CA1149290A

CA1149290A - Method of treating waste water from fats-and-oils refining process

Info

Publication number: CA1149290A
Application number: CA000360129A
Authority: CA
Inventors: Kohei Watanabe; Tokushichi Funaji
Original assignee: Nisshin Oil Mills Ltd
Current assignee: Nisshin Oillio Group Ltd
Priority date: 1979-09-14
Filing date: 1980-09-11
Publication date: 1983-07-05
Also published as: JPS602117B2; JPS5644089A

Abstract

METHOD OF TREATING WASTE WATER FROM
FATS-AND-OILS REFINING PROCESS

ABSTRACT OF THE DISCLOSURE

An improved treating method of waste water discharged from refining processes of vegetable fats and oils is provided. In this method, the waste water is adjusted to a pH of from 5 to 9 to form an emulsion, and then, the formed emulsion is separated, with a semipermeable membrane, into a concentrated fraction of oil-in-water type emulsion containing n-hexane-soluble matters and a membrane-permeable fraction containing substantially no n-hexane-soluble matter.

Description

METliIOD OF TR:E:ATING WASTE~ WATER FROM
FATS--AND-OILS REFINING PROCESS

The present invention relates to an improved method of treating waste water from refining processes of vegetable fats and oils with a semipermeable membrane. More parti-cularly, the present invention relates to a simple and economic, improved method of treating waste water discharged from refining processes of vegetable fats and oils, wherein alkaline homogeneous solutions discharged from said refining processes are adjusted to a pH of from 5 to 9 to form an emulsion, and said emulsion is then separated with a semi-permeable membrane; and, further, i~ desired, fatty acidsare efficiently recovered from a co,ncentrated fraction of said emulsion, which is obtained by the separation with said semipermeable membrane.
Vegetable fats and oils, such as salad oil, frying oil and the like, are generally refined by such processes as outlined in Fig. 1. However, since waste water, particu-larly that from a deacidification process, contains a large amount of substances to be treated, it is difficult to treat the waste water and, therefore, the treatment of the waste water has been a problem to be solved in the art~
For the treatment of waste water from the deacidifica-tion process, two main methods have heretofore been used, i.e., 1) the coagulation-flotation under pressure method , ~

and 2~ the flotation-activated sludge method, which are outlined in Figs. 2 and 3, respectively.
However, in the case of the coagulation-flotation under pressure method, it is extremely difficult to make 5 flocks which can be easily dehydrated and, therefore, a large amount of heavy oil, which is a valuable resource, is wastefully incinerated after the inefficient dehydration of the flocks. Further, in this case, there is also a problem that persons skilled in controlling each step are 1~ required.
On the other hand, the flotation-activated sludge method involves a great economic loss, since valuable fatty acids and/or soaps oE fatty acids cannot be recovered, and this method also creates a problem regarding industrial wastes since a large amount of wast~e sludge is produced.
Furthermore, the waste water contains a large amount of substances to be treated and, therefore, a large amoun~ of microorganisms are required to treat the waste water. In this regard, it should be noted that a large amount of microorganisms is difficu7t to handle and control. Further, because a large installation space and large plant investment are required, this method is also disadvantageous from an economic point of view. Therefore, because -the flotation--activated sludge method has such disadvantages as mentioned ~5 above, this method does not satisfy the demand to reduce industrial wastes as much as possible, and recover and reuse as many valuable substances as possible.
The present inventors have studied the separation of ~ ~ ~39 ~9 ~

n-hexane-soluble matters from alkaline waste water discharged from refining processes of vegetable fats and oils. They have found that, even if a semipermeable membrane method was directly applied to said waste water, the quality of water contained in a membrane-permeable fraction was not very different from that contained in a concentrated fraction. That is, the direct application of a semipermeable membrane method to the waste water discharged from refining processes of vegetable fats and oils was not practical.
Accordingly, an object of the present invention is to obviate the above-mentioned problems of the prior arts and to provide a simple and economic, improved method of treating waste water discharged fro~ refining processes of vegetable fats and oils.
Another object of the present lnvention is to provide a method of recovering fatty acids from said waste water containing the same.
Other objects and advantages of the present invention will be apparent from the description set forth hereinbelow.
In accordance with the present invention, there is provided a simple, reliable and economic method of treating alkaline waste water discharged from refining processes of vegetable fats and oils which does not require a skilled operating technique and a difficult management of micro-organisms, which method comprises the steps of:
ad~usting said waste water to a pH of from 5 tc 9 to form an emulsion, and;
then separating said emulsion, with a semipermeable . -..

~92913 membrane, into a concentrated fraction of oil-in-water type emulsion containing n-hexane-soluble matters and a membrane-permeable fraction containing substantially no n-hexane soluble matter.
In accordance with the present invention, there is also provided a more efficient and more economic method, than any method of the prior arts, of treating waste water discharged from refining processes of vegetable fats and oils by carrying out the separation operation with a semipermeable membrane at a temperature higher than the melting point of the mixture of neutral oils, fatty acids and/or soaps of fatty acids contained in the emulsions, because such a separation operation remarkably increases the permeability per unit time per unit area of the semi-permeable membrane and makes it possible to keep thepermeability stable for a long time.
Further, in accordance with the present inven-tion, there is provided a method of recovering fatty acids which comprises the steps of: taking out the concentrated fraction which has been fractionated by the above-mentioned separation step; adding an acidic substance to said con-centrated fraction to lower the pH value thereof; des-troying the oil-in-water type emulsion contained in said concentrated fraction by heating it up to a temperature of 70C or more; separating the destroyed emulsion into two layers, i.e., upper and lower layers, and; recovering said upper layer as a raw material of fatty acids. The lower layer contains only a trace amount of n-hexane extract and, .. . .

therefore, can be discharged in sewers, only by effect-ing a simple neutralization operation. Therefore, the recovery of the concentrated fraction is very useful, from the points of view of the saving of resources, plant investment efficiency and the prevention of environmental pollution.
The present invention will be better understood from the description set forth below with reference to the accompanying drawings, wherein:
Fig. 4 is a typical flow sheet of the method according to the present invention;
Fig. 5 is a graphical drawing illustrating a corre-lation between a rate of filtration and a magnification of concentration in Example l; and Fig. 6 is a graphical drawing illustrating a corre-lation between a rate of filtration and a liquid temper-ature in Example 2 and Reference Example 1.
The method of the present invention is directed to the treatment of waste water, mainly, from a deacidifi-cation process but, if desired, any waste water, such aswaste water from a pressing process, waste water from a deodorizing process, waste water from acidlysis of soapstock, waste water from vacuum pump and the like, can also be treated by the method of the present invention. The waste waters from these processes contain, as main ingredients, fatty acids and soaps of fatty acids, neutral oils and gum substances, `~

9'~9V
- 5a -and further contain a small amount of proteins, water-soluble pigments, sterols and sugars. The waste water normally contains n-hexane-soluble matters in a concen-tration of from 5QO to 10,000 ppm.
The pH-adjusting and stirring step is an important step of themethod of thepresent invention, andcomprises neutralizing soaps of fattyacids, inthe form of alkaline homogeneous solutions, contained in the waste water from the above refining processes, toreduce the solubility of said soaps of fatty acids, and;emulsifying fatty acids or g~

soaps of fatty acids, and neutral oils and the like in the neutral.ized waste water to form emulsion particles having such a size that the emulsion particles can be separated with the semipermeable membrane in the below--mentioned step. The allowable pH range of this step is from 5 to 9, preferably from 6.5 to 8.5. When the pH value is higher than 9, the content of n-hexane extract cannot be reduced to a satisfactory extent. On the other hand, when the pH value is lower than 5, although the content of n-hexane-soluble matters contained in the membrane-permeable fraction is satisfactory, the stability of filtration capacity of the semipermeable membrane is unpreferably reduced with time, and the permeability thereof per unit time per unit area is unpreferably reduced in the below-mentioned separation step with the semipermeable membranle. The acidic sub-stance as utilized in this pH-adjusting step can in-clude any substance which is generally acknowledged as an acidic substance, for example, inorganic acids, such as hydrochloric acid, sulfuric acid, nitric acid and the like, and organic acids, such as acetic acid, lactic acid, formic acid and the like.
In the next step, the emulsion, having a pH of from 5 to 9, the pH of which has been adjusted in -the preceding step, and which contains n-hexane-soluble matters ln a concentration of from 500 to 10,000 ppm, is separa-ted into a concentrated fraction containing about 5 to 30~ by weight of n-hexane-soluble matters and a membrane-permeable ~9~

fraction containing substantially no n-hexane-soluble matter. It is technically possible to raise the concen-tration of n-hexane-soluble matters in the concentrated fraction to be separated until the phase reversal of the emulsion occurs from oil-in-water type to water-in-oil type. However, the increase of more than 30% by weight in a concentration of n-hexane-soluble matters in the concen-trated fraction is not preferable from an economic point of view and the point of view of space for the installation, because it results in a decrease in permeability per unit time per unit area of the semipermeable membrane and maXes it necessary to utilize large equipment comprising the semipermeable membranes. Such an increase is also not preferable from the point oE view of the putrefaction of the emulsion, because the residence time in the equipment oE the semipermeable membranes is allowed to lengthen. On the other hand, the concentration of less than 5% by weight is no-t preferable, because it is then difficult to effect the post-treatment of~the concentrated fraction.
The concentrated fraction which has been separated in this s-tep is usually incinerated, unless the fatty acids contained in the concentra-ted fraction are recovered. The concentrated fraction is suitable for incineration, because the amount of n he~ane-soluble matters therein is as high as about 5 to 30~ by weight and, therefore, only a small amount of fuel additive is required. The membrane-permeable fraction which has been separated in this step is treated either by the activated sludge method or by discharging it in sewers.

9~

The membrane-permeable fraction is suitable for either treatment, because the amount of n-hexane extract therein is as small as 30 ppm or less. The separation with a semipermeable membrane which is carried out in this step S refers to a filtration with a membrane, ultrafilter, microfilter and reverse osmosis membrane, which comprises applying pressure to the solution (normally operating at a pressure of from 0.2 to 10 kg~cm ), preventing permeation of bacteria, high-molecular substances and emulsion par-ticles, and permeating water and low-molecular substances dissolved in water through a large number of micropores which exist in the membrane. The size of each micropore in the memhrane is generally in the range of from 5 A to tens of thousands A, dependiny on the material and the preparation of the membrane. The semipermeable membrane O O
having a pore diameter of from 10 A to 5000 A is preferable in the present invention. When the pore diameter is far smaller than 10 A, although the removability of n-hexane--soluble matters is increased and the quality of water in the membrane-permeable fraction is improved, the filtration efficiency is poor and large equipment comprising the semipermeable membranes is required. ~urthermore, in this case, due to a low osmotic pressurer it is difficult to effect the filtration unless a high pressure is applied.
On the other hand, when the pore diameter is far larger than 5000 A, although the filtration efficiency is still goodr the amount of n-hexane-soluble mattexs in the membrane--permeable fraction is increasedr and thereforer the .

<329~
g fraction is not suitable for discharging in sewers and for the activated sludge treatment. The material of the semipermeable membrane as used in the present invention may be any known material which has a semipermeable property, such as cellulose acetate, polyester, polyacrylonitrile, polycarbonate, polysulfone, polyamide and the like~ and any of these materials can be made into a flat membrane and a hollow fiber membrane by any conventional method.
The shape of the filteration unit of the sPmipermeable membranes can be tubular, spiral, plate and frame-type or hollow fiber~type.
The temperature of the emulsion when it is separated by a semipermeable membrane is preferably higher than the melting point of the mixture of neutral oils, fatty acids and/or soaps of fatty acids. ~hen the temperature is higher than the melting point of the mixture,the separation operation can be stably carried out with a high filtration efficiency for a long time and the equipment comprising the semipermeable membranes can be small. Therefore, in this case, waste water can be economically treated. Since the melting point of the above-mentioned mixture is normally in the range o~ from 30 to 40C, the separation operation is preferably carried out at a temperature of 40C or more. The upper limit of temperature is limited to such a temperature that the emulsion is not changed in quality and the semipermeable membrane can be operated. Normally, waste water from the acidification process is at a temper-ature of from 90 to 100C and waste water from other ~9290 refining processes is at room temperature. Th~refore, the separation operation is preferably carried out at a temper-ature of 90C or less.
As ~entioned hereinabove, the concentrated fraction can be suitably treated, for example, by incineration.
However, according to the present invention, valuable raw fatty acids can be economically recovered from the concen-trated fraction, if desired.
The concentrated fraction, of a pH of from 5 to 9, containing about 5 to 30% by weight of n-hexane extract is adjusted to a pH of 3 or less by the addition of an acidic substance and, then, heated to destroy the emulsion, whereby the concentrated fraction is separated into the upper oil layer and the lower water layer. The preferable heating temperature is within the range oE 70 to 120C.
When the pH is higher than 3, it is difficult to separate the concentrated fraction into two layers. The heat treatment is preferable, since it accelerates the destruction of the emulsion and, therefore, makes it possible to shorten the operation time and makes the recovery plant compact. The upper oil layer includes, as a main ingredient, C18 fatty acids, such as stearic acid, oleic acid, linoleic acid and the like, and palmitic acid r and further, contains myristin, lauric acid and the li~e, and is recovered as valuable raw fatty acids. On the other hand, the lowex water layer contains only several ppm or less of n-hexane--solu~le matters and, therefore, can be neutralized by a conventional neutralization operation, and then, discharged

2~1~

into sewers. The fatty acids contained in the upper oil layer can be recovered in any conventional manner. For instance, the fatty acids can be recovered by adding water to the upper oil layer containing the fatty acids; then adding Twitchell reagent and concentrated sulfuric a~id to the solution; heating the resulting solution by blowing steam into it; washing the solution, and; finally distilling the washed solutlon.
The present invention will now be illustrated by, but is by no means limited to, the following examples.
Example 1 A sample of waste water, from refininy processes of vegetable fats and oils, having a p~I of 12~ was adjusted to a pH of 7.5, with a 70% sulfuric acid solution, to form an emulsion having the properties indicated in Table 1 below.

T ~ B L E
Properties oi L~Lsion pH 7.5 . . ... _ . _ .. _ . ...
Liquid temperature 45C

n-Hexane-soluble matters 2500 ppm .. ~ ._. . .. __ _ Perc~ntages of main ingredients Fat~y acids or Soaps of fatty acids 60~ by weight ~'eutral oils 30~ by weight _ Gum subst~nces 10% by weight 9Z~

The above-mentioned emulsion was subjected to the separation operation with an internal pressure-type separator provided with hollow ultrafilters having a performance as indicated in Table 2 below. The results are indicated in Table 3, below.

Performance of Ultrafilters Material of ultrafilters Polyacrylonitrile copolymer Shape E~llow Micrcpore diameter About 20 A
.
Effective membrane area 4.7 m / module _ Water permeation rate 20 m3 / day-kg / cm2 ~ . ' o .
Results of Operation . . . ___ . __ Concentration of n-hexane-soluble matters 2500 ppm in the starting liquid .
Concentration of n-hexane-soluble matters 15 pEm in-the filtrate Concentration of n-hexane-soluble mat.ers 124000 ppm in the concentrated liquid Magnification of concentration50 times . _. ~
Rate of filtration see Fig. 5 Comparative Example 1 A sample of the same was-te water from re~ining processes of vegetable fa-ts and oils as utilized in the above Example 1 was not pH-adjusted~ and, another two samples of the same waste water were adjusted to pHs of 3 and 10, respectively, to form emulsions. Thereafter, the waste water, which had not been pH-adjusted, and the resulting two emulsions were separated with the same ultrafilter as utili~ed in Example 1, respectively. The results are indicated in the following Table 4.

z~ ~

Results of Operation . ___ - - - * 1 1 pH of the liquid Concentration of n-hexane-soluble Rate cf filtration or emulsion matters in the filtrate Q/min m~d.
.. _ (ppm) 12 (no pH- 2400 17.0 adjustment3

3 3 0.5 7.5 (EXample 1) 15 7.0 300 10.0 *1 : Liquid temperature of 45C

Example 2 Eight samples of the same waste water of refining processes of vegetable fats and oils as utiliæed in the above Example 1 were adjusted to a pH of 7.5 with a 70%
sulfuric acid solution to form emulsions. The resulting eight emulsions were adjusted to eight different temperatures of from 15C to 50C, respectlvely and separated with the same ultrafilter as utilized in the above Example 1. The results of this Example are indicated in a graph in Fig. 6 together with the results of Reference Example 1 below.
Normally, the filtration capacity linearly increases as a liquid temperature increases, as illustrated in the Reference Example 1. However, in the case of waste water, the filtration capacity increases in a sigmoid curve as a liquid temperature increases, as indicated by the graph of Fig. 6. The melting point of the mixture of neutral oils, ` - fatty acids and/or soaps of fatty acids in the waste water 9~

as utilized ln this Example was in the range of from 30 to 40C~ The graph of Fig. 6 shows that the separation operation can be very effectively carried out at a liquid temperature higher than the above-mentioned melting point~
Reference Example 1 The same procedures as those described in Example 2 were carried out, except that the eight samples of the waste water were replaced by seven samples of clarified water. The results are indicated in the graph of Fig. 6.
Example 3 The concentrated fraction containing 12.4~ by weight of n-hexane-soluble matters, which had been separated in the above Example 1, was adjus-ted to a pH of 2, heated to 90C under stirring, and allowed to stand for three hours to separate it into two layers. l'he separated upper layer of a solution of crude fatty acids was transferred to another reaction tank, 30~ by weight Oe water was added to the solution, 1% by weight of Twitchell reagent was then added to the solution, together with 2% by weight of concentrated sulfuric acid, and thereafter, the resulting solution was heated by blowing steam into it for 40 hours.
Then, the solution was washed and subjected to the dis-tillation operation to obtain refined fatty acids. The recovery of fatty acids is approximately 90~O

As is clear from the results obtained in the above Examples and Reference Example, the present invention allows the separation of waste water discharged from refining processes of vegatable fatty acids into a concentrated s~sv fraction of oil-in-water type emulsion containing n--hexane--soluble matters and a membrane-permeable fraction containing subs-tantially no n~hexane-soluble matter, and therefore, makes it possible to simply and economically treat said waste water. Furthermore, the present invention allows the recovery and reuse of the concentrated fraction.
Therefore, the present invention produces excellent effects which are advantageous from an economic point of view, and contributes to a great extent to prevention of environmental pollution.

Claims

1. A method of treating alkaline waste water dis-charged from refining processes of vegetable fats and oils, comprising the steps of:
adjusting said waste water to a pH of from 5 to 9 to form an emulsion, and;
then, separating said emulsion, with a semi-permeable membrane, into a concentrated fraction of oil-in--water type emulsion containing n-hexane-soluble matters and a membrane-permeable fraction containing substantially no n-hexane-soluble matter.

2. A method as claimed in claim 1, wherein the temperature of said emulsion is allowed to be raised to a temperature higher than the melting point of the mixture of neutral oils, fatty acids and/or soaps of fatty acids in the emulsion.

3. A method as claimed in claim 2, wherein the temperature of said emulsion is within the range of from 40 to 90°C.

4. A method of treating alkaline waste water dis-charged from refining processes of vegetable fats and oils, comprising the steps of:
adjusting said waste water to a pH of from 5 to 9 to form an emulsion;
then, separating said emulsion, with a semi permeable membrane, into a concentrated fraction of oil-in--water type emulsion containing n-hexane-soluble matters and a membrane-permeable fraction containing substantially no n-hexane-soluble matter, and;
thereafter, recovering fatty acids from said concentrated fraction of water-in-oil type emulsion.

5. A method as claimed in claim 4, wherein said recovery of the fatty acids is effected by adjusting a pH
of the concentrated fraction to 3 or less by the addition of an acidic substance and, then, by heating the resultant concentrated fraction to a temperature of from 70 to 120°C, whereby the concentrated fraction is separated into -the upper oil layer containing the desired fatty acids and the lower water layer.