity decker) is treated in a dispersed bubble flotation tank. An example of this type of equipment is the Voice Flotation Machine. This equipment differs from, for example, a DAF purifier in its design and operation. The remaining surfactant in the wash deinking process provides sufficient foam with the air, so no additional conventional suspension aid chemicals are required to produce the foam. However, additional suspending aids (eg, block alkoxylated tallow fatty acids) improve the ink removal rate than when washing surfactants alone.

The mixture of the suspension aid and the cationic polyelectrolyte may be mixed into the filtrate before starting to float. The polyelectrolytes are branched or linear epichlorohydrin-dimethylamine condensates (polyamines), poly-diallyldimethylammonium chloride (poly-DADMAC), DADMAC-acrylamide copolymers (DADMAC / AM), polyethyleneimine (PEI) , Modified PEI, or polyamino-amide epichlorohydrin condensates (PAE), but is not limited thereto. The polymer has a relatively low molecular weight (generally less than 2,000,000 and a molecular weight of less than 1,000,000 is preferred) and acts as a coagulant rather than a coagulant. Application of the flocculant is believed to significantly increase the amount of fibers removed with the foam rejects.

The mixture of cationic polyelectrolyte and nonionic surfactant modifies the surface charge of small anionic ink particles and reduces their surface energy, allowing more particles to adhere to the bubble surface in the sorting tank and be removed with the bubble rejects. .

The product charge density for the compound (based on the active agent) is about 3 mEq / g for DADMAC / acrylamide copolymer and polyamidoamine-epichlorohydrin condensate to about 20 mEq / g for polyethyleneimine. Products with low charge densities of 1 mEq / g (based on active agent) are effective. The DADMAC / acrylamide copolymer may comprise from about 25 mole% DADMAC to about 75 mole% DADMAC, with the remainder of the copolymer composition being acrylamide.

Suspension aid dosages of about 10 to 30 ppm with respect to the product based on the total volume of the filtrate are preferred. Suspension aid dosages of about 1 to about 500 ppm based on the total volume of the filtrate can be effective.

The alkoxylated tallow fatty acids of the present invention are based on tallow, a naturally occurring substance. Tallow acid is approximately 40% C-18 mono-unsaturated fatty acid (oleic acid), 28% C-16 saturated fatty acid (palmitic acid), 22% C-18 saturated fatty acid (stearic acid), 4% C-14 saturated fatty acid (Mylistic acid), and 2% C-18 di-unsaturated fatty acid (linoleic acid), and other trace components are present. Fatty acid molecules each have an average of 21 moles of ethylene oxide and an average of 19 moles of propylene oxide bonded in block form. The molecule is capped propylene oxide. The fatty acid and propylene oxide ends on the molecule form a hydrophobic region, while the middle ethylene oxide moiety is hydrophilic. It is expected that different molar ratios of alkoxylates of different fatty acids are also effective as long as the compound remains water soluble.

A total polymer dosage of up to 10 ppm of active agent based on the total filtrate volume is preferred. A total polymer dosage of up to 5 ppm active agent based on total filtrate volume is preferred. Polymer dosages of 20 ppm active based on total filtrate volume have been found to reduce fiber recovery without significantly contributing to further ink removal.

Note that introducing only air into the float sorting tank substantially removes ink from the filtrate. Mixing of the polymer / surfactant has a synergistic effect on air in increasing the removal efficiency. This means that (1) the addition of a coagulant without subsequent high molecular weight flocculant is generally regarded as an inefficient treatment for DAF detergents; (2) It is surprising that the general dispersed air suspension process for pulp (as opposed to filtrate) is carried out in a matrix of long fibers, fines and contaminating particles. It is believed that the long fiber matrix traps particulates and limits yield loss. In the present invention, little or no long fibers are present. It was expected that fines, fillers, and inks would all be removed along with the foam rejects, which was reinforced by the high concentration of cleaning surfactants present in the bubbly water. In contrast, although there was selective separation of the filler and ink, many of the fiber fines could be retained in the filtrate and subsequently removed.

The method of the present invention is to pass most of the cleaning filtrate through the DAF detergent so that it can be reused in the process for dilution without increasing ink cycle-up and reducing the quality of the product.

A first stage washer filtrate sample was collected at a Wash Newsprint decontamination plant in Southeastern USA. Samples of the filtrate were placed in a laboratory suspension sorter. Several polyelectrolyte treatments were carried out prior to addition of the dispersed air in the suspension sorting bath (generally combined with block alkoxylated tallow fatty acids, respectively as described above). The branched polyamines and DADMAC / AM compounds tested are commercially available as CPS Agefloc A30VHV and CPS Agequat C3204, respectively.

Air was dispersed through the sorting bath for 5 minutes. Stock pulp pads were prepared before and after suspension. The ash content in the selected samples was measured at 525 ° C. to calculate process yield or fiber recovery and to separate the effect of total solids recovery (fiber + filler) from the effect of fiber recovery. Recovery of fibers or fiber fines by selective separation of ink and filler is considered advantageous. Ink removal efficiency was calculated based on the measurement of the Effective Residual Ink Concentration (ERIC) value. ERIC values were calculated based on scattered light reflection of pads formed from filtrate solids at a wavelength of 950 nm in the near infrared region of the spectrum. It is reported to be more sensitive to ink content compared to conventional photometric measurements measured at 457 nm. In an example, the process filtrate feed has, on average, an ERIC value of 2290 ppm, a total suspended solids of 3100 ppm, and a 16.3% ash content of the total suspended solids. The results are shown in Tables 1 and 2 below.

As shown in Tables 1 and 2, addition of 20 ppm of suspension aid removes 34% of the remaining ink, increases the total ink removal rate by 90%, and reduces fiber recovery to 63%. The addition of a low dose of polymer (5 ppm as active agent) maintained the removal rate of the ink at 90% (ie, about 33% improvement over the control) and increased fiber recovery to about 67%. Administering higher doses of the polymer (10-20 ppm as active agent) moderately increased the ink removal rate but reduced the process fiber recovery.

Ash measurements indicate that, in addition to the ink, the sorting tank selectively fractionated the filler into a foam reject, which is considered advantageous. With no air treatment, the ash was reduced from 16% in the sorter feed to 5% in the allowed pulp. The addition of the suspension aid alone reduced the allowed pulp ash content by 4%. Application of the suspension aid and the cationic polymer further reduced the allowed pulp ash to 2-3%. The reduction in ash content while maintaining fiber recovery is considered an advantage of the process.

While the present invention has been described with respect to specific embodiments thereof, it is evident that numerous other forms and modifications of the invention will be apparent to those skilled in the art. In general, the appended claims and the invention should be considered to cover all obvious forms and modifications that fall within the true spirit and scope of the invention.

Claims (15)

(a) alkoxylated tallow fatty acid surfactants, and (b) epichlorohydrin-dimethylamine condensates, poly-diallyldimethyl-ammonium chloride, diallyldimethylammonium chloride-acrylamide copolymers, polyethyleneimines and polyamino A mixture of up to about 20 ppm of cationic polyelectrolyte selected from the group consisting of -amide epichlorohydrin condensates, in an effective amount, added to the filtrate after washing the pulp, A method for simultaneously improving the ink removal rate and fiber recovery rate of the filtrate in the dispersed bubble suspension of the waste paper denitrification filtrate. The method of claim 1, Wherein the cationic polyelectrolyte has an average molecular weight of less than about 2,000,000. The method of claim 1, The filtrate is derived from waste paper and a pulping slurry of water. The method of claim 1, Up to about 10 ppm of cationic polyelectrolyte is added to the filtrate. The method of claim 4, wherein Up to about 5 ppm of cationic polyelectrolyte is added to the filtrate. The method of claim 1, About 1 to 500 ppm of a surfactant is added to the filtrate. The method of claim 6, About 10 to 30 ppm of a surfactant is added to the filtrate. The method of claim 1, Wherein the alkoxylated tallow fatty acid surfactant is capped propylene oxide. adding an effective amount of a mixture of (a) an alkoxylated tallow fatty acid surfactant and (b) up to about 20 ppm of cationic polyelectrolyte having an average molecular weight of less than about 2,000,000, to the filtrate after washing the pulp. A method for simultaneously improving the ink removal rate and fiber recovery rate of the filtrate in the dispersed bubble suspension of the waste paper denitrification filtrate. The method of claim 9, The filtrate is derived from waste paper and a pulp slurry of water. The method of claim 9, Up to about 10 ppm of cationic polyelectrolyte is added to the filtrate. The method of claim 11, Up to about 5 ppm of cationic polyelectrolyte is added to the filtrate. The method of claim 9, About 1 to 500 ppm of a surfactant is added to the filtrate. The method of claim 13, About 10 to 30 ppm of a surfactant is added to the filtrate. The method of claim 9, Wherein the alkoxylated tallow fatty acid surfactant is capped propylene oxide.