GB2159140A

GB2159140A - Process for the purification of acid effluents

Info

Publication number: GB2159140A
Application number: GB08511094A
Authority: GB
Inventors: Jacques F J Grootjans
Original assignee: Labofina SA
Current assignee: Labofina SA
Priority date: 1984-05-02
Filing date: 1985-05-01
Publication date: 1985-11-27
Also published as: DE3515470C2; BE902322A; GB2159140B; LU85346A1; GB8511094D0; DE3515470A1

Abstract

A process for the purification of streams of aqueous acid solutions coming from a unit for the removal of nitrogen impurities, which comprises the steps of (a) neutralizing the stream of aqueous acid solution, (b) contacting the resulting stream with a platformate or other hydrocarbon stream or other solvent in a mixer to form an emulsion and (c) sending the emulsion in a decanter to recover the platformate or other hydrocarbon stream or other solvent on the one hand and the purified aqueous solution on the other hand.

Description

SPECIFICATION Process for the purification of acid effluents The present invention relates to a process for the purification bf acid effluents and in particular to the purification of acid effluent streams coming from a unit for washing hydrocarbon mixtures containing nitrogen impurities.

The Applicant has already studied and described in several patents a process to remove the nitrogen impurities from a liquid hydrocarbon mixture by means of an aqueous acid solution. An aqueous solution of sulfuric acid or hydrochloric acid is used most often.

The processes described in the Belgian Patents 884.149 and 886.082 are very advantageous because they are characterised by the use of highly dilute acid solutions to remove the nitrogen impurities from the liquid hydrocarbon mixtures.

However, in the processes to remove the nitrogen impurities, the stream of aqueous acid solution should be completely treated before being sent through the waste water lines. This treatment has to be applied even when a process using highly dilute acid solutions is employed, as disclosed in the Belgian Patents 884.149 and 886.082. Such a treatment needs therefore the use of a waste water treatment unit of a known capacity, which must take into account the amount of aqueous acid solution to be treated.

Moreover, in some cases, there is no water treatment unit available and other ways must be used to purify the acid effluents.

There is therefore a need for a process to purify the streams of aqueous acid solutions coming from a unit for the removal of nitrogen impurities. Such a process should provide the following three main features: - to have an acceptable C.0.D., i.e. lower than 2000; - to have a high extraction rate of the nitrogen compounds, generally about 90%; - to have a residual aqueous stream which is substantially colourless and haze free.

The C.0.D. (chemical oxygen demand) of a solution may be defined as being the necessary amount of oxygen, expressed in mg/l of solution, which is equivalent to that portion of the organic matter in the sample of solution that is susceptible to oxidation by potassium dichromate.

An object of the present invention is to provide a process for the purification of streams of aqueous acid solutions, which provides the features referred to above.

Accordingly, the present invention provides a process for the purification of a stream of an aqueous acid solution coming from a unit for the removal of nitrogen impurities, the process comprising the steps of: (a) neutralizing the stream of an aqueous acid solution with an inorganic or an organic base, (b) contacting said stream with a platformate or another hydrocarbon stream or organic solvent in a mixer, (c) sending the resulting stream to a decanter wherein a purified stream of aqueous neutralized solution is recovered from an organic phase.

In accordance with the process of the invention, it is very important first to neutralize the stream of aqueous acid solution with a base, in order to decompose the nitrogen compound salts which are present in the medium, the most often in the form of sulfate or chloride, with further formation of free nitrogen compounds which remain dissolved.

Moreover, the amount of base to be used should be sufficient to neutralize substantially the whole amount of free acid which is present in the medium.

Typical examples of bases which may be used in the process of the invention are NaOH and KOH, which are the most often used due mainly to their ready availability.

The amount of base to be used may be easily determined by the fact that the flow rate of the aqueous base solution is adjusted in order to make the pH of the mixture from 7 to 14 and preferably from 8.5 to 11. The resulting neutralized stream may not yet be discharged, because it still contains the nitrogen impurities.

The Applicant has now unexpectedly found that by contacting the neutralized stream with a light or heavy platformate, a stream of aqueous solution is obtained with an acceptable C.0.D., that is to say lower than 2000, whereas the C.0.D. of the stream to be treated is about 20,000.

Generally the platformate is mixed with the neutralized mixture in a volume ratio of from 0.5 1 to 3 1.

The result is really surprising because if other organic solvents are used for the removal of the nitrogen impurities, they do not provide all the three features mentioned above, and particularly the features concerning the extraction rate or the quality of the residual aqueous stream.

According to an embodiment of the invention, the stream of neutralized aqueous solution is introduced together with the platformate into a mixer wherein an emulsion is formed. The emulsion is thereafter sent to a decantation zone where the emulsion is broken up.

In this way a purified stream of aqueous solution is recovered on the one hand, while the platformate containing the nitrogen compounds is recovered on the other hand.

Suitable mixers which may be used in the process of the invention are a centrifugal pump or a static mixer.

An embodiment of the invention will now be described by way of example only with reference to the acompanying drawing in which: Figure 1 represents a schematic diagram of a purification unit for use in the process according to the invention.

Referring now to Figure 1, the stream of aqueous acid solution which is sent through line 2 constitutes the purge stream of a process for removing the nitrogen impurities from a hydrocarbon mixture, said process employing a hydrocarbon feed (4), a source of fresh aqueous acid solution (6) and the recycle of aqueous acid solution by line 8.

The purged aqueous solution is first sent through line 2 and is thereafter neutralized by means of an aqueous solution of a strong base which is introduced into line 2 through the line 10.

In the case of the treatment of a dilute aqueous acid solution, the aqueous solution of strong base is obtained by mixing within mixer 12, a stream 14 of concentrated base with water which is brought to the mixer 12 by line 16.

The mix consisting of an aqueous acid solution and an aqueous solution of a strong base is then introduced into the mixer 18 in order to ensure a convenient neutralization.

The neutralized mixture is then sent through line 20 wherein the pH is adjusted.

The platformate is pumped by pump 22 into line 24 in order to send it through line 20.

The resulting mixture which comprises the neutralized mixture and the platformate is sent into the pump 26 through line 28 in order to emulsify the mixture. The obtained emulsion is there-after sent directly to a decanter 30 through line 32.

The emulsion rapidly breaks up in the decanter, and the platformate is recovered at the top of the decanter and is thereafter sent in a storage drum 34 through line 36, while the purified aqueous solution is withdrawn from the bottom of the decanter through line 38.

The following examples are given in order to better illustrate the process of the invention, but without limiting its scope.

Example 1 A purge stream coming from the decanter of the unit for the removal of nitrogen impurities was treated. The purge stream which consisted of an aqueous acid solution, had a pH of 1.6 and a C.O.D. of 18,300 mgO2/l. The flow rate of the purge stream was about 0.75 m3/hr.

The purge stream was neutralized with a 17% aqueous solution of NaOH used at a flow rate of 0.05 m3/ hr.

The resulting neutralized mixture was blended with a heavy platformate having a specific density of 0.847 and which was fed at a flow rate of 1.5 m3/hr.

This mixture had a pH of 9 and was introduced at the aspiration side of a centrifugal pump in order to form an emulsion which was thereafter introduced into a decanter where breaking up of the emulsion was achieved.

The heavy plafformate was recovered and sent to a storage drum, and then the aqueous solution coming from the decanter was analyzed.

This aqueous solution contained no more nitrogen compounds and had a C.O.D. of 980 mg 02/1.

Example 2 A purge stream coming from the decanter of the unit for the removal of nitrogen impurities was treated. The purge stream, which consisted of an aqueous acid solution, had a pH of 1.7 and a C.O.D. of 19,500 mg Odl. The flow rate of the purge stream was about 0.75 m3/hr. The purge stream was neutralized with a 17% aqueous solution of NaOH used at a flow rate of 0.05 m3/hr.

The resulting neutralized mixture was blended with a heavy platformate having a specific gravity of 0.847 and which was fed at a flow rate of 1.5 m3/hr.

This mixture had a pH of 10.4 and was introduced at the aspiration side of a centrifugal pump in order to form an emulsion which was thereafter introduced into a decanter where breaking up of the emulsion was achieved.

The heavy platformate was recovered and sent to a storage drum, and then the aqueous solution coming from the decanter was analyzed.

This aqueous solution contained 18 mgll basic nitrogen compounds and had a C.O.D of 1010 mgO2/l.

By way of comparison, the same purge stream as that described above was treated, after neutralization, with various hydro-carbons instead of the heavy platformate.

The stream of aqueous solution coming from the decanter was analyzed for each of the hydrocarbons used. The results are indicated in the following Table.

TABLE Heavy Heavy Light Cycle Platformate Cycle oil oil Kerosene Specific gravity 0.847 0.940 0.880 0.800 C.O.D. of aqueous Solution (mgO2/l) 1010 1840 1450 1730 Extraction rate of N-compounds 90% 82.5% 84% 80% Colour of aqueous reddish Solution clear very hazy hazy clear These comparative examples clearly show that only the heavy platformate gives greatly improved results as compared with those obtained with other solvents, with respect to C.0.D., extraction rate and colouration of the aqueous solution.

Example 3 A purge stream coming from the decanter of the unit for the removal of nitrogen impurities was treated. The purge stream, which consisted of an aqueous acid solution, had a pH of 1.7 and a C.O.D. of 19,500 mg 02/in The flow rate of the purge stream was about 0.75 m3/hr.

The resulting neutralized mixture was blended with a light platformate having a specific gravity of 0.660 and which was fed at a flow rate of 1.5 m3/hr.

This mixture had a pH of 10.2 and was introduced at the aspiration side of a centrifugal pump in order to form an emulsion which was thereafter introduced into a decanter where breaking up of the emulsion was achieved.

The light platformate was recovered in order to be sent to a storage drum, and the aqueous solution coming from the decanter was analyzed.

The aqueous solution contained 15 mg/l basic nitrogen compounds and had a COD. of 1130 mg 021.

Claims

1. Process for the purification of a stream of an aqueous acid solution coming from a unit for the removal of nitrogen impurities, the process comprising the steps of: (a) neutralizing the stream of an aqueous acid solution with an inorganic or an organic base, (b) contacing said stream with a platformate or another hydrocarbon stream or organic solvent in a mixer, (c) sending the resulting stream to a decanter wherein a purified stream of aqueous neutralized solution is recovered from an organic phase.

2. Process according to Claim 1, wherein the base is in aqueous solution and is added in an amount such that the pH of the neutralized stream is from 7 to 14.

3. Process according to Claim 2, wherein the pH of the neutralized stream is from 8.5 to 11.

4. Process according to any one of Claims 1, 2 or 3, wherein an aqueous solution of NaOH or KOH is used to neutralize the aqueous acid solution.

5. Process according to any foregoing claim, wherein the neutralized stream is contacted in the mixer with a light or heavy platformate or with other hydrocarbon streams or with organic solvents, in order to form an emulsion which is thereafter sent to the decanter in which the emulsion is broken up into an aqueous purified stream and the organic phase.

6. Process according to Claim 5, wherein the mixer is a centrifugal pump.

7. Process according to Claim 5, wherein the mixer is a static mixer.

8. Process according to any one of Claims 5 to 7, wherein the platformate and the neutralized mixture are mixed together in a volume ratio of from 0.5:1 and 3 : 1.

9. Process for the purification of a stream of an aqueous acid solution substantially as hereinbefore described with reference to the accompanying drawing.

10. Process for the purification of a stream of an aqueous acid solution substantially as described in Example 1, Example 2 or Example 3.