US20100263812A1

US20100263812A1 - System and method for repulping of paper products and improvement of water quality with dipolar solvents and recovery

Info

Publication number: US20100263812A1
Application number: US12/747,713
Authority: US
Inventors: Salah Awadel-Karim
Original assignee: Sanata Tech Inc
Current assignee: Sanata Tech Inc
Priority date: 2007-12-12
Filing date: 2007-12-12
Publication date: 2010-10-21
Also published as: WO2009073948A1; CA2721460A1

Abstract

An enhanced method of repulping paper and improving water quality by placing used paper product material in an aqueous solution of dipolar aprotic protophylic solvent, processing it, and recovering recycled pulp based on two physical reactions of the dipolar solvent: first with water from one part of the solvent, and second with cellulosic material from the other part of the solvent. The water reaction involves a rearrangement of hydrogen bonds within the water, improving its reactivity and solvent capacity, and the cellulosic reaction involves dissolution of hemicellulose in a manner which results in reduced fibre loss and improved pulp quality. The net result is more efficient pulping and reduced environmental impact.

Description

FIELD OF THE INVENTION

This invention relates to the treatment of water and the repulping of paper products.

BACKGROUND OF THE INVENTION

In the pulp manufacturing industry water is used extensively and is a vital element of the process of repulping paper. It is used for dissolving pulp, and as a component in loading, sizing, and coloring ingredients as well as in the transportation of pulp fibres through the manufacturing process as it moves through storage tanks, screens, refiners and paper-making machines.
The current process of repulping paper involves pulping, screening, cleaning, and de-inking by processes like bleaching and the application of alkaline chemicals which contaminate the water. Waste paper treatment methods are variable depending on the type of paper and may involve de-inking of toner from laser printers or photocopiers, or the removal of other contaminants from the paper.
Pollution sometimes causes water molecules to form large clusters which surround molecules of pollutant due to hydrogen bonding Even after most of the pollutant molecules have been removed there can still be clustering of water molecules due to residual electrostatic interference. This clustering can reduce the capacity of the water to dissolve, carry, and transport solutes including pulps and can also cause it to become anaerobic, reducing its capacity to support marine life. With the increasing scale of the pulp and paper industry, these problems are becoming increasingly relevant. As environmental standards tighten, new methods of repulping paper that are less harmful to water quality and methods of treating wastewater to restore its quality are increasingly needed.
Part 1—System and Method for Repulping of Paper Products with Dipolar Solvents and Recovery
The global demand for paper and paperboard has risen steadily in recent years and is expected to continue to rise. This demand increase has coincided with a decrease in the supply of pulp-producing timber due to deforestation. The result of these two factors is increased demand for recycled paper. Pulp for recycled paper is typically obtained by applying various alkaline pulping processes with bleaching conditions selected in the attempt to obtain some of the following desired qualities for the resultant pulp:
1. high yield of recovered fibres;
2. suitable amount of surface adsorbed hemicellulose;
3. specific strength properties;
4. high levels of brightness;
5. sufficient smoothness.
The feasibility of manufacture of recycled pulp and its competitiveness is largely dependent on the yield and the quality of the pulp from a given amount of waste paper as starting material. The quantity of the recovered pulp and the characteristics of the fibrous material (i.e., no less than those of the virgin pulp) represent important parameters of the recycled pulp. The losses during repulping (pulping, screening and cleaning, kneading, soaking, flotation, washing, de-inking, and bleaching) operations are fairly high and account for a remarkable shrinkage in industrial revenue due to the considerably low pulp yield and inferior fibre quality. Current alkali treatment technology is quite inefficient for pulping of waste paper. Methods for attainment of high quality pulp from the recycled paper are complex and a number of schemes for pulping and bleaching of recycled paper materials with various, chemicals, oxidizing and reducing agents have been proposed, but have resulted in yield and the quality of the recovered fibrous material being still far below the desirable norms.
Current repulping and bleaching operations generally include pulping, screening, cleaning, and de-inking by a combination of kneading, soaking, flotation and washing. In some cases, depending on the end-use, the bleaching follows. However, each mill typically has its own technological line that differs from the others, depending on the type and quality of waste paper and the individual mill's condition. There is usually no tailor-made process for waste paper treatment. This is due to the fact that most technical problems change with time. For example, years ago, removal of objectionable substances, such as stickies, adhesives, and hot melt was the primary issue. Nowadays, de-inking of toner from xerography or laser printing is the central concern.
For pulping waste paper different chemicals, such as sodium sulfite, sodium carbonate, sodium hypochlorite, and sodium hydroxide, are employed for defibration. A conventional pulper is the most popular type of equipment used for pulping of waste paper material. However, for pulping in de-inking systems, it is still controversial as to whether low or high consistency is the most effective. The high consistency approach is based on the ground that a high consistency pulping is favorable for ink particle dispersion into minute particles. Nonetheless, this kind of treatment increases the number of ink particles and lowers considerably the brightness after pulping. On the other hand, in low consistency pulping, 50% of ink can be dispersed from the fibres by this method, which can be easily removed by washing before kneading and flotation. However, the choice of pulping is always judged by considering the complete de-inking.
In the screening and cleaning subprocess, for effective removal of objectionable materials, such as stickies and hot melt, fine slot screen is used. For coarse contaminants, a plate screen with hole perforations is commonly employed. Recently, a plate screen with both holes and slots has also been in operation. In cleaning, a reverse-type centrifugal cleaner is widely employed to remove light weight contaminants, such as debris of polyethylene film, polypropylene string and polystyrene foam and tiny stickies. Also, a gyro-type horizontal cleaner, now, is in use, with the advantage of rendering rejects without fibres.
Kneading is usually applied for the detachment of ink from the fibres. Many types of kneading machines are used to detach ink particles from fibres under high shearing force by using chemicals at a high consistency pulp. Such machines are called processors, deflakers, or dispersers. Kneading has improved de-inking efficiency. Hence, two-stage kneading is sometimes employed.
Soaking is introduced in many cases after kneading. The purpose of soaking is to increase the effects of de-inking chemicals, such as surface active agents, caustic soda, and hydrogen peroxide (i.e., in most cases with sodium silicate) for bleaching. The functions of soaking are considered as follows; in the case of de-inking old news, soaking enhances paper strength as well as brightness. However, yellowness of paper increases when soaking is performed in caustic soda solution at a higher temperature for a longer period (8-10 hr). On the other hand, conditions involving the use of lower caustic soda concentration (i.e., about 0.6% at a high consistency ˜25%) are recommended for corrugated container waste paper treatment in order to ease defibration and improve the strength characteristics.
Floating usually follows the soaking There are many types of flotation units in the industry. The main characteristic of these units is a high air-to-liquid ratio so as to ensure effective separation of ink particles from the fibres. Recently, a new flotation unit was manufactured to produce minute air bubbles by the use of a turbine blade which has the ability to detach ink particles smaller than several micrometers. Those in the past were considered as being impossible to remove by flotation techniques.
Then a washing stage occurs. The function of washing is to remove minute ink and fibre particles detached from the fibres. It is known that the resolution by the naked eye is only possible for particles larger than around 35 micrometers. Thus, smaller ink particles are not visible and detrimental to pulp brightness. These can only be removed by washing. Decker and screw-press type washers are used in washing.
Caustic soda is a primary de-inking agent and also it is considered as a defibration promoter in the pulper. Pulping of the recycled paper is usually carried out at about 50 degrees C. However, cold pulping is also gaining popularity because at lower temperature it has been claimed that the disintegration of stickies is more controllable and easy to remove by screening. Surface active agents are used for promoting defibration by improving alkali penetration, especially during soaking, wetting ink during kneading and generating foam to gain control over aggregated ink particles. There are a number of de-inking agents available in the market such as fatty acids, fatty oil derivatives, higher alcohol derivatives, fatty acid derivatives, and non-ionic detergents. Surfactants with high penetrability in pulping of recycled paper are also in use. For the removal of undetached and small ink particles remaining on the fibres after kneading, a surfactant, capable of both de-inking and ink particle flocculation, is necessary. For bleaching hydrogen peroxide in the presence of sodium silicate has a wide use in the industry. In some cases like tissue producing mills are still using hypochlorite for bleaching. This has been allowed after proving that most of the dioxins and AOX (adsorbable organic halides) go into the sludge. AOX and dioxins in the sludge can easily be incinerated.
Bleaching results in removal of residual lignin and colouring materials from pulps. However, with the current conventional fibre recovering processes (e.g., pulping and bleaching operations), the bleached pulp from recycled paper is of low yield, rich of hornified fibres, of low hemicellulose content, and low levels of brightness. This downgradability makes it unsuitable for the manufacture of high quality papers. Pulp intended for quality papers must meet exacting specifications with respect to alpha cellulose, strength and optical properties. A low content of ash and extractives is also desirable. In current pulping and bleaching technology of recycled paper attainment of high level of brightness and removal of stickies is usually achieved by caustic soda treatment in most operations. Also, it is worth mentioning that additional alkaline pulping steps, in some times, are carried out in connection with bleaching in order to attain high brightness. In turn, the yield of fibrous material is fairly low and hemicellulose losses are severe. The strength of paper can be very dependent upon the interfelting of fibres and upon the cellulose mucilage which bonds the fibre into a homogeneous sheet. Currently, ozone and oxygen are in wide use in paper pulp bleaching. This is because they are effective oxidizing agents and offering a highly stable brightness. Nonetheless, pulp delignification proved to occur at the expense of cellulose yield and degree of polymerization since significant hydrolytic degradation takes place on cellulose fibres. On the other hand, the brightness results obtained from peroxide bleaching are found to be poor and below the standards. This is attributed to various difficulties encountered in dispersion of residual ink, which masks brightness increase and peroxide decomposition during bleaching. Biological phenomena and metal ions were also contributed to peroxide breakdown. In order to obtain pulp with brightness up to 75%, a two step bleaching should be taken into consideration; first step peroxide bleaching, the second one after washing a bleaching with a reducing agent (e.g., sodium hydrosulfite) is recommended. For removing stickies and attaining high brightness, high alkali and soap charges in pulping are important.
The shortfalls of current pulping operations for recycled papers are that the current technology demands great exertion by operators and at the same time is inefficient. This can easily be perceived from the very low yield and the inferior quality of the recovered pulp. There are unfavorable characteristics of the fibres recovered from recycled paper such as fibre shortening, generation of fines, fibre fatigue and hornification. The conventional methods of recovering and upgrading of pulp from the recycled paper are inadequate and imprecise. This is based on the fact that the alkaline treatment is an ineffective approach to secure a better impregnation and hence, defibration, particularly, in the crystalline cellulose. As a result, great losses in fibrous material are to be expected. The paper pulp yield is not extensive unless it is associated with high lignin content. In addition the multiple and prolonged use of alkaline treatment for the recovered fibrous material will lead to a considerable loss of hemicelluloses. This has been verified by investigating xylans from esparto grass holocellulose, using sodium hydroxide, dimethylsulfoxide (DMSO), and hot water. Each extractant gave a different yield of xylans, however the sodium hydroxide one was found to be the highest. In addition, the sodium hydroxide extract gave precipitate during dialysis, indicating that alkali soluble polysaccharides always contain water insoluble fraction. In turn, it has been found that the removal of hemicelluloses from the pulp has a negative impact on paper strength characteristics, and that the effect of surface adsorbed xylans on burst and tensile strengths is profound.
On the other hand, caustic soda treatment for recycled paper is an inappropriate approach for influencing hydrogen bonding (e.g., inter- and intramolecular), of the crystalline cellulose of recycled fibrous material. In other words, one may speculate that the loss in fibre flexibility is due primarily to the fibre modification.
The two primary factors responsible for the fibre modification are the hemicellulose removal during various repulping and bleaching processes and the large rearrangement of hydrogen bonding due to the adhesives and drying effects. In hemicellulose removal, the surface adsorbed xylans have a significant impact on the interfibre bonding of the paper sheet.
Part 2—Improvement of Water Quality with Dipolar Solvents and Recovery
Water as a natural resource, is a vital element and necessity in the manufacture of pulp, paper and paperboard and for the generation of power in the industry's steam plants. Mills using up to 350 cubic meter per ton of paper are not uncommon in pulp and paper industry. A large percentage of the water requirements for the mills comes from surface supplies, i.e., rivers and lakes and the remainder comes from wells of a few feet to over a number of thousands feet deep. Good quality water in large quantities is as essential to the manufacture of pulp and paper as cellulose. As a matter of fact, water is one of the most critical of all materials used by the pulp and paper industry. It is used directly in the processing of pulp, it dissolves or is mixed with the various loading, sizing and coloring ingredients; and in addition, it is the medium which carries the fibres through the storage tanks, screens and the refiners to the paper-making machine where it plays a most important role in the making of a sheet of paper.
However, today's water has encountered serious pollution problems. Pollution causes water molecules to gather together in larger clusters than they would naturally be, and hence as the water “wraps up” dissolves the pollutant. Even if the pollutant is filtered the water molecule cluster still remains in unnaturally large cluster due to its lasting electromagnetic frequency influence on the water, this frequency keeps the water molecules in the same unnatural structure they were when the pollutant was present, despite its absence.
Water pollution comes in many forms such as chemicals, thermal, farm run-off, frictional and electromagnetic. Even methods or devices that we typically use for the removal of pollution from water are themselves contribution to water pollution on the molecular/frequency level. In other words, pollution saturates water with unnatural amounts of substances and electromagnetic influences, that all leave their influence in the form of frequency on water, reducing its capacity to dissolve, carry, transport and be microbiological stable (e.g., limitation of bacteria and enzyme growth). As water becomes over polluted it can no longer clean or regenerate itself, it is simply too full of the frequency influence of pollution, causing larger than natural water molecule clusters (i.e., free oxygen trappers). If water can not dissolve and transport oxygen effectively it can become anaerobic.

Objects of the Invention

The invention is designed to provide an enhanced method of repulping paper and improving water quality with dipolar solvents and recovery. These objects are discussed in two parts, first with respect to the repulping objects, and second with respect to the water quality improvement objects. Essentially the repulping objects are to reduce fibre losses and improve pulp quality. There are a number of aspects to this as discussed below under part 1. The primary water quality improvement objects are to increase its reactivity and solvent capacity. This has numerous advantages as discussed below under part 2.
Part 1
It is an object of this part of invention to avoid great fibre losses and inferior pulp quality, resulting from the current pulping and bleaching technology used in the recycling of paper material. Regarding the fibrous material (Part1), the current invention uses dipolar aprotic protophylic solvent in a novel technique, providing the following advantages:
1. high yield of recovered pulp fibres with considerable fibre flexibility can be attained by the effectively uniform interaction of dipolar solvent with both amorphous and crystalline cellulose, i.e., effective breakdown of interfibre bonding of the cellulosic material;
2. ease of defribration and recovery of fibres with attenuated H-bonds, i.e., accessible cellulose;
3. fibres can be recycled continuously due to open hydrogen bond packing;
4. dissolution-hydration of hemicellulose (e.g. surface adsorbed xylans) and better degree of hemicellulose retention;
5. ease of detachment of additives, adhesives, and ink particles due to greater specific molecular surface area exposure to de-additive, de-adhesive, de-inking reactions.
6. energy savings by reduction in other operations (e.g., kneading, soaking, de-inking);
7. ease of bleaching, i.e., greater exposed surface area of fibres for reaction;
8. better sheet strength properties;
9. enhanced paper machine operation;
10. Ease of draining; less fines for blocking screens due to breakage of stiff particles;
11. Smoother paper sheets from re-pulpled material due to fibres being flexible and comfortably in pressed position; less fluffiness on sheets due to stiff fibres sticking out;
12. environmentally benign.
The tensile strength, burst strength, and smoothness of paper sheets prepared from the re-pulpled material are expected to be improved due to the flexibility of the fibres and the increased amount of hemicellulose attained by the method and system. The flexibility of the fibres and the increased amount of hemicellulose retained by the fibres are directly proportional to the weakening of the hydrogen bonds in the cellulose. The optimizing loops are thus both easy and important to implement for a given batch of repulpable material. The recovered fibres are continuously recyclable using the method of the present invention, as the fibres are always in a comfortable H-bonding position. The system and method of this part of invention is thus compatible with sustainable development principles that aim at a rational and effective use of renewable resources, while providing a significant increase in industrial revenue.
Part 2
Dipolar aprotic solvents (DAS) improve the water quality by organizing its internal structure. In other words, dipolar solvent interaction with water physically enhances the quality of water for the pulp and paper industry in many different ways. For example, in paper industry where huge amounts of water are consumed (i.e., in most cases over 100 m3 of water/ton of fibres (dry weight), these solvents, through rearrangement of hydrogen bonding of water, offer a reactive water which is of importance for water consuming pulp and paper industry. The aim of alteration water structure is to increase its reactivity. This can be achieved through the interaction of (DAS) with water; the hydrogen bonding of water is rearranged in a way that the water molecules acquire almost their natural conformation, i.e., tetrahedral lattice. For instance, by one of (DAS) family such as DMSO when added to the water, the water molecules are assumed to regain more OH stretch that could approach the natural H—O—H angle which is 109.47°. As a result, the DMSO restructured water acquires several positive properties such as smaller water clusters, lower surface tension, better carrying efficiency, increased hydration capacity, improved power of microbiological stability (i.e., the rearrangement of hydrogen bonding through dipolar aprotic solvent is to render a water structure of almost without free oxygen which is a favorable environment for bacteria and enzymes to grow and proliferate) and greater interfibre bonding power. These dipolar aprotic solvent restructured water qualities are superior for pulp and paper various technological processes where highly purified and interactive “reactive” water is crucial for pulping, pulp washing, screening, soaking, mixing, and refining. Also, microbiological stability of the dipolar aprotic solvent rearranged water is of significance since the main components (e.g., cellulose, lignin and hemicellulose) of the fibres are all biodegradable and hence this quality of the solvent restructured water will limit the bacteria and fungi growth in the process water. Thus, the dipolar aprotic solvent hydrogen bond rearranged water (Part2) offers the following advantages:
1. Increased fibrous material hydration capacity through water-water weaker hydrogen bonds and smaller water clusters interaction with cellulosic material, i.e., better interfibre bonding
2. Ease of detachment of adhesives, additives and ink particles due to high dissolving power quality of dipolar aprotic solvent treated water (i.e., dissolution of extraneous substances)
3. Improved fibrous mass transfer due to high dissolving quality and greater carrying efficacy of aprotic solvent-water system
4. Lesser sludge load due to microbiological stability of water, i.e., highly tetrahedral lattice water with no free oxygen for bacteria and enzymes to grow and proliferate
5. Limited use of biocides
6. Enhanced fibrous material mixing, i.e., uniform defibration due to lower surface tension, greater carrying efficiency and increased dissolving power of aprotic solvent water
7. Limitation in the use of sheet strength and sizing agents
8. Reduction in water consumption
9. Cutting down in electricity and chemical consumption
Chemistry of Dipolar Solvents and Cellulose
It is well known that acid or base strength depends on the acidity or basicity of the solvent, however, other properties of the solvent should be taken into account. One of these is the dielectric constant, which is important because it is a measure of the ion-solvating ability of the solvent. Solvents with high dielectric constant such as water are capable to solvate each ion. At lower dielectric constant, ions aggregate in a manner ion pairs and larger aggregations are present. This situation makes little difference when the equation has the same total charge on both sides as indicated below, HA++B=HB++A. However, when the total charge increases, for instance, HA+B=HB++A−, then a solvent with high dielectric constant forces the equilibrium further to the right than does one with a lower dielectric constant. Even when the charge is unchanged, the dielectric constant of the solvent may still make a difference if the ion (or ions) on the left are more solvated than the ones on the right. Also, the solvent may cause differential solvation in another way, which is different from the effect of the dielectric constant, originating from the difference in solvation of anions by a protic solvent (which is a hydrogen bond donor HBD) and an aprotic one HBA (hydrogen bond acceptor). However, the effect could be extreme: in dimethylformamide (DMF), picric acid is stronger than HBr. This particular result could be attributed to the size of the molecule. In other words, the large ion (O2N)3C6H2O— is better solvated by dimethylformamide (DMF) than the smaller ion Br—; while in protic solvent like water the solvation of an anion is by the small unshielded proton H. This Hydrogen bond is a molecular interaction that involves the sharing of a hydrogen atom by a weakly acidic donor and a weakly basic acceptor atom. Hence, hydrogen bond is an important structural element particularly in supermolecular structure of the cellulose. In other words, hydrogen bonds are crucial elements of the three dimensional conformation that allow fibrils to form and coalesce in stronger lateral order. On the other hand, the dipolar aprotic hydrophylic solvent treatment in a major fraction of water is expected to bring about, within the cellulosic material, irreversible H-bonding rearrangement that will cause spacing in the previously deformed (closed) hydrogen bonding of the substrate due to reactions of adhesives and the impact of drying. The probable explanation of the hydrogen bond attenuation is due to the interaction of dipolar solvent (HBA) with the polar hydroxyl groups of the cellulose molecules (HBD). On the other hand, with regard to the water, it is not well understood to what extent water can penetrate the crystalline cellulose, but in any case it is known that such penetration does not bring about any change of spacing in the crystallites. In this respect, dipolar aprotic solvents such as dimethylsulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMA), with their unique solvation characteristics will ensure better impregnation (e.g., amorphous and crystalline zones) to an extent that can not be offered by other solvents. In conclusion, their role can also be understood as swelling agents of cellulose.
Chemistry of Dipolar Solvents and Water
Water-dipolar aprotic solvent binary mixtures are powerful solvent systems used frequently in many branches of chemistry and industries, and their efficient application in chemical processes will contribute to reduce a global environmental impact. Solvent effects in these mixtures depend nonlinearly on the mixing ratio, and studies of preferential solvation have offered important results.
Water is a fairly malleable substance. Its physical shape easily adapts to whatever environment is present. But its physical appearance is not the only thing that changes, the molecular shape is also susceptible to change. The energy or vibrations of the environment has a quite effect on changing the molecular shape of the water. In this sense water not only has the ability to visually reflect the environment but it also molecularly reflects the environment.
It is known that low concentrations of some solvents such as dipolar aprotic solvents modify the water structure in such a way that suppresses the protic (H-bond donor) reactivity of water and enhance its basic (H-bond receptor) reactivity. These reactivity changes within the water structure are well responsible for rendering water with unique qualities such as smaller water clusters, increased dissolving power (i.e., dissolution of extraneous substances such as stickies, minerals and ink), lower surface tension, better microbiological stability and greater self-purification capacity. Additionally, dipolar aprotic solvents are fairly effective OH free radical scavenging agents. These characteristics imply that aprotic solvents induce a more intensive structuring of water and they are effective in producing highly structured smaller clusters of six water molecules. These predominating ice-like clusters of water are believed to represent the highly structured part of liquid water. The dipolar aprotic solvent molecules create these structural effects in part because dipolar aprotic solvent is a hydrogen bond acceptor but not donor and in part because aprotic solvent bonds with water more strongly than water bonds to water. Accordingly, the solvated aprotic solvent is supposedly bonded to two water molecules, and the average angle between the two hydrogen atoms, bond in the dipolar aprotic solvent.2H2O (e.g., DMSO.2H2O), is nearly tetrahedral. A water molecule is hydrogen bonded to water one but near the oxygen of a dipolar aprotic solvent can simultaneously bond with aprotic solvent or readily switch its bonding from water to the aprotic solvent. In other words, the rearrangement of hydrogen bonding by a dipolar aprotic solvent produces weaker hydrogen bonds between water-water molecules than those produced between aprotic solvent and water molecules. These water molecules with weak hydrogen bonds are ready to interact through intermolecular hydrogen bonding with the sugar units and produce substantial hydration within the cellulosic material. Also, the predominance of smaller water clusters in water-aprotic solvent systems will give rise to increased weaker hydrogen bonds between the clusters themselves. Similarly, these small clusters would contribute to better impregnation and hydration throughout the fibrous material (i.e., amorphous and crystalline cellulose), which are essential for detachment of adhesives, additives, ink particles, interfibre bonding and uniform defibration.
In conclusion, the rearrangement of water structure through the hydrogen bonding by a dipolar aprotic solvent will offer the following; weaker hydrogen bonds between water-water molecules and among the small water clusters as well. These characteristics will render water with superior qualities such as reactive water, greater fibrous material hydration power, increased detachment of adhesives, additives and ink particles, microbiological stability (e.g., limitation of bacteria and enzymes growth) and better fibre mixing performance.

SUMMARY OF THE INVENTION

This invention provides a system and method of repulping and water quality improvement using an aqueous dipolar aprotic protophylic solvent in an agitator vat, or pulper, with optimization of process variables depending on the reactivity of dipolar aprotic solvent water system, type of material being re-pulpled and the desired characteristics of the pulp resulting from the process. The mechanism of waste paper repulping in an aqueous dipolar aprotic protophylic solvent is based on two physical reactions of the dipolar solvent, first with water from one part of the solvent and second with cellulosic material from the other part of the solvent.
The first physical reaction is caused by the substantial alteration of water structure through the rearrangement of its hydrogen bonding system. The dipolar aprotic solvent molecules (e.g., DMSO) create these structural changes within the water in part because aprotic solvent is a hydrogen bond acceptor and in the other part because dipolar aprotic solvent bonds to water more strongly than water bonds to water. Accordingly, to the simulation analysis, the solvated aprotic solvent molecule (e.g., DMSO) is bonded to two water molecules, and the average angle between the two hydrogen bonds in the aprotic solvent.2H2O (e.g., DMSO.2H2O) is almost tetrahedral. A water molecule is hydrogen bonded to another water one but near the oxygen of a dipolar aprotic solvent (e.g., DMSO) molecule the water molecule can simultaneously bond with the aprotic solvent or readily switch its bonding from water to the aprotic solvent. However, if the water molecule was instead near the methyl groups of aprotic solvent no such alternative bonding would be possible.
The second physical reaction may be attributable to the greater accessibility of cellulose as a result of disruption/destruction of hydrogen bonding by the dipolar solvent. The second physical reaction is the dissolution of hemicellulose by chemical and mechanical actions of the treatment. Furthermore, since the dipolar solvent is a strong hydrogen bond acceptor and has a high solvating power, this technique may ease and lead to a total detachment of ink and adhesives from the fibres.
The group of dipolar aprotic protophylic solvents comprises hexamethylphosphorictriamide (HEMPT) and acetone, as well as the above-noted dimethylsulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMA). HEMPT however has the disadvantage that it is considered to be carcinogenic, mutogenic and toxic to reproduction in animals. Acetone as a repulping solvent has the disadvantage that it brings about considerable disproportionality on the cellulose chain, by forming isopropylidene derivatives on the sugar rings of the residual cellulose. This would provide a low degree of polymerization of the cellulose and would have a negative impact on the strength of a paper sheet formed from the re-pulpled material. Pyridine is also considered to be a dipolar aprotic protophylic solvent, but it has nitrogen, which forms hydrogen bonds that are less strong than those formed with oxygen, as formed by the other dipolar aprotic protophylic solvents. DMSO2 (i.e., the metabolite of DMSO) can also be used as a hydrogen bond acceptor. However DMSO2 is a crystalline solid, less soluble in water and has a high melting point (109 degrees C.). The remaining three noted dipolar aprotic protophylic solvents, namely, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMA), are each highly suited to use for H-bond disruption in the system and method of this invention. The process is characterized by:
1.* H-bond disruption/destruction by the dipolar aprotic protophylic solvent treatment to offer an accessible cellulose;
2. Lesser dissolution of hemicellulose by the chemical and mechanical action of the technique.
The process ensures a concerted disruption/destruction of hydrogen bonding of the cellulose (carbohydrate) by dipolar solvent and minimizes the removal of hemicellulose by avoiding alkaline treatment. This is achieved by penetration of dipolar solvent molecules into the cellulose (e.g., amorphous and crystalline), and interaction of dipolar solvent with cellulose (carbohydrate) molecules through their hydroxyl groups. This presumably brings about stereochemical changes (i.e., rotational) that disrupt and permanently weaken the H-bond of both amorphous and crystalline cellulose, thereby providing accessible cellulose. Collateral benefits include recovered fibres being continuously recyclable, less removal of hemicellose, uniform defibration of the cellulosic material, better interfibre bonding, easy detachment of adhesives and ink particles, and ease of bleaching.
In a similar manner, the process offers water with structural changes through the rearrangement of its hydrogen bonding system by the dipolar aprotic solvent; water molecules with weaker hydrogen bonds and smaller water clusters that can easily interact with cellulosic material and bring about considerable hydration within it. As a result several benefits can be attained including better fibrous material hydration power, increased detachment quality of adhesives, additives, and ink particles, enhanced microbiological stability, improved pulp mixing quality, greater inter-fibre bonding capacity and minimum use of sheet strength and sizing agents.
For optimum results, the temperature, solvent concentration, type of dipolar solvent, solid/liquid consistency, and mechanical agitation (the “Adjustable Factors”) should be adjusted in accordance with known and test effects of those factors on the type of paper material to be pulped: unprinted pre-consumer paper, printed paper, newsprint, paperboard, old corrugated containers, tissue paper liners, packaging paper boxes, coated paper, mixed papers, office waste, old magazines.
The temperature of the solvent mixture should be in the range of 5 to 90 degrees C., with a range of 5 to 40 degrees C.° often producing optimal results for a typical mix of recyclable papers. The concentration of the appropriate dipolar solvent should be in the range of 0.001% to 40%, the remainder water, with a range of 0.1% to 5% often producing the optimal result for a typical mix of recyclable papers. The solid/liquid consistency should be in the range of 1% to 33% by weight, with a range of 1% to 10% often producing the optimal results for a typical mix of recyclable papers. The mechanical agitation of the re-pulpable material should be in the normal range of the equipment used for agitation and mixing in repulping processes. The time of the mixing should be in the range of 1 to 90 minutes. Bleaching should be performed on the material.
The effect of varying these parameters (temperature, type of dipolar solvent, solvent concentration, and liquor/solid ratio) on pulp quantity and quality can be assessed by sugar analysis, alpha cellulose content, infrared (IR), and drainability analysis.
The dipolar aprotic solvent influence on water structure occurs through the alteration of the hydrogen bonding lattice; weaker hydrogen bonds can be examined using IR absorption spectroscopy, and water cluster size can be studied using Mass Spectrometric analysis of dipolar aprotic solvent-water binary mixture. Microbiological stability of aprotic solvent-water binary system can be examined through microscopic analysis for bacteria count.
Different standards and Tappi standard techniques such as kappa number, effective residual ink concentration (ERIC) holocellulose content, xylan content, burst strength, and tensile strength should be employed to evaluate pulping, bleaching, and optimization of the recovered pulp, in order to optimize the process for any given type of repulpable material. For the removal of residual lignin and coloring materials, different types of bleaching can be applied: peroxide bleaching; OZEP (ozone/extraction/peroxide), and biobleaching using microorganisms.
The novel application of aqueous dipolar solvents in pulping of recycled paper is designed to address the major problem of stiffness of the recovered fibres. Fibre hornification (stiffness) has been a crucial drawback in the quality of the pulp from recycled paper and will remain a major problem if paper industry continues to apply alkaline pulping in the recycled paper manufacturing. The fibre stiffness is attributable to fibre modification that has been brought about during the original pulping, bleaching and drying operations in making the initial paper products that are to be recycled. And conventional repulping by alkaline and bleaching treatment increases the fibre stiffness. The two factors responsible for modification of the recovered fibre are considered to be the hemicellulose removal by mechanical and alkali treatment and largely alteration of hydrogen bonding due to the action of various adhesives (if applied) and drying of paper. As a remedy for fibre stiffness, the use of aqueous dipolar solvent as a pulping liquor in recycled paper is excellent. On one hand, this treatment will render an accessible cellulose (amorphous and crystalline) ready to form a new hydrogen bond packing On the other hand, the application of aqueous dipolar solvents in recycled paper manufacturing will limit the excessive drainage of hemicellulose from the fibrous material. In this respect, the proposed technique is suitable to treat all types of recycled paper, each at certain optimum conditions. Further on, in the proposed technique, the recovery of dipolar solvents and de-inking chemicals are taken into account. In addition, the dipolar solvents (DMSO, DMF and DMA) recommended for pulping of recycled paper are cost- effective, have a high boiling point, a high flash point, and are generally considered to be non-carcinogenic.
The process is flexible enough to accommodate any of oxidizing, reducing, deinking, swelling, dispersing, chelating, buffering, filling, strength enhancing, detackifying agents if needed. However, aqueous DMSO repulping alone is capable of offering high yield and superior fibre quality for all types of recycled papers.
The recovery and reuse of process solvents (H2O, DMSO, and petroleum ether) makes both environmental and economic sense for the recycled paper industry. Well designed recovery systems can pay for themselves in a relatively short period.
Using conventional distillation techniques, the separation of DMSO and water is both impractical and uneconomical, simply because it requires a large amount of energy to be consumed. Thus, based on the experimental data obtained in this work (see FIGS. 8 & 9), the following three-stage solvent separation is recommended:
Liquid Extraction
Distillation
Solid/Liquid Separation

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the formation of a 6-water molecule cluster with a dipolar aprotic solvent dimethylsulfoxide S(CH3)2.

FIG. 2 is an illustration of the stretch of an H-bond from 104.47 degrees to 109.47 degrees as a result of the influence of dipolar aprotic solvents.

FIG. 2B shows the adoption of H-bond angle tetrahedral form caused by the influence of dipolar aprotic solvents.

FIG. 3 is a block diagram showing the steps of repulping using the method of this invention.

FIG. 4 is a diagram showing cellulose molecules in repulpable material, and the chemical structure of three suitable dipolar aprotic protophylic solvent molecules.

FIG. 5 is a diagram showing the effect of dipolar aprotic protophylic solvent on the hydrogen bond of cellulose.

FIG. 6 is a diagram showing the apparatus used in the system of this invention.

FIG. 7 is a diagram illustrating an extractive distillation subprocess.

FIG. 8 is a diagram illustrating the liquid extraction subprocess.

FIG. 9 is a diagram showing the distillation unit.

DETAILED DESCRIPTION

FIG. 1
Referring to FIG. 1, the formation of a 6-water molecule cluster is illustrated with the dipolar aprotic solvent dimethylsulfoxide shown in the upper left comprised of oxygen atom 103, sulfur atom 104 and two methane (CH3) molecules, 100 and 102. The dimethylsulfoxide forms hydrogen bonds with the water at 101 and 105. These bonds prevent other water molecules from bonding with the water molecules in the same place, thereby reducing the size of the water cluster. The 6-water cluster is defined by a ring of oxygen atoms 111, 112, 113, 114, 115, and 116 and hydrogen atoms such as 106 and 107 which are connected to oxygen atoms 114 and 115 respectively with hydrogen bonds represented by single lines 108 and 109 respectively. The molecules in the 6-water cluster may be connected to other water molecules or other molecule clusters by any number of branching hydrogen bonds.
FIG. 2A
Referring to FIG. 2A, the effect of a dipolar aprotic solvent on the H—O—H angle 210 defined by hydrogen atom 201, oxygen atom 200, and hydrogen atom 202 is to stretch it from an angle of 104.47 degrees to 109.47 degrees. This is also called an H-bond angle because it is the angle of the H-bond 203 in relation to the covalent bond 204. The initial angle is the residual effect of bleaching agents on the water.
FIG. 2B
Referring to FIG. 2B, the final H-bond angle results in a molecular arrangement close to the normal tetrahedral structure of water shown by the water molecule comprised of oxygen atom 206 and hydrogen atoms 205 and 207. This structure results in reduced water molecule clustering and improves the reactivity of the water, reducing trapped oxygen and resulting in increased solvent capacity of the water which enables more pulp to be dissolved per unit volume of water.
FIG. 3
Referring to FIG. 3, the steps of the repulping process using the method of this invention is shown starting with the printed paper raw material 1 which is heated, agitated and pulped in a solution of dipolar aprotic protophilic solvent 2; followed by an optimization loop 3, comprising tests and analysis 4 and control of adjustable factors 5, which is performed to adapt the process to the particular kind of printed paper raw material 1. The recovery of the dipolar aprotic protophylic solvent 6 is ecologically sound, and can be done by using petroleum ether for example to recover DMSO by an extractive distillation loop such as that shown in FIG. 7. (Referring to FIG. 7 extractive distillation is a well-known subprocess that involves adding an extractive component that imbalances the relative volatilities of a binary system of components and allows separation of the binary components to take place.) In step 7 of FIG. 3, the coarse screening 7 allows for subsequent typical repulping procedures 8, and in combination with the earlier steps, provides a yield of high quality reusable pulp 9 that can be used to make recycled paper products.
In the solvent pulping of recycled paper (FIG. 3, steps 2-6), the runs for obtaining solvent recovered fibres with open hydrogen bonding system should be conducted at a temperature in the range of 5-90 C. Based on initial strength and the type of pulp the fibres were made of, the aqueous solvent concentration to break-down interfibre bonding and to ensure sufficient defibration should be in the range of 0.1 to 1 percent, (e.g. 0.5%25% of o.d. fibrous material). Solid to liquid consistency will be close to 1:15, i.e., similar to those conditions of conventional pulping. Hemicellulose extract can be isolated from the recovered pulp by filtration through a funnel. The filtrate should be filtered 2 to 5 times through the fibre mat in order to completely remove the fines. Then the filtrate should be dialyzed for 48 hours in order to get rid of the solvent and low molecular weight impurities. The filtrate should be reduced to a small volume by rotary evaporating. Freeze drying can be used to test yield and to store for further analysis. The fibre mat should be diluted to a consistency of 2% according to Tappi standard (T 205 om-88) and disintegrated. Then the pulp slurry will be screened through a pulp strainer with a slot cut width 0.15 mm. After yield determination, the screened pulp will be ready for further evaluation and adjustments to the process to optimize the variable factors of temperature, solvent concentration, liquid to solid ratio. To remove undetached and small ink particles remaining on to the fibres after solvent treatment, a de-inking agent such as fatty acids, fatty acid derivatives, higher alcohol derivatives, or fatty oil derivatives will be introduced to the fibrous material in the disintegrator.
In step 5, after each change of the adjustable factors, some or all of following tests 4 should be conducted to analyze the effect of the change, with a view to achieving a balance in the desired characteristics of the re-pulped material:
4.1 Solvent Effect on H-bonding of Cellulose : Infrared spectra of the re-pulpled material will be analyzed to determine the effect of the solvent on the H-bonding of the material. The test results are directly proportional to the amount of cellulose fibre disruption that has occurred. An example of IR analysis by Diffuse Reflectance Infrared Fourier Transformer (DRIFT) test is: obtaining the average absorbance peak height around 3400 cm−1 (gross hydroxyl range) of differently treated cotton specimens, in a way that the intensity of the hydroxyl band could be read without being influenced by the intervening factors. Such factors that could be taken into consideration are the variations in peak locations due to stereochemical changes and noise perturbation. The analysis is performed on Perkin-Elmer 1610 Fourier transform infrared spectrometer equipped with Perkin-Elmer diffuse reflectance attachment, with the sample incorporated in ground potassium chloride was ratioed against that of each sample. The spectra from measurements involving 64 scans at a spectral resolution of 8 cm−1. The hydrogen bonding test is the mean for three measurements.
4.2 Solvent Effect on H-bonding of Water: The Fourier Transform Infrared difference spectra between plain dipolar aprotic solvent, dipolar aprotic solvent-water binary system, and untreated water will be analyzed for the 3750-3450-cm−1 to determine the effect of the solvent on the H-bonding of water.
4.3 Alpha Cellulose test: This test is again of an effect that is directly proportional to the effect of the weakening and disruption of the hydrogen bonding during the repulping process of the current invention, as it measures how much hemicellulose remains after treatment, and how much the crystalline cellulose responded to the treatment. The carbohydrate fraction of holocellulose, resistant to dissolution in 17.5% NaOH, is termed alpha cellulose. That percentage is a significant parameter of wood and chemical pulps and is used to assess the approximate quality of dissolving pulps, and in paper pulp it gives information about the residual hemicellulose content and degree of disruption and defibration of cellulose fibres which occurs during the repulping process. The air-dried holocellulose is treated with several portions of 17.5% NaOH, washed and dried. The residual remaining in a filter crucible is the alpha cellulose. The outcome of the swelling depends on the disruption since the filter material passes through maximum swelling at 10% NaOH during the washing. Analysis can also be done of the dissolved fraction which consists of beta- and gamma-celluloses (hemicellulose).
4.3 Solvent Effect on Water Cluster Size: For the determination of water cluster size, such as argon gas clusters will be doped in a an aprotic solvent untreated water pick-up cell, and the subsequent electron impact ionization of the doped clusters in a mass spectrometer or gas analyzer produce ionized cluster fragments that retain water. Water is supplied under pressure to the pick-up cell disposed within a vacuum chamber, and the water pressure is metered by a metering valve and monitored by a pressure gauge. A vacuum pump is coupled to the vacuum chamber that generates a vacuum within the vacuum chamber and pick-up cell. Interaction between the gas clusters and the water in the pick-up cell produces doped clusters, some of which retain water. The electron impact ionized doped cluster fragments are analyzed using the mass spectrometer or gas analyzer permits determination (detection) of the mean cluster size of the clusters. The variation in intensity of the untreated water-containing fragments versus water pressure in the pick-up cell exhibits a Poisson behavior, from which the cross-section and mean cluster size is derived. Similar test will be carried out on a dipolar aprotic solvent-water binary system and plain dipolar aprotic solvent and the mean cluster size of the solvent treated water is derived.
4.4 Drainability test: The results of this test are also directly proportional to the H-bond disruption in the repulpable material. The test is also known as a Freeness test, a measure of the drainage rate of a pulp stock suspension through a fibre pad formed on a wire or perforated plate. The Canadian Standard Freeness tester is a North American standard. The less stiff and more flexible the fibres resulting from the repulping, the fewer fines break off to clog drain screens. In the finished paper sheet produced from the re-pulpled material, the fluffiness of the sheet, which consists of fibres sticking out from the general plane of the sheet, the stiffness again plays a role. The more flexible the fibres, the more comfortable the fibres will be in their pressed position in the finished paper sheet.
4.5 Microscopic Analysis: To investigate microbiological stability of dipolar aprotic solvent-water mixture compared to untreated water, microscopic analysis is to be conducted for bacteria count.
4.6 Crystallinity Index: The crystallinity index of the re-pulpled material should be checked for acceptability
4.7 Image Analysis: For sheet formation, cell wall cross section, and fibre response Sigma Scan Pro software can be used to track changes in these aspects.
4.8 Sugar Analysis: Water-soluble polysaccharides should be analyzed.
4.9 Viscosity Measurement: The degree of polymerization (DP) should be determined according to the Tappi standard 230 os-76.
4.10 Handsheet Preparation: Handsheets from the pulp of recycled paper should be prepared according to Tappi standard.
4.11 Grammage: This will be measured according to Tappi standard T410 os-68.
4.12 Burst Strength: To determine burst strength a Mullen burst tester will be used.
4.13 Tensile Strength: The force required to break a strip of paper of 15 mm width and 100 mm length will be determined according to Tappi standard T 494 om-88.
4.14 Tear Strength: This will be carried out according to Tappi standard T 414 om-88.
4.15 Brightness: Brightness of handsheets from recycled paper will be determined according to Tappi standard UM 438.
4.16 Smoothness: To measure smoothness of a handsheet a Bendtsen smoothness and porosity tester can be employed.
4.17 Thickness: This will be determined using a Messmer micro-electronic thickness tester.
After these step 4 tests are performed, if undesirable results are obtained the factors in step 5 can be modified until the desired results are obtained. The foregoing optimization procedures can be performed on small test batches, with the volume of equipment and material increased when the results are optimized. For example the optimum conditions for printed paper may have been determined under the optimization loop of step 3 to be as follows: i) dipolar solvent is dimethylformamide (DMF), ii) dimethylsulfoxide (DMSO) dipolar solvent to water ratio is +0.5 solvent:99.5 water, iii) solid to liquor ratio is 1:20,11 and iv) pulping temperature is 20 C35° C. v reaction time 10.5 min. These optimized conditions can then be replicated in the large batch.
Once the conditions are optimal as indicated by the test results, we return to step 2 where the pulp is once again sealed, heated, and agitated in a solution of dipolar aprotic solvent. The solvent is recovered in step 6, then the pulp is sealed, heated and agitated again 2, then it is screened using the coarse filter 134 and fine screen 137 shown in FIG. 6 and detailed in the description of FIG. 6 below.
After screening the pulp undergoes the typical repulping procedures of steps 8-8.5, including de-inking 8, mechanical disintegration,8.1, recovery of de-inking compound 8.2, fine cleaning 8.3, washing and thickening 8.4, and ozone bleaching 8.5, which is performed to attain high brightness levels of the solvent pulp. The standard bleaching method is peroxide and can be used. Brightness of bleached pulp will be checked according to Tappi standard UM 438. Ozone bleaching is capable of further delignifying de-inked pulp prepared by aqueous dipolar technique. Incorporating it in an OZEP (ozone/extraction/peroxide) sequence can produce a brightness of 90% ISO. Ozone is an aggressive oxidizer, compared to hydrogen peroxide, which is a mild oxidizer. The resulting pulp properties if compared to those of conventionally prepared and bleached recycled pulp would much be better off. Effluent characteristics would also be much improved. Toxic effluents from chlorine-free bleaching are extremely low and there are no dioxins, AOX in the effluent. Biobleaching with the use of enzymes can decrease the use of oxidizing chemicals in bleaching of recycled paper pulps. Treatment of de-inked pulp with selected enzymes can remove a greater fraction of the lignin without affecting the degree of polymerization (DP) of the cellulosic material. The biobleaching technique has been successfully tried in commercial trials. Environmentally, biobleaching is attractive. However, biobleaching entails high manufacturing costs for the enzymes and the slowness of the reaction.
Referring to FIG. 4, the hydrogen atoms 20, 21, 22, form the bonding between two adjacent cellulose molecules 63 and 64. The dipolar aprotic protophylic solvent molecules 91, 92, 93 are respectively dimethylformamide (DMF), dimethylacetamide (DMA), and dimethylsulphoxide (DMSO). They are adjacent to the cellulose in FIG. 2, ready to be placed into a solution where they will interact with the hydrogen as shown in FIG. 5 These solvent molecules have a substantial dielectric constant and dipole moment. They have no acidic hydrogen to enable the formation of hydrogen bonds. Because of their shape, they are better able to solvate cations than anions. This can be measured by the transfer of energy from methanol to dimethylsulphoxide (DMSO), for example. The reactions of cations in such dipolar aprotic solvents is therefore much higher than in hydroxylic solvents. It is this property which will cause the H-bond disruption shown in FIG. 5. The dipolar aprotic protophylic solvent molecules 91, 92, 93 will act as hydrogen bond acceptors with cellulose material.
Referring to FIG. 5, the dipolar aprotic protophylic solvent molecules 60, 61, 62 disrupt the hydrogen bonding in the cellulose by positioning themselves between the oxygen atoms 65 and 66. This occurs because the oxygen has an electronegativity of 3.5 and the hydrogen an electronegativity of 2.1. Hydrogen has a low electron affinity, and oxygen has a high electron affinity in the mixture of the solution and the repulpable cellulose material.
Referring to FIG. 6, the pulping can be performed in a batch open vat pulper 31, allowing observation of the process. The process starts with recycled paper (e.g., printed paper 32) pulping. The agitator 131 and its motor 132 are controlled by the Adjustable Factors control panel 133. The coarse filter 134 allows the re-pulpled material to fall through, where is drawn off by outlet pipe 135 and suction pump 136. The fine screen 137 allows the solution to be drawn off through solvent outlet pipe 138 and solvent suction pump 139, by which it is recycled to solvent storage tank 140.. The dipolar aprotic protophylic solvent inlet pipe 141 supplies the solvent to the solvent storage tank 140, and a water inlet pipe 142 allows for a dilution of the solution. The repulpable material is supplied via inlet chute 143. Heat can be supplied by steam boiler 144, taking into account its effect on the concentration of the solution.
The optimization process involves fibre samples subjected to an infrared spectrometer 70, preparation in accordance with the selected tests as noted above in test tubes 71, 72, 73 for analysis under a microscope 74, preparation of test sheets 75, 76, 77 for the handsheet tests noted above, and feedback 145 to the Adjustable Factors control panel 133. The knobs 81 through 85 control respectively the temperature, solvent concentration, type of dipolar solvent, solid/liquid ratio, and the degree/duration of the mechanical agitation. The re-pulped material is dumped into hopper 146 for transport to washing facilities, using a conical centrifuge washer 147, for example.
Referring to FIG. 7 the extractive distillation subprocess is shown. The effluent 700, which consists of water, fibrous material, additives, resinous material and DMSO, will be pumped in the extraction tower 701, where petroleum ether 702 from the tank 703 will be added through the pump 704. Then vigorous mixing of the effluent 700 with petroleum ether 702 will be conducted. After a proper mixing time, two distinct liquid layers are formed in the extraction tower 701. The upper layer 712 is composed of petroleum ether, resinous material and DMSO, whilst the lower one is the sludge 710, which contains mainly fibrous material, additives and some other organic substances. The sludge 710 is selectively separated from the upper layer through a sensor system and pumped out of the extraction tower 701 for further treatment. The upper layer 712 will be forwarded through the pump 711 to the distillation tower 713. In the tower 713 the distillation of petroleum ether takes place at low temperatures (35-60° C.) and then the ether is pumped through the pump 705 into the tank 706 and after it is sent out to the extraction tower 701 through the pump 709 for reuse, whilst the mixture 708, of resinous material and DMSO (boiling point 189° C.) remains at the bottom of the distillation tower (G), will be sent out to the 3rd and final stage—solid/liquid separation unit where DMSO will be separated as a pure solvent for reuse.
Distillation is recommended in this project as a second step, i.e., following liquid extraction process. In this invention, distillation is applied for the separation of petroleum ether from DMSO+Sludge (mainly resinous material).
Distillation is defined as a process in which a liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity by the application and removal of heat. Distillation is based on the fact that the vapor of a boiling mixture will be richer than the components that have lower boiling points. Therefore, when this vapor is cooled and condensed the condensate will contain more volatile components. Distillation columns are designed to achieve this separation efficiently. Petroleum ether recovered through the distillation process will be reused in DMSO extraction from the spent repulping liquor.
Solid/liquid separation is the 3rd and final stage in the solvent separation. It is recommended for the separation of DMSO from the sludge which is mainly resinous material. Solid-liquid separation is a major unit operation that exists in almost every flow scheme related to the chemical process industries. Solid/liquid separation has a wide application in pharmaceutical, mining, sugar, pulp and paper, waste water treatment, mining, ceramics, food and other industries.
Referring to FIG. 8, liquid extraction is employed for the separation of DMSO from the spent repulping liquor (process water+DMSO). In the extraction process the heavy liquid solution mixture (H2O and DMSO) to be separated is passed through inlet pipe 801 and contacted, through mixing, with the extracting solvent (petroleum ether) which enters through the light liquid inlet 803.. The DMSO is extracted through the light liquid outlet 802 in a solution of DMSO and petroleum ether. The raffinate or portion of the original liquid that remains (primarily water) exits through the heavy liquid outlet 804. Note that petroleum ether has been chosen as the preferred extracting solvent due to the following characteristics.
i. Selectivity—petroleum ether is quite selective in removing DMSO from the water.
ii. Solvent recoverability—easily recovered (bp 35-60 degrees C.) from DMSO (bp 189 degrees C.).
iii. Density differences—petroleum ether has the density of 0.64 g/ml, while DMSO has the density of 1.1004.
iv. Interfacial tension of petroleum is large.
v. Non-reactivity—petroleum is non-reactive with DMSO.
The recovered water from liquid extraction will be sent to the repulping section for further reuse. Applications include, thickening, clarification, cake and deep-bed filtration, centrifugation, sedimentation, and hydrocycloning, Their mechanisms are the relative solid/liquid motions such as flow-through porous media and sedimentation. Fundamental aspects of solid/liquid separations are the properties of suspensions (e.g., particle size and shape, particle-particle interactions, particle surface characteristics, and concentration) of sediments and cake (porosity, permeability, compressibility, viscosity and yield stress). The recovered DMSO will be reused in the preparation of fresh repulping liquors.
In general, liquor-displacement technology applies to recycled paper pulping and provides the context for the above process. At the end of the pulping a preset volume of cooler wash filtrate is pumped into the pulper, where it displaces warm black liquor, which is transferred to an accumulator. From the accumulator the black liquor is pumped to extraction/distillation towers for DMSO recovery for further use. Then the pulping slurry will be subjected to coarse screening to remove contaminants that are non-fibrous material. This is followed by addition of de-inking chemical and then the pulp undergoes mechanical disintegration where the small ink particles will be detached. The filtrate of the disintegrated pulp will be pumped to a designated ion-exchange unit to separate de-inking chemical (e.g., fatty oil derivatives) for further use. The resultant disintegrated pulp will be subjected to fine cleaning and screening at fine screen in order to remove fine ink particles, minute contaminants, and some of the fine pulp fibres. At the end process tub, washing and thickening will be applied to completely remove fine ink particles and fine pulp fibres.
Application of aqueous dipolar solvents in pulping of recycled paper pulping aims, to a greater extent, to limit the chances of fibre loss to the minimum. In other words, the primary goal of the proposed project is focused on the attacking the root cause of fibre loss, i.e., which is the fibre stiffness. The use of aqueous dipolar solvents in waste paper pulping will enable a uniform defibration in both amorphous and crystalline zones of the substrate. Thus, dipolar solvent technique is capable of offering a high quality pulp that may approach the quality of virgin pulp. With this method and system it is realistic to expect less than 10% fibre loss during cleaning and washing operations, with a net pulp yield of 90%.
In the system and method of this invention, the breakdown of hydrogen bonding of the cellulose substrate (recycled paper) by the interaction of dipolar solvent (e.g., DMSO, DMF, DMA) in the presence of a major fraction of water enables a minimal removal of hemicellulose (eg., surface adsorbed carbohydrate) compared to standard pre-existing repulping techniques. The advantages are immediate and allow for optimization as explained above. The higher process efficiency is expected to bring about significant impact on the economic feasibility and competitiveness of manufacturing of pulp from recycled paper, producing high pulp yield and competitive fibre quality at less cost and involving fewer technological operations than conventional methods of repulping.
The within-described invention may be embodied in other specific forms, systems and methods and with additional options and accessories without departing from the spirit or essential characteristics thereof. The presently disclosed embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.

Claims

1. A method for repulping of paper products and improving water quality, comprising the steps of:

a) placing paper product material in an aqueous solution of dipolar aprotic protophylic solvent in a pulper, in which the water structure in the aqueous solution has been altered and optimized toward a tetrahedral lattice of natural hydrogen-oxygen-hydrogen angles through the rearrangement of its hydrogen bonding system, the water structure acquiring smaller cluster pattern, lower surface tension, increased dissolving powers, higher carrying efficiency, microbiological stability and greater reactivity;

b) agitating a mixture of the paper product material and the aqueous solution of dipolar aprotic protophylic solvent in the pulper until stereochemical alterations within the paper product material have occurred, rendering an open hydrogen bond packed cellulose, and a target degree of repulping has occurred;

c) draining off the aqueous solution of dipolar aprotic protophylic solvent from the pulper;

d) removing resultant pulp from the pulper

e) optimizing of process variables depending on the reactivity of dipolar aprotic solvent water and the type of material being repulped and the desired characteristics of the pulp resulting from the process

2. The method of claim 1, in which process variables are optimized to enable each solvated aprotic solvent molecule to be bonded to two water molecules, and to make the average angle between two hydrogen bonds in the aprotic solvent almost tetrahedral.

3. The method of claim 1, in which process variables are optimized to provide that water molecules are hydrogen bonded to other water molecules but near oxygen components of dipolar aprotic solvent molecules, enabling simultaneous water bonds with aprotic solvent and a readiness to switch bonding from water to the aprotic solvent.

4. The method of claim 1, in which the process variables are optimized to keep water molecules away from methyl groups of an aprotic solvent where there would be no alternate bonding between water molecules and the aprotic solvent.

5. The method of claim 1, in which the dipolar aprotic protophylic solvent comprises one of the group of dimethylsulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMA).

6. The method of claim 1, in which the pulper is in an open vat during the agitating to allow observation of the process.

7. The method of claim 1, further comprising the steps of optimizing at least one adjustable process factor from among the group of:

a) temperature of the mixture;

b) concentration of the dipolar solvent in an aqueous solution;

c) liquid to solid ratio of the solution to the paper product material;

d) mechanical action of the agitator;

e) duration of the agitation;

by testing the effect of varying such adjustable process factor on the resultant pulp for a given type of paper product material against desired characteristics of the resultant pulp, and for testing water bonding to aprotic solvent.

8. The method of claim 1, in which the:

a) temperature of the mixture is in the range of 5 to 90 degrees Centrigrade;

b) dipolar aprotic protophylic solvent is in the range of 0.001% to 40% by volume of the solution;

c) solid to liquid to ratio of the solution to the paper product material is in the range of 1% to 33%;

d) the mechanical action of the agitator is such that substantially maximal repulping within the mixture occurs within one hour of agitating;

e) the duration of agitation is in the range of 1 to 90 minutes.

9. The method of claim 1, in which at least one of the following tests is applied to the resultant pulp and water to assist in the optimization of at least one adjustable process factor:

a) infrared spectra analysis to determine process effect on hydrogen bonding in the resultant pulp;

b) alpha cellulose test to determine process effect on hydrogen bonding in the resultant pulp;

c) Drainability test to determine process effect on hydrogen bonding in the resultant pulp;

d) test of Solvent Effect on H-bonding of Water, with Fourier Transform Infrared difference spectra between plain dipolar aprotic solvent, dipolar aprotic solvent-water binary system, and untreated water being analyzed;

e) test of Solvent Effect on Water Cluster Size, by doping argon gas clusters in an aprotic solvent untreated water pick-up cell, and the subsequent electron impact ionization of the doped clusters in a mass spectrometer or gas analyzer

f) microscopic analysis to investigate microbiological stability of dipolar aprotic solvent-water mixture compared to untreated water, and bacteria count.

10. The method of claim 1, in which at least one of the following tests is applied to the resultant pulp to assist in the optimization of at least one adjustable process factor:

a) Crystallinity Index

b) Image Analysis of sheet formation, cell wall cross section, and fiber response;

c) Sugar Analysis

d) Viscosity Measurement

e) Handsheet Preparation

f) Grammage

g) Burst Strength

h) Tensile Strength

i) Tear Strength

j) Brightness

k) Smoothness

l) Thickness

m) CMT Test, Flat crush of corrugating medium, T809 om, 93

n) STFI, short span compression strength of containerboard, T826 pm

o) Kajaani FS 200

p) Fiber Quality Analyzer

11. The method of claim 10, in which:

a) a de-inking process is applied to the resultant pulp;

b) a bleaching process is applied to the resultant pulp;

c) a further test is applied to assist in optimization of at least one adjustable process factor is bleaching analysis of recycled paper made from the resultant pulp.

12. The method of claim 1, in which the draining off of the aqueous solution of dipolar aprotic protophylic solvent from the pulper recycles the aqueous solution of dipolar aprotic protophylic for re-use in a further repulping cycle.

13. The method of claim 2,

a) in which the pulper is an open vat during the agitating to allow observation of the process.

b) further comprising the steps of optimizing at least one adjustable process factor from among the group of:

i) temperature of the mixture;

ii) concentration of the dipolar solvent in an aqueous solution;

iii) liquid to solid ratio of the solution to the paper product material;

iv) mechanical action of the agitator;

v) duration of the agitation;

by testing the effect of varying such adjustable process factor on the resultant pulp for a given type of paper product material against desired characteristics of the resultant pulp;

c) in which:

i) temperature of the mixture is in the range of 5 to 90 degrees Centrigrade;

ii) dipolar aprotic protophylic solvent is in the range of 0.1 to 5% of the solution;

iii) solid to liquid ratio of the solution to the paper product material is in the range of 1% to 33%;

iv) the mechanical action of the agitator is such that substantially maximal repulping within the mixture occurs within one hour of agitating;

v) the duration of agitation is in the range of 1 to 90 minutes;

d) in which at least one of the following tests is applied to the resultant pulp to assist in the optimization of at least one adjustable process factor:

i) infrared spectra analysis to determine process effect on hydrogen bonding in the resultant pulp;

ii) alpha cellulose test to determine process effect on hydrogen bonding in the resultant pulp;

iii) Drainability test to determine process effect on hydrogen bonding in the resultant pulp;

e) in which at least one of the following additional tests is applied to the resultant pulp to assist in the optimization of at least one adjustable process factor:

i) Crystallinity Index;

ii) Image Analysis of sheet formation, cell wall cross section, and fiber response;

iii) Sugar Analysis;

iv) Viscosity Measurement by determination of the degree of polymerization according to the Tappi standard 230 os-76.

v) Handsheet Preparation according to Tappi standard.

vi) Grammage measured according to Tappi standard T410 os-68;

vii) Burst Strength determined with a Mullen burst tester;

viii) Tensile Strength, determining the force required to break a strip of paper of 15 mm width and 100 mm length according to Tappi standard T 494 om-88;

ix) Tear Strength, according to Tappi standard T 414 om-88;

x) Brightness of handsheets from recycled paper will be determined according to Tappi standard UM 438;

xi) Smoothness of handsheets using a Bendtsen smoothness and porosity tester;

xii) Thickness determined using a Messmer micro-electronic thickness tester;

xiii) bleaching analysis of recycled paper made from the resultant pulp;

f) in which:

i) a de-inking process is applied to the resultant pulp;

ii) a bleaching process is applied to the resultant pulp;

iii) a further test is applied to assist in optimization of at least one adjustable process factor is bleaching analysis of recycled paper made from the resultant pulp.

g) in which the draining off of the aqueous solution of dipolar aprotic protophylic solvent from the pulper recycles the aqueous solution of dipolar aprotic protophylic for re-use in a further repulping cycle;

h) in which process variables are optimized to provide that water molecules are hydrogen bonded to other water molecules but near the oxygen of a dipolar aprotic solvent molecule, enabling simultaneous water bonds with the aprotic solvent and a readiness to switch bonding from water to the aprotic solvent, by keeping water molecules away from methyl groups of aprotic solvent where there would be no alternate bonding between water molecules and the aprotic solvent

14. A system for repulping of paper products, comprising:

a) a pulper having an agitator mechanism and a controllable heat supply;

b) a supply of dipolar aprotic protophylic solvent, with controllable inflow piping to the pulper;

c) a water supply with controllable inflow piping to the pulper;

d) a drain mechanism for the pulper;

e) a coarse screen for filtering repulpable material from resultant pulp;

f) a fine screen for filtering resultant pulp from the dipolar aprotic protophylic solvent;

g) controls for optimizing of process variables depending on the reactivity of dipolar aprotic solvent water and the type of material being repulped and the desired characteristics of the pulp resulting from the process

15. The system of claim 14, comprising controls and mechanisms to keep water molecules away from methyl groups of aprotic solvent where there would be no alternate bonding between water molecules and the aprotic solvent.

16. The system of claim 15, in which there are sensors and controls to sense and control at least one of the following adjustable process factors:

a) temperature of the mixture;

b) concentration of the dipolar solvent in an aqueous solution;

c) liquid to solid ratio of the solution to the paper product material;

d) mechanical action of the agitator;

e) duration of the agitation.

17. The system of claim 15, further comprising test facilities for performing at least one of the following tests:

18. The system of claim 15, further comprising test facilities for performing at least one of the following tests:

a) Crystallinity Index

c) Sugar Analysis

d) Viscosity Measurement

e) Handsheet Preparation

f) Grammage

g) Burst Strength

h) Tensile Strength

i) Tear Strength

j) Brightness

k) Smoothness

l) Thickness.

19. The system of claim 15, further comprising a de-inking module and a bleaching module.

20. The system of claim 15, further comprising a distillation module and a liquid extraction module for solvent recovery and recycling.

21. The system of claim 15, further comprising:

a) further comprising test facilities for performing at least one of the following tests:

b) test facilities for performing at least one of the following tests:

i) Crystallinity Index;

iii) Sugar Analysis;

v) Handsheet Preparation according to Tappi standard.

vi) Grammage measured according to Tappi standard T410 os-68;

vii) Burst Strength determined with a Mullen burst tester;

ix) Tear Strength, according to Tappi standard T 414 om-88;

xi) Smoothness of handsheets using a Bendtsen smoothness and porosity tester;

xii) Thickness determined using a Messmer micro-electronic thickness tester;

xiii) bleaching analysis of recycled paper made from the resultant pulp;

c) a de-inking module and a bleaching module.

d) a distillation module and a liquid extraction module for solvent recovery and recycling the dipolar aprotic solvent hydrogen bond rearranged water.