IE69255B1

IE69255B1 - A process for manufacturing aluminium sulphate

Info

Publication number: IE69255B1
Application number: IE922699A
Authority: IE
Inventors: Edward Anthony Storey
Original assignee: Chemifloc Tech Ltd
Priority date: 1992-10-02
Filing date: 1992-10-02
Publication date: 1996-08-21
Also published as: GB2271105A; IE922699A1; GB9317510D0; BE1004926A6

Abstract

A low energy process for manufacturing aluminium sulphate comprises preparing an aluminium tri-hydrate slurry of aluminium tri-hydrate and water which is brought to a temperature of >/= 18 DEG C and delivered into a reactor vessel simultaneously with sulphuric acid at a rate so as to maintain the temperature of the exothermic reaction in the reactor vessel in the range of 113 DEG C to 130 DEG C.

Description

A process for manufacturing aluminium sulphate f The present invention relates to a process for manufacturing aluminium sulphate, and the invention also relates to aluminium sulphate manufactured by the process.

Known processes for the manufacture of aluminium sulphate where the aluminium sulphate is being prepared by dissolving aluminium tri-hydrate in sulphuric acid require the addition of heat to the mixture of aluminium tri-hydrate and sulphuric acid.

In particular, heat is required to start the reaction.

Although the reaction itself is exothermic, in order to maintain control over the temperature of the reaction mixture, a combination of cooling and heating is required to sustain the process. Such processes are relatively costly, since both heating and cooling tend to be relatively costly, and in particular, heating tends to be relatively costly.

There is therefore a need for a process for manufacturing aluminium sulphate which reduces the manufacturing costs. There is also a need foxaluminium sulphate produced according to such a process.

The present invention is directed towards such a process and aluminium sulphate.

According to the invention there is provided a process for manufacturing aluminium sulphate comprising the steps of preparing an aluminium tri-hydrate slurry by mixing aluminium tri-hydrate and water to form a slurry, the aluminium tri-hydrate and water being mixed in a ratio in the range of 0.5 parts aluminium tri-hvdrate to one part water to one part aluminium tri-hydrate to one part water by weight, and reacting the slurry with sulphuric acid by delivering the slurry and sulphuric acid simultaneously into a reactor vessel at a combined delivery rate of slurry and sulphuric acid of at least 250 kgs per minute for maintaining the temperature of the mixture of slurry and sulphuric acid in the vessel caused by the exothermic reaction between the slurry and sulphuric acid in the range of 113 °C to 130°C, the temperature of the slurry being not less than 18°C, and the slurry and sulphuric acid being delivered into the reactor vessel in a ratio in the range of 0.95 parts slurry to one part sulphuric acid to 1.5 parts slurry to one part sulphuric acid by weight.

Advantageously, the combined delivery rate of the slurry and sulphuric acid into the reactor vessel is approximately 500 kgs per minute.

By maintaining the temperature of the slurry at or above 18°C as it is being delivered into the reactor vessel, it has been found that the reaction between the slurry and the sulphuric acid commences instantaneously without the need for external heat to be applied to the mixture in the reactor vessel. Furthermore, by maintaining the ratio of aluminium tri-hydrate to water in the slurry in the range of 0.5:1 to 1:1, and furthermore, by maintaining the ratio of the slurry to sulphuric acid in the range of 0.95:1 to 1.5:1, it has been found that the slurry and sulphuric acid continue to react in the reactor vessel without the need to provide external heat to the reaction mixture in the reactor vessel.

Delivering the slurry and sulphuric acid into the reactor vessel at a combined rate of at least 250 kgs per minute has been found to be sufficient to maintain the reaction in the reactor vessel without the need for the addition of external heat. When the combined rate of delivery of the slurry and sulphuric acid is approximately 500 kgs per minute, it has been found that the temperature of the reaction mixture in the reactor vessel can be maintained at the preferred temperature of approximately 122°C.

In one embodiment of the invention the temperature of the slurry being delivered into the reactor vessel is in the range of 20°C to 27°C. Preferably, the temperature of the slurry is in the range of 20°C to 24°C. Advantageously, the temperature of the slurry is approximately 20°C.

It has been found that preferred results are achieved when the temperature of the slurry being delivered into the reactor vessel is maintained in the range of °C to 27°C» and optimum results are achieved when the temperature of slurry being delivered into the reactor vessel is approximately 20°C.

In another embodiment of the invention the ratio of aluminium tri-hydrate to water is in the range of 0.55 parts aluminium tri-hydrate to one part water to 0.91 parts aluminium tri-hydrate to one part water by weight. It has been found that by maintaining the ratio of aluminium tri-hydrate to water within this range optimum results are achieved.

In a further embodiment of the invention the ratio of the slurry to sulphuric acid is in the range of 0.99 parts slurry to one part sulphuric acid to 1.2 parts slurry to one part sulphuric acid by weight. It has been found that by maintaining the ratio of slurry to sulphuric acid within this range optimum results are achieved.

In a further embodiment of the invention the temperature of the miircure of slurry and sulphuric acid in the reactor vessel is maintained in the range of 118°C to 127°C. Preferably, the temperature of the mixture of slurry and sulphuric acid in the reactor vessel is maintained in the range of 120°C to 125°C. Advantageously, the temperature of the mixture of slurry and sulphuric acid in the reactor vessel is maintained at approximately 122°C.

In one embodiment of the invention vapour from the reaction of the slurry and sulphuric acid is condensed and the condensate stored, and preferably, the condensate is stored in a heat insulated vessel for minimising heat loss from the condensate. Preferably, the aluminium tri-hydrate slurry is prepared by adding the condensate for raising the temperature of the slurry prior to delivery into the reactor vessel. Advantageously, the condensate added to the slurry is condensate collected from a previous reaction. By using the stored condensate to bring the temperature of the slurry to at least 18°C, the need for applying any external heat to the process is eliminated.

Additionally, the invention provides aluminium sulphate produced according to the process of the invention.

The invention will be more clearly understood from the following description of some preferred non-limiting examples which are described with reference to the accompanying drawing which schematically illustrates apparatus for carrying out the process of the invention.

Referring to the drawing there is illustrated apparatus indicated generally by the reference numeral 1 for carrying out the process according to the invention for manufacturing aluminium sulphate also according to the invention. The apparatus 1 comprises a mixing vessel 3 within which aluminium tri-hydrate and water are mixed to form a slurry as will be described below. A storage vessel 4 stores sulphuric acid. Aluminium tri-hydrate slurry and sulphuric acid are delivered simultaneously from the vessels 3 and 4, respectively, through pipelines 8 and 9, respectively, into a reactor vessel 5 where the slurry is reacted with the sulphuric acid to produce aluminium sulphate. The slurry and sulphuric acid are delivered into the reactor vessel 5 at a rate which controls the rate of the exothermic reaction between the slurry and the sulphuric acid so that the temperature of the mixture of slurry and sulphuric acid in the reactor vessel 5 is maintained in the range of 120°C to 125°C. This is described in detail below with reference to the examples. Vapour, in this case, steam from the reactor vessel 5 is delivered through a steam line 10 to a condenser 11 where the steam is condensed. The condensate from the condenser 11 is delivered through a pipeline 14 and collected in a heat insulated vessel 12 to minimise heat loss from the condensate. The condensate is used for subsequent mixing with aluminium tri-hydrate to form a slurry for a subsequent batch, and for raising the temperature of the slurry in the mixing vessel 3 prior to delivery to the reactor vessel 5 to a temperature of approximately 20°C so that the temperature of the slurry as it is being delivered into the reactor vessel 5 is approximately 20°C. A pipe line 15 from the vessel 12 delivers the condensate into the mixing vessel 3. Aluminium sulphate is delivered from the reactor vessel 5 through an outlet 16 for collection in a suitable collection tank 17, or in trays (not shown).

Because the aluminium tri-hydrate slurry and sulphuric acid are delivered into the reactor vessel 5 at a rate to control the reaction so that temperatures maintained in the range of 120°C to 125°C there is no need for the addition of heat to the reaction. The reaction is self-sustaining, both during the period while the slurry and sulphuric acid are being delivered into the reactor vessel 5, and thereafter while the reaction mixture is baking in the reactor vessel 5.

Four types of aluminium sulphate manufactured using 10 the process according to the invention in the apparatus 1 will now be described in the following examples.

Example 1 In this example a liquid solution of aluminium 15 sulphate with an aluminium oxide content of approximately 8% by weight is prepared. The aluminium sulphate is prepared from the following ingredients in the following quantities: Slurry aluminium tri-hydrate (powder form) 2,500 kgs water 2,500 kgs sulphuric acid 5,014 kgs diluting water 11,450 kgs The aluminium tri-hydrate and water to the amount of 2,500 kgs are mixed in the mixing vessel 3 to form an aluminium tri-hydrate slurry. The water is derived from a mains or any other suitable water supply source and also from the condensate in the vessel 12. The mains water is made up with sufficient water from the vessel 12 stored from a orevious reaction so that the temperature of the slurry is approximately 20°C. The sulphuric acid is stored in the storage vessel 4 ready for use. The aluminium tri-hydrate slurry and the sulphuric acid are delivered simultaneously through the respective pipelines 8 and 9 into the reactor vessel 5. In this embodiment of the invention the slurry and sulphuric acid are delivered at a constant rate into the reactor vessel 5 at a combined rate of delivery of the aluminium tri-hydrate slurry and the sulphuric acid of approximately 500 kgs per minute. This rate of delivery into the vessel has been found to be the optimum for maintaining the temperature of the reaction of the slurry and the sulphuric acid in the reactor vessel 5 at approximately 122°C while the slurry and sulphuric acid are being delivered into the reactor vessel 5. During the reaction in the reactor vessel 5 the condenser 11 condenses approximately 25 kgs of steam per minute from the reactor vessel 5, which is delivered to and stored in the vessel 12 for use in a subseouent batch. After the slurry and sulphuric acid have been delivered into the reactor vessel 5 the reaction is allowed to continue in the vessel 5 for approximately 55 minutes to bake the reaction mixture to form the aluminium sulphate. At the end of the bake period the aluminium sulphate is diluted in the reactor vessel 5 by adding the diluting water to the amount of 11,450 kgs to the aluminium sulphate solution in the reactor vessel 5. The diluted aluminium sulphate is drained from the reactor vessel 5 and collected and stored in the tank 17 in liquid form. This liquid aluminium sulphate has an aluminium oxide content of approximately 8% by weight.

Example 2 In this example slabs of aluminium sulphate with an aluminium oxide content of approximately 14% by weight are prepared. The aluminium sulphate is prepared from the following ingredients in the following quantities.

Slurry aluminium tri-hydrate 3,000 kgs water 5,800 kgs sulphuric acid 5,017 kgs The water and aluminium tri-hydrate are mixed in the mixing vessel 3 to form an aluminium tri-hydrate slurry. The water is derived from a mains or any other suitable water supply source and also from the condensate in the vessel 12. The mains water is made up with sufficient water from the vessel 12 stored from a previous reaction so that the temperature of the slurry is approximately 20°C. The aluminium trihydrate slurry and the sulphuric acid are delivered simultaneously through the respective pipelines 8 and S into the reactor vessel 5. In this embodiment of the invention the slurry and sulphuric acid are delivered at a constant rate into the reactor vessel 5 at a combined rate of delivery of the aluminium tri» hydrate slurry and the sulphuric acid of approximately 500 kgs per minute. During the reaction in the reactor vessel 5, the condenser 11 condenses approximately 37 kgs of steam per minute from the reactor vessel 5, which is stored in the vessel 12. After the slurry and sulphuric acid have been delivered into the reactor vessel 5 the reaction is allowed to continue in the vessel 5 for approximately 55 minutes to bake the reaction mixture to form the aluminium sulphate. At the end of the bake period, the aluminium sulphate is delivered from the reactor vessel 5 into trays (not shown) for the formation of slabs. The slabs of aluminium sulphate have an aluminium oxide content of approximately 14% by weight.

Example 3 In this example slabs of aluminium sulphate with an aluminium oxide content of approximately 16% by weight are prepared. The aluminium sulphate is prepared from the following ingredients in the following quantities.

Slurry aluminium tri-hydrate 3,000 kgs water 4,100 kgs sulphuric acid 6,017 kgs The water and aluminium tri-hydrate are mixed in the mixing vessel 3 to form an aluminium tri-hydrate slurry. The water is derived from a mains or any other suitable water supply source and also from the condensate in the vessel 12» The mains water is made up with sufficient water from the vessel 12 stored from a previous reaction so that the temperature of the slurry is approximately 20°C. The aluminium trihydrate slurry and the sulphuric acid are delivered simultaneously through the respective pipelines 8 and 9 into the reactor vessel 5. In this embodiment of the invention the slurry and sulphuric acid are delivered at a constant rate into the reactor vessel 5 at a combined rate of delivery? of the aluminium tri13 hydrate slurry and the sulphuric acid of approximately 500 kgs per minute. During the reaction in the reactor vessel 5, the condenser 11 condenses approximately 25 kgs per minute of steam from the reactor vessel 5 which is stored in the vessel 12. After the slurry and sulphuric acid have been delivered into the reactor vessel 5 the reaction is allowed to continue in the vessel 5 for approximately 55 minutes to bake the reaction mixture to form the aluminium sulphate. At the end of the bake period, the aluminium sulphate is delivered from the reactor vessel 5 into trays (not shown) for the formation of slabs. The slabs of aluminium sulphate in this example have an aluminium oxide content of approximately 16% by weight.

Example 4 In this example slabs of aluminium sulphate with an aluminium oxide content of approximately 17% by weight are prepared. The aluminium sulphate is prepared from the following ingredients in the following quantities.

Slurry aluminium tri-hydrate 3,000 kgs water 4,000 kgs sulphuric acid 6,017 kgs The water and aluminium tri-hydrate are mixed in the mixing vessel 3 to form an aluminium tri-hydrate slurry. The water is derived from a mains or any other suitable water supply source and also from the condensate in the vessel 12. The mains water is made up with sufficient water from the vessel 12 stored from a previous reaction so that the temperature of the slurry is approximately 20°C. The aluminium trihydrate slurry and the sulphuric acid are delivered simultaneously through the respective pipelines 8 and 9 into the reactor vessel 5. In this embodiment of the invention the slurry and sulphuric acid are delivered at a constant rate into the reactor vessel 5 at a combined rate of delivery of the aluminium trihydrate slurry and. the sulphuric acid of approximately 500 kgs per minute. During the reaction in the reactor vessel 5, the condenser 11 condenses approximately 25 kgs per minute of steam from the reactor vessel 5 which is stored in the vessel 12. After the slurry and sulphuric acid have been delivered into the reactor vessel 5 the reaction is allowed to continue in the vessel 5 for approximately 55 minutes to bake the reaction mixture to form the aluminium sulphate. At the end of the bake period, the aluminium sulphate is delivered from the reactor vessel 5 into trays (not shown) for the formation of slabs. The slabs of aluminium sulphate in this example have an aluminium oxide content of approximately 17% by weight.

The advantages of the invention are many. However, a particularly important advantage of the invention is the fact that the process does not require the addition of any external heat for reacting the slurry with the sulphuric acid. Accordingly, the process according to the invention is a relatively low energy process, and accordingly, is a relatively low cost process. Furthermore, because the temperature of the reaction in the reactor vessel is controlled by controlling the delivery rate of the aluminium trihydrate slurry and sulphuric acid into the reactor vessel the life of the reactor vessel is considerably extended. Furthermore, by virtue of the fact that the aluminium tri-hydrate slurry is delivered into the reactor vessel at a temperature of 20° the reaction between the slurry and the sulphuric acid is instantaneous and does not require the addition of external heat to start the reaction.

While a particular construction of apparatus has been described, it will be appreciated that other suitable constructions of apparatus may be provided for carrying out the process according to the invention.

Claims

1. CLAIMS;

1. A process for manufacturing aluminium sulphate comprising the steps of preparing an aluminium trihydrate slurry by mixing aluminium tri-hydrate and water to form a slurry, the aluminium tri-hydrate and water being mixed in a ratio in the range of 0.5 parts aluminium tri-hydrate to one part water to one part aluminium tri-hydrate to one part water by weight, and reacting the slurry with sulphuric acid by delivering the slurry and sulphuric acid simultaneously into a reactor vessel at a combined delivery rate of slurry and sulphuric acid of at least 250 kgs per minute for maintaining the temperature of the mixture of slurry and sulphuric acid in the vessel caused by the exothermic reaction between the slurry and sulphuric acid in the range of 113°C to 130°C, the temperature of the slurry being not less than 18°C, and the slurry and sulphuric acid being delivered into the reaction vessel in a ratio in the range of 0.95 parts slurry to one part sulphuric acid to 1.5 parts slurry to one part sulphuric acid by weight.

2. A process as claimed in Claim 1 in which the combined delivery rate of the slurry and sulphuric acid into the reactor vessel is approximately 500 kgs per minute.

3. A process as claimed in Claim 1 or 2 in which the temperature of the slurry is in the range of 20°C to 27°C.

4. A process as claimed in Claim 3 in which the temperature of the slurry is in the range of 20°C to 24 °C.

5. A process as claimed in Claim 4 in which the temperature of the is approximately 20°C.

6. A process as claimed in any preceding claim in which the ratio of aluminium tri-hydrate to water is in the range of 0.55 parts aluminium tri-hydrate to one part water to 0.91 parts aluminium tri-hydrate to one part water by weight.

7. A process as claimed in any preceding claim in which the ratio of the slurry to sulphuric acid is in the range of 0.99 parts slurry to one part sulphuric acid to 1.2 parts slurry to one part sulphuric acid by weight.

8. A process as claimed in any preceding claim in which the temperature of the mixture of slurry and sulphuric acid in the reaction vessel is maintained in the range of 118°C to 127°C.

9. A process as claimed in Claim 8 in which the temperature of the mixture of slurry and sulphuric acid in the reaction vessel is maintained in the range of 120°C to 125°C. 5

10. A process as claimed in Claim 9 in which the temperature of the mixture of slurry and sulphuric acid in the reaction vessel is maintained at approximately 122°C.

11. A process as claimed in any preceding claim in 10 which vapour from the reaction of the slurry and sulphuric acid is condensed and the condensate stored.

12. A process as claimed in Claim 11 in which the aluminium tri-hydrate slurry is prepared by adding the condensate for raising the temperature of the slurry 15 prior to delivery into the reaction vessel.

13. A process as claimed in Claim 12 in which the condensate added to the slurry is condensate collected from a previous reaction.

14. A process for manufacturing aluminium sulphate 20 substantially as described herein with reference to and is illustrated in the accompanying examples. 15. Aluminium sulphate produced according to the process of any preceding claim.

15. Aluminium sulphate substantially as described herein with reference to and is illustrated in the 5 accompanying examples .