Desenvolvimento de um procedimento analítico para determinação indireta de cloreto a partir da concentração de seus contraíons Na, Ca, Mg, Sr e Fe em amostras de extratos de petróleo por ICP OES

• Autor(a) principal: Souza, Murilo de Oliveira
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/4724
• topic: Crude oil; Chloride counterions; Experimental design; Exploratory analysis; Petróleo; Petroquímica - Experiências; Análise exploratória; Espectrometria de emissão óptica por plasma acoplado indutivamente; Contraíons do cloreto; Planejamento de experimentos; Química; 54

Among the present salts in the crude oil, sodium, calcium, magnesium, strontium and iron chlorides are the most common and abundant, and the main causes of corrosion in oil refineries. Thus, the purpose of this study was to develop an analytical procedure for the indirect determination of chloride from the concentration of its main counterions Na, Ca, Mg, Sr and Fe using the Optical Emission Spectrometry with Inductively Coupled Plasma (ICP OES) after hot solvent extraction (modified ASTM D 6470-99). Initially, a 23 factorial planning was performed to select the most significant instrumental variables of ICP OES. Therefore, it was established that the radio frequency power and the gas nebulizer flow were the most significant variables. Subsequently, the optimum condition for the simultaneous determination of Na, Ca, Mg, Sr and Fe in the aqueous oil extract was optimized using a central composite design (P = 1272 W and C = 0.53 L min-1 ). The developed procedure allowed to work with post-salt samples of different °API (17.4 to 30.2). Yttrium was used as internal standard to correct the interference on the analytical signal. The developed procedure reached detection limits in the order of 0.99 mg L?1 , 0.025 mg L?1 , 0.33 µg L ?1 , 0.06 ng L?1 and 0.26 µg L?1 for Na, Ca, Mg, Fe and Sr, respectively. The accuracy of the procedure was verified by addition/recovery tests (91-120%) and by comparison between the results of the proposed procedure and those obtained by Atomic Absorption Spectrometry Flame (F AAS). The modified ASTM D 6470-99 extraction was compared to the acid digestion assisted by microwave, and extractions over 92% for Na (at E12 and E13 extracts) and 81% for Sr (E9 and E12 extracts) were obtained. From the comparison between chloride results obtained by potentiometric titration and ICP OES (by analysis of chloride from its counterions), in the aqueous extract, we can suggest that Na, Ca, Mg, Sr and Fe are mainly associated to chloride. The chloride recoveries obtained by ICP OES compared to those obtained by potentiometry were 105.10%, 102.12% and 99.33% for the E9, E12 and E13 extracts, respectively. After the development of the analytical procedure, a chemometric study was carried out in order to classify 18 samples of aqueous oil extract (E1 to E18) from three production fields (A, B and C) and from refining (R). The Exploratory Analysis of these extracts was performed by Principal Components Analysis (PCA) to give an explanation of 90.9% of the data’s variability, Hierarchical Cluster Analysis (HCA) separating the 18 samples into three big groups and Linear Discriminant Analysis (LDA) getting a percentage of 92.6% of correct prediction. The concentrations of the metals Na, Ca, Mg, Sr and Fe, determined by ICP OES, were used as original variables.