Estudo, desenvolvimento e implementação de metodologias que permitam otimizar processos de tratamento de efluentes de Refinaria e minimizar de impacte na envolvente

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Study, development and implementations of methodologies that allow optimizing refinery wastewater treatment processes and minimize impact risks on the surrounding

Publication . Rita, Ana Isabel Batista; Sanches, Sandra; Madeira, Luís; Santos, Maria António

The main objective of the work developed in this thesis was to address spent caustic treatment as a way to decrease the high organic load of this effluent and reduce its great impact on the quality of the wastewater sent to wastewater treatment plants, particularly in terms of oil and grease (O&G) contamination. The naphthenic spent caustic generated by Galp refinery in Sines was used as case study. Spent caustic effluents are very challenging due to their very hazardous nature in terms of toxicity as well as their extreme pH (approximately 12-13). Spent caustic treatment is presently a challenge for refineries, due to its composition rich in mercaptans, sulphides and other aromatic compounds. In general, proton nuclear magnetic ressonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gas chromatography mass spectromery (GC-MS) analyses suggested that aromatic structures account for a significant part of the organic structures that constitute naphthenic spent caustic, which are also present in the final wastewater. It was found that acid crudes processing with lower molecular-weight acid components seem to have a great impact on polar O&G concentration increase in spent caustic and therefore in the final wastewater. Nanofiltration (NF) is a very effective technology when treatment and separation/recovery of specific components is required since it is able to remove low molecular weight organic molecules like hydrocarbons and phenolic compounds. The potential application of polymeric and ceramic membranes was addressed by conducting ageing studies (only in the case of polymeric membranes) and NF experiments to assess their retention properties and lifespan. Contrarily to expectations, neither of the tested types of membranes presented attractive results for spent caustic treatment, due to very quick losses of their retention properties; analysis by FT-IR and Inductively coupled plasma atomic emission spectroscopy (ICPAES) corroborated the ocurrence of desintegration mechanisms in the structure of the tested membranes. A different strategy based on chemical treatments was followed to treat spent caustic: (i) neutralization, followed by Fenton oxidation post-treatment (approach 1) and (ii) neutralization, followed by liquid-liquid extraction (approach 2). Approach 1 (lab scale tests) allowed to remove 95 % of polar O&G, with a 70% decrease in the acute toxicity after treatment. Approach 2 (pilot scale tests) allowed to remove 99 % of polar O&G. Both technologies allowed direct discharge of treated spent caustic into the Sines refinery wastewater circuit, with approach 2 being the best option since it presented the highest annual savings (1.5 yearly effluent management cost. The results obtained in the present thesis may be useful for the development/optimization of industrial-scale plants in petroleum refineries for the treatment of naphthenic spent caustic effluents, providing an effective treatment technology proposal, with interesting effluent management cost reduction.

2021-02-23Tese de doutoramento

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Entidade financiadora

Fundação para a Ciência e a Tecnologia

Programa de financiamento

FARH

Número da atribuição

PD/BDE/114356/2016