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This study is based on a two-stage approach.

The field performance of hydraulic oils depends on factors such as the viscosity index (VI), flash point (FP), pour point (PP), and demulsibility. A hydraulic oil formulation was performed by applying a multiresponse optimization, for which the PP was minimized, the FP, demulsibility, and VI were maximized. The range of viscosities at 40 and 100 °C was selected according to the International Organization for Standardization (ISO) viscosity grade for hydraulic oil. The experiments were accomplished according to an extreme vertices mixture design using solvent neutral-100 (SN-100) and SN-500 as major components and polyisobutene (PIB) as minor component. The results shows that the optimum formulation consisted of 37.5% SN-100, 60% SN-500, and 2.5% PIB, and the values of FP, PP, VI, demulsibility at 30 mins and viscosities at 40 and 100 °C were equal to 227 °C, −6 °C, 107.5, 28/2012/40, 67.3 cS, and 9 cS, respectively.

ABSTRACT. In this study, optimisation of the photocatalytic behaviour of crystal violet (CV) by thiourea (Tu)-codoped TiO2 thin film in fixed bed photoreactor was investigated by central composite designs (CCDs). The effective variables were pH, the concentration of CV dye, flow rate and reaction time. The results of the CCD model showed a good agreement with experimental results, with R 2 = 0.9680 (p < 0.0001) and maximum degradation efficiency was obtained at the optimum conditions: dye concentration 8.5 mg/L, pH 9, flow rate 6 mL/min and reaction time 80 min. Subsequently, three absorbing chemical compounds presented in the degradation reaction were obtained by using singular value decomposition (SVD) method and evolving factor analysis (EFA). Then a multivariate curve resolution with alternating least squares (MCR-ALS) was performed to achieve the concentration and spectral profiles for each component. Finally, a hard modelling method was applied to determine the kinetic constants of distinct reactions occurred in the photocatalytic degradation process. The reaction rate constants were calculated for the first and second steps as k1 = 0.08327 (SD = ±0.0015) /min and k2 = 0.045 (SD = ±0.0006)/min, respectively.