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).

Introduction

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.

Methology

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.

Experimental

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.

Reactor Loading

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.

Operating Conditions

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.

Feedstock

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.

Results

Mass Balance

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.

VO Conversion

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

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

Product Sulfur

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

Conclusions

  • 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

Single-Pellet-String-Reactors (SPSR)

No dead-zones, no bed packing & distribution effects. The catalyst packing 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. This applies to single catalyst systems, as well as stacked-bed systems. The use of a narrow reactor avoids any maldistribution of gas and liquid over the catalyst bed, thereby eliminating catalyst-bed channeling and incomplete wetting of the catalyst.

The most accurate and stable pressure regulator for 16-parallel reactors

The most accurate and stable pressure regulator for a multi-parallel reactors with just ±0.1bar RSD at reference conditions. The Reactor Pressure Controller (RPC) uses microfluidics technology to individually regulate the back-pressure of each reactor. By measuring the inlet pressure of each reactor, the RPC maintains a constant inlet pressure by regulating the backpressure. As a result, the distribution of the inlet flows over the 16 reactors is unaffected and a low reactor-to-reactor flow variability is achieved.

Reactor pressure control is not only important to ensure accurate pressure control, but also to help maintaining equal distribution of the inlet flow over the 16 reactors.

Automated liquid sampling system

Programmable, fully automated liquid product sampling robot for 24/7 hands-off operation. Robot equipped with a compact manifold aiming at depressurizing the effluent immediately after each reactor to atmospheric pressure. Reactor effluent is depressurized by a miniaturized (low volume) parallel dome regulator, allowing a stable control of gas or gas/liquid product streams. This eliminates the use of valves at high pressure (such as multi-position valves), which are prone to leakage.

Gas liquid separation is sone directly by collecting the liquid products in sample vials and directing the gas products to the online gas analyzer. This approach minimizes required flushing times in the downstream section of the reactor eliminating the need for high pressure gas-liquid separators, level sensors, and drain valves.

EasyLoad® reactor closing system

Unique reactor closing system, no connections required. With a rapid reactor replacement minimizing delays, improving uptime and reliability. Sealing of up to 16 reactors by simply closing the ‘top-box’ in a single action. No leak testing required!

Stable evaporation by liquid injection into reactor

The direct injection of liquid into the top of the reactor and the consecutive conditioning zone allows feeding of broad range of liquids and concentrations. Various types of liquids, both aqueous and oil phase are successfully evaporated and fed to the reactors.

Tube-in-tube reactor technology with effluent dilution

This unique tube-in-tube feature allows an easy and rapid exchange of the reactor tubes (within minutes!) with a single o-ring at the top of the reactor without the need for any connections. The use of an inert diluent gas (outside of reactor) to maintain the pressure stops undesirable reactions immediately after the catalyst bed while serving as a carrier gas to the GC, facilitating the analysis of high boiling point components, preventing dead volumes and back flow, and reducing the time required to transfer gas and liquid effluent products to the analytical instruments.

The tube-in-tube design enables the use of quartz reactors at high pressure applications.

Compact TinyPressure module glass-chip holder with integrated pressure measurement

Holds the microfluidic glass-chips for gas distribution and measures inlet (and outlet) pressure of the 16 parallel reactors at ambient temperature, allowing online measurement of catalyst bed pressure drop.

No high-temperature pressure sensors required. Pressure range of 10 – 200 bar (high pressure) or 0.5 – 10 bar (low pressure).

The modular design enables easy calibration and quick exchange of the microfluidic glass-chip, without the need for time-consuming leak testing.

Microfluidics modular gas distribution

Unrivalled accuracy in gas distribution with patented glass-chips for 4 and 16 reactors, tested with a guaranteed flow distribution of 0.5% RSD channel-to-channel variability. Quick exchange for different operating conditions, offering the unique flexibility to cover a wide range of applications using the same reactor system.

Auto-calibrating liquid feed distribution, measurement, and control

The most accurate liquid distribution for high throughput systems with real-time liquid flow measurement and control for 16-parallel reactors. Auto-calibrating function enabled by a single flow sensor guarantees that all 16 reactors are continuously operated at the desired LHSV, all the time. Innovative design based on our microfluidic glass-chips with integrated temperature-control. The system continuously regulates the liquid distribution to all 16 reactors, and together with our Reactor Pressure Control technology, eliminates the impacts of pressure variations in the flow distribution.

Proven technology with difficult feedstocks with high viscosity, such as VGO, HVGO and DAO: no blockage and or breakage observed. Different glass-chips available for different viscosities.

Liquid distribution errors below 0.2% RSD, making it the most accurate parallel liquid flow distribution device on the market.

Option to selectively isolate the liquid flow to any of the 16-parallel reactors.

 

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