April 2026

Process Optimization

Innovations in hydrotreating: Process improvements for better hydrogen utilization

IP: 10.1.228.95

Hydrotreating is an essential refining process that removes sulfur, nitrogen and metal contaminants while saturating hydrocarbons to meet fuel quality standards. However, traditional fixed-bed hydrotreaters consume a lot of energy and are inefficient in hydrogen (H2) use, resulting in high operating costs and environmental impacts. This article reviews recent advancements in hydrotreating technology, emphasizing process improvements and H2 utilization techniques. It covers new reactor designs, improved H2 mixing methods, energy efficiency upgrades, H2 recovery and advancements in process control. The article also highlights emerging trends and potential innovations aimed at enhancing hydrotreating efficiency, reducing H2 consumption and lowering emissions. 

Hydrotreating. Hydrotreating is a critical refinery process that uses high-pressure H2 and catalysts to remove impurities and saturate hydrocarbons.¹ However, conventional hydrotreaters (typically fixed-bed trickle reactors) are energy-intensive and often inefficient in H2 usage​.² Large H2 excess is fed to ensure impurity removal, but much of this H2 is not effectively utilized​.¹ Inefficient gas-liquid contacting, H2 losses and limited mass transfer lead to high H2 consumption and operational costs. There is a strong incentive to innovate processes that improve H2 utilization, reduce energy use and enhance overall efficiency, both for economic and environmental benefits. The following will explore potential innovations—from novel reactor designs and advanced H2 mixing to energy integration and control strategies—highlighting emerging trends, recent patent activity and gaps where new patents could be filed. Each section compares the conventional approach to improved methods, identifying opportunities for patentable solutions.  

Novel reactor designs for improved H2 utilization. Traditional hydrotreaters use downflow trickle-bed reactors, where liquid oil and H2 gas co-currently pass through a catalyst bed. These simple designs suffer from H2 maldistribution and accumulation of reaction byproducts [H2 sulfide (H₂S), ammonia (NH₃)], along the reactor length, which lowers effective H2 partial pressure and reaction rates.¹ They also require high H2-to-oil ratios to push reactions to completion, causing vaporization of lighter hydrocarbons and high pressure drop.¹ The following innovations in reactor configuration can address these issues:  

• Crossflow reactor (radial flow). A recently patented crossflow fixed-bed reactor introduces H2 laterally across the catalyst bed instead of only co-currently.1 In this design, H2 and byproduct gases flow radially outward and are continuously removed while liquid flows downward. This maintains a high H₂ partial pressure uniformly and prevents inhibitors (H₂S, NH₃) from building up in the bed.1 The result is more efficient H2 use, higher reaction rates and lower required gas/oil ratios​.¹ A U.S. patent has been granted for this technology​, and studies show it can achieve the same desulfurization performance as a trickle-bed reactor with 15%–20% less H2 heating duty (due to eliminating interstage quenching)​.¹  

Further novel reactor designs (e.g., radial flow multi-stage reactors, membrane-integrated reactors) could be patented to enhance H2 contact or selectively remove inhibiting gases in situ, building on the crossflow concept. 

• Ebullated-bed and slurry reactors. For heavy oil hydrotreating, ebullated-bed (expanded catalyst bed) or slurry reactors have been used to improve mixing and allow continuous catalyst addition. Recent patent activity includes improved ebullated-bed processes with enhanced kinetics.³ These reactors provide better H2-oil contact than fixed beds and handle heavier feeds. Novel configurations (e.g., hybrid fixed-fluidized beds or staged ebullated beds) that maximize H2 mass transfer while minimizing back-mixing are the other possibilities that can be explored. Integrating internal devices to distribute H2 evenly in these reactors is another area for innovation. 

In conventional trickle-bed, one-pass, co-current flow, significant excess H₂ is needed, resulting in substantial H₂S and NH₃ buildup, as well as a drop in H₂ partial pressure along the reactor, and high pressure drops. Possible innovations could involve crossflow or radial flow reactors that remove spent H2 and inject fresh H2 along the reactor, maintaining reaction driving force and reducing H2 waste.¹ Fluidized/ebullated beds improve mixing, tackling feeds that foul fixed beds. The new designs promise lower H2 requirements and longer catalyst life by alleviating H2 mass transfer limits inherent in older reactors. 

Advanced H2 mixing and dissolution technologies. Even with improved reactor designs, the way H2 is introduced and mixed with oil is crucial. In conventional units, H2 is simply blended with the feed or added via quench points, which can lead to suboptimal dispersion. Advanced mixing methods aim to create finer H2 bubbles and better contact, thus dissolving more H2 into the liquid phase where the reactions occur: 

• Venturi jet ejectors and static mixers. Using a jet ejector (venturi mixer) to entrain H2 into the oil feed can create high shear and turbulent mixing. The pressure drop through a venturi mixer aspirates H2 and disperses it as small bubbles in the oil. A technology licensora has proposed using ejector-type devices (thermocompressors) within hydroprocessing units to combine streams and boost H2 pressure​.⁴ Such devices could serve dual purposes: mixing H2 and even recovering H2 from low-pressure streams. Probable innovations can include custom-designed feed injection nozzles or venturi mixers that maximize H2 dissolution. For example, an integrated feed injector that uses the feed’s kinetic energy to atomize H2 into microbubbles could significantly improve H2 mass transfer. 

• Microbubble injection (micro-interface technology). Micro- and nano-bubble generators are an emerging innovation to intensify gas-liquid contact. A recent Chinese patent describes a micro-interface hydrogenation system, where a microbubble generator (with a microporous venturi and an ultrasonic unit) disperses H2 into micron-scale bubbles.⁵ The H2 is injected through a porous medium and broken into tiny bubbles, aided by ultrasonic vibrations, creating a fine gas-liquid emulsion. This dramatically increases interfacial area and H2 dissolution in the oil. The result is more complete H2 utilization and the ability to operate at lower overall H2 feed rates for the same performance​.⁵  

Building on this, new innovations could target retrofittable microbubble mixers for existing hydrotreaters or the use of nano-bubbles. For instance, an innovation might involve inline ultrasonically assisted spargers that can be installed at reactor inlets or between catalyst beds—a solution that could be patented to upgrade current units for better H2 efficiency. 

• H2 saturation devices. Another approach is to pre-saturate the feed with H2 before it contacts the catalyst. This could involve a high-pressure contactor where H2 is dissolved into the oil (like a scrubber or saturator) so that the liquid entering the reactor is already rich in dissolved H₂. While conventional units rely on H2 dissolving within the catalyst bed, a saturator or diffuser upstream ensures the liquid phase is H2-loaded. A novel idea could be a compact H2 saturator using rotating packed beds or advanced contactor materials to dissolve H2 into heavy feeds that normally have low H2 solubility. This would optimize the H2-oil interface and could be integrated with feed heating.  

H2 is often not fully utilized because of poor dispersion—large bubbles rise through the catalyst quickly, and a significant amount of H2 leaves unused.¹ By generating smaller bubbles or dissolving H2 into oil, the contact time and surface area increase, improving the reaction rate per unit of H2. Jet ejectors and microbubble generators ensure H2 is finely distributed, leading to more uniform reactions and less excess H2 needed. These innovations can address the mass transfer gap in traditional hydrotreaters, directly attacking the limitation that many hydrotreating reactions are gas/liquid mass-transfer limited.⁶   

Optimizing H2-to-oil ratio and utilization. The H2-to-oil ratio is a key operating parameter in hydrotreating: it is the amount of H2 (typically in Nm³ of H₂/m³ of oil) supplied relative to feed throughput. Traditional practice uses large excess H₂ (e.g., > 400 Nm³ H₂/m³ of oil in diesel hydrodesulfurization) to ensure enough H2 is dissolved in the oil and to suppress coke formation.1 However, once H2 dissolution and mass transfer are improved, it becomes possible to lower the H₂-to-oil ratio without sacrificing performance—directly reducing H2 consumption. Innovative strategies include: 

• Distributed H2 injection. Instead of adding all H2 at the reactor inlet, adding H2 in stages along the reactor (or in multiple reactors) can match the active H2 concentration to what the reaction needs at each point. Conventional units partly do this with inter-bed quench, but future designs could use targeted injection points or membranes that feed H2 only where a deficiency is detected. The crossflow reactor’s approach of uniform H₂ delivery along the catalyst length is one example that lowers the required overall H₂-to-oil ratio while maintaining reaction rates​.¹  

A probable way to implement this technology could be an advanced control system that dynamically adjusts H2 injection rates at different reactor segments based on real-time measurements (e.g., measuring H₂ concentration in the liquid). This would prevent over-supplying H2 in early stages and ensure sufficient H2 in later stages, optimizing the ratio. 

• Low H₂-to-oil process schemes: Researchers have proposed flow schemes specifically to operate at low H₂ ratios. One patent, for example, discloses a “low hydrogen-oil ratio hydrotreating method” where H2 is introduced directly into the reactor’s vapor space and a special liquid distributor ensures good contact​. By improving the contacting, the process can run with less H2 than normal. Another approach demonstrated in a refinery experiment is to fractionate the feed and only hydrotreat the portion requiring heavy hydrogenation, allowing a lower H2 rate for the bulk of the feed.⁷ In trials, Dhar et al. achieved significant H2 savings by treating heavy diesel fractions separately, cutting H2 consumption from 0.82% to 0.62% of feed by weight​.⁷  

These concepts, such as integrated feed fractionation with hydrotreating or novel reactor internals (like packed vapor spaces or enhanced liquid distributors) that enable ultra-low H₂-to-oil operation, open new vistas to improve the reactor performance at lower H2 availability. In addition, combining catalysts or additives that promote H2 solubility could be another path (e.g., using a solvent or dispersant to carry more dissolved H₂ into the feed). 

• Enhancing H2 solubility. Ultimately, the minimum H₂-to-oil ratio is limited by how much H2 can dissolve into the oil under operating conditions. Innovations that effectively increase H2 solubility or availability can reduce the excess needed. For example, microbubble injection, as discussed, can allow sufficient H2 at much lower bulk flowrates, essentially “doing more with less” H2 by utilizing it efficiently.⁵ Also, maintaining high H2 purity in the recycle gas increases the effective H2 partial pressure, which can allow a lower total gas rate for the same H2 partial pressure. Removing diluents like light hydrocarbons and byproduct gases from the recycle stream increases H2 concentration, improving utilization efficiency.^4,8​  

A possible way to improve H2 dissolution might include in-situ solvent additives or the use of mildly polar co-solvents that carry more H2 (a speculative but interesting idea). Another gap is real-time adjustment of H2 rates based on feed properties—a control algorithm could be patented that lowers the H₂-to-oil ratio when feeds are easier (low-sulfur) and raises it for more difficult feeds, always keeping just the necessary amount; therefore, using smarter distribution and mixing to cut the required H₂-to-oil ratio closer to the true consumption, plus a small margin. Each improvement in mixing, contacting and purity pushes the minimum necessary H₂-to-oil ratio downward while still achieving target sulfur/olefin removal. Lower H₂ circulation means smaller compressors and lower H2 make-up costs—a direct economic win for refiners, and thus a hot area for patentable process improvements. 

Integrated H2 recovery and recycling. H2 that is not consumed in the reactions is typically recycled in hydrotreaters. However, losses still occur. H2 dissolves in liquid products and ends up in downstream separators or fractionators, where it can be lost to fuel gas.⁴ Also, impurities like H₂S build up in recycle gas, requiring purging that sacrifices some H2. Innovations in H2 recovery aim to recapture or reuse this H2 more effectively, reducing the need for fresh make-up H2:  

• Membrane separations. Gas separation membranes (often polymeric or palladium alloy for H₂) can be integrated to treat the recycled or purge gas. A membrane unit can selectively permeate H2 from a mixed gas (H₂, H₂S, light hydrocarbons), producing a purified H2 stream to return to the process. Integrating a H2-selective membrane after the high-pressure separator or in the purge line can recover a significant portion of H2 that would otherwise be lost. Several refiners have implemented membrane systems for hydrotreater purge gas to improve H2 recovery.   

Possible developments could focus on high-temperature membranes that can be placed closer to the reactor (even inside the reactor effluent line) to separate H₂ before it mixes with H₂S in the low-pressure section. Another patentable concept is combining a membrane with a reactive absorber (for H₂S) in one unit, effectively creating a compact H2 purifier tailored for hydrotreating recycle gas. 

• Ejector (thermocompressor) systems. As mentioned earlier, ejectors can use a high-pressure motive stream to boost a lower-pressure stream. A licensing company’sa recent patent application proposes using a liquid jet ejector (thermocompressor) driven by high-pressure separator gas to suck H2 from a low-pressure source (like fractionator offgas) and reintroduce it into the cycle.⁴ In this scheme, an ejector elevates the pressure of an impure H2 stream, then that stream is sent to a purification unit [pressure swing adsorption (PSA) or membrane] to extract H2, which is recycled back to the reactor.4 This clever integration captures H2 that would otherwise go to fuel.   

Multi-stage ejector systems can be used to scavenge H2 from various points (e.g., from the stripper overhead or from multiple separators). Also, using process liquids as the motive fluid (instead of steam or gas) in ejectors to recompress H2 is a novel twist—for instance, using a high-pressure naphtha stream to entrain H2. Such innovations can improve H2 recovery without major rotating equipment.  

• PSA and advanced scrubbing. PSA units are standard for H2 purification in refineries but usually operate as large central units. For hydrotreaters, a smaller PSA could be integrated to treat recycle gas or purge gas, removing H₂S/CH₄ and returning > 90% pure H₂ to the reactor loop. Additionally, improved H₂S scrubbing (e.g., amine units) to deeply remove H₂S from recycle gas will increase H2 partial pressure in the loop and reduce purge requirements​.8 Increasing H2 purity (by purification and better H₂S removal) can extend catalyst life and allow higher conversion at the same pressure8, effectively doing more with the same H2. A probable improvement might involve a compact PSA or metal hydride absorber integrated directly at the unit, or a novel swing adsorption process that operates cyclically in sync with the hydrotreater’s cycle to recover H2. Another area is catalytic decomposition of H₂S (splitting it into H₂ and sulfur), an advanced concept under research that, if tied into a hydrotreater’s gas loop, could regenerate some H2 from H₂S byproduct (this would be a breakthrough, and any practical implementation would be highly patentable). 

Integrated recovery devices (membranes, PSA, ejectors) can capture H2 that escapes the immediate recycle loop and reintroduce it, cutting losses​.⁴ The result is a higher H2 utilization percentage in the unit—more of the H2 ends up reacting with oil and less is wasted. These improvements directly reduce the need for fresh H2 production (or purchase), which also means lower energy use in H2 plants and a lower CO₂ footprint for the refinery. 

In a co-current downflow trickle-bed reactor involving hydrotreating and hydrocracking reactions, the liquid phase is typically mixed with a gas or vapor phase, and the mixture is passed over a particulate catalyst maintained in a packed bed in a downflow reactor.  Because of an exothermic chemical reaction, heat is produced. Therefore, quenching the effluent and adding a reactant at different locations are required. A well-practiced process is quenching the hot liquid stream with cold H2 gases by injecting it between two catalyst beds and mixing through quench mixing devices or quench boxes. Generally, quench boxes or mixing devices are comprised of major components: 

• A quench box conduit with a sparger 

• A quench tray or collection tray  

• A mixing chamber 

• Distributor trays. 

Quench mixing devices. Various quench mixing devices are described in journals and patents. Most of these devices can be grouped into the following types: 

• Vortex mixers with an inlet channel from the collection tray 

• Vortex mixers with radial inlet 

• Baffled box mixers 

• Mixers with separate mixing of the vapor and liquid 

• Bubble cap-type quench mixer. 

Baffled box-type quench mixers have various designs where liquid and gas pass through channels, changing flow directions. These fluids may pass through constrained spaces or orifices in the flow path. Mixing occurs as the fluid passes through areas of increasing and decreasing cross-sectional spaces. This type of quench device has a higher pressure drop, as the fluid must pass through constrained spaces and longer paths. An example of this type of quench device is available in literature.⁹ 

In vortex-type quench mixers, liquid and gas swirl in a mixing chamber. Although there can be good gas mixing and acceptable liquid mixing, the interphase mixing is low, as the liquid and gas are separated out in the mixing chamber due to the density differences between them. In this kind of quench mixer, there is only rotational mixing.¹⁰ The gas enters the swirl mixing zone above the liquid level. As a result, the momentum for inducing rotations is reduced.  

Takeaways. The central challenge in hydrotreating hydrocarbons is no longer just catalytic activity—it is how effectively every mole of H2 is used. With detailed analysis, this article has shown that meaningful gains come from integrating three levers rather than optimizing any one in isolation:  

1. Contacting and flow architecture (cross-/radial-flow, staged/ebullated concepts) to sustain high, uniform H₂ partial pressure and remove inhibitors in situ 
2. Intensified gas–liquid contacting (venturi/ejectors, micro-/nano-bubble generation, pre-saturation) to push H2 from the vapor phase into the liquid where reactions occur 
3. Loop purity and recovery (membranes/PSA, ejector-assisted scavenging, deeper H₂S removal), so the recycle carries more active H₂ and less inert burden.  

When coordinated with smarter distribution of H₂ along the reactor, improved quench/mixing internals and advanced control that matches H₂ supply to instantaneous demand, units can step down from traditional excess H₂ operation while holding—or improving—product quality, catalyst life and pressure-drop performance. 

A probable practical roadmap is proposed as:  

• For near-term gains, retrofitting of quench and feed-injection hardware, debottlenecking of gas/liquid mixing and cleaning the recycle to raise effective H₂ partial pressure 

• For the medium term, adding targeted H₂ injection and compact purification/recovery (membranes/PSA, ejector loops) tied into advanced process control for ratio trimming by bed/zone 

• For the longer term, pursuing cross-/radial-flow or membrane-integrated reactors and micro-interface saturators to re-baseline H₂-to-oil at markedly lower setpoints.  

Measured through a consistent key performance indicator (KPI) set—H₂ utilization (%), H₂-to-oil, ΔP, bed temperature spread, catalyst run length and net CO₂/m³ product—this integrated program can convert H2 from a cost and emissions driver into a competitive advantage. 

NOTE  

^a Honeywell UOP 

LITERATURE CITED 

1 Kumar, V., A. Quiyoom, P. K. Rakshit and R. Kumar, “Novel reactor for three-phase hydroprocessing applications,” Digital Refining, November 2023. 

2 Hearn, A., D. Brown, B. Yeung, P. Christensen and T. Yeung, “Technical solutions for hydrotreating,” Digital Refining, November 2023. 

3 James J. Coylar, “Simplified ebullated-bed process with enhanced reactor kinetics,” U.S. Patent US6436279B1, 2000. 

4 Hoehn, R., et al., “Enhanced hydrogen recovery,” U.S. Patent No. US9084945B2, 2013. 

5 Sinopec, “Micro-bubble generator for reinforced hydrogenation technology,” Luoyang Petrochemical Engineering Corp., September 2015. 

6 Zhang, Z., et al., “Overview of microinterface intensification in multiphase reaction systems,” Chinese Journal of Chemical Engineering, 2022. 

7 Dhar, P. K., et al., “Reducing hydrogen consumption in diesel hydrotreating,” Digital Refining, September 2018. 

8 Emerson, “Hydrogen purity: Increase hydrogen partial pressure,” Micro Motion, 2012, online: https://www.emerson.com/documents/automation/training-point-solutions-brief-refining-hydrogen-micro-motion-en-65906.pdf  

9 Muller, M., “Mixing device for two-phase concurrent vessels,” U.S. Patent No. US7276215B2, 2007. 

10 Xu, Z., “Hydroprocessing reactor internals having reduced height,” U.S. Patent No. US10589244B1, 2020. 

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