Filtration method

Abstract

To provide a filtration method in which a removal rate of a suspended matter can be increased by filtration of drain water containing the suspended matter generated by cutting of a resin composition.SOLUTION: Provided is a filtration method in which a device is provided, the device being configured to use a filter to filter drain water containing a suspended matter generated by cutting of a resin composition. The filter is a spring type filter formed by spirally winding a wire. A suspended matter amount (SS) measurement of the filtered drain water indicates less than 1.0 mg / L.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a filtration method for filtering wastewater containing suspended solids produced by cutting a resin composition. [Background technology]

[0002] While plastics are used in a variety of fields, they are also considered to be a cause of marine pollution, such as microplastics. Conventionally, filtration with a metal mesh filter has been disclosed as a means for recovering microplastics (for example, Patent Document 1).

[0003] Other filtration devices and methods disclosed include a method of filtering suspended wastewater, such as turbid construction water, using a spring filter (eg, Patent Documents 2 and 3).

[0004] Furthermore, Patent Document 4 discloses a method for efficiently removing suspended solids and oil from wastewater generated by cutting or grinding a material containing at least one of metal, plastic, ceramic, and glass, using a spring-loaded filter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-066030 [Patent Document 2] JP 2020-006281 A [Patent Document 3] JP 2010-207790 A [Patent Document 4] JP 2012-110815 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the case of a filtering device using punched metal or metal mesh, the filter is easily clogged, and efficient recovery is not possible. In addition, although filtration using a spring-type filter is also exemplified, there is a problem that the filter is easily clogged with viscous wastewater such as oil, and the filter differential pressure increases quickly. In particular, there is a problem that the filter is easily clogged with viscous wastewater containing short fiber-like particles generated by cutting the resin composition in the pelletizing process.

[0007] The present invention provides a method for recovering suspended matter, which is short fibrous particles produced by cutting a resin composition during a pelletizing process, at a high removal rate from wastewater containing suspended matter. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following configuration. (1) A filtration method for filtering wastewater containing suspended solids produced by cutting a resin composition, the filter being a spring-loaded filter formed by spirally winding a wire, and the suspended solids (SS) of the filtered wastewater being less than 1.0 mg / L. (2) The filtration method according to (1), in which the removal rate of suspended matter having a particle size of 0.6 to 480.0 μm is 85% or more when particle size distribution is measured by a number counting method. (3) The filtration method according to (1), wherein the suspended matter of the resin composition contained in the wastewater before filtration has a major axis size of 1 to 10,000 μm. (4) The filtration method according to (1) or (2), wherein the amount of suspended solids (SS0) of the wastewater before filtration is 2 to 1000 mg / L. (5) The filtration method according to any one of (1) to (3), wherein the spring-loaded filter has a mesh size of 10 to 150 μm. (6) The filtration method according to any one of (1) to (4), wherein the wastewater before filtration has a residual chlorine concentration of 0.1 to 5.0 ppm by mass. (7) The filtration method according to any one of (1) to (5), further comprising a backwashing step in which the filter is housed in a container and deposits adhering to the filter surface are removed from the filter surface by applying a back pressure to the inside of the container through an outlet of the container. (8) A method for producing a polyester resin composition, using the filtration methods (1) to (7). Effect of the Invention

[0009] According to the present invention, a method for filtering wastewater containing suspended solids generated by cutting a resin composition can be provided, which has a high rate of suspended solids removal and provides good filter backwashability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0011] According to one embodiment, the present invention relates to a method for filtering wastewater containing particles generated by cutting a resin composition in a step of pelletizing the resin composition.

[0012] A representative resin composition is a polyester resin composition, and among these, a polyethylene terephthalate composition can be mentioned.

[0013] In the production method of polyethylene terephthalate, for example, an esterification reaction is initiated between terephthalic acid and ethylene glycol, and after the reaction is completed, the mixture is transferred to a polymerization tank, an antimony compound, a magnesium compound, and a phosphorus compound are added, and the mixture is depressurized to a high vacuum while being heated to about 290° C. and the temperature is increased to carry out a polycondensation reaction until the target intrinsic viscosity is reached. Thereafter, the obtained polyester composition is discharged in the form of a strand from the discharge nozzle of the polymerization tank, cooled with water, and then pelletized with a cutter to produce pellets of polyethylene terephthalate.

[0014] Examples of antimony compounds include antimony trioxide, antimony pentoxide, antimony acetate, and antimony salts of aliphatic carboxylic acids. Among these, antimony trioxide is preferably used in view of its polycondensation reactivity, the color tone of the resulting polymer, and its inexpensive availability.

[0015] The magnesium compound includes magnesium acetate, magnesium hydroxide, etc., with magnesium acetate being particularly preferred.

[0016] Examples of phosphorus compounds include trimethyl phosphate, phosphoric acid, sodium dihydrogen phosphate, phosphorous acid, and phosphonic acid, with trimethyl phosphate being preferred.

[0017] In the pelletizing process, the wastewater containing particles generated by cutting polyethylene terephthalate has short fiber shapes and a major axis size of 1 to 5000 μm before filtration. The suspended solids (SS0) of the wastewater before filtration is preferably 2 to 1000 mg / L.

[0018] The spring filter used for filtration is a filter formed by spirally winding a wire material. From the viewpoints of preventing clogging and ease of cleaning, the mesh size (gap) of the spring filter is preferably 10 to 150 μm, more preferably 20 to 120 μm, and further preferably 30 to 100 μm.

[0019] The suspended solids (SS) after filtration with a spring filter is less than 1.0 mg / L, and more preferably less than 0.5 mg / L, which reduces the particles contained in the wastewater to a level that cannot be seen with the naked eye.

[0020] The number of suspended particles having a particle diameter of 0.6 to 480.0 μm measured by particle counting method after filtration with a spring filter is preferably less than 2000 particles / 10 ml, more preferably less than 1600 particles / 10 ml, and the removal rate is preferably 85% or more. This reduces the particles contained in the wastewater to a level that cannot be visually confirmed.

[0021] The suspended matter in the wastewater generated in the pelletizing process can also be used as a filter aid that can pre-coat the surface of a spring filter. By having the suspended matter cover the gaps in the spring filter, it becomes possible to remove suspended matter smaller than the filter openings contained in the wastewater before filtration. In addition, it is preferable that the suspended matter has a short fiber shape and an aspect ratio (ratio of long diameter / short diameter) of 3 or more. The suspended matter being in the form of short fibers allows for high-precision filtration while maintaining water permeability, and in backwashing, the suspended matter has good peelability from the filter surface, making the backwashing effective.

[0022] The residual chlorine concentration in the wastewater before filtration is preferably 0.1 to 5.0 ppm by mass, more preferably 0.1 to 3.0 ppm by mass, and even more preferably 0.2 to 2.0 ppm by mass. If the residual chlorine concentration is less than 0.1 ppm by mass, microorganisms such as bacteria will grow and become entangled with particles in the wastewater, and the viscosity of the particles captured on the surface of the spring-type filter will increase, making the filter more likely to become clogged and making it difficult to efficiently collect the particles. In addition, if the residual chlorine concentration exceeds 5.0 ppm by mass, it is not preferable because it places a burden on the environment and increases the economic burden, such as increasing costs.

[0023] There is no particular limitation on the means for incorporating chlorine into the circulating water, but simple methods include injecting chlorine gas, immersing a tablet that slowly releases chlorine, such as a tablet containing a chloroisocyanurate, in cooling water, immersing a tablet containing a hypochlorite in cooling water, and electrolyzing magnesium chloride, sodium chloride, or the like.

[0024] Among these, from the viewpoints of ease of handling and durability of effect, it is desirable to use chlorine gas, hypochlorous acid compounds (more preferably sodium hypochlorite, potassium hypochlorite, or calcium hypochlorite), isocyanuric acid or isocyanuric acid salts or compounds thereof (more preferably sodium dichloroisocyanurate, trichloroisocyanuric acid), and chlorides of hydantoin derivatives (more preferably dichlorodimethylhydantoin, bromochlorodimethylhydantoin).

[0025] The temperature of the wastewater entering the filter is preferably 40 to 65°C, more preferably 45 to 55°C. If the temperature is below 40°C, microorganisms such as bacteria will not be killed, the water permeability of the filter surface will be poor, and the filter life will be long. Also, if the temperature exceeds 65°C, the energy required for heating will be large.

[0026] The index of filter life is (A) = filter housing capacity m 3 (B) is the amount of suspended solids recovered by backwashing in kg, and is expressed by formula (1). The longer the filter life, the less the number of backwashing cycles can be, so a filter life index of 10 or more is preferable. (B) / (A) ···(1)

[0027] When the amount of material to be filtered increases, clogging occurs. When this occurs, backwashing is performed by flowing compressed air or the like back from the inner hollow part of the filter element to the outside of the coil, which removes the filter aid together with the material to be filtered from the gaps and clears the clogging. The mixture of filter aid and material to be filtered is then disposed of.

[0028] In particular, the spring-loaded filter of the present invention is preferably installed in an element in which the filter is stored in a container, and backwashing can be performed to remove deposits adhering to the filter surface by applying back pressure to the inside of the container from the outlet of the container.

[0029] This element is installed along the outer circumference of a cylindrical housing made of a coil spring, with the ends of the wire fixed to the top and bottom of the housing. The unevenness of the wire acts in the same way as a filter aid, making the filtration gaps finer and enabling precision filtration. When the amount of material to be filtered increases and the filter becomes clogged, the material to be filtered is removed from the gaps by backwashing, and the clogging is easily cleared. At this time, the auxiliary wire stretches (bulges) due to the backwashing pressure, opening up the wire spacing and making it easier for the material to be filtered to separate, but the auxiliary wire itself does not come off the housing, allowing repeated filtration to continue indefinitely. EXAMPLES

[0030] The present invention will be described in detail below with reference to examples. The methods for measuring physical properties and evaluating effects are as follows.

[0031] (Evaluation method) (1) Amount of suspended solids (SS) The method for measuring SS is specified as suspended solids in JIS K 0102. 1 L of wastewater sample was filtered through filter paper with a pore size of 1 μm and a diameter of 47 mm, and dried in an oven at 105°C for 90 minutes. The dry weight of the material remaining on the filter paper was calculated from the weight of the filter paper before and after drying, and this value was divided by the amount of filtered wastewater to obtain the value (mg / L).

[0032] (2) Removal rate by counting number of pieces A 10 ml sample of the wastewater was measured using an AccuSizer to determine the number of particles with diameters between 0.6 and 480.0 μm. The removal rate (%) using the particle counting method was calculated by dividing the number of particles after filtration by the number before filtration.

[0033] (3) Size of suspended matter The suspended solids were diluted with water to a concentration of 0.01% by mass, dispersed, and air-dried on the sample stage. After that, images of the suspended solids were measured in 10 fields of view using image processing software Image-ProPremier (Nippon Roper Co., Ltd.), and the average values ​​of the major and minor axes were calculated to calculate the aspect ratio (ratio of major axis to minor axis). Note that the calculations were performed excluding aggregated suspended solids.

[0034] (4) Residual chlorine concentration in wastewater One packet of DPD reagent and one spoonful of potassium iodide were added to 10 ml of the sample, and the residual chlorine concentration was calculated by measuring it using a residual chlorine meter (DPD method) manufactured by Shibata Scientific Co., Ltd.

[0035] (5) Filter life indicators The index of filter life is expressed as follows (1). (A) is the capacity m 3 , (B) is the amount of suspended solids collected in kg. In the case of a spring-loaded filter, when the differential pressure between the filter inlet and outlet rises to 0.20 MPa, it is determined that the filter has become clogged and backwashing of the filter is carried out. The amount of suspended solids collected (B) was calculated by collecting the backwashing liquid from the backwashing in a collection net, drying it at 20°C for 24 hours, and then measuring its weight. (B) / (A) ···(1).

[0036] (6) Backwashing ability When the pressure difference between the inlet and outlet of the spring-loaded filter rose to 0.20 MPa, it was determined that the filter had become clogged, and backwashing of the filter was carried out. After backwashing the filter, the discharge volume was 45 m 3 Filtration was started at 1000 ml / h, and the time until the filter pressure difference rose to 0.20 MPa was measured again. The backwashing performance was evaluated based on the following times: The amount of suspended solids before filtration remains unchanged. ○: More than 24 hours △: 1 to less than 24 hours ×: Less than 1 hour.

[0037] Example 1 Terephthalic acid and ethylene glycol were subjected to an esterification reaction at 250°C. After the esterification reaction was completed, antimony trioxide, magnesium acetate, and trimethyl phosphate were added, the reaction system was gradually lowered to 100 Pa, and the temperature was raised to 290°C to complete the polycondensation reaction. The system was then discharged by leaking with nitrogen and pelletized using a strand cutter. The wastewater from the pelletization had a residual chlorine concentration of 0.3 ppm and a suspended solids content (SS0) of 14.2 mg / L. The wastewater was then passed through a filter housing with a capacity of 0.3 m 3 The wastewater was filtered using a spring-loaded filter manufactured by Monobe Engineering Co., Ltd. The filter surface was precoated with suspended matter having an aspect ratio of 4.1 before filtration, and the suspended matter amount (SS) after filtration was 0.1 mg / L, and the suspended matter removal rate was 99.3 wt%, which was a high removal rate. In addition, the filter backwashing was performed by applying back pressure from the outlet of the filter container to the inside of the container to remove the deposits attached to the filter surface from the filter surface. After the filter backwashing, the wastewater was filtered again, and it took 28 hours for the filter differential pressure to increase, and the backwashing property was good with a rating of ○. The results are shown in Table 1.

[0038] (Examples 2 to 6) Except for changing the residual chlorine concentration before filtration, filtration was performed in the same manner as in Example 1. The amount of suspended solids (SS) after filtration was 0.1 mg / L, and the backwashability was good, with a rating of ○. The results are shown in Table 1.

[0039] (Examples 7 to 11) Except for changing the mesh size of the filter, filtration was performed in the same manner as in Example 1. The results are shown in Table 1.

[0040] (Examples 12 to 20) The filtration was carried out in the same manner as in Example 1, except that the aspect ratio and suspended solids amount (SS0) of the wastewater before filtration were different. The suspended solids amount after filtration was 0.1 mg / L, which was good. The results are shown in Table 1.

[0041] (Examples 21 to 23) Except for changing the filter temperature, filtration was performed in the same manner as in Example 1. The results are shown in Table 1.

[0042] Comparative Example 1 The wastewater from Example 1 was filtered through a metal mesh basket with 33 μm openings, but there was a lot of clogging and the backwashing performance was very poor, with a score of x. The results are shown in Table 1.

[0043] Comparative Example 2 Wastewater containing oil from metal cutting processing, with a suspended solids (SS0) of 17.0 mg / L and a residual chlorine concentration of 0 ppm before filtration, was filtered through a spring-loaded filter pre-coated with diatomaceous earth. After filtration started, the filter differential pressure rose to 0.20 MPa in 43 minutes, and backwashing was poor, with the filter differential pressure rising to 0.20 MPa again in 37 minutes after filtration started. In addition, because diatomaceous earth was used as a pre-coating agent, it was difficult to separate and dispose of the metal cuttings captured on the filter. The results are shown in Table 1.

[0044] Comparative Example 3 Filtration was carried out in the same manner as in Example 1, except that the mesh size of the spring filter was changed to 200 μm. The suspended solids (SS) after filtration was high at 1.3 mg / L. The results are shown in Table 1.

[0045] Comparative Example 4 Filtration was carried out in the same manner as in Example 1, except that the residual chlorine concentration in the wastewater was changed to 0 ppm. The collected suspended solids were viscous like clay, and after backwashing the filter, it took only 30 minutes for the filter differential pressure to rise, which was very short, and the backwashing performance was rated as x. The results are shown in Table 1.

[0046] [Table 1]

[0047] [Table 2]

Claims

1. A filtration method for filtering wastewater containing suspended solids produced by cutting a resin composition, the method being characterized in that the filter is a spring-type filter formed by spirally winding a wire, and the amount of suspended solids (SS) of the filtered wastewater is less than 1.0 mg / L.

2. 2. The filtration method according to claim 1, wherein the removal rate of suspended matter having a particle size of 0.6 to 480.0 μm is 85% or more when particle size distribution is measured by a number counting method.

3. 2. The filtration method according to claim 1, wherein the size of the suspended matter of the resin composition contained in the wastewater before filtration is 1 to 10,000 μm in major axis.

4. Suspended solids in wastewater before filtration (SS ０ 2. The method according to claim 1, wherein the concentration of the ion exchange solvent is 2 to 1000 mg / L.

5. 2. The filtration method according to claim 1, wherein the spring filter has a mesh size of 10 to 150 μm.

6. The filtration method according to claim 1, wherein the residual chlorine concentration in the wastewater before filtration is 0.1 to 5.0 ppm by mass.

7. 2. The filtering method according to claim 1, further comprising a backwashing step in which the filter is housed in a container, and deposits adhering to the filter surface are removed from the filter surface by applying a back pressure to the inside of the container through an outlet of the container.

8. A method for producing a polyester resin composition, comprising the filtration method of claim 1.

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