TECHNO FEASIBILITY FOR REFINING OF USED LUBRICATING OILS AS A VALUE ADDITION STRATEGY

Royal Academy of Engineering Conference-Enriching Engineering Education in Africa-

Victoria Falls, Zimbabwe: 23-24 July 2015

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TECHNO FEASIBILITY FOR REFINING OF USED LUBRICATING OILS AS A

VALUE ADDITION STRATEGY

1T. O. Nengiwa and

2*M.M. Manyuchi

1Department of Chemical & Process Systems Engineering

Harare Institute of Technology, Box BE 277, Belvedere, Harare, Zimbabwe

[email protected]

2Department of Chemical & Process Systems Engineering

Harare Institute of Technology, Box BE 277, Belvedere, Harare, Zimbabwe

[email protected]

ABSTRACT

Refining is a process of refurbishing used oil to high-quality base oil by removing

contaminants, water and spent additives. The study involves refining of 1tonne per day used

lubricating oil to produce 0.75 tonnes per day refined oil with 80% plant utilization. The

process involved dehydration, solvent extraction, hydro-treating and agitated thin film

evaporation. Process conditions were experimentally determined. Optimum conditions of 4:1

solvent ratio and 4 mBar evaporation pressure produced refined oil of 24% ash content, 98cP

viscosity, -11oC pour point, 180

oC flash point and specific gravity 0.909. Detailed major

equipment design of an agitated thin film evaporator, its process control and HAZOP was

done.

Keywords: refining, used oils, lubricating oil, agitated thin film evaporation

1. INTRODUCTION

Huge amounts of used lubricating oils from automotive sources are being disposed of as

harmful waste into the environment and the cost and availability of oil and its products is

significantly impacting quality of life, thus; environmental stability, health of national

economies and even relationships between nations. Thus there is need to refine used

lubricating oil. Used lubricating oil is generated mainly from the transport sector, with its

disposal polluting the environment and also its combustion as a low grade fuel causing air

pollution. The disposal of oil does not only have a negative impact on the environment but a

waste of a valuable resource. Waste oil from the engines gets contaminated but does not lose

its original properties, thus it can be refined to retain its initial characteristic for re-use.

mailto:[email protected]



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2. MATERIALS AND METHODS

Virgin oil was purchased from the local market and used oil was collected from different

garages. The used oil mixture was stirred for 5 minutes before use to insure homogeneity. All

experiments were carried out with used oils taken from this mixture. Methyl ethyl ketone

(MEK) used was of 98% purity obtained from the HIT laboratory. This study used methyl

ethyl ketone (MEK) as solvent for treatment instead of butyl alcohol and isopropyl alcohol.

This choice was due to the ease of recovery, low boiling point and low cost of the MEK and

its capability as a solvent to separate contaminants from used oil is closely related to its

solubility parameters

Apparatus

The vacuum distillation apparatus consisting of heating metal, vacuum pump, divider,

condenser and receiver, solvent extraction-settler mixer tank were used.

Experimental Procedures

The used lubricating oils were collected from various automobiles garages around Harare

CBD. The used oil mixture was then stirred for 5 minutes before use to insure homogeneity.

All experiments were carried out with used oil samples taken from this mixture.

Determination of the optimum pressure for oil dehydration

The dehydration of used lubricating oil was performed in a simple batch vacuum distillation.

Water and oil were separated by dehydration. The amount of used oil was 500ml and heat

rate was fixed at 600W. Three different vacuum pressures were investigated, 4, 8 and 12

mBar. Distillation was carried out until no further distillate was produced. The dehydrated

used oil was then collected for the next step of solvent extraction.

Determination of optimum solvent to oil ratio

The dehydrated used oil was prepared in amount of 50 mL (about 45 g) for each experiment.

The investigated solvent (MEK) to oil ratios were (2, 3, 4, 5 and 6). Solvent to oil ratio less

than 2 produced viscous mixture during separation. While when the ratio was higher than 6 to

1, operation was considered economically not feasible. According to these ratios the solvent

amounts added were (100, 150, 200, 250 and 300 mL). Adequate mixing of the solvent-oil

mixture was obtained by stirring for 5 minutes. The mixture was allowed to settle for 4 hours

in order to separate the extract phase (solvents and oil base dissolved) from the raffinate

phase (contaminants or sludge). Separation of the two phases was carried out in 1 liter

separating funnels. After 4 hours the extract phase was separated and turned to another



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separation funnel and allowed to settle in order to ensure that no contaminants will remain in

the solution. This experiment was repeated two times. The extract phase was subjected to

simple batch atmospheric distillation to recover the solvent from the oil by heating up to 200

°C. The produced oil was weighed and tested for ash content.

Determination of the optimum residence time

Hydro treating of extracted oil took place by feeding the sample into a trickle bed reactor

which serves for laboratory study of heterogeneous catalytic processes under pressure

occurring in liquid or gaseous phase. The reactor contains catalyst of Nickel. The process was

operated at: temperature: 350⁰C, pressure: 5 bars, residence time: 0.7 and hydrogen to oil

ratio: 300 mL/L. Hydrogen gas stream was supplied to the unit from a hydrogen cylinder

having a maximum pressure of 8 bars. The unit was first flushed with nitrogen to remove air,

and then kept for 4 hours under a hydrogen gas pressure of 5 bars to check any leakage. The

liquid feed and the hydrogen gas streams were injected under pressure at the top of the

reactor, both cross the different zones of the reactor in down-flow direction.

Determination of the optimum pressure for high oil recovery

The experiment was carried out by the evaporator apparatus. After each experiment, the

apparatus were washed with n-hexane solvent in order to remove any contaminants that

accumulated in the column, condenser and vacuum lines. The n-hexane washed the

contaminants and accumulated them at the bottom of the still pot where they can be removed.

After washing, all connections and joints were re-lubricated, and prepared for the next

experiment. The evaporator operation variable that was studied was: Vacuum pressure: 4 and

8mbars.

3. EXPERIMENTAL RESULTS

Dehydration of Lube Oils

Several experiments were carried out for the dehydration of used lubricating oil and the

amount of water removed is indicated in Fig. 1. The first experiment at 4 mbar was

considered the best dehydration condition. The presence of excessive water contamination

will affect the viscosity of the oil and this may give rise to emulsion formation and can also

lead to gear tooth and bearing problems.



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Fig. 1: Amount of water removed at different pressures

Determination of Optimum Solvent to Oil Ratio

Fig. 2 indicates that the maximum ash reduction is achieved for solvent to oil ratio of 4:1.

The oil recovery and ash reduction for the same ratio are better than that obtained for solvent

to oil ratio of 3:1 and 2:1.

Fig. 2: Solvent -oil ratio vs. percent weight product

25

14.5

9.9

0

5

10

15

20

25

30

4 8 12

Mas

s o

f w

ater

re

mo

ved

(g)

Pressure used (mBar)

Amount of water removed at various pressures

0

10

20

30

40

50

60

70

80

90

100

2:1 ratio 3:1 ratio 4:1 ratio 5:1 ratio 6:1 ratio

Pro

du

ct w

eigh

t %

Solvent to oil ratio

Solvent to oil ratio vs. weight percent product

Oil recovery (wt%)

Ash reduction (wt%)

Sulfur reduction (wt%)



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Hydro-treating of the solvent treated oil to remove sulphur

Hydro-treating was done to remove sulphur. There was increasing of sulphur removal at high

reaction temperature as shown in Fig. 3.

Fig. 3: Effect of residence time and temperature on sulphur removal

4. DISCUSSION

Table 1 summarizes the analytical test results for the refined lube oil.

Table 1: Refined used oils physicochemical characteristics

Flash point - The decrease in value of flash point for the used oil could be as result of the

presence of light ends of oils.

Pour point - This decrease in pour point is because of degradations of additives, which were

present in fresh oil as pour point depressants. The decrease in pour point observed also

implies that considerable amount of paraffin responsible for the initial high pour point has

15

25

35

45

55

65

75

85

1.4 2.2 3 3.8

% s

ulp

hu

r co

nte

nt

residence time (1/hr)

Effect of residence time and temperature on

sulphur removal Temp=393K

Temp=403K

Temp=413K

Temp=423K

Parameter Virgin lube oil (SN50) Used lube oil Refined lube oil

Flash point (oC) 245 120 230

Pour point (

oC) - 12 - 3 - 15

Specific gravity 0.9 0.93 0.909

Viscosity @ 100 oC 18.6 40 15

Viscosity Index 98 20 87



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been removed, thereby reducing the difficulty of pumping the oil to burners. These results

show that the refining method is comparatively better than other methods used in the past.

Specific gravity - The value of specific gravity of used engine oil is slightly above that of

fresh oil. It could be lower or higher than fresh engine oil depending on the nature and type of

contaminations.

Viscosity - The decrease in viscosity of used oil value is attributed to the removal of aromatic

contents that are normally responsible for the high viscosity value. The result of the viscosity

test shows that, the used lube oil has lost most of its viscosity due to contamination.

However, refining has restored most of its viscosity. This can be attributed to possible

conversion of contaminants by hydrogenation and their removal.

Table 2: SPSS analysis of dehydration results

The value R= -0.999 shows that there is a strong negative correlation between the pressure

used and the amount of water removed, thus the lower the pressure the more water removed

from the oil and R2=0.997 implies that 99.7% of the water removed is attributed to the

pressure applied thus in order to remove maximum water in the oil, pressure has to be

optimized and monitored.

SPSS analysis of solvent-oil ratio experiment

SPSS software was used to analyse the results as shown in Table 3.

Table 3: SPSS analysis of optimum solvent ratio results

Beta value for temperature is 0.058 implying temperature has no impact on the oil recovery

yield since the value is very small and that for solvent to oil ratio is 0.894. This means that

solvent to oil ratio has an impact on the oil recovered and has to be optimised in order to

recover the highest amount of oil possible.



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SPSS analysis of effect of residence time and temperature on sulphur removal

SPSS was used to analyse the correlation between the dependent (sulphur removal) and the

independent variables (temperature and residence time) as in Table 4.

Table 4: SPSS on effect between residence time, temperature on sulphur removal

Since R= 0.993, it means that there is a strong correlation between the various parameters

which were being investigated. R2

= 0.984, means that 98.4% of the changes in sulphur

content of the oil are being caused by the changes in residence time and temperature.

Table 5: SPSS analysis on the effect of residence time on sulphur removal

Beta value for temperature is 0.848 and that for residence time is -0.517. This means that

both variables have an impact on the sulphur removal with residence time having a negative

one implying that the smaller the residence time the higher the sulphur content removed.

The best oil recovery and ash reduction by extraction that were obtained using optimum

evaluated solvent to oil ratio of 4:1 were 65% ash reduction and 75 % oil recovery. On the

basis of experimental work, it was found that this method effectively removed contaminants

from used lubricating base oil and returned the oil to a quality essentially equivalent to oils

produced by fresh lube oil stocks. The results have clearly showed that during purification of

fuel oil, the sulphur content as major impurity is significantly reduced. Also, there is

improvement in viscosity, specific gravity, pour and flash points. This has shown that

aromatics, carbon residues, and ash of the oil have been reduced. Therefore, it is possible to

refine used lubricating oil.

Equipment Design

Agitated thin film evaporator spreads a thin layer or film of liquid on one side of a metallic

wall, with heat supplied to the other side. It has a vertical cylinder where the feed material is

distributed to the inner surface. As the liquid flows downward, axially arranged blades

distribute the liquid as a thin film, which is constantly mixed. This type of equipment can



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operate at very low pressure and provides minimum pressure drop. Because of low pressure

drop during gas flow inside the evaporator the boiling temperature of liquid, which is

evaporated, depends only on its composition and does not depend on liquid position in the

evaporator.

Fig 3: Agitated thin film evaporator 2D drawings

Chemical engineering design for the agitated thin film evaporator

Table 6 below shows the chemical engineering design parameters for the ATFE.

Table 6: Agitated thin film evaporator design specifications

Item Agitated Thin film Evaporator

No. required 1

Function Purification of used lube oil into base oil

Operation Continuous

Effective Heat transfer area 7.1m2

Total Heat Transfer Area 8.7m2



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Overall heat transfer coefficient (Ua) 280 kcal/hr-m2o

C

Diameter 0.5 m

Total height 2.2 m

Design pressure 6 mbar

Temperature 250 0C

Jacket Thickness 10 mm

Insulation Thickness 45 mm

Material of Construction Low carbon steel 304

Agitator Design

A 3 - level agitator was designed.

Table 7: Agitator design summary

Agitator

Number required 1

No. of blades 9

Blade Length 0.21 m

Blade Width 0.033 m

Blade Arrangement 120 0 apart

Impeller diameter 0.17 m

No. of baffles 4

Baffle height 1.6

Baffle Width 0.05 m

Agitator speed 115 rpm

Agitator Power 0.5 hp

Material of construction Low carbon steel 301

Mechanical Design

The mechanical design specifications are given in Table 8.



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Table 8: Agitated thin film evaporator mechanical specifications

Parameter Value

Stress on the walls 0.04 Pa

Weight of contents 1 774 N

Maximum tensile strength 6.72 N

Maximum compressive strength 18.962 N

Shell thickness 15 mm

Wind load 5.6 kN

Temperature Control

The temperature of the crude oil is raised from 100⁰C to 250⁰C. A Proportional Integral (PI)

controller was used. Thermocouples were used as sensing elements and were implemented in

the control architecture. The liquid temperature is maintained at 250⁰C. At this temperature

only base oil is in gas form. The flow rate of steam is manipulated to control the temperature

of the process fluid. A combination of feedback and feed-forward control schemes was used

to ensure good results.

Feed forward scheme was achieved by measuring the inlet temperature of oil and sending the

information to the PI controller. If the temperature has deviated from the set point (250⁰C)

the thermocouple sensor sends information to the transmitter. The transmitter converts the

reading from the thermocouple to a standard signal and transmits it to the PI controller. PI

control uses an algorithm that is proportional to the difference between a set point (SP) and a

process variable (PV) which in this case is temperature, and integral time-function

algorithms, which provide a continuous-control process output to meet the desired set point.

The PI controllers sends a correcting signal to a converter which converts the correction

signal to pneumatic signal and send it to an actuator. If the temperature is too hot, the control

valve was adjusted to decrease steam flow rate. If the temperature is too low the valve is

adjusted to increase steam flow rate, thus increasing the amount of heat exchanged and

temperature of the process fluid increases. Pressure is controlled as it affects relative

volatility, temperature difference as well as process safety. A vacuum pump is installed to

maintain the vacuum system needed. If there is an excessive increase in pressure the bypass

valve opens and releases pressure. The control loop is given in the Fig 4 below.



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TC

thermocouple

converter

steam

Base Oil at 523K

T

I-1

actuator

V-1

transmitter

EVAPORATOR

V-1

Lube oil

373KL

FC

Convertor

actuator

Pressure

sensor

V-2

to vacuum pumpPC

actuator

convertor

Fig 4: Agitated thin film evaporator process control loop

HAZOP Analysis of agitated thin film evaporator

HAZOP Analysis for the agitated thin film evaporator was done in Table 9.

Table 9: HAZOP Analysis for the Agitated thin film evaporator

Parameter Guide

word

Possible causes Possible

consequences

Action required

Temperature More More available

steam

Failure of control

valve

Product quality low

as residue can also

evaporate

PI control action

Less Less available

steam

High fouling rate

Low base oil yield

Poor heat transfer

PI control

Pressure High Vacuum pump

valve failure

Low product yield Operator alert.

Proper

maintenance.

Low Vacuum pump

failure

No separation

Oil quality poor

Repair pump



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5. CONCLUSION

Optimum conditions of 4:1 solvent ratio and 4 mBar evaporation pressure produced refined

oil of 24% ash content, 15cp viscosity at 100 oC, -15

oC pour point, 230

oC flash point,

viscosity index of 87 and specific gravity 0.909. These parameters if slightly adjusted using

additives results in refined lubricating oil grade 50.

Refining of used lubricating oils promotes sustainable development since it deals with

chemical waste management and disposal.

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TECHNO FEASIBILITY FOR REFINING OF USED LUBRICATING OILS AS A VALUE ADDITION STRATEGY

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