Advances in Hydroprocessing Technologies
Dr Anil Kumar Sinha (Principal Scientist) Head - Hydroprocessing Area, Refining Technology Division, Indian Institute of Petroleum, Dehradun

Hydroprocessing is used in every major refinery. It is also termed as the work horse of the refinery as it is the hydroprocessing units that ensure several significant product quality specifications, provide feeds of desired specifications for other units and increase the refinery margin. This article explains about this element and talks about hydrocracking and hydrotreating technologies.

Increasing awareness about the impact of environmental pollution by automobiles has shifted the responsibility of pollution control to the refineries side. As a consequence of this, the gasoline and diesel sulfur specifications are made increasingly stringent. The sulfur level is being lowered, all over the world to less than 10 ppm for gasoline and diesel and 0 ppm for fuel cell application range. To achieve such low sulfur levels in fuels, the activity of the present catalyst need to be increased to about 7 to 10 times. In order to reach such low level sulfur many approaches are required among which variation of support is an important one .

In modern refinery, sulfur in fuels is removed by means of hydrotreating process, in which the Hydrodesulphurisation (HDS) catalyst is the core of the technique. Due to increasingly heavier crudes, it has however become difficult to achieve the future sulfur specification with current catalysts and processes [1]. To meet the challenges related to the HDS of various petroleum fractions, development of newer generation of catalysts is a continuous target of all the catalyst vendors and institutes involved in this area. There have been various attempts to improve catalyst activity such as changes in active metal composition, use of different types of active metals, additives and supports etc, among which variation of support is an important one [2-4]. Most of the HDS catalysts employed for industrial applications are molybdenum based promoted with cobalt and nickel and supported on alumina.

The effect of support on catalyst activity has already been subject of intense research; however, their low surface area, limited thermal stability and unsuitable mechanical properties hindered commercial exploitation of these materials. CoMo catalysts that have a higher desulphurisation activity are able to reduce sulfur in gas oil to 10 ppm. This catalyst is based on newer catalyst technologies that enhance the number and activity of active sites [5].

Nanosized core-shell type metal/metal oxide mesoporous nanocatalysts and nanostructured porous thermally stable crystalline alumina & silica coated alumina are some of the potential candidates for these high temperature reactions like hydrotreating and hydrocracking, as well as oxidation, hydrogenation and isomerisation reactions.

These newer materials can provide better hydrogen utilisation (atom efficiency), prevent sintering, coke deposition, etc. Nanosized catalysts with less steric hindrance will be more effective in removal of sterically hindered refractory substituted dibenzothiophenes. Deep-desulfurisation of diesel fractions is an issue due to three reasons, ie, low reactivity of 4,6 -DMDBT, inhibiting effects of PAH, H2S and N2 compounds, and polyaromatics competing with S compounds on surface of hydrotreating catalysts and H2S affects direct C-S hydrogenolysis.

Technologies have been developed, including that by us, for hydroprocessing various plant-derived oils like soybean oil, sunflower oil, palm oil, rapeseed oil, tall oil, jatropha oil and waste cooking oil either directly or co-processing with gas oil [6-8]. There are several challenges for these newer technologies in Fixed Bed Reactor (FBR) which are less in typical hydroprocessing reactions such as sediment-induced fouling, catalysts deactivation, product quality deterioration, pressure drop, high exothermicity, undesirable high oxygen content along with sulfur, nitrogen, oxygen, metals & insoluble, and where the end-of-run temperature is reached more quickly.

Development of Hydrotreating Technology has also been continuous as follows:
  • 2005 to present: Miniature microfluidic HDS units for cleaner feedstocks to be used in fuel cell hydrogen reformer; ULSD; S-free feed for fuel cell
  • 1980 to 2000: Stringent product specifications and environmental regulations (Metals, Aromatics, Sulfur) resulted in development of newer NiMo/CoMo systems such as trilobes and tetra lobes
  • 1974: Advances analysis techniques provided crystallographic data leading to better understanding and modelled CoMo2S4 form for HDT activity. Increased active phase loading was possible.
  • 1964: Base oil hydrotreating, upgradation and stabilisation were the main target.
Catalyst modification is done to enhance hydrogenation of aromatic ring, induce isomerisation of methyl groups by providing acidic feature, and remove inhibiting substances. Use of novel supports with high surface area for high activity per unit weight, uniform mesopore to facilitate polycyclic S compounds diffusion, mild acidity to promote metal dispersion & possible isomerisation and with high degree of active-site exposure than conventional catalysts.

Deep desulphurisation of naphtha for Ultra Clean Gasoline for S removal by catalytic HDS results in decrease in octane number which can be managed by catalyst modification, and process modification besides using FCC Naphtha.

In the transportation fuels the perspective for hydroprocessing has been continuously changing. The focus for hydroprocessing was more in terms of environmental concerns (S and N reduction) which have been gradually shifting towards sustainable supply hence the demand of newer catalytic technologies for Natural Gas-to-Liquid (GTL) and Biomass-to-Liquid (BTL) have been increasing.

Scope of Innovation in the current refinery catalytic hydro-conversion processes exist in several areas - production of ultra-clean gasoline, deep desulfurisation of petroleum fractions, selective hydrogenation of pyrolysis gasoline for quality solvent, aromatics and sulfur reduction from middle distillates for specialty solvent, hydroprocessing of biomass derived oils, aromatics production from biomass derived oil, process intensification for fuel from biomass, gas and refinery feedstocks, production of hydrogen from biomass as well petroleum derived feedstocks.

Common approaches to upgrading hydrotreaters and hydrocrackers includes upgrading feedstock and integrating processes, implementing a higher -activity catalyst, replacing reactor internals for increased efficiency, adding reactor capacity, increasing H2 partial pressure.

Depending on feed, throughput and economics, different reactors are used in hydroprocessing. FBRs are used for conventional feedstocks while more heavy feedstocks, specifically residues require reactors with larger residence time such as ebullated bed reactors and slurry system.

Interbed quenching is a newer approach for hydroprocessing of newer and unconventional feeds types for improved catalyst cycle length, product quality, unit reliability and process safety. It involves injecting feed in between two catalyst bed. Either gas quench or liquid quench is used. It helps avoid under-utilisation of the catalyst and the formation of local hotspots.

Heavy crude hydroprocessing, renewable hydroprocessing and residue conversion processes and technologies have acquired much importance in order to secure steady supplies of ultra-clean transportation fuels, to increase the use of heavy crudes and residues (adding from bio-mass, algae lipids, vegetable oils and animal fats - carbon-neutral and sustainable), due to depletion of light sweet crudes, to reduce emission of greenhouse gases, to raise productivity and improve energy efficiency.

There are challenges and opportunities to refiners for innovation in hydroprocessing R & D by developing new (nano)materials based catalysts, alternative route for fuel production, and technologies which can be integrated with the present refinery infrastructure - aromatic reduction from middle distillates due too stringent specifications on gasoline, diesel and aviation fuel; processing of heavier crudes; residue upgradation; production of strategic fuel with high energy density (such as THDCPD) [9]; selective hydrogenation of naphtha (py-gas) for aromatic solvent production; application of modern reactors such as micro channel reactors for process intensification.

References:
  1. Song, C, An overview of new approaches to deep desulfurization for ultra -clean gasoline, diesel fuel and jet fuel. Catal Today, 2003, 86, 211; Topsoe, H, Clausen, B S, Massoth, F E, in: J R Anderson, M Baudart (Eds), Hydro- treating Catalysis- Science and Technology, Vol 11, Springer- Verlog, New York, 1996.
  2. Okamoto, Y, Breysse, M, Dhar, G M, Song, C, Effect of support in hydrotreating catalysis for ultraclean fuel. Catal Today, 2003, 86 1.
  3. Muralidhar, G, Srinivas, B N, Rana, M S, Kumar, M, Maity, S K, Mixed oxide supported hydrodesulfurization catalysts - a review. Catal Today, 2003 ,86, 45.
  4. Breysse, M, Afanasiev, P, Geantet, C, Vrinat, M, Overview of support effects in hydrotreating catalyst. Catal Today, 2003, 86,
  5. http://www.topsoe.com/business_areas/refining/~/media/PDF%20files /Refining/Topsoe_TK- 576_BRIM_ULSD.ashx
  6. Transportation fuels from co-processing of waste vegetable oil and gas oil mixtures, B S Rana, R Kumar, R Tiwari, R Kumar, R K Joshi, M O Garg, A K Sinha, Biomass and Bioenergy, 56, 4352.
  7. Development of Hydroprocessing Route to Transportation Fuels from Non -Edible Plant-Oils, A K Sinha, M Anand, B S Rana, R Kumar, S A Farooqui, M G Sibi, R Kumar, R K Joshi, Catalysis Surveys from Asia 17(1), 1-13.
  8. Aviation fuel production from lipids by a single-step route using hierarchical mesoporous zeolites, D Verma, R Kumar, B S Rana, A K Sinha, Energy & Environmental Science 4(5), 1667-1671.
  9. Single-step catalytic liquid-phase hydroconversion of DCPD into high energy density fuel exo-THDCPD, M G Sibi, B Singh, R Kumar, C Pendem, A K Sinha, Green Chemistry 14(4), 976-983.