Recent Submissions

  • Fast water transport and molecular sieving through ultrathin ordered conjugated-polymer-framework membranes

    Shen, Jie; Cai, Yichen; Zhang, Chenhui; Wei, Wan; Chen, Cailing; Liu, Lingmei; Yang, Kuiwei; Ma, Yinchang; Wang, Yingge; Tseng, Chien-Chih; Fu, Jui-Han; Dong, Xinglong; Li, Jiaqiang; Zhang, Xixiang; Li, Lain-Jong; Jiang, Jianwen; Pinnau, Ingo; Tung, Vincent; Han, Yu (Nature Materials, Springer Science and Business Media LLC, 2022-08-08) [Article]
    The development of membranes that block solutes while allowing rapid water transport is of great importance. The microstructure of the membrane needs to be rationally designed at the molecular level to achieve precise molecular sieving and high water flux simultaneously. We report the design and fabrication of ultrathin, ordered conjugated-polymer-framework (CPF) films with thicknesses down to 1 nm via chemical vapour deposition and their performance as separation membranes. Our CPF membranes inherently have regular rhombic sub-nanometre (10.3 × 3.7 Å) channels, unlike membranes made of carbon nanotubes or graphene, whose separation performance depends on the alignment or stacking of materials. The optimized membrane exhibited a high water/NaCl selectivity of ∼6,900 and water permeance of ∼112 mol m−2 h−1 bar−1, and salt rejection >99.5% in high-salinity mixed-ion separations driven by osmotic pressure. Molecular dynamics simulations revealed that water molecules quickly and collectively pass through the membrane by forming a continuous three-dimensional network within the hydrophobic channels. The advent of ordered CPF provides a route towards developing carbon-based membranes for precise molecular separation.
  • Evaluative screening of kinetic models for simulating the performances of oxidative coupling of methane catalysts

    Gobouri, Abdullah (2022-07-27) [Thesis]
    Advisor: Castaño, Pedro
    Committee members: Ruiz-Martinez, Javier; Hauser, Charlotte
    In this work, multiple kinetic models have been screened as potential candidates for simulating the performances of three oxidative coupling of methane (OCM) catalysts. Two of the proposed models were subjected to testing and optimization. The types of models screened covered both kinetic and microkinetic type models, i.e., radical omitting and radical considering. Some of the models only accounted for catalytic heterogeneous pathways, while others have expanded on the homogeneous gas-phase mechanism of the OCM reaction. The optimization process was carried out in MATLAB® R2020a using an error minimization tool. The range of experimental conditions examined was as follows: 740–800◦C, 100 kPa, 2–4 CH4/O2 ratio, 1–6 gcat h molC –1 spacetime. The results show successful optimization of both models as well as discrepancies in terms of their performances in predicting experimentally obtained values of CH4 and O2 conversions, as well as selectivities towards COx and C2+ products. While a kinetic model served as an easy option to optimize, it expressed limits in terms of achievable performance, mainly failing to simulate experimental runs conducted at low spacetimes. A microkinetic model on the other hand, managed to simulate all experimental conditions, with less accuracy towards COx species and much greater computational demand.
  • Formation of Organic Acids and Carbonyl Compounds in n-Butane Oxidation via γ-Ketohydroperoxide Decomposition

    Popolan-Vaida, Denisia Maria; Eskola, Arkke J.; Rotavera, Brandon; Lockyear, Jessica F.; Wang, Zhandong; Sarathy, Mani; Caravan, Rebecca L.; Zádor, Judit; Sheps, Leonid; Lucassen, Arnas; Moshammer, Kai; Dagaut, Philippe; Osborn, David L.; Hansen, Nils; Leone, Stephen R.; Taatjes, Craig A. (Angewandte Chemie, Wiley, 2022-07-27) [Article]
    A crucial chain-branching step in autoignition is the decomposition of ketohydroperoxides (KHP) to form an oxy radical and OH. Other pathways compete with chain-branching, such as “Korcek” dissociation of γ-KHP to a carbonyl and an acid. Here we characterize the formation of a γ-KHP and its decomposition to formic acid + acetone products from observations of n ‑butane oxidation in two complementary experiments. In jet-stirred reactor measurements, KHP is observed above 590 K. The KHP concentration decreases with increasing temperature, whereas formic acid and acetone products increase. Observation of characteristic isotopologs acetone‑ d 3 and formic acid- d 0 in the oxidation of CH 3 CD 2 CD 2 CH 3 is consistent with a Korcek mechanism. In laser-initiated oxidation experiments of n -butane, formic acid and acetone are produced on the timescale of KHP removal. Modelling the time-resolved production of formic acid provides an estimated upper limit of 2 s ‑1 for the rate coefficient of KHP decomposition to formic acid + acetone.
  • Pdzn/Zro2 + Sapo-34 Bifunctional Catalyst for Co2 Conversion: Further Insights by Spectroscopic Characterization

    Ticali, Pierfrancesco; Morandi, Sara; Shterk, Genrikh; Ould-Chikh, Samy; Ramirez, Adrian; Gascon, Jorge; Chung, Sang-ho; Ruiz-Martinez, Javier; Bordiga, Silvia (Elsevier BV, 2022-07-26) [Preprint]
    The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT Pd carbonyl band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2.The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd carbonyls appear due to Pd2+ ionic exchange into SAPO-34 framework.
  • Pdzn/Zro2 + Sapo-34 Bifunctional Catalyst for Co2 Conversion: Further Insights by Spectroscopic Characterization

    Ticali, Pierfrancesco; Morandi, Sara; Shterk, Genrikh; Ould-Chikh, Samy; Ramirez, Adrian; Gascon, Jorge; Chung, Sang-ho; Ruiz-Martinez, Javier; Bordiga, Silvia (Elsevier BV, 2022-07-26) [Preprint]
    The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT Pd carbonyl band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2.The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd carbonyls appear due to Pd2+ ionic exchange into SAPO-34 framework.
  • A functional-group-based approach to modeling real-fuel combustion chemistry – III: Application to biodiesels

    Zhang, Xiaoyuan; Xu, Qiang; Xie, Cheng; Di, Qimei; Liu, Bingzhi; Wang, Zhandong; Sarathy, Mani (Proceedings of the Combustion Institute, Elsevier BV, 2022-07-25) [Article]
    Real biodiesel fuels are mixtures comprising many high molecular weight components, making it a challenge to predict their combustion chemistry with detailed kinetic models. Our group previously proposed a functional-group approach (FGMech) to model the combustion chemistry of real gasoline and jet fuels; this approach has now been extended to model real biodiesel combustion and mixtures with petroleum fuels. As in our previous work, a decoupling philosophy is adopted for construction of the model. A lumped reaction mechanism describes the (oxidative) pyrolysis of fuels, while a detailed base chemistry model represents the oxidation of key pyrolysis intermediates. However, due to the presence of the ester group, several oxygenated species are identified as additional primary products and incorporated into the lumped reaction steps. In addition to the lumped reactions initiated by unimolecular decomposition and H-atom abstraction reactions, a lumped H-atom addition-elimination reaction is also incorporated as a new reaction class to account for the presence of double bonds. Stoichiometric parameters are obtained based on a multiple linear regression (MLR) model, which establishes relationships between the fuel's functional group distributions and the stoichiometric parameters of the lumped reactions. Global rate constants are developed from consistent rate rules obtained from pure fuels. New pyrolysis experimental data for methyl pentanoate/methyl nonanoate and methyl heptanoate/n-heptane mixtures (50%/50% in mol) are obtained in a jet-stirred reactor at atmospheric pressure. In general, kinetic models developed using the FGMech approach can reasonably reproduce all the validation targets obtained in this work, as well as those in the literature, confirming that functional-group-modeling is a promising approach to simulate combustion behavior of diesel/biodiesel surrogate fuels and real biodiesels.
  • Machine learning to predict biochar and bio-oil yields from co-pyrolysis of biomass and plastics

    Alabdrabalnabi, Aessa; Gautam, Ribhu; Sarathy, Mani (Fuel, Elsevier BV, 2022-07-25) [Article]
    Because of high oxygen content, pH and viscosity, pyrolysis bio-oil is of low quality. Upgrading bio-oil can be achieved by co-pyrolysis of biomass with waste plastics, and it is seen as a promising measure for mitigating waste. In this work, machine learning models were developed to predict yields from the co-pyrolysis of biomass and plastics. Classical machine learning and neural network algorithms were trained with datasets, acquired for biochar and bio-oil yields, with cross-validation and hyperparameters. XGBoost predicted biochar yield with an RMSE of 1.77 and R2 of 0.96, and the dense neural network was able to predict the bio-oil yield with an RMSE of 2.6 and R2 of 0.96. The SHapley Additive exPlanations analysis technique was used to understand the influence of various parameters on the yields from co-pyrolysis. This study provides valuable insights to understand the co-pyrolysis of biomass and plastics, and it opens the way for further improvements.
  • Maximizing Active Fe Species in ZSM-5 Zeolite Using Organic-Template-Free Synthesis for Efficient Selective Methane Oxidation

    Cheng, Qingpeng; Li, Guanna; Yao, Xueli; Zheng, Lirong; Wang, Junhu; Emwas, Abdul-Hamid M.; Castaño, Pedro; Ruiz-Martinez, Javier; Han, Yu (Research Square Platform LLC, 2022-07-22) [Preprint]
    The selective oxidation of CH4 in the aqueous phase to produce valuable chemicals has attracted considerable research attention due to its mild reaction conditions and simple process. As the most widely studied catalyst for this reaction, Fe-containing ZSM-5 zeolite (Fe-ZSM-5) demonstrates high intrinsic activity and selectivity; however, Fe-ZSM-5 prepared using conventional methods has a limited number of active Fe sites, resulting in low CH4 conversion per unit mass of the catalyst. To address this issue, this study reports a facile organic-template-free synthesis strategy that enables the incorporation of more Fe into the zeolite framework with a higher dispersion degree compared to conventional synthesis methods. Because framework Fe incorporated in this way is more readily to transform into isolated extra-framework Fe species under thermal treatment, the overall effect is that Fe-ZSM-5 prepared using this method (Fe-HZ5-TF) has three times as many catalytically active sites as conventional Fe-ZSM-5. When used for the selective oxidation of CH4 (30.5 bar) with 0.5 M H2O2 at 75°C, Fe-HZ5-TF produced a record high C1 oxygenate yield of 106.3 mmol gcat−1 h− 1 (a HCOOH selectivity of 91.3%), surpassing other catalysts reported to date. Spectroscopic characterization and density functional theory calculations revealed that the active sites in Fe-HZ5-TF are mononuclear Fe species in the form of [(H2O)3Fe(IV) = O]2+ bound to Al pairs in the zeolite framework. This differs from conventional Fe-ZSM-5, where binuclear Fe acts as the active site. Analysis of the catalyst and product evolution during the reaction suggests a radical-driven pathway to explain CH4 activation at the mononuclear Fe site and subsequent conversion to C1 oxygenates.
  • New era of sustainable design for molecular motors

    Szekely, Gyorgy (Chem Catalysis, Elsevier BV, 2022-07-21) [Article]
    Native lignocellulose can be used to create light-driven molecular motors via a “green” synthetic approach. In the May issue of Green Chemistry, Barta, Feringa, and co-workers provided new insights into the sustainable design of molecular motors through reductive catalytic fractionation using a lignocellulose platform.
  • Shockwave impact on the stability of anatase titania nanoparticles

    Slama de Freitas, Ana Luiza; Subburaj, Janardhanraj; Navarro, Juan Carlos; Khan, Hassnain Abbas; Kashif, Touqeer Anwar; Hakimov, Khaiyom; Ruiz-Martinez, Javier; Farooq, Aamir (Materials Today Communications, Elsevier BV, 2022-07-20) [Article]
    The stability of anatase titania nanoparticles was investigated under exposure to repeated loading of shockwaves produced in a diaphragm-driven high-pressure shock tube. The titania samples were exposed to 20 shocks with pressure, temperature, and steady exposure time in the range of 20.5 – 26 bar, 1399 – 2101 K, and 1.74 – 1.83 ms, respectively. The crystal structure and surface morphology were analyzed before and after the shockwave treatment using various characterization techniques. After repeated shock exposure, there was reduction in crystallite size by ~ 40%, modification in the surface charge, and an increase in the hydroxyl groups in titania. The onset of phase transformation from anatase to rutile was observed after 20 shocks. This work gives insights into the structural changes induced by shockwaves in anatase nanoparticles which can help improve their performance as a catalytic support in heterogeneous catalysis.
  • Decreasing the Coking and Deactivation of a Reforming Ni-Ce/Al2o3 Catalyst with Intraparticle Sic in Hydrogen Production Routes

    Tavares, F.; Mohamed, Hend Omar; Kulkarni, Shekhar Rajabhau; Morlanes, Natalia Sanchez; Castaño, Pedro (Elsevier BV, 2022-07-19) [Preprint]
    Steam reforming processes are under pressure to fuel the hydrogen economy, cutting its significant carbon footprint and transitioning to renewable feedstock while improving catalyst performance and lifetime. A seemingly inert material, such as silicon carbide (SiC, also known as carborundum), introduced in catalytic particles significantly influences catalytic performance, particularly during deactivation. We synthesized different catalysts with similar amounts of active materials (20 wt% of Ni and 2 wt% of Ce) and varied the proportion (0 to 78 wt%) and particle size (38 to 112 µm) of SiC within the alumina support. We used various techniques to characterize the catalysts and test them in reforming heptane, which was employed as the model molecule. The maximum enhancement with SiC occurs using 20 wt% of SiC with a size of 38 µm. Further, the enhancement with SiC is due to the control of the Ni particle size, leading to a 26% improvement in the apparent reaction rate (per exposed Ni) and a 117% decline in the deactivation rate compared to the SiC-free counterpart.
  • Scalable Fabrication of Solvent-Free Composite Solid Electrolyte by a Continuous Thermal-Extrusion Process

    Li, Zhen; Aboalsaud, Ammar M.; Liu, Xiaowei; Thankamony, Roshni; Chen, I-Chun; Li, Yangxing; Lai, Zhiping (Journal of Colloid and Interface Science, Elsevier BV, 2022-07-19) [Article]
    Composite solid-state electrolytes (CSEs) are regarded as a promising alternative for the next-generation lithium-ion batteries because they integrate the advantages of inorganic electrolytes and organic electrolytes. However, there are two issues faced by current CSEs: 1) a green and feasible approach to prepare CSEs in large scales is desired; and 2) the trace solvents, remaining from the preparation processes, lead to some serious concerns, such as safety hazard issues, electrolyte-electrode interfacial issues, and reduced durability of batteries. Here, a continuous thermal-extrusion process is presented to realize the large-scale fabrication of solvent-free CSE. A 38.7-meter CSE membrane was prepared as a demonstration in this study. Thanks to the elimination of residual solvents, the electrolyte membrane exhibited a high tensile strength of 3.85 MPa, satisfactory lithium transference number (0.495), and excellent electrochemical stability (5.15 V). Excellent long-term stability was demonstrated by operating the symmetric lithium cell at a stable current density of 0.1 mA cm−2 for over 3700 h. Solvent-free CSE lithium metal batteries showed a discharge capacity of 155.7 – 25.17 mAh g-1 at 0.1 – 2.0 C, and the discharge capacity remained 78.1% after testing for 380 cycles.
  • Water Effect on the Methanol to Olefin Conversion over SSZ-13 Catalyst with an Operando Spectroscopy

    Alsindi, Mohammed (2022-07-18) [Thesis]
    Advisor: Ruiz-Martinez, Javier
    Committee members: Pinnau, Ingo; gomez-cabrero, David
    For more than 50 years, the methanol to olefins (MTO) reaction remains to be a hot topic within the catalysis community. The recent discoveries about it and the industrial implementation made it even receive more attention. The best way this process can be used is by hydrogenation of CO2 to make methanol and undergo after that the MTO reaction. This method will save energy, be more environmentally friendly, and be sustainable, but it requires advancement regarding carbon capture. The purpose of this paper is to understand the effect of water on SSZ-13 commercial zeolite when it is used for MTO reaction by a combination of gas chromatography (GC) analysis and operando UV – vis spectroscopy. It was observed that water with a ratio of 2:1 methanol to water would increase the lifetime of the catalyst from 3 h to 6.5 h, and the ratio of 1:1 would increase it to 9 h. However, a higher amount of water hadn’t been analyzed, but theoretically, it would cause dealumination to the zeolite invoking a different type of deactivation. This increase in catalyst lifetime was first due to the competitive adsorption between water and methanol; leading to a lower methanol reactivity toward methoxide formation. Second, because of the competition between water and propylene, it resulted in a longer induction period and a delay in the formation of hydrocarbon pool. Hence, less coke was formed from the reaction and more species were able to diffuse into the inner pores. Also, it was observed that ethylene selectivity increased with the addition of water to the feed. The UV-vis analysis proved the longer induction period and showed the formation of more species due to that. The deactivating materials were identified to be polyaromatic carbocation and phenanthrene, while the main activating species was methylated naphthalene carbocation. In addition, multiple characterization techniques, such as nitrogen physisorption, ammonia TPD, and SEM, were performed to understand the nature of the catalyst. It was found that it has weak and strong Bronsted acid sites, BET surface area of 665.7 m2/g, and crystal size of about 0.5 – 2 µm.
  • Dual Experimental and Computational Approach to Elucidate the Effect of Ga on Cu/Ceo2–Zro2 Catalyst for Co2 Hydrogenation

    Attada, Yerrayya; Velisoju, Vijay Kumar; Mohamed, Hend Omar; Ramirez, Adrian; Castaño, Pedro (Elsevier BV, 2022-07-14) [Preprint]
    Intermetallic Cu–Ga catalysts are potential candidates for activating the selective and stable hydrogenation of carbon dioxide to methanol and dimethyl ether. This work explores the structure–function relationship in specific Cu–Ga/CeO 2 –ZrO 2 catalysts with different Ga loadings. Combining experiments with density functional theory calculations, we find the most well-balanced intermetallic Cu–Ga interphase (structure) and promote specific mechanistic pathways of the reaction (function). The experiments yielded the highest selectivity of the desired products when the Cu and Ga amounts were equal. The experimental work and density functional theory calculations demonstrated that methanol is formed through the carboxyl pathway on the Cu catalyst, while Ga promotes the formate pathway. Consequently, the productivities of both methanol and dimethyl ether are enhanced. The experimental results match well with the theoretical calculations. Comparing our results with other Ga-promoting systems, we also prove that Cu achieves better balance than Ni and Co.
  • Quinuclidinium-piperidinium based dual hydroxide anion exchange membranes as highly conductive and stable electrolyte materials for alkaline fuel cell applications

    Patil, Smitha S.; V, Madhura; Kammakakam, Irshad; Swamy, MH Halashankar; Patil, K. Sadashiva; Lai, Zhiping; Rao H N, Anil (Electrochimica Acta, Elsevier BV, 2022-07-12) [Article]
    Anion-exchange membrane fuel cells (AEMFCs) utilizing quaternary ammonium functionalized poly(arylene ether sulfone)s have been rapidly advanced in the clean energy research arena. However, it is highly desirable to integrate the benefits of quaternary ammonium cations in the polymeric membrane systems to achieve a high-power output together with substantial stabilities that significantly reduce the material costs. Herein, we report the tethering of two different quinuclidinium and piperidinium cations separated by a flexible –(CH2)4˗ spacer as a dual hydroxide conductor in the poly(arylene ether sulfone)s copolymer membrane (QP-PES) for enhancing the structural and physical properties as well as the ionic conductivities. The results proved that the tethering of dual hydroxide conductor in the PES backbone led to show maximum hydroxide conductivity of 88 mS cm−1 at 80 °C while enabling a hydrophilic/hydrophobic micro-phase separation due to the presence of flexible alkyl spacer. We also investigated the properties of a single hydroxide conductor exclusively comprising the quinuclidinium cation (Q-PES) and compared it with that of QP-PES. Interestingly, both the Q-PES and QP-PES membranes displayed superior thermal, mechanical, and dimensional stabilities. Most importantly, the QP-PES membrane demonstrated excellent alkaline stability over the period of 1000 h due to the existence of dual hydroxide conductor together with alkyl spacer units. Furthermore, the maximum power density of a H2/O2 single cell using QP-PES (92.3 mWcm−2) is higher than that of QP-PES (70.0 mWcm−2). The results provide a greater perception to design the high performance AEM materials.
  • Elucidating the Promoting Role of Ca on Pdzn/Ceo2catalyst for Co2 Valorization to Methanol

    Sharif, Zaman Fakhruz; Ojelade, Opeyemi A.; Alhumaide, Hesham; Majumder, Jahirul; Castaño, Pedro (Elsevier BV, 2022-07-11) [Preprint]
    The viability of catalyzed CO 2 conversion routes strongly depends on improving the catalytic performance and understanding of the process. Herein, we investigate the effect of Ca loading on PdZn/CeO 2 catalysts prepared using the sol-gel chelatization method for CO 2 hydrogenation to methanol. A remarkable improvement in catalyst performance was revealed with the optimum amount of Ca (0.5 wt%) in synergetic cooperation with the PdZn alloy (main active phase for the CO 2 hydrogenation to methanol reaction), compared to the Ca-free counterpart. The following key performance indicators are attained at 230 o C, 20 bar, and 2400 h -1 GHSV for the optimized catalyst: 16% CO 2 conversion, > 93% methanol selectivity, and ~124 g/kg cat /h methanol space-time yield. The overall catalytic performance observed is attributed to the optimum Ce 3+ /Ce 4+ ratio, Ca 2+ promotion, surface area, pore volume, and basic sites, as revealed by various characterization techniques. Results shown here indicate that the presence of Ca in the vicinity of the PdZn active enhances basicity, creates oxygen vacancies, and phase may have improved the spill-over ability of H 2 , consequently favoring CO 2 activation and methanol formation.
  • Solar-driven ultrafast lithium extraction from low-grade brine using microfluidics-mediated vortex in scalable electrochemical reactors

    Zhang, Xianyun; Li, Zhen; Liu, Jiang; Xu, Fuzong; Zheng, Leiliang; De Wolf, Stefaan; Lai, Zhiping; Lu, Xu (Research Square Platform LLC, 2022-07-05) [Preprint]
    Electrochemical lithium (Li) extraction from low-grade salt lake brine, when powered by off-grid renewables, represents a potential approach to meeting the substantially increasing demand for battery-grade Li2CO3. However, this technology has been drastically challenged by the low extraction rate and high production cost, largely due to the lack of research on reactor engineering and system scale-out. Herein, we rationally designed a scalable spiral-microstructured electrochemical reactor (SMER) to accomplish ultrafast and economical Li extraction under harsh brine conditions by virtue of significantly accelerated mass transfer. We showcased that the SMER was stably operated at a Li extraction rate over 5.6 times as much as that of state-of-art devices, and could be up-scaled for commercial production of battery-grade Li2CO3 driven by solar cells. This work lays the ground for sustainable Li extraction from remote low-grade salt lake brine and can be readily applied to more minable Li reserves/resources.
  • The Effects of Gasoline Composition and Additive Concentration on the Lubricity of Gasoline Blends

    Al Ashkar, Youssef (2022-07) [Thesis]
    Advisor: Sarathy, Mani
    Committee members: Roberts, William L.; Szekely, Gyorgy
    Under current regulations, gasoline engines are facing lubricity and wear challenges that need to be met by enhanced gasoline lubricity. Gasoline lubricity can be enhanced by lubricity improvers such as heavy fatty acid methyl esters. This thesis presents the ‘High Frequency Reciprocating Rig’ (HFRR) tests carried out on a standardized tribological test rig as per a modified version of ASTM D6079, to account for the effects of volatility of gasoline. Testing 5 gasoline types (gasolines A-E) blended with 2 lubricity improver types (LI1-2) at 2 concentrations, 250 and 500 ppm, provided insights on the changes in lubrication behavior with different gasoline composition, LI type, and concentration. The gasoline types with higher aromatic content and average carbon number (lower volatility) resulted in less wear and better lubricity regardless of LI concentration. The highly aromatic gasoline “A” performed better with the fatty acid-based LI1. Gasolines “B-E”, which are less aromatic, resulted in less wear with the ester-based LI2. The decrease in wear volumes with LI2 was more pronounced with the highly volatile gasolines B and E. These insights were mainly challenged by the failure of some tests due to the high volatility of gasoline. To mitigate this effect and confirm the findings, less volatile gasoline surrogates were designed to mimic the composition of the gasoline types on functional group basis, and were blended with the same lubricity improvers, and then tested using the same method. This improved the results and showed that high aromaticity enhanced the lubricity of the gasoline blends, especially with fatty-acid based LI1, but degraded it beyond 50% aromatic content. The enhancement of lubricity with higher average carbon number was also highlighted. To create deeper understanding of the lubrication mechanisms involved, it is recommended to study the rheological properties of the blends, analyze the chemical composition of the deposits on the wear tracks, and repeat the tests with continuous supply of lubricant to further decrease the effect of gasoline volatility
  • Fuel production via catalytic cracking of pre-hydrotreated heavy-fuel oil generated by marine-transport operations

    Izaddoust, Sepideh; Hita, Idoia; Zambrano, Naydu; Trueba, David; Palos, Roberto; Zhang, Wen; Epelde, Eva; Arandes, Jose M.; Castaño, Pedro (Fuel, Elsevier BV, 2022-07-01) [Article]
    We examine the conversion of heavy-fuel oil waste generated by marine-transport operations into drop-in transportation fuels. The proposed conversion process comprises two steps: (i) hydrotreatment and (ii) fluid catalytic cracking (FCC) under industrially relevant conditions. CoMo/Al2O3 is employed as the catalyst for hydrotreating, primarily aimed at sulfur reduction. In the second stage, a highly intensive study of the FCC over an equilibrated steamed zeolite catalyst is performed. We provide a complete analytical overview of all the products and byproducts of these two reactions, including the coke deposited over the FCC catalysts using various characterization techniques, including high-resolution mass spectrometry. The hydrotreatment eliminates 67% of sulfur present in the original ship oil, while the cracking yields up to 47 wt% high-quality gasoline, containing 37 wt% aromatics, and 23 wt% i-paraffins. Based on the molecular-level characterization of the formed coke species and the performed parametric study, this work provides insights into the optimum operational conditions for minimizing coke deposition and improving the gasoline yield and quality.
  • Synthesis, Modification, and Evaluation of MXene as a Novel Anode Electrode Material for Bio-electrochemical Systems

    KOLUBAH, PEWEE DATOO (2022-07) [Thesis]
    Advisor: Castaño, Pedro
    Committee members: Szekely, Gyorgy; Saikaly, Pascal
    Bioelectrochemical systems (BESs) show promising prospects for recovering energy and chemicals from industrial and municipal wastewater. Despite the advances in the development of this technology, there is still a significant need for efficient electrode materials with high conductivity, hydrophilicity, and good biocompatibility to boost their performance and increase productivity. In this work, metal nanoparticle-two-dimensional MXene (W2N-Ti3C2Tx and Fe-W2N-Ti3C2Tx) composite electrocatalysts were synthesized using a simple impregnation method and deposited on carbon cloth (CC) to be used as a cheap and high performing anode in BESs. The plain CC, Ti3C2Tx-CC, W2N-Ti3C2Tx-CC, and Fe-W2N-Ti3C2Tx-CC were characterized using several techniques including scanning electron microscopy, transmission electron microscopy, water contact angle, and atomic force microscopy. The prepared anodes were tested in a single chamber air cathode microbial fuel cell inoculated with industrial wastewater for power generation and wastewater treatment simultaneously. The obtained results show that carbon cloth modified with W2N-Ti3C2Tx and Fe-W2N-Ti3C2Tx exhibited improved power density of 548 mW m-2 and 327 mW/m-2 with 81% and 44%, coulombic efficiency, respectively. The obtained power densities were 6 and 3.7 times higher, respectively than that achieved for pure carbon cloth (88 mW m-2). This study demonstrates the potential of combining two-dimensional MXene with metal nanoparticles to form an active composite anode catalyst for enhancing power generation and wastewater treatment using microbial fuel cells.

View more