Pd Membrane Research Articles

Comparative analysis of hydrogen production from ammonia decomposition in membrane and packed bed reactors using diluted NH3 streams

Ammonia decomposition is a key technology for its use as a hydrogen carrier and in the recovery of H2 from waste streams containing ammonia. The coupling of the catalytic decomposition of ammonia with an H2 permeoselective membrane improves the process by mitigating thermodynamic constraints and producing a flux of high-purity hydrogen, not requiring further separation/purification. In this study, we compare the behaviour of an eggshell catalyst 1.3 wt % Ru/Al2O3 catalyst in a packed bed reactor (PBR) and a packed bed membrane reactor (PBMR) using an ultrathin Pd membrane (3.4 μm). Tests were made at 11 bar(a) with a weight hourly space velocity of NH3 in the 0.560–1.68 Lꞏg−1ꞏh−1 range and temperatures of 350–400 °C, e.g. milder conditions than the conventional ammonia cracking catalysts. Under optimised conditions (0.56 Lꞏg−1ꞏh−1, 400 °C, sweep gas flow 0.55 L min−1), the PBMR shows excellent performance, achieving NH3 conversion, H2 productivity and recovery factor of 99%, 47 mmolH2·gRu−1·min−1, and 94.9%, respectively. PBMR increases by ∼50% the conversion rate compared to PBR. Without a sweep gas, PBMR performances are lower, even still higher than in PBR. For the first time, superior or comparable performance was demonstrated compared to similar systems using pure ammonia in terms of conversion, hydrogen recovery, H2 productivity, and Ru utilisation. These results can be further enhanced with vacuum systems to convert diluted ammonia streams into high-purity hydrogen for small-scale distributed systems and can be extended to other reactions.

Modeling of hydrogen separation through Pd membrane with vacuum pressure using Taguchi and machine learning methods

The performance of hydrogen purification using palladium (Pd) membrane is analyzed by Taguchi and machine learning (ML) methods. Three system factors are considered: the feed gas mixture composition (i.e., H2, CO2, and H2O), retentate-side total pressure, and vacuum pressure. The Taguchi method designs the experimental cases based on the constructed orthogonal array. In addition, the hydrogen flux is investigated by the analyses of variance (ANOVA) and artificial neural networks (ANN) methods. The results show that the effects of the considered factors on the hydrogen permeation performance can be ranked as feed gas mixture composition > retentate-side total pressure > vacuum pressure. Both the retentate-side pressure and vacuum pressure present a positive effect on hydrogen flux. The average relative error of hydrogen flux between the experimental results and predictions by ANN is 2.1%, which proves that the ANN method is an effective technique for predicting the hydrogen flux through the Pd membrane. The ML classification test is then performed for hydrogen purity by three machine learning methods: decision tree (DT), support vector machine (SVM), and ensemble method. Among the various classification models, the Quadratic SVM model exhibits a relatively high average training accuracy but shows overfitting. However, the bagged model of the ensemble method can achieve an impressive training accuracy of 91.4% and a prediction accuracy of 85.7%.

Analysis of vacuum operation on hydrogen separation from H2/H2O mixture via Pd membrane using Taguchi method, response surface methodology, and multivariate adaptive regression splines

The influence of vacuum pressure applied on H2 separation from a palladium membrane is explored in this study. Three factors with three levels are considered, including the membrane chamber temperature with levels 320 °C, 350 °C, and 380 °C; the retentate-side total pressure with levels 1, 2, and 3 atm; and the permeation-side vacuum pressure with levels 0, 25, and 50 kPa. The Taguchi, response surface methodology (RSM), and multivariate adaptive regression splines (MARS) methods are employed to analyze the effects of the three parameters on hydrogen separation and predict their optimal combination. The retentate-side total pressure exhibits the highest impact on H2 permeation, following the permeation-side vacuum pressure and then the membrane chamber temperature. The maximum H2 flux is 0.226 mol∙s−1∙m−2, with H2 recovery of 91 % obtained at the optimal conditions with a temperature of 380 °C, a total pressure of 3 atm, and a vacuum pressure of 50 kPa. The improvement in H2 flux reaches 21.6 % compared with the case without the imposed vacuum pressure at the same temperature and total pressure. This result shows the imposed vacuum pressure is an efficient way to enhance H2 permeation. The maximum relative errors between the experimental data and the predictions from the Taguchi, RSM, and MARS methods are 6.74 %, 3.37 %, and 8.08 %, respectively. The RSM method presents higher accuracy than Taguchi and MARS, perhaps due to a more precise analysis of the interaction terms. The smaller amount of input data and ignoring the temperature effect in MARS could be the reason for the lower accuracy. Nevertheless, the MARS method still demonstrates acceptable results. The cost of the Taguchi method is lower than that of the RSM method since it requires fewer experimental cases. In a word, the choice of the prediction method depends on the desired accuracy and the experimental cost.

Highly efficient dual-phase hydrogen-transporting membranes for NH3 decomposition coupling with CO2 reduction

Hydrogen-transporting membrane reactors play active roles in ammonia (NH3) decomposition and carbon dioxide (CO2) reduction by combining reaction and separation in one unit, simplifying the processes and reactor design and therefore saving the cost. These important reactions normally occur at high temperatures and in reducing and acidic atmosphere, thus posing great challenges on the membrane stability. Previous effort was devoted to thin Pd membranes, which however, suffer the shortcomings of hydrogen embrittlement, CO poisoning and high costs. Herein, we develop a H2-COx-tolerant and non-noble metal-ceramic dual-phase hydrogen permeable membrane reactors with a nominal composition of 60 vol% Ni-40 vol% La5.5WO11.25-δ (Ni-LWO). NH3 decomposition and hydrogen permeation was observed via the developed mixed protonic and electronic conducting membrane. A considerable production of CO in the sweep (CO2) side could also be achieved from CO2 reduction when the membrane was coupled by NH3 decomposition where the permeated hydrogen can consume the produced oxygen from favorable CO2 decomposition. Furthermore, we systematically investigated the performance of NiO–CeO2 catalyst coated Ni-LWO membrane reactor for CO2 reduction. Noteworthy that the CO generation rate obtained from Ni-LWO membrane reactor was increased in the presence of NiO–CeO2 catalysts. Hydrogen separation process coupled with surface reactions is jointly controlled by hydrogen surface exchange and bulk diffusion kinetics. These findings reveal a vital step towards the development of efficient hydrogen-transporting membrane reactor for the integration of chemical reactions and separation processes.

Development of pure hydrogen generation system based on methanol steam reforming and Pd membrane

Methanol steam reforming (MSR) has been used for in-situ hydrogen production, while hydrogen purification remains a technical challenge to limit the applications of using hydrogen for fuel cells. This study presents a pure hydrogen generation system (PHGS) by integrating MSR and hydrogen purification modules, this system enables low-temperature reforming and high-temperature purification to achieve high yield and recovery of hydrogen. To investigate the combined effects of feedstock flow rates and pressure on MSR and purification, the performance of each module and overall PHGS system were tested. The results showed that PHGS can stably produce high purity hydrogen (>99.99%) under different conditions, the synergistic effects of two modules lead to hydrogen yield exceeding the numerical sum of individual modules. At methanol feed rate of 1.00 g/min and system pressure of 5.0 bar, the pure hydrogen flow rate, CO content, pure hydrogen yield, hydrogen recovery and thermal power output were tested about 1.70 ± 0.01 L/min, 2.4 ± 0.1 ppm, 81.1 ± 0.5%, 87.6 ± 0.5% and 350 W. The PHGS can deliver up to 500 W of thermal power and is suitable for small range-extended electric vehicles. Our work on the developed PHGS can provide a significant reference for future practical applications of systems combining MSR and membrane purification.

Enhanced ammonia-cracking process via induction heating for green hydrogen: A comprehensive energy, exergy, economic, and environmental (4E) analysis

Ammonia (NH3) is gaining attention as a hydrogen carrier due to its high H2 storage capacity and ease of liquefaction at ambient temperatures. The conventional method of ammonia decomposition is thermal cracking through fossil fuel combustion, resulting in significant carbon dioxide (CO2) emissions. Therefore, developing an eco-friendly and highly efficient ammonia decomposition process is important. This study proposed four high-efficiency processes without carbon emissions by improving the induction-heating-based ammonia decomposition process designed in a previous study. The four proposed processes were designed to utilize the H2 discarded as off-gas of the PSA unit in the existing induction-heating-based ammonia decomposition process. The proposed processes incorporate various unit components, including a proton exchange membrane fuel cell (PEMFC), solid oxide fuel cell (SOFC), burner, and palladium (Pd) membrane. These units were integrated with the PSA outlet to achieve enhanced thermodynamic efficiency compared with the conventional process without carbon emissions. Energy, exergy, economic, and environmental analyses were conducted to assess the feasibility of each case. Thermodynamic analysis revealed that integrating the Pd membrane yields the highest thermal (78.29 %) and exergy (64.02 %) efficiencies. Integrating a PEMFC exhibits the lowest levelized cost of H2 (6.93 USD/kg H2). Finally, When the four proposed processes are operated with renewable energy, clean hydrogen can be produced at 2.45 to 3.21 kgCO2/kgH2 emission levels. The enhanced processes presented in this study can serve as a blueprint for achieving carbon-free green H2 production at on-site H2 refueling stations.

3D-Continuous Nanoporous Covalent Framework Membrane Nanoreactors with Quantitatively Loaded Ultrafine Pd Nanocatalysts.

The confinement effect of catalytic nanoreactors containing metal catalysts within nanometer-sized volumes has attracted significant attention for their potential to enhance reaction rate and selectivity. Nevertheless, unregulated catalyst loading, aggregation, leaching, and limited reusability remain obstacles to achieving an efficient nanoreactor. A robust and durable catalytic membrane nanoreactor prepared by incorporating palladium nanocatalysts within a 3D-continuous nanoporous covalent framework membrane is presented. The reduction of palladium precursor occurs on the pore surface within 3D nanochannels, producing ultrafine palladium nanoparticles (Pd NPs) with their number density adjustable by varying metal precursor concentrations. The precise catalyst loading enables controlling the catalytic activity of the reactor while preventing excess metal usage. The facile preparation of Pd NP-loaded free-standing membrane materials allows hydrodechlorination in both batch and continuous flow modes. In batch mode, the catalytic activity is proportional to the loaded Pd amount and membrane area, while the membrane retains its activity upon repeated use. In continuous mode, the conversion remains above 95% for over 100h, with the reactant solution passing through a single 50µm-thick Pd-loaded membrane. The efficient nanoporous film-type catalytic nanoreactor may find applications in catalytic reactions for small chemical devices as well as in conventional chemistry and processes.

Weakening surface hydrogen to enhance permeation in hydrogen selective membranes

Hydrogen selective metallic membranes made of palladium and its alloys are superior to membranes made of other metallic materials due to their unique surface properties. However, the prohibitive cost of Pd has prevented their widespread application. Although the basic mechanisms are known, the link between hydrogen at the surface and that in the bulk has been missing to explain the prominent position of Pd. To provide the missing link between surface and bulk, we measured the hydrogen concentration and depth distribution on the downstream side of a Pd membrane at realistic permeation conditions (temperature and pressure) using a membrane electron spectroscopy setup. We find hydrogen in the vicinity of the surface with intermediate stability. In general, hydrogen on the surface is more stable and thus more concentrated than in the bulk. Subsurface hydrogen with intermediate stability mitigates the difference between surface and bulk concentration and thereby facilitates overall hydrogen permeation. The observations link the results of UHV-compatible hydrogen adsorption experiments with observations made on hydrogen permeation in membranes under technical conditions. This link enables the application of the wealth of surface science based knowledge to the optimization of hydrogen permeable membrane materials.

Progress and perspectives on electrocatalytic transmembrane hydrogenation

This review summarizes the developments of Pd membrane reactors to drive electrochemical hydrogenation of unsaturated compounds including gaseous reagents. It highlights the design of Pd-based catalysts and their utilization to drive hydrogenation.

Ultrasound assistance in the sensitization and activation of porous Al2O3 supports for improving the hydrogen separation of Pd/Al2O3 composite membranes

Pd membrane on porous Al2O3, an important composite membrane for H2 separation, is typically fabricated by electroless plating, and thus the quality of the Pd membrane is critically dependent on the seeding process. Here, a facile ultrasonication-assisted sensitization-activation process is used to load catalytic particles on porous Al2O3, subsequently followed by electroless plating of 5-μm-thick Pd membranes for H2 separation. Uniformly distributed catalytic particles with even sizes are loaded onto Al2O3 only under an optimal power of the ultrasonic agitation, then catalyzing electroless Pd membranes with a better surface topography and less defective microstructure. The optimal Pd membrane achieves a sound hydrogen flux of 0.157 mol m−2 s−1 and high H2/N2 selectivity of 1835 under 723 K and 105 kPa pressure difference. Moreover, this particular Pd/Al2O3 exhibits high stability in (a) Pd membrane microstructures and (b) H2/N2 permeating fluxes without elemental interfacial diffusion even under long-term (156 h) at a high temperature (723 K).

Preparation of Pd membrane with high permeability and thermal stability on porous YSZ-Al2O3 tubes by two-step CeO2modification

Pd membranes were deposited on porous YSZ-Al2O3 tubes after different modification methods using an electroless plating technology. SEM, AFM, XRD and gas permeation tests were applied to investigating the effects of different modification methods on the surface quality of porous tubes and the permeation performance of the Pd composite membranes. The results showed that the surface of the porous tubes after the two-step CeO2 modification exhibited smaller pore distribution and roughness. Pd membranes on the porous tubes after the two-step CeO2 modification exhibited higher hydrogen permeation flux (0.549 mol·m−2·s−1) and H2/N2 selectivity (14241) at 500 °C and a pressure difference of 700 kPa. The results of different thermal cycling tests and the long-term permeation tests of 1000 h showed that Pd membranes on the porous tubes after the two-step CeO2 modification had higher permeation stability.

Techno-economic Analysis and Optimization of Intensified, Large-Scale Hydrogen Production with Membrane Reactors.

Steam methane reforming (SMR) currently supplies 76% of the world's hydrogen (H2) demand, totaling ∼70 million tonnes per year. Developments in H2 production technologies are required to meet the rising demand for cleaner, less costly H2. Therefore, palladium membrane reactors (Pd-MR) have received significant attention for their ability to increase the efficiency of traditional SMR. This study performs novel economic analyses and constrained, nonlinear optimizations on an intensified SMR process with a Pd-MR. The optimization extends beyond the membrane's operation to present process set points for both the conventional and intensified H2 processes. Despite increased compressor and membrane capital costs along with electric utility costs, the SMR-MR design offers reductions in the natural gas usage and annual costs. Economic comparisons between each plant show Pd membrane costs greater than $25 000/m2 are required to break even with the conventional design for membrane lifetimes of 1-3 years. Based on the optimized SMR-MR process, this study concludes with sensitivity analyses on the design, operational, and cost parameters for the intensified SMR-MR process. Overall, with further developments of Pd membranes for increased stability and lifetime, the proposed SMR-MR design is thus profitable and suitable for intensification of H2 production.

Fabry-Pérot Cavities with Suspended Palladium Membranes on Optical Fibers for Highly Sensitive Hydrogen Sensing.

Hydrogen (H2) sensors are critical to various applications such as the situation where H2 is used as the clean energy for industry or the indicator for human disease diagnosis. Palladium (Pd) is widely used as the hydrogen sensing material in different types of sensors. Optical fiber H2 sensors are particularly promising due to their compactness and spark-free operation. Here, we report a Fabry-Pérot (FP)-cavity-based H2 sensor that is formed with a freestanding Pd membrane and integrated on a conventional single-mode optical fiber end. The freestanding Pd membrane acts both as the active hydrogen sensing material and as one of the reflective mirrors of the cavity. When the Pd film absorbs H2 to form PdHx, it will be stretched, resulting in a change of the cavity length and thus a shift of the interference spectrum. The H2 concentration can be derived from the amplitude of the wavelength shift. Experimental results showed that H2 sensors based on suspended Pd membranes can achieve a detection sensitivity of about 3.6 pm/ppm and a detection limit of about 3.3 ppm. This highly sensitive detection scheme is expected to find applications for sensing low-concentration H2.

An investigation of water gas shift reaction in a Pd-alloy membrane reactor with an optimized crossflow configuration

In this study, the performance of a high-temperature water gas shift reaction (WGSR) using a Fe-Cr catalyst along with a Pd alloy membrane was simulated by computational fluid dynamics (CFD). The influences of using Pd membranes, catalytic layer thickness ratio (R/R0), Reynolds number, and steam-to-CO ratio (S/C) on the reaction were investigated by comparing CO conversion and hydrogen recovery (HR). In the CFD simulation, one-tube and four-tube systems were simulated at 500 °C. This study also compared the performance between tandem and optimized configurations. The results show that the CO conversion can be improved up to 22.9% when the WGSR reactor system uses a Pd membrane compared to the system without a Pd membrane. The system has the best hydrogen recovery performance at S/C = 4 and R/R0 larger than 1.5. At Re=5, the optimized configuration for CO conversion has better performance when R/R0 is larger than 1.75. Compared to the tandem configuration, the optimized configuration also shows better performance for HR at every R/R0. The results indicate that a Pd membrane and optimized configuration can significantly improve CO conversion and that R/R0 and S/C optimization is very important for effective reactor performance.

Reaction Environment Impacts Charge Transfer but Not Chemical Reaction Steps in Hydrogen Evolution Catalysis

Heterogeneous electrocatalysis involves elementary chemical and charge transfer reaction steps, with the kinetics of each step contributing to the overpotential requirement at a given reaction rate. Typical experiments report on the aggregate rate-overpotential profile with no information about the relative contributions from charge transfer and chemical steps. For the hydrogen evolution reaction (HER), the applied overpotential can be partitioned into a charge transfer overpotential, the overpotential necessary to drive proton-coupled electron transfer (PCET) to and from the surface, and a chemical overpotential, corresponding to a change in surface H activity. Reaction conditions can affect either or both the charge transfer and chemical components. Herein, we employ a Pd membrane double cell to spatially separate the charge transfer and chemical reactions steps of HER catalysis, enabling quantification of the chemical and charge transfer overpotential. We further analyze how each depend on pH, and the introduction of HER poisons and promoters. We find that for a given rate of H2 release, the chemical overpotential is constant across diverse reaction environments whereas the charge transfer overpotential is strongly sensitive to reaction conditions. These findings suggest that reaction condition dependent-HER efficiencies are driven predominantly by changes to the kinetics of charge transfer rather than the chemical reactivity of surface H.

Solar-driven multichannel membrane reactor for hydrogen production from ammonia decomposition

Solar-driven ammonia decomposition is one of the most promising carbon-free pathways to release hydrogen from ammonia. Enhancing the heat and mass transfer processes within an ammonia decomposition membrane reactor is crucial to improve the hydrogen production rate. The multichannel reactors can reduce hydraulic diameters by raising the number of channels while the lateral surface areas of reactors keep the same, which can enhance heat and mass transfer without enlarging re-radiation losses. In this paper, a solar-driven multichannel membrane reactor for ammonia decomposition is proposed, which is promising to improve the conversion without deteriorating the efficiency. Models are developed to simulate the proposed multichannel membrane reactor under solar irradiation. A multichannel membrane reactor with three Pd membrane channels is designed and built. Experiments have been conducted to validate the reactor model. With the validated model, two consecutive parametric studies have been conducted for catalyst volume decreasing and increasing scenarios, respectively. The results show that enlarging permeation area by increasing membrane channels is worthwhile to improve the conversion although the catalyst volume decreases. Under the same solar flux and inlet ammonia properties, a six-channel membrane reactor can achieve a conversion of 0.76, while a single-channel membrane reactor can only achieve a conversion of 0.49. Additionally, the maximum temperature difference within the six-channel reactor is 47 °C lower than that within single-channel membrane reactor, which is favorable for the Pd membrane operating temperature range.

H2 -free Semi-hydrogenation of Butadiene by the Atomic Sieving Effect of Pd Membrane with Tree-like Pd Dendrites Array.

H2 -free semi-hydrogenation at room temperature shows great advantage for replacing the thermocatalytic process in industry owing to the high energy and resource saving, however, remains great challenges. Herein, a tree-like Pd dendrites array decorated Pd membrane was constructed as the core device in an electrochemistry assisted gas-fed membrane reactor for butadiene semi-hydrogenation. It reveals that hydrogen atomic sieving effect of this Pd-based membrane under electrochemical condition was the key for semi-hydrogenation. The configuration study of Pd nanostructured membrane demonstrates that the penetration of hydrogen atoms through Pd membrane from electrochemical side to chemical side is affected by the consumption of hydrogen atom in semi-hydrogenation step. Such atomic sieving property of nanostructured Pd membrane with 5.1 times increase in catalytic active surface area brings above 14 times higher in butadiene conversion than that of bare Pd foil, with ≈90 % of butenes selectivity at butadiene conversion ≈98 % over 300 h of H2 -free reaction under 15 mA cm-2 .

H2‐free Semi‐hydrogenation of Butadiene by the Atomic Sieving Effect of Pd Membrane with Tree‐like Pd Dendrites Array

AbstractH2‐free semi‐hydrogenation at room temperature shows great advantage for replacing the thermocatalytic process in industry owing to the high energy and resource saving, however, remains great challenges. Herein, a tree‐like Pd dendrites array decorated Pd membrane was constructed as the core device in an electrochemistry assisted gas‐fed membrane reactor for butadiene semi‐hydrogenation. It reveals that hydrogen atomic sieving effect of this Pd‐based membrane under electrochemical condition was the key for semi‐hydrogenation. The configuration study of Pd nanostructured membrane demonstrates that the penetration of hydrogen atoms through Pd membrane from electrochemical side to chemical side is affected by the consumption of hydrogen atom in semi‐hydrogenation step. Such atomic sieving property of nanostructured Pd membrane with 5.1 times increase in catalytic active surface area brings above 14 times higher in butadiene conversion than that of bare Pd foil, with ≈90 % of butenes selectivity at butadiene conversion ≈98 % over 300 h of H2‐free reaction under 15 mA cm−2.

Efficient processing of tritiated water by using a two-stage Pd membrane reactor with Pt/TiO2 catalyst

Large amounts of tritiated water (HTO) will be produced during the operation of nuclear power plants and fusion devices, which is harmful to the environment and human due to its radioactivity and toxicity. So, the tritium concentration of tritiated water must be reduced to a very low value before discharge. Hydrogen-water isotope exchange reaction (H2 + HTO→H2O + HT) based on palladium membrane reactor has been proposed to process tritiated water. However, a comprehensive study about the influence of operation parameters on the membrane reactor performance is insufficient, which is not conducive to the design of reactor in practical application. Moreover, the commonly used Pt/Al2O3 or Ni/SiO2 catalysts are not active for tritiated water dissociation, so the catalytic activity of these catalysts is not high. In order to process tritiated water more effectively, a two-stage membrane reactor has been designed and established in this work, and Pt/TiO2 catalyst with rich oxygen vacancies is used to catalyze the hydrogen-water isotope exchange reaction for the first time. The membrane reactor performance shows an approximate linear relationship with a new combined parameter S0.5P1.5R/F2 (S is membrane area, F is water flow rate, P is vapor partial pressure, R is swamping ratio), which can be used predict the membrane performance. The isotope exchange reaction activity of Pt/TiO2 is better than that of Pt/Al2O3 due to its good ability for water dissociation and the hydrogen spillover effect. At last, a tritiated water processing experiment by using two-stage membrane reactor with Pt/TiO2 catalyst with rich oxygen vacancies has been carried out. The tritium decontamination factor reaches 40588, which is the highest experimental value so far. The results indicate that the two-stage Pd membrane reactor based on hydrogen-water isotope exchange reaction is an efficient technology for tritiated water processing.

Palladium-based membranes for potential application in bio-jet fuel production unit

ABSTRACT The hydrogen in the vent gas stream of the hydrocracker (used to produce bio-jet fuel) cannot be reused since it has many impurities. The metal membrane can be a potential candidate for recovering hydrogen from this vent gas. In this work, the authors report the development of a composite palladium membrane and its application, for the first time, in the recovery of hydrogen from a simulated vent gas environment. A dense thin film (thickness ∼3 µm) of Pd metal was coated on a ceramic support tube by the sputter deposition technique. The hydrogen permeance of the Pd membrane was found to be 18.75 × 10−6 mol·m−2·h−1·Pa−1, which was reduced to 3.25 × 10−6 mol·m−2·h−1·Pa−1, with an exposure of 100 h in the simulated bio-jet fuel environment. To avoid the loss of permeability, a thin layer of Pt can be coated over the Pd membrane. The present study used MATLAB software to simulate the Pt-coated Pd composite membrane performance in the bio-jet fuel production environment. Simulation studies confirmed that a membrane area of ∼95 cm2 (250 mm length and 12 mm OD) is sufficient for the complete recovery of hydrogen from the vent gas stream of hydrocracker at a feed velocity of 0.075 m/s.