Hydroprocessing Catalysts and Processes

The following sections are included:

• Preface
• About the Editors
• Contents

Hydroprocessing is a conventional operation in the petroleum refinery. Recent developments in biofeedstock-derived fuels and stringent environmental legislation brought up new challenges in this traditional area. This chapter reviews hydroprocessing reactions including hydrodesulfurization, hydrodenitrogenation, hydrodeoxygenation, hydrogenation, hydrocracking, and hydrodemetallization, reactivity and reaction pathways of typical chemicals resulted from biofeedstock and petroleum, surface chemistry of hydroprocessing catalysts, and hydroprocessing catalyst models.

Fast pyrolysis is considered to be the simplest and most cost-effective approach to produce liquid oil (bio-oil) from biomass. Bio-oil is not suitable to substitute for petroleum as high-quality fuels and significant upgrading such as hydrotreating is required to remove oxygen, add hydrogen, and rearrange the carbon backbone of bio-oil. However, the grand challenge in bio-oil hydrotreating technology is bio-oil instability, which limits the lifetime of catalyst and operation. To enable a sustainable and economically viable process for bio-oil hydrotreating, it is vital to develop effective technologies for stabilizing bio-oils. This chapter will be devoted to bio-oil stabilization. The current understating of the major cause of bio-oil instability, condensation of reactive species such as sugar, aldehydes, ketones, and phenolics, is elucidated. The reported physical and chemical methods for bio-oil stabilization are summarized in detail, with a specific focus on bio-oil catalytic hydrogenation for stabilization. The impact of stabilization on bio-oil hydrotreating is discussed as well.

Conventional hydroprocessing catalysts are usually sulfided to retain their active forms. However, sulfuration may cause sulfur dioxide emissions, corrosion of equipment and sulfur residues in the products, since plant oils are free of sulfur compounds. The high price of noble metals also limits their industrial applications. Therefore, the nonsulfided nonnoble-metal catalysts, which can get rid of the presulfurization step and avoid the harm of sul.de to environment and human health, have received a lot of research interests. Recent development of less expensive metallic catalysts, like nickel (Ni)- based catalysts, has shown promising results. The purpose of this chapter is to review current developments in the species and application of inexpensive Ni-based nonsulfided hydroprocessing catalysts.

The objective of this study was to synthesize carbon-encapsulated bimetallic Co–Mo carbides and sulfides nanoparticles by carbothermal reduction (CR) of molybdenum-promoted biochar and post sulfiding. The bimetallic Co–Mo carbides and sulfides nanoparticles were characterized for physicochemical properties by multiple morphological and structural methods (e.g., SEM, TEM, and XRD). These nanoparticles were tested for catalytic upgrading of the pyrolysis bio-oil from pinewood in a continuous packed-bed reactor. Hydroprocessing experiments were performed at a temperature of 350–425°C, 6.89–12.41 MPa (1,000–1,800 psig) hydrogen pressure with a hydrogen flow rate of 500 ml/min at a liquid hourly space velocity of 0.1–1.0 h⁻¹. The results from sulfided catalytic experiments were compared with CoMo carbide nanoparticles. Sulfided CoMo nanoparticles demonstrated higher catalytic activity and resulted in increased hydrocarbon fraction yields. Moreover, the quality of the hydrocarbon fraction, as determined by the acid value, higher heating value, and water content analyses, also improved.

Algae have been considered as a promising biofuel feedstock, which can be converted to the precursor chemicals of drop-in fuels. Due to the high protein content in algal species and the limitations of conversion technologies, these biofuel precursors require further catalytic removal of heteroatoms such as nitrogen and oxygen, being upgraded to biofuels like green diesel and aviation fuel. This chapter reviews the state-of-the-art in hydroprocessing of microalgae-based biofuels, as well as the catalyst development, the effect of process parameters on hydrotreated algal fuels, and the standards suitable for characterization of algal biofuels. Hydroprocessing of algal fuels is a new and challenging task and still underdeveloped. For the long term, an ideal catalyst for this process should possess following characteristics: high activities towards deoxygenation and denitrogenation, strong resistance to poisons, minimized leaching problems and coke formation, and an economically sound preparation process.

A significant amount of attention has been given to the development of the catalyst supports that might lead to enhanced catalytic hydroprocessing properties over last 30 y. This chapter reviews the support effects of oxides (Al₂O₃, SiO₂, TiO₂, and ZrO₂), carbonaceous materials, and molecular sieves including MCM-41, SBA-15, SAPO, ZSM-5, zeolite Y, and zeolite beta.

Over the past decade, there have been several technologies developed by refinery operators and technology development companies aimed at processing renewable feedstocks into transport fuels. These processes are generally centered on a hydrotreating step in which a renewable feedstock, generally but not necessarily a vegetable oil or fat, is hydrogenated to produce an aliphatic hydrocarbon chain, which after further processing and distillation produces a fuel suitable for use as gasoline, jet fuel or diesel. This process is sometimes complemented by an isomerization step which further improves the properties of the fuel. This paper reviews the development and status of these processes as described in the patent literature and commercial brochures.

In order to continually reduce vehicle pollution and greenhouse gas emissions, fuel standards and regulations are in a state of constant change and tightening. These changes and future trends have an impact on the take-up of renewable fuels for both gasoline and diesel fuels. This chapter discusses current and future fuel standards and illustrates how the hurdles experienced by ethanol and bio-diesel blends have been overcome. Nevertheless, ethanol and bio-diesel still remain and are likely to remain a minor part of the world fuel market.

Ideally new renewable fuels should be drop-in fuels with minimum compatibility issues with conventional fuels. This is illustrated by bio-refinery operations to produce green diesel which is compatible with conventional diesel.

There may be a role for a new renewable additive to improve gasoline octane as octane requirements rise. The market for such an additive could justify large-scale manufacture.

As the energy demand continues to rise and the environmental regulations are more stringent, both the use of refinery catalysts and the quantity of spent hydroprocessing catalysts are increasing. When the performance of the catalysts is unable to meet the desired level, they will be unloaded as the spent catalysts, which might be subject to a series of treatments. If the spent hydroprocessing catalysts meet the requirements of the regenerability, they are regenerated via oxidative regeneration and resulfided or reactivated via the rejuvenation process that combines the thermal and chemical treatments. When the catalytic activity cannot be restored, metals are recovered from the spent catalysts, and remaining materials can be used to prepare other useful products. Finally, the residue of spent hydroprocessing catalysts is stabilized and disposed by using an environmentally sound method. The goals of the treatment of spent hydroprocessing catalysts are always to maximize the life of the catalysts and minimize the generation of hazardous wastes.

A significant amount of hydrogen is required for hydroprocessing processes to satisfy the needs of petroleum refinery, natural gas cleaning, and biofuel upgrading. The first section of this chapter introduces the background of hydrogen production technologies. The second section reviews resources that can be used to manufacture hydrogen. The third section provides an overview of the current development of methane reforming, gasification, electrolysis, and other technologies. The last section concludes the chapter and presents the future trends.

The following section is included:

• Index