ZA200807265B - Vibrating membrane micro-filtration of used oil - Google Patents

Description

LIJIE Co

Technical field | | oo

The present invention relates to the recycling of used oil, particularly lubricating oil.

The process incorporates a vibrating membrane micro-filtration process for removing : 5 physical contaminants. | :

Background of the Invention Co

Oils are used for lubricating, hydraulic, heat transfer, dielectric or other purposes and ) during use are contaminated by physical or chemical impurities making them : unsuitable for the purpose for which they were originally intended. The expression “used oil” means any such semi-solid or liquid product consisting totally or partially of _ mineral oil or synthetic oil. oo : Economic considerations are a primary driver in the adoption of a particular recycling process for used oil, and typically recycling costs are very sensitive to the scale of - the operation, so yields and throughput rates from contaminant-removal processes . 15 are very important. It is also essential to have the ability to efficiently process a range of waste oils since the quality of waste oil can seriously affect the technical performance of the regeneration processes, and their ability to produce lubricating or similar products of sufficiently good quality.

Whether used oils are recycled for reuse by substantially restoring the original properties of the oil or to produce a lower grade product such as fuel, the removal of these contaminants can be performed by a number of steps. Physical contaminants such as ash, additives, metal particles, environmental dust etc can be removed by mechanical separation methods such as sedimentation, centrifugation and filtration.

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With continual advancements made in the construction and materials of membrane filters, considerable development work has been done in the application of this technology to recycling used oil. ~~

A prior art recycling process includes a micro-filtration treatment for removing most of the physical impurities from the waste oil using membranes having a pore size of 0.01um to 1um. After initial sedimentation, the used oil is heated to between 50° and 90°C and passed through a dynamic membrane filtration system in which it flows past a porous membrane. The membranes must be periodically cleaned to maintain filtration efficiency, and this is typically accomplished by backwashing, that is by reversing oil flow through the membrane, and using the clean liquid from the : permeate side 0 dislodge the layer of foulant formed on the membrane during filtration. However as the used oil becomes more concentrated a separate layer of : foulant is less well defined and correspondingly cannot be readily removed. The a alternative of physically removing the membranes, is costly, resulting in substantial lost production.

To address these drawbacks it has been found that vibrating the membrane " advantageous. Heating the oil to reduce its viscosity, combined with the dynamic : action of the membranes provides a turbulent flow regime producing satisfactory throughput rates while making the membrane less susceptible to fouling by the contaminants. As the unfiltered used oil becomes more concentrated with contaminants there is a reduction in throughput, and while satisfactory membrane flux can be maintained by increasing the flow pressure pushing the oil through the membrane to counteract the restrictions caused by membrane fouling, this is disadvantageous because the fragile membrane can be damaged by the application : 25 of excessive pressure and the quality of the permeate is reduced.

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It is an object of the invention to provide a method which overcomes or substantially ameliorates the above disadvantages or more generally to provide an improved gy method of regenerating used oil. It is a further object of the invention to provide an improved method of vibrating membrane filtration of used oil and a method of regenerating used oils so that the regenerated oil can be used, for example, as a : base stock for blending different types of lubricant. - ~~ Disclosure of the Invention :

According to one aspect of the present invention there is provided a method for processing used oil containing contaminants to recover regenerated oil having a

N lower concentration of contaminants, the process including the following steps: ~. a) directing a stream of used oil under driving pressure against the outer : surface of a porous micro-filtration membrane sheet having a 0.01um.to Tum : : pore size; b) vibrating the membrane to separate the stream of waste oil into a retentate on the outer side of the membrane and regenerated oil on the inner side of the membrane; : } c) centrifuging the retentate to separate a contaminant-rich component from a "used oil concentrate; d) diluting the used oil concentrate with a solvent to provide an oil solution with a ~ viscosity equivalent of 50 to 90 cSt at 40°C; e) directing a stream of the oil solution under pressure against the outer surface of a vibrating micro-filtration membrane sheet having a 0.01um to 1pm pore size and extracting a permeate solution from the inner side of the membrane, and : f) evaporating the solvent from the permeate solution to produce regenerated ! . = J oil and a solvent vapour. : A : Prior to step a) the used oil is held in a sedimentation tank to allow debris and free. ~ water to be separated out, such that the used oil stream has a free water content of less than 5% by volume. - B

Used oil from the sedimentation tank is preferably heated to a temperature between 60°C to 120°C before step a). ~The used oil at between 60°C to 120°C is exposed to a vacuum to evaporate water and volatile fractions and reduce the free water content of the used oil to less than 1% by volume before the used oil is directed against the micro-filtration membrane.

The method is preferably used in a batch mode wherein steps b) and e) are ~~ 15 performed using the same micro-filtration membrane sheet. Optionally the method : may be performed in a continuous mode using one micro-filtration membrane sheet, or in a cascading continuous mode in which steps b) and e) are performed using separate micro-filtration membrane sheets.

The driving pressure is modulated during step b) based upon measurement of the rate of extraction of regenerated oil at step b) and a desired extraction profile determined by an assessment of the degree of contamination of the used oil, and when a maximum driving pressure has been reached and the rate of extraction of regenerated oil falls below a minimum, the retentate is then centrifuged.

The oil solution is preferably exposed to vacuum to evaporate the solvent.

Preferably the solvent vapour is condensed and recovered for reuse at step d).

Preferably the regenerated oil is the regenerated oil is further post-treated by clay : polishing or solvent extraction to remove one of colour and odour.

This invention provides a micro-filtration method which economically produces regenerated oil which is substantially free from metallic impurities. Variations in the levels of contamination in the input used oil have less of an impact on the process and the membrane is less susceptible to irreversible fouling.

Brief Description of the Drawings : : ) Preferred forms of the present invention will now be described by way of example : with reference to the accompanying drawings, wherein: : Figure 1 is a schematic illustration of a system for regenerating used oil according to the method of the invention. : "15 oo :

Description of the Preferred Embodiments : Referring to Fig. 1, the method of the present invention may be performed in a batch mode using the system illustrated. The used oil is initially treated in the Co sedimentation tank 1 to separate free water and debris. It is held in tank 1 for Co : 20 between 8 to 24 hours until a free water content of less than 5% by volume. :

The used oil from the sedimentation tank 1 is then transferred to a holding tank 2. A stream of used oil is fed by a pump 3 through a heater 4, which heats the oil to a feed temperature of between 60 to 120°C. The stream of heated used oil then passes into a flash evaporator 5, in which a vacuum is drawn to reduce the water content of the used oil to a level of less than 1% water by volume.

The dewatered feed stream is then transferred by pump 6 through a pre-filter 7 with : around 20 — 100 pum pore size to remove large particles and debris before entering oo the vibrating membrane micro-filtration system 8. The membrane system 8 may include an inorganic microporous membrane (e.g. ceramic or metallic) or an organic ~ membrane (e.g. a polymeric membrane). The membrane pore size should not be less than 0.01 pm to ensure satisfactory throughput of the system. The maximum pore size may depend upon the specification of the recycled oil, however when 95% of the rejected particle size should be greater than 0.2 um the nominal membrane ; pore size should be below 0.2 (m. The driving pressure is controlled by valve 9 on the retentate side of membrane filtration system 8. Permeate from the membrane filtration system 8is drawn off to an output tank 12.

The driving pressure across the membrane filtration system 8 is modulated based upon measurement of the rate of extraction of regenerated oil to tank 12 and a desired extraction profile determined by an assessment of the degree of contamination of the used oil. The minimum operating pressure must be greater than about 2 bar to ensure membrane does not delaminate by the vibrating shear. Once the system has achieved the operating pressure, the filter must vibrate to resist fouling. When a maximum driving pressure has been reached and the rate of extraction of regenerated oil falls below a minimum, the viscosity of the retentate is approximately double that of the original feed. This retentate is then processed in the decanter centrifuge 10 at approximately at 1,500 — 3,500 g-force to separate a

. | . 7 high viscosity ash-rich component from an oil-enriched concentrate that is then transferred back to holding tank 2.

The concentrate is diluted with a light solvent fed from holding tank 13 to produce an : oil solution having a viscosity of 50 _ 90 cSt at 40°C. The solvent may be organic or oC inorganic with good solubility in oil, a light colour so as not to darken the oil and a low boiling point. This oil solution is then fed into the membrane system 8 for the “second bass”, the output permeate solution being transferred to the flash : evaporator 5 where solvent vapour is extracted and passes through the condenser 14 to the holding tank 13. With the solvent removed, the regenerated oil is directed tothe tank 12. :

A controller 11 controls the operation of the system in the above-described manner based upon inputs from flow rate and pressure sensors (not shown). The controller 11 also controls the temperature of the oil stream from the heater 4, which is initially held at the lower end of the feed temperature range, and is increased as the process progresses. The viscosity: of used oil increases with increased levels -of contamination. This temperature increase therefore tends to maintain the viscosity of the used oil on the retentate side of the microporous membrane, or at least to reduce the reduction in viscosity which would otherwise occur as the used oil on the retentate side becomes more concentrated with contaminants. Similarly the temperature is varied to offset the viscosity changes according to the varying contamination level in used oil fed from the tank 2.

The overall recovery rate achieved by the method is between 50 — 80% by volume.

The following examples are provided as a further non-limiting illustration of the invention. -

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Example 1:

In the batch process used motor oil without free water and debris was heated to - ae 85°C and transferred to the vibrating membrane filtration system which held porous polymeric membrane sheet with a nominal pore size of 0.05 um. The stream of used oil is directed to flow tangentially past the membrane sheet was continuously vibrated in a torsional mode at an amplitude of 0.06 radians or 16mm and frequency - of 50 Hz. In the first pass the driving pressure was initially maintained at 2.4 bar until the membrane flux dropped to 250 litres/hr following which the pressure was gradually increased to a maximum of 5 bar to maintain membrane flux. When the : 10 rate of extraction of regenerated oil fell below 100 litres/hr, the retentate was : centrifuged. The retentate was processed at 1500G for 20 minutes, and a concentrate that was 90% by weight of the retentate was decanted. The concentrate - was diluted with kerosene to a viscosity of 75 cSt at 40°C before the second pass : and recovery of the kerosene. . 15 :

Table 1 compares the measured properties the used oil and the regenerated oil.

Table 1. | oo ris fn motor oil Regenerated oil |% Change

SE

Co bueem bbb

I

EE ET YE

I "a vom bbb vscostyaroroesy hos bo bw : In preferred embodiments of the method of the invention, the regenerated oil is

- . further processed by clay polishing or solvent extraction to remove one of colour and odour. .

Example 2: oo

In an experimental process 500 ml of regenerated oil produced by the method of - 5 Example 1 was post-treated by solvent extraction. The regenerated oil was mixed with N-methyl-2-purrodine (NMP) at 1:3 ratio and heated to 125°C for 30 minutes. : : After contacting with the oil a solvent phase separates from the mixture as the NMP solvent and the oil are of different densities and generally immiscible. The mixture was transferred to separating funnel and settled for 12 hours. Following separation the raffinate was analysed and compared with the starting regenerated oil to examine the contaminant removal performance. The regenerated oil had an ASTM : D1500 colour 8.0 and following the solvent extraction process, this was reduced to colour 3.0. : a

Table 2 compares the concentration of contaminants in the starting regenerated oll and following solvent extraction using NMP.

Table 2 - |Regenerated |After NMP solvent

Contaminant oil extraction % Removal ) ppm ppm cecmonmy pb ha oo 11 | | i

NE TT

ET EE

EE ST

.

PE TE EY

BT ST YE

Example 3: | | .

a. oo | 0” | | : : In an experimental process 500 ml of regenerated oil produced by the process of

Example 1 received ‘a clay polishing posttreatment. The regenerated oil was mixed with 12 weight % of clay absorbent and heated to 100°C for 120 minutes. The used clay was filtered off and the resulting clear and bright colour regenerated oil sample was analysed for metal content. oo

Table 3 compares the concentration of metals in the starting regenerated oi and : following clay polishing.

Table 3 Co irgin Purocel clay

Regenerated oil (light) % removal :

Metal . : (ppm) DY 2.5-3

VE SE TE TE

ME TE TE bo hs bh we

SE TE ow bbb hb bh eh bes ob bb oo So 13

SE

ME

BE TT

: | Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. } -. : Co

Units which are used in this specification and which are not in accordance with the Sl system may be converted to the Si system with the aid of the following table: 1 bar = 1 x 10° Pa 1cSt=1x10°m?s :

Claims (13)

. : ’ — : L— “ | \\ \ Cc. Jeg gs ~ oT . ANS — a CLAIMS: :

1. A method for processing used oil containing contaminants to recover regenerated oil having a lower concentration of contaminants, the process including the following steps: | oo oo a. directing a stream of used oil under driving pressure against the outer surface of a porous micro-filtration membrane sheet having a 0.01um to 1um pore size; | :

b. vibrating the membrane to separate the stream of waste oil into a retentate on the outer side of the membrane and regenerated oil on : 10 the inner side of the membrane; : | B ) : of centrifuging the retentate to separate a contaminant-rich component from a used oil concentrate; : : : d. diluting the used oil concentrate with a solvent to provide an oil solution with a viscosity equivalent of 50 to 90 cSt (5 x 10°to 9 x 10° m%s) at 40°C;

: e. directing a stream of the oil solution under pressure against the outer surface of a vibrating micro-filtration membrane sheet having a Co 0.01pm to 1pm pore size and extracting a permeate solution from the inner side of the membrane, and Co | 20 f. evaporating the solvent from the permeate solution to produce regenerated oil and a solvent vapour.

2. The method of claim 1 wherein prior to step a) the used oil is held in a - sedimentation tank to allow debris and free water to be separated out, such that the used oil stream has a free water content of less than 5% by volume.

3. The method of claim 1 or claim 2 wherein used oil from the sedimentation : tank is heated to a temperature between 60°C to 120°C before step a).

4. The method of any one of claims 1 to 3 wherein prior to step a) the used oil at between 60°C to 120°C is exposed to a vacuum to evaporate water and volatile fractions and reduce the free water content of the used oil to less than 1% by volume before the used oil is directed against the micro-filtration membrane. -

5. The method of any one of claims 1 to 4 performed in a batch mode wherein steps b) and e) are performed using the same micro-filtration membrane sheet. | | oo :

6. The method of any one of claims 1 to 6 wherein the oil solution is exposed to vacuum to evaporate the solvent.

7. The method of claim 6 wherein the solvent vapour is condensed and Co recovered for reuse at step d).

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8. The method of any one of claims 1 to 7 wherein the regenerated oil is further post-treated by solvent extraction to remove one of colour and odour.

9. The method of claim 8 including the steps: mixing N-methyl-2-purrodine (NMP) with the regenerated oil at a ratio of between 1:3 and 1:5 parts of NMP per part of regenerated oil by volume ratio to produce a mixture; heating the mixture to a temperature between 100°C and 150°C for 30 minutes, and recovering the regenerated oil.

10. The method of claim 8 or claim 9 wherein the regenerated oil is further post- treated by clay polishing to remove one of colour and odour.

11. The method of any one of claims 1 to 7 wherein the regenerated oil is further a post-treated by clay polishing to remove one of colour and odour. :

12.The method of claim 10 or claim 11 including: mixing the regenerated oil with a clay absorbent at a ratio of between 15% and 20% by weight of clay; reacting the mixed clay and regenerated oil for between 30 and 120 minutes, : and recovering the regenerated oil by filtering to remove the clay.

13. The method of clam 1, substantially as herein described with reference to any ft the illustrative Examples.

DA A 3 22° DAY OF AUGUST 2008 NS SPOOR& FISHER =~ = APL QANTS PATENT ATTORNEYS