Aug-2021

Catalysts and adsorbents in the energy transition

Catalysts and adsorbents play a crucial role in the energy transition, from the development of biofuels and the circular economy to green hydrogen production.

Dr Meritxell Vila
MERYT Catalysts & Innovation

Article Summary

Energy transition means the shift from current energy production systems, which are based mainly on non-renewable energy sources (oil, natural gas and coal), to energy systems based on renewable energy sources. Catalysts and adsorbents, used in around 90% of current industrial production processes, are therefore key players in the energy transition. They will be responsible for new processes, or must be improved or modified for current processes. 

Catalysts by themselves are essential in the energy management of chemical reactions. Thanks to them, we can perform reactions under lower temperature and pressure and in a reasonable time. In this sense, catalysts are the main energy savers of the industry. Therefore, their role in the energy transition is crucial, as we will see in this article.

Together with the energy transition, there is a change in fuel demand compared with chemical derivatives. Environmental protection legislation and the increase in consumption of chemicals from developing countries could set the stage for a future world with lower demand for transportation fuels and higher demand for petrochemical feedstocks.1 This demand is also favoured due to the higher margin of petrochemical products. As a consequence, refineries are switching to biofuels and crude oil to chemicals (COTC). Figure 1 shows detailed current and announced refinery conversions to biofuels and COTC. With these transformations, new technologies to produce green hydrogen will be critical to achieving the energy transition.

Catalysts and adsorbents in crude oil to chemicals refineries
The main objective of a COTC refinery is to convert oil to chemicals, from a traditional refinery conversion of 8-12% to more than 50%, even to 70-80%.2 To achieve this ambitious modification, researchers, catalysts companies and licensors have been working hard for many years to develop different proposals. The best solution would be a unique multifunctional catalyst that could transform the oil into chemicals, crack, dehydrogenate, remove sulphur and all the desired reactions.

Researchers at King Abdullah University of Science and Technology (KAUST), in partnership with Aramco, have recently designed a new catalyst based on zeolites, clay and silicon carbide to convert Arabian Light crude into light olefins, with yields per pass of over 30 wt% and minimum production of dry gas, in a single reactor system.

In parallel to developing this unique multifunctional catalyst, the industry is tackling the COTC strategy in three different ways, as already pointed out in 2017 by Dr Avelino Corma:⁴

➊    Direct processing of crude oil in steam cracking This process requires preconditioning of the crude oil before being fed into the steam cracker to avoid too much coke formation. The steam cracker requires a packing bed and a catalyst bed. This catalyst bed may be disposed of at the bottom of the vaporiser to enhance cracking, and will help to remove metals such as Ni, Fe, V and trap non-vapourisable material such as asphaltenes. Materials such as alumina, silica-alumina, molecular sieves and natural clays may be used. Industrial references for this technology come from ExxonMobil (Singapore refinery) and Shell.

âž‹    Integrated hydroprocessing/deasphalting and steam cracking Saudi Aramco has patented an integrated hydrotreating, steam pyrolysis and coker process for the direct processing of crude oil to produce olefinic and aromatic petrochemicals. In this scheme, the role of the hydrodemetalisation catalyst before the hydroprocessing catalyst is vital to protect it.⁵

➌ Processing of middle distillates and residues using new hydrocracking ebullated bed technology This scheme has been adopted by Hengli Petrochemical Ltd to produce diesel and naphtha range stream, which can later be processed to produce aromatic compounds.⁶

In these new COTC schemes, the most affected processes produce naphtha, which is the source of olefins and aromatics, feeds to chemicals. These processes are fluid catalytic cracking (FCC) and hydrocracking.

In hydrocracking, new developments present ebullated catalytic beds, as in Axens H-Oil process.7 In this process, fresh catalyst is continuously added to the reactor, and the spent catalyst is withdrawn to control the level of catalyst activity. This technology provides higher conversion and no limit on catalyst life compared to traditional fixed beds.

Other hydrocracking technologies with moving catalytic beds are LC-fining, from CLG, VCC from KBR, EST from Eni, Uniflex from UOP and ORH from TIPS RAS. In the last four technologies, the conversion reached of the residue with recycling is higher by 95% (see Table 1).⁸

Regarding FCC trends, the selection of catalyst and optimal operation conditions are crucial to increasing the yield of propylene and naphtha. Characteristics that need to be improved in this type of catalyst are metal poisoning tolerance, hydrothermal stability, fluidisation properties, attrition resistance and accessibility. Increasing the addition of ZSM-5 helps to obtain more propylene, but only to a certain extent.

For example, Honeywell UOP’s RxPro process has a catalyst optimised to maximise the propylene yield to more than 20 wt% of feed and an aromatic rich naphtha stream for BTX recovery. Light cycle oil can also be further upgraded to BTX aromatics using the company’s LCO-X process.⁹

In future refineries, the CO2 emitted will be captured and profited to produce hydrocarbons. In this respect, numerous catalysts are being developed to carry out the reactions of conversion of CO2 to hydrocarbons, via methanol or directly.¹⁰ For the first route, via methanol, several catalysts are needed: a metal oxide to convert the CO2 to methanol, a zeolite to convert the methanol to hydrocarbon, a noble metal with non-noble metal catalyst to convert the CO to methane, and an iron base catalyst to convert the CO to hydrocarbon (Figure 2).

For the direct conversion of CO2 to hydrocarbon, many catalysts based on the reverse water gas shift (RWGS) reaction and the Fisher-Tropsch synthesis reaction (FTS) are currently under research and development. These catalysts include zeolitic imidazole frameworks (ZIFs), covalent organic frameworks (COFs) and metal organic frameworks (MOFs), among others.¹¹

Production of biofuels and circular economy
Another critical role for catalysts and adsorbents is producing biofuels, as many refineries are converting to biorefineries to adapt to new regulations and process not only biomass but also prepare to process recycled materials.

IEA Bioenergy Task 42 has developed a classification scheme to describe different biorefineries. Based on the feature of the platform that links feedstocks and final products, we can find several different biorefinery configurations: syngas, pyrolysis oil, sugars, oil, biogas, organic solutions, lignin, hydrogen, and power and heat.¹²