Process control in the chemical industry is indispensable. Large chemical companies use measuring instruments for safe and cost-saving handling in synthesis processes. This increases efficiency and output while maintaining product quality. At the same time, expensive and time-consuming laboratory tests can be reduced. How exactly does the ColorPlus Ex from Sigrist monitor a chemical synthesis?
The reaction mixture is colored during the course of the reaction. The decolorization is measured to determine the completion of the reaction. The on-line process monitoring and control ensures reproducibility in the process. The measurement is carried out quickly and continuously in the process line, thus saving the costs of laboratory tests
The measurement of Hazen is used, for example, in the synthesis of propene acid (trivial name: acrylic acid, CAS number: 79-10-7). The colorless product is produced from the two-step oxidation of propene. An explosive mixture with oxygen occurs from concentrations of 3.8 vol%. The use of Ex-certified measuring devices is therefore an absolute must.
In the first stage, propenal (trivial name: acrolein) is produced, which has a slightly yellowish color. In the second stage, the propenal is converted by a molybdenum- vanadium catalyst at high temperatures.
The Hazen color number is suitable for determining yellowish colorations. The diagram shows schematically how it works. When the reaction is complete, the Hazen value is 0, this means that the mixture is colorless. An increased value indicates that starting material is still present.
Scheme of a chemical synthesis: When the reaction is complete, the Hazen value is 0, i.e. the mixture is colorless. The ColorPlus Ex measures the decolorization to determine the completion of the reaction.The ColorPlus Ex is available with a customer specific measuring cells. A version with flameproof encapsulation is offered for installations in areas requiring explosion.
Initial situation at the customer: Production volume of 1.5 million tons at a market price for acrylic acid of CHF 1.5 - 2.5 /kg.
Measuring device can be fitted with up to three LEDs (fitted according to exact customer require ments)
The ColorPlus Ex is also used worldwide in the synthesis of maleic anhydride, phthalic anhydride or methacrylic acid. It is used in oil refineries around the world. There, after the distillation of crude oil, the quality of the products (petrol, diesel, naptha) is determined using color numbers such as Saybolt or ASTM. This is where the Sigrist photometer device scores with its high accuracy and reliability.