Properties of AR.
This chapter describes an iron oxide catalyst containing Zr and Al for production of light hydrocarbons by catalytic cracking of petroleum residual oil in a steam atmosphere. The catalyst was hematite structure and useful for decomposition and desulfurization of residual oil. After lattice oxygen of iron oxide reacted with heavy oil fraction of residual oil, oxygen species generated from steam were supplied to iron oxide lattice and reacts with heavy oil fraction, producing light hydrocarbons and carbon dioxide. When the oxygen species were generated from steam, hydrogen species were simultaneously generated from steam. The hydrogen species were transferred to light hydrocarbons, hydrogen sulfide, and residue deposited on the catalyst. Supplies of the hydrogen species to light hydrocarbons suppressed alkene generation. Generation of hydrogen sulfide indicated decomposition of sulfur compounds of residual oil. The sulfur concentration of product oil decreased compared to the concentration of residual oil. Some oxygen species could be transferred to sulfur dioxide. Accordingly, hydrogenation and oxidation by the hydrogen and oxygen species derived from steam provided the decomposition and desulfurization of residual oil with the iron oxide-based catalyst in a steam atmosphere.
- iron oxide catalyst
- atmospheric residue
- steam catalytic cracking
Petroleum refineries require production of transportation fuels by decomposition of petroleum residual oil. The residual oil has low H/C ratio, high viscosity, and impurities, such as sulfur, vanadium, and nickel. Hence, decomposition of the residual oil is not easy.
The conventional process to convert heavy oil, such as petroleum residual oil, to light hydrocarbons was coking, visbreaking, residue fluidized catalytic cracking (RFCC), and hydrocracking [1, 2]. Heavy oil was decomposed with Ni-Mo or Co-Mo catalysts to produce light hydrocarbons with less coke under high hydrogen pressure in the hydrocracking process. The hydrocracking is a useful technique to produce light hydrocarbons, which has high H/C ratio, although hydrogen is expensive.
Steam can be an alternative hydrogen source for conversion of heavy oil to light hydrocarbons with catalysts. This technique requires the following catalyst properties: (i) a high ability to decompose heavy oil, (ii) stable activity under high steam temperature, and (iii) resistance to deposition of coke, sulfur, and metals. Iron oxide is not expensive and can be a candidate the catalyst to decompose heavy oil in a steam atmosphere.
This chapter describes an iron oxide-based catalyst for decomposition of heavy oil to produce light hydrocarbons. Properties of the catalyst and catalyst activity to decompose residual oil and desulfurization in a steam atmosphere are discussed.
2. Properties of iron oxide catalyst
Several studies reported the catalytic cracking of heavy oil with iron oxide catalysts. Fumoto et al. developed the ZrO2-supporting
2.1. Preparation of
α-Fe2O3 catalyst containing Zr and Al
2.2. Structure of
α-Fe2O3 catalyst containing Zr and Al
The morphology of the
The crystalline construction of the catalyst was analyzed by X-ray diffraction (XRD, M03XHF22, Mac Science Co. Ltd.). Figure 2 showed the XRD patterns of the catalyst and regent iron (III) oxide (
3. Activity of
α-Fe2O3 catalyst containing Zr and Al for decomposition of heavy oil
3.1. Decomposition of AR
Catalytic cracking of AR was conducted using a downflow-type fixed-bed reactor loaded with 1.5 g of catalyst at 748 K under atmospheric pressure [9, 12]. A 10 wt% solution of AR with toluene was fed to the reactor at flow rate (
Figure 3 showed the composition of AR and product yield of the AR cracking at flow rate ratio of steam to AR solution (
Figure 4 showed the XRD patterns of the used catalysts after the catalytic cracking of AR with and without steam . The patterns of reagent iron (III) oxide (
When dodecylbenzene was used as a model compound of heavy oil, a small amount of oxygen containing compounds, such as phenol, acetophenone, undecanone, and hydroxybiphenyl, was produced in the catalytic cracking of dodecylbenzene . Kondoh et al. reported that the catalytic cracking of heavy oil with heavy oxygenated water (H218O) produced CO2 containing heavy oxygen (CO18O) . Accordingly, most of oxygen species were supplied to form CO2, and a small amount of oxygen species was supplied to oxygen –containing compounds.
3.2. Effect of steam on product of AR cracking
To examine the effect of steam flow rate on product yield of AR cracking, catalytic cracking of AR was conducted at various steam flow rates (
When oxygen species were generated from steam and reacted with heavy oil, hydrogen species were simultaneously generated from steam . Consumed amount of steam was calculated from the CO2 yield in the catalytic cracking of AR at flow rate ratio of steam to AR solution (
Supplies of hydrogen species from steam to liquid hydrocarbons and residue resulted in decrease in alkene generation and increase in H/C of residue . Figure 7 showed the alkene/alkane ratio of aliphatic hydrocarbons and H/C ratio of residue produced by the catalytic cracking of AR with and without steam. The aliphatic hydrocarbons in the liquid product were analyzed by gas chromatography with a flame ionization detector (GC-FID, 6890N, Agilent Technologies) and mass spectrometry (GC-MS, HP6890-HP5973, Agilent Technologies) with capillary columns. The alkene/alkane ratio of light hydrocarbons (C9–C13) decreased with increase in flow rate ratio of steam to AR solution, suggesting that hydrogen transfer from steam to light hydrocarbons suppressed alkene generation. The H/C ratio of residue produced by the AR cracking with steam was higher than that produced by the AR cracking without steam. Some hydrogen species supplied from steam to the residue and others supplied to light hydrocarbons.
4. Activity of
α-Fe2O3 catalyst containing Zr and Al for desulfurization of heavy oil
The petroleum residual oil including AR contains sulfur. Hydrodesulfurization is the useful method to remove sulfur from petroleum, producing high-quality oil. The residual oil contains acyclic sulfur compounds, such as thiols and disulfides, and cyclic compounds including thiophene ring. The decomposition of the cyclic sulfur compounds was harder than acyclic compounds .
The catalytic cracking of heavy oil with steam using the
4.1. Desulfurization of AR
Catalytic cracking of AR with the
Catalytic cracking of AR produced approximately 61 mol%-C of oil product, 4 mol%-C of gas product, and 35 mol%-C of residue. Sulfur concentration in the product oil decreased to 1.4 wt% compared to the 2.5 wt% of sulfur in AR, and H2S was generated, indicating that sulfur compounds in AR were decomposed . When desulfurization was conducted using dibenzothiophene as a model compound of a cyclic sulfur compound in AR, dibenzothiophene was decomposed producing CO2, H2S, hydrocarbons, and sulfur compounds . Hence, acyclic and cyclic sulfur compounds might be decomposed with the catalyst in a steam atmosphere.
4.2. Effect of steam on desulfurization of AR
To examine the effect of steam on desulfurization of AR, catalytic cracking of AR was conducted at various steam flow rates (
The SO2 was detected only in the reaction without steam. The lattice oxygen of iron oxide reacted with sulfur compounds, producing SO2 in the catalytic cracking of AR without steam. The SO2 has high solubility in water (1.4 mol/kg at 25°C ). Hence, no SO2 might be detected in the catalytic cracking of AR with steam, even if oxygen species generated from steam reacted with sulfur compounds to form SO2. Some H2S produced in the reaction also could be dissolved in water. When nitrogen was injected into the water collected in this reaction, H2S was detected . The difference was approximately 23 mol%-S because of sulfur content, such as H2S and SO2, in water and measurement errors of sulfur concentration.
Sulfur content in residue decreased with increase in flow rate ratio of steam to AR solution. Larger amounts of hydrogen species were generated at higher ratio of steam to AR solution and reacted with heavy sulfur compounds deposited on the catalyst to produce light sulfur compounds and H2S. Sulfur concentration in the oil decreased because sulfur compounds were decomposed to produce H2S. Increase in sulfur concentration in the oil at
Decomposition and desulfurization of AR were examined using
This work was partially supported by Grants-in-Aid for Young Scientist B (21760622, 23760733) and Scientific Research C (25420822) from the Japan Society for the Promotion of Science (JSPS).