Investigations into the characteristics of oils produced from co-pyrolysis of biomass and tire

Abstract

Co-pyrolysis of wood biomass and waste tire with such catalysts as SBA-15, MCM-41 and HZSM-5 was carried out in a fixed-bed reactor. The influences of the mixture composition on liquid yield and characteristics of the oil were investigated. The properties of the oil were determined by gel permeation chromatograph (GPC), elemental analyzer (EA), thermal analyzer (TA), densimeter, ubbelohde viscosimeter and compared with that of diesel oil 0#. The contents of the polycyclic aromatic hydrocarbons (PAHs) in the oils were also determined by gas chromatograph (GC). The result shows that co-pyrolysis is in favor of inhibiting the formation of polycyclic aromatic hydrocarbons (PAHs) produced from tire. There exist a hydrogen transfer and a synthetic effect during co-pyrolysis of the biomass and tire. They improve the quality of the oil. SBA-15 as a catalyst is more significant than MCM-41 or HZSM-5 for reducing the density and viscosity of the oil and it can effectively decompose some large molecular compounds into small ones.

Introduction

Many researchers are widely being concerned by environmental-friendly disposal and utilization of waste tire and biomass as a resource [1], [2], [3], [4], [5]. Especially, with the gradual decrease of fossil reserves these recycled matters are firstly considered as an alterative resource of energies and chemicals [6], [7]. Although the bio-oil obtained by pyrolyzing biomass possibly becomes a type of potential transporting fuel, some problems such as higher oxygen content, lower high heat value (HHV), lower volatile and delayed ignition time in engine severely hinder its use in practice [8], [9]. It is hence necessary to study how to upgrade the bio-oil. At present, the following pathways were used. The first one was a high pressure hydrogen processing and catalytic cracking [10]. Al-MCM-41 as a catalyst pyrolyzing vapors of spruce wood could lower the yield of phenols with higher molecular mass [11], and sulfided Co–Mo–P as a catalyst could obviously reduce oxygen content in the oil in an autoclave under hydrogen pressure of 2.0 MPa [12]. A steam reforming of oil for the production of hydrogen with catalyst was also studied [13]. Using a high pressure in the system for upgrading the bio-oil not only increased the cost for the production of the oil, but also enhanced the demand for the equipment. The second way was a co-pyrolysis for the mixture of synthetic polymers and biomass [14], [15], [16], [17], [18], which were converted into the liquids with conversation yield of 78 wt.% to 79 wt.% under a nitrogen atmosphere [17]. Another way was esterification for the pyrolysis oil with a high boiling alcohol in the presence of acid catalyst under reduced pressure [19], [20]. In this process, only partial compounds were esterified and consumed a great deal of energy. Emulsion of pyrolysis oil and diesel with a surface active agent was also studied [21]. However, use of the surface active agent increased the cost of the oil.

It is well-known that the result of the ultimate analysis for biomass has a strong function with the types used. The C content for the most biomass is between 47 wt.% and 51 wt.%, whereas the O content is between 42 wt.% and 46 wt.%, leading to very high O content in the pyrolysis oil. In contrast, the C content is very high and O content is very low in the waste tire, whose corresponding content is about 84 wt.% and 1.5 wt.% respectively. If biomass and tire are co-pyrolyzed, C, O and H contents of the feedstock will be balanced. Also, it is conducive to change the C, O and H contents in the oil. In addition, a great deal of free radical species produced by the pyrolysis of biomass possibly destroy or suppress the formation of some long chain hydrocarbon compounds and undesired matters like PAHs from the pyrolysis of tire alone. Although there are some data about the oil from wood biomass and some synthetic polymers like polypropylene, there are less data about the oil from the mixture of biomass and tire because tire property is completely different from polypropylene. In the previous study [14], we reported the influence of different pyrolysis temperatures on the liquid yield and limonene content in the co-pyrolysis oil. In this paper, the thermal behavior of feedstock and oil properties like molecular weight distribution, PAHs and elemental contents with and without catalysts were emphatically investigated.