Carrier Particles Research Articles

Numerical investigation of capture efficiency of carrier particles in a Y-shaped vessel considering particle-particle interaction and Non-Newtonian behavior

Chemotherapy kills the cancer cells by disrupting cell division. Although chemotherapy is an efficient treatment of cancer, it has many side effects since drugs circulate throughout the body. A promising approach to reduce these side effects is targeted drug delivery. The present study investigates the capture efficiency of carrier particles in a Y-shaped vessel under the effect of an external magnetic field produced by a current-carrying wire. Different parameters including magnetic, drag, buoyancy, and Lorentz forces have been considered. In addition, the effect of particle-particle interaction and non-Newtonian behavior of blood have been included. The generalized power-law (GPL) and modified Casson models are used for modeling non-Newtonian behavior. Results show that capture efficiency (CE) is increased as the blood velocity and the particle diameter are reduced and increased, respectively. Besides, it was found that considering particle-particle interaction has led to a reduction in CE in all cases. For example, the CE of nanoparticles for the case without interaction force is 51.66%, while for the case with interaction force is 43.33%, showing a nearly 16% reduction. Besides, it was observed that modified Casson provides a more accurate prediction for blood behavior than the GPL model.

Industry-scale production of a perovskite oxide as oxygen carrier material in chemical looping

How to upscale the production of oxygen carrier particles from laboratory level to industrial level is still challenging in the field of chemical looping. The upscaled oxygen carrier must maintain its physical and chemical properties. In the present contribution, a spray drying granulation protocol was developed to produce a perovskite oxygen carrier (CaMn0.5Ti0.375Fe0.125O3-δ) at an industrial scale. The micro-fluidized bed thermogravimetric (MFB-TGA) experiments were performed to measure the oxygen uncoupling and redox reaction kinetics under the fluidization state with enhanced heat and mass transfer, and the obtained experimental data at different temperatures were fitted by a fluidized-bed reactor coupled with a semi-empirical kinetic model. The physical and chemical properties of granulates were compared with those of the same perovskite composition prepared at the laboratory level. The results show the volume fraction of particle size at 75–500 μm is greater than 90% for the upscaled granulats, and the particles show no degradation in reactivity and no agglomeration for more than 20 redox cycles at high temperatures. The heterogeneous reaction rates are high, especially for the oxidation, e.g. it only spent ∼ 5 s to achieve full oxidation. Low attrition index of 3.74 wt% was found after the five-hour attrition test. The industrial-scale particles possess similar chemical and physical properties as the laboratory-scale particles with regards to the reaction kinetics, attrition index, crystalline phase, etc. The required bed inventories and fan energy consumption were finally estimated and found to be lower than other oxygen carriers reported in the literature.

Formulation and evaluation of proniosome loaded sertaconazole nitrate for topical application

Proniosomal technology is a novel solution for poorly soluble drugs. Proniosomes are water-soluble carrier particles which are coated with non-ionic surfactants. Proniosomal gels were prepared by coacervation phase separation method using non-ionic surfactants, lipid carriers and cholesterol as a membrane stabilizer. FTIR compatibility studies revealed that the drug and excipients were compatible. All formulations were evaluated for pH, drug content, extrudability, spreadability, viscosity, in-vitro, ex-vivo, skin irritation and stability studies. Among formulations prepared, F80H1 has shown higher % EE (83.02) and least diffusion through dialysis membrane i.e., 17.68%. With ex-vivo studies, F80H1 formulation has shown highest skin deposition and lower flux of sertaconazole nitrate through the rat skin. F80H1 was selected as final optimized formulation. F80H1 exhibited good stability and SEM studies revealed that the vesicles were spherical in shape. The optimized formulation was found to follow zero order release kinetics and korsmeyer-peppas release mechanism. F80H1 found to be non-irritant and stable from skin irritation and stability studies.

Numerical study on collision and breakage characteristics of oxygen carrier particles in cold state in chemical looping combustion

Chemical looping combustion has become a promising combustion technology for its inherent advantage of CO2 separation. Oxygen carrier particles play a vital role in this technology, however, they usually suffered from serious attrition in the long-term operation. Due to large quantity of particles and the complex fluidization process, it is difficult to obtain particle collision characteristics by experimental study, and the existing fluid-solid flow model does not consider the particle breakage model. This study combined the convex polyhedral particle model and the Ab-T10 breakage model based on the Euler-Lagrange two-way coupling method to reveal the actual particle attrition process during fluidization. Comparison of particle size distribution between simulation and experimental results further verified the accuracy of the simulation model. The result shows that the average collision frequencies on the geometric surface of particles with sizes of 0.27, 0.3 and 0.33 mm are 740.9, 717.4, and 841.5 1/s, respectively. The average velocity and impact energy of particles have similar periodic variation, and with the progress of breakage, those two factors lead to the approximately normal distribution of particles with size between 60 and 240 μm.

PRONIOSOMES: A VESICULAR DRUG DELIVERY SYSTEM

In the development of new dosage forms, drug delivery using nanotechnology is playing a vital role. Vesicular drug delivery systems have gained wide attention in the field of nanotechnology, such as niosomes, liposomes and proniosomes. Among the vesicular carriers, proniosomes are superior. Proniosomes are water-soluble carrier particles that are coated with surfactant so these are dry formulations. They are rehydrated to use on agitation in hot aqueous media within minutes to form niosomal dispersion immediately. Both hydrophilic and lipophilic drugscan be incorporated into these proteasomes. The physical stability problems of niosomes like aggregation, fusion and leaking are minimized in proniosomes, routes, such as oral, parenteral, dermal and transdermal, ocular, oral mucosal, vaginal, pulmonary, and intranasal. Proniosomes prolong the existence of the drug in the systemic circulation and finally reduces toxicity. This review focuses on different aspects of proniosomes such as preparation, characterization, in vitro drug release, entrapment efficiency, applications in the present scenario in the market and future trends.

Carrier particle emission and dispersion in transient CFD-DEM simulations of a capsule-based DPI

The dispersion of carrier-based formulations in capsule-based dry powder inhalers depends on several factors, including the patient's inhalation profile and the motion of capsule within the device. In the present study, coupled computational fluid dynamics and discrete element method simulations of a polydisperse cohesive lactose carrier in an Aerolizer® inhaler were conducted at a constant flow rate of 100 L/min and considering an inhalation profile of asthmatic children between 5 and 17 years approximated from literature data. In relevant high-speed photography experiments, it was observed that the powder was distributed to both capsule ends before being ejected from the capsule. Several methods of ensuring similar behavior in the simulations were presented. Both the constant flow rate simulation and the profile simulations showed a high powder retention in the capsule (7.37–19.00%). Although the inhaler retention was negligible in the constant flow rate simulation due to consistently high air velocities in the device, it reached values of around 7% in most of the profile simulations.In all simulations, some of the carrier powder was ejected from the capsule as particle clusters. These clusters were larger in the profile simulation than in the constant flow rate simulation. Of the powder discharged from the capsule, a high percentage was bound in clusters in the profile simulation in the beginning and at the end of the inhalation profile while no more than 10% of the powder ejected from the capsule in the 100 L/min constant flow rate simulation were in clusters at any time.The powder emission from the capsule was studied, indicating a strong dependency of the powder mass flow from the capsule on the angular capsule position. When the capsule holes face the inhaler's air inlets, the air flow into the capsule restricts the powder discharge.The presented results provide a detailed view of some aspects of the powder flow and dispersion of a cohesive carrier in a capsule-based inhaler device. Furthermore, the importance of considering inhalation profiles in addition to conventional constant flow rate simulations was confirmed.

LIPASES: AN EFFICIENT BIOCATALYST FOR BIOTECHNOLOGICAL APPLICATIONS

Lipases (3.1.1.3) are ubiquitous, biogenic enzymes which hydrolyses the triacylglycerols at the water-oil interface. Many species of animals, plants, and microbes produces lipases. The organisms able to produce lipases which could tolerate organic solvents, high temperature, is of industrial interest. Apart from its natural aqueous catalysis it also performs synthetic reactions in non-aqueous conditions, which have undergone tremendous development in last decade and have become a part of growing biotechnological applications. Immobilization of lipases on the particulate carriers have also been widely used for the enzyme’s efficient use. Vast industrial applications have been established such as detergent formulations, oleochemical, nutrition, textile, agrochemical industry, food technology, pharmaceutical field and fine chemical processing. Except latter three, most commercial applications do not requisite excessive purification or high degree of purity.

Iron-based oxygen carrier particles produced from micronized size minerals or industrial wastes

The production of highly reactive oxygen carrier particles based on low-cost iron materials is explored for chemical looping processes. Ten different low-cost Fe-based materials in the micronized size, both minerals and industrial residues, have been tested as precursors of oxygen carrier particles. The redox reactivity of each of the materials is evaluated and compared to the state-of-the art with particulate materials, including one new material introduced in this work. Due to its excellent reactivity, Promifer material was used to produce oxygen carrier particles by pelletizing and granulation. Considering a trade-off between crushing strength and reactivity, pelletizing process was selected. This material calcined at 950 °C showed high reactivity with CH4. If a higher operating temperature was required, e.g. 1000 °C with solid fuels, the reactivity decreased. Low attrition rates and good fluid-dynamic behavior with the pelletized particles, without agglomeration along the redox cycles, were found in a fluidized bed reactor.

Targeting of Inhaled Therapeutics to the Small Airways: Nanoleucine Carrier Formulations.

Current dry powder formulations for inhalation deposit a large fraction of their emitted dose in the upper respiratory tract where they contribute to off-target adverse effects and variability in lung delivery. The purpose of the current study is to design a new formulation concept that more effectively targets inhaled dry powders to the large and small airways. The formulations are based on adhesive mixtures of drug nanoparticles and nanoleucine carrier particles prepared by spray drying of a co-suspension of leucine and drug particles from a nonsolvent. The physicochemical and aerosol properties of the resulting formulations are presented. The formulations achieve 93% lung delivery in the Alberta Idealized Throat model that is independent of inspiratory flow rate and relative humidity. Largely eliminating URT deposition with a particle size larger than solution pMDIs is expected to improve delivery to the large and small airways, while minimizing alveolar deposition and particle exhalation.

Prediction of the carrier shape effect on particle transport, interaction and deposition in two dry powder inhalers and a mouth-to-G13 human respiratory system: A CFD-DEM study

Documentation of comparability between generic inhaler designs and the reference listed drug (RLD) inhalers is essential for regulatory approval of the products. Such assessments need high-fidelity numerical methods to accurately predict the transport, interactions, and deposition of orally inhaled drug products (OIDPs) in the human respiratory systems delivered via inhalers such as dry powder inhalers (DPIs). To explicitly model the particle-particle and particle-wall interactions for OIDPs, this study developed a computational fluid dynamics (CFD) and discrete element method (DEM) to examine drug delivery efficiency, determine emitted aerodynamic particle size distributions (APSDs), and quantify the resultant lung depositions of both lactose carriers and active pharmaceutical ingredient (API) particles. Numerical parametric studies were also performed with multiple actuation flow rates, carrier shapes, and DPI designs. Spiriva™ Handihaler™ (SH) and a generic DPI were selected in this study. The comparability assessment between the generic DPI and SH has been numerically performed. Specifically, CFD-DEM simulations were run at actuation flow rates of 30, 39, 60, and 90 L/min. Simulations were performed for both spherical and elongated lactose carrier particles with aspect ratios of 1, 5, and 10. Using the emitted APSDs as the mouth inlet conditions, the transport and deposition of API and lactose carriers from mouth to the tracheobronchial tree were also simulated. Numerical results indicate that with the same particle volume, the shape of lactose carriers can significantly influence the DPI delivery efficiency without a monotonic trend, due to the complex resuspension effect after deposition. However, the shape effect of lactose carriers is not significant on the lung deposition patterns of the API. Low actuation flow rates could potentially enhance the overall DPI-airway drug delivery efficiency. Using spherical lactose carriers, the comparability between the generic DPI and SH is demonstrated at all four actuation flow rates. The CFD-DEM model provides a feasible pathway on how to use CFD and DEM to evaluate the comparability between inhalers. The modeling framework also can help obtain new insights on transport dynamics of actines in DPIs to lung, thereby reducing the cost of generic product innovations and accelerating product review and approval.

Miniatured Fluidics-Mediated Modular Self-Assembly of Anticancer Drug–Amino Acid Composite Microbowls for Combined Chemo-Photodynamic Therapy in Glioma

A particulate carrier with the ability to load a combination of therapeutic molecules acting via diverse modes to initiate cancer cell ablation would help heighten anticancer therapeutic outcomes and mitigate harmful side effects due to high doses of mono drug therapy. Moving a step closer, herein, we have developed doxorubicin-curcumin-amino acid-based composite microbowls (CMBs) following miniaturized fluid flow-based self-assembly. The CMBs were further exploited as dual chemo-photodynamic therapeutic agents in C6 glioma cells cultured in both two-dimensional (2D) monolayer and as three-dimensional (3D) spheroids. These CMBs showed synergistic and visible (blue)-light-sensitive cell-killing effects in both C6 cells and 3D spheroids. Furthermore, these bowl-shaped structures also demonstrated good stability and excellent in vitro cytocompatibility in C6 glioma cells. Our results indicated that CMBs with asymmetric cavities could potentially be used as a combinatorial drug carrier enabling simultaneous chemo- and phototherapy for effective cancer treatment. The use of blue light, from the visible part of the electromagnetic system, to generate the phototherapeutic effect further advocates for the ease and widespread applicability of the systems.

Effects of dose loading conditions and device geometry on the transport and aerosolization in dry powder inhalers: A simulation study

The transport and aerosolization of particles are studied in several different dry powder inhaler geometries via Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations. These simulations combine Large Eddy Simulation of gas with Discrete Element Model simulation of all the carrier particles and a representative subset of the active pharmaceutical ingredient (API) particles. The purpose of the study is to probe the dominant mechanism leading to the release of the API particles and to demonstrate the value of the CFD-DEM simulations where one tracks the motion of all the carrier and API particles. Simulations are performed at different inhalation rates and initial dose loading conditions for the screen-haler geometry, a simple cylindrical tube inhaler, and five different geometry modifications that took the form of bumpy walls and baffles. These geometry modifications alter the residence time of the powder sample in the inhaler, pressure drop across the inhaler, the severity of gas-carrier interactions, and the number of collisions experienced by the carrier particles, all of which are quantified. The quality of aerosolization is found to correlate with the average air-carrier slip velocity, while collisions played only a secondary role. Some geometry modifications improved aerosolization quality with very little increase in the pressure drop across the device.

Composite Electroforming As Novel and Innovative Synthesis Method of Additive-Free Cathodes for Li-S Batteries

The increasing requirements for high power and energy storage systems have led to the implementation of a considerable number of electrode materials. Several crucial parameters such as energy, power density, rate capability and cyclability can be significantly influenced by modifying, in addition to the active materials chemistry, the manufacturing process of the electrode in the metal matrix. The novel electrodes for Li-S batteries proposed in the present work are intended to make a significant contribution to overcoming the concept-related disadvantages of the state-of-the-art conventional coating processes. Their basic development and suitability were investigated by our research group in various projects [1-4].The recently self-developed composite electroforming [5] is a very promising electrodes production process. It is significantly improving the existing conventional coating technology in terms of reduced technological steps, low costs and better electrochemical performance. The aforementioned manufacturing process consists on electroforming the metal matrix, which operates as a current collector foil, in a one-step process. Simultaneously, the active material is incorporated into the metal matrix by means of composite plating [6]. In contrast to the state-of-the-art approach using non-conducting binders such as PVDF and non-binding conductive agents such as carbon black, conductivity and mechanical stability can be synergistically optimized.In the present work, composite electroformed foils, composed of Ni matrix and sulfur loaded on Al alloy carrier particles AlSi10Mg, are used as cathodes for Li-S batteries. The synthesis procedure consists on the selective etching of the Al particles which are used as dispersoids in the composite electroforming process. BET results proved that after etching, the specific area is remarkably increased. Afterwards, the etched Al alloy particles are cemented with cobalt nanocrystallites, as these act as ideal electrocatalysts for the sulfur half cell [7].In a way to optimize the composite electroformed cathodes, which should ideally consist of a dense monolayer of sulfur loaded carrier particles without Ni overgrowth, several parameters can be evaluated. In the present work, parameters such as particle concentration in the electrolyte, current density, nickel concentration, pH value, temperature and convection are kept constant. Only the current and thus the corresponding time to achieve the desired composite thickness are varied. Moreover, the experimental conditions were extended to the application of pulse and pulse reverse plating.Therefore, in order to evaluate the parameter-structure relationships and to assess the efficacy of the presented approach, a broad range of morphological testing by SEM of all the composite electroformed cathodes was carried out. Furthermore, the electrochemical behavior of the novel cathodes that were galvanostatically cycled at slow and moderate rates was investigated and will be presented.[1] C. Erhardt, Ş. Sörgel, S. Meinhard, T. Sörgel, J. Power Sources, 296 (2015) 70-77.[2] T. Sörgel, ZVO report, 1 (2019) 46.[3] S. Meinhard, O. Kesten, K. Jäger, I. Hägele, T. Sörgel, Galvanotechnik, 8 (2020) 1164-1169.[4] A. K. Jäger, S. Meinhard, O. Kesten, I. Hägele, T. Sörgel, WoMag, 4 (2020) 25-26.[5] T. Sörgel, S. Meinhard, Ş. Sörgel, Film Composite Material, EP 3114721 B1, 2015.[6] T. Sörgel, J. Meyer, WOMag, 9 (2013) 24–33.[7] Ş. Sörgel, O. Kesten, A. Wengel, T. Sörgel, Energy Storage Mater. 2018, 10, 223-232.

Investigating the effect of injection rate on the capture efficiency of nanoparticles in different geometries of stenosed vessel

In this study, the effect of injection speed on the capture efficiency (CE) of nanoparticles under the influence of a magnetic field produced by a current-carrying wire is investigated. Three scenarios have been considered for the geometry of stenosis: (1) symmetrical stenosis, (2) upper wall stenosis, and (3) lower wall stenosis. The non-Newtonian behavior of blood has been modeled using the Carreau model. The effect of different parameters, including magnetic field, drag force, particle diameter, injection speed, blood velocity, and the shape of stenosis on the CE of nanoparticles, is investigated. Considering the injection speed along with non-Newtonian model in a vessel with stenosis is not addressed yet, and are investigated in the present study. The results show that blood velocity and particle diameter have a significant effect on the CE of nanoparticles. Besides, it was revealed that there is a threshold for current intensity (I = 0.009A). At the threshold, CE of nanoparticles is maximum (27.5%), and further increase in current intensity resulting in a dramatic reduction in CE. In all scenarios, as the injection speed increases, the CE of nanoparticles decreased. For example, for scenario 3, as the injection speed increased from 75 mm/s to 200 mm/s, the CE of nanoparticles reduced from 25% to 7.5%, respectively. Besides, for same injection speed, for example 75 mm/s, the CE of scenarios 1, 2, and 3 are 3%, 22.5%, and 25%, respectively. The upper wall stenosis is desired scenario in which the maximum carrier particles are captured at tumor site.

Double adjustment of Co and Sr in LaMnO3+δ perovskite oxygen carriers for chemical looping steam methane reforming

As a key factor for chemical looping steam methane reforming, the oxygen carrier with high quality is essential. In this work, both high reactivity and coking resistance of the La1−xSrxMn1−yCoyO3+δ oxygen carriers are achieved by double adjustment of Co and Sr. The redox tests and characterization results showed that the introduction of cobalt provided surface active sites to accelerate the activation of methane on the surface, and the Sr doping increased the oxygen vacancies which facilitated the migration of oxygen anion in the bulk of the oxygen carrier particles. The doping of Co and Sr can match the supply of oxygen from the bulk and the need of oxygen on the surface of the oxygen carrier particles. The best substitution proportion of Co and Sr could be set in range of 0.4–0.5 and 0.2–0.4, respectively. The La0.8Sr0.2Mn0.5Co0.5O3+δ exhibited satisfactory performance and good stability in the cyclic redox tests.

Study on the reaction performance of Ce‐doped NiFe 2 O 4 oxygen carriers in the process of chemical looping hydrogen production

Chemical looping hydrogen production is a kind of hydrogen production technology with great potential. NiFe2O4 is one of the oxygen carriers with the best comprehensive hydrogen production performance, but the oxygen carrier still has the disadvantages of low hydrogen production and poor reaction stability. In this paper, a small amount of Ce was doped in the oxygen carrier to improve the hydrogen production efficiency. And the reaction stability of the oxygen carrier was improved by loading an inert carrier. The experimental results showed that the 6 wt% Ce-NiFe2O4 oxygen carrier had the highest H2 yield, and the hydrogen yield per unit mass of oxygen carrier was increased from 194 to 367 mL/g. Thermodynamic simulation and characterization results showed that the doping of Ce could enhance the oxygen release capacity and hydrogen production capacity. In the cyclic experiment, due to the damage of the oxygen carrier spinel structure and the sintering of oxygen carrier particles, the reaction activity of the 6 wt% Ce-NiFe2O4 oxygen carrier gradually reduced and the hydrogen production in the steam reactor decreased significantly after 15 cycles. After the loading of Al2O3 inert support on the 6 wt% Ce-NiFe2O4 oxygen carrier, the hydrogen production was greatly improved and remained stable after 15 cycles. The modification of the oxygen carrier could not only increase the hydrogen production but also the economic efficiency for the reduced amount of Ce and Ni.

Biophysical targeting of high-risk cerebral aneurysms.

Localized delivery of diagnostic/therapeutic agents to cerebral aneurysms, lesions in brain arteries, may offer a new treatment paradigm. Since aneurysm rupture leading to subarachnoid hemorrhage is a devastating medical emergency with high mortality, the ability to noninvasively diagnose high‐risk aneurysms is of paramount importance. Moreover, treatment of unruptured aneurysms with invasive surgery or minimally invasive neurointerventional surgery poses relatively high risk and there is presently no medical treatment of aneurysms. Here, leveraging the endogenous biophysical properties of brain aneurysms, we develop particulate carriers designed to localize in aneurysm low‐shear flows as well as to adhere to a diseased vessel wall, a known characteristic of high‐risk aneurysms. We first show, in an in vitro model, flow guided targeting to aneurysms using micron‐sized (2 μm) particles, that exhibited enhanced targeting (>7 folds) to the aneurysm cavity while smaller nanoparticles (200 nm) showed no preferable accumulation. We then functionalize the microparticles with glycoprotein VI (GPVI), the main platelet receptor for collagen under low‐medium shear, and study their targeting in an in vitro reconstructed patient‐specific aneurysm that contained a disrupted endothelium at the cavity. Results in this model showed that GPVI microparticles localize at the injured aneurysm an order of magnitude (>9 folds) more than control particles. Finally, effective targeting to aneurysm sites was also demonstrated in an in vivo rabbit aneurysm model with a disrupted endothelium. Altogether, the presented biophysical strategy for targeted delivery may offer new treatment opportunities for cerebral aneurysms.

High Adsorption of α-Glucosidase on Polymer Brush-Modified Anisotropic Particles Acquired by Electrospraying-A Combined Experimental and Simulation Study.

In this particular contribution, we aim to immobilize a model enzyme such as α-glucosidase onto poly(DMAEMA) [poly(2-dimethyl amino ethyl methacrylate)] brush-modified anisotropic (cup- and disc-shaped) biocompatible polymeric particles. The anisotropic particles comprising a blend of PLA [poly(lactide)] and poly(MMA-co-BEMA) [poly((methyl methacrylate)-co-(2-(2-bromopropionyloxy) ethyl methacrylate)] were acquired by electrospraying, a scalable and convenient technique. We have also demonstrated the role of a swollen polymer brush grafted on the surface of cup-/disc-shaped particles via surface-initiated atom transfer radical polymerization in immobilizing an unprecedentedly high loading of enzyme [441 mg/g (cup)-589 mg/g (disc) of particles, 15-20 times higher than that of the literature-reported system] as compared to non-brush-modified particles. Circular dichroism spectroscopy was used to predict the structural changes of the enzyme upon immobilization onto the carrier particles. An enormously high amount of enzymes with preserved activity (∼85 ± 13% for cups and ∼78 ± 15% for discs) was found to adhere onto brush-modified particles at pH 7 via electrostatic adsorption. These findings were further explored at the atomistic level using a coarse-grained dissipative particle dynamics simulation approach, which exhibited excellent correlation with experimental results. In addition, accelerated particle separation was also achieved via magnetic force-induced aggregation within 20 min (without a centrifuge) by incorporating magnetic nanoparticles into disc-shaped particles while electrojetting. This further strengthens the technical feasibility of the process, which holds immense potential to be applied for various enzymes intended for several applications.

Effect of the Presence of Siloxanes in Biogas Chemical Looping Combustion

Siloxanes are a group of Si-based impurities, common in biogas. Although normally present in relatively small amounts, their presence could be highly problematic, as the generated Si could be a precursor to abrasion and wear in downstream components. In this work, the siloxane effect in biogas chemical looping combustion (CLC) was evaluated. CLC of biogas could be an efficient way of achieving CO2 negative emissions. Two oxygen carriers (CuO-based and Fe2O3-based residue) were used in the combustion of a simulated biogas stream in a batch fluidized bed reactor. Here one of the most common siloxane compounds (hexamethyldisiloxane, L2) was utilized together with methane, the most common combustible component in biogas. The siloxane decomposed in the batch reactor, forming gaseous compounds and Si-based particles. The gaseous compounds formed (mainly CO, H2, CH4, and C2) were able to react with the oxygen carrier, whereas the Si originating from the siloxane interacted with the oxygen carrier particles. Elemental analyses of samples obtained from the reactor bed after combustion experiments revealed that significant amounts of Si from siloxane could be found in the oxygen carrier. The X-ray photoelectron spectroscopy (XPS) analyses of the same samples showed that silica in the oxygen carrier was mainly found at the surface of the particles and in the form of SiO2 or silicates/aluminosilicates. The XPS results were in agreement with a theoretical thermodynamic analysis performed to determine the possible stable Si-based species that may be formed. Although the deposition/formation of silica compounds in the oxygen carrier may lead to the agglomeration of particles, such a phenomenon was not observed in the present work.

In-situ catalytic effect of potassium on petroleum coke gasification with a Mn ore-based oxygen carrier

Potassium was used as a catalyst for Chemical Looping Gasification (CLG) process in order to accelerate petroleum coke gasification. Two catalytic modes were applied, one was to use potassium to modify coke and another one was to a Mn ore based oxygen carrier. The in-situ catalytic effect of potassium during CLG process was experimentally evaluated in a fluidized bed. The influences of reaction temperature, oxygen carrier to fuel ratio, potassium introduction modes and cycles on syngas yields and distribution, carbon conversion and potassium evolution were investigated. Results indicated that both catalytic modes can accelerate coke conversion. Beneficial coke conversion was brought into play after several cycles’ activation for the potassium-modified Mn ore oxygen carrier applied for CLG process. Its activation with cycles led to an increase of the average carbon conversion rate, obtaining a stable value of 4.39%/min, higher than the one of 3.91%/min for the condition without potassium addition. Part of potassium on the surface of oxygen carrier was partially lost in the initial cycles and then fixed on the oxygen carrier particles. The remaining potassium existed in the form of K2Si4O9. The catalytic model of using the potassium to modify coke for CLG process accelerated coke conversion remarkably, obtaining an average carbon conversion rate of 7.8%/min, which is 1.78 times higher than that of using potassium to modify the Mn ore. Besides, the potassium into the reaction process had little effect on the oxygen carrier’s reactivity, but accelerated the water gas shift reaction, producing more H2 and less CO in the syngas.