Carbon Support for Extra-Heavy Crude Oil Upgrading Catalysts: Asphaltene Adsorption Capacity

Carbon Support for Extra-Heavy Crude Oil Upgrading Catalysts: Asphaltene Adsorption Capacity

Type	Conference Paper
Author	Luis D. Virla
URL	https://nam.confex.com/nam/2015/webprogram/Paper11989.html
Date	2015/06/15
Conference Name	24th North American Catalysis Society Meeting
Abstract	Introduction The increase in fossil fuel demand in conjunction with the decline of conventional oil resources has required the use of extra-heavy crude oils. One of the heaviest and most polar fractions of these feeds is the asphaltene fraction. Asphaltenes are problematic because they can cause well plugging, clogging of pipelines, and strengthening of oil and water emulsions, which increase production costs [1]. Carbon materials have been studied in the past for extraheavy crude oil upgrading applications, and preliminary studies are encouraging [2]. A good understanding of the interaction between asphaltenes and carbon surfaces is required to develop better supports that will decrease the energy consumption and environmental impacts of upgrading processes. In this work, the capacity for asphaltene adsorption was evaluated for four different carbon materials obtained from wood and oil industry by-products - forestry residue and petroleum coke - in order to determine their potential application as supports for extra-heavy crude oil upgrading catalysts. Materials and Methods For this study, biochar from Aspen wood (Biochar), Activated Carbon from Aspen wood (BioAC), Activated Carbon from petroleum coke (PetAC) and a Commercial Activated Carbon from lignite coal (Colorsorb®, Jacobi) were evaluated. Biochar was prepared through pyrolysis of Aspen wood chips at 873 K for 2 h under N2, and BioAC was obtained by physical activation of Biochar using CO2 at 1053 K for 2 h [3]. PetAC was obtained by chemical activation of petroleum coke using KOH at 1023 K for 2 h under N2 flow [4]. The asphaltene solutions contained various concentrations of Athabasca extra-heavy crude oil C5 asphaltenes in toluene. The solutions were mixed with each adsorbent for 24 h at room temperature at a solid to solution ratio of 1:1000. The concentration of the solution was measured using a UVVis spectrometer Thermo Scientific Evolution 200, following the peak at 288 nm-1. Porous structure analysis by N2 physisorption, and surface chemistry analysis by temperatureprogrammed (TP) decomposition of the oxygenated surface groups (heating at 10 K/min in N2) were performed to characterize the samples. Results and Discussion BET surface area and pore size distribution results are presented in Figure 1. PetAC had the highest surface area (2500 m2/g) while the commercial carbon Colorsorb® had the largest mesopore fraction. The surface functional groups on the samples were different according to the CO2 profiles obtained during TP decomposition (Figure 2). CO2 evolved from the Colorsorb® and BioAC samples between 400 K and 600 K suggests the presence of carboxylic and lactone surface groups [5]. CO2 evolved above 800 K on all samples suggests the presence of carboxylic anhydride groups [5]. The Biochar sample, in particular, had a large peak at 950 K. This sample had not previously been exposed to temperatures above 873 K and so this peak may be from the evolution of volatile species. The Asphaltene adsorption capacities (mg asphaltene/g carbon material) were, in increasing order, 1.3 mg/g for Biochar, 29 mg/g for PetAC, 37 mg/g for BioAC, and 69 mg/g for Colorsorb®. This order does not correspond to increasing surface area among the samples, but does correspond to increasing mesoporosity, which is consistent with the large size of the adsorbates. The TP decomposition (Figure 2) suggested that the samples with a significant number of surface functional groups have the highest adsorption capacities, namely BioAC and Colorsorb®. To verify the importance of these surface groups for adsorption capacity, the Colorsorb® sample was heated in N2 to 823 K and 1223 K and held at these temperatures for 1 h to remove these groups. After the treatments, part of each sample was analyzed with TP decomposition while another part was tested for asphaltene adsorption. After heat treatment, surface groups were removed but the adsorption capacities did not decrease: after treatment at 823 K and 1223 K, the adsorption capacities were 75 mg/g and 70 mg/g, respectively. The increases relative to the value before heat treatment (69 mg/g) are within experimental error. Based on these results, the asphaltene adsorption capacity on carbon materials is limited by the accessibility of the surface through mesoporosity. Work is ongoing to develop materials with sufficient mesoporosity and different surface functionalities. Significance: Sustainability of the upgrading process can be improved if by-products of other processes, including forestry residue and petroleum coke, can be used as catalyst supports. Rational design of these heterogeneous catalysts, however, requires knowledge of the adsorption process of the reactants, which include asphaltenes. Through the current work, new catalysts will be developed that will improve the economic efficiency and decrease the environmental impact of the upgrading process.