Catalysis 2025 Issue

Reactive feedstock hydrogen decient olen and aromatic species

Foulant formation reactor conditions promote formation of coke precursors

Foulant adsorption coke precursors form soft coke on the active phase

Hyperactive sites active sites free of reaction inhibitors

Low ppH / high temperature reactive species consume hydrogen and generate heat

Permanent activity loss soft coke condenses to form hard coke

Figure 3 Reactive feedstock coke deactivation pathway

stored products from the HEFA unit itself are the most readily available feedstock with low activity. However, HEFA product is unsuitable for catalyst break-in since it has no ability to generate the species needed to temper catalyst hyperactivity. In addition, no hydrogen con- sumption or heat of reaction is generated from processing HEFA product as feedstock. Some amount of reactive HEFA feedstock has to be added to HEFA product to make it suit- able for catalyst break-in. This is easier in principle than in practice, but with careful control of HEFA feedstock addi- tion rate, a good outcome is possible. Protecting biofeedstock What if the catalyst break-in period could be avoided alto- gether? If catalyst could be delivered already activated and pre-conditioned to mitigate hyperactivity, reactive feed- stocks could be added immediately upon start-up. Eurecat’s proprietary pre-activated catalyst conditioning treatment for HEFA units, Totsucat BFP, eliminates the challenges associated with properly breaking in HEFA catalyst. The proprietary BFP stands for Bio Feedstock Protection, a conditioning treatment applied to Totsucat catalyst such that the catalyst’s hyperactivity is tempered by pre-carbon- isation. Both catalyst hyperactivity and reactive feedstocks are necessary to initiate the rapid formation of coke precur- sors. BFP removes a catalyst’s hyperactivity so that reactive HEFA feedstocks can be introduced immediately without fear of promoting accelerated catalyst deactivation. Totsucat eliminates the problems of H₂S and heat input common to in-situ sulphiding of HEFA unit catalysts. BFP eliminates the necessity for catalyst break-in before reactive feedstock introduction. HEFA feedstock can be added imme- diately upon unit start-up. Since the catalyst is already active, the heat of reaction will be available to supplement the fur- nace in raising the reactor to normal operating temperature. Restoring RD and SAF capacity The net result of using Totsucat BFP is full restoration of RD

and/or SAF production capacity much more quickly than is possible with in-situ catalyst activation. The carbon source for BFP’s pre-carbonisation treatment is a bio-oil, suitable for use as a HEFA feedstock. That makes BFP fully compatible with all HEFA unit operational and regulatory requirements. The case for using pre-activated catalyst in the HDO section of HEFA units is compelling, but what about pre- activation of downstream dewaxing and/or cracking cata- lysts? Hydroisomersation dewaxing catalysts are used to improve the cold flow properties of RD while minimising yield loss to less valuable products. After the HDO section of the HEFA unit, where oxygen and olefins are removed, the resulting product stream consists of pure normal paraf- fins 16-18 carbon atoms in length. The material boils in the correct range to be suitable for use as diesel fuel, but the cloud point is far too high at 45-50°C. Cold flow properties must be improved to meet diesel fuel specifications. To reduce cloud point without excessive RD yield loss, catalysts with both cracking and isomerisation functionality are used. The normal paraffins are first catalyt - ically cracked, followed by isomerisation of the fragment(s). Paraffin isomerisation greatly reduces the cloud point of the original n-paraffin without significantly changing the boiling point. Ideally, the isomerised paraffin would retain a similar carbon number to the original n-paraffin. Dewaxing unit designs RD technology licensors offer single-stage and two-stage dewaxing unit designs. Since single-stage designs have small H₂S amounts in the gas, a base metal (NiW) is used for the catalyst’s hydrogenation functionality. Two-stage designs have a ‘sweet’ second stage and typically use noble metal (Pt and/or Pd) for the catalyst’s hydrogenation functionality. Acidity for the cracking functionality of the catalysts used in both single- and two-stage unit designs comes from a shape-selective zeolite (MFI/ZSM-5) or an amor- phous silica-alumina (ASA) incorporated into the support.

Catalysis 2025