Evaluating Naphtha Reforming Catalysts

The ability to test all catalysts simultaneously, under rigorously the same feed and conditions, combined with the proprietary Flowrence® technology used to accurately control all the key process parameters, provides unparalleled precision to discriminate the fine differences between the various catalysts.

Every reforming unit has its own constraints, and the portfolio of catalyst vendors often tries to strike the right balance between performance and the ability to accommodate those constraints. Further than paper estimates, the possibility to simultaneously compare catalysts under various plant conditions and with specific feed properties (e.g. amount of coke precursors, the presence of contaminants such as sulfur, etc.) is thus critical to determine the right catalyst.

The approach presented here for CCR catalysts can be applied to any system that has a noticeable deactivation over the duration of days, or even up to months e.g Semi Regen Reforming Catalysts.

 

Background

Avantium provides comparative catalyst testing for refineries. Our industry-proven Flowrence® 16-reactors pilot plant enables the parallel comparison of multiple catalysts under the exact same conditions. For some years now, Avantium has been helping refineries select the best-reforming catalysts. The tools, methods applied and resulting data quality (precision, accuracy and reproducibility) have been independently verified and accepted by the catalyst vendors.

Axens wanted to evaluate the performance of some naphtha reforming catalysts. Four Axens CCR reforming catalysts were evaluated in a fixed-bed 16 parallel reactor high throughput Flowrence® micro-pilot plant. The performance of the catalysts, defined by activity (temperature required), selectivity (C5+ yield) and stability, was evaluated at fixed product severity. For this test, two octane targets were used but aromatic yield can also be targeted.

Result

The so-called iso-RON operation is achieved by using an automated feedback loop between the GC analysis of the effluent and the reactor’s temperature which is thus continuously adjusted. Key results for catalyst performance with time-on-stream are shown in Figure 1.

Results obtained through iso-RON operation are easy to interpret for fixed-bed units (SR reforming) but also provide invaluable information about catalyst performance for moving-bed CCR units, which would otherwise be too difficult to operate on a lab scale. Lower temperature-required (higher activity) to reach the specific octane means greater flexibility for CCR operation, while a lower temperature slope is typically indicative of a low coke-make.

For a CCR unit, the lower coke-make will provide greater flexibility to increase the product severity (e.g. increased aromatic yield) or to process more demanding feeds like thermal cracked Naphtha. Finally, high catalyst selectivity (C5+ yield) is always desired as long as product severity can be maintained. The stability of the selectivity is typically measured by the length and slope of the stable C5+ yield output before the temperature rises sharply.

Analysis of the coke content (Table 1) of the all the spent catalysts confirms the relationship between coke-make and catalyst stability.

Table 1 – Relative coke content (%wt) on spent samples.

 Catalyst Coke (%wt) for RON = base samples Coke (%wt) for RON = base+ samples
A Ref±0.02 Ref±0.1
B +2.40±0.01 +2.33±0.04
C +5.99±0.07 +4.11±0.22
D +2.71±0.23 +1.99±0.12

Due to differing yield stabilities the selectivities of the catalysts are different relative to one another at different Time on Stream (hr). The appropriate interpretation of this data is dependent upon the coke content in the spent samples. For typical CCR operation, the weight percentage coke on catalyst passing out of the last reactor and entering the regenerator is generally specified to be less than 5%. Since the CCR catalyst’s coke content increases as it passes through the CCR reactors, the average coke for the CCR catalyst, averaged over all the CCR reactors, is then less than 5%.

It is therefore relevant to make the comparison of the relative catalyst yields and activities at appropriate (i.e. coke content <5%) Time on Stream in the iso-RON test analogous to the Time on Stream seen commercially.

These trends are completed with the continuous analysis of the product effluent, which provides vendors and refineries with a complete hydrocarbon breakdown for every point in time. The baseline separation of ethyl-benzene and all xylenes isomers, or the breakdown of the C1 to C6 products for example, are crucial for economic and integration studies.

An example of the precision and discriminative power obtained is illustrated in Figure 2 plots, where key selectivities are plotted against temperature required at a fixed time-on-stream (80 hrs), with clearly non-overlapping confidence intervals.

Thanks to the availability of multiple reactors in the micro-pilot plant, each catalyst system was tested in duplicate for each octane target, in order to provide repeatability and confidence interval on the results.

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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