Catalyst testing for hydrocracking and hydrotreating
High throughput experimentation techniques enable performance testing of commercial catalysts with real feedstocks such as deasphalted oil
JOCHEN BERG, TILMAN SAUER, CHRISTOPHER FEDERSEL, SASCHA VUKOJEVIC, PHILIPP HAUCK, FLORIAN HUBER
and ALFRED HAAS
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Increasing global demand for fuels and heavier feedstocks as well as tightening environmental regulations create a pressing need for the refining and petrochemical industry to optimise or develop new processes to generate and secure today’s fuels for mobile transportation (CNG, LNG and LPG, gasoline and diesel) as well as platform chemicals for the petrochemical industry (C2-C8 olefins, alcohols, aromatics). However, while demand for fuels and especially diesel is increasing, crude oils are becoming ever heavier. Furthermore, environmental regulations stipulate lower sulphur and nitrogen content. There is a need for refineries to optimise or develop new processes for the conversion of products derived from the bottom of the atmospheric distillation column such as atmospheric residue or atmospheric/vacuum gas oils. In this context, it is necessary to develop new catalysts or evaluate several commercial catalysts. By using a traditional approach with a single pilot plant reactor set-up, the process of testing several catalysts can be very time-consuming and a large amount of feedstock and catalyst is needed. Keeping all process parameters constant over time without any influence from the seasons, changing technical equipment or aging of feed/catalysts is very difficult.
Instead, this process can be facilitated tremendously by using high throughput experimentation (HTE) technology with many reactors in parallel, which allows several catalysts and process conditions to be tested at the same time.1,2 Furthermore, the amount and cost of catalyst and feed can be minimised since only a few grams of the catalysts are needed. hte GmbH, located in Heidelberg, Germany, is a provider of such high throughput technology.
In this article, we present two case studies that were performed for customers using the HTE technology in the field of vacuum gas oil (VGO) hydrocracking and hydrotreating of atmospheric residue (AR). These studies show the capability of handling very heavy feedstocks and full-size commercial catalysts with high throughput technology while achieving very high data quality and reproducibility.
Integrated workflow solutions
Over the last 10 years, hte has developed a comprehensive hydrotreating workflow. The workflow is defined as the experimental cycle comprising catalyst synthesis, reactor filling, catalytic performance testing, product analysis, data evaluation and reporting. In high throughput experimentation, many experiments are performed simultaneously. The amount of data increases by at least an order of magnitude when compared to conventional testing. Manual data handling is not an option due to the complexity and huge number of working steps. This necessitates automation of the workflow cycle. Therefore, the company implemented its own fully integrated software workflow.
A typical HTE experiment consists of several steps: catalyst and feed preparation and characterisation, reactor loading, unit set-up, experimental process control, processing of analytical data and data treatment. Each step generates data which is important for the catalyst evaluation. All process data, online analytics and oil samples for off-line analytics generated by the test unit are collected by hte’s process control software hteControl4. Additional offline analysis data from oil samples (for instance viscosity, SimDist, sulphur, nitrogen) are labelled with unique barcodes and sent for analysis. The test unit and all analytical instruments are integrated into the scientific data warehouse myhte. All results are merged in the data warehouse. The data treatment is done with an automated calculation protocol. Data evaluation and reporting in tabulated or graphical form completes the workflow cycle. Using the hte workflow, the history of each catalyst from the beginning to the end of the experiment can be followed and analysed.
The reactor packing is essential for good data quality and reproducibility. Failures in the packing method can compromise the validity of the test results. Powders and full-size extrudates can be tested in the units. When using full-size commercial extrudates in small-scale reactors, wall effects have a considerable influence on the hydrodynamics of gas and liquid flow. To ensure plug flow, extrudates are embedded in an inert matrix, minimising channelling and by-pass effects.3 Processing heavy feeds is a challenging task, especially in small-scale units, due to waxy feed and asphaltenes which need high processing temperatures to avoid plugging in the unit. hte’s units can be heated up to 150°C in all wetted parts.
In hydrocracking applications in particular, closing the mass balance is an important task. Offline liquid phase data (for instance mass flow, sulphur/nitrogen, boiling fractions) and gas phase data (H2, hydrocarbons, H2S) need to be combined to get the overall picture. hte’s hydroprocessing workflow makes it possible to merge automatically all the required data (catalyst and feed characteristics, process data and on/offline analytics) in the myhte database. The raw data is stored in a protected area. On the basis of the raw values, calibration data can be added and powerful calculations started. The reporting function of myhte allows different types of data plots and Excel spreadsheets to be generated easily and exported. The use of additional software such as Excel is in most cases no longer necessary.
Hydrocracking of VGO
This first study illustrates the reproducibility and accuracy of high throughput testing of full-size commercial extrudate catalysts in the application of VGO hydrocracking in a 16-channel trickle bed unit. Four commercial hydrocracking catalysts (called A, B, C, D) and a hydrotreated VGO spiked with dimethyldisulphide (DMDS) and tributylamine (TBA) were used. The test was performed at four temperatures with a duration of 3-5 days each at a reactor pressure of 140 bar. The product gas streams were analysed on the basis of online gas chromatography and thermal conductivity detection (hydrocarbons up to C20, H2 and H2S) and the liquid offline samples based on total sulphur/nitrogen, density/API and simulated distillation. Using this analytical data, the mass balance was closed based on mass flow rates. Yields and conversions were calculated and several correlations plotted.
The four extrudate catalysts (A, B, C, D) were mounted four times in the same way to test reproducibility. The catalyst volume used was 2 ml calculated from the settled bulk density of the pure full-size extrudates. Prior to catalyst packing, the extrudates were sorted by length in the range 2-4 mm in order to ensure an almost constant length to diameter ratio and hence ensure a constant particle Reynolds number of the full-size catalyst particles when embedding the extrudates in the diluent material. The characteristic length for diffusion/mass flow limitation is the diameter of the full extrudates. To ensure plug flow hydrodynamics of liquid and gas flow through the catalyst bed, extrudates (Ø ≈ 1.3 mm, length 2-4 mm) were diluted with silicon carbide (SiC) as inert material with a particle size range of 125-160 µm in order to ensure that the void space between particles and wall effects (inner diameter of reactor 5 mm) are minimised. This ensures equivalent linear velocity of gas and liquid around the SiC-embedded extrudates (equivalent Reynolds particle numbers). Different catalyst properties such as density, diameter, length and shape have an influence on the packing behaviour. To ensure a good packing quality by avoiding void spaces and demixing of extrudates and SiC, the packing of unknown catalysts is tested in glass tubes prior to reactor packing.
After activation of the catalysts using a liquid sulphiding procedure with DMDS the catalysts were lined out for several days. The catalyst activity is shown in Figure 1 by comparing the conversion of the +350°C boiling fraction at different reactor temperatures. It can be seen that catalyst A has the lowest and D the highest activity. Catalysts B and C exhibit similar activity. The VGO was cracked to lighter products: gases (C1-C4), naphtha, kerosene, diesel and tail oil. In Figure 2 the yields of the boiling fractions are plotted versus the conversion of the +350°C fraction. In the left plot, the data for catalysts A, C and D are given from all 12 reactors. The data suggest that catalysts A, C and D are derived from the same catalyst type but use different amounts of active mass (see Figure 2a). With catalyst B, over-cracking starts at lower conversions (see Figure 2b).
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