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Research Project
Centro de Química Estrutural
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Publications
Electrochemical assessment of corrosion-fatigue degradation stages
Publication . Simões, Alda Maria Pereira; Canut, Felipe; Reis, Luis; Napoleão Bastos, Ivan; Mamiya, Edgar
ABSTRACT: The study is focussed on the joint effect of corrosion and mechanical cyclic stresses observed on mooring chains of Floating Production Storage and Offloading (FPSO) units. The tests were performed using grade R4 steel in artificial sea water, under stress-controlled and fully reversed loading. The corrosion-fatigue
degradation was monitored using open circuit potential measurements simultaneously with the cyclic
mechanical load. The open circuit potential response varies during the corrosion-fatigue test, depending on
the stage of degradation of the material. This technique has proven to be capable of identifying important
phenomena, such as crack initiation and crack propagation, on the material under corrosion-fatigue loading
condition.
Lipid and carotenoid production by a Rhodosporidium toruloides and Tetradesmus obliquus mixed culture using primary brewery wastewater supplemented with sugarcane molasses and urea
Publication . Dias, Carla; Nobre, B. P.; Santos, J. A. L.; Reis, Alberto; Silva, Teresa Lopes da
ABSTRACT: In this study, Rhodosporidium toruloides and Tetradesmus obliquus were used for lipid and carotenoid production in mixed cultures using primary brewery wastewater (PBWW) as a culture medium, supplemented with sugarcane molasses (SCM) as a carbon source and urea as a nitrogen source. To improve biomass, lipid, and carotenoid production by R. toruloides and T obliquus mixed cultures, initial SCM concentrations ranging from 10 to 280 g L-1 were tested. The medium that allowed higher lipid content (26.2% w/w dry cell weight (DCW)) and higher carotenoid productivity (10.47 mu g L-1 h(-1)) was the PBWW medium supplemented with 100 g L-1 of SCM and 2 g L-1 of urea, which was further used in the fed-batch mixed cultivation performed in a 7-L bioreactor. A maximum biomass concentration of 58.6 g L-1 and maximum lipid content of 31.2% w/w DCW were obtained in the fed-batch cultivation. PBWW supplemented with SCM was successfully used as a low-cost medium to produce lipids and carotenoids in a R. toruloides and T obliquus mixed culture, with higher productivities than in pure cultures, which can significantly reduce the cost of the biofuels obtained.
Hydrometallurgical recovery of platinum-group metals from spent auto-catalysts: Focus on leaching and solvent extraction
Publication . Paiva, A. P.; Piedras, Francisco Vega; Rodrigues, Pedro G.; Nogueira, Carlos
ABSTRACT: To ensure the supply of raw materials for products of extreme importance in strategic sectors, the recovery of critical metals from secondary sources becomes increasingly urgent. Platinum group metals (PGMs), being rare and very valuable, fall into this demand, and the catalytic converters that contain them are recognized as one of the main sources. Hydrometallurgical processes have been proposed as an alternative to pyrometallurgical ones, with leaching and separation by solvent extraction being core operations in this type of processing. This article investigates these two operations, seeking to optimize conditions and propose new arrangements to improve them. Two different catalyst samples were considered in the experimental work. Leaching was carried out involving concentrated HCl solutions (with H2O2 as oxidant) and low liquid/solid ratios, seeking to maximize PGMs recovery, guaranteeing their high concentration in leachates and minimizing aluminum co-dissolution. Cerium leaching was also followed since this is a rare-earth metal with potential interest. Temperature, HCl concentration, liquid/solid ratio (L/S), time and particle size factors were evaluated, and the optimized conditions found were 11.6 mol L-1 HCl, 1%vol H2O2, 60 C, L/S = 2 L kg(-1) and 3 h, leading to PGM yields of 90-98% Pt, 99% Pd and 70-96% Rh, and leachate compositions of 0.41-0.78 g L-1 Pt, 1.6 g L-1 Pd, 0.062-0.066 g L-1 Rh, depending on the catalyst sample.& nbsp;For solvent extraction (SX), several commercial extractants dissolved/diluted in toluene were checked, firstly with a model solution, and then applied to the real spent auto-catalyst (SAC) leachates produced in-situ. The overall results showed that the most promising SX systems among those tested were Cyanex (R) 471X and Cyphos (R) IL 101. Cyanex (R) 471X allowed the quantitative extraction of Pd(II) and Fe(III), but the latter was conveniently scrubbed by water prior to Pd(II) stripping by an acidic thiourea solution. Pt(IV) and Pd(II) extraction values by Cyphos (R) IL 101 were very encouraging, as only Fe(III) and Zn(II) were appreciably co-extracted, however, scrubbing of the contaminating metals, and Pd(II) and Pt(IV) stripping, did not work. Hence, investigation to find proper scrubbing/stripping agents for Cyphos (R) IL 101 SX system, to recover PGMs from recycled SACs, is further needed.
Solid-gas reactors driven by concentrated solar energy with potential application to calcium looping: A comparative review
Publication . Rivero, Mayra Alvarez; Rodrigues, Diogo; Pinheiro, Carla I.C.; Cardoso, João P.; Mendes, Luís Filipe
ABSTRACT: The calcium looping process, based on the reversible calcination-carbonation reaction cycle of CaCO3-CaO, is an emerging and promising technology for thermochemical energy storage in concentrating solar power plants. In this process, concentrated solar energy is used to carry out the endothermic solar-driven calcination of CaCO3 with formation of CaO and CO2 as products in a solid-gas reactor. In this review, a number of experimental studies of solid-gas reactors driven by concentrated solar energy are discussed, with a particular focus on solar reactors for calcination of CaCO3 or with that potential application. The solid-gas reactors for solar-driven calcination of CaCO3 reported in the literature achieved a total efficiency of 16.6%-88% for a mass flow rate up to 25 kg h(-1) and a power up to 55 kW. Also, a detailed comparison of the different types of solid-gas reactors driven by concentrated solar energy is provided by outlining their advantages and disadvantages according to several relevant criteria. This review is intended to be a valuable tool for the selection of a reactor configuration for future studies related to solar-driven calcination of CaCO3.
Naphthenic corrosion using electrochemical and analytical techniques
Publication . Simões, Alda Maria Pereira; Pereira Da Silva, Rejane Maria; Suffredini, Hugo; Santos, Luis; Bastos, Ivan Napoleão
ABSTRACT: Naphthenic acid corrosion of steel was studied in a stagnant, biphasic oil/aqueous phase system, by means of electrochemical measurements and surface analysis. Corrosion was restricted to the region of the aqueous phase, as crater-shaped pits that eventually coalesced, generating a nearly uniform attack in the vicinity of the oil phase. In-situ electrochemical impedance spectroscopy (EIS) reveals the processes occurring at the aqueous phase, which nevertheless increase with the fraction of oil phase and with degree of acidity of the oil.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
6817 - DCRRNI ID
Funding Award Number
UIDB/00100/2020