PTQ Q1 2024 Issue

Crude to chemicals: Part 2

Part 1 covered the basics of crude-to-chemicals. Part 2 explains how hydroprocessing technology can be used to convert any crude to chemicals to maximise yields

Kandasamy M Sundaram, Ujjal K Mukherjee, Pedro M Santos and Ronald M Venner Lummus Technology

S audi Aramco Technologies Company, Lummus Technology, and Chevron Lummus Global (CLG) conducted several years of research to develop an improved thermal crude-to-chemicals technology known as Thermal Crude to Chemicals (TC2C). This proprietary tech- nology can produce high chemicals yields while extending the feedstock range beyond just very light crudes or con- densates typically considered. The research and subsequent commercialisation of the technology involved the following vital steps: • Very detailed componential analysis of crudes and heavy oils • Development of specialised separation devices to separate the crude into fractions for optimised processing without having to utilise energy and Capex-intensive crude atmos- pheric and vacuum distillation • Utilisation of commercially proven integration of fixed bed, ebullated bed, and slurry reactor systems in crude condition- ing so that the products from the crude conditioning section could be routed directly to the steam cracker • Development of unique catalyst systems for the fixed bed and ebullated reactors that would provide the right amount of hydrogenation without overcracking to naphtha, LPG, and light ends • Rigorous testing of the impact of varying amounts of pyrolysis fuel oil recycled from the recovery section. TC2C successfully upgrades the pyrolysis fuel oil to steam cracker reactor feed. Throughout the development, particular attention was paid to minimising equipment count (Capex), energy input, carbon footprint, emissions, catalyst deactivation rate, and the reactor fouling rates for various feeds. Overall, hydro- genation improved the steam cracking reactor feed quality. The integrated crude conditioning/steam cracking reactors/ recovery systems formulate the integrated TC2C technology. Crude analysis and conditioning There have been many attempts to characterise crude through detailed compositional analysis. 1,3 In the lower carbon numbers, the total number of n-paraffins, i-paraf - fins, naphthenes, and aromatics is reasonable and easily identified. With increasing carbon numbers, the number of possible compounds increases exponentially. Boduszynski 3 started evaluating crude using detailed compositional anal- ysis. It is well known that diverse compounds with similar molecular weight cover a broad boiling range. Boduszynski

evaluated compounds with a hydrogen deficiency or ‘Z’ value. He showed that complete hydrogenation and ring opening with no change in carbon number could consume vastly different amounts of hydrogen depending on the ‘Z’ value. The general formula is:

C n H 2n+Z

where Z = 2-2 * (R+DB) n = number of carbon atoms R = number of rings, DB = number of double bonds, Z = hydrogen deficiency.

In all crudes, the hydrogen deficiency increases with boil - ing point with a higher concentration of condensed rings, as previously shown in Part 1 (PTQ, Q4 2023). Typically, the highest boiling fractions in crude (containing what is broadly termed asphaltenes) are the most difficult to convert to transportation fuels or petrochemical feedstocks. Indeed, the analysis of asphaltenes using advanced techniques formed part of the research. In TC2C, a naturally abundant n-paraffin-rich light stream is separated with a novel separation device such that it elim- inates heavier molecules from the product that is routed to the steam cracker, as previously shown in Part 1. This step uses dilution steam to vapourise the light cut. Bottoms from the separation device are routed through another separation

Truncated VGO (470-495˚C BP)

Full range VGO (500-525˚C BP)

VR (580-605˚C BP)

Figure 1 DBE values of some species (DBE=C+1-H/2- X/2+N/2; X is halogen, C, H, N are carbon, hydrogen, and H atoms respectively)

PTQ Q1 2024