WO1995011061A1

WO1995011061A1 - P4s10 waste disposal method

Info

Publication number: WO1995011061A1
Application number: PCT/FR1994/001236
Authority: WO
Inventors: Paul Bourdauducq; Laurent Penel
Original assignee: Elf Atochem S.A.
Priority date: 1993-10-22
Filing date: 1994-10-24
Publication date: 1995-04-27
Also published as: EP0684859A1; DE69412070D1; FR2711558A1; FR2711558B1; DE69412070T2; EP0684859B1

Abstract

A method for disposing of waste generated during the manufacture, packaging and use of P4S10 by preparing an alkaline solution of said waste and biologically oxidising said solution.

Description

P4S10 WASTE DISPOSAL PROCESS

The present invention relates to a process for eliminating waste formed during the manufacture, packaging and use of phosphorus polysulphides and in particular of P4S- _| r _j -

P4S10 is prepared from liquid sulfur and liquid phosphorus in substantially stoichiometric quantities at temperatures between 300 ° C and 515 ^β C.

The products obtained generally pass through a packed column making it possible to retain the impurities liable to come from the reagents as well as the by-products liable to form during the reaction.

Then the products are condensed in a tubular exchanger and exit in liquid form which can undergo rapid cooling to lead to a solid which can be crushed and finally conditioned in metal containers or drums.

The waste formed during the preparation and packaging of P4S10 comes essentially from the cleaning of devices such as scaly, conveyor screw, condensers, etc. and are found to be in the form of powders or flakes which represent at least 10% of all of the waste; periodic emptying of the reactor and happen to be in the form of large blocks which represent approximately 25% of the total waste; washing of the return containers and are in the initial form of flakes or powders which represent the largest amount of waste estimated at around 55% and of the vents and effluents which happen to be initially in the form of gases containing P4S10 dust . traces of H2S. The latter source represents some 10% of all waste.

Initially, the majority of the waste happens to be in solid form. This is particularly the case for waste from emptying the reactor, cleaning of equipment and containers. This waste cannot be recycled in the manufacturing cycle for reasons of quality in particular.

They consist mainly of P4S10 associated with small quantities of phosphorus polysulfides such as P4S9, P4S7. Organic impurities and metallic impurities such as iron, arsenic, nickel, chromium, antimony are also detected there. This waste is more or less sensitive to hydrolysis and cannot be stored in landfills or buried because the slow hydrolysis of this waste is likely to produce significant quantities of gas (H2S) and toxic materials likely to irreparably contaminate groundwater. Also, for better protection of the environment, rigorous standards concerning the disposal of phosphorous and sulfurous waste have been established in order to avoid, or even prohibit any excessive storage of untreated waste in landfills or their disposal, in lakes, rivers or seas. Patent DD 122 058. teaches that the waste originating from the synthesis of P4S10 can be treated ^by washing with soda and then injecting chlorine.

This treatment makes it possible to transform the waste essentially consisting of P4S10 into a mixture of products consisting of phosphates, phosphites, thiophosphates, sulfates and chlorides. However, this method has a number of drawbacks.

In particular, it requires the use of large quantities of reagents. Indeed, for a ton of P4S-10 to be treated, it is necessary to use no less than 35 m ³ of 20% sodium hydroxide solution (approximately 42 tonnes) and 6.3 tonnes of chlorine.

In patent DD 156 902, the procedure is similar except that less reagents are used, in particular less sodium hydroxide.

The waste is treated with sodium hydroxide solution and then undergoes a treatment with chlorine so as to obtain a pH close to 7-8. Chlorination is continued while adding sodium hydroxide in order to maintain said pH at 7-8.

Thus, for a ton of P4S10 to be treated, 1.3 to 1.6 tonnes of chlorine and 10 m ³ of 20% sodium hydroxide are used.

However, this method has the disadvantage of generating significant amounts of elemental sulfur and also has the disadvantage of using chlorine.

US Pat. No. 4,301,014 relates to the treatment of water resulting from the elimination of waste from the manufacture of P S- | o- This waste is hydrolyzed with water, then brought into contact with lime in order to precipitate the sulphides, sulphites, sulphates and phosphates in the form of calcium salts, then treating the solution freed from these salts with an oxidant such as chlorine or calcium hypochlorite at a pH close to 9 in order to reduce the "chemical demand for oxygen "(COD) before rejection.

This process has many drawbacks. First, hydrolysis requires significant quantities of water, approximately 235 m ³ per tonne of P4S-10 to be treated, which requires very large reactors, which is prohibitive for an economical industrial process. Furthermore, this hydrolysis generates significant quantities of H2S requiring specific equipment for its destruction.

Then, this process requires numerous filtration operations: filtration after hydrolysis, filtration after precipitation with lime, filtration after chlorination, which are likely to increase the cost and the complexity of operating the process. A simple and economical process has now been found for eliminating the waste formed during the manufacture, packaging and use of phosphorus polysulphides, said process being characterized in that it consists in:

- dissolving said waste by alkaline attack, - collecting the various solutions obtained in a buffer tank, and

- Biologically oxidize the solutions thus obtained containing thiophosphates of formula Mββ PS _X 04_ _x in which Me represents NH4, an alkali metal such as Na, K and x is an integer ranging from 1 to 4, phosphates, sulfides and phosphites before discharge in the form of a solution consisting essentially of sulfates and phosphates.

This process is particularly applicable to waste from the manufacture, packaging and use of P4S <| 0-

According to the present invention, the waste can be put into alkaline solution in different ways depending on the one hand, their source and, on the other hand their physical state.

The vents and / or gaseous effluents originating in particular from the reactor and from the conditioning consisting essentially of suspended powders and traces of H2S are generally knocked down by an alkaline solution which consists of washing against the current with an alkaline solution (A). The waste from washing the containers with pressurized water is introduced into an alkaline solution (B).

"Solid" waste in different forms (more or less coarse blocks, powders, scales) from both washing of devices such as scaly, conveyor screw, reactor, condensers and out of specification products are collected and then introduced into a solution alkaline (C).

The various alkaline solutions (A), (B) and (C) are generally sodium hydroxide solutions, potassium hydroxide solutions or ammoniacal solutions. These solutions can have identical or different concentrations of alkaline agent. Preferably, sodium hydroxide solutions having a NaOH concentration by weight of between 5% and 30% and preferably between 10% and

20%.

P4S10

The molar ratio Rm = is at least equal to 13

NaOH and preferably between 15 and 32.

Whether the waste is treated separately or simultaneously, it is preferably carried out by introducing the waste into the alkaline solution with stirring at a temperature between 20 ° C and 80 ° C and, preferably, between 25 ° C and 60 ° C.

The duration of the dissolution can vary to a large extent. It is generally a function of the physical state of the waste. It is at least equal to 30 minutes and, preferably, between 2 and 6 hours.

The different solutions (A), (B) and (C) are collected, in particular in a so-called "buffer" tank. The solution obtained is generally clear.

In the case where the solution was carried out with sodium hydroxide solutions, the solution of the buffer tank consists of sodium thiophosphates of formula Naβ PS _X 04_ _x ; x being an integer ranging from 1 to 4, Na2S, sodium phosphates and sodium phosphite. The final solution obtained must be at a pH greater than 7 in order to avoid any release of H2S.

This is advantageously achieved by using a slight excess of soda which is at most 5% at the time of the alkaline solution.

This alkaline solution operation is generally carried out in reactors provided with a stirring system, a temperature measurement, heating and cooling systems.

In the event of a slight insoluble matter, separation can be carried out by known methods such as filtration or centrifugation.

The alkaline solution thus obtained is then biologically oxidized. To this end, the solution is introduced into a so-called "activated sludge" reactor of a biological station treating wastewater coming in particular from an industrial site.

These activated sludges are made up of microorganisms and bacteria which, in aerobic environment, destroy carbonaceous pollution of industrial effluent (reduction of COD) and also oxidize sulfides and thiophosphates.

The "activated sludge" reactor is supplied with air or pure oxygen, thus allowing the aeration of the medium.

The pH of the medium must be as stable as possible and as close as possible to neutrality, see slightly basic. Therefore, although the effluent to be treated generally constitutes only a small part of the diet of the biological station, it is necessary to avoid a free soda content of this effluent that is too high.

After passing through the reactor, the effluent is separated from the sludge which consists of microorganisms and bacteria, in a clarifier before discharge. The decanted sludge is largely recycled in the reactor, part of the decanted sludge is sent to a thickener where the maximum amount of water is extracted. The water is recycled to the reactor while the sludge is eliminated in a landfill. The advantage of the process according to the present invention is to eliminate the waste in the form of aqueous effluents essentially consisting of sulfates and phosphates in accordance with the standards in force concerning discharges.

The following example illustrates the invention. We carried out an industrial test which led to the treatment of an amount equal to 6.4 tonnes consisting of solid waste formed during the preparation of P4 S- | rj from the cleaning of devices such as reactor, scaler, conveyor screw and products out of specification.

To do this, 8 effluents of approximately 15 m ³ are prepared. Effluent preparation

650 kg to 850 kg of the abovementioned waste are gradually and manually introduced into a 15 m ³ stirred tank containing approximately 5.4 m ³ of sodium hydroxide at 20% by weight.

The introduction of the waste is regulated in such a way that the temperature does not exceed 50 ° C.

The duration of the operation is approximately 6 hours.

Once the introduction is complete, water is introduced to complete the level up to 15 m ³ .

It is ensured throughout the duration of the operation that the quantity of sodium hydroxide used is greater than the stoichiometric quantity of sodium hydroxide necessary for the hydrolysis so as to obtain an effluent containing free sodium hydroxide making it possible to avoid any release of H2S.

On each effluent we determine:

- the concentration of total phosphates - the concentration of free soda.

The table below collates the results obtained.

EFFLUENT CONCENTRATION IN CONCENTRATION IN TOTAL PHOSPHATE NUMBER FREE SODA

(g / i) (g / i)

1 42.9 50.8

2 36 13.4

3 32 22.7

4 52 16.9

5 50 16.9

6 37.5 25.8

7 48.8 25.6

47.5 11.6

⁸⁸

NMR analysis of P ³¹ indicates that the effluents consist essentially of: - Na3PS _x θ4_ _x with x ranging from 1 to 4,

- Sodium phosphates - Na ₂ S ^"Na 3P0 ₃

Biological oxidation of effluents (Plate 1/2)

Each aqueous effluent (1) previously prepared is sent to a biological treatment station. It is deposited in a tank (2) continuously supplied with effluents of the same nature (3) (sodium hydroxide solutions made up of Na2S). The content of this tank is then injected continuously (4) into the "active" sludge reactor (5) at the same time as all of the wastewater from an industrial site (6).

"Activated" sludge consists of microorganisms and bacteria evolving in an aerobic environment.

The aeration of the medium is ensured by an air supply (7) and also by a supply of pure oxygen (8). Oxidation takes place at atmospheric pressure, at room temperature and at a pH of around 8.

After passing through the reactor (5) the effluent (9) is separated from the sludge in a clarifier (10) before discharge (11). Decanted sludge is largely recycled to the reactor (5) via

(12). Part of these goes to a thickener (13) in which a maximum quantity of water is extracted which is recycled to the reactor (5) via (14), the thickened sludge is eliminated in a landfill (15).

Soluble phosphates are analyzed regularly during biological oxidation operations and 15 days after the treatment of the last effluent (No. 8) in the discharges (11) from the biological station.

The single graph below shows the results obtained. In this graph: P denotes the phosphate content expressed in mg / l,

J denotes the duration of the operations in days, the asterisks correspond to the injections of the effluents to be treated, the line carrying black squares designates the total phosphates, the line carrying white squares designates the soluble phosphates.

By carrying out a phosphorus assessment on the biological station, approximately 70% of the phosphorus is found in the aqueous discharge, the rest being entrained by the sludge sent to the landfill.

We also did not observe any impact on the functioning of the biological station.

KIT OF LOCATION J (RULE 6)

Claims

1. Method for eliminating waste formed during the manufacture, packaging and use of phosphorus polysulphides, characterized in that it consists of:

- dissolving said waste by alkaline attack,

- collect the different solutions obtained in a buffer tank, and

- Biologically oxidize the solutions thus obtained containing thiophosphates of formula Mβ3 PS _X 04_ _x in which

Me represents NH4 an alkali metal such that Na, K and x is an integer ranging from 1 to 4, phosphates, sulfides and phosphites before rejection in the form of a solution consisting essentially of sulfates and phosphates.

2. Method according to claim 1, characterized in that the phosphorus polysulfide is P4S-J O- t

3. Method according to claim 1 or 2, characterized in that the alkaline attack of the waste is carried out by a solution of sodium hydroxide, potassium hydroxide or an ammoniacal solution.

4. Method according to claim 3, characterized in that the alkaline solution is a sodium hydroxide solution.

5. Method according to claim 4, characterized in that the sodium hydroxide solution has a concentration by weight of sodium hydroxide (NaOH) of between 5% and 30% and, preferably, between 10% and 20%.

6. Method according to any one of claims 1 to 5, characterized in that the waste is introduced into the alkaline solution with stirring at a temperature between 20 ° C and 80 ° C and, preferably, between 25 ° C and 60 ° C.

7. Method according to any one of claims 1 to 6, characterized in that the alkaline solutions are collected in a buffer tank.

8. Method according to claim 7, characterized in that the collected alkaline solutions are sodium hydroxide solutions.

9. Method according to claim 8, characterized in that the sodium hydroxide solutions consist essentially of sodium thiophosphate of formula

SUBSTITUTE SHEET (RULE 2φ Na3PS _x θ4_ _x in which x is an integer ranging from 1 to 4, Na2S, sodium phosphates and sodium phosphites.

10. Method according to one of claims 8 or 9 characterized in that the sodium hydroxide solutions are introduced into an activated sludge reactor consisting of microorganisms and bacteria evolving in aerobic medium.

11. Method according to claim 10, characterized in that the activated sludge reactor is supplied with air.

12. Method according to any one of claims 1 to 11 characterized in that the waste is discharged in the form of a solution containing sulfates and phosphates.

SITE SHEET (RULE 26)