An experimental study on bio-oil production from co-pyrolysis with potato skin and high-density polyethylene (HDPE)
Highlights
► Co-pyrolysis of potato skin with pure and waste HDPE is investigated to optimize the experimental conditions for bio-oil production. ► When pS/HDPE ratio is increased to 1:2, the yield of bio-oil is increased to 50.88 %. ► The addition of HDPE to the mixture seemed to have increased the liquid production and decreased the gas formation. ► In the co-pyrolysis of HDPE and biomass, oxygen content in the oils were significantly reduced which can be attributed to influence of the HDPE. ► High amounts of 2-alkenes, 1-alkenes and alkadienes are obtained in the co-pyrolysis liquids fractions.
Introduction
The increasing consumption of polymeric materials in modern daily life causes loss of natural resources, the environmental pollution, and the depletion of landfill space [1]. Nevertheless, the non biodegradable polymeric waste materials such as plastics, tires require the main difficult disposal methods. Presently, the most common solution to deal with organic wastes, namely land filling and incineration do not appear to be the most suitable ones since they present various problems related with the environment. For instance; landfill areas are limited. Also, land filling could pollute environment such as phthalates and various dyes found in plastic additives leak into ground water. Incineration is an alternative to landfill. However, this process causes formation of unacceptable emissions of gases such as nitrous oxide, sulfur oxides, dusts, dioxins and toxins [1], [2].
The utilization of such waste materials is indeed of importance from economical and environmental aspects. Especially, packing materials make up the 50–70% of the total plastic disposal, containing mainly 89% polyolefins (polyethylene, polypropylene, polystyrene, polyvinyl chloride). Nevertheless, decomposition of polyethylene and polypropylene do not give high yields of ethylene and propylene with the ordinary recovery techniques [3], [4]. Pyrolytic processes are suitable to convert polyolefins and cellulose (or lignin) derived materials into valuable feedstock and the specific benefits of these methods potentially include: the reduction of the volume of waste, the recovery of chemicals, and the replacement of fossil fuels [5].
The aim of mixing polymers with biomass wastes is to improve the liquid fraction of the products, and to evaluate the H-donor effect of polymers. There are several studies about co-pyrolysis of biomass–polymers which has indicated the synergistic effect on liquid production [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. According to these studies, the composition and the nature of the biomass and synthetic polymer as well as the pyrolysis conditions have a great influence on the yield, the chemical structure and the physical properties of the products. The addition of polymer to biomass has a positive effect on the yield and basic physical properties of bio-oil.
Potato skin is a promising biomass candidate. According to our previous study, resultant oil from pyrolysis of potato skin has a high aliphatic content which is very beneficial for artificial fuel production. Potato is an essential nutrition in the world. In Turkey, potato is grown on 200 thousand ha, and 4.5 million tons of potato is produced every year. Revealed residue amount is 495,000–594,000 tons/yr. Converting the organic matters in residues such as polymers and food industry waste into more valuable, concentrated forms of energy by pyrolysis will be a sustainable way for waste management [16].
The thermal degradation of the organic materials, the product distribution and consequently the economics of the process are strongly influenced by the experimental conditions used. In the present work, co-pyrolysis of pS with pure and waste HDPE was investigated for the first time to optimize the experimental conditions for bio-oil production. Obtained bio-oils were analyzed in detail with various spectroscopic and chromatographic methods. As a result, the addition of HDPE caused an increase of yields and also improvement of fuel properties.
Section snippets
Raw material
Potato chips industry waste was obtained from the Kar Chips Factory in Turkey. As reasoned waste was dried in air and then ground in a rotary cutting mill to obtain a grain size lower than 2 mm. After milling, biomass sample was screened to obtain seven different particle sizes (Dp), namely 1.8 > Dp > 1.25 mm; 1.25 > Dp > 0.85 mm; 0.85 > Dp > 0.6 mm; 0.6 < Dp < 0.425 mm; 0.425 < Dp < 0.224 mm. Average particle size range was found to be as 0.81 mm. Pure and waste High Density Polyethylene (HDPE) were brought from a
Thermal analysis
The TG and DTG curves for potato skin (pS) and HDPE recorded from room temperature to 900 °C are shown in Fig. 1. The initial slight mass loss occurs up to 180–200 °C due to the evaporation of moisture from pS. Second weight loss occurred between 200 and 575 °C corresponds to main pyrolysis process, devolatilization. DTG data of biomass showed that initial mass loss gives its maximum peak at 95.8 °C. Second major weight loss starts at about 175 °C, having its maximum point at 293 °C, finishes at
Conclusions
In this study, co-pyrolysis of pS with synthetic and waste polymers in various proportions was carried out at 500 °C by semi-batch process in an inert atmosphere under fixed bed reactor conditions. The co-pyrolysis of pS/HDPE with ratio of 1:2 is resulted in the most pronounced synergistic effect with the high liquid yield. Results of FT-IR, GC–MS, column chromatography and elemental analyses of bio-oils have showed that HDPE addition into biomass sample in the application of co-pyrolysis
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