Article pubs.acs.org/EF
Production of Lighter Fuels from Spent Lubricating Oil via Pyrolysis over Barium-Substituted Spinel Ferrite Imtiaz Ahmad,*,† Razia Khan,† Mohammad Ishaq,† Hizbullah Khan,‡ Mohammad Ismail,† Kashif Gul,† and Waqas Ahmad† †
Institute of Chemical Sciences, University of Peshawar, 25120 Peshawar, Khyber Pakhtunkhwa, Pakistan Department of Environmental Sciences, University of Peshawar, 25120 Peshawar, Khyber Pakhtunkhwa, Pakistan
‡
ABSTRACT: The present work addresses the catalytic conversion of spent lubricating oil (SLO) into reusable diesel-like product over laboratory-prepared barium ferrite (abbreviated as BF, formula BaFe2O4) using pyrolytic distillation. Soot, carbon, water, and other detrital contaminants were removed from SLO by prior treatment using pre-baked clay as adsorbent. The BF was characterized by scanning electron microscopy, energy-dispersive X-ray scattering, X-ray diffractometry, and surface area analysis and used in the concentration range of 1−5 wt%. The influence of BF concentration on overall conversion (OC) and yields of liquid fraction (LF), gas (G), and solid residue (SR) was studied in comparison with the thermal uncatalyzed run. A catalyst loading of 5 wt% was found to be optimum, giving yields of 97.67 wt% OC, 92.91 wt% LF, 2.33 wt% G, and 4.76 wt% SR. Fourier transform infrared and gas chromatographic−mass spectrometric analyses showed the preponderance of aliphatic (79.38%) and olefinic (11.18%) hydrocarbons in the derived LF. The fuel properties of the derived fraction were also investigated using ASTM/IP standard methods. The results showed that a 5 wt% concentration of BF possessed high activity and selectivity toward formation of diesel-range hydrocarbons in appreciable yields.
1. INTRODUCTION Lubricating oil acts like the blood in running machines and is used extensively to minimize friction and reduce wear and tear. However, after a finite usage period, its useful life ends and the degraded/spent oil is ultimately disposed of as waste. Due to the increasing number of vehicles and other means of transportation used on a daily basis, a substantial quantity of spent lubricating oil (SLO) is disposed of in landfills or subjected to incineration.1−5 Owing to the presence of various toxic substances such as airborne dust, wear metals, sulfur, polyaromatic hydrocarbons, soot, oxidation products, depleted additives, etc., careless disposal of SLO is considered to be a serious threat to the environment. As an alternative, its reuse by reclamation or re-refining has been studied with great success, wherein the degradation products are removed from the oil by extraction, adsorption, distillation, etc., and the reclaimed oil is reused in engines.6−10 However, these methods are also restricted by environmental regulations due to the formation of secondary pollutants as well as poor quality of the reclaimed oil.11,12 Lubricating oil consists of valuable hydrocarbons; therefore, in order to save this valuable resource, it should be recycled in a more effective way, instead of throwing it into landfills or subjecting it to incineration. A number of methods have been studied for its conversion into products that can be used as petrochemical feedstock or potential fuels for automobiles.13−17 These methods include high-temperature cracking to produce olefin-rich, low-grade fuel oil13and pyrolysis in the presence of various catalysts such as Fe2O3 supported on SiO2 and Al2O3,14 sulfated zirconia,15 Y-zeolite and ZnO,16 or Nb2O5 and activated natural zeolites.17 However, in spite of the concerted efforts being made, most of the methods have encountered problems in terms of process and operation cost, inadequate product quality with bad odor and corrosive and tarry nature of © 2016 American Chemical Society
the resultant pyrolysates, catalyst poisoning, catalyst recovery and regeneration, etc. Hence, development of new, efficient, cheap, and highly active and selective catalysts is needed in order to derive value-added products from SLO that will be satisfactory for use in the energy market as fuels to substitute for petroleum-based oils. Spinel ferrites (denoted by M-Fe2O4, where M is a divalent cation) have versatile magnetic, optical, adsorption, electrical, and catalytic properties,18 and can be used as chemical sensors,19,20 as adsorbents for removal of toxic materials,21,22 in electronic devices,23,24 and as pigments.25 They are also used as catalysts in a wide range of important chemical reactions, such as oxidation, oxidative dehydrogenation, hydroxylation, decomposition, alkylation of different organic compounds, etc.,26,27 owing to their surface, textural, and acidic properties. In the present work, barium ferrite (abbreviated as BF, formula BaFe2O4) was synthesized in the laboratory and used in pyrolysis of SLO to get lighter fuels. The SLO collected from a local workshop was pre-treated using pre-baked clay (PBC) as adsorbent in order to remove soot and carbonaceous contaminants, remains from additives, airborne dust, etc. The pre-treated/clarified oil was then subjected to a second stage of pyrolysis in the presence of laboratory-prepared BF as catalyst under a nitrogen atmosphere in order to get light distillate fuels.
2. EXPERIMENTAL SECTION 2.1. Chemicals, Reagents, and Preliminary Characterization. Analytical-grade iron oxide (Fe2O3, 99%, Sigma), barium carbonate (BaCO3, 99%, Alfa Aesar), and 2-propanol (Merck) were used in the Received: April 7, 2016 Revised: May 16, 2016 Published: June 6, 2016 4781
DOI: 10.1021/acs.energyfuels.6b00796 Energy Fuels 2016, 30, 4781−4789
Article
Energy & Fuels synthesis of BF. PBC was acquired from a local brick kiln industry and used as adsorbent. SLO (PSO DEO 8000), which had been used in a passenger bus over a running mileage of 3000 km, was acquired from a local mechanical workshop and pre-treated with PBC. Preliminary characterization of the SLO was performed to record properties including density, specific gravity, API gravity, kinematic viscosity, ash content, Conradson carbon residue (CCR), aniline point, pour point, distillation temperatures, etc. Elemental analysis of the SLO was also carried out using a CHNS analyzer (Elementar Vario EL II). 2.2. Preparation of Catalyst. The catalyst was synthesized in the laboratory by slurry-milling. In a typical procedure, stoichiometric amounts of BaCO3 and Fe2O3 were mixed together in a small amount of 2-propanol diluted with water in order to prepare a slurry. The slurry was then milled in a ball mill using steel balls of 5 mm for a period of 4 h so as to form a homogeneous paste, and then dried in an oven at 80−120 °C for 18 h to get a cake. The resultant cake was then crushed, ground, and sieved through a No. 70 mesh in order to get a powder. The powder phase was pressed into a disc and calcined at 900 °C, heating at a rate of 5 °C/min for 3 h, in a muffle furnace. The calcined phase was milled again into a fine powder and stored for characterization and activity tests. 2.3. Pyrolysis Reactor. Figure 1 provides a schematic of the pyrolysis apparatus, which consists of a steel microreactor, tube furnace,
out by using X-ray diffraction (XRD; JEOL model JDX-9C, Japan). The surface characterization was done by using a surface area analyzer (Quantachrome Nova Station A). 2.4.2. Analysis of the Derived Lighter Liquid Fractions. 2.4.2.1. Compositional Analysis. The composition of the catalytically derived lighter liquid fraction (under optimum catalyst concentration) was investigated by Fourier transform infrared (FT-IR, Shimadzu Prestige-21, Japan) and gas chromatography−mass spectrometry (GC-MS, Shimadzu QP 2010, Japan). The peaks in the chromatogram were identified by comparison with data from a NIST MS library search. The derived lighter liquid fraction (pyrolysate) is denoted as CDLP in the following discussion. 2.4.2.2. Fuel Properties. Fuel properties such as density (ρ), specific gravity (SG), API gravity, CCR, ash content, kinematic viscosity (ν), pour point, aniline point, diesel index, cetane number, heat of combustion, etc. of the CDLP were investigated using American Society for Testing Materials (ASTM) and Institute of Petroleum (IP) standard methods29,30 for comparison with the diesel oil.
3. RESULTS AND DISCUSSION 3.1. Preliminary Characterization of SLO. The properties of the SLO, including color, density, API gravity, CCR, aniline point, acid number, and distillation behavior, were determined by ASTM/IP methods. The results are provided in Table 1. Increases were noticeable in color, carbon residue, and Table 1. Physicochemical Properties of Spent Lubricating Oil fuel property color density @ 15 °C specific gravity @ 60 °F API gravity @ 60 °F residue/ash content kinematic viscosity @ 40 °C aniline point CCR acid number distillation: initial boiling point recovery (10 mL) recovery (70 mL)
Figure 1. Pyrolysis reactor: (A) steel microreactor, (B) tube furnace, (C) nitrogen cylinder, (D) Liebig condenser provided with (E) water inlet and (F) outlet, (G) receiving flask, and (H) gas vent. nitrogen cylinder, Liebig condenser provided with water inlet and outlet, receiving flask, and gas vent. In a typical run, 50 g of the SLO was taken into the reactor, which was heated to the desired temperature using a tube furnace in a flow of nitrogen. The cracked vapors from the reactor were allowed to pass through a Liebig condenser arrangement. The condensates were collected in a receiving flask, and the uncondensed phase (gas) was sent out to vent. The reactor was then cooled to ambient temperature and opened. The liquid collected in a receiving flask was weighed and stored for further analysis. The residue was collected as coke and weighed. The gas fraction was calculated by difference. 2.3.1. Pre-treatment of Spent Lubricating Oil. The SLO was pretreated using PBC as adsorbent in order to remove soot, carbon, catalyst remains, wear metals, etc. The clarified SLO was then used in a catalytic pyrolysis study over BF under the following set of experimental conditions: SLO/PBC ratio, 1:2; temperature, 500 °C; residence time, 90 min. 2.3.2. Pyrolysis. Catalytic pyrolysis of the pre-treated SLO was carried out under the optimized conditions of temperature and residence time, as we have reported elsewhere.28 The catalyst was used in different concentrations (1−5 wt%). Optimum catalyst concentration was decided on the basis of the maximum yield of the lighter oil. 2.4. Analyses and Characterization. 2.4.1. Catalyst Characterization. The morphological and elemental characterization of the BF was performed by using scanning electron microscopy (SEM) combined with energy-dispersive X-ray scattering (EDX; JEOL model Jsm-5910, Japan). The crystallographic and phase analyses were carried
unit
level
g/cm3 − − wt% mm2/s °C wt% mg KOH/g
C30
62.70 16.90 9.32 6.77 3.38
catalyzed run ID no.
in Table 8. As we reported earlier,28 the relative distributions of C6−C12, C13−C16, C17−C20, C21−C30, and >C30 range hydrocarbons were observed to be 62.7, 16.95, 9.32, 6.77 and 3.38%, respectively in case of the thermal run wherein the proportion of different carbon range hydrocarbons linearly decreased as their molecular weights increased. The result of the catalyzed run shows no obvious difference with the thermal run. As reported in the literature, diesel fuel contains hydrocarbons, particularly saturated hydrocarbons (paraffins) and unsaturated (olefins) and aromatic chains that contain from 10 to 19 carbon atoms.40 The results indicate that these carbon range compounds are present in CDLP in appreciable quantities, and the derived fraction can be used as diesel fuel or can be blended with commercial diesel fuel. 3.4.2.3. Individual Compounds. The individual compounds identified in the derived liquid fraction along with their relative concentration determined by GC-MS analysis are given in Table 9. It can be observed that CDLP consists of individual hydrocarbons with minor differences in their relative concentrations, as determined in the case of the thermal run.28 The paraffinic hydrocarbons identified included heptane, 3-ethyl-2,4dimethylpentane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, henicosane, docosane, tetracosane, and pentacosane and their alkyl derivatives. The concentrations of most of the individual compounds ranged from 1 wt% to as high as 6 wt%. However, the alkyl derivatives of these compounds were present in small proportions, i.e.,
