Laboratory of Separation and Reaction Engineering - Laboratory of Catalysis and Materials

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Publications

Biphasic oxidative denitrogenation with H2O2 of a simulated fuel using sustainable carbon nanotube catalysts

Publication . Piccinin, Larissa; Roman, Fernanda; Freitas, Isabella Veronica; Díaz de Tuesta, Jose Luis; Silva, Adrián; Faria, Joaquim; Vieira, Admilson L.; Lenzi, Giane G.; Gomes, Helder

The presence of nitrogenated compounds in liquid fuels (e.g. quinoline (QN), azapyrene, pyrrole, indole or carbazole) is associated with a series of environmental and health issues [1], as upon their combustion, noxious NOx gases are formed. Typically, those heteroatoms are removed by hydrodenitrogenation (HDN), a process based on the application of H2 under high temperature and pressure [2]. However, due to the type of nitrogenated compounds found in crude oils, which consist mostly of cyclic structures containing two double bonds between N and C atoms, HDN fails to efficiently remove nitrogen without affecting the properties of the fuel [1]. Thus, alternatives to HDN have been sought, the removal of those nitrogenated compounds via oxidative processes being found as promising [1]. In oxidative denitrogenation (ODN), nitrogen-based compounds are oxidized towards more polar compounds, which can be further removed from the fuel with an extractant [3]. Furthermore, another contemporary issue is the production and accumulation of residues, especially plastic solid waste (PSW). PSW can be used as precursors for the synthesis of sustainable carbon nanotubes (CNTs), which could be further applied as catalysts in ODN. In this work, a nitrogen-rich fuel was simulated by dissolving QN (CQN-i-octane,0 = 1 g L-1) in 2,2,4-trimethylpentane (i-octane), and ODN was carried out using H2O2 as oxidant and CNTs (derived from a mixture of polymers simulating PSW) as catalysts, under a biphasic system (oxidation and extraction co-occurrence).

2022Conference object

Open access

Amphiphilic carbon nanotubes for catalytic wet peroxide oxidation of 4-nitrophenol

Publication . Roman, Fernanda; Sanches, Flávia Kim; Díaz de Tuesta, Jose Luis; Marin, Pricila; Machado, Bruno; Serp, Philippe; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Carbon nanotubes (CNTs) were synthesized via chemical vapor deposition (CVD) over an AlCoFeO4 catalyst by a sequential feed of ethylene (E, as carbon source) and acetonitrile (A, as nitrogen source). The resulting samples were noted E20 (hydrophobic), E10A10 (amphiphilic), and A20 (hydrophilic), the number referring to the feed time (minutes) of each precursor, as reported elsewhere1. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of 4-nitrophenol (4-NP). The reaction was monitored by HPLC (to determine the concentration of 4-NP and respective intermediates), TOC analyzer, and UV-vis spectrophotometry (to quantify H2O2) (Figure 1). After 8 h of reaction, A20 led to the highest consumption of H2O2 (90%), followed by E10A10 (61%) and E20 (52%). On the other hand, the highest degradation of 4-NP was observed with the amphiphilic E10A10 material (98%) followed by E20 (95%), whereas A20 only led to a removal of 69%. Similar behavior was found when analyzing the formation of reaction intermediates (data not shown), i.e., while A20 resulted in the accumulation of 4-nitrocatechol (4-NTC) and hydroquinone (HQ) E10A10 and E20 led to the total conversion of formed 4-NTC and HQ. This resulted in a lower TOC removal for A20 (37%) than to E10A10 and E20 (53%). Therefore, the amphiphilic E10A10 material is a promising catalyst for the CWPO of 4-NP.

2021Conference object

Open access

Removal of gaseous ammonia released from leachate by adsorption on carbon-based adsorbents prepared from agro-industrial wastes

Publication . Perdigão-Lima, Thalles; Díaz de Tuesta, Jose Luis; Feliciano, Manuel; Furst, Leonardo; Roman, Fernanda; Silva, Adriano S.; Pereira Wilken, Adriana A.; Silva, Adrián; Gomes, Helder

Landfill facilities and organic waste treatment plants typically are known sources of odour pollution, such as gaseous NH3, among others. In this work, the removal of gaseous NH3 released from a composting line of a mechanical and biological treatment plant of undifferentiated municipal solid waste was assessed in a fixed-bed column loaded with carbon-based adsorbents (CBAs) prepared from olive stone and malt bagasse as carbon precursors. CBAs were prepared by hydrothermal carbonization (HTC) assisted by H2SO4 and pyrolysis, resulting in materials with different physical and chemical properties. The hydrochar derived from olive stone by H2SO4-assisted HTC was found as the best adsorbent for NH3 removal (10.4 mg g-1). This result was ascribed to the high acid character of the adsorbent (2.34 mmol g-1), since it was found that acidity contributed significantly more than the specific surface of the adsorbents for the removal of NH3 (BET surface of 4 m2 g-1 was obtained for the CBA with the highest uptake capacity, whereas other adsorbents reach values of 172 m2 g-1 and NH3 uptake capacities of 0.07 mg g-1). The NH3-saturated hydrochar was regenerated by washing with water and subsequently reused in the adsorption of NH3, with a performance more than 70% compared to its first use.

2024Journal article

Restricted access

Nano-hydroxyapatite Pickering emulsions as edible mayonnaise-like food sauce templates: A novel approach for food design

Publication . Relvas, Maria Eduarda; Ghirro, Larissa Camargo; Martins, Isabel M.; Lopes, José Carlos B.; Dias, Madalena M.; Barreiro, M.F.; Ribeiro, Andreia

Pickering emulsions have the potential to enhance product stability and provide opportunities to create functional solutions that align with labelling requirements. The present work aims to develop Pickering emulsions stabilised by nano-hydroxyapatite (n-HAp) particles to replace traditional mayonnaises. The study addresses the effect of n-HAp solid particle concentration (5–15 wt%) and oil-water ratio (50:50, 60:40, 70:30, and 80:20, v/v) on emulsion stability, rheological properties, and oxidative stability. The results indicate that the produced Pickering emulsions have good stability for the tested period of 90 days, except for the 80:20 o/w emulsion that undergone a prompt quick phase separation. The Pickering emulsions produced with higher n-HAp concentration or oil content have a semi-solid structure, rendering them desirable options for replicating the texture of traditional mayonnaises. Regarding oxidative stability, the Pickering emulsions showed considerably improved stability compared to commercial mayonnaises (∼13 times higher), suggesting higher resistance to peroxidation and a longer shelf-life.

2024Journal article

Open access

Carbon nanotubes synthesized from LDPE for application in wet peroxide oxidation of paracetamol

Publication . Roman, Fernanda; Lopes, Jéssica Paula Marim; Díaz de Tuesta, Jose Luis; Lenzi, Giane G.; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Carbon nanotubes (CNTs) were produced by chemical vapor deposition (CVD) considering low-density polyethylene (LDPE) as a carbon source and as an alternative to upcycle plastic solid waste. The CNTs were synthesized over bimetallic catalysts (Ni and Fe) supported on Al2O3 and purified with H2SO4 to dissolve the metal particles from the material. Both original (CNT-O) and purified materials (CNT-P) were tested as catalysts in catalytic wet peroxide oxidation (CWPO) of paracetamol (PCM). Both catalysts promoted the complete conversion of PCM within 8 h of reaction and were able to mineralize 60% of the organic content of the effluent (measured as TOC) in 24 h. Catalyst CNT-O was able to completely decompose hydrogen peroxide (H2O2) within 24 h, whereas CNT-P was only able to decompose ~80%. Therefore, the efficiency of H2O2 consumption, measured as XTOC/XH2O2, was higher for catalyst CNT-P (0.75) than for CNT-O (0.61). Metal leaching, especially Ni, was observed during the CWPO run with CNT-O, while it is avoided when using CNT-P. Thus, purified CNTs have proved to be active in CWPO of PCM, allowing a more controlled decomposition of H2O2 and avoiding leaching of metal species.

2021Conference object

Open access