Inline analysers have become commonplace in the 21st century. Not only for classic ones such as pH and conductivity analysers, but also optical, photometric and spectrophotometric sensors are installed directly in the reactor or pipeline. Often equipped with automatic cleaning systems. That’s why it’s surprising that people often rely on time-consuming analyses in the lab where sampling is the main source of error for determining concentrations or following up the reaction or formation of certain reaction products. There are, however, possibilities whereby these measurements can also be done inline and real-time. What do you think about inline measurement of the refractive index?
Unknown is unloved
Which index? That’s right, refractive index. And you measure that with a refractometer. The refractive index indicates the degree to which a light beam is refracted as it passes through the separation of two different media. This refraction of light depends on the concentration. If you know one of the media and keep it constant, you can determine the concentration of the other product in this way. Refractive index is historically mainly known in the food industry where it was and is used to determine the sugar concentration. The sugar concentration is expressed in %Brix.
The refractive index itself is the ratio of the speed of light in the two different media. It is therefore a dimensionless number. Using the latest technology, this can be exactly measured. Since the refractive index is a pure optical measurement, this technology is very suitable for inline measurements.
Inline refractometry is insensitive to gas bubbles and undissolved particles (or fibres) in the liquid. Liquid speed or flow rate (fluctuations) also have no influence whatsoever. Through the correct choice of materials, the refractometer is chemically resistant and empty pipes and reactors are also no problem. The sensor is resistant to high pressure and temperature. Furthermore, vibrations and shocks are also no problem for properly constructed sensors. A temperature sensor built in at the right place ensures automatic compensation.
The most important thing is that an inline refractometer requires little or no maintenance. There are no moving parts or components that are susceptible to wear. The list of spare parts is therefore very limited, which is also very interesting from an economic point of view.
Digitization of the measurement signal in the sensor itself guarantees high accuracy and reproducibility. At K-Patents, the technology leader in this field, all sensors are pre-calibrated over the entire measurement area (1.3200 - 1.5300) by means of the digitization of the measurement signal. The sensor is inherently stable and therefore doesn’t need to be calibrated periodically. Verification is possible with internationally traceable standards. In a second phase, the value of the refractive index is converted to product concentration according to a chosen curve.
A refractometer can be used just about anywhere. From large reactors to small sample lines, a solution is available for everything. Flange mounting and, if desired, hygienic couplings are standard. Even a "retractable" version is possible.
Inline refractometers are used in chemical processes for concentration determination. This of course works best in binary mixtures. Typical examples are acids, salts and bases, but concentrations of organic substances can also be determined without any problems.
In addition to direct concentration measurement, refractometry offers even more possibilities. Some examples are phase separation, determining the degree of purity or contamination, product identification and prescription monitoring. Owing to this, refractometry has a whole range of application options available for you to discover.
Refractometry is clearly a versatile and promising technology. Erroneously, this technology is seldom used for concentration measurement and process control. If you inform yourself well and make the right choice, measuring the refractive index will yield a lot.
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