Thirteen billion gallons of used motor and other oils are generated annually
(Ciora and Paul, 2000). These waste oils are considered
a hazardous waste (Rincon et al., 2007) because
of their high content of pollutants (contaminated with oxidation and degradation
products, water, fine particulates, metals and carbon oil additive products).
The used oil generally contains ~0.5 wt. % of ash residue after combustion and
for reuse as fuel, this ash creates air pollution concerns. Nevertheless, the
used oil still contains a large proportion of valuable base oil that may be
used to formulate as a new lubricant, such as crank case fluid if the contaminants
are properly removed, odor is eliminated and the color is improved. Thus, the
recovery and purification of this base oil not solely give the economic contributions
but also an attempt to meet the environmental objections.
In recent years, there are several processes available for the recycling of
used lubricant oil. The traditional method used was chemical cracking using
acid treatment of the used oil to flocculate carbonaceous particles and other
impurities from the used oil. However, this process generates acid sludge, creating
environmental concerns and disposal problems. Other popular conventional method
used was acid clay treatment, where the base oil was separated from the used
lubricant using sulfuric acid as a separate medium. At the end of the process,
the acidic sludge was disposed of while the base oil was treated with clay for
color and odor removal. Other alternative, evaporation/distillation of the used
lubricant oil has been suggested to separate ash and other contaminants from
the oil. The high boiling point of the used oil at atmospheric pressure with
the assistance of vacuum and high operating temperature was reported to effectively
evaporate oil and leave the contaminants and impurities as residue. Although,
this process to be technically feasible, it is energy intense due to the phase
change involve in evaporation. In addition, to deliver an acceptable quality
of color and smell, a polishing step is required.
Solvent extraction has been used for the recycling of used lubricant oil. Studies
such as by Lim (2001) and Gary (1999)
concluded that solvent extraction technique can be an alternative to be commercialized
for re-refining of base oil. This method involves the extraction of base oil
from used lubricants via addition of composite solvent. At the end of this process,
organic sludge with huge potential as burning fuels was produced. Unfortunately,
the recovered base oil is still in darkish color with stink odor. Thus, a need
has arisen for an effective method of purifying the recovered base oil in order
to achieve the desired product quality.
Adsorption process was found to be an effective method of metals removal in
recovered base oil for purification purpose (Ahmad et
al., 2005). This technique was highly efficient for the removal of color
in terms of initial cost, simplicity of design, ease of operation and insensitivity
to toxic substances (Juang et al., 1997). Many
substances can be used as an adsorbent, but chitinand chitosan were widely used.
Chitin is the second most abundant biopolymer in nature next to cellulose (Majeti,
2000). Chitosan is a partially acetylated glucosamine polymer encountered
in the cell wall of some fungi such as the Mucorales strains. It also results
from deacetylation of chitin (Feng et al., 2000).
Chitosan has excellent features such as its hydrophilicity, biocompatibility,
biodegradability and anti-bacterial properties and remarkable affinity for proteins.
This adsorbent is effective in the uptake of metals since the amine groups on
the chitosan chain can serve as chelation sites for metals (Giubal
et al., 1994).
In this study, metals removal from recovered base oil using chitosan was investigated. Two level factorial design was applied to investigate the effects of the parameters and their interactions on metals removal by batch adsorption. In the end, the regression equation was obtained.
MATERIALS AND METHODS
Sample preparation: The base oil from used lubricants was extracted
using solvent extraction method. In order to increase the capability to remove
sludge from the waste oils, several proportion of potassium hydroxide (KOH)
was added and dissolved in 500 mL of solvent (Ping et
al., 2000). The used oil was then mixed with the solvent (n-hexane and
2-propanol mixture) and KOH in a beaker. Then, the mixture was subjected to
intense agitation for 15 min at 300 rpm to allow good mixing between the oil
and the solvent. After strong agitation, it was then left at room temperature
for 24 h to allow extraction-flocculation. Consequently, the oil was introduced
into simple filtration process to allow separation of base oil from the oil
sludge. The recycled base oil with darkish color was later collected and kept
in a close drum of 20 L where the content have to be homogenized prior to any
Adsorption process: The recovered base oil was mixed with chitosan in
a beaker. The samples were analyzed at various conditions according to the design
matrix in factorial design analysis. The upper and lower levels for each parameter
were shown in Table 1. The recovered base oil was then analyzed
for their metals content before and after the adsorption process.
||Actual and coded values of parameters in 24 full
factorial design for metals removal by adsorption
Factorial design: The 2k factorial designs were found to
meet the majority of the experimental needs of those engaged in the improvement
of quality. This type of factorial design was easy to use in sequential experimentation,
so that even complex systems with many variables can be studied in depth using
these relatively simple designs (Box et al., 1978).
In this study, there were four quantitative variables involved, namely temperature,
contact time, chitosan grain sizes and chitosan dosage. Table
1 shows the parameters involved in the studies. The responses variables
used in this study were the percentage of Zinc (Zn), Magnesium (Mg) and Ferum
(Fe) removal. For a two-level factorial design with four variables, sixteen
runs (24 = 16) of experiment were conducted.
The main effects were the difference between two averages:
|| Average response for (+) stage variables
||Average response for (-) stage variables
Using Eq. 1, the most influential parameter that effects
the metals removal in the recovered base oil was obtained and shown by the variable
with the highest response value. The same method was also used in the analysis
on the interacting effects between the selected parameters.
RESULTS AND DISCUSSION
Full factorial design: A design matrix with the responses Y1 (percentage of Zn Removal), Y2 (percentage of Mg Removal) and Y3 (percentage of Fe removal) are illustrated in Table 2.
|| Factorial design result
|| Analysis of variance for metals removal (%)
Factorial design analysis: Statistica 6.0, a Statistical Software release (Version 15) was used to analyze the effects, coefficients, standard deviation of coefficients, and other statistical parameters of the fitted models, besides the statistical plots. Table 3 shows the analysis of variance for each of response.
From the analysis of variance, the R2 value for each response shows a good agreement between experimental data and the model when the values were greater than 0.80.
The regression equation for the matrix is represented by the following expression:
The effect of individual variables and interactional effects can be estimated using the above equation. According to Eq. 2, each response can be represented respectively by the following expression:
The effects of individual variables and interactional effects were estimated from the above equations. According to these equations, chitosan grain size has a positive effect, while temperature, contact time and chitosan dosage have a negative effect on the metals removal by chitosan adsorption in the range of each variable studied. The greatest effect found was from the chitosan grain size.
The interaction effect between temperature and time, and temperature and chitosan dosage have a positive effect on metals removal. On the other hand, the interaction between temperature and chitosan grain size has a negative effect. The triple effect was found to be almost negligible.
The major conclusions derived from the present work were:
||From the studies of parameters involved in the process, the
most influential parameter effecting the metals removal was the chitosan
||In the interacting effect study, the metals removals greatly depended
on the temperature of the process and chitosan dosage
The authors would like to acknowledge the financial support from the Ministry of Science, Technology and Environment (MOSTI), through e-Science fund.