Adsorptive Desulfurization: Fast On-Board Regeneration and the Influence of Fatty Acid Methyl Ester on Desulfurization and <i>in Situ</i> Regeneration Performance of a Silver-Based Adsorbent

Adsorptive on-board desulfurization units require a high desulfurization and regeneration performance for a wide range of fuels to keep them small and ensure long maintenance intervals. A novel thermal regeneration strategy was investigated in this work, fulfilling all requirements for <i>in situ</i> on-board regeneration. In this strategy, a temperature-controlled flow rate (TCFR) of air was used to control the temperature inside the adsorber. With this dynamic approach, the regeneration time was reduced significantly in comparison to other thermal regeneration strategies. The novel regeneration strategy was tested using Ag–Al₂O₃ as an adsorbent to desulfurize a benzothiophen (BT)-enriched road diesel (300 ppmw of total sulfur). A commercial diesel containing fatty acid methyl ester (FAME) was used to evaluate the fuel flexibility regarding desulfurization and regeneration performance. In the case of 6.63 wt % FAME and 300 ppmw of sulfur, the breakthrough adsorption capacity of sulfur decreased from 1.04 to 0.17 mg/g. In TCFR regeneration experiments, the breakthrough adsorption capacity was restored to over 94% in the case of both fuels. Thereby, the Brunauer–Emmett–Teller (BET) surface area of the regenerated adsorbent decreased by only 1.5%, and negligible carbon deposits were detected

Thermal in Situ and System-Integrated Regeneration Strategy for Adsorptive On-Board Desulfurization Units

This work deals with the introduction and investigation of a novel system-integrated thermal regeneration strategy based on hot off-gas for on-board desulfurization units. A highly thermally stable Ag–Al₂O₃ material was used as the adsorbent because it has the advantage of being active in the oxidized form so that it requires no activation after regeneration in an oxidative atmosphere. Dibenzothiophene (DBT) was used as the representative polycyclic aromatic sulfur heterocycle (PASH) in Jet A-1 fuel with a total sulfur concentration of 900 ppmw. This PASH has a stronger adsorption energy and is significantly more stable than benzothiophene or thiophene. This is why oxidative thermal regeneration strategies had formerly been failing to fully regenerate any type of adsorbent after the adsorption of DBT. This work reports excellent regeneration results upon the use of the hot off-gas from a solid-oxide-fuel-cell- (SOFC-) driven auxiliary power unit (APU) as the regeneration medium. The highly thermally stable Ag–Al₂O₃ showed a high breakthrough adsorption capacity of 2.2 mg-S/g-adsorbent in the first desulfurization cycle that was fully recovered by regeneration with hot APU off-gas. This is the first time that 100% regeneration has been reported for thermal regeneration after the adsorption of DBT. Additional investigations were performed to gain deeper insight into the overall desorption mechanism. The H₂O content has an especially significant influence on the overall desorption mechanism of DBT. With a H₂O content of 12.4 mol %, full regeneration was also obtained by reducing the final regeneration temperature from 525 to 450 °C. The results reported herein show that this novel regeneration strategy requires no additional regeneration medium, no additional tanks, and no additional bulky equipment and is thus fully integrated into the concept of an SOFC-operated APU

On the origin of degradation in fuel cells and its fast identification by applying unconventional online-monitoring tools

The key advantage of solid oxide fuel cells (SOFC) – high fuel flexibility – still remains the main challenge disturbing their stability, reliability and durability. Specific operating conditions induce and accelerate various degradation mechanisms and reduce the overall fuel cell lifetime. Identifying and predicting the onset of degradation at the preliminary stage is of crucial importance, in order to provoke appropriate countermeasures and to prolong the service time of the fuel cell technology. This is not possible when using available conventional monitoring tools. When employing appropriate online-monitoring tools the principle of which differs from the most common measurement of a linear stationary system, relevant information about the occurring failure modes can be obtained. An example for it is a total harmonic distortion (THD) tool, which is based on identification of the system non-linearity and its alternation from the stable state. Taking this into account, this study moves from the traditional concepts and we show that: (i) non-conventional methodologies can be used to identify relevant failure modes at their preliminary stage, (ii) it is possible to in-operando differentiate individual degradation mechanisms, and (iii) advanced unconventional online-monitoring tools are time-efficient and required measuring time can be reduced by factor up to 20

Impact of Iodine Electrodeposition on Nanoporous Carbon Electrode Determined by EQCM, XPS and In Situ Raman Spectroscopy

The charging of nanoporous carbon via electrodeposition of solid iodine from iodide-based electrolyte is an efficient and ecofriendly method to produce battery cathodes. Here, the interactions at the carbon/iodine interface from first contact with the aqueous electrolyte to the electrochemical polarization conditions in a hybrid cell are investigated by a combination of in situ and ex situ methods. EQCM investigations confirm the flushing out of water from the pores during iodine formation at the positive electrode. XPS of the carbon surface shows irreversible oxidation at the initial electrolyte immersion and to a larger extent during the first few charge/discharge cycles. This leads to the creation of functional groups at the surface while further reactive sites are consumed by iodine, causing a kind of passivation during a stable cycling regime. Two sources of carbon electrode structural modifications during iodine formation in the nanopores have been revealed by in situ Raman spectroscopy, (i) charge transfer and (ii) mechanical strain, both causing reversible changes and thus preventing performance deterioration during the long-term cycling of energy storage devices that use iodine-charged carbon electrodes

Mechanical strength of microspheres produced by drying of acoustically levitated suspension droplets

Spray drying is widely used in pharmaceutical manufacturing to produce microspheres from solutions or suspensions. The mechanical properties of the microspheres are reflected by the morphology formed in the drying process. In suspension drying, solids dissolved in the carrier liquid may form bridges between the suspended primary particles, producing a microsphere structure which is resistant against mechanical loads. Experiments with individual, acoustically levitated droplets were performed to simulate the drying of suspension droplets in a spray drying process. The suspensions studied consisted of a binary liquid mixture as the carrier liquid, and primary particles of suspended lactose material which is partially soluble in the liquid. The solubility of lactose was varied by the composition of the liquid mixture. The experiments revealed longer first and second drying stages for higher lactose solubility. Electron micrographs revealed the morphology of individual microspheres produced by drying in the levitator. Microspheres with only primary particles and no visible crust were obtained for low lactose solubility, whereas higher contents of dissolved lactose resulted in a more densely packed microsphere with crust formation. To quantify the hardness of individual microspheres, the maximum breaking force upon mechanical loading was measured for a range of varying suspension compositions. These measurements confirmed that densely packed structures with a thick crust reveal high mechanical strength. It was shown that, for primary lactose particles to be conserved in spray drying, the dissolved lactose mass loading Xd must be below 5.2%

Fast fuel variation and identification of SOFC system changes using online health monitoring tools and fault diagnosis

The greatest challenges of the solid oxide fuel cell (SOFC) technology are its reliability and durability, both of them considering a variety of possible fuels. To address those issues, understanding of the ongoing processes in SOFCs is of crucial importance. The ability to monitor electrochemical processes online and to identify fast alternating operating conditions offers a possibility to determine degradation-inducing processes at their preliminary stage. Thus, their early identification would provide timely counteractions and inhibit irreversible SOFC degradation. To guarantee the safe SOFC operation, the present study focuses on: (1) investigation of SOFC behavior during feeding with different fuels, (2) development and application of non-conventional tools for online-monitoring, and (3) identification of failure modes at the early stage