JPH0470933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for filtering liquids by membrane filtration. In more detail, when filtering liquids using reverse osmosis membranes, ultrafiltration membranes, etc., membrane tears that occur during filtration and leaks in the seal separating the raw solution side and the filtrate side (hereinafter referred to as "membrane tears") etc.)
A method of filtering the filtrate without contaminating the filtrate by detecting changes in the characteristics of the liquid on the secondary side of the membrane and stopping or switching the flow of liquid to the filtration membrane based on the detection signal. Regarding.

In recent years, research on membranes has progressed, and it has become possible to mass-produce membranes that can be used industrially. In addition, with membranes, it is possible to obtain a degree of purification according to the pore size of the membrane,
It has become possible to achieve a level of precision that could never be achieved with conventional methods such as pre-coated filters.

As a result, an application field for membranes was found in the purification of manufacturing water used in the fields of semiconductor production and pharmaceutical manufacturing.

In the field of semiconductor production, it would have been impossible to increase the degree of integration of LSIs without the use of large amounts of cleaning water using the membrane method.

In the field of pharmaceutical manufacturing, it is used cheaply and in large quantities as an alternative to conventional distilled water, making a major contribution to the GMP standardization of production.

As stated in many literatures, membrane filtration methods used under appropriate conditions (1) can achieve extremely precise filtration that cannot be achieved with conventional methods;

(2) It is very easy to operate and does not require advanced driving skills.

(3) Since it is used in a closed system such as a pipeline, there is no contamination from the outside.

(4) It is an operation that simply uses pressure and does not involve a phase change, so energy can be saved.

(5) Continuous discharge of concentrated liquid allows continuous operation without clogging.

It has the following characteristics.

Normally, membrane filtration is performed using methods other than the membrane method, such as those found in sand filters and filter presses, in which all of the stock solution is passed through a filter layer, and the filtrate is left in the filter layer. ”
This method is relatively rare; the stock solution is pumped from the stock solution tank to one end of the membrane surface, allowed to flow along the membrane surface, and then returned to the stock solution tank as a concentrated solution from the other end of the membrane surface. A circulating filtration method in which filtration is performed only while in contact with the surface, or a partial filtration method in which part or all of the concentrated liquid is taken out of the filtration system in circulating filtration is performed. Due to this unique filtration method of the membrane, it has become established as an easy-to-handle filtration unit operation despite the membrane's extremely small pore size.

However, the biggest disadvantage of membranes is that the primary and secondary sides of the membrane are separated by a single extremely thin membrane, and the seal that supports the membrane has to have an extremely delicate structure due to the thinness of the membrane. be.

As a result, the following concerns arise.

(1) Membranes and seals may be damaged due to physical effects such as pressure and temperature, or chemical effects of processing liquids and cleaning liquids.
Pinholes appear because the skin gradually ages overall.

(2) The weak parts that remained during the film forming stage are damaged by the shock of operation.

Such accidents occur suddenly or gradually, and it is extremely difficult to predict their timing in advance. If the problem occurs gradually, the filtration effect gradually deteriorates, and by the time the problem is noticed, a large amount of poor quality product has already been produced. If an accident occurs suddenly, there is a possibility that clearly defective products will be produced, leading to a shortage in production volume and an increase in production costs.

For those employing membranes, the possibility of the aforementioned accidents was of great concern.

The conventional solution to these problems was to estimate the membrane lifespan rather short and replace the membrane as soon as possible, but there was no need to worry about troubles for several years when there was a sufficient track record. Nakatsuta. Furthermore, in cases where a high degree of safety is required, there are cases in which it is necessary to hesitate in adopting the membrane method.

The inventor has been conducting extensive research in order to resolve the above concerns and increase credibility of membrane filtration technology.

In other words, in order to detect membrane breaks, etc., a tracer is mixed into the stock solution, and the tracer that leaks out in small amounts is concentrated and detected using magnetism.
-Proposed No. 44817 "Method for detecting pinholes in partition walls". However, although this method is easy to apply because it uses a tracer that is easy to detect, since it mixes components that are not originally included in the original solution, there may be adverse effects if the tracer mixes with the filtrate or the chemical physics between the tracer and the solution. There were many problems that needed to be solved, such as compatibility with other people, and it was not necessarily possible to use it generally.

Therefore, while continuing to study appropriate tracers and methods for detecting them, we unexpectedly arrived at the present invention. That is, in the filtration of liquid by the membrane filtration method, the present invention arranges in series a first membrane and a second membrane consisting of either a reverse osmosis membrane or an ultrafiltration membrane having almost the same characteristics, and the first membrane is used for circulation. Using filtration, partial filtration, or total filtration, the second membrane is passed through both membranes sequentially by total filtration, and the difference in characteristics between the liquid pair between the two membranes and the liquid after passing through the second membrane is evaluated. A membrane filtration method characterized by detecting a break in the first membrane and stopping filtration or switching to another filtration device based on the detection signal, which is a normal membrane filtration device (first membrane). All or a part of the filtrate is filtered and concentrated through a second membrane having a pore size approximately equal to that of the first membrane, and the characteristics of the liquid on the primary side and the liquid on the secondary side of the second membrane are determined. By detecting the difference between the two, it is possible to detect a break in the first film.

To detect the difference in characteristics between the primary and secondary sides of the second membrane, appropriate characteristics can be selected depending on the nature and amount of the substance to be filtered contained in the stock solution. Properties such as electrical conductivity and endotoxin concentration can be conveniently used.

In the present invention, since there is no load to be removed by the second film while the first film is intact, the difference in the characteristics between the primary side and the secondary side of the second film exhibits an almost constant value. , less fluctuation. If the first membrane is torn or the like and the filtered material begins to leak, the second membrane is installed in a total filtration and concentration type, so it will be immediately concentrated on the surface of the second membrane, preventing pressure rise and concentration. turbidity, the number of fine particles, endotoxin concentration, etc. begin to increase. Therefore, the object of the present invention can be achieved by measuring, recording, and managing these characteristics continuously or periodically.

If the present invention is not carried out, for example, the amount of material to be filtered that flows out from a single very small pinhole will be extremely small, and will be diluted in a large amount of filtrate that is normally filtered, so that it will not reach a concentration that can be analyzed. do not have.

On the other hand, when the present invention is implemented, even if the leakage of the material to be filtered is extremely small, it is reliably captured and concentrated on the surface of the second membrane, and the second membrane used for comparison of measurements is Since the filtrate has undergone two filtration steps, the substances to be filtered are completely removed, so it is much easier to detect an increase in the difference.

If the substances to be filtered accumulate on the membrane surface and increase the filtration resistance of the membrane, install pressure gauges on the primary and secondary sides of the second membrane, or detect the differential pressure. A differential pressure gauge such as the one described above can be attached to monitor the increase in clogging of the membrane surface, that is, the leakage of the first membrane.

If the object to be filtered is fine particles and the turbidity and number of fine particles can be measured, the object of the present invention can be achieved due to these characteristics.

When the substance to be filtered is an ion, the object of the present invention can be achieved by measuring electrical conductivity or electrical resistance.

When the amount of material to be filtered is extremely small, such as ultrapure water, it is difficult to detect differences in characteristics using the measurement method described above, but the purpose of the present invention can be achieved by measuring the concentration of endotoxin. It can be achieved.

The important features of the present invention are that the tracer uses a substance to be filtered that is already contained in the stock solution, and that the filtration membrane is deliberately installed in two stages, which in a sense makes it uneconomical. , the second membrane uses a means of total concentration that ignores common filtration principles. This technical concept is the exact opposite of that of ordinary membrane filtration, and was something that our predecessors had never thought of.

The present invention will be explained in more detail using the drawings.

FIG. 1 is an example of a flow sheet for a membrane filtration device not according to the present invention. The stock solution entering from the left side 1 of the flow sheet is pressurized from the circulation tank 2 by the pressure pump 3 and enters the membrane module 4. The filtrate is sent to the next step through a pipe 6, and the undiluted solution that flows along the membrane surface while washing the membrane surface becomes a concentrated solution through filtration and returns to the circulation tank 2 through the pipe 5.

FIG. 2 is an example of a flow sheet for a membrane filtration device according to the present invention. The stock solution entering from the left side 11 of the flow sheet is pressurized by the pressurizing pump 13 from the circulation tank 12 and enters the first membrane module 14. The concentrated liquid returns to the circulation tank 12 through the pipe 15, and the filtrate flows through the pipe 16 to the second membrane module 17, where the entire amount is filtered without being circulated, and the filtrate is sent to the next process through the pipe 18. .

In Figure 2, the first membrane and the second membrane are depicted as being installed in separate locations, but in some cases, two membranes can be stacked one on top of the other, as in the case of flat membranes.

FIG. 3 is another example of a flow sheet for a membrane filtration device according to the present invention. The filtrate of the first membrane is pipe 16
In this case, the entire amount of the second membrane does not flow, and only a portion is supplied to the second membrane. However, there is no circulation return pipe from the second membrane, and the liquid supplied to the second membrane is completely filtered.

The molecular weight cutoff (the unit of expression of the pore size in which the size of the smallest particle blocked by the membrane is expressed by its molecular weight) of the first membrane can be arbitrarily set depending on the size of the nonwoven fabric to be separated.

If the molecular weight cutoff of the second membrane is larger than that of the first membrane, only particles with large particle sizes can be detected among the leakage of the first membrane, resulting in poor detection accuracy.

If the molecular weight cut-off of the second membrane is smaller than that of the first membrane, even if there is no leakage in the first membrane, particulates passing through the first membrane will always accumulate on the second membrane. Decreases detection accuracy.

Therefore, the molecular weight cutoff of the second membrane is the same as that of the first membrane, or the molecular weight cutoff of the first membrane is 1/10 or less.
A range of 10 times is preferred.

Before use, it is necessary to confirm that the second membrane has a detection accuracy suitable for the purpose of use, such as a bubble test or an endotoxin challenge test. Furthermore, from an economical point of view, rather than expecting a long service life for the second membrane, it is better to always use a new, unaged membrane and ensure accuracy.

The membrane area of the second membrane depends on the difference between when all the filtrate is filtered as shown in Figure 2 and when a part of the filtrate is filtered as shown in Figure 3, and the allowance for the second membrane. It should be selected appropriately depending on the range of pressure drop to be achieved.

Example 1 An apparatus for producing pyrogen-free water for pharmaceutical use was assembled as follows and an experiment was conducted.

First membrane: An ultrafiltration membrane with a membrane area of 9.4 m ² and a molecular weight cut off of 6000 was used. Second film: The same film as the first film was used in the same area. The flow sheet of the device was as shown in Figure 2.

Ion-exchanged water was used as the supply water. The operating conditions were such that the pressure was constantly adjusted to maintain a load of 1.5 m ³ /Hr.

The performance of the operation was determined by taking a sample from the area shown in FIG. 2, 16, and measuring the presence or absence of endotoxin using the rimural test method, ie, Pregel R (manufactured by Teikoku Kinki Co., Ltd.). The results are shown in circles in Figure 4.

In the figure, - indicates that endotoxin was not observed, ± indicates that it was clearly not observed, + indicates that it was clearly observed, and ++ indicates that a large amount of endotoxin was observed.

Until the 10th day, the endotoxin blocking ability of the first membrane was insufficient, so no increase in endotoxin concentration was observed. As a result of continuing the experiment by actively drilling one pinhole with a diameter of approximately 0.7 mm on the 11th day,
Concentration of endotoxin was observed after measurement on day 15. Figure 4 shows the results. For reference, the first membrane filtrate was analyzed after the 15th day, but the endotoxin concentration was below the detection limit and the effect of the pinholes could not be detected.

Example 2 According to the flow shown in FIG. 3, an ultrafiltration membrane with a size of about 10 square meters was used as the first membrane, and an ultrafiltration membrane with a similar pore size of about 0.2 square meters was used as the second membrane. Electrodeposition paint was used as the filtration stock solution, and turbidity was used as the detection device before and after the second membrane.

Conventionally, a turbidity detector was installed in the middle of the filtrate pipe of the first membrane to detect leakage from the first membrane, but by using the second membrane of the present invention, the detection sensitivity was much higher than that of the conventional one. It was found that leaks can be detected with high sensitivity.

As described above in the embodiments, according to the present device, an abnormality can be detected at a stage that is still sufficiently safe for practical use. The detection accuracy can be adjusted in any way by appropriately selecting the balance between the filtration amount of the second stage membrane and the sample amount, making it extremely convenient and safe.

It is expected that the embodiments of the present invention will improve the drawbacks of membrane filtration methods, which were considered to lack reliability in the past, and will be widely applied industrially in the future.

[Brief explanation of the drawing]

FIG. 1 is an example of a flow sheet for a membrane filtration device not according to the present invention. FIG. 2 is an example of a flow sheet of a membrane filtration device according to the present invention, and FIG. 3 is also another example of a membrane filtration device according to the present invention. FIG. 4 shows the results of the Rimura test on the concentrated liquid using the second membrane in Example 1, in relation to the number of operating days.

Claims (1)

[Claims] 1. In liquid filtration by membrane filtration, a first membrane and a second membrane consisting of either a reverse osmosis membrane or an ultrafiltration membrane having substantially the same characteristics are arranged in series, and the first membrane The liquid is filtered through both membranes successively by circulation filtration, partial filtration, or total filtration, and the second membrane is filtered by total filtration.
A membrane filtration method characterized in that a break in the first membrane is detected by detecting a difference in the characteristics of the liquid after passing through the membrane, and filtration is stopped or switched to another filtration device based on the detection signal. 2. The membrane filtration method according to claim 1, wherein the means for detecting the difference in liquid properties is based on measurement of turbidity, number of particles, pressure, or electrical conductivity. 3. The membrane filtration method according to claim 1, wherein the means for detecting the difference in liquid properties is based on measurement of endotoxin concentration.