IE42108B1 - Process for the dehydration of fatty sludge and the recovery of chemicals - Google Patents

Abstract

1468092 Recovering fatty substances APOTHEKERNES LABORATORIUM FOR SPECIAL-PRAEPARATER AS 6 Aug 1974 [28 Jan 1974] 34670/74 Addition to 1468091 Heading C5C Fatty substances are recovered from aqueous effluents as described in the parent Specification but in addition the stabilized sludge containing the stabilized fatty substance or degradation product thereof is acidified so that it separates into an upper concentrated fatty sludge phase and a lower aqueous phase. The acids used may be hydrochloric acid or soap stock (as defined). The upper fatty sludge phase is separated from the aqueous phase and the former is heated to form an upper phase containing technical fatty acid and a lower aqueous phase containing the precipitation chemicals used to precipitate the original stabilized aqueous fatty sludge, these two phases then being separated.

Description

The present invention relates to a process for removing fatty substances or degradation products thereof from aqueous effluents containing these materials and is particularly concerned with an improvement in or modification of the process described and claimed in our Application No. 231/74.

Our Application No. 231/74, describes a method for recovering a stabilised fatty substance or degradation product thereof or a proteinaceous substance or degradation product thereof from an aqueous effluent containing said substances or degradation products thereof whefein an acid hydrolysing metal salt of the type defined below is added to the effluent in an amount sufficient to complex the substances or degradation products thereof, if the pH of the effluent is above 5 the pH is reduced to 5 or below, and the resulting complex precipitated in the presence of added alkaline earth metal ions by raising the pH to 6 or more. s .s The method^jrftec-uT Appl i cat ion No. 231/74 produces ...^'-Stabilised fatty substance or degradation product thereof in the form of an aqueous sludge. These aqueous sludges have a high water - 2 42108 content and consequently are of relatively large volume and from the practical point of view, it is desirable to reduce the volume of this fatty sludge by dehydration. The fatty sludge contains, in addition to water, the chemicals that are used in the precipitation process which produces the fatty sludge and it is also desirable, from the practical point of view, to be able to recover these precipitation chemicals from the sludge for further use. We have now discovered how it is possible to dehydrate this fatty sludge easily and quickly to produce a concentrated sludge of smaller volume and also, if desired, to recover from this concentrated sludge the precipitation chemicals so that they can be reused.

The present invention provides a method for dehydrating a sludge comprising a fatty substance or degradation product thereof stabilized against oxidation^ obtained from an aqueous effluent containing said substances or degradation products thereof, said method comprising adding an acid hydrolysing metal salt (as hereinbefore defined) to an aqueous effluent in an amount sufficient to complex the substance or degradation products thereof, if the pH of the effluent is above 5 reducing the said pH to 5 or below, and precipitating the resulting complex in the presence of added alkaline-earth metal ions, by raising the pH to 6 or more wherein a stabilized sludge comprising said complex is separated from the effluent and the separated sludge is acidified so that the acidified sludge separates into an upper concentrated fatty sludge phase and a lower aqueous phase. -342108 The acid hydrolysing metal salt used in the precipitation is a salt of a metal whose aquo ion undergoes acid dissociation in water and is preferably a salt of trivalent iron or aluminium, such as ferric sulphate, ferric chloride or aluminium sulphate. The reduction of the pH to 5 or below, prior to the precipitation, is preferably effected, as in the method of the parent case, by adding mineral acid at the same time as or after the addition of the acid hydrolysing metal or salt.

The acidification of the stabilised aqueous fatty sludge may be brought about by addition of a mineral acid. One particularly suitable mineral acid is the so-called soap stock which is the highly acidic effluent obtained from the decomposition of soap in the fat refining industry.

Another mineral acid which can be used with advantage is hydrochloric acid as when this acid is used, the problem of calcium sulphate precipitation is avoided. -4_ Phase separation occurs when the stabilised aqueous fatty sludge is acidified in accordance with the present invention. The upper concentrated fatty sludge phase may then be separated from the lower aqueous phase and it has been found, in accordance with a further feature of the invention, that if this concentrated fatty sludge phase is heated, for example to its boiling point, further phase separation occurs and an upper phase, containing technical fatty acid, separates from a lower aqueous phase which contains the precipitation chemicals that are used to precipitate the original stabilised aqueous fatty sludge. Separation of these two phases means that the precipitation chemicals can be recovered in a form in which they can be reutilised for the precipitation of the fatty materials in an aqueous effluent.

The following Examples are given to illustrate the invention: EXAMPLE 1 The sludge used was sludge from pilot plant experiments for the stabilisation and recovery of fats and fatty substances from process water in a combined fat refining/margarine factory using FeClg CaCl2 and Ca(0H)2 as precipitating chemicals in accordance with the nrocess described in Irish Application No. 231/74 or ,r British Specification No. 1468091.

The following experiments were then carried out on the precipitated sludge: 1.1 150 ml sludge was heated on a hotplate almost to boiling point. This resulted only in slight non-homogeneity in the sludge, which disappeared upon stirring. 1.2 Concentrated sulphuric acid was added to 150 ml sludge dropwise while stirring until rapid separation into two phases occurred. This was after the addition of 2.5 ml concentrated sulphuric acid when the pH was 1.5.

The floating concentrated sludge phase, which was porous, was easily removed with a spoon and was collected as a specimen marked sludge cone. 1.2; the hydrous phase was filtered and collected as a specimen marked hydrous phase 1.2. 1.3 3 ml concentrated sulphuric acid was added to 150 ml sludge dropwise while stirring. Rapid separation into two phases occurred when the pH reached 1.2.

The floating concentrated sludge phase appeared more compact and had a volume of only 25 ml.

The hydrous phase was slightly cloudy. The whole mixture was heated, whereupon the layer of sludge that had formed turned darker and contracted to a volume of about 10 ml. Large -642108 light gypsum flocks formed in the hydrous phase and sank to the bottom. Upon boiling, the fatty acid separated from the sludge phase as dark drops on the surface, while the separated hydrous phase was turned yellow by the iron (111) ions.

The fatty acid drops collected in a coherent layer and were collected as a specimen marked fatty acid 1.3. 1.4 7 ml concentrated nitric acid was added to 150 ml sludge. This avoids precipitation of gypsum. When the pH dropped below 2, a spongy and coherent concentrated sludge phase separated and floated up to the surface. A specimen was taken from the concentrated sludge phase and marked sludge cone.1.4. 1.5 3 ml concentrated sulphuric acid was added quickly to 150 ml sludge while stirring well. A coherent sludge of 20 ml volume which floated well separated rapidly when the pH dropped below 2. A specimen of the concentrated sludge was taken and marked as sludge cone. 1.5.

The various specimens were analysed for their fat content and the analysis results; volume of the sample and brief reference to its method of preparation are set out below. -742108 % of total fat O'OOL 96.9 2.7 5.S 93.3 94.4 95.7 Fat content, grams 1 .803 1.746 0.048 0.107 1.683 1.702 CO CJ r— Volume ml OS L CJ CO tn cn m in cj CJ cj ·— r— 30 20 Treatment None ε ε ο ο to tn to tn CJ · Od · IN X CJ «a· ε s M- σ ό oj γιο o to Ο «I- τ- ου · CJ · s- o X CO X co co co - s co o o X ♦ X r^· * r— «3- ε o to o CJ - X Specimen Sludge Concentrated sludge Hydrous phase Concentrated sludge Hydrous phase Fatty Acid Concentrated sludge Concentrated sludge I JTest - Cl 1.3 1.4 1.5 J <2108 The hydrous phases from tests 1.2 and 1.3 were different to one another, as hydrous phase 1.3, which was removed after the deacidised sludge specimen had been boiled, had a strong yellow colour. When both specimens were neutralised by NHg sedimentation from specimen 1.3 was heavy and brownish in colour, while sedimentation from specimen 1.2 was sparse and almost white.

Rhodanide reaction of the dissolved sediments clearly identified a high Fe content in hydrous phase 1.3, while hydrous phase 1.2 contained only an insignificant amount of Fe.

These results made it clear that it is possible to recover the precipitation agent by heating the sludge which separates into the free fatty acid which floats up and the precipitation agent (cation) used remains in the lower hydrous phase.

EXAMPLE 11 The sludge used was a fatty sludge obtained by flotation 2o and recovered from process water from a margarine factory by sedimentation and stabilisation using AI2(S04)3 CaClg and NaOH in accordance with the procedure described in Irish Application No. 231/74 or uritish Patent Specification No. 1468091. -942108 Hydrochloric acid was added to the fatty sludge until its pH was 1.6, when the sludge split into two phases, an upper concentrated sludge phase and a lower aqueous phase. Fat analyses of the two phases were carried out and the volume of the phases was measured, the results are set out below.

Analyses Specimen Treatment Fat content, grams Volume in ml. Sludge None 2.648 250 Concentrated sludge Aci d 2.622 14 Hydrous phase Acid 0.023 236 SIudge None 2.701 250 Concentrated sludge Acid 2.625 13 Hydrous phase Acid 0.076 237 As the analyses show, only a very small portion of the fat passes into the anhydrous phase (about 100-300 ppm) and at the same time a good concentration of the fatty sludge is obtained i.e. from about 1000 ml to about 56 ml. -1042108 EXAMPLE 111 The sludge used was a fatty sludqe obtained by flotation, and recovered from condensate effluents as they occur from the production of meat/bone meal (sterilising, boiling drying) by sedimentation and stabilisation using FeClg, HgSO^ and Ca(0H)2 in i accordance with the procedure claimed in Application No. 231/74.

The sludge was acidified to pH 1.8 with hydrochloric acid, and two phases separated, an upper concentrated sludge phase and a lower aqueous phase. The concentrated sludge phase was removed by skimming and was treated further by boiling for 10 minutes.

During the boiling, dark drops of liquid fatty acid jr> separated and collected as a separate liquid phase.

This liquid fatty acid phase was separated in a separating funnel and its fat content determined. The following results were obtained which show that substantially all of the fat in the original 250 ml 2o sample is transferred to the 8 ml fatty acid phase.

Analyses Specimen Treatment Fat content, grams Volume in ml Sludge None 2.593 250 Concentrated sludge HCl to pH 1.8 - 18 Fatty acid phase 2.532 -8 i ______ _ _____ ____ ............ 1

Claims (17)

CLAIMS:

1. A method for dehydrating a sludge comprising a fatty substance or degradation product thereof a stabilized against oxidation, obtained from an 5 aqueous effluent containing said substances or degradation products thereof, said method comprising adding an acid hydrolysing metal salt (as hereinbefore defined) to an aqueous effluent in an amount sufficient to complex the substance or degradation products 10 thereof, if the pH of the effluent is above 5 reducing the said pH to 5 or below, and precipitating the resulting complex in the presence of added alkalineearth metal ions, by raising the pH to 6 or more whereimstabi 1 ized sludge comprising said complex is 15 separated from the effluent and the separated sludge is acidified so that the acidified sludge separates into an upper concentrated fatty sludge phase and a lower aqueous phase.

2. A method according to claim 1 wherein in obtaining the 20 stabilized sludge the pH of the effluent is reduced to 5 or below by adding mineral acid at the same time as or after the addition of the acid hydrolysing metal salt.

3. A method according to claim 1 or 2 wherein in 25 obtaining the stabilized sludge the acid hydrolysing metal salt and a soluble calcium salt (as the source of alkaline-earth metal ions) are added simultaneously as an aqueous solution. -1242108

4. A method according to any preceding claim wherein in obtaining the stabilized sludge a ferric salt and/or an aluminium salt, are used as the acid hydrolysing salt.

5. 5. A method according to claim 4 wherein in obtaining the stabilized sludge the salt is ferric sulphate, ferric chloride or aluminium sulphate.

6. A method according to any preceding claim wherein iri obtaining the stabilized sludge a dissolved protein 10 is present in the effluent, the acid hydrolysing metal salt is added in an amount at least sufficient to complex the substances and degradation products thereof present, and if the pH after this addition is above 4, a mineral acid is added to reduce the pH 15 to below 4.

7. A method according to any preceding claim wherein in obtaining the stabilized sludge CaO or Ca(0H)2 is used both as the source of alkaline-earth metal ions, and to raise the pH to 6 or more. 20

8. A method according to any preceding claim wherein in obtaining the stabilized sludge the precipitated material is removed by sedimentation, centrifugation or flotation.

9. A method according to any preceding claim wherein in obtaining the stabilized sludge the precipitated -1342108 material is removed by release of air dissolved in water under pressure,

10. A method according to any preceding claim wherein the separated sludge is acidified to a pH below 2. 5

11. A method according to any preceding claim wherein the separated sludge is acidified with mineral acid.

12. A method according to claim 11 wherein the mineral acid is a soap-stock as hereibefore defined.

13. A method according to claim 11, wherein the mineral 10 acid is hydrochloric acid.

14. A method according to any one of the preceding claims, wherein the upper concentrated fatty sludge phase is separated from the lower aqueous phase and the concentrated sludge phase heated to bring about the 15. Formation of an upper phase containing technical fatty acid and a lower aqueous phase containing acid hydrolysing metal salt or a metal-containing derivative thereof.

15. A method according to claim 14, wherein the lower aque20 ous phase containing the salt or derivative thereof is separated from the upper fatty acid phase.

16. A method according to any of claims 1 to 9 substantially as hereinbefore described. -1442108

17. Λ m ( eta1, salt or a derivative thereof recovered by a method according to claim 15.