Hydrocracking

Hydrocracking (including hydrocracking ) is a catalytic cracking process of the petrochemical in the presence of hydrogen to produce higher molecular weight hydrocarbon fractions in intermediates for the production of motor gasoline , kerosene and diesel fuel transform. The process is carried out with a hydrogen-rich gas under a pressure of up to 200 bar and at temperatures of up to 480 ° C. The resulting products are largely olefin-free , depleted in relation to the starting materials aromatics and hardly contain any sulfur or nitrogen compounds.

history

As early as the 1920s and 1930s there were studies and attempts at hydrocracking. Due to the high costs involved, the processes were not economical. It was not until the beginning of the 1960s that the process became technically and economically established. The reasons were, on the one hand, improved zeolite- based catalysts and the growing interest in low-sulfur and low-nitrogen diesel fuels and in components for the production of motor gasoline. Furthermore, the residues of Fluid Catalytic Cracking (Light Cycle Oil (LCO), Heavy Cycle Oil (HCO) cleaned from "fines", cleaned slurry) could be worked up by means of hydrocracking. Other sources that are becoming increasingly important are Koker heavy gas oil and Deasphalted Oil (DAO) . In 2001 more than 150 hydrocrackers with a capacity of more than 500,000 tons per day were installed worldwide.

raw materials

• H ₂
• Heavy vacuum gas oil ("standard" feed)
• Light vacuum gas oil (less common)
• Heavy gas oil (less often if it makes economic sense)
• LCO (rarely, if available and economically reasonable)
• HCO (seldom, if available, must be cleaned of "fines", otherwise there is a risk of erosion of the pumps and clogging of the reactors)
• Slurry (rarely, if available, must also be cleaned)
• DAO (rarely if available)
• Coker heavy gas oil (rare when available)
• Visbreaker Flashed Distillates (often, if available, but feed content limited by the so-called Conradson Carbon Test (CCT))

Procedure

In hydrocracking, bifunctional catalysts are used which have both a hydrogenating metal function and a carrier such as aluminosilicates with an acid function. The metal combinations cobalt and molybdenum (so-called CoMo-Cat) but also nickel / molybdenum (NiMo-Cat) and nickel / tungsten are usually used for sulfur-containing feedstocks, while platinum- doped catalysts can also be used for the sulfur-free starting material of the 2nd stage (see below) . To carry out the process, quantities of up to 500 m³ of hydrogen per ton of input material are necessary. The process requires hydrogen partial pressures of up to 200 bar pressure and temperatures of up to 480 ° C.

The process can be carried out in one or two stages in a fixed bed reactor . Only sulfur-resistant cobalt-molybdenum catalysts are used in the one-step process. These have the disadvantage of a rather low activity, but remove the heterojunctions and hardly deactivate. Unconverted product (so-called HCU bottoms or unconverted oil, see also Hydrowax ) is normally used as an alternative feedstock for a steam cracker . The one-step process has the advantage that the expensive hydrogen-resistant high-pressure equipment does not have to be installed twice.

In order to take advantage of the higher catalytic activity of nickel- or platinum-containing catalysts, multi-stage processes are increasingly used. As in the one-step process, a CoMo catalyst is usually used in the first step. The resulting HCU bottoms, freed of sulfur and nitrogen, are converted in a second step with other highly active catalysts (recirculated until they “disappear”).

Products

• hydrogen-rich gas (if a "bleed" is required)
• Refinery gas
• LPG
• HCU light naphtha (boiling range: ~ 25–70 / 85 ° C, directly as a blending component for gasoline , but also as a steam cracker feed)
• HCU heavy naphtha (boiling range: ~ 70 / 85–170 ° C, as reformer feed, but also as steam cracker feed)
• HCU kerosene (boiling range: ~ 170–250 ° C, directly as a jet A1 component, but also as a diesel blending component)
• HCU gas oil (boiling range: ~ 250–340 / 360 ° C, directly as a diesel blending component)

and with a one-step process:

HCU bottoms (boiling range: ~ 340 / 360–560 ° C, as steam cracker or FCC feed, but also for the production of semi-synthetic lubricating oil )

variants

In mild hydrocracking, only about 20–60% (at 50–100 bar) of the educt is cracked. The process is mainly used for gas oil production and for the manufacture of FCC feed.

The GtL process requires a special hydrocracker process for isomerizing cracking of the highly paraffinic feedstock.

literature

• J. Scherzer, AJ Gruia: Hydrocracking Science and Technology. Marcel Dekker Inc, 1996, ISBN 978-0-8247-9760-7 .
• KH Schmidt, I. Romey, F. Mensch: Coal, petroleum, natural gas: chemistry and technology. Vogel Verlag, 1981, ISBN 978-3-8023-0684-6 .
• W. Keim , A. Behr , G. Schmitt: Fundamentals of industrial chemistry. Technical products and processes. Verlag Salle, Frankfurt 1991, ISBN 978-3-7935-5490-5 .

Individual evidence

1. ^ S. Bhatia: Zeolite Catalysts: Principles and Applications . CRC Press, Boca Raton 1989, ISBN 978-0-8493-5628-5 , pp. 251 ( limited preview in Google Book search).
2. ↑ DSJ Jones, PR Pujad: Handbook of Petroleum Processing . Springer Science & Business Media, Dordrecht 2006, ISBN 978-1-4020-2819-9 , p. 287 ( limited preview in Google Book search).
3. ↑ M. Bhaskar, G. Valavarasu, KS Balaraman: Mild hydrocracking of FCC feeds yields more fuels, boosts margins. In: Oil & Gas Journal. October 6, 2002, accessed August 21, 2017 . 
4. ^ Mild hydrocracking. 2B1st Consulting, July 11, 2012, accessed on August 21, 2017 .