Elsevier

Fuel

Volume 285, 1 February 2021, 119155
Fuel

Full Length Article
A Cu doped TiO2 catalyst mediated Catalytic Thermo Liquefaction (CTL) of polyolefinic plastic waste into hydrocarbon oil

https://doi.org/10.1016/j.fuel.2020.119155Get rights and content

Highlights

  • Less stringent reaction conditions [300 °C, 30 min.].

  • Selective, inexpensive and recyclable catalyst.

  • Maximum carbon recovery in form of HC-Oil.

  • Energy enriched hydrocarbon oil can be used for multiple energy applications.

  • Multiple plastic waste LDPE, HDPE, PE and PP etc can be processed.

Abstract

Plastic waste has been identified as a potent feedstock for liquefaction to produce hydrocarbon liquid oil (HC-Oil) by employing Catalytic Thermo Liquefaction (CTL). The resulting process for liquefaction of plastic was termed as Poly-Urja process and produced hydrocarbon oil was termed as HC-Oil. The CTL explores copper doped TiO2 (Cu@TiO2) catalyst as a selective, robust, non-toxic, inexpensive and promising material for liquefaction of polyolefinic plastic waste with minimum char and gas formation. The use of simple, non-expensive and non-complex co-precipitation method has provided a series of Cu@TiO2 catalysts with variable composition of the metal. Of the synthesized catalysts, Cu@TiO2 with 5% metal loading gave maximum conversion and yield of HC-Oil in laboratory batch reactor. The physicochemical and surface morphological properties of the catalyst were studied by using ATR-FTIR, XRD, SEM-EDX, BET and ICP-MS. Process intensification study was conducted to obtain maximum conversion and yield. The intensified CTL process gave >85% conversion and >80% yield of HC-Oil at less stringent conditions. HC-Oil is a carbon rich substrate comprises of 75–85% carbon, 5–15% hydrogen, 5–10% other elements and have a calorific value of ~42 MJ/kg thus it can be used for multiple applications of energy, fuels and chemicals etc. Physicochemical characterization of HC-Oil showed the presence of long and short; straight and branched chains of hydrocarbons (C8-C28). Moreover, CTL can convert any combination of plastic waste into HC-Oil with minimum carbon loss and >80% yield. Thus, the CTL process for polyolefinic waste provides an efficient, sustainable and environmentally friendly alternative to convert plastic waste into energy.

Introduction

Plastics are one of the fastest-growing and demanding versatile materials with a broad array of applications. The characteristic non-biodegradability, relatively low cost, lightweight, non-reactivity, easy molding, rust-free, reusability and recyclability have increased its popularity and use in multiple sectors [1]. However, plastics has provided a potential replacement to wood, glass, metals and ceramics etc. Conversely, the uncontrolled use and inefficient disposal has created a serious challenges associated with plastic pollution [2]. Out of total plastic waste generated, 91% was not recycled and get discarded into landfills or littered in open environment including rivers, lakes and oceans [3]. Physically, plastic waste remains on the surface in undegraded form for many years, thus it clogs the waterways and creates problems of water dissemination [4]. In addition to this, about 60% of plastic waste floats on the water surface and due to long term sunlight exposure, temperature variations and waves current, it degrades into microparticles which harm foodchain [5]. Thus, the safe, eco-friendly and cost-effective management of plastic waste becomes an urgent need as well as a challenge to modern society.

Recycling and reuse offers an affordable alternative to manage plastic waste but only limited varieties of plastics can be operated by this approach [6]. However, due to variation in physicochemical properties, multiple times recyclability is not possible [7]. Thus, the energy recovery from plastic waste can be seen as one of the attractive alternative. The high carbon and hydrogen content in plastic waste projects it as a potential feedstock for energy generation [8], [9]. Incineration and Refuse Derived Fuel (RDF) burning are traditional technologies used for treatment of plastic waste. But the incineration and RDF burning releases toxic chemicals and gases such as hydrochloric acid, sulfur dioxide, dioxins, furans and heavy metals as well as particulates which causes signifcant hazard to the environment [10]. Since last few decades, most popular thermochemical techniques such as pyrolysis, hydroliquefcation, and gasification etc. were explored for the energy recovery from plastic waste [11]. Papuga et al. have reported 32.8% yield of liquid product through thermal pyrolysis of mixed plastic at 500 °C [12]. Metecan et al. have used hydroliquefaction process for converion of plastics into naphtha at 450 °C under cold hydrogen pressure of 5 MPa [13]. Ishii et al. gasified the plastics thermally with flame retardant at about 1200 °C [14]. However, these processes are associated with several drawbacks such as (a) extensive energy requirement, (b) high capital cost, (c) low productivity and (d) low energy efficiency [15], [16]. The integrtion of catalysts can overcome these drawback to some extent. Thus, of the possible thermochemical methods, catalytic pyrolysis was reported as a most promising option to convert the plastic waste into liquid oil [17].

In case of catalytic pyrolysis, catalyst plays a crucial role to improve the process efficiency by reducing the activation energy, reaction temperature and time. Moreover, catalytic pyrolysis has several process economical benefits such as low energy requirement as compared to pyrolysis and gasification, maximum energy efficiency, high conversion and better oil yield and low GHGs (green house gases) emission [18]. But, uncontrolled cracking of C–C bond at elevated temperature, long residence time, acidity, porosity and pore size of catalyst are some of the factors which are responsible for decrease in the yield of pyrolysis oil and increase in char and gases formation [19]. In order to maximize the process efficiency of catalytic pyrolysis process, extensive research has been conveyed by advancement in the acidity, porosity, pore size of the catalyst for enhancing selectivity and lowering residence time and temperature etc. [20]. Thus, a wide range of catalysts such as Fluid Catalytic Cracking (FCC) catalyst, H-ZSM-5, ultra-stable Y (USY) zeolite, natural zeolite, were tested for catalytic pyrolysis of plastic waste [21], [22], [23], [24], [25], [26], [27]. Several plastics have been studied for liquefaction via pyrolysis by exploring number of catalysts under different operating conditions.

The catalytic pyrolysis of polyethylene and polystyrene have been reported by using zeolite, silica-alumina, H-ZSM-5 and S-ZrO2 catalysts [22], [23]. Fernandes et al. [24] have reported SAPO-37 molecular sieves as a catalyst for polyethylene degradation. Achilias et al. [25] have used FCC catalyst for catalytic pyrolysis of LDPE (Low-density Polyethylene), HDPE (High-density Polyethylene) and PP (Polypropylene) at 450 °C that resulted in 65% oil yield. Sriningsih et al. [26] have tested fuel production from LDPE using natural zeolite supported Ni, Mo and Co catalyst to obtain 72% oil yield at 350 °C. Kassargy et al. [24] have reported the catalytic pyrolysis of polyethylene and PP using USY zeolite as the catalyst at 450 °C with 71% and 82% oil yield, respectively [27]. Miandad et al. [28] have studied catalytic pyrolysis of the plastic waste at 450 °C to obtain 54% oil yield using activated natural zeolites and 50% oil yield using synthetic zeolite. Some of the metal salts, oxides, transition metal-doped metal oxides (ZnO, MgO, CaC2, BaTiO3, Pb/BaTiO3, Co/BaTiO3 and Pb-Co/BaTiO3) were also reported as the catalysts for pyrolysis of plastic waste to obtain >80% oil yield at >400 °C [18], [29], [30], [31], [32]. Although the catalytic pyrolysis seems a relatively better process than the available options but still there are several challenges and barriers in theirs industrial viability such as a) relatively stringent conditions (>400 °C), b) formation of char and gases c) low oil yield and d) recyclability and reuse of catalyst etc. The associated drawbacks can be conquered by integrating selective and efficient catalysts. Thus, researchers are directed in search of selective, robust, non-toxic, inexpensive and abundantly available metal catalysts for the production of liquid fuel from plastic waste.

In this context, the present manuscript has introduced, Cu doped TiO2 assisted Catalytic Thermo Liquefaction (CTL) which is further abbreviated as the “Poly-Urja” process for conversion of plastic waste into hydrocarbon liquid abbreviated as “HC-Oil ” (The acronym Poly depicts the Polymer and Urja depicts energy) at non-stringent reaction conditions. The synthesised Cu@TiO2 was found as a robust, selective, non-toxic, cheap and recyclable catalyst for present Poly-Urja process. The synthesized catalyst was characterized for its chemical and surface morphological properties by using analytical techniques ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy), XRD (X-Ray Diffraction analysis), SEM-EDX (Scanning Electron Microscopy & Energy Dispersive X-ray Spectroscopy), and BET (Brunauer-Emmett-Teller) surface area etc. The process intensification study was conducted by using transparent LDPE bags as a classical feed to study the influence of temperature, time, catalyst loading, metal loading, feedstock composition and catalyst reusability/regeneration on conversion and yield of HC-Oil. Different types of waste plastics were collected from the local area in the vicinity and tested for CTL. HC-Oil derived from the CTL process was characterized by GC–MS, ATR-FTIR, elemental analysis, TGA-DSC (Thermogravimetric analysis- Differential Scanning Calorimetry) and calorific value analysis.

Section snippets

Materials

Plastic waste acquired from nearby areas of Matunga, Mumbai (India) washed with water to remove dirt and then cut down into small pieces of approximately 1.0 X 1.0 cm size. All types of plastic waste samples were characterized by ultimate analysis and calorimetry as shown (Table 1). The copper nitrate trihydrate extra pure (98%) and Titanium tetra isopropoxide (TTIP) extra pure procured from Sisco Research Laboratories Pvt. Ltd., analytical grade aqueous ammonia solution about 25%, laboratory

Proximate and ultimate analysis of plastic waste

The plastic packaging materials and daily used plastics that contributes to the generation of plastic waste such as transparrnt LDPE bags, blue LDPE bags, black LDPE bags, PP straws and wrappers were sourced from local market and surrounding areas and subjected to ultimate analysis. The collected plastic materials were cleaned with soap for removing soil, dirt etc. and dried before subjecting to analysis. In detail characterization of different plastics used for liquefaction is shown (Table 1).

Process intensification studies

Reaction parameters such as reaction temperature, retention time, catalyst concentration, metal loading, and feed composition could affect the productivity of catalytic liquefaction process. Some other significant parameters are reactor heating rate, the particle size of feedstock etc. [44]. Thus, to study the influence of variables of reaction conditions to obtain intensified operating conditions with high conversion and yield following parameters were studied and optimized.

Reuse and recyclability of the catalyst

The development of economic and viable catalytic processes at bulk scale implicated with recyclability of catalyst and other cost consuming reagents [52]. In the present CTL study, the recyclability of the catalyst was studied by separating it from the reaction mixture and reused for further CTL run. The CTL catalyst was recovered from the reaction mixture simply by vacuum filtration. The catalyst recyclability study was conducted for four consecutive recycle runs. The influence of recycled

Characterization of HC-Oil

The characterization of HC-Oil is very important to the study its further fuel and energy applications. The characterization of HC-Oil was conducted by using ATR-FTIR, elemental analysis, calorific value, TGA-DSC and GC–MS.

Conclusions

The PolyUrja process explores new horizons for the conversion of different types of plastic waste into carbon densified HC-Oil. The present research work has integrated the Cu@TiO2 catalyst for CTL of different types of polyolefnic plastic waste into HC-Oil with maximum carbon recovery. CTL process offers several remarkable advantages such as (a) requires less stringent condition (300 °C and 30 min.), (b) maximum carbon recovery, (c) >85% feedstock conversion, (d) >80% HC-Oil Yield, (e)

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors are grateful for the financial support from the Department of Biotechnology (DBT), Ministry of Science and Technology India.

References (53)

  • D.S. Achilias et al.

    Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP)

    J Hazard Mater

    (2007)
  • C. Kassargy et al.

    Experimental study of catalytic pyrolysis of polyethylene and polypropylene over USY zeolite and separation to gasoline and diesel-like fuels

    J Anal Appl Pyrolysis

    (2017)
  • R. Miandad et al.

    Plastic waste to liquid oil through catalytic pyrolysis using natural and synthetic zeolite catalysts

    Waste Manag

    (2017)
  • A. López et al.

    Catalytic pyrolysis of plastic wastes with two different types of catalysts: ZSM-5 zeolite and Red Mud

    Appl Catal B Environ

    (2011)
  • M.V. Singh

    Waste and virgin high-density poly(ethylene) into renewable hydrocarbons fuel by pyrolysis-catalytic cracking with a CoCO3 catalyst

    J Anal Appl Pyrolysis

    (2018)
  • I. Ahmad et al.

    Catalytic efficiency of some novel nanostructured heterogeneous solid catalysts in pyrolysis of HDPE

    Polym Degrad Stab

    (2013)
  • D.K. Chattopadhyay et al.

    Thermal stability and flame retardancy of polyurethanes

    Prog Polym Sci

    (2009)
  • I. Ganesh et al.

    Preparation and characterization of Cu-doped TiO 2 materials for electrochemical, photoelectrochemical, and photocatalytic applications

    Appl Surf Sci

    (2014)
  • I. Ganesh et al.

    Preparation and characterization of Co-doped TiO 2 materials for solar light induced current and photocatalytic applications

    Mater Chem Phys

    (2012)
  • F. Bensouici et al.

    Optical, structural and photocatalysis properties of Cu-doped TiO 2 thin films

    Appl Surf Sci

    (2017)
  • S. Sun et al.

    Impact of Surface Area in Evaluation of Catalyst Activity

    Joule

    (2018)
  • R. Govindaraj et al.

    Synthesis of nanocrystalline TiO2 nanorods via hydrothermal method: An efficient photoanode material for dye sensitized solar cells

    J Cryst Growth

    (2017)
  • R. Yin et al.

    Enhanced photocatalytic reduction of chromium (VI) by Cu-doped TiO2 under UV-A irradiation

    Sep Purif Technol

    (2018)
  • P. Pushpaletha et al.

    Correlation between surface properties and catalytic activity of clay catalysts

    Appl Clay Sci

    (2005)
  • A. López et al.

    Influence of time and temperature on pyrolysis of plastic wastes in a semi-batch reactor

    Chem Eng J

    (2011)
  • J.A. Onwudili et al.

    Composition of products from the pyrolysis of polyethylene and polystyrene in a closed batch reactor: Effects of temperature and residence time

    J Anal Appl Pyrolysis

    (2009)
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