Special Issue “Heavy Oil In Situ Upgrading and Catalysis”

Until now, fossil fuels have played an important role in the daily life of human beings and civilization. However, recent demographic growth and energy demand has led to a significant shortage in conventional oil reserves and driven the world toward economic crisis and geopolitical instability. Despite the negative effects that could be associated with the decline of conventional reserves of energy sources, scientists, researchers and experts still consider the unconventional reserves to improve and sustain energy demand for the coming decades and generations. Unconventional oil reserves include shale oil, bitumen, heavy oil and extra heavy oil [1,2]. Heavy oil reserves are generating considerable interest with regard to replacing light oil due to their rich composition and higher energy supply. One of the most significant limitations of heavy oil reserves is the lack of efficient technologies required for their extraction and development because of their higher viscosity and density, as well as their low mobility in reservoirs.

Various approaches and methods have been proposed to improve heavy and extra-heavy oil recovery from unconventional reserves [3]. These methods are known in the literature as enhanced oil recovery methods (EOR). EOR methods were developed to recover oil in place after tertiary recovery. They are classified into different categories based on the chosen technique [4,5]. The first category is devoted to chemical methods, including the injection of chemicals and polymers into reservoirs in order to modify the physico-chemical properties of the oil containing system, consequently easing its extraction. The second category is based on applying electromagnetic energy and directing it towards the oil-containing rock to decrease heavy oil viscosity and improve its mobility and flow [6]. The third category is known as thermally enhanced oil recovery, which is essentially based on decreasing the viscosity of heavy oil in place by means of injecting hot water steam or by generating heat in situ by means of burning a part of the oil in place, such as the process of in situ combustion.

Recent developments in the field of thermally enhanced oil recovery have led to the use of different additives and catalysts being proposed in order to improve the quality of the produced oil from heavy oil by in situ upgrading. The present Special Issue presents new approaches to apply different catalytic systems in the in situ upgrading processes of heavy oil. For instance, Mukhamatdinov et al. [7] have studied the process of Aschalcha heavy oil aquathermolysis products in the presence of a cobalt-containing catalyst precursor and a hydrogen donor. The authors have analyzed the properties of the obtained oil by studying the resins fraction. The authors found out that the average molecular weight resins increase from 698 to 1245 amu as a result of aromaticity increment and aliphaticity decrement during the process of aquathermolysis in the presence of a cobalt-based catalyst and hydrogen donor promotion effect. Furthermore, they have studied the composition and structure of ultra-dispersed mixed oxide (ii, iii) particles and their influence on the heavy oil in situ upgrading process [8] by proposing a set of physico-chemical analyses and modeling the process of aquathermolysis in a high-pressure autoclave. The obtained results of this study suggest that an ultra-dispersed mixture of iron oxide (ii, iii) at 250 °C is able to decrease the amount of resins and asphaltenes as a result of destructive hydrogenation stimulation. These catalysts were found to increase both the amount of saturates and aromatics in the post aquathermolysis oil for the same reason. The use of iron-based nanoparticles decreases the amount of undesirable metals because it improves the reactions of desulfurization and the cleavage of C–S bonds within the structure of oil-heavy components.

Nickel-based catalysts play a major role in a diverse field of petroleum-refining processes. In this Special Issue, Vakhin et al. [9] have investigated the effect of nickel-based catalysts on aquathermolysis of Boca de Jaruco (Cuba) extra heavy oil, as well as studying its transformation during heavy oil upgrading. The authors have used gas chromatography, SARA analysis, GC-MS, FT-IR spectrometry, elemental analysis and matrix-activated laser desorption/ionization (MALDI). The authors claim that nickel tallates transform into 80–100 nm nickel sulfide nanoparticles at 300 °C. The obtained results showed that nickel tallates enhance the quality of aquathermolysis products while simultaneously being able to decrease the amount of asphaltenes and resins. Equally, this catalyst increased the amount of saturates and aromatics. The active form of the obtained catalyst showed a higher performance in the desulfurization of heavy compounds of heavy oil. In addition, the cracking of the weak C–S bonds, which was mainly concentrated in resins and asphaltenes, ring-opening reactions, detachment of alkyl substitutes from asphaltenes and inhibition of polymerization reactions in the presence of the catalytic complex, reduced the average molecular mass of resins (from 871.7 to 523.3 amu) and asphaltenes (from 1572.7 to 1072.3 amu).

The application of catalytic systems is relevant to other processes, such as cracking and hydro-conversion. In the present Special Issue, Kaieva et al. [10] have studied the effect of Mo-based nano-sized catalysts on petroleum residue hydro-conversion. The authors synthesized molybdenum sulfide nanoparticles by reverse emulsions containing water-soluble molebdenum salt and S-containing agents (elemental sulfur, thiocarbamide). The obtained catalyst was suspended and stabilized in the petroleum residue medium in the absence of a solid carrier. The authors claimed the possible dispersion of catalysts with 6 to 10 wt% of molybdenum content. The catalytic activity of the obtained catalysts during petroleum residue hydro-conversion was expressed by the higher conversion by the pass and the lower yield of the obtained coke even at a longer feed residence time. The authors have revealed a 0.2 wt% coke yield and 55.5 wt% yield of petroleum conversion in the presence of the chosen catalysts. Senter et al. [11] have also provided a quantitative visual characterization of contaminant metals and their mobility in fluid catalytic cracking catalysts. The authors have demonstrated that metal contaminants have clear pathways of imparting negative effects in fluid catalytic cracking units. Therefore, they developed a novel algorithm for automated quantitative visual characterization. The evidence from this study suggests that understanding the mobility and distribution of contaminant metals can help to clarify the sources of contaminant metals (feed, catalyst, additive), evaluate the efficacy of metal passivators, determine metal effects on different catalysts and additives, and serve as a source of direction for laboratory-scale experimental studies. This idea was confirmed by the work of Liao et al. [12] who provided a comparison of laboratory simulation methods for the iron contamination of fluid catalytic cracking catalysts. The authors developed a new approach that allows the recognition of the real mechanism of iron contamination, understanding of the main factors that affect the physical and chemical properties of an iron-contaminated catalyst and predictions of the actual reaction performance and product distribution of a laboratory-based catalyst. The authors claim that this can effectively reduce the time and economic costs caused by the failure of laboratory simulations.

The present Special Issue extends our knowledge of the different processes and mechanisms of heavy oil upgrading in the presence of transition-metal-based catalysts. In addition, it improves our understanding of metal contamination during oil treating and processing. This topic warrants further study and support given its crucial role in our daily life and industry. We wish to offer our special thanks to all the anonymous referees, editors and assistants who provided this Special Issue with all the necessary tools, constructive comments and sources.