(13b) Conversion of Organic Waste to Liquid Fuel by Pyrolysis Over Alumina Catalyst

Introduction

 In recent years strong efforts were being devoted to the substitution of fossil raw materials with renewable sources in the production of energy. Different kinds of treatments were considered to produce second generation biofuels in order to overcome these drawbacks (Naik et al., 2010). Most interest is concerned to the development of gasification technologies followed by syngas purification and Fischer-Tropsch synthesis (Damrtziset and Zabaniotou, 2011): however efficiency of this process is estimated to be quite low (Manganaro et al., 2011).

Simple thermal treatments, with or without catalysts, were also being considered to produce either fuel gases, gasoline or bio-oils applicable as fuels. Similar thermal processes could also be applied to different kinds of residues, including plastic wastes, in order to recover energy and reduce waste material. High temperature processes may allow the production of gasoline and gases potentially applicable as fuels (Buekens and Huang, 1998; Al-Salem et al., 2009; Al-Salem et al., 2010). The focus of this work was on the utility of low-temperature pyrolysis to maximize the production of liquids from organic waste like vegetable and animal fats and auto shredder residues. The samples were pyrolyzed using a batch reactor process working at 350 °C for 3 hours.

 Material and methods

 Two vegetable fats (VFa and VFb), chicken fat (CF), beef tallow (BT) and Auto Shredder Residue (ASR) were used in this study. Diathermic oil (thermex 32) was purchased from Essex. Siralox 1.5/40 was used as catalyst.

The samples were pyrolyzed in a stirred reactor (250 ml) at a temperature of 350 °C for 3 hours. The liquid product (LP) was distilled during the reaction using an integrated distiller and was characterized by gas chromatography mass spectrometry (GC-MS). A heating mantle (in stainless steel) was used to achieve the reaction temperature. The top of the reactor vessel was equipped with a water cooling jacket (condenser) aimed to condensate the gaseous products (GP) formed during the reaction. At the top of the condenser a special pure latex balloon was positioned in order to collect the incondensable gaseous products. The bulk temperature of the vessel was monitored by a thermometer positioned in the backside of the reactor. For VFa, VFb, CF, BT and VFa/CF/BT (in the same amount) the vessel was loaded with 107 g of the samples, while for ASR, 21 g of sample were dissolved in 86 g of diathermic oil. In all experiments 3% (wt/wt) of catalyst was used. After replacing the reaction atmosphere with nitrogen the heating jacket was turned on. After the reaction, the residue product (RP) was distilled separately at 350 °C. The liquid distillate (LD) was analyzed by GC-MS.

For the GC-MS analysis an Agilent 4890D gas chromatograph with Electron Ionization Detector (250 °C) and heated injection equipped with a Hewlett Packard G1800B-GCD system with a quadrupole mass detector was used. The gas chromatograph utilizes a HP-VOC (stationary phase volatiles) 30 m × 0.32 mm, film thickness 1.8 μm, capillary column. Helium (>99.9%) as carrier gas at a flow rate of 1.6 mL min⁻¹was used. The maximum column temperature is 250 °C. The initial temperature of the column was 70 °C than was used the following temperature ramp: one level of ten minutes at 130 °C and a second level at 230 °C with a rate of temperature increase of 10 °C/min.

Results and discussions

 Table 1 represents the yield of gas, liquid and residue products from pyrolysis reaction and distillation of residues. GP yields shows similar values in all experiments while LP varies notably using different kinds of biomass. The highest LP yield was achieved using CF (36.0 g/100g) as biomass followed by PO/CF/BT (20.6 g/100g) and ASR (20.3 g/100g).

Table 1. Yields (g/100g) in gas, liquid and residue products from catalytic pyrolysis reaction and from the distillation of the residue products

¹ gas product; ² liquid product; ³ residue product; ⁴ gas from distillation; ⁵ liquid from distillation; ⁶residue from distillation.

After distillation of the reaction residue (RP), VFb resulted to produce highest amount of liquid (38.9 g/100g). Considerable amount of gas was produced using BT (26.1 g/100g).

Table 2 summarizes the main classes of substances of liquids coming from the reaction and distillation identified by GC-MS.

Table 2. Total peak area of liquid products (LP) and liquid distillated (LD) identified by GC-MS analysis.

GC-MS analysis of distillates revealed that they mainly contain hydrocarbons followed by oxygenated and nitrogenated compounds. Chlorinated compounds were identified only in ASR (0.2%).

Generally, pyrolysis of vegetable fats did not result in a considerable amounts of gas and liquid yields while distillation of residue produced high quantity of LD. Chicken fat produced great amount of liquid during the reaction. Distillation of RP and BT was concluded with considerable quantity of LD and GD. In the case of chicken and beef fats, the overall gas and liquid yield were almost similar (56.6 and 52.3 g/100g, respectively) and were higher than the other biomasses. ASR resulted to the less amount of overall yield which was 32.5 g/100g.

From the results of this study it can be concluded that catalytic pyrolysis of different organic wastes at relatively high temperature (350 °C) resulted to produce acceptable amounts of biofuels (gas-liquid) higher than 50 % wt/wt. In order to optimize these catalytic conversions, considerable attention must be taken into account about the interaction between different compounds from organic waste mixtures.

References

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