JPS602117B2 - Treatment method for oil and fat refining process wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for treating wastewater from a vegetable fat refining process using a semipermeable membrane.

More specifically, the alkaline homogeneous solution discharged from the above step is pH-adjusted to form an emulsion with a pH of 6.5 to 9.
A simple and rational method for treating wastewater from the vegetable oil refining process in which a suspended solution of 100% is separated using a semi-permeable membrane, and a more efficient method in which fatty acids can be recovered from the concentrated fraction as necessary. This invention relates to a method for treating wastewater from a vegetable oil refining process. Vegetable oils and fats such as salad oil and vegetable oil are generally refined through the process roughly shown in Figure 1, but the wastewater from the deoxidizing process is particularly high-loaded and large in volume.
Its treatment is difficult and has become one of the issues to be solved in this industry.

Conventionally, the deoxidation process wastewater has been treated mainly by the m coagulation pressure flotation method and the '21 flotation separation + activated sludge method (the general flowcharts are shown in Figures 2 and 3, respectively). .

However, with the '11 coagulation pressure flotation method, it is extremely difficult to make a cake that is easy to dehydrate, and cakes with poor dewatering efficiency waste a large amount of heavy oil, a valuable resource, when incinerated. There is also the problem that skilled manpower is required to manage each process. On the other hand, in the flotation separation + activated sludge method (■), fatty acids and/or
Otherwise, the fatty acid soap cannot be recovered, resulting in a large economic loss, and a large amount of waste sludge is generated, resulting in the problem of industrial waste.

In addition, due to the high load, it is difficult to control microorganisms.
Furthermore, it requires a vast site and requires a large capital investment, making it uneconomical.Therefore, it is important to reduce waste as much as possible and collect and reuse valuable materials as much as possible. This did not satisfy the demands of the era of resource and energy conservation. Therefore, the present inventors investigated a method of separating n-hexane soluble components using a semipermeable membrane, but it is difficult to directly apply the semipermeable membrane method to the alkaline solution discharged from the vegetable oil refining process. There was no significant difference in water quality between the fractional fraction and the permeation fraction, making it impractical. As a result of further intensive research, by adjusting the pH of the alkaline solution to 6.5 to 9 and turning it into an emulsion,
It was discovered that separation could be achieved using a semipermeable membrane, and satisfactory results were obtained, leading to the creation of this invention. That is, this invention improves the alkaline solution discharged from the vegetable oil refining process to pH 6.
．． 5 to 9, and then separated by a semipermeable membrane into an oil-in-water emulsion concentrated fraction containing n-hexane solubles and a permeation fraction containing substantially no n-hexane solubles. The present invention provides a simple, reliable, and rational method for treating wastewater from vegetable oil refining processes that does not require skilled operation or difficult microbial control. The present invention also provides temperature conditions for the emulsion liquid when it is separated by the semipermeable membrane. That is, according to the present invention, if the emulsion liquid is separated using the semipermeable membrane at a temperature of 40° C. or higher, the permeation capacity per unit time per unit membrane area of the semipermeable membrane increases dramatically. This makes it possible to stably maintain the permeation ability over a long period of time, thereby providing a more efficient and economical method for treating wastewater from the oil and fat refining process. Furthermore, the present invention also provides a method for recovering the concentrated fraction of the oil-in-water emulsion separated by the semipermeable membrane.

That is, according to the present invention, the concentrated fraction separated by the separation process is taken out, the pH is further lowered with an acidic substance, and the oil-in-water emulsion in the concentrated fraction is heated preferably to 70 qo or more. Destroy, top and bottom 2
It becomes possible to separate into layers and recover the upper layer as a raw material for fatty acids. In addition, the lower layer contains only a small amount of n-hexane extract and can be discharged with only a simple neutralization operation. In this way, collecting concentrated fractions saves resources and
This is an extremely useful method from the standpoint of equipment investment efficiency and pollution prevention. A detailed explanation will be given below with reference to FIG. 4 showing a process diagram of the present invention.

The vegetable oil and fat refining process wastewater to be treated according to the method of the present invention is mainly the deacidification process wastewater, and in addition to this, if necessary, squeezing process wastewater, deodorizing process wastewater, oilwort decomposition wastewater,
Can contain any waste water such as vacuum pump waste water,
The main components of these wastewaters are fatty acids or fatty acid soaps, neutral oils, and gums, with small amounts of proteins, water-soluble pigments,
Contains sterols and bran, and usually contains 500 to 1000 pm of n-hexane soluble content.

The pH adjustment and filtration steps are important steps in carrying out the present invention, and neutralize the fatty acid soap in the purification process wastewater, which is an alkaline homogeneous solution, and reduce the solubility of the fatty acid soap. This is a process in which fatty acid soap, fatty acids, neutral oil, etc. are emulsified into emulsion particles having a size that enables separation using a semipermeable membrane as described below.

Acceptable pH range is 6.5-9, preferably 6.5-9
It is 8.5. If the pH is higher than 9.0, the amount of n-hexane extract in the permeate fraction cannot be collected to a satisfactory extent. On the other hand, when the pH is lower than 6.5, the amount of n-hexane soluble content in the permeation fraction is satisfactory, but in the separation process using a semipermeable membrane described below,
This is undesirable because it reduces the stability of the furnace permeability over time and the permeation capacity per unit area per unit time. As the acidic substance used in this pH adjustment step, any substance that is generally recognized as an acidic substance can be used.
For example, inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid, lactic acid, and formic acid can be used. In the next step, a semi-permeable membrane designed to prevent oil-in-water emulsion particles from passing through but allow water and low-molecular weight substances to pass through allows the n-hexane, pH-adjusted in the previous step, to be used at a concentration of 500 to 1000 pm. The emulsion liquid with a pH of 6.5 to 9 containing soluble components is separated into a concentrated fraction containing approximately 5 to 30% by weight of n-hexane soluble components and a permeated fraction containing substantially no n-hexane soluble components. be done. n- of the concentrated fraction separated in this step
Technically, it is possible to increase the amount of hexane soluble content until the oil-in-water emulsion undergoes a phase transformation into a water-in-oil emulsion, but if the concentration is increased to more than 3% by weight, it will be half that amount. The permeation capacity per unit time per unit cocoon area of the membrane decreases, and the semipermeable membrane device becomes large, which is not only unfavorable from an economical and installation space standpoint, but also reduces the residence time in the semipermeable membrane device. This is not preferable because it has the disadvantage that the emulsion liquid becomes spoiled due to a long period of time. Further, if the concentration is less than 5%, it becomes difficult to post-process the concentrated fraction, which is not preferable. The concentrated fraction separated in this step is treated by incineration, etc. if the recovery described below is not carried out, but in the case of incineration, the amount of n-hexane soluble fraction is about 5 to 3% by weight.
This is suitable because the amount of combustion improver used is small. The permeate fraction separated in this step is treated by the activated sludge method or by being discharged into the sewage of local governments, but in either case, the amount of n-hexane extract in the permeate fraction is It is suitable because the amount is 30 ppm or less. Separation using a semipermeable membrane carried out in this process involves applying pressure to the solution (usually operated at a pressure of 0.2 to 10 kg') to prevent the passage of bacteria, high molecular weight substances, and emulsion particles. Filtration is performed using membranes, ultrafilter membranes, microfilters, and reverse osmosis membranes that allow water and low-molecular-weight substances dissolved in water to permeate through countless micropores on the membrane surface. The size of the micropores on the membrane surface ranges from 5A to tens of thousands of A, and is controlled to various sizes depending on the membrane material and manufacturing method. preferable. If this pore size is too small, the ability to remove n-hexane solubles will increase and the quality of the water in the permeate fraction will improve, but the furnace efficiency will be poor and the semi-permeable device will be large, as well as the osmotic pressure will increase. If the pressure is not extremely high, there is a tendency for the furnace to fail. On the other hand, if the pore size is too large, the furnace efficiency is good, but the amount of n-hexane soluble content in the permeate fraction increases, making it impossible to pass through discharge or activated sludge treatment, which is not preferable. The material of the semipermeable membrane used in this invention may be any conventionally known semipermeable material such as cellulose acetate, polyester, polyacrylonitrile, polycarbonate, polysulfone, or polyamide. Both flat membranes and hollow fiber membranes can be formed using known methods, and the shapes of furnace units made of these semipermeable membranes include tubular, spiral, and
Either plate and frame type or hollow fiber type may be used. In the method of the present invention, the temperature condition of the suspension solution during separation using a semipermeable membrane is such that the temperature of the emulsion solution must be 40° C. or higher.

This is because in such a temperature range, it is possible to perform stable separation operations over a long period of time with high filtration efficiency, and the semipermeable membrane device can be made smaller, which is more economical and suitable. The upper limit temperature condition is defined as a temperature range in which the emulsion does not change in quality and in which the semi-transparent material used can be operated, but usually the deoxidation process wastewater is 90 to 100%
oo. Since other wastewater is supplied at room temperature, it is better to perform the separation operation at a temperature of 90 qC or less. oo. The concentrated fraction can also be suitably treated by incineration, etc. as described above, but the method provided by the present invention According to , it is more economical and rational because valuables are recovered as raw materials for fatty acids.

The concentrated fraction containing about 5-3% by weight of n-hexane extract is reduced from pH 6.5-9 to pH 3 by addition of acidic substances.
After the above adjustment, the emulsion is broken by further heating and separated into an upper oil layer and a lower water layer.

When the pH is higher than 3.0, it becomes difficult to separate the concentrated fraction into two layers. Heat treatment is preferable because it promotes emulsion breakage and shortens operation time, allowing the apparatus to be compact. The upper oil layer contains stearic acid, oleic acid,
The main components are C, 8 fatty acids such as linoleic acid and palmitic acid, and it is recovered as a raw material for useful fatty acids, including myristic acid, lauric acid, etc. In addition, since the lower aqueous layer contains only a few ppm or less of n-hexane soluble matter, it can be neutralized by a normal neutralization operation and discharged. Examples of the present invention will be described below. Example 1 Wastewater from a vegetable oil refining process with a pH of 12 was adjusted with 70% sulfuric acid to obtain an emulsion liquid with properties as shown in Table 1.

Table 1 Properties of Emulsion Liquid The above suspension solution was separated using an internal pressure separator using a hollow ultrafilter membrane having the performance shown in Table 2.

The results are shown in Table 3 and the graph in FIG. Table 2 Performance of ultrafurnace filtration membrane Table 3 Comparative example of operation results 1 The wastewater from the vegetable oil refining process used in Example 1 was prepared with no pH adjustment, and the wastewater was adjusted to pH 3 and 10 with 70% sulfuric acid to form an emulsion solution. And so.

Thereafter, separation was performed using the ultrafilter membrane used in Example 1.
Table 4 also shows the results. Table 4. Operation results [Note 1] Liquid temperature: 45°C Example 2 The vegetable oil refining process wastewater used in Example 1 was adjusted to pH 7.5 with 70% sulfuric acid, and the liquid temperature was changed from 15q0 to 5q0 to create a suspension solution. , separated by the ultrafilter membrane used in Example 1.

The results are shown in the graph of FIG. 6 together with Control Example 1. Normally, the furnace throughput increases linearly as the liquid temperature rises, as shown in Control Example 1, but in the case of the waste water, the furnace throughput increases in an S-shaped curve as shown in the graph of FIG. The melting point of the mixture of neutral oil, fatty acid, or fatty acid soap in the wastewater used in this example is between 30 and 40°C, and from the graph in Figure 6, the separation operation is performed at a liquid temperature above the melting point. It turns out that this is extremely effective. Control Example 1 The filtration operation was carried out in the same manner as in Example 2, except that the temperature of the clear water was changed from 15 to 50°C.

The results are shown in the graph of FIG. Example 3 12.4% n-hexane soluble content separated in Example 1
Adjust the concentrated fraction to pH 2 and heat at 90°C.
After 3 hours, separate directly.

Separated upper layer crude fatty acid liquid was subjected to another reaction
% of water was added, 1% of Teutchel's reagent was added together with concentrated sulfuric acid, and then heated by blowing steam for 4 hours. Thereafter, it was washed and subjected to a distillation process to obtain purified fatty acids. The yield was 1% by weight based on the concentrated fraction. As is clear from the above Examples and Comparative Examples, according to the present invention, in the wastewater treatment of the vegetable oil refining process, the oil-in-water emulsion concentrated fraction and the permeation fraction containing substantially n-hexane soluble matter are treated. Since the wastewater can be separated into two parts, the treatment of the wastewater is not only simple and rational, but also the concentrated fraction can be recovered and reused, so its economic effects and contribution to pollution prevention are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a process diagram schematically showing a general refining process for vegetable oils and fats. FIG. 2 is a process diagram schematically showing the flow of the conventional agglomeration and pressure flotation method. FIG. 3 is a process diagram schematically showing the flow of the conventional flotation separation + activated sludge method. FIG. 4 is a process diagram schematically showing the flow of the semipermeable membrane method according to the present invention. FIG. 5 is a graph showing the results of the separation operation in Example 1. 6th
The figure is a graph showing the operational results of the separation operations of Example 2 and Comparative Example 1. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. An alkaline solution discharged from a vegetable oil refining process is adjusted to a pH of 6.5 to 9 to form an emulsion, and then the emulsion is converted into an n- A method for treating wastewater from an oil and fat refining process, which comprises separating an oil-in-water emulsion concentrated fraction containing a hexane soluble fraction and a permeation fraction containing substantially no n-hexane soluble fraction. 2 The alkaline solution discharged from the vegetable oil refining process is adjusted to pH 6.5 to 9 to form an emulsion, and then the emulsion liquid is heated to a temperature of 40°C or higher using a semipermeable membrane to contain the n-hexane soluble content. Separating the oil-in-water emulsion concentrated fraction and the permeation fraction substantially free of n-hexane soluble fraction, and recovering fatty acids from the oil-in-water emulsion concentrated fraction containing the n-hexane soluble fraction. A method for treating wastewater from an oil and fat refining process, characterized by: