Advances in catalyst testing
A refining and petrochemical company relied on high throughput experimentation to select a change-out option from competing catalysts for the best ROI.
IOAN-TEODOR TROTUS, JEAN-CLAUDE ADELBRECHT and FLORIAN HUBER
NATTAPONG PONGBOOT and THANAWAT UPIENPONG
PTT Global Chemical Public Company Limited
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Independent catalyst testing has become a useful tool for refiners to support their catalyst selection process. Actual testing enables a customised catalyst evaluation under industrially relevant conditions including different industrial operational cases and different representative industrial feedstocks. The comparability of different catalyst systems is based on one and the same foundation, thus significantly lowering the degree of uncertainty as compared to paper studies describing each individual vendor’s catalyst systems.
High throughput experimentation has become the state-of-the-art industrial standard in independent catalyst testing and offers the technical means to compare different catalyst systems head to head at the same time under uniform and identical conditions in an efficient and cost-effective way. It has proven to provide industrially significant data in a timely manner with a high degree of accuracy and precision on the basis of relative catalyst ranking as well as absolute data transferability to industrial scale. It is the ideal way to identify properly the optimal catalyst system for a refinery’s specific process. Given the high stakes involved in the choice of catalyst for an operation cycle, selecting the appropriate testing technology for conversion units is pivotal, as it has a dramatic and lasting impact on the profitability of a refinery. High throughput experimentation is utilised in the catalyst selection process in a wide array of refinery processes, such as (but not limited to) hydrocracking, hydrotreating, reforming, (de-)alkylation, resid upgrading, lubes processing, and also (co-)processing of biofeedstocks.1, 2, 3
In classic high throughput experimentation set-ups, testing is accelerated by running multiple reactors simultaneously and in parallel for direct comparison of the catalysts under investigation. The gas and liquid distribution technology ensures a uniform feedstock distribution over all reactor positions. The principal methodology in trickle-bed catalyst testing is straightforward: gas and feedstock are fed through a catalyst-loaded reactor under defined conditions. Depending on the nature of the reaction and the product spectrum, the products are analysed by online methods or collected as liquids and later analysed offline. For processes with a consecutive reactor configuration, such as single-stage hydrocracking with mainly a pretreat and a cracking catalyst system, each reactor stage is either investigated separately or the combined reactors are simulated in one test reactor.2 In cases where the consecutive reactors are operated at a similar operating temperature level, this approach is viable. However, in many cases, pretreat and cracking reactors are operated at different temperatures. It is beneficial that a laboratory method takes this temperature difference into account to properly simulate the industrial process. In addition, when performing independent catalyst testing for refinery applications, the catalyst systems are typically compared under a constant conversion operation, with the temperature being the tuning parameter to reach the desired conversion level. In order to reach a predefined conversion level in the consecutive reactors as well as for the different catalyst systems in comparison, an independent temperature control on each reactor is required. Moreover, when evaluating consecutive reactor stages in one and the same test, an inter-stage quantification between the reactors is highly desirable to evaluate the performance of the first reactor. In classic pilot scale testing, the quantification of the upstream reactors is obtained by interstage sampling. Interstage sampling typically has the drawback that only concentration based information is obtained, since only a sample is taken, whereas the flow rate of the gas and liquid phase is left unmeasured. As a second drawback, the required amount of reactant to perform all required analyses is taken away from the downstream reactor. In pilot scale, this reactant loss to the following reactor is typically negligible, likely corresponding to an interruption of feed supply to the order of a few minutes.
In the case of high throughput experimentation with smaller catalyst amounts, removing a few ml of interstage product is equivalent to cutting off the feed supply to the downstream reactor for about 0.5-1 hour and would cause significant disturbances.
These drawbacks in utilising classic high throughput experimentation in simultaneous testing of consecutive reactor stages led hte to develop a new approach for testing consecutive reactor stages in an industrially significant as well as efficient and cost-effective way.4 The core principle of the new test approach is illustrated in Figure 1. The new concept contains reactors connected in series. The consecutive reactors are equipped with an independent temperature control. Interstage quantification is not performed by classic interstage sampling, but a third mirror-type reactor reflects the performance of the upstream reactor. The mirror reactor is placed in one and the same heating block as its reference reactor to ensure high comparability. This approach enables a comprehensive mass flow rate based gas and liquid analysis, constituting a clear improvement compared to the traditional concentration based interstage sampling information. With this new concept, interstage dosing of gas and/or liquid becomes a proven reality in high throughput experimentation too.
This new approach is demonstrated in a case study performed for PTT Global Chemical Public Company Limited (GC), a leading Asian integrated petrochemical and refining company, to evaluate commercial hydroprocessing catalysts under commercially relevant conditions for a catalyst change-out in its refinery at Rayong, Thailand. GC selected hte for the evaluation study to benchmark five commercial hydroprocessing catalyst systems using a 24-fold high throughput reactor system optimised for single stage hydrocracking under commercially relevant conditions. The project was completed in 2018 with the overall aim of measuring catalyst performance (activity, selectivity, and stability) and determining key fractional product properties.5
An advantage of the 24-fold testing unit lies in the freedom to adjust the temperatures of all pretreat and cracking reactors individually and actually measure the impact of temperature on each of the catalyst systems connected in series. This freedom minimises the need to extrapolate data when comparing product properties between the different catalyst systems, because each cracking system can be run at an accurately set conversion with the pretreat reactor set to an accurate nitrogen slip.
All reactors share one liquid feed supply and one gas supply, which are respectively equally distributed between the reactors. In a typical test, the catalyst systems are all operated under identical pressure, liquid hourly space velocity (LHSV), and gas-to-oil ratio to ensure an optimal comparison. If the catalyst systems are to be tested at different LHSVs, this can be accommodated by adjusting the amount of catalyst loaded in order to reach the targeted LHSV at the given flow rate. If a second parallel feed supply is required, this can be realised by adding a second feed module.
Catalyst activation in general involves individual procedures for the different catalyst systems, such as different feed composition and temperature protocols. This requires a certain flexibility of the test units. In a typical approach, the different activation protocols are harmonised to an extent acceptable for all catalyst vendors. The remaining and essential differences in the protocols need to be facilitated by the test unit.
The aim of an independent catalyst test is to find the catalyst system that best meets the requirements of the refinery. This generally implies having a high yield of a target fraction, achieving this yield at a lower temperature, minimising the yield of C1-C4 hydrocarbons, and having the properties of the targeted fraction meet various quality standards. As indicated in Figure 1, state-of-the-art catalyst systems for single stage hydrocracking comprise a multistack of different catalysts for the pretreat, cracking, and post-treat function. In order to perform an industrially relevant ranking, the catalysts have to be tested in their commercial size and shape. A typical independent catalyst test on a 24-fold unit requires all participating catalyst vendors to provide catalysts and activation protocols, to assist in finding harmonised activation protocols, to provide a target value for the nitrogen slip of the pretreat system and the oil conversion or other parameters of the cracking system, as well as to provide an estimate for the required pretreat and cracking temperatures to reach the targeted values.
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