Concentration Analysis Of Dyestuffs In Dye Solution

With such merits as high sensitivity, good selectivity, rapid determination, a wide range of usage and lower price of the instruments, the spectrophotometry is the basic method for determination of dye concentration, which is also the most feasible means for online detection of dye concentration at present. Online monitoring of dye concentration in the dyeing process should be an important direction of dyeing technological progress. Online monitoring of dye concentration by spectrophotometry has many advantages, such as convenience, high-speed and low cost and so on. But the Online monitoring technique of dye concentration is still in the initial stage around the world, and essentially blank in the dyeing process now. There are many technical problems to be solved. The main problem is how to measure the dyestuff concentration of dye bath in a wide range rapidly and accurately, especially for the solution of mixed dyes.Normally,λmax of the dyes more different each other, the errors of determined by spectrophotometry will be smaller. When the dye's color is close to the other, their absorption spectra overlap seriously, or the concentration of one component is relatively lower than others', the measurement errors will be larger. In this paper, through in-depth exploration for the dye concentration determination by spectrophotometry, it is expected to obtain the determination methods of dye concentration and equipment conditions, in order to provide a reference for the development of online monitoring technology of dye concentration in the dyeing process.At first, through dyeing and color difference measurement, the dye concentration and its ratio range in combination dyeing possibly needed to determine in the practical production was obtained.Under the status quo of the instruments'conditions and measurement error's requirements, the dye concentration and its ratio range of mixed dyes which can be measured by trial and error method and interpolation were also obtained. Then, a variety of analysis and treatment processes were compared to explore the approach to break through the limits of current testing device. Finally, through monitoring of the dyeing experiment process, the relevant methods and application result of the device were explored.Results showed that the concentration range of dye need to be measured in practical dyeing is about 0.0015-5g/L.For conventional spectrophotometer, the cuvette with fixed optical pathlength can not reach the practical concentration range of dye, so the application of different optical pathlengths to expand the range of concentration which can be determined is possible.Through combination dyeing of two dyes and their concentration determination by the maximum absorption wavelength-simultaneous equations method which is commonly used, parts of the concentration ratio range of two dyes can be accurately measured, but mostly, the concentration ratio range of blending dyes in practical dyeing exceeded what can be accurately measured by conventional spectrophotometer a lot. Absorption spectrum-peak area method, first order derivative and first derivative-ratio spectrophotometric method were applied to expand the ratio range of bi-component dyes which can be measured accurately was explored. Compared to the maximum absorption wavelength-simultaneous equations method, the absorption spectrum-peak area method has a larger ratio range of blending dyes, but it still can not reach all the proportion range in practical dyeing.For the mixed concentration of two dyes with similar color, a small measurement error was acquired by absorption spectra-peak area and first derivative-ratio spectrophotometric method. Maximum absorption wavelength-simultaneous equations and absorption spectra-peak area method were more accurate than first derivative-ratio spectrophotometric method for concentration determination of ternary mixture of dyes.Through influence test of additives and conditions in the dyeing process of reactive dyes on absorption, the influences of neutral salt, alkali and temperature were investigated, which were modified and which effect tests were carried out, and a data correctional solution with small error and applicability on concentration determination of dye in the dyeing process was acquired.The change of dye concentration in dyeing process was real-time determined by fiber optical spectrometer. Experimental results showed that, measuring the dye concentration in the dye bath using fiber optical spectrometry is a relatively ideal method for online monitoring. But its defect exists, that is, the absorption of the dye bath is extremely high even if the optical pathlength is minimum, which is due to high dye concentration in the early stage of dyeing process, thus the spectrometer with a smaller optical pathlength is required for online monitoring.The results of the project provide some supports for the feasibility and development of online monitoring technology of dye concentration in dyeing process. However, to achieve the industrial application of online monitoring of dye concentration, there are many difficulties to be solved currently, and many determination conditions remain to be further studied and the equipment performance has yet to be improved.