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Raman analyzer improves the quality of petrochemical products

rosemount analyzer is based on Raman's laser technology to help the factory achieve 99.7% product purity by reducing the change of feed during the purification of p-xylene. The case in this article describes how to apply Raman analyzer in the production line

huntsman petrochemicals' factory in Wilton, UK, produces 360kt p-xylene every year. P-xylene is the key raw material for manufacturing polyester and chemical fiber, which are widely used in the production of clothing, film, beverage bottles and food containers. The purity of the product lies in the separation of the isomers of the other two xylenes, o-xylene and m-xylene. Through selective crystallization and centrifugal suspension during cooling. The best purity can be achieved by controlling the combination of feed

the equipment used to monitor the combination process is the melting point analyzer, which needs to often obtain samples and send them to the laboratory for analysis and confirmation. The time lag in data transmission will cause a 2% - 3% change in feed composition. The role of Rosemount analytical Raman analytical lubricating oil installed at the beginning of 2003 is mainly to ensure better equipped operators, which can comprehensively monitor the synthesis. Since the synthesis information is updated every minute, the production change is reduced to 0.25%, which significantly improves the stability of production

"Raman analyzer has indeed improved the production quality" Tom Liddle, the person in charge of p-xylene production plant, said: "by reducing the changes in the synthesis process, we can achieve the optimal production conditions, improve the stability, and reach the quality level of 99.7% for the first time."

steve gill, process engineer of Huntsman petrochemicals, was the first to use Raman spectrometer. He said, "I am very satisfied with its effect. The main advantage of purification control is to give consistent solid materials to the separator. In addition, since it is stable, we can see the impact of changes in the previous process on the subsequent process. We have not been able to monitor in real time before."

tom Liddle is also glad to see that the plant operates more smoothly: "without Raman's control, changes in production sometimes lead to excessive solid loading in the separator, causing vibration and potential bearing damage. Now we produce with maximum output and reduce the wear of the centrifuge."

laser detection

raman spectrometer uses a single wavelength laser to detect samples. At the molecular level, the light intensity is scattered in very small segments, which occur at the same laser wavelength (Rayleigh scattering), and a smaller part of the incident light is transferred to a longer wavelength (Raman scattering). This laser transfer represents the energy conversion with small molecules. Qualitative (molecular fragment) and quantitative (concentration) information can be obtained from the mode and intensity of wavelength transfer in Raman scattering. In practical application, it is necessary to develop a multivariable calibration model to realize the analysis of multiple components

the Raman analyzer used in Wilton will be used simultaneously to measure the purity of paraxylene in four separate production locations: feed, recycled material, and two final product lines. "We are still learning about the use of analyzers," Tom Liddle said. "We have a better understanding of detection."

The analyzer is placed in the control room. The laser is transmitted to four measuring positions through the optical fiber: the optical probe provides the interface to the production line. At each probe, the scattered light generated by the sample is collected and transmitted back to the analyzer through the return fiber. The initial analysis and concentration data are sent to Emerson DeltaV production control system via MODBUS to control feed dilution

installation requirements

the design standard of Raman analyzer is very different from that of laboratory instruments. It is not only a "durable experimental instrument". The whole system, from analyzer to probe and optical fiber, needs to meet the requirements of production line installation

considering the long-term stability of continuous use, the repeatability of analysis data, sample interface, diagnosis and preventive maintenance, laser safety, appropriate data output protocol and related cost control are the basis of the basic design

the excitation source adopts NIR multi-mode semiconductor laser to minimize fluorescence interference and has a long service life (generally two and a half years) under the condition of continuous operation. The linear shape of this laser is relatively wide, and the returned spectral resolution is extracted from the green paper on technological innovation in the key fields of made in China 2025, with a low rate. The linear instability caused by mode jumping is compensated by using an internal reference

it is considered that there is a problem with the system setting. The monochromatic radiation is transmitted to the sample through the optical fiber, optical filter and Raman, with a year-on-year increase of 8.3%. The probe also collects the light scattered by the sample. Rayleigh and Raman scattering are transmitted back to the analyzer through different optical fibers, and optical filters are used to filter unknown wavelengths. Raman scattered light is dispersed into a spectrogram, which is recorded by a highly sensitive CCD camera. The Rayleigh fiber ends in a photodiode as part of the laser safety function of the analyte

the combination of the geometric arrangement of laser, controller and detector (spectral camera and camera) enables the Raman analyzer to simultaneously measure four industrial production streams (and record the internal reference spectrum) with a spectral camera and CCD camera

the interphase correction process of patented technology produces a standard spectrum, making the internal channels comparable. Its advantage is that the correction can be shifted to multiple monitoring points, and it avoids re correction when replacing optical components. In addition, factor based standardization can help remove changes in bulk samples, such as bubbles. The combination of standardization process and internal reference can ensure good repeatability of spectral results

for quantitative analysis, the spectral data is converted into the content of components by using multivariable correction methods (typically, such as partial least squares expression). The data processing is completed by the analyzer, so the real data of component content can be obtained in one minute of update time. Rosemount analytical Raman service team works on both sides of Atlanta to provide early project guidance and consultation, engineering application and correction together with engineers from Huntsman petrochemicals. Emerson engineers remotely monitor the Rosemount Raman analyzer in Ohio to complete remote optimization of debugging and calibration modes

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