US3338816A

US3338816A - Separation of waxy hydrocarbons from oils by flotation

Info

Publication number: US3338816A
Application number: US433180A
Authority: US
Inventors: Tritsmans Paul Albert
Original assignee: BELGE PETROLES SA
Current assignee: BELGE PETROLES SA; Industrielle Belge Des Petroles Sa Ste
Priority date: 1964-08-21
Filing date: 1965-02-16
Publication date: 1967-08-29
Anticipated expiration: 1984-08-29
Also published as: CH478221A; FR1424938A; DE1545346A1; GB1022429A; DK111629C; NL6502143A; DK111629B; NO115406B; BE652105A; NL143981B

Description

United States Patent 3,338,816 SEPARATION OF -WAXY HYDROCARBONS FROM OILS BY FLOTATION Paul Albert Tritsmans, Antwerp, Belgium, assignor to Societe Industrielle Belge des Petroles S.A., Antwerp, Belgium, a Belgian joint-stock company No Drawing. Filed Feb. 16, 1965, Ser. No. 433,180 Claims priority, application Belgium, Aug. 21, 1964, 43,900, Patent 652,105 7 Claims. (Cl. 208-28) This invention relates to the separation of waxy hydrocarbons from oils by flotation.

It is known to separate waxy hydrocarbons from oils by cooling in the presence of solvent and separating the solid wax by filtering. It has also been proposed to separate waxy hydrocarbons by flotation. In this process bubbles of gas are passed upwardly through the cooled oil so that the wax separates as a froth at the top of the oil. This process has the advantage that no filtering or centrifuging is required and it is, in essence, a simple process. Nevertheless, as far as is known, the process has never been developed on a large scale. One possible reason for this is that the conditions necessary to achieve satisfactory flotation, involving as they do interaction of three phases, the liquid oil phase, the solid wax phase and the gas phase, are extremely critical and that different oils can give markedly different results. This difliculty is, in fact, reflected in earlier attempts to improve the process, many of which suggest the need for additional components such as solvents or surface-active agents to provide the necessary physical conditions for good flotation.

It has now been found that the process can be operated Without the need for added components when the feedstock contains at least a proportion of cracked material and when the feedstock viscosity is carefully controlled.

According to the present invention, therefore, a process for the separation of waxy hydrocarbons from oils by flotation in which gas is passed upwardly through the 'oil cooled to a temperature below its cloud point is characterised in that the oil being treated contains at least a proportion of cracked material and in that the oil has a viscosity, at the separation temperature, of not more than 20 centistokes.

' Without being bound by any theory it is suggested that the cracked material may contain compounds which exert a strong influence on the physical conditions and. allow the ready coalescence of the gas and solid phases. Whatever the theory, however, it has been found that quite small amounts of cracked material have a marked effec and that increasing the amount of cracked material does not lead to a position where the effect becomes overdominant and causes complications in another direction. The proportion of cracked material may thus range from 0.5 to 100% vol., preferably 2 to 907 The cracked material may be derived from either 3,338,816 Patented Aug. 29, 196 7 material the maximum viscosity may thus be 20 centistokes decreasing to 15 when the percentage of cracked material is 2%. If necessary a feedstock which has too high a viscosity may be diluted with lower-boiling material preferably boiling in the kerosine boiling range. This can be either a straight run or cracked petroleum fraction and it has not been found necessary to use diluent materials such as the previously proposed conventional solvents used in filtration de-waxing.

Waxy hydrocarbons can cause problems in oils boiling in the kerosine, gas oil and wax distillate range (i.e. 150 to 650 C.) and the process may be used on any of these feedstocks although with the heavier feedstocks more diluent will naturally be required to lower the viscosity. It has also been found that the presence of asphalt or other materials functioning as pour point depressants is deleterious, even in very small quantities, and their presence should thus be avoided. The cloud points of the oils being treated may vary over a fairly wide range and hence the flotation temperature may also vary. Likely temperatures will however be in the range 0 F. to 80 F., especially 20 F. to F. The cloud point of the dewaxed oil will with efficient operation be substantially equal to the temperature used.

The amount of gas used is not critical and satisfactory results have been obtained with a ratio by volume of gas at S.T.P. to oil feedstock of as low as 0.2 and with no indication that this is a limiting ratio. Higher rates are not detrimental although they add little further benefit and a suitable range is thus from 0.1 to 10. Any convenient gas may be used, for example nitrogen, gases thermal or catalytical cracking and may be of any suitable boiling range within the limits of the range of fractions that can be treated. Preferred materials are those derived from catalytical cracking of gas oils or waxy distillates to gasoline, or the kerosine boiling-range fractions from the same process. I

The importance of viscosity'has previously been noted. one prior suggestion indicating that the viscosity shou ld not exceed 50 centipoises at the working temperature, being preferably 25 to 50 centipoises. It has now been found that these suggested limits are not sufliciently precise and that the maximum viscosity is 20 centistokes at the working temperature. The proportion of cracked material in the oil does have a small effect on the maximum allowable viscosity, causing it to increase with increase in cracked material. With oils which are 10% cracked rich in nitrogen such as flue gas, hydrogen or normally gaseous hydrocarbons. Air is also suitable, but its use may be limited on a commercial scale by safety regulations regarding fire hazard.

The gas 'should naturally pass upwardly through the oil in the form of bubbles and if necessary it can be introduced into the bottom of the flotation bath through known bubblers and dispersers. It has been found, how ever, that the gas can be introduced quite simply and effectively by injecting it into the suction side of the pump feeding oil to the bath. Nevertheless, in that case, the pump discharge pressure must not be below certain limits, in order to dissolve at least part of the gas in the oil. Suitable pressures are in the range of 2 to 10 kg./cm.

The rate of flow of the oil into and the withdrawal of dewaxed oil from the flotation zone should be adjusted to give a suitable residence time and these can readily be determined by experiment. In practice residence times of upwards of 7 hours have been found suitable.

The cooling of the oil to a temperature below the cloud point is preferably carried out by cooling a stream of oil which is withdrawn from the bath, cooled and recycled, which method of cooling is described and claimed in Belgian application No. 43,901. This application also gives details of a suitable apparatus for carrying out the present process.

From the present process one can obtain a dewaxed oil of reduced cloud and pour points and also wax. When in the form of froth at the top of the flotation zone the wax may contain significant quantities of entrained oil. However, much of this oil separates on standing and any oil still remaining can be further separated by known techniques to give waxes equivalent in quality to waxes separated for example by filtration in the presence of solvents. If the wax is not required for specialised purposes it may be used, for example, as a high quality catalytic cracker feedstock.

The invention is illustrated by the following examples:

3 Example 1 The following example compares the effect of different viscosities on the ease of Wax removal by flotation.

The feedstock used had the following inspection data:

Runs were carried out using this oil alone and also using this oil diluted with straight-run kerosine of 170 to 230 C. ASTM boiling range to give oils with viscosities of 20, 15, and 10 centistokes at 32 F.

The conditions used for the flotation were:

Temperature of oil F 32 Oil feed rate l./hr Gas feed rate l./hr 50 Recycle oil rate l./hr 250 Residence time hrs The gas used was air which was injected into the suction side of the oil feed pump.

The results obtained were as follows:

Oil viscosity 50 20 10 Yield of Wax 15 20 Yield of dewaxed oil 85 80 80 Properties of dewaxed oil Cloud point, F 78 40 30 30 Pour point, F 70 35 25 It will be seen that satisfactory results were only obtained at viscosities of 15 and 10 centistokes and that there is a marked change in the results when altering the viscosity through the relatively small range of 20 to 15 centistokes.

Example 2 This example compares the effect of diflerent amounts of catalytically cracked material on the ease of wax removal by flotation.

Four blends of gas oil and kerosine were made up to give four feedstocks having a viscosity of less than 15 centistokes at 32 F. and having an ASTM boiling range of 160 to 370 C. They had the following compositions and inspection data:

Blend Straight run material, percent vol 100 96 0 Cat. cracked material, percent vol 0 4 70 100 Cloud point, F 54 54 62 62 Pour Point, F 50 50 60 50 Viscosity at 32 F., cs 14 14 13 12 Sulphur, percent wt 1. 4 14. 1.6 1. 7

The straight run matenals were obtained by distillation of Kuwait crude oil. The conditions used for the flotation Wfi j 4 Temperature of oil F 30 'Oil feed rate m. /h 10 Gas feed rate Nm. /h 5 Recycle oil rate -m. /h 200 Residence time hrs 40 The gas used was flue gas which was injected into the suction side of the oil feed pump.

The results obtained were as follows:

Blend 1 2 3 l 4 Yield of wax 15 20 20 20 Yield of dewaxed oil 80 80 80 Properties of dewaxed oil: Cloud point, F 44 30 34 30 Pour point, F 35 25 30 20 It will be seen that markedly better results were obtained with blends 2, 3 and 4 with 4% or more of cracked material, the oil having cloud points reduced from 50 or more to 30 F., the latter being substantially the temperature to which the oil was cooled. With blend 1 the cloud point was only reduced to 44 F.

The experiment also shows that all the blends treated contained appreciable quantities of sulphur and that this had no noticeable afiect on the results.

I claim:

1. A process for the flotation separation of waxy hydrocarbons from waxy oils to produce dewaxed oil having reduced cloud and pour points which comprises passing a flotation gas upwardly through the waxy oil which has been cooled to a temperature below its cloud point, said waxy oil containing a proportion of cracked material from 0.5 to volume and having a viscosity, at the separation temperature, of not more than 20 centistokes with the maximum viscosity range being 20* centistokes when using 100% of cracked material to 15 centistokes with 2% cracked material; said gas treatment producing a wax-containing foam layer and a dewaxed oil layer, and separating the dewaxed oil layer therefrom having reduced cloud and pour points.

2. A process as claimed in claim 1 wherein the proportion of cracked material is from 290% vol.

3. A process as claimed in claim 1 wherein the cracked material is the product of a catalytic cracking process.

4. A process as claimed in claim 1 wherein feedstock boils within the range to 650 C.

5. A process as claimed in claim 1 wherein the dewaxing temperature is from 0 F. to 80 F.

6. A process as claimed in claim 1 wherein the gas feed ratio is 0.1 to 1'0.

7. A process as claimed in claim 1 wherein the gas is injected into the suction side of a feed pump, while maintaining the pump discharge pressure at 2 to 10 kg./cm.

References Cited UNITED STATES PATENTS 2,107,137 2/1938 Adams et al 208--33 2,370,453 2/1945 Dons et a1. 208-33 2,719,817 10/1955 Doorn 208-37 2,904,496 9/ 1959 Bloch et a1 208-28 FOREIGN PATENTS 945,281 7/ 1956 Germany.

DANIEL E. WYMAN, Primary Examiner. P. KONOPKA, Assistant Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,338,816 August 29, 1967 Paul Albert Tritsmans It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1 line 14 for "solvent" read solvents line 72, for "10%" read 100% column 3, in the last table 1n the column headed "2", line 6 thereof, for "14 read 1.4

Signed and sealed this 22nd day of October 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. A PROCESS FOR THE FLOTATION SEPARATION OF WAXY HYDROCARBONS FROM WAXY OILS TO PRODUCE DEWAXED OIL HAVING REDUCED CLOUD AND POUR POINT WHICH COMPRISES PASSING A FLOTATION GAS UPWARDLY THROUGH THE WAXY OIL WHICH HAS BEEN COOLED TO A TEMPERATURE BELOW ITS CLOUD POINT, SAID WAXY OIL CONTAINING PROPORTION OF CRACKED MATERIAL FROM 0.5 TO 100% VOLUME AND HAVING A VISCOSITY, AT THE SEPARATION TEMPERATURE, OF NOT MORE THAN 20 CENTISTOKES WITH THE MAXIMUM VISCOSITY RANGE BEING 20 CENTISTOKES WHEN USING 100% OF CRACKED MATERIAL TO 15 CENTISTOKES WITH 2% CRACKED MATERIAL; SAID GAS TREATMENT PRODUCING A WAX-CONTAINING FOAM LAYER AND A DEWAXED OIL LAYER, AND SEPARATING THE DEWAXED OIL LAYER THEREFROM HAVING REDUCED CLOUD AND POUR POINTS.