Hydroconversion Introduction Hydroconversion is a term used to describe all different processes in which hydrocarbon reacts with hydrogen. To describe the process of the removal of sulphur, nitrogen and metal impurities in the feedstock by hydrogen in the presence of a catalyst. Hydrotreating The process of catalytic cracking of feedstock to products with lower boiling points by reacting them with hydrogen. Hydrocracking Hydrogenation aromatics are saturated by hydrogen to the corresponding naphthenes.
Hydrotreating Objectives of Hydrotreating 1. Removing impurities, such as sulphur, nitrogen and oxygen for the control of a final product specification or for the preparation of feed for further processing. 2. Removal of metals, usually in a separate guard catalytic reactor when the organo-metallic compounds are hydrogenated and decomposed, resulting in metal deposition on the catalyst pores. 3. Saturation of olefins and their unstable compounds.
Hydrotreating Role of hydrotreating (HT) in the refinery HT are located before the reformer, hydrocracker and FCC They are also needed to adjust the final product specification for various streams, such as light naphtha, kerosene and low sulphur fuel oils (LSFOs).
Hydrotreating Main role of hydrotreating 1. Meeting finished product specification. Kerosene, gas oil and lube oil desulphurization. Olefin saturation for stability improvement. Nitrogen removal. De-aromatization for kerosene to improve cetane number. Cetane number is the percentage of pure cetane in a blend of cetane and alpha-methyl-naphthalene. The latter matches the ignition quality of kerosene sample.
Hydrotreating Main role of hydrotreating 2. Feed preparation for downstream units: Naphtha is hydrotreated for removal of metal and sulphur. Sulphur, metal, polyaromatics and Conradson carbon removal from vacuum gas oil (VGO) to be used as FCC feed. Pretreatment of hydrocracking feed to reduce sulphur, nitrogen and aromatics.
Hydrotreating 1.The liquid feed is mixed with hydrogen and fed into a heater and then fed into a fixed bed catalytic reactor. 2.The effluent is cooled and hydrogen-rich gas is separated using a high pressure separator. The main elements of a hydrotreating process
Hydrotreating 3. Before the hydrogen is recycled, hydrogen sulphide can be removed using an amine scrubber. 4. Some of the recycle gas is also purged - To prevent the accumulation of light hydrocarbons (C1–C4) - To control hydrogen partial pressure.
Hydrotreating 5. The liquid effluent for the reactor is introduced to a fractionator for product separation.
Hydrotreating Operating Conditions The operating conditions of the hydrotreating processes pressure temperature catalyst loading feed flow rate hydrogen partial pressure
Hydrotreating Operating Conditions Increasing hydrogen partial pressure improves the removal of sulphur and nitrogen compounds and reduces coke formation. Higher temperatures will increase the reaction rate constant and improve the kinetics. However, excessive temperatures will lead to thermal cracking and coke formation. The space velocity is the reverse of reactor residence time (y). High space velocity results in low conversion, low hydrogen consumption and low coke formation.
Hydrocracking Hydrocracking is a catalytic hydrogenation process in which high molecular weight feedstocks are converted and hydrogenated to lower molecular weight products. The catalyst used in hydrocracking is a bifunctional one. It is composed of a metallic part, which promotes hydrogenation, and an acid part, which promotes cracking. Hydrogenation removes impurities in the feed such as sulphur, nitrogen and metals. Cracking will break bonds, and the resulting unsaturated products are consequently hydrogenated into stable compounds.
Hydrocracking It is mainly used to produce middle distillates of low sulphur content such as kerosene and diesel. If mild hydrocracking is used, a LSFO can be produced. It has been used to remove wax by catalytic dewaxing and for aromatic removal by hydrogen saturation. This has been applied to the lube oil plants and is gradually replacing the old solvent dewaxing and aromatic solvent extraction.
Hydrocracking Feeds and Products VGO is the main feed for hydrocrakers
Hydrocracking Hydrocracking Catalysts The cracking function is provided by an acidic support, whereas the hydrogenation–dehydrogenation function is provided by active metals.
Hydrocracking Hydrocracking Process The following factors can affect operation (product quality), yield (quantity), and the total economics of the process: 1. Process configuration: one stage (once-through or recycle) or two stages 2. Catalyst type 3. Operating condition (depends on process objective) - Conversion level - Maximization of certain product - Product quality - Catalyst cycle - Partial hydrogen pressure - Liquid hourly space velocity - Feed/hydrogen recycle ratio
Hydrocracking Process Configuration Simplified flow diagram of one-stage hydrocracking process with and without recycle In commercial hydrocrackers, a conversion of 40–80% of the feed can be achieved. However if high conversion is required the product from the bottom of the distillation tower is recycled back to the reactor for complete conversion. This configuration can be used to maximize a diesel product, and it employs an amorphous catalyst.
Hydrocracking Process Configuration Conventional two- stage hydrocracker The effluent from the first stage reactor is sent to a separator and fractionator. The fractionator bottoms are sent to the second reactor. The catalyst in the first stage has a high hydrogenation/acidity ratio, causing sulphur and nitrogen removal In the second reactor, the catalyst used is of a low hydrogenation/acidity ratio in which naphtha production is maximized