Nano MgO catalyst for chemical depolymerization of polyethylene terephthalate (PET)

Transcription

1 DOI: /ijp Nano MgO catalyst for chemical depolymerization of polyethylene terephthalate (PET) Mohammed A. Alhussain Alzuhairi, Bassam Ibrahim Khalil, Rusul Salah Hadi Materials Engineering Department, University of Technology Abstract This paper focuses firstly on the production of monomers bis (2- hydroxyethyl) terephthalate (BHET) and oligomers by using two different form of MgO light active and Nano Magnesium oxide with different weight ratio (0.15, 0.25 and 0.5) by using chemical recycling glass condenser at 190 C. The second purpose is to study the effect of catalyst ratio, time of reaction and yield of products of the product. Elemental analysis for Carbon Hydrogen and Nitrogen (CHN), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) have been investigated. Results indicated the catalytic activity was found to correlate with surface area; however, LA MgO has shown an exceptional activity, still it is higher than Nano MgO in order to reduce the reaction time till 30 minutes instead of 7 hours without catalyst. The analysis of the thermograms has indicated the presence of various kinds of monomer, dimer and oligomers that are formed during the recycling; this is particularly evident due to new peaks indicating the formation of BHET monomer and oligomer of lower molecular masses. Key words Polyethylene terephthalate (PET), bis (2-hydroxyethyl) terephthalate, depolymerization, waste bottle plastic. Article info. Received: May Accepted: Sep Published: Mar اعاده البلورة الكيويائي لواده بولي اثلين تيريفثاالث )PET) باستخذام العاهل الوساعذ نانوهغنيسيوم اوكسايذ )MgO( هحوذ عبذالحسين الزهيري, بسام ابراهين خليل, رسل صالح هادي قسى ذسة ان اد, انصايعة انحك ن ش ة الخالصت انبحد ش ز انى ا اعاد جذ ز ق ا ان اء انبالسح ك ان ص ع ي ياد ب ن اذه ج زفراالت )PET) ح ث ا ي ان عش ف عذو تحهم ز ان بد ب ش س ان قت تعتبش يشكه يضشة ببنب ئ ح ث ذف انبحث انى اعبد انتذ ش انك بئ ببنبحث نق ب ان بء ي خالل ع ه (Glycolysis) باسحخذاو االذه كال ك ل ك ذ ب يع جى اضاف ع ي انع ايم ان ساعذ اال ل ا كس ذ ان غ س و ان ا ي انرا ا كس ذان غ س و انخف ف انفعال ب سب س يخحهف )0.5,0.15(,0.25 غى ببستخذاو ظبو يغهق صجبج بذسج حشاس )091( و. ال حاز ي ي ز ب س )2 ا ذر كس اذ م( ج ز فراالت انك ي ز Bis (2-hydroxyethyl) terephthalate.(bhet) بذنك ا حص ا ياد شذ ذ جسحخذو ف جطب قات عذ ذ ا ضا جححهم بس ن بذنك حهث يشكه انحه خ بسبب ق ا ان اء انبالسح ك ة. ايب ان ذف انثب دساس تأث ش سب انعبيم ان سبعذ, سي انحفاعم ا حاش ان اد ان اجص. انححه م نهع اصز كارب, ذر ش حز ش )CHN( ان سعشان بسح انتفبضه,(DSC( ي ظبس انتحه م انط ف )FTIR( انتحه م انحشاسي.(TGA( ان حائس انح حصه ا عه ا ا ا كس ذ ان غ س و انخف ف انفعال MgO( )LA اكثش فعبن ال اكبش يسبح سطح ي ا كس ذ ان غ س و ان ب ي نك ببنشغى ي رنك فب فعبن ا كس ذ انىغ س و ان ا ي ا ضا ش ذ شذا ح د قههث سي انحفاعم انى )01( دق ق بذل ي ) 7 (سبعبت بذ استخذاو ي اد يسبعذ. انححه م انحزاري حذد ش د ا اع يخحهف ي ان ي ز, انذا ش ان نك ي ز جك ث اذ اء اعاد انحذ ز ذا دن م عهى جك ي ي ز.(BHET( 85

2 Iraqi Journal of Physics, 2018 Mohammed A. Alhussain Alzuhairi, et al. Introduction Poly Ethylene Terephthalate (PET) is considered as polyester with functional ester groups that are cleaved by reagents, like acids, bases or water (hydrolysis), alcohols (alcoholysis), amines (aminolysis), ammonia (ammonolysis) and glycols (glycolysis). Two main standard processes of recycling post user PET exist: chemical recycling and mechanical recycling [1, 2]. The previous is most usually practiced and includes arranging, cleaning and drying post user PET before meltprocessing to create a new material. The research aims to study the chemical recycling, chemical recycling involves degradation of the polymer to its initial monomer, decontamination, and next following depolymerization to yield great quality plastic. Depolymerization methods for chemical recycling mostly contain methanolysis, hydrolysis, and glycolysis [3, 4], in the glycolysis reaction is the molecular degradation of PET polymer by glycol, basically by using ethylene glycol as solvent. The ester linkages of PET polymer are broken and replaced by hydroxyls terminals to give bis (2-hydroxyethyl terephthalate) (BHET), which is the raw material of producing PET. Which are usually shown at elevated temperature in the presence of catalysts such metal acetates (Zn, Co, Pb and Mn) as catalysts [5]. Studies on the kinetics of PET glycolysis have revealed that glycolysis without using a catalyst seems to be very slow and complete depolymerization of PET to BHET cannot be achieved. In addition, it yields an end product which has significant amount of other oligomers in addition to the BHET monomer. These results face difficulty in recovering the BHET monomer when it is the aimed product. So, the efforts of recent research is directed towards duplicating the rate and BHET monomer yielded through the development of highly efficient catalysts and other techniques, in addition to optimizing the reaction conditions (such as time, temperature, PET/catalyst ratio, PET/EG ratio) [6, 7]. In the current paper two series of catalysts Light Active Magnesium Oxide (LA MgO) and nano Magnesium oxide (Nano MgO) has been investigated with PET using Close system with reflux. The main purpose of this paper is to evaluate the effect of catalyst ratio, time of reaction, yield of products and characterization of the products by FTIR, DSC, CHN and AFM. Materials and methods A. Chemical materials The procedure that has been devised in this study is that Waste (PET) bottles have to be cleaned then dried; they are cut into square chips to particle size of (3 3) mm. The whole chemicals used are of high purity degree and are used without purification. Ethylene glycol (EG), which is used as a solvent for glycolysis and supplied by (AAG, Espana). Light active magnesium oxide RA 70 (LA MgO) is supplied by (Parchem, USA) whereas Nano magnesium oxide (N MgO) is supplied by (SkySpring Nanomaterials, USA) which is used as a catalysis. B. Experimental methods Firstly, the mixture of 100 gm of PET, (4:1, EG: PET, molar ratio) without catalyst is heated in 190 º C for 7 hours and with Zinc acetate for 5 hours until it becomes in the wax state. The heat treatment included totally condensation (reflux) in close system with (no material losing), by using glass condenser water cooling, 86

3 then separation of unreacted ethylene glycol solution from the previous mixture. After reaction, the reactor could be cooled to room temperature. In order to purify the product from EG, about 200 ml of water that is distilled is being added to the product mixture with heating and mixing by magnetic stirrer hot plate, which would dissolve the remaining EG. The product was cooled to room temperature and the mixture was filtered. Whereas crystalline flakes of BHET monomers were being formed in the filtrate, after that they were separated by filtration method using (Buchner funnel) and dried in an oven at 60 º C. In the second step, light active MgO is used as catalyst in different percentage (0.05, 0.15, 0.25, 0.5) % and Nano MgO is used as catalyst in different ratio (0.01, 0.025, 0.04, 0.15, 0.25 & 0.5) gm. Fig. 1 shows the product after chemical degradation of PET In the current paper, the measurement of the catalytic activity of catalysts on glycolysis of PET was done through testing the conversion of PET (%) in addition to selecting BHET (%), which were calculated in Eqs. (1). BHET Yield%= (1) A B Fig. 1: A- Product before filtration, B- product after purification. Moreover, EG attacks the ester group of PET and degrades the polymer into an oligomer, a dimer, and monomer BHET. The catalysts (LA MgO) and (Nano MgO) were used in the glycolysis of PET to test their catalytic activity and yield percentage, time reaction, color and melting point of these products are presented in Table 1. To verify the chemical structure of the reaction product, the monomer BHET was separated in pure crystalline and an analysis of elemental (CHN) for the products is used LA MgO and Nano MgO as catalyst in depolymerization PET. Table 2 demonstrates the obtained results, when comparing the ratio of hydrogen and carbon of the products. It has been found that there is a similarity between the theory ratio for hydrogen and carbon at monomer BHET and dimer BHET. 87

4 Iraqi Journal of Physics, 2018 Mohammed A. Alhussain Alzuhairi, et al. Table 1: Yield percentage, time reaction, color and melting point of products. Catalyst Reaction Physical Yield Melting point wt % MgO time, min state % C LA LA LA LA Nano Crystals Nano white Nano Nano Nano Nano Table 2: Elemental analysis chn for products depolymerization of PET. Catalyst MgO C% H% O% N% S% Molar mass g mol 1 Nano LA BHET Monomer BHET Dimer C. Characterizations The particle size distribution of these powders was carried out by Atomic Force Microscopy (AFM) PHYWE (GmbH und Co. KG). Furthermore, Melting points were recorded by using Stuart Digital melting points- SMP 20 (UK). The elemental analyses of the carbon, hydrogen and nitrogen contents were determined by using a Euro EA CHN 3000 (Italy). FTIR spectra data were obtained by FTIR Spectrometer. Model: WQF-520A (china) in the wave number range of cm -1 which was included in KBr discs. In addition, DSC can be performed on the instrument of a Linseis DSC, in that the size of the sample around 10 mg, under a nitrogen stream with a heating/cooling rate of 10 C min -1 (which is considered standard) in the temperature range of about C. Finally, the crystallization temperature (Tc) and the melting (Tm) of the BHET monomer, in addition the obtained PET were considered as the onset temperatures. Results and discussion In PET glycolysis, PET chains react with (EG) to produce a monomer, BHET. The overall reaction scheme of glycol with an ester bond in the PET chain shown in Fig. 2 [8]. Fig.3 (a & b) shows the particle size distribution of Light active magnesium oxide and Nano magnesium oxide, respectively. In Fig. 4, it is easy to notice that time is reduced through using Nano MgO & LA MgO, Nano MgO as catalyst provided better conversion of PET to monomer and dimer BHET in comparison to LA MgO catalysts. Where few amounts of 0.01 gm is used from Nano MgO to get a good yield in the perfect time. In addition, the BHET yield is increased dramatically in the presence of a catalyst and decreased reaction time. The BHET yield is decreased with decreasing catalyst 88

5 ratio. Nano MgO with a small diameter 60 nm lead to the better distribution due to their high specific surface areas and specific pore volumes and highest catalytic activity. This is resulted in the highest monomer yield [9]. Fig. 2: Scheme reaction de-polymerization of PET. Fig. 3: (a) AFM Test of the LA MgO & (b) is Nano MgO. 89

6 Iraqi Journal of Physics, 2018 Mohammed A. Alhussain Alzuhairi, et al. Fig. 4: Time reduction through Nano & LA MgO. Table 3 shows infrared spectroscopic band (cm -1 ) of PET bottles data & product after depolymerized. Whereas Fig. 5(a) presents the FTIR spectra of PET for waste PET bottles and the peaks which have been obtained for PET, ND is nearly in agreement with the reported one previously mentioned in the literatures [11]. Table 3: Infrared spectroscopic band (cm -1 ) data of pet bottles & product after depolymerized. Band name Bottle PET BHET, Nano BHET, LA O-H band C-H Asymm & & & 2875 C=O Ester Ar C-C bond C-H bending C-H def. in alkane C-H def. in alkane C-C-O Asymm O-C-C Asymm C-H Bend. Inplane Ar C-H out of plane Ar C-H Wagg After the de-polymerization, the chain lengths of PET are degraded and configured to monomer BHET. This will lead to different modification number of ( CH) groups that leading to quite changes of significant intensity of the bands. Additionally, in the presented spectra Figs. 5 (b and c), the presence indicating of OH groups that related to the formation of oligomers in the bands at 3510 cm -1 and 3421 cm 1 (acid hydroxy and alcohol end of groups) and monomer BHET due to the chemical bonds was breaking. Glycolysis of PET with ethylene glycol mainly producing a monomer BHET along with others (dimers and oligomers) [10]. The FTIR in spectra for product (BHET) by using light active MgO in Fig.6 shows clearly band of -OH at 3421 cm 1, at 2958 cm 1 for alkyl CH, C=O stretching at 1720 cm 1 and at 1504 cm 1 for aryl group, present in 90

7 monomer of BHET and the FTIR in spectra for product (BHET) by using Nano MgO in Fig. 5 (c) shows clearly - OH band at 3421 cm 1, 2962 cm 1 for alkyl CH, C=O stretching at 1724 cm 1 and 1508 cm 1 for aryl group, present in monomer BHET. Fig.6(a) illustrates the DSC thermograms obtained for the degradation of waste water bottle PET. It can be observed that glass transition temperature (Tg) (83 C), crystalline temperature (146 C) melting temperatures are (255 C) of PET. The value of Tg and Tm which has been obtained for PET, is nearly in agreement with that reported previously in the literatures Tg between (67 to 80 C), Tc (150 C) and a Tm of (267 C) [12]. In TGA thermograms for waste water bottle PET, the mass-loss were observed in the thermal degradation at the beginning in C and losing % of its initial mass. (a) (b). (c) Fig. 5: (a) FTIR spectra for (PET), (b) for product (BHET) by LA. & (c) for product (BHET) by nano. DSC thermograms of PET that melting temperatures are glycolysis products (BHET) are (151.7 C) of PET products obtained presented in Fig. 6b by using Nano MgO as catalyst. It can be observed after glycolysis. Both DSc and TGA thermograms mass-loss were observed 91

8 Iraqi Journal of Physics, 2018 Mohammed A. Alhussain Alzuhairi, et al. beginning of the thermal degradation in C and losing % of its initial. mass DSC thermograms of PET glycolysis products (BHET) are presented in Fig. 6c by using LA MgO as catalyst. It can be observed that melting temperatures are (153.5 C) of PET products obtained after glycolysis and TGA thermograms in the thermal degradation at the beginning in C and losing % of its initial mass.. The analysis of the thermograms has indicate the presence of various kinds of monomer, dimer and oligomers that are formed during the recycling, this is particularly evident due to new peaks indicating the formation of BHET monomer and oligomer of lower molecular masses. (a) (b) Fig. 6: (a) DSC for (PET), (b) for BHET by Nano MgO (c) for BHET by LA catalyst. (c) 92

9 Conclusions From the results of the investigation, it has been found that there are various quantity of catalyst used in this work, i.e. the results of yield were convergent. Several metal catalysts quantity was screened for the depolymerization of PET. Generally speaking, the catalytic activity was found to correlate with surface area; however, LA MgO has shown an exceptional activity higher than the stronger Nano MgO in order to reduce the reaction time till 30 minutes instead of 7 hours without catalyst. These fundamental investigations of organic catalysts will be beneficial to the progress of PET waste in chemical recycling. Throughout the current research, it can be observed that the particle size distribution of catalysts was carried out by Atomic Force Microscopy (AFM), the result of particle size distribution of Light active magnesium oxide is shown the average value of diameter is (104 nm). While the result of particle size distribution of Nano magnesium oxide is shown the average value diameter is (60 nm). The result of (FTIR) shows group of (-OH) and this indicated to formation of monomer (BHET), and result of (DSC) shows that not presented of glass temperature (Tg) or crystallization temperature (Tc) and that indicated to formation of monomer (BHET). References [1] D. Paszun, T. Spychaj, Ind. Eng. Chem. Res, 36 (1997) [2] S. D. Mancini, M. Zanin, Mat. Res., 2, 33 (1999) [3] D. Carta, G. Cao, C. D Angeli, Environ Sci. Pollut. Res., 10 (2003) [4] Alzuhairi, Mohammed, Ahmed MH Al-Ghaban, ZANCO Journal of Pure and Applied Sciences, 28, 2 (2016) [5] M. Zhu, S. Li, Z. Li, X. Lu, S. Zhang, Chemical engineering Journal, 185 (2012) [6] J. Campanelli, M. Kamal, D. Cooper, J. Appl. Polym. Sci., 11, 54, (1994b) [7] Mohammad Khoonkari, Amir H. H., S. Yahya, Sh. Khadijeh, G. Abolfazl, International Journal of Polymer Science, 11, 2015 (2015) [8] Park, Sang Ho, Kim, Seong Hun., Fashion and Textiles, 1, 1 (2014) [9] R. Wi, M. Imran, K. G. Lee, S. H. Yoon, B. G. Cho, D. H. Kim, Journal of Nanoscience and Nanotechnology, 11, 7 (2011) [10] S. Vijayakumar & P. Rajakumar, International Letters of Chemistry, Physics and Astronomy, 4 (2012) [11] A. Ptiček Siročić, A. Fijačko, Z. Hrnjak-Murgić, Chemical and Biochemical Engineering Quarterly, 27, 1 (2013) [12] Demirel, Bilal, A. Yaras, Hüseyin Elcicek, Journal of Journal of Bau Fen Bil. Enst. Dergisi Cilt., 13, (2011)