Hydroprocessing of renewable feedstocks
Testing Vegetable Oil hydrotreating catalysts in high-throughput micro-pilot plants
- With the current megatrend of renewable feedstocks (vegetable oils, liquefied waste plastics), refineries face new technical challenges. With limited renewable feedstock availability for testing, Avantium small-scale reactors technology offers new opportunities to scout process conditions and new designs of catalyst loading sequences.
- Avantium Catalysis developed small-scale parallel fixed bed reactor systems designed for catalyst intake up to 1 ml, trade name Flowrence®, in order to enhance catalyst development and selection. Flowrence® high-throughput technology is extensively used for the parallel testing of hydroprocessing catalysts over a wide range of process conditions and applications.
- We continuously evaluate the feasibility of processing new feedstocks. Our micro-pilot plant technology allows for the highly efficient testing of hydroprocessing catalysts; smaller volumes will reduce the amount of feed required, avoiding the typical issues associated with obtaining large quantities like handling, shipping, and storage (also for longer-term availability of reference feed material).
Accurate catalyst evaluation is an important step in optimizing catalytic processes with respect to product yield, energy efficiency and overall product quality. High-throughput catalyst testing and small-scale reactors offers several advantages when compared to larger reactor systems (C. Ortega, 2021).
Avantium Catalysis continuously evaluates the feasibility of processing new feedstocks at our Flowrence® systems. In this paper, we present the results of processing blends of soybean oil and Straight Run Gas Oil (SRGO) and 100% Vegetable Oil (VO) for renewable diesel production.
In this testing program, we used a commercial ULSD NiMo catalyst to hydrotreating the VO.
The Micro-Pilot Plant
This testing program was conducted in a 16-parallel fixed bed reactors system with a diameter of 2.0-2.6 mm. Figure 1 shows a schematic overview of the 16-parallel reactors micro-pilot plant. This unit employs Flowrence® Technology, which enables the tight control of process conditions – temperature, flow rates, and pressure. See (C. Ortega, 2021) for a detailed description of the Micro-Pilot Plant.
We performed this testing program in collaboration with a catalyst supplier global market leader. For this program, only 8 reactors were used; the high-throughput 16-reactors system allows for the selective isolation of unused reactors.
The catalyst packing in the Single-String-Pellet Reactors (SPSR) is straightforward and does not require special procedures. A single string of catalyst particles is loaded in the reactors with an internal diameter (ID) that closely matches the particle average diameter. To enhance hydrodynamics, an inert nonporous diluent material (with a defined average particle size distribution) is used as a filler. Before doing the final loading in a steel reactor tube, we often perform a trial loading in quartz reactors to confirm the packing (Figure 3). The extrudates are not sorted for length or otherwise.
A commercial ULSD NiMo catalyst was loaded in 8 reactors (561.0 mm length and 2.0 mm internal diameter) with 2 different bed lengths to test 2 different LHSVs (Liquid Hourly Space Velocity) simultaneous (Figure 4). All reactors were tested at 70 barg pressure.
Pressure drop issues is one of the main challenges when processing vegetable oils in hydroprocessing units. This is even more evident when using pilot plants with small diameter reactors as catalyst fouling can quickly lead to plugging. For this reason, the approach of the current test was the co-feeding of the vegetable oil (soybean oil, see properties in Table 2) blended with a SRGO at different ratios as shown in Table 1.
Table 1 lists the different feed blends tested over a period of 400 hours on stream (HOS) and 100% vegetable oil (VO) over 150 hours (6 days). The feed blends with 70%VO and 100%VO were spiked with DMDS up to 2 wt.% sulfur.
An accurate mass balance is an internal control of the data quality obtained.
The mass balance calculation includes the water in the gas stream measured with the online GC.
Reactor pressure regulation and pressure drop over the reactors
Reactor pressure regulation is not only important to ensure accurate pressure control at operating pressures, but also to help maintaining equal distribution of the inlet flow over all reactors.
The pressure drop for all reactors is very small with an overall average of 0.2 barg.
At the predefined testing conditions, we obtained a total conversion of the VO without apparent effect of the LHSV.
Figure 7 shows an example SimDist for the 40% VO feedstock where we can see the conversion of triglycerides (BP > 480°C) into paraffins (apparently mostly C16 to C18).
Liquid Product Yields
Figure 8 presents the Diesel, Kerosene and Naphtha yields for 40% VO, 70% VO and 100%VO feedstocks.
The Yield to Diesel is around 80% for the 100% VO feedstock
- Liquid product analysis (ASTM D5291) confirmed that there was no Oxygen left
- As expected, there isn’t any Naphtha or Kerosene produced from the conversion of the VO – there is a direct conversion of triglycerides to C12+ paraffins
- The small effect of the higher LHSV (1.5 l/l/h) on the VO products yield
- Overall a good reactor-to-reactor repeatability for the product yields
Gas Product Yield
Figure 9 shows the gas make yield (C1, C3 and C4) – only traces of C2 were observed (not presented in the graph) – for all feedstocks tested.
As expected, methane and propane are the main gas hydrocarbons products
- Increasing gas product yields as the amount of VO is increased on the feed
- Up to 5 wt.% propane produced when processing 100% VO
- Good reactor to reactor repeatability for the gas product yields
- Small but consistent effect of LHSV on the gas yields
Figure 10 shows the CO, CO2 and H2O yields.
Increasing gas product yields as the amount of VO increases
- Up to 3 wt.% CO and 5 wt.% CO2 produced when processing 100% VO
- The yield to water presented does not include the small amount of water remaining in the liquid product
- Good reactor to reactor repeatability for the gas product yields
- Clear differences in CO and CO2 yield when using a higher LHSV
Hydrogen consumption was measured using the online GC by comparing the outlet flow of hydrogen with the inlet flow.
As we can see in Figure 11, there is an expected step increase in the hydrogen consumption with increasing amount of VO in the feedstock.
- Around 20% of the hydrogen fed into the system is consumed when processing the 100%VO feed
- Good reproducibility for H2 consumption among duplicated reactors
- Clear effect of LHSV on the LGO and LGO blends hydrotreating
The product sulfur was measured for the 40% and 70% VO blends at ULSD conditions. Note the very good repeatability of the S results for the duplicate reactors at such high conversion.
The reactors temperature was adjusted in order to produce < 5 ppmw S for the LHSV = 1 l/l/h
- Very good reproducibility for product sulfur among duplicated reactors
- No plugging was observed of any of small-scale reactors during the test of 23 days with various VO blends and 6 days running 100% VO
- Quantifying the amount of water in the gas effluent using the online GC is a feasible method for closing the mass balance
- The accuracy of the Mass Balance and Yields obtained during the test are similar to conventional hydroprocessing catalyst testing
- High temperature SimDis is a feasible method for evaluating the conversion of triglycerides during VO hydrogenation tests
- The reactor-to-reactor repeatability obtained during this test is similar to conventional hydroprocessing tests
- The test allowed measuring accurately the HDS capacity of the catalyst at SOR conditions when processing LGO / VO blends
- The Flowrence high-throughput 16-parallel reactors system produces consistent and reliable high data quality with outstanding reactor-to-reactor repeatability for Hydrotreating of Vegetable Oils
- This opens new options for R&D in the field of renewables processing, reducing the amount of the scarcely available feedstocks required for studies