Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2000-03-21
2001-08-07
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C208S179000, C208S181000, C208S183000, C210S721000, C210S724000, C210S726000, C210S737000, C210S756000, C210S759000, C210S763000, C210S772000, C210S909000
Reexamination Certificate
active
06270678
ABSTRACT:
The present invention relates to a method of treating alkaline waste water originating from washing spent oil which has undergone an alkaline treatment with water and which contains organic material. This method can produce water which can be discharged into conventional industrial water treatment facilities or which can be used directly as a base for preparing fertilizers or for preparing and agent for preventing ice formation on road surfaces.
Within the context of the present invention, the expression “washing spent oil which has undergone an alkaline treatment with water and which contains organic material” means the water washing step carried out in the refining method of used oils as claimed in International patent application WO-97/00928 published on Jan. 9
th
, 1997. That method, which can produce reusable refined oils, comprises specific successive steps consisting in distilling a spent oil, carrying out an alkaline treatment on the resulting distillate, washing the reaction medium formed with water, and distilling the oily phase recovered after settling out at the end of the water washing step.
When refining spent oils, the water washing step thus produces an aqueous phase, hereinafter termed “alkaline waste water”, in the form of an excessively colored and odoriferous solution (ASTM color not measurable; appearance of black coffee and phenolic type odor) which cannot be discharged into conventional industrial water treatment facilities and which cannot be recycled in any form.
Alkaline waste water generally has the following principal characteristics:
TABLE 1
Characteristics
pH
Over 13
Color
ASTM not measurable
(appearance of black coffee)
Specific gravity
1 to 1.250
Alkaline agent (sodium or
1-20
potassium hydroxide;
% by weight)
Salts of organic acids
5-50
(% by weight)
Various mineral salts of
0.1-4.5
alkaline agent
(% by weight)
Phenolic compounds (mg/l)
0-8000
Water (% by weight)
30-90
The alkaline agent is sodium or potassium hydroxide, which alkaline agents are in normal use in alkaline waste water treatments, and in particular in the alkaline treatment step of the method described in International application WO-97/00928, the conditions of which are such that there always subsists a proportion of the alkaline agent which has not reacted and which is thus present in the alkaline waste water to be treated. The organic acid salts have a variety of origins but they originate mainly from the organic acids initially present in the spent oil and which are transformed into the corresponding salts during treatment with the alkaline agent. They can also originate from esters conventionally present in commercial lubricating oils, which esters are decomposed during the high temperature alkaline treatment to form acids and alcohols which are themselves transformed into acids given the oxidizing nature and the temperature of the reaction medium; those acids form the corresponding salts with the alkaline agent.
The various mineral salts of the alkaline agent present in the alkaline waste water were formed during the alkaline treatment by the action of the alkaline agent on the various contaminants present in the treated spent oil, such as chlorine, phosphorous and silicon compounds, the corresponding anions of which are, for example, Cl
-
, PO
4
3-
and SiO
3
2-
.
Finally, the phenolic compounds are those which are normally present in spent oils such as those treated in the method of WO-97/00928. In particular, those phenolic compounds include phenol, o-, m- and p-cresols and di- and tri-methylpehnols (including, of course, all isomers thereof). They are present in small quantities which are, however, sufficient to produce a color and an odor which must be eliminated. They are measured using the method described in French standard NF XPt 90109 from AFNOR [French Standards Committee].
It should be understood, however, that such alkaline waste water is a complex solution which is difficult to define, in particular the exact nature of the organic esters and acids present, because of confidential nature about the compositions of the spent lubricating oils from which they originate.
A first solution for treating such alkaline waste water consisted of incinerating it, but clearly the heat balance for such a method is not economically viable. Evaporation prior to incineration has also been attempted but there again such a method is not economically viable. Attempts have also been made to separate the organic compounds from the alkaline waste water, firstly using physical separation methods such as filtration, tangential filtration, ultrafiltration, or centrifuging, but without producing any satisfactory results when the alkaline waste water to be treated is in the form of a single liquid phase.
In addition to such unsuccessful physical methods, neutralization of the alkaline waste water has been attempted, but it has proved impossible to obtain any separation of the organic compounds under such conditions. Attempts have been made to encourage separation by increasing temperature during neutralization, which has again proved completely unsuccessful even when the alkaline waste water is left in contact with the neutralization agent for a longer period.
Surprisingly and unexpectedly, it has now been discovered that it is possible to obtain clear decolorized water which is free of organic compounds from alkaline waste water using a method comprising a specific succession of steps, the order of which is essential in order to produce such a result.
Thus the present invention provides a method of treating alkaline waste water originating from a step of washing spent oil which has undergone alkaline treatment with water, said alkaline waste water also containing organic material, the method being characterized in that it comprises a set sequence of steps comprising:
a) bringing the alkaline waste water into contact, at a temperature in the range about 60° C. to 105° C. and for a period in the range about 5 to 60 minutes, with a mineral acid in a quantity 1% to 20% higher than that corresponding to the stoichiometry of the reaction, thus transforming all of the alkali atoms present in the alkaline waste water to be treated into a mineral salt;
b) allowing the organic and aqueous phases obtained to settle at a temperature in the range about 60° C. to 105° C., to recover the acidic aqueous phase;
c) bringing the acidic aqueous phase into contact, at a temperature in the range about 65° C. to 95° C., with an alkaline solution in a quantity sufficient to obtain a pH in the range 7.5 to 9 in the reaction medium, then allowing the reaction medium to stand at a temperature in the range about 40° C. to 95° C. to allow a flocculate to form and then settle out, and filtering to recover and aqueous phase.
In particular, the mineral acid used in step a) is selected from the group formed by hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and mixture thereof.
The quantity of mineral acid used in step a) is thus calculated from that corresponding to the stoichiometry of the reaction transforming all o the alkali atoms present in the alkaline waste water to be treated into a mineral salt. To this end, the total number of alkali atoms is determined, usually by measuring the proportion by weight of sodium and/or potassium atoms present in various forms in the alkaline waste water to be treated, for example by plasma analysis in accordance with ASTM D5185 [American standard]. Depending on the mineral acid used, the stoichiometry of the reaction transforming an alkali atom (sodium or potassium) into a mineral salt is reduced and thus the quantity of mineral acid necessary to react with all of the alkali atoms, measured as indicated above, is determined so as to deduce the value which is higher than that quantity by 1% to 20%, that value corresponding to the quantity of mineral acid which must be used in step a). Surprisingly and unexpectedly, it has been shown that only this 1% to 20% higher quantity combined with the temperature employed e
Hruskoci Peter A.
Nixon & Vanderhye P.C.
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