FI56861C - OIL SEPARATION AND OIL TILLER VARIETY AV AVOESLIGA AMNEN FRAON CELLULOSAHALTIGA LOESNINGAR - Google Patents

Description

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Patent- and register-offices' utίΜβΙαη utlagd och utUkrlfUn publkerad 31-12. (9 (32) (33) (31) Requested «tolirdus —Begird prlorlttt 13 · 10.72 USA (US) 297U06 (71) ITT Industries, Inc., 320 Park Avenue, New York 22, NY, USA (US) (72 ) Edmund M. LaPolla, Parsippany, New Jersey, Charles F. Murphy,

Morristown, New Jersey, Arthur Sarkisian, Cranford, New Jersey, USA (US) '(7U) Oy Kolster Ah (5U) Method for the separation and recovery of insoluble substances from cellulose-containing solutions

The invention relates to a process for the separation and recovery of insoluble substances from cellulosic solutions, comprising the step of filtering this solution and the step of solubilizing the insoluble cellulosic residue using a granular filter bed and basic solvents.

Before extruding viscose into fibers or films, the viscose must be filtered to remove gels, fiber particles, and other insoluble material. This improves the strength, evenness and appearance of the finished regenerated cellulosic product and prevents clogging of the orifices. The filtration step is one of the worst bottlenecks in the viscose process. Normally, filtering is performed as a batch process. Usually, when a filter made of cotton, nylon, or other man-made fiber felts or various nonwovens becomes clogged, the insoluble material and the filter are removed together, or the material is washed from the filter and removed before reuse. The difficulty in making the process continuous and recirculating the insoluble material has been the lack of efficient equipment to remove the rubbery, r * ·: - 'K. ’· 2 56861 insoluble matter from the filter and the lack of economic conditions to dissolve the gels and fiber particles. The problem is particularly difficult because even small amounts of insoluble residues cannot be allowed when extruding viscose fibers and films.

Filtration through the particle bed is quite well known, as is washing to remove solid or gel-like residues from a clogged filter. However, such systems have never been used on an economic scale to completely recover and recycle cellulosic residues from cellulose filtration. Other systems are relatively expensive or cannot recover all of the filtered cellulosic material.

The object of the invention is to provide a simple, economical and yet very efficient method for filtering cellulosic solutions.

The object of the invention is to provide a method for filtering cellulosic solutions which enables the recovery of almost all cellulosic material. Normally, this material is discarded, causing an ever-increasing waste problem.

It is a further object of the invention to provide a continuous or near-continuous process for filtering, recovering and recycling the insoluble cellulosic material of a viscose filtration process.

The invention is characterized by the following sequential steps: a) the insoluble matter is separated from the cellulosic solution by filtration through the latter layer, which is a granular material inert to the cellulosic solution and has a particle size of -20 (0.81 * mm). ) and +325 (0.01 * 1 * mm); b) the granular layer and the accumulated insoluble matter are mixed with a solvent with stirring to partially dissolve the cellulosic residue, the resulting solution being very concentrated compared to its concentration in the original cellulosic solution; c) adding to the resulting concentrated solution, with stirring, a solubilizing reagent to completely dissolve the insoluble cellulose residue; d) the resulting cellulosic material solution is separated and recovered from the granular layer.

The cellulosic material solution can be recycled to the unfiltered cellulosic solution, eliminating the waste of conventional methods.

The invention is particularly suitable for the industrial filtration of viscose and, for the sake of clarity, will be described in connection with the filtration of viscose solutions. However, it is clear that the invention is generally applicable to cellulose-containing solutions which, in addition to viscose, are: cellulose acetate, hydroxyethylcellulose and hydroxypropylcellulose.

In the production of viscose, cellulose is extracted into cellulose xanthate by reacting the cellulose with carbon disulphide followed by treatment with a base solution. The xanthate is then dissolved in a dilute base solution, usually sodium hydroxide solution. The present filtration method utilizes this reaction by using carbon disulphide as a solvent and a dilute base solution as a solvent to completely dissolve the insoluble cellulosic material of the viscose solution. The use of a sufficient amount of sulfur-carbon in the whole viscose solution for this purpose would be far too expensive for economic reasons. However, in the present invention, carbon disulphide is used in only a small proportion of insoluble gels and fibers that are effectively concentrated to a small volume. Of the cellulose in the stock solution, sulfur-carbon affects less than one percent. Normally this amount is about 0.1-0.2. The amount of sulfur carbon required to dissolve cellulose residues in the form of this concentrated precipitate is in fact a small amount relative to the total amounts in the process. In addition, recycling this small amount of sulfur carbon as part of the manufacturing solution for the next high viscosity filtration does little to increase raw material costs.

The reagents and solvents used for the complete dissolution of the cellulose residues are either those used thermally to prepare the cellulose derivative or those compatible with the unfiltered cellulose solution preparation solution, whereby the dissolved cellulose material can be recycled and used in continuous or near continuous filtration. In the preparation of cellulose acetate, the solvent is a solution of acetic acid in the range of 75 to 90 μl instead of the sodium hydroxide solution, and the cellulose residues as the solvent are acetic anhydride in an amount of 175 to 250 by weight of the reacting cellulose. In the preparation of hydroxyethylcellulose, the solvent is, as in the viscose process, a dilute sodium hydroxide solution, but in this case the reactant is 20 to 70 l of ethylene oxide by weight of the cellulose. In the preparation of hydroxypropylcellulose, the solvent may also be dilute sodium hydroxide solution, but the reactant is 25 to 75 l of propylene oxide by weight of the cellulose.

The particle layer and the resulting insoluble cellulosic material may first be washed as a solvent to partially dissolve the insoluble cellulose, after which the washing liquid is treated with a solvent to complete the dissolution, or the solvent and the solvent may be added simultaneously. In the case of a viscose solution, the accelerated dissolution of cellulosic gels, fibers and particles can be carried out completely with as little sulfur carbon as $ 50 by weight of cellulose residues. However, normally it is necessary to use an excess of carbon disulphide based on the weight of the cellulose residues and sometimes it is necessary to use more than twice the weight of the cellulose residues.

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The upper limit is not · critical as long as all insoluble cellulose dissolves · Again, it should be noted that such an amount of sulfur carbon is not in fact uneconomical because it affects the highly concentrated form of cellulose residues compared to the parent solution and can be completely recycled in the process.

The particle layer may, although not necessarily, become completely clogged before it is mixed with the base solution or other solvent. Filtration can be interrupted when the filtration rate has decreased to the extent that some or significant clogging has occurred. As used herein, the term "disturbance of the continuous flow of liquid" means any degree of reduction in the filtration rate, whether it is partial, substantial, or complete clogging of the particle layer.

The use of filtration particle layers is, of course, known. However, they have been found to play a unique role in the present method. They clog or otherwise interfere with fluid flow much more slowly than porous plates, meshes, or other filters used in conventional cellulose filtration. One explanation for this is believed to be the way in which the cellulosic fibers and gels dissolve. In order for the xanthated cellulose fiber to dissolve properly in the base solution, both time and mixing are required. When the solvent wets the xanthized fiber, a concentrated, highly viscous solution layer8 is formed around it. Stirring facilitates the scraping of this thick layer into the surrounding liquid phase, diluting it to its final average viscosity while exposing new surfaces of the reactive fiber to the solvent. Without mixing, the rubbery shell surrounding the individual fibers becomes so viscous that further penetration of the solvent becomes difficult and poorly stable masses of swollen gels form.

In the non-particulate layer, the rubbery gel particle may protrude into the cavity, but is still partially exposed to the comparative solution. If it has reacted properly, the gel "scraped" by the flowing solution may dissolve further. However, poorly reacted or otherwise damaged fibers eventually fill the entire free space of the layer.

In addition, the particle layers facilitate the separation of cellulose residues for the next dissolution step. After clogging, porous plates and nets are difficult to wash clean. Instead, insoluble cellulose residues are quite easy to remove from the particle layer with a dilute base solution or other solvent. The particle layer can be any material that withstands the corrosive effect of the material to be filtered, which in the case of viscose is basic and acidic or neutral in the case of various other cellulose derivatives. A very suitable layer of viscose solutions consists of powdered, stainless steel, although other metal powders may be used, e.g. nickel, carbon steel and other metals and alloys which do not react with the preformed solution. Also useful are organic polymers, e.g., polyethylene, polypropylene, polyvinyl chloride, and Teflon (trade name for polytetrafluoroethylene). Ceramic powder and other unreacted particulate matter will be apparent to those skilled in the art. Powders usually have a mesh size of -20 to +325 U.S. standard screen size.

The invention will now be described in more detail in connection with viscose filtration.

Normally the viscose solution is pumped through the particle bed at a pressure of o 1.8-10.5 kp / cm, but in some special cases the upper pressure limit may be o 28.0 kp / cm. After a certain amount of solution has flowed through the filter, a relatively small portion of the partially dissolved cellulose golds and gels partially or completely clogs the powder layer until the layer resembles an almost solid cake, preventing continuous fluid flow. Typically, more than 200 liters of viscose solution flows through 0.3 liters through a layer of stainless steel with a mesh size of -20 to +70 and a thickness of 2.54 to 1 91 cm, before almost complete clogging. The layer can then be removed and washed with stirring or shaking with about half a liter of 9 # sodium hydroxide solution, which partially dissolves the insoluble cellulosic material and separates the attached gels and fibers. The remaining insoluble material appears as a turbidity floating on top of the aqueous solution and the stainless steel powder layer. The solution can then be decanted and treated with excess carbon disulphide, e.g., one milliliter per 20 milliliters of $ 9 sodium hydroxide solution. At the same time, the solution is stirred to transfer the remaining cellulose residues to the solution.

Alternatively and preferably, carbon disulphide is added to the base solution and the common solution is added in one portion to the stationary occluded or partially occluded layer. The resulting turbidity disappears when the layer and solvent are mixed and the cellulose residues dissolve in a reactive, low-viscosity medium. The wash solution containing dissolved cellulose star, $ 9 sodium hydroxide solution and carbon disulphide is then decanted from the stainless steel layer and recycled as part of the preparation of the next 200 liters of viscose filtration solution. The powder layer can be used in the next filtration cycle.

The initial, unfiltered preformulant-containing solution contains a small amount by weight of insoluble matter. A typical, unfiltered viscose solution containing 9 ° regenerating cellulose contains 0.1-0.1 96 insoluble cellulose. · After the insoluble residue is recovered, it is partially dissolved in a dilute base solution with a concentration 20-200 times higher than in the parent solution. The weight of the dilute base solution is about 0.5-4 $ and usually about 1 ia origin s of the weight of the solution * In volume, the volume of the dilute base solution is twice the volume of the clogged filtration layer 6 56861. The concentration of the dilute mother liquor should be between 7 and 11 $ based on the weight of the alkali metal hydroxides. The choice of a particular base is not critical, although sodium hydroxide is commonly used in its viscose process due to its widespread use. However, other bases can be used, e.g. lithium and potassium hydroxides and the like. the choice of base will be apparent to one skilled in the art.

Periodically, magnetic or pulmonary separation can be used to purify the metal novel silica or other non-cellulosic impurities that would otherwise be enriched in the powder layer. Metal particles that sometimes detach from the surrounding, filtered solution can be recovered by a magnetic device, leaving the layer at 100%.

In a highly preferred embodiment of the invention, the filtration is performed through a layer of particles with a coarse and a fine layer (or through two separate layers, one coarse and the other fine). Viscose solutions filtered through such a double powder layer give filtered solutions and rayon of excellent quality. The mesh size of the first or usually upper part of the layer can be e.g. -20 to +40 and the second or finer part -40 to +70. By using powders with different magnetic or density properties, a double powder layer can be made into a coarse particle layer on top of a fine particle layer.

The following examples illustrate the practice of the invention. Unless otherwise indicated, all parts by weight are parts by weight and all mesh sizes are U.S. standard sizes.

Example 1

A stainless steel powder layer with a thickness of 2.54-1 * 91 cm and a diameter of 12.70 cm was prepared. The lowest 2.54 cm of the layer was stainless steel powder with a mesh size of -20 to +40. Filtration was performed in a closed pressure vessel with a constant feed pressure of 2.8 kp / cm. The composition of the viscose solution was $ 9 regenerable cellulose (based on total solution), $ 6 sodium hydroxide (based on total solution) and $ 28 carbon disulphide (based on the amount of cellulose in the solution). After 235 kg of viscose solution had flowed through the apparatus with only partial clogging (i.e. the filtration rate had decreased by about $ 10-30), the layer was extracted n * in one liter of 9 * 0 $ sodium hydroxide solution, which also contained 5 * 0 ml of carbon disulphide. Per 100 ml of sodium hydride solution. The amount of carbon disulphide was about $ 250 of the calculated amount of insoluble cellulose remaining in the bed. After one hour of treatment, the extraction liquid was separated from the bed by decantation and a slurry was used as part of the preparation liquor of the batch. This batch is filtered through the same layer of stainless steel. The post-incant layer was placed in place and prepared for reuse. The cycle was repeated four times, each cycle consisting of two 200-240 kg batches of viscose (190-227 l). in the second and fourth stages, 2 kg of extraction wash water from the previous stage was used.

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To determine their clogging, separate but similar solutions were filtered through a layer of stainless steel and a standard viscose filter with a layer of 56 grams of double-sided cotton fabric and a carrier layer of 16 grams of Canton flannel. The filtered solutions were then re-filtered through a standard filter until the filter became clogged. The clogging coefficient obtained as a particle filter was at least as good or better than that of a conventional filter. In addition, the filtration efficiency was not reduced by recirculation, whereby the particle layer was reused or insoluble cellulose particles were regenerated and returned to the viscose stream as part of the preparation liquor.

Example 2

The most important feature of filtration is its effect on the spinning of viscose fibers. A series of four-liter samples were taken from a single batch of 114 liters and each sample was treated with different filtration methods, i. one was filtered through a nylon felt-non-hygroscopic cotton wool-cotton flannel, the other a non-hygroscopic cotton wool-cotton flannel, and the third through a powder layer having a mesh size of -40 to +70 and stainless steel according to Example 1. In each case, the composition of the viscose solution was typical of autorence fiber: $ 7 regenerable cellulose (based on total solution), 6 ° fo sodium hydroxide (based on total solution) and 34 # carbon disulphide (based on cellulose). The results showed that the fatigue strength, tensile strength and iron retention capacity of the sample filtered through the stainless steel layer according to Example 1 were as good or better than the usual nylon felt-non-hygroscopic cotton-wool-cotton flannel or non-hygroscopic cotton-cotton. The method presented is, of course, almost wastewater-free.

It has been found that in the present process, which uses stainless steel with a diameter of 12.7 cm and a thickness of 2.5-1.9 cm

A

Imrro achieves an average flow rate of 2.8 kp / om and an operating pressure of 80.6 l / m / h. This flow rate is more than four times the flow rate of conventional viscose filters (the literature mentions

Λ A

9.2-18.5 l / m / h) with an operating pressure often higher than 7-10.5 kp / cm.

Thus, the present invention offers several advantages over conventional filtration methods. These include long periods of use, less maintenance and downtime, and the prevention of contamination due to the use of attached viscose and insoluble gels. Filtration can be fully automated, eliminating the need to operate the filter and reducing maintenance costs. The method also allows for the future use of useful pulps in compositions that cannot be used in conventional filtration.

Claims (12)

A method for separating and recovering the insoluble particles from cellulosic solutions comprising a step of filtering this solution and a step of solubilizing an insoluble cellulose residue using a granular filtration bed and alkaline solvent, characterized by the following step: a) the insoluble material is separated from the cellulosic solution by filtration of the latter through a bed of a granular material which is inert with respect to the solution and having a particle size of US standard mesh between -20 (0.8U mm) and + 325 (0, 0UH mm); b) mixing the granular bed and the insoluble material collected therein with a solvent and stirring to partially dissolve the cellulose residue, the obtainable solution being highly concentrated compared to its concentration in the original cellulosic solution; c) adding to the resulting concentrated solution, with stirring, a solubilizing reagent to dissolve the insoluble cellulose residue completely; d) the obtained cellulosic material solution is separated and recovered from the granular bed. 2. A process according to claim 1, in the filtration of a cellulosic solution which is a viscous solution and treated by adding the same carbon sulfur to convert the viscose into cellulosic acidate, characterized in that the insoluble cellulose soluble cellulose collected in the granular bed is collected. alkaline solvent, which is a sodium hydroxide, lithium hydroxide or potassium hydroxide solution, solubilization is completed by the addition of carbon sulfur as a reagent in an amount of about 50% by weight calculated on the amount of the cellulose residue. 3. A process according to claim 1, characterized in that as a solvent for the cellulose residue consisting of cellulose acetate, a 75 ~ 90 - $ 40 acetic acid solution and as an acetic anhydride reagent are used in an amount of 175-250% by weight of the amount of cellulose acetate. Process according to claim 1, characterized in that as a solvent for the cellulose residue consisting of hydroxyethyl cellulose, a dilute sodium hydroxide solution and as reagent ethylene oxide are used in an amount of 20-70 w / w calculated on the amount of the cellulose residue. 5. A process according to claim 1, characterized in that, as a solvent for the cellulose residue consisting of hydroxypropyl cellulose, a dilute sodium hydroxide solution and reagent propylene oxide are used in an amount of 25-75 w / w calculated on the amount of cellulose.