GB1563957A - Method for separating water from oil - Google Patents

Description

(54) METHOD FOR SEPARATING WATER FROM OIL (71) We, THE BRITISH PETROLEUM COMPANY LIMITED, of Britannic House, Moor Lane, London, EC2Y 9BU, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a material suitable for removing water from oil contaminated with water and in particular to a material suitable for removing traces of water from petroleum products.

In the refining of petroleum products, particularly middle distillates, the products are frequently submitted to a stream stripping operation to remove light ends and other contaminants. Occasionally traces of moisture are left behind in the product in the form of a dilute water-in-oil emulsion which gives the product an undesirable hazy appearance. Such emulsions can be difficult to break.

Similar emulsions can also be formed as a result of storage. In storage tanks oil absorbs water which eventually separates as a layer on the bottom. When product is pumped out the resulting dislurbance disperses the water throughout the oil producing an unsightly hazy dispersion.

These emulsions can give rise to corrosion problems caused by the precipitation of water from wet products. There is a particular need for water removal from aviation kerosine since its presence would cause operational difficulties.

Sand filters are used to remove traces of water from oil by coalescence (and vice versa) but to date they have not been found capable of consistently removing haze. Salt filters can also be used but these can lead to excessive corrosion downstream.

We have now discovered that treating sand and similar coalescing media with certain polymers improves their coalescing power and enables them to remove haze from middle distillates.

Thus according to the present invention there is provided a method for separating water from oil contaminated with water which method comprises passing a contaminated oil stream through a purification bed containing solid particles treated by contacting the solids with an aqueous solution of a water soluble polymer containing cations which are adsorbed on to the surface of the particulate material, in such manner that the water coalesces, an oil phase and a water phase are formed and a substantially water-free oil is recovered.

Suitable polymers include medium to high molecular weight polyamides and polyacrylamides.

The terms "medium" and "high" molecular weights relate to values in the order of 0.5-1.0 X 106 and 10--12 X 106 respectively.

The preferred polymer is a high molecular weight polyacrylamide.

Suitable particulate solids include such materials as anthracite, charcoal, polystyrene, polyethylene, polypropylene, vermiculite and glass beads. The preferred solid is itself basically hydrophilic rather than hydrophobic and should contain suitable adsorption sites on its surface. Example of such materials are river gravel and sand.

The solids may be contacted with the polymer solution by soaking in it or by passing the solution through the bed of par tickles prior to use.

At low flow rates there is little advantage to be gained in using the improved material of the present invention. The difference between treated and untreated material becomes more marked with higher flow rates, e.g., hydraulic loading of at least 2 /m2 thr.

Preferred hydraulic loadings are in the range W10 m3/m2/hr.

Petroleum distillates having a hazy appearance due to water are suitable feedstocks, particularly gas oils.

After lengthy use the efficiency of the purification bed may deteriorate. It may be regenerated by treating it again with the water soluble polymer in a similar fashion.

The invention is illustrated by the following examples.

Example 1 200 gm of river sands were added to 750 ml of a 50 ppm solution of Magnafloc 140 in distilled water, contained in a flask and rotated for 16 hours in an end-over-end shaker.

The sand was filtered from the liquid and dried in an oven at 500 C.

Simulated hazy gas oil containing about 500550 ppm water was produced by mixing in a Vortex mixer for 20 seconds in quantities of 500 ml. The resultant hazy gas oil will remain stable for long periods of time.

Hazy gas oil was pumped at 500 ml/hr in downward flow through a column 13 cm long X 1.2 cm diameter containing 20 gm of treated sand which had been saturated in situ with distilled water.

The void volume of bed was 5 ml.

Filtered gas oil remained clear for 7 hours, i.e., 700 bed volumes.

In a parallel experiment, using untreated sand, the gas oil emerged hazy immediately.

Magnafloc 140 is a polyacrylamide supplied by Allied Colloids Limited.

Example 2 A solution of Zetag 76 was prepared in the laboratory by dissolving 0.5 of Zetag 76 in 3 ml of methanol, followed by 97 ml of water, (Solution A).

Two 20 gm beds of river sand were prepared using a mixture of 10 gm > 30 mesh sand in the bottom oif a tube similar to that used in Example 1 with 10 gm of 30--44 mesh sand packed into the top of the tube.

The first bed (Column A) was left standing overnight in 100 ml of distilled water.

The second bed (Column B) was left overnight in 10 ml of Solution A which had been shaken with 90 ml of distilled water.

Simulated hazy gas oil containing 600 ppm water was produced by mixing in an Atomix mixer was 60 seconds on maximum speed. The resultant hazy gas oil will remain stable for long periods of time.

Hazy gas oil was pumped through the beds at 500 ml/hr in a downward flow. Initially the gas oil from Column A was hazy while the gas oil from Column B was almost clear. After 7 hours the untreated bed pro duced slightly hazy gas oil while the treated bed gave a clear gas oil.

Zetag 76 is a water soluble cationic polyelectrolyte supplied by Allied Colloids Limited.

WHAT WE CLAIM IS: 1. A method for separating water from oil contaminated with water which method comprises passing a contaminated oil stream through a purification bed containing solid particles treated by contacting the solids with an aqueous solution of a water-soluble polymer containing cations which are - adsorbed on to the surface of the particulate solids, in such manner that the water coal esces, an oil phase and a water phase are formed, and a substantially water-free oil is recovered.

2. A method according to Claim 1 wherein the polymer is a high molecular weight polyacrylamide.

3. A method according to either of the preceding claims wherein the solids are hydrophilic.

4. A method according to Claim 3 wherein the solids are gravel or sand.

5. A method according to any of the preceding claims wherein the hydraulic loading of the stream with respect to the purification of the bed is at least 2 m2/m3/hr.

6. A method according to Claim 5 wherein the hydraulic loading is in the range 410 m3m2/hr.

7. A method according to any of the preceding claims wherein the feedstock is a gas oil having a hazy appearance due to water and a clear gas oil is recovered.

8. A method for the clarification of hazy gas oil as hereinbefore described with reference to the Examples.

9. Products whenever prepared by a process according to any of the preceding

Claims (1)

1. claims.