GB2334034A

GB2334034A - Waste oil recovery process using sodium tripolyphosphate

Info

Publication number: GB2334034A
Application number: GB9902178A
Authority: GB
Inventors: Barry Partington; Denis Bowes Verity
Original assignee: FIRSTEC SYSTEMS Ltd
Current assignee: FIRSTEC SYSTEMS Ltd
Priority date: 1998-02-06
Filing date: 1999-02-02
Publication date: 1999-08-11
Also published as: ZA99817B; GB9902178D0; GB9802563D0

Abstract

A process for the removal of metals from waste oil comprises the steps of dissolving an inorganic metal binding agent in water to form an aqueous solution and mixing that solution with metal-containing waste oil so as to extract metal from the waste oil as metal compounds. The mixture so formed is then separated into an oil phase and an aqueous phase and the oil phase separated from the aqueous phase and the metal compounds to produce a processed oil having significantly lower metal content than the waste oil. The preferred inorganic metal binding agent is a tripolyphosphate compound, most preferably sodium tri-polyphosphate (STPP). A range of optional additional ingredients may be added to assist in the metal removal process. Such additives can include electrolytes (e.g. sodium nitrate), or the commercial alkoxylate compounds monolan OM103 or Ethomene C25) which aid in separation of the oil and aqueous phases. Non-metal contaminants present in the oil may be removed with the addition of a C 6 - to C 12 - fatty amine ethoxylate of the cocoamine family, such as the commercial product Ethylan TLM. The metal compounds formed, usually as precipitates, may be removed from the aqueous phase so that this aqueous solution can be recycled for further use.

Description

WASTE OIL RECOVERY PROCESS The present invention relates to a process for recovery of waste oil products, for example old lubricating oil, hydraulic fluid etc. and particularly to the removal of metals from waste oils.

Although there are ways of extending the life of oils, they ultimately become contaminated (particularly with metals e.g. calcium, copper, zinc, iron and tin), depleted in additives, highly oxidised and are unfit for further use. For companies involved in heavy industry (e.g. mining raw materials and precious minerals), transpdrtation or manufacture, the disposal of significant quantities of waste oil can be expensive. If the oil is burned, toxic heavy metals and greenhouse gases are introduced into the environment. Controlled incineration requires transportation of the waste oil to a suitable incineration plant, or the building of such a plant on-site, which in most cases will be economically unfeasible.

Alternatively, the waste oil may be reprocessed. Known methods of reprocessing include: (1) Feeding the waste oil into the front end of a crude oil refinery stream. The resultant base oil is likely to contain traces of metals and odour. The waste oil must be transported to the refinery site.

(2) Acids/Clay treatment. This process requires the use of hazardous acids and also results in an inferior base oil.

(3) Thin film evaporation with clay contact finishing or hydrotreatment.

These processes are complex and expensive (temperatures up to 650 OC and vacuum distillation are required).

It is an object of the present invention to provide an improved process for the removal of metals from waste oils which obviates or mitigates the disadvantage of prior art processes.

According to the present invention, there is provided a process for the removal of metals from waste oil comprising the steps of: (i) dissolving an inorganic metal binding agent in water to form an aqueous solution; (ii) mixing the solution formed in step (i) with metal-containing waste oil; (iii) extracting metal from the waste oil as metal compounds formed from the metals and the metal binding agent; (iv) separating the mixture formed in step (ii) into an oil phase and an aqueous phase; and (v) separating the oil phase from the aqueous phase and the metal compounds whereby to produce a processed oil having a lower metal content than the waste oil.

The metal binding agent may be a metal chelating compound (e.g. tetra potassium pyrophosphate) in which case the metal is removed from the waste oil as a water soluble metal chelate.

Preferably, the metal compounds are substantially insoluble in the oil phase and the aqueous phase.

Preferably, the process comprises an additional step of (vi) separating the metal compounds from the aqueous phase. Advantageously, after separation of the metal compounds from the aqueous phase, the aqueous phase can be used in step (i) of the process.

Separation of the insoluble metal compounds from the oil phase and aqueous phase in steps (v) and (vi) respectively may be effected by filtration.

Preferably, the metal binding agent used in step (i) is a polyphosphate compound, more preferably a tripolyphosphate compound and most preferably sodium tripolyphosphate (STPP), so that the metal compounds formed are metal phosphates.

Preferably, the solution formed in step (i) is a saturated solution.

Preferably, an oil/water emulsion is formed in step (ii).

Preferably, during steps (ii) to (v) (and more preferably during the entire process) the temperature is maintained at or below 1 10 C. More preferably, during steps (ii) to (v) (and most preferably during the entire process) the temperature is maintained in the range 650C to 1 10 OC.

One or more additional substances may be mixed with the waste oil (preferably at substantially the same time as step (ii)). Such substances may be (i) metal removing agents to assist in removal of metal from the waste oil in step (iii) and/or (ii) non-metal contaminant removing agents to remove non-metal contaminants (e.g. sulphur and phosphorus) from the waste oil and/or (iii) phase separating agents to assist in the separation of the oil and aqueous phases in step (iv).

Examples of suitable non-metal contaminant removing agents include fatty amine alkoxylates. C6- to C2efatty amine ethoxylates (and particularly C12to Cl4-fatty amine ethoxylates) of the cocoamine family, preferably having 6 to 12 moles of ethylene oxide per mole of amine (e.g. the ethoxylate sold under the trade name Ethylan TLM) are highly preferred.

Examples of phase separating agents include electrolytes (e.g. inorganic metal salts; e.g. sodium nitrate, sodium metasilicate), the alkoxylate sold under the trade name Monolan OM103 and the agent sold under the trade name Ethomene C25).

In the case where the fatty amine alkoxylate is present, a distinct third (organic) phase may be formed between the oil and aqueous phases. The use of additives (e.g. electrolytes) promotes the formation of such a third phase. This organic phase contains, in addition to the fatty amine alkoxylate, non-metal contaminants extracted from the waste oil, reaction and degradation products and non-colloidal carbon. The non-metal contaminants present are dependent upon the composition of the waste oil and may include sulphur and phosphorus compounds.

A highly preferred embodiment of the process comprises the steps of: (i) dissolving STPP in water to form a saturated solution of STPP; (ii) mixing the saturated STPP solution with metal-containing waste oil, a quantity of a C12- to C14-fatty amine ethoxylate of the cocoamine family having 10 moles of ethylene oxide per mole of amine and a phase separating agent so as to form an emulsion; (iii) extracting metal as precipitated metal phosphates, and non-metal contaminants from the raw waste oil; (iv) coagulating the emulsion to form an oil phase and an aqueous phase containing unreacted STPP and precipitated metal phosphates; (v) separating the oil phase from the aqueous phase whereby to produce a processed oil having lower metal and non-metal contaminant content than the waste oil; and (vi) filtering the precipitated metal phosphate compounds from the aqueous phase.

Advantageously, the above process can be a batch process or a continuous process.

Prior to the process, the waste oil is preferably pre-treated to remove particulate metals by magnetic filtration. Waste oil entrained with petrol (e.g. oil originating from petrol engines) is pre-treated to remove the petrol, preferably by evaporation.

Subsequent to the process, the processed oil obtained may be dried and polished by, for example, passing it through a coalescer.

An embodiment of the present invention will now be described with reference to the accompanying drawing which is a schematic diagram of a plant for carrying out the process of the present invention.

The plant basically comprises an aqueous liquid supply vessel 2, an organic liquid supply vessel 4, a waste oil pre-processing unit 6 and a reactor vessel 8, interconnected by pipework 10.

The waste oil pre-processing unit 6 comprises sequentially in a downstream direction a waste oil feed supply 12, a waste oil feed strainer 14, a suction filter 16, awaste oil feed pump 18, primary and secondary heat exchangers 20, 22, a waste oil heater 24 and an evaporator vessel 26.

A first outlet 28 from the evaporator vessel 26 is vented to the atmosphere with the aid of an air blower 30. A second outlet 32 from the evaporator vessel 26 feeds via a waste oil recirculation pump 34 back into the secondary heat exchanger 22.

The aqueous liquid supply vessel 2 has a mixing/heating compartment 40 equipped with a motor driven overhead stirrer 42 and a heater 44, and a loading compartment 46 separated from the mixing/heating compartment 40 by a mesh screen 48. An inlet 50, 52 is provided in each of the mixing/heating and loading compartments 40, 46 and an outlet 54 is provided in the mixing/heating compartment 40. The outlet 54 in the mixing/heating compartment 40 feeds downstream via a filter 56 and an aqueous liquid feed pump 58 through a reaction vessel supply heater 60 and a centrifugal pump 62 to the reaction vessel 8.

The organic liquid supply vessel 4 is provided with an inlet 70 and an outlet 72. The outlet 72 feeds downstream via a filter 74 and an organic liquid feed pump 76 to a first mixing point A with the aqueous liquid feed upstream of the reaction vessel supply heater 60.

The secondary heat exchanger 22 of the pre-processing unit 6 feeds via a pump 78 to a second mixing point B with the organic/aqueous liquid supply immediately downstream of the first mixing point A and upstream of the reaction vessel supply heater 60.

The reaction vessel 8 is equipped with a trace heater 80 and a motor driven overhead stirrer 82. A first outlet 84 at the base of the reaction vessel 8 feeds via a pump 86, a bag filter 88 and a plate and frame filter 90 back into the aqueous liquid supply vessel 2 through the inlet 50 in the mixing/heating compartment 40 thereof. A filter bypass 92 allows either of the filters 88, 90 to be removed for cleaning or replacement. A second outlet 94 at an upper region of the reaction vessel 8 feeds via a pump 96 and a coalescer 98 back through the primary heat exchanger 20 to oil storage tanks (not shown). The-reaction vessel 8 is supplied with a third outlet 100 which feeds via a pump 102 to residue storage tanks (not shown). The reaction vessel 8 is vented to the atmosphere.

Valves, temperature sensors and controllers (e.g. known platinum resistance thermometers and thyristor controlled regulators), pressure gauges and vessel level indicators (not shown) are provided to allow flow, temperature and pressure within the vessel to be monitored and control led.

In use, the waste oil is first pre-processed in the pre-processing unit 6 to remove undesirable solid residues and volatile components e.g. petrol.

The waste oil is pumped at ambient temperature through the strainer 14 and suction filter 16 where any solid residues are removed, through the primary and secondary heat exchangers 20, 22 (where it is heated by the processed oil stream and pre-processed oil stream respedively) to the waste oil heater 24 where the filtered waste oil is heated to approximately 103"C. In the evaporator vessel 26 volatiles are removed from the oil and are mixed with air from the air blower 30 at a volume that allows them to be vented to the atmosphere in accordance with Directive 94/63/EC (emission of volatile organic compounds). The pre-processed oil passes back through the secondary heat exchanger 22 (thereby heating the oil flowing downstream to the evaporator vessel 26) where it is pumped to the second mixing point B by the pump 78.

Granular sodium tripolyphosphate (STPP) of particle size 50 to 900 CLm is charged into the loading compartment 46 of the aqueous liquid supply vessel 2 and water is fed into the inlet 52 in the loading compartment 46.

Saturated STPP solution leaches through the mesh screen 48 and is heated with vigorous stirring (careful control of the temperature is required, since the rate of breakdown of tripolyphosphate to mono- and dipolyphosphates is exponential and rises very quickly above approximately 700C. Temperatures above 70"C may be employed if the solution is used in a relatively short time). The heated STPP solution is filtered to remove any particulates and is pumped downstream to the first mixing point A where it is mixed with Ethylan TLM and Monolan OM103 pumped from the organic supply vessel 4 at between 0.1 to 1 1% by weight of the waste oil feed. The organic/aqueous mixture is mixed with the pre-processed oil stream at the second mixing point B (the flow rates being such that approximately equal volumes of oil and STPP solution are mixed) and the resultant mixture heated by the reaction vessel supply heater 60 so as to raise the temperature to approximately that of the STPP solution in the aqueous liquid supply vessel 2, before being emulsified by the centrifugal pump 62. The resultant emulsion is passed into the reaction vessel 8 (maintained at substantially the same temperature as the emulsion entering the reaction vessel 8) and gently stirred so as to allow the emulsion to coagulate into three distinct phases. The (lower) aqueous phase containing precipitated metal phosphate salts is fed through the outlet 84 in the base of the reaction vessel 8 and filtered before being passed back into the inlet 50 of the aqueous supply vessel mixing/heating chamber 40.

The processed oil (upper phase) is pumped from the outlet 94 in the upper region of the reaction vessel 8 through the coalescer 98 (where the oil is dried) and back through the primary heat exchanger 20 to the storage drums. The residence time of the oil in the reaction vessel 8 can be adjusted by controlling the rate of flow into the reaction vessel 8 and takeoff rates out of the reaction vessel 8. The level of the aqueous phase and oil phase are automatically maintained at desired levels. The organic (intermediate) phase contains non-colloidal carbon, unreacted amine and organic reaction/degradation products. This phase gradually builds up and is periodically pumped out of the reaction vessel 8 through the outlet 100 to storage for subsequent disposal - preferably by incineration at between 1000 and 1 500 C.

It will be appreciated that the size of the plant may be chosen for the expected volume of oil to be processed by the user. The plant can be made sufficiently compact for it to be vehicle mounted and thereby movable from one location to another.

The process is highly efficient, with 85 to 95% of the input waste oil being recoverable (depending on the content of the waste oil) and has a relatively low power requirement. No toxic chemicals are used or generated and the small volume of waste material is relatively easily disposed of by incineration. Tests have shown that as much as 95% (and in some cases as much as 99.5%) of dissolved metals are removed from waste oil using the above-described process.

The recovered oil can be used as a fuel oil, in which case it produces a good burn (the colloidal carbon left in the oil produces thermal efficiency gains over normal diesel fuels) with reduced ash, sulphur and chlorinated products. Alternatively, if the input waste oil is a single purpose oil, the processed oil may be re-inhibited with additives and used as, for example, a lube, a transformer or hydraulic oil.

Claims

CLAIMS 1. A process for the removal of metals from waste oil comprising the steps of: (i) dissolving an inorganic metal binding agent in water to form an aqueous solution; (ii) mixing the solution formed in step (i) with metal-containing waste oil; (iii) extracting metal from the waste oil as metal compounds formed from the metals and the metal binding agent; (iv) separating the mixture formed in step (ii) into an oil phase and an aqueous phase; and (v) separating the oil phase from the aqueous phase and the metal compounds whereby to produce a processed oil having a lower metal content than the waste oil.
2. A process as claimed in Claim 1, comprising an additional step of (vi) separating the metal compounds from the aqueous phase.
3. A process as claimed in Claim 1 or Claim 2, wherein the metal compounds are substantially insoluble in the oil phase and the aqueous phase.
4. A process as claimed in Claim 3, wherein the metal binding agent is a tripolyphosphate compound.
5. A process as claimed in Claim 4, wherein the metal binding agent is sodium tripolyphosphate (STPP).
6. A process as claimed in any preceding claim, wherein during steps (ii) to (v) the temperature is maintained at or below 110"C.
7. A process as claimed in Claim 6, wherein the temperature during steps (ii) to (v) is maintained in the range 65 "C to 1 1 O OC.
8. A process as claimed in any preceding claim, wherein one or more additional substances are mixed with the waste oil.
9. A process as claimed in Claim 8, wherein said additional substance is selected from the group consisting of C6- to C2o fatty amine ethoxylates of the cocoamine family, electrolytes and phase separating agents.
10. A process as claimed in Claim 9, wherein said fatty amine ethoxylate is a C12- to Cl4-fatty amine ethoxylate.
11. A process as claimed in Claim 9 or Claim 10, wherein said fatty amine ethoxylate has from 6 to 12 moles of ethylene oxide per mole of amine.
12. A process as claimed in any preceding Claim, wherein an oil/water emulsion is formed in step (ii).
13. A process for the removal of contaminants from waste oil comprising the steps of: (i) dissolving STPP in water to form a saturated solution of STPP; (ii) mixing the saturated STPP solution with metal-containing waste oil, a quantity of a C12- to C14-fatty amine ethoxylate of the cocoamine family having 10 moles of ethylene oxide per mole of amine and a phase separating agent so as to form an emulsion; (iii) extracting metal as precipitated metal phosphates, and non-metal contaminants from the raw waste oil; (iv) coagulating the emulsion to form an oil phase and an aqueous phase containing unreacted STPP and precipitated metal phosphates; (v) separating the oil phase from the aqueous phase whereby to produce a processed oil having lower metal and non-metal contaminant content than the waste oil; and (vi) filtering the precipitated metal phosphate compounds from the aqueous phase.
14. A process as claimed in Claim 1, substantially as hereinbefore described with reference to the drawing.
15. A process as claimed in Claim 13, substantially as hereinbefore described with reference to the accompanying drawing.