Arno de Klerk

Fischer–Tropsch refining: technology selection to match molecules

On a molecular level Fischer–Tropsch syncrude is significantly different from crude oil. When syncrude is treated as if it is a crude oil, its refining becomes inefficient. Refining technologies developed for crude oil can be employed to refine Fischer–Tropsch syncrude, but in order to conform to green chemistry principles (preventing waste; maximising atom economy; increasing energy efficiency) the technology selection must be compatible with the syncrude composition. The composition of Fischer–Tropsch syncrude is discussed in relation to the molecular requirements of transportation fuels and the refining gap that needs to be bridged. Conversion technologies are evaluated in terms of their refining objective, chemistry, catalysts, environmental issues, feed requirements, and compatibility to Fischer–Tropsch syncrude, in order to suggest appropriate technologies for efficient refining of Fischer–Tropsch products. The conversion technologies considered are: double bond isomerisation, dimerisation/oligomerisation, skeletal isomerisation, etherification, aliphatic alkylation, aromatic alkylation, metathesis, hydrogenation/hydrotreating, hydroisomerisation, hydrocracking, catalytic cracking, coking, thermal cracking, catalytic reforming, aromatisation, alcohol dehydration and olefin hydration.

Desulfurization of heavy oil

Strategies for heavy oil desulfurization were evaluated by reviewing desulfurization literature and critically assessing the viability of the various methods for heavy oil. The desulfurization methods including variations thereon that are discussed include hydrodesulfurization, extractive desulfurization, oxidative desulfurization, biodesulfurization and desulfurization through alkylation, chlorinolysis, and by using supercritical water. Few of these methods are viable and/or efficient for the desulfurization of heavy oil. This is mainly due to the properties of the heavy oil, such as high sulfur content, high viscosity, high boiling point, and refractory nature of the sulfur compounds. The approach with the best chance of leading to a breakthrough in desulfurization of heavy oil is autoxidation followed by thermal decomposition of the oxidized heavy oil. There is also scope for synergistically employing autoxidation in combination with biodesulfurization and hydrodesulfurization.

Fischer–Tropsch fuels refinery design

Carbon sources, such as coal, natural gas, biomass and waste, can be converted into transportation fuels by combining appropriate gasification, Fischer–Tropsch and refining technologies. Efficient refining of the Fischer–Tropsch synthesis derived syncrude requires a different approach to refinery design than commonly applied to crude oil refinery design. The design of refineries to optimise the production of on-specification motor-gasoline, jet fuel and diesel fuel respectively from both high temperature Fischer–Tropsch (HTFT) syncrude and low temperature Fischer–Tropsch (LTFT) are considered. Refinery designs are presented for the production of motor-gasoline and jet fuel with better than 50% yield (better than 70% selectivity on transportation fuel), without resorting to very complex designs. Only diesel fuel refining presented a problem, since the production of on-specification EN590:2004 diesel fuel is limited by a Fischer–Tropsch specific cetane-density-yield trade-off. The compound classes that are required to produce diesel fuel in high yield that meet both minimum cetane number and minimum density requirements are not abundant in Fischer–Tropsch syncrude. Refinery designs for diesel fuel production was limited to a yield of less than 25% EN 590:2004 compliant diesel fuel. This yield restriction does not apply when diesel fuel specifications do not have a minimum density requirement.

Environmentally friendly refining: Fischer–Tropsch versus crude oil

Projected changes in crude oil refinery design to meet future fuel specifications require that intermediates are produced that are already present in Fischer–Tropsch syncrude. A qualitative comparison is made between syncrude and crude oil, and the refinery designs needed to convert these raw materials into transportation fuels. Syncrude is sulfur free, nitrogen free and contains no heteroatom rich residues, making its purification and separation less complex than that of crude oil. The conversion units needed to produce motor-gasoline, jet fuel and diesel from syncrude are of similar complexity to that of crude oil, but crude oil residue conversion is much more involved. Furthermore, cleaner conversion technologies can be used to upgrade syncrude. A Fischer–Tropsch refinery consequently has a smaller environmental footprint than a crude oil refinery.

HYDROISOMERIZATION OF 1-PENTENE TO ISO-PENTANE IN A SINGLE REACTOR

It has been shown that hydroisomerization of an olefinic feed to an iso-paraffinic product can be performed in a single reactor using a platinum on mordenite (Pt-MOR) zeolite catalyst. This conversion finds application in a Fischer-Tropsch refinery where the syncrude is rich in olefins and conventional hydroisomerization would require hydrogenation of the feed as a feed pretreatment step. In order to demonstrate that the proposed process configuration is viable from a catalysis point of view, the hydroisomerization of 1-pentene over Pt-MOR has been investigated experimentally in the range 200°–270°C, 2 MPa, WHSV 1–3 h−1, and H2:1-pentene molar ratio of 3:1–5:1. The catalyst was stable during one week of continuous operation. The highest iso-pentane yield (69%) was obtained at 250°C. Side reactions (dimerization and cracking) increased with increasing temperature, decreasing H2:1-pentene ratio, and increasing space velocity.

Chapter 12 – Transport Fuel: Biomass-, Coal-, Gas- and Waste-to-Liquids Processes

Processes for the production of transport fuels (gasoline, jet fuel and diesel fuel) from biomass, coal, natural gas and organic waste are described. Direct liquefaction processes reduce the complexity of the raw material to produce synthetic oil. In doing so, some of the identity and impurities of the raw material are retained. Indirect liquefaction processes convert the raw material into synthesis gas. Impurities are removed from the gas and all identity of the raw material feed is lost. The clean synthesis gas is then converted into a synthetic liquid by Fischer–Tropsch or methanol synthesis. Irrespective of how the synthetic liquid product is produced, it must be refined in order to produce transport fuels. The refining of the different synthetic liquids to produce on-specification ‘drop-in’ transport fuels is discussed. The technical challenges are pointed out and illustrated with examples of synthetic fuels in relation to fuel specifications. An assessment is also made of the future of synthetic fuel facilities for the production of transport fuels.

Research for industry

Petrochemical production accounts for a 6% of global energy consumption. Although this seems like a small percentage, in absolute numbers it is close to 30 EJ, i.e. 3 9 10 J. Consequently, industrial application of petrochemical research has a meaningful impact on the global economy and on the environment. Although the justification for petrochemical research in both industry and academia is clear, one may rightfully ask: why do we need yet another journal? The answer lies in the name: Applied Petrochemical Research. There are journals dealing with the many disciplines that support petrochemical research, such as catalysis, conversion chemistry, chemical engineering and material science. There are also journals dealing with the products from petrochemical research, such as polymers, lubricants and pharmaceuticals. However, applied petrochemical research requires integration across disciplines and products, even though studies may focus on only specific aspects. Applied studies do not have the same resolution of detail as discipline specific studies, but the relevance of applied studies is immediately apparent to practitioners that want to translate the research into actual processes and products. By its nature, Applied Petrochemical Research is home to multiand inter-disciplinary research dealing with petrochemicals, as well as single discipline studies that are of a more applied nature.

Autoxidation of aromatics

Autoxidation is a conversion pathway that has the potential to add value to multinuclear aromatic-rich coal liquids, heavy oils and bitumens, which are typically considered low-value liquids. In particular, autoxidation of these heavy materials could lead to products that may have petrochemical values, e.g., lubricity improvers and emulsifiers. Proper assessment of an oxidative transformation to ring-open the multinuclear aromatics present in heavy feeds relies on the understanding of the fundamentals of aromatic oxidation. This work reviews the selective oxidation chemistry of atoms that form part of an aromatic ring structure using oxygen (O2) as oxidant, i.e., the oxidation of aromatic carbons as well as heteroatoms contained in an aromatic ring. Examples of industrially relevant oxidations of aromatic and heterocyclic aromatic hydrocarbons are provided. The requirements to produce oxygenates involving the selective cleavage of the ring C–C bonds, as well as competing non-selective oxidation reactions are discussed. On the other hand, the Clar formalism, i.e., a rule that describes the stability of polycyclic systems, assists the interpretation of the reactivity of multinuclear aromatics towards oxidation. Two aspects are developed. First, since the interaction of oxygen with aromatic hydrocarbons depends on their structure, oxidation chemistries which are fundamentally different are possible, namely, transannular oxygen addition, oxygen addition to a carbon–carbon double bond, or free radical chemistry. Second, hydrogen abstraction is not necessary for the initiation of the oxidation of aromatics compared to that of aliphatics.

Chapter 3 – Coal Processing and Use for Power Generation

Coal is an important source of energy and raw material for electric power production. Despite climate change legislation, growth in coal consumption thus far outpaced that of other fossil fuels in the twenty-first century. Coal is a reliable energy source, abundant, easily transported, easily traded and competitive in terms of price compared to other fossil fuels. The technology of coal preparation, coal cleaning and use in power generation is discussed. It covers issues such as coal properties and how these relate to coal performance in power generation, as well as ways to remove sulphur, mineral matter and water before coal combustion to improve the efficiency of power generation and reduce emissions from coal use.