 Open Access
 Total Downloads : 233
 Authors : Edsel B. Calica, Jude Anthony O. Billiones , Allan Joseph V. Jumaquio , Viel E. Villalon
 Paper ID : IJERTV6IS060146
 Volume & Issue : Volume 06, Issue 06 (June 2017)
 Published (First Online): 06062017
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Optimization of the Recovery Parameters of Poly (Ethylene Terephthalate) Depolymerization through Aminolysis in the Presence of an Organotin Catalyst
Edsel B. Calica
Instructor III, Chemical Engineering Department University of Santo Tomas
Manila City, Philippines
Allan Joseph V. Jumaquio
Student, Chemical Engineering Department University of Santo Tomas
Manila City, Philippines
Jude Anthony O. Billiones
Student, Chemical Engineering Department University of Santo Tomas
Manila City, Philippines
Viel E. Villalon
Student, Chemical Engineering Department University of Santo Tomas
Manila City, Philippines
AbstractPlastics had been of good use in various industries. However, poly(ethylene terephthalate) (PET) plastic take a long time to decompose, hence, need to recycle PET waste must be taken into consideration. Chemical recycling is one of the most effective methods of plastic recycling and one type of this is aminolysis which yields terephthalic diamines which are used as stabilizers for the manufacture of Low Density Polyethylene (LDPE). This study aimed to optimize the recovery parameters of PET depolymerization through aminolysis by total reflux condensation with ethanolamine (EA) in the presence of an organotin catalyst specifically Dibutyltin Oxide (DBTO) by varying the catalystPET ratio, PETEthanolamine molar ratio and reaction time. A mathematical model that would predict the yield of Bis(2hydroxy ethylene) terephthalamide (BHETA) was deduced. The product was subjected to Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) in order to confirm the identity of BHETA. The generated model was given as Yield (%) = 204.8 40.7 (Time) + 29.7 (CatalystPET ratio) 1040 (PETEthanolamine ratio + 212.9 (Time) (PETEthanolamine ratio) and optimized values of the chosen parameters were 6 hours of reaction time,

w/w catalystPET ratio and 0.25 molar ratio of PET Ethanolamine. Recovery using the optimum values produced a 42.184% BHETA yield. The FTIR spectra confirmed the presence of peaks corresponding to functional groups that comprise BHETA and DSC results show that the melting point of the product sample was within the range of BHETA compound.
Keywords Chemical recycling, Depolymerization, Aminolysis, Ethanolamine, Bis(2hydroxy ethylene) terephthalamide, Dibutyltin Oxide (DBTO)

INTRODUCTION
Due to its versatility, plastics had provided our generation with convenience through varied applications. Plastics are generally inexpensive, lightweight materials having good strength and durability, and offer a good resistant against gases and other chemicals. Moreover, thermoplastics are plastics that may be reformed after heating. Because of these
physical and mechanical properties, plastics became one of the most widely used packaging materials for food and beverages. However, PET plastics take a long time to decompose in an ecosystem due to its molecular structure; hence, the PET waste quantities are increasing dramatically [1]. This problem motivated the researchers to explore the possible recycling strategies that would help lessen pollution brought about by plastic wastes.
PET recycling can be classified into four categories according to the manner of recycling namely primary, secondary, tertiary and quaternary. Primary recycling simply is reusing the material without altering the product. Secondary recycling, also known as mechanical recycling, is achieved by cutting or grinding, melting, and reforming the plastic waste mixtures. Chemical recycling involves completely breaking down a product into its monomers by means of chemical processes. Lastly, quaternary recycling uses combustion or incineration to recover energy from plastic products [2].
Chemical recycling, also known as depolymerization, should be promoted among other recycling techniques because it conforms to the principles of sustainable development by being able to produce raw materials. Furthermore, chemical recycling also lessens the production of virgin polyethylene for the manufacture different thermoplastic products, thus, reducing the potential amount of plastic waste generated.
Aminolysis is a method of depolymerization of PET which, compared to other depolymerization techniques, has been least investigated [3]. This technique involves the degradation of PET by an aqueous amine in the presence or absence of an organotin catalyst [4]. This process yields terephthalic diamines which are used as stabilizers for low density polyethylene (LDPE).
In this study, postconsumer PET bottles were reacted with ethanolamine with organotin oxide catalyst in order to produce the yield, bis(2hydroxy ethylene) terephthalamide (BHETA).The main objective of this study was to determine the effectiveness of ethanolamine (EA) in the aminolysis of poly(ethylene terephthalate) in the presence of Dibutyltin Oxide as an organotin catalyst.
Specifically, the study aimed to:

chemically recycle PET through laboratory scale aminolysis under ambient conditions;

confirm the presence and purity of BHETA in the end product; and

deduce a mathematical model on the process parameters considered such as PETcatalyst ratio, PET EA ratio, and reaction time to identify the optimal recovery of BHETA.


METHODOLOGY
Raw Materials

PET Bottles
Approximately 30 pieces of empty postconsumer 350 ml natures spring bottles, collected inside the vicinity of the University of Santo Tomas, were used in the study. Labels and caps were removed. After collecting, the bottles were washed with dishwashing liquid and water, and were sundried for 30 minutes. The bottles were cut approximately to one mm by one mm (1mm x 1mm) chips.

Ethanolamine solution
Concentrated solution (> 99%) of ethanolamine was purchased at Belman Laboratories in Quezon City, Philippines. The concentration of the aqueous solution prepared was 20% by volume. It was done by adding 2.52 ml,
3.36 ml and 5.04 ml of water to 0.63 ml, 0.84 ml and 1.26 ml of ethanolamine, respectively.

Dibutyltin oxide (DBTO)
The catalyst was also purchased at Belman Laboratories. The amount used for the experiment was based on the desired catalystPET weight ratio which varied from 0.25, 0.50 and 0.75, the same weight ratios as with those used by Parab et al. (2012).

Formulation of the Solution for Depolymerization
Depolymerization of PET was performed with varying PETethanolamine molar ratio, DBTOPET ratios and reaction time. Half a gram of PET was used for each reaction. All reaction formulations for the 17 runs are shown in Table 1. The reaction time varies from four, five and six hours. The catalystPET weight ratio varies from 0.25, 0.5 and 0.75 and the PETethanolamine molar ratio varies from 0.125, 0.1875 and 0.25. As an example, the reaction parameters for the first run were five hours of reaction time, 0.25 grams of catalysts and 0.84 milliliter of pure ethanolamine.
Two preset combination runs were required by Box Behnken as base line for the 17 runs. The first reference run has a combination of four hours reaction time, 0.125 grams of catalysts and 0.84 ml of ethanolamine. The second reference run has a combination of six hours reaction time, 0.125 grams of catalyst and 0.84 ml of ethanolamine. Half a gram of PET was used for both reactions.
Experimental Procedure

Depolymerization (Aminolysis)
The PET flakes, ethanolamine solution, ad the catalyst were mixed together in a threeneck flask under total reflux condensation. The mixture was subjected to heating at 120 130 degrees Celsius and constant stirring of the oil bath at 500 rpm for homogeneity purposes. Two ml of water was added and the temperature was recorded in 30minute intervals with respect to the reaction time.

Cooling of the mixture.
At the end of every reaction, the mixture was allowed to cool under room temperature until the mixture reached temperatures between 5060 degrees Celsius. The cooled mixture was then subjected inside a household refrigerator for 24 hoursFirst, confirm that you have the correct template for your paper size. This template has been tailored for output on the A4 paper size. If you are using US lettersized paper, please close this file and download the file MSW_USltr_format.

Filtration and precipitation of product
The reaction mixture was filtered using a preweighed grade 40 Whatman filter paper and the product was obtained by precipitation.
Primary Residue. The residue obtained from the first filtration process contained the unreacted PET flakes. It was washed twice with five ml distilled water and oven dried at 80 degrees Celsius for two hours.
Primary Filtrate. The primary filtrate contained the BHETA, ethylene glycol, water and catalyst. The main product, bis(2hydroxy ethylene)terephthalamide (BHETA), was precipitated in powdered form by freezing the mixture inside a household refrigerator at 0Â°C for 24 hours. The precipitate obtained was again filtered to separate BHETA from the water, ethylene glycol and catalyst.
Secondary Residue. The secondary residue contained the product BHETA that underwent the determination of the yield.
Table 1. Reaction Formulations for the Aminolysis of PET
Run
Time (hours)
Catalyst PET Ratio
(w/w)
PETEthanolamine molar ratio
Weight of Catalyst
(grams)
Volume of Pure Ethanolamine (mL)
1
5
0.50
0.1875
0.250
0.84
2
5
0.75
0.2500
0.375
0.63
3
5
0.50
0.1875
0.250
0.84
4
4
0.75
0.1875
0.375
0.84
5
5
0.50
0.1875
0.250
0.84
6
6
0.50
0.2500
0.250
0.63
7
5
0.50
0.1875
0.250
0.84
8
5
0.25
0.1250
0.125
1.26
9
4
0.50
0.1875
0.250
0.63
10
5
0.25
0.2500
0.125
0.63
11
5
0.75
0.1250
0.375
1.26
12
5
0.50
0.1875
0.250
0.84
13
6
0.50
0.1250
0.250
1.26
14
4
0.50
0.1250
0.250
1.26
15
4
0.25
0.1875
0.125
0.84
16
6
0.75
0.1875
0.375
0.84
17
6
0.25
0.1875
0.125
0.84
Preset 1
4
0.25
0.1875
0.125
0.84
Preset 2
6
0.25
0.1875
0.125
0.84

Yield recovery
The primary filtrate was boiled for 30 minutes in a water bath. Crystals of BHETA were produced by freezing the boiled primary filtrate inside a household refrigerator at 0Â°C for 24 hours.

Determination of the yield.
The secondary residue was dried in an oven dryer at 80 degrees Celsius. The weight of the empty filter paper and the dried filter paper containing the secondary residue were determined using an Ohaus PA214 Pioneer analytical balance. The yield estimate was determined by weighing by difference and using the equation 1 below.
W

Model fitting and Analysis of Variance
A stepwise multiple regression analysis was used for determining the mathematical model that can predict the recovery of the desired product. The yield response from the experiment was plotted with its corresponding reaction time, catalystsPET ratio and PETethanolamine molar ratio for 17 runs using Design Expert 7.0 Box Behnken. The simulation and statistical diagnostic tests were performed using Minitab.


RESULTS AND DISCUSSION


Aminolysis
Postconsumer Natures Spring PET flakes were subjected to aminolysis in ethanolamine solution with dibutyltin oxide catalyst to produce bis(2hydroxyethylene) terephthalamide and ethylene glycol.
BHETAyield(%) BHETA x100
WBHETA,o
F. Characterization of the product
(Eqn.1)
In this reaction, two nucleophilic centers were found in ethanolamine, nitrogen and oxygen, with nitrogen being less electronegative than oxygen. Since the carbon atom in the ester linkage is highly positive, the less electronegative
A sample of BHETA was subjected to characterization through Fourier Transform Infrared Spectroscopy (FTIR) analysis and Differential Scanning Calorimetry to determine the compound present and the melting point of the polymer, respectively. Both tests were done at Thomas Aquinas Research Center in the University of Santo Tomas.
nitrogen attacks this carbon to form a more stable bond which forms BHETA and byproducts ethylene glycol and water.
For the degradation of PET in ethanolamine solution, 0.5 grams of postconsumer PET flakes were reacted. The catalyst to PET ratio, molar concentration of ethanolamine to PET ratio, and the reaction time were varied within the considered range in order to determine the optimal yield solution of the synthesis.
Table 2. % PET Degradation and % BHETA yield
Run 
% Degraded 
%Yield 
1 
25.655 
7.983 
2 
58.088 
34.557 
3 
42.546 
17.273 
4 
26.564 
11.051 
5 
52.347 
37.225 
6 
45.437 
32.847 
7 
22.308 
17.197 
8 
21.378 
15.881 
9 
16.101 
14.944 
10 
33.641 
22.284 
11 
81.525 
41.066 
12 
62.411 
10.753 
13 
48.252 
0.000 
14 
46.270 
35.321 
15 
9.551 
8.799 
16 
37.396 
25.272 
17 
5.929 
5.600 
Preset 1 
11.614 
8.616 
Preset 2 
59.120 
40.554 
In order to determine the percent degradation of PET, Equation 2 below was used.

Characterization of Products
In order to confirm that the identity of the product was BHETA, the purified sample was subjected to FTIR analysis. The results were compared to the FTIR spectrum of BHETA presented by Achilias (2007), et al.
According to the characteristics of the spectra, BHETA compound was identified from the significant peaks. Wavelengths approximately at 3365 cm1 and 1050 cm1 indicated the presence of hydroxyl particularly of a primary alcohol (CH2OH); wavelengths observed at 3300, 1650, 1550 and 1320 cm1 represented a Nsubstituted benzamide; the peaks appearing at 2850, 2880, 2950 and 3000 cm1 corresponded to stretches of alkyl groups such as CH2CH2. Therefore, the wavelengths identified above would correspond to the chemical compounds that comprise BHETA. All spectra obtained are similar to the FTIR spectrum presented by Achilias (2007), which confirmed the presence of the recovered BHETA.
Optimization

Mathematical Modeling
PET
(%) WPET ,0 WPET , f
x100
(Eqn.2)
In order to determine the optimal conditions to maximize the
deg redation
WPET ,0
BHETA recovery, the gathered experimental data were subjected to multiple regression analysis using Minitab. The
The yield of BHETA was calculated using Equation 3 shown below.
candidate variables for the stepwise selection of terms were set as Time, CatalystPET ratio, PETEthanolamine ratio, Time*Time, CatalystPET ratio*CatalystPET ratio, PET Ethanolamine ratio*PETEthanolamine ratio based from the
Where:
BHETAyield
(%)
WBHETA
WBHETA,o
x100
(Eqn.3)
Box Behnken design. Performing a stepwise selection of terms that maintains a hierarchical model at each step, the selected terms with their corresponding Pvalues are shown in Table 3.
WPET,0 = initial weight of PET WPET,f = final weight of PET
WBHETA = experimental weight of BHETA WBHETA,0 = theoretical weight of BHETA
Using the given equations, % PET Degradation and % BHETA yield was computed for each run given by Box Behnken design. Table 2 shows the summary of the data calculated as well as sample calculations. The highest % degradation and % yield was 81.525% and 41.066% respectively. Both of which were obtained from run 11 having five hours of reaction time, 0.75 CatalystPET ratio, and 0.125 PETEthanolamine molar ratio.
The scattered plot of PET degradation versus yield of BHETA on Figure 2 shows that most of the trials performed have relatively higher %PET degradation rather than %Yield. Given that all of the points lied just above the diagonal line, most results show that the recovery of BHETA from the solution was inadequate.
Table 3. Stepwise Selection Results
Terms
1st model
2nd model
Coefficient
Pvalue
Coefficient
P
value
Constant
20.67
20.67
Time
0.80
0.841
0.80
0.841
PETEthanolamine
ratio
1.55
0.700
1.55
0.700
(Time)( PET
Ethanolamine ratio)
13.31
0.036
13.31
0.036
CatalystPET ratio
7.42
0.086
Rsq
32.70%
49.18%
Rsq(adj)
11.80%
28.85%
Mallows Cp
6.83
5.15
The Mallows CP was evaluated in order to determine which among the two generated models would be the better equation to predict the future responses, as desired. It should be close to the numbers of predictors in the model which includes the constant. In this regard, the Mallows CP should be close to five taking into account the constant and the considered terms in the model which are Time, PETEthanolamine ratio, (Time)(PETEthanolamine ratio) and CatalystPET ratio. The second model has a Mallows CP of 5.15 which is closer to
5.00 as compared to the first model that has a Mallows CP of 6.83; thus, the second model is relatively precise and unbiased in estimating the true regression coefficients and predicting the future responses
Further analyzing the 2nd model using ANOVA in order to obtain the Pvalues of the predictors, the results show that the CatalystPET ratio has a Pvalue that is significant at 5% level of significance whereas a twoway interaction of Time and PETEthanolamine ratio has a Pvalue that is significant at 10% level of significance. The summary of the results is shown in Table 4.
By default, Minitab analyzes designs using coded units. Although it is convenient to think of the data in uncoded units, it is better to analyze the data using coded units. Coding simplifies comparisons of factors with different measurement scales. For example, Time versus CatalystPET ratio. In addition, using uncoded units often leads to multicollinearity among the terms in the model. This inflates the variability in the coefficient estimates and makes them difficult to interpret. Using coded units help to eliminate this problem.
Using uncoded units provides estimated regression coefficients in the original factor scales. However, it may change the results of the statistical tests of hypotheses used to determine whether each term is a significant predictor of the response. Table 5 shows the summary of coded coefficients used to derive the mathematical model.
On the other hand, the generated regression equation in uncoded units is:
Yield(%) = 204.8 40.7(Time) + 29.7(CatalystPET ratio)
1040(PETEthanolamine ratio + 212.9(Time)(PET Ethanolamine ratio) (Eqn. 4)
Lastly, multicollinearity test was performed through variance inflation factor. As per rule of thumb, the value of the VIF must be less than the value of 5 to depict that the variables considered were truly independent. The results of the VIF for the four respective models showed less than the value of 5. Hence, there was no multicollinearity among the variables.

Diagnostic Check
Performing a diagnostic check on the deduced mathematical model, the residuals generally appear to follow a straight line as shown in Fig 1. Given the said figure, there is no evidence of an outlier, skewness and nonnormality. Moreover, evaluating the test for normality using KolmogorovSmirnov, the residual is normal at 5% level of significance with pvalue > 0.150. Therefore, the error terms were normally distributed and this assumption check did not violate the normal distribution assumption.
Fig 1. Normality Test
Table 4. Analysis of Variance
Source
DF
Adj SS
Adj MS
F
Value
P
Value
Model
4
1173.19
293.298
2.42
0.117
Linear
3
465.01
155.005
1.28
0.334
Tim
1
5.11
5.114
0.04
0.841
CatalystPET ratio
1
440.79
440.787
3.64
0.086 *
PETEthanolamine
ratio
1
19.11
19.113
0.16
0.700
2Way Interaction
1
708.18
708.179
5.84
0.036
(Time)( PET
Ethanolamine ratio)
1
708.18
708.179
5.84
0.036
**
Error
10
1212.47
121.247
LackofFit
8
765.96
95.745
0.43
0.841
Pure Error
2
446.51
223.253
Total
14
2385.66
*Significant at 10% level of significance
**Significant at 5% level of significance
Fig 2. Plot of Residuals vs. Fitted Value
Table 5. Coded Coefficients
Term
Effect
Coefficient
TValue
PValue
VIF
Constant
20.67
7.27
0.000
Time
1.60
0.80
0.21
0.841
1.00
CatalystPET ratio
14.85
7.42
1.91
0.086
1.00
PETEthanolamine ratio
3.09
1.55
0.40
0.700
1.00
(Time)(PETEthanolamine
ratio)
26.61
13.31
2.42
0.036
1.00
Fig 2 shows the plot of Residuals vs. Fitted Value. Based from the said plot, the residuals appear to be randomly scattered about zero. Therefore, there is no evidence of non constant variance or outlier exists.
Optimization
PET
In order to determine the optimal conditions in attaining the maximum recovery of BHETA, the contour plot as shown in Fig 3 was established. It shows the distribution of the yield, while holding the catalyst ratio level at 0.5 as the center point. A greener hue signifies higher yield. Based on the contour plot, the combination of PETEthanolamine ratio and Time that will give the highest yield would be at the area where the PETEthanolamine ratio is at 0.14 and Time at 4 hours and PETEthanolamine ratio at 0.24 and Time at 6 hours.
Contour Plot of Yield (%) 1 vs PET, time
Yield (%)
0.24 1
< 6
6 12
0.22 12 18
18 24
24 30
0.20 > 30
Hold Values catalyst 0.5
0.18
0.16
0.14
4.0
4.5
5.0
time
5.5
6.0
Fig 3. Contour Plot of Yield vs and PETEthanolamine ratio and time
Optimization plot on Fig 4 shows the graph of predicted yield in each variable. The dash line indicates the target requirements. Red line indicates the intersection of the predicted yield line and the target requirements. The intersection shows the optimum level of each variable.
Several diagnostic checks above show that the model is viable in estimating the yield based from the given variable settings. Table 6 shows the optimum solutions based on the model derived.
Optimization uses the model to estimate the optimal variable settings. As the predicted responses to the target requirements would be closer, the value of the desirability would approach 1. Hence, based on the deduced model, the determined maximum yield are Time at 6 hours, CatalystPET ratio at 0.75 and PETEthanolamine ratio at 0.25.
Fig 4. Optimization Plot
Table 6. Optimum solutions based on the model
Solution
Time
CatalystPET Ratio
PETEthanolamine Ratio
Yield (%) Fit
Composite Desirability
1
6
0.75
0.25
42.1484
1.00000
2
5.91346
0.75
0.25
41.0661
1.00000
3
4
0.75
0.125
40.6560
0.99002
4
6
0.309112
0.25
29.0578
0.70759
5
4
0.321898
0.125
27.9451
0.68049
6
4.72984
0.75
0.207107
27.6696
0.67378
7
5.14943
0.75
0.180973
27.6079
0.67228
8
5.38632
0.661409
0.196799
26.1519
0.63682


CONCLUSION
A laboratory scale experiment was performed in order to determine the effectiveness of ethanolamine (EA) in the aminolysis of poly(ethylene) terephthalate (PET) depolymerization with the presence of dibutyltin oxide (DBTO) as an organotin catalyst. Process parameters such as PETcatalyst ratio, PETEA ratio and reaction time were varied throughout the investigation. The reaction was in total reflux at temperatures ranging from 120 – 130C. The gathered experimental data show that BHETA recovery is inadequate because the % PET degradation is relatively higher than the % yield. The identity of BHETA was verified through FTIR analysis and DSC spectroscopy. The significant peaks present in the FTIR analysis consists of the compounds that make up BHETA.

Based on the generated multiple regression equation yield = 204.8 40.7(Time) + 29.7(CatalystPET Ratio) – 1 040(PETEthanolamine Ratio) +212.9(Time)(PET Ethanolamine Ratio), maximum yield can be obtained when Time is at 6 hours, CatalystPET ratio at 0.75 and PET Ethanolamine at 0.25. These optimal variables shall result to a 42.148 4% yield.
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