KR790001111B1 - Filtration of cellulosic solutions - Google Patents

Abstract

Viscose solns. used for spinning were filtered through stainless steel powder layers with redissolution of the insol. particles with NaOH soln. contg. CS2 for insol. cellulose material recovery. Thus, viscose contg. 1% (based on total soln.) regenerable cellulose, 6% NaOH, and 28% (based on cellulose) CS2 was filtered through a double layer of stainless steel particles of-40 to+70 mesh at the top at 2.8kg/cm2. The layer was treated with 9wt% NaOH soln. contg. 5 vol% CS2 after filtration of viscose.

Description

Filtration of Cellulose Solution

The present invention relates to a filtration process of a cellulosic solution and, in particular, to a continuous process for removal and recycling of undissolved cellulosic gels and fibers from cellulosic solutions.

Prior to making the viscose extract into a fiber or film, the viscose must be filtered to enhance the strength, smoothness and appearance of the gel, fibrin and undissolved final regenerated cellulose products and not block the extraction pore (orifice).

The filtration step is one of the severe difficulties in the viscose process. Filtration is generally carried out by a batch filtration process.

After filtration, if generally thin cotton, nylon or other synthetic felt, or various nonwoven fabrics are disturbed, undissolved substances are generally removed by decanting or re-washing from the media before re-use. . The difficulty in recycling the undissolved material by running the process continuously is that there has been no effective way of separating the adhesive undissolved material from the filtrate and an economical method of dissolving gels and fibers. This problem is particularly important because extremely small amounts of undissolved residues make it difficult to extract the viscose fibers and films.

Filtration by the particle bed is well known as rewashing to remove solids or gel residues from the packed filtration media. Moreover, such a system has never been economically applied for complete recovery and recycling of cellulose residues resulting from filtration of cellulose. In use, other systems are not able to recover all of the valuable cellulose that is inexpensive or expensive.

It is therefore an object of the present invention to provide a filtration method for a simple, economical and efficient cellulose solution.

It is another object of the present invention to provide recoverable cellulosic solution filtration and full utilization of all undissolved cellulosic materials which make the problem of waste disposal more common.

It is still another object of the present invention to provide a continuous process for filtering, recovering and recycling undissolved cellulosic material in a viscose filtration process.

This object of the present invention is achieved by effectively separating the undissolved material from the cellulose solution by filtration and by using a meltable reactant to make an artificial solution of the concentrated form of the undissolved cellulosic component. Separation of the undissolved cellulosic material is performed by a particle layer or a powder layer which is found to be particularly suitable for the present step, as described below. The undissolved cellulosic artificial solution is made by using an extremely uneconomical amount of dissolved reactants in a highly concentrated solution of cellulose residues.

Furthermore, the present invention is to filter the cellulose solution through the granular material layer in which the cellulose solution is inert so as to partially dissolve the undissolved substance (some solution of the undissolved substance has a higher concentration than the concentration of the cellulose stock solution). In order to dissolve the harmful substances with the solvent and to dissolve the undissolved substances, a dissolution reactant is added to the partial concentrated solution, and two steps of recovering the reactants including the solution of the undissolved substances. At this time, the present solution can be recycled to the unfiltered cellulose solution to remove the waste stream generated in the known method.

The present invention is particularly applicable to industrial filtration of viscose, and will be clearly explained by the filtration method of the viscose solution. However, it is particularly important that the present invention is generally applicable to cellulose solutions including cellulose acetate, hydroxy ethyl cellulose, hydroxypropyl cellulose and the like, in addition to biscose.

The preparation of the viscose is promoted by the conversion of cellulose to cellulose xanthate by treatment with an alkali solution followed by reaction with carbon disulfide (CS2) and also by dissolving cellulose xanthate in a dilute alkaline solution, usually sodium hydroxide (NaOH).

This filtration process is enhanced by the use of carbon disulfide as a meltable reactant and a dilute alkaline solution as a solvent to completely dissolve the undissolved cellulosic components of the viscose solution.

The use of sufficient carbon disulfide for the entire viscose solution for this purpose is expensive and difficult to perform commercially. In the present invention, however, carbon disulfide can be applied to resistant gels and fibers that are efficiently concentrated in small amounts. Carbon disulfide is generally used in the range of 0.1% -0.2 of the cellulose in the stock solution. The amount of carbon disulfide required to dissolve the cellulose residues resulting from this concentrated form of sediment is virtually small relative to the total process volume.

Moreover, recycling small amounts of carbon disulfide as part of the solution for large amounts of viscose filtration in the next process does not increase the overall raw material cost increase. The reactants and solvents used to completely dissolve the cellulosic residues are those commonly used in the preparation of particulate cellulose derivatives or reactants, and the solvents and reactants are continuous or nearly continuous filtration processes of dissolved cellulose components. It is compatible with solution preparation of the unfiltered cellulose solution to be recycled and used in the process. In the case of cellulose acetate, 75-90% acetic acid solution is used instead of sodium hydroxide solution, and the reactant for dissolving cellulose residue is 175-250% by weight acetic anhydride of the reactive cellulose.

In the case of hydroxyethyl cellulose, the solvent is a dilute sodium sudanate solution, as in the case of viscose, and the reactants are ethylene oxide, 20-70% by weight of cellulose. In the case of hydroxypropylcellulose, the solvent is dilute alkaline sodium hydroxide and the reactant is propylene oxide, 25-75% by weight of cellulose.

The particle layer of the undissolved cellulosic material and the undissolved cellulosic product may first be washed with these solvents to partially dissolve the undissolved cellulose, and then treated with the dissolution reaction material to dissolve completely, or the solvent and reactants may be added simultaneously. have. In the case of a viscose solution, the undissolved cellulosic gel and the artificial solution of cellulose may be completed in a small amount of about 50% by weight of carbon disulfide based on the weight of the cellulose residue. Generally, however, excess carbon disulfide is used based on the weight of the cellulose residue, sometimes more than twice the weight of the cellulose residue. As long as undissolved cellulose is dissolved, the upper limit is not important. It should be noted that the amount of carbon disulfide is not in fact excessive or uneconomic. This is because it acts on cellulose residue in a form that is extremely concentrated than the concentration of the stock solution and can also be recycled mostly in the process. The particle layer is not necessary, but it is better to block completely before it is mixed with alkaline solution or other solvents. The filtration should be stopped when the filtration rate drops to a degree that indicates some or complete clogging.

As used herein, the term "interfering with the liquid no longer flowing" is intended to indicate the degree of all filtration rates when it partially or completely blocks the granular layer. The use of the granular layer for filtration is of course known. However, it has been found in the process of the present invention that they perform one unique function. These blockages or other actions are extremely slow in blocking the flow of the liquid by blocking the passage of pores than porous plates, screens or other filters used for known cellulose filtration. Description of this can be seen from known methods for dissolving cellulose fibers and gels.

In order to completely dissolve the cellulose subjected to the xanthate reaction in the caustic solution, both a fixed time and a stirring operation are required. Since the solvent immerses the xantified fibers, a concentrated solution layer having a high viscosity is formed to surround the fibers. Upon stirring, the thick layer is impacted and fragmented into a surrounding liquid layer, which is diluted to a maximum average viscosity while simultaneously exposing a new surface of the reacted fiber to the solvent. Without agitation, the adhesive surrounding each fiber exhibits mucus, which prevents further penetration by the solvent, resulting in a very stable flat gel.

In the granular layer, the viscous gel fragments may enter some pores or may be partially exposed to the fluid. If it is fully reacted, the gel "fragmented" by the fluid can dissolve extremely well. However, incompletely reacted or otherwise damaged fibers eventually block all space in the granules. The use of a granular layer also facilitates the separation of cellulosic residues in the next dissolution step.

If the porous plate and screen are clogged, they cannot be completely cleaned. On the other hand, the undissolved cellulosic residue can be simply removed from the granular layer completely using a dilute alkaline solution or other solvent. The granular layer may be alkaline in the case of viscose in the form of particles or powder suitable for the corrosiveness of the filter device, and acidic or neutral in the case of cellulose derivatives.

Particularly suitable granular layers for the viscose solution are a kind of stainless steel powder, and other powder metals, other metals, alloys, etc., which are inert and non-reactive in nickel, carbon steel and cellulose solutions are sometimes used. Organic polymers such as polyethylene polypropylene, polyvinyl chloride and teflon (trade name of polytetrafluoroethylene) may also be used. Vitreous powder and other inert particulates are readily available to those skilled in the art, and powder sizes generally range from -20 to +325 mesh, which is a US standard particle size.

The method of the present invention provides a metal powder having a particle size of -20 to +325 which is inert to the cellulose solution when the undissolved material is filtered off from the cellulose solution through a granular layer using a solvent together with a reactant. The cellulose solution is filtered through an organic polymer or ceramic layer, and in the case of acetic acid, hydroxyethyl or hydroxypropyl cellulose when the cellulose solution is cellulose acetate. In the mixture, acetic anhydride in the case of cellulose acetate, ethylene oxide in the case of hydroxyethyl cellulose, and propylene oxide in the case of hydroxypropylene cellulose are added as a solubilizing agent to completely dissolve the undissolved substance and Recover the reactants containing the substance The solution is recycled to an unfiltered cellulose solution.

The present invention is described in more detail as follows.

Viscose solution is usually introduced through the granular material layer under pressure conditions up to 25-150 psig, but in certain cases up to 400 psig.

After a certain amount of solution has passed through the filter, the relatively small fragments of incompletely dissolved cellulose fibers and gels form a nearly solid structure in the compaction layer, partially or partially through the powder layer until it hinders the flow of the excess solution. It is completely blocked. Typically, more than 200 liters of viscose solution pass through 4.5 liters (1¾ inch) of a 0.3 liter stainless steel powder layer equally divided into -20 to +70 mesh before complete blockage occurs. The solution is partially dissolved and washed with stirring using about 0.5 liter of 9% sodium hydroxide solution to separate the gel and fibers. Residual undissolved material appears as a turbidity that floats on top of the freshwater solution and the stainless steel powder layer. At this time, the solution is stirred to artificially dissolve the remaining cellulose residues, discarded along the solution and treated with an excess of carbon disulfide, for example, 1 milliliter of carbon disulfide per 20 milliliters of a 9% sodium hydroxide solution.

Preferably, carbon disulfide is added to the alkaline solution and the mixed solution is added to the clogged or partially clogged powder layer so that the powder layer is not removed. The turbidity formed becomes apparent when the powder layer and the solution are stirred to react the cellulose residue to dissolve in a low viscosity medium. At this time, the 9% sodium hydroxide solution containing the dissolved cellulose residue and the carbon disulfide washing solution were drained from the stainless steel layer, and the 200 liter solution of the biscose solution to be filtered and part was recycled. The powder layer can be reused in the next filtration cycle.

Unfiltered cellulose stock contains undissolved substances that are very light in weight. In a typical unfiltered viscose solution containing 9% renewable cellulose, 0.1-0.2% of cellulose will not dissolve.

Unreacted residue is filtered and dissolved in dilute alkaline solution at a rate of about 25-200 times at much higher concentrations than the stock solution.

The weight of the alkaline solution is about 0.5-4% by weight of the stock solution, generally about 1% by weight. The capacity of the dilute alkaline solution is about twice the volume of the clogged filter. The dilute alkali solution concentration should be 7-11% by weight of the alkali metal hydroxide. Although there is no limit to the selection of a particular alkali or base, sodium hydroxide is widely used in the viscose method. However, other basic materials such as lithium hydroxide or potassium hydroxide are also used, and the selection of a particular base can be readily performed by those skilled in the art. On the other hand, magnetic or gravity separation methods may be used to clean metal silica powder or other non-cellulosic contaminants generated in the powder layer by other means. The metal particles coming out of the powder layer in the filtered solution are also dropped by the magnetic device so that the holding of the layer is 100% secured.

In one embodiment of the present invention, the filtration uses a granular layer having a coarse layer and a fine layer, or two separate layers, one rough and the other fine. The viscose solution filtered through these two particle size powder layers produces a significant amount of filtrate and artificial silk thread.

The first part of the powder layer (usually the upper part) has a particle size of -20 to 40 mesh, while the second part of the powder layer has a particle size in the range of -40 to 70 mesh. Powders with different magnetic or specific gravity can be placed on the microlayers to form a coarse grain layer.

In the following examples, unless otherwise indicated, all percentages are in weight percent and all mash sizes are US standard particle size standards.

Example 1

A layer of stainless steel powder that is 4.45 cm (1 3/4 inch) deep and 12.7 cm (5 inch) in diameter is made. The bottom 2.54 cm (1 inch) of the powder layer is the US standard grain size -40 to 70 mesh. The upper 1.91 cm (3/4 inch) of the powder layer is made of -20 to 40 mesh stainless steel powder.

Filtration in a closed pressure press with air compressed to 40 psig to maintain a constant supply pressure. The viscose solution has a composition of 9% (for the total solution) of renewable cellulose 6% sodium hydroxide (for the total solution) and 28% of carbon disulfide (for the cellulose content of the solution). To obtain the fill, a separate but identical solution was filtered through a stainless steel powder layer, with a standard double-sided 57.70 grams (2 oz.) Cotton and 169.60 grams (6 ounces) Guangdong flannel. It was filtered through a viscose filter medium. The filtered solution was refiltered through standard media until the filter was clogged. The fill value obtained from the granular filtration was at least equal to, and generally better than, the known filter media. Moreover, the filtration efficiency was not reduced as a result of the reuse of the granular layer and the regeneration of the undissolved cellulose particles and the recycling of them back into the viscose stream as part of the caustic solution.

Example 2

)에 사용하였던 형태의 조성. 예를들면 7%의 재생 가능한 셀룰로오스(전체용액에 대하여), 6%의 수산화나트륨(전체 용액에 대하여) 및 34%의 이황화탄소(셀룰로오스에 대하여)를 가지고 있었다. 그 결과는 실시예 1에 따라 스테인레스강 분말층을 통하여 여과시킨 시료의 피로기(疲勞期), 코오드 강도 및 철분제거는 나일론 펠트 얇게 튼 솜 면 플란넬 또는 얇게 튼 솜 면 플란넬을 통과시키는 공지의 방법으로 여과시킨 시험시료의 그것과 같거나 또는 더 좋다는 것을 나타내었다. 물론 이러한 결과는 폐유출물이 거의 생성하는 일이 없이 달성되었다.The basic test of filterability is the spinning effect of viscose fibers. A series of 4 liters viscose was taken from one 18.93 liter (5 gallon) batch and each of them was filtered by a separate method. One was filtered through a nylon thin cotton cotton flannel and the other was filtered through a thin cotton cotton flannel and a third through a -40 to 70 mesh stainless steel powder bed. In each case the viscose solution is

Composition in the form used. For example, it has 7% renewable cellulose (relative to total solution), 6% sodium hydroxide (relative to total solution) and 34% carbon disulfide (relative to cellulose). The result is a known method of fatigue, cord strength and iron removal of a sample filtered through a stainless steel powder layer according to Example 1, through a nylon felt thin cotton flannel or thin cotton flannel. It was shown to be equal to or better than that of the test sample filtered with. This result, of course, was achieved with little generation of waste streams.

/m²(19.2gal/ft²hr)이다. 이 유속은 몇배 이상의 압력(100-150psig)을 작동시키는데 필요한 공지의 비스코오스 여과기 압력에 의한 유속보다 시간당 7.66-15.2

/m²(2.2-4.4gal/ft²/hr) 4배이상이다.The average flow velocity in the method of the present invention using a stainless steel powder layer of 12.7 cm (5 inches) in diameter and 4.45 cm (1 3/4 inch) in depth is 78.1 per hour at a pressure of 40 psig.

/ m ² (19.2 gal / ft ² hr). This flow rate is 7.66-15.2 per hour than the flow rate due to known viscose filter pressures required to operate several times more pressure (100-150 psig).

/ m ² (2.2-4.4gal / ft ² / hr) more than four times.

Therefore, the method of the present invention can prevent contamination and recover the filter medium by maintaining many advantages compared to known filtration methods having a longer circulating operation period-retention and rest time, that is, dropping viscose and undissolved gel. The spheres provide the ability to fully automate the filter bed. It also allows the economic use of various pulp with compositions that are unacceptable by known filter systems.

Claims (1)

Metal powders, organic polymers or ceramic powders having a particle size of -20 to +325 which are inert to the cellulose solution in the separation of undissolved materials from the cellulosic solution through the granular layer using a solvent together with the reactants. The cellulose solution was filtered through a layer, acetic acid if the cellulose solution was cellulose acetate, or a dilute alkaline solution and the granular layer containing the undissolved substance were mixed if the cellulose solution was hydroxyethyl or hydroxypropyl cellulose and the mixture In the case of cellulose acetate, in the case of cellulose acetate anhydride, in case of hydroxyethyl cellulose, ethylene oxide, and in case of hydroxypropylene cellulose, propylene oxide is added as a solubilizing reaction agent to completely dissolve the undissolved substance and to contain a cellulose substance. Recover Unfiltered Cellulite Filtration of the cellulose solution, characterized by recirculating the solution in Sikkim Oz solution.