| The traditional methods detecting the acid number of conductive oil are the GB/T methods, which contain the acid-base titration and potentiometric titration. But acid-base titration is often difficult to visualize the end point of the titration because of the dark color of the used oil. Potentiometric titration also suffers from the difficulty in the end point judgment, which often needs to refer to the electrode potential of non-aqueous buffer solution. These methods are often non-automated, laborious, time-consuming and using a large amount of toxic solvents. Thanks to the fast detecting speed, low reagent consumption, simple equipment, easy to be automated, the flow injection analysis(FIA) titration technique has been widely applied to the acid-base titration. The application that FIA combined with other detection methods is more extensive. For those detections that need pre-treatments to samples, harsh reaction conditions and complicated operations, continuous detection can be completed by FIA technique. Therefore the FIA can be considered to achieve the automatic detection of oil acid number(AN).In this paper, two automatic detection methods were tried to apply to detect AN. The FIA technique combined with flat p H detector and spectrophotometry respectively was used in detecting the AN automatically. Based on the flow system of the FIA-p H, a three-dimensional model was designed by Pro/E software, and the model was printed by 3D printer. The main results are as follows:(1) The FIA combined with p H detector method was developed for the rapid and environmentally friendly determination of the acidity in the oil. The AN of the conductive oil sample was obtained by online monitoring the concentration change of the standard KOH solution before and after the interaction with the oil sample. The parameters, such as the mixing ratio of KOH with oil, the length of mixing tube, and the flow rate of the two mixing streams, were optimized to achieve adequate reaction of the KOH solution and the acid in the oil. In addition, the parameters of FIA were optimized. The results showed that the AN in the range of 0.20~6.4 mg of KOH/g oil can be accurately determined with a limit of detection of 0.17 mg of KOH/g. The precision expressed as RSD was always <1.0 %, indicating a good precision and reproducibility of the method.(2) The FIA-spectrophotometry system was developed to detect the AN. The concentration of the KOH was detected by the FIA system that has been optimized, and calibration curves with good linearity were obtained in the concentration range of 0.00182~0.0163 mol/L. The AN in the range of 0.21~3.1 mg KOH/g oil can be accurately determined with a limit of detection of 0.18 mg KOH/g and a sampling frequency of 10~12 /h.(3) The internal pipe size of the 3D model was designed by referring to the sizes of the traditional FIA system that have been optimized. The mixture tube, the separator and the flow cell were placed in an appropriate location in the 3D block. The 3D block was applied in detecting the AN successfully, and the results were consistent with those obtained from the standard method.The feasibility and practicability in this paper show that the FIA combined with the p H detector and spectrophotometry can be used in the detection of AN automatically, and 3D printing can be used in the integration and miniaturization of equipment. Furthermore, it can be achieved for remote monitoring and on-line monitoring of the AN by connecting with the computer. |
PDF Full Text Request