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The Rosemount analyzer, based on Raman laser technology, helps factories achieve a product purity of 99.7% during xylene purification by reducing feedstock variations. The case study in this article illustrates how to apply Raman analyzers in production lines. Huntsman Petrochemicals’ plant in Wilton, UK, produces 360kt of p-xylene per year. p-Xylene is a key raw material for manufacturing polyesters and synthetic fibers, which are widely used in the production of clothing, films, beverage bottles, and food containers. The purity of the product lies in the separation of the other two isomers of xylene, namely o-xylene and m-xylene. Through selective crystallization during the cooling process and centrifugal suspension. The best purity can be achieved by controlling the composition of the feed. Previously, the device used to monitor the reaction process was an online melting point analyzer, which required samples to be taken frequently and sent to a laboratory for analysis and confirmation. Delays in data transmission can cause a 2% to 3% variation in feed synthesis. The Rosemount Analytical Raman analyzer, installed at the beginning of 2003, enables comprehensive online monitoring of the synthesis process; since the synthesis data is updated every minute, production variations are reduced to 0.25%, thereby significantly improving the stability of production. “The Raman analyzer has indeed improved production quality,” said Tom Liddle, the head of the p-xylene production plant. “By reducing variations during the synthesis process, we were able to achieve optimal production conditions, enhancing stability and reaching a quality level of 99.7% for the first time. ” Steve Gill, a process engineer at Huntsman Petrochemicals, was the first to use the Raman online spectrometer. He said, “I’m very satisfied with its performance.” The main advantage of purification control is to supply a consistent solid material to the separator. Furthermore, due to stability, it is possible to observe the impact that changes in earlier processes have on subsequent processes. We never had the capability to monitor in real time before. ” Tom Liddle was also pleased to see the factory operating more smoothly: “Without Raman’s online control, changes in production can sometimes lead to an excessive amount of solids being fed into the separator, causing vibrations and potential damage to the bearings.” Now we are producing at maximum capacity while reducing the wear on the centrifuges. ” Laser-induced Raman spectrometers use a laser of a single wavelength to probe the sample. At the molecular level, light intensity is scattered in very small fragments; this scattered light occurs at the same laser wavelength (Rayleigh scattering), while an even smaller portion of the incident light is shifted to a longer wavelength (Raman scattering). The transfer of this laser represents energy conversion with small molecules. In Raman scattering, the patterns and intensities of wavelength shift provide qualitative (molecular fragments) and quantitative (concentration) information. In practical applications, it is necessary to develop a multivariate calibration model to enable the analysis of multiple components. The Raman analyzer used in Wilton will be employed simultaneously to monitor the purity of p-xylene at four separate production locations: feeding, recycled materials, and the two final product lines. “We are still learning how to use the *analyzer,” said Tom Liddle. “We have gained a better understanding of online testing. ” The analyzer is installed in the control room. The laser is transmitted to four measurement locations through optical fibers: the optical probe provides an interface to the production line. At each probe, the scattered light generated by the sample is collected and transmitted back to the analyzer via a return fiber. The initial analysis and concentration data are sent to the Emerson DeltaV production control system via Modbus, thereby controlling feed dilution. Installation requirements: The design standards for Raman analyzers differ significantly from those of laboratory instruments. It is not just a “durable experimental instrument”; the entire system, from the analyzer to the probes and optical fibers, must meet the requirements for installation on a production line. Considering the long-term stability of continuous use, the repeatability of analysis data, sample interfaces, online diagnostics and preventive maintenance, laser safety, appropriate data output protocols, and related cost control, all are fundamental aspects of the design. The excitation source uses a NIR multi-mode semiconductor laser, which minimizes fluorescence interference and has a long service life of around two and a half years when operating continuously. The line width of this laser is relatively wide, resulting in low spectral resolution of the reflected light. The linear instability caused by mode hopping is compensated for by using an internal reference. Monochromatic radiation is transmitted to the sample through optical fibers, optical filters, and a Raman probe, which also collects the light scattered back by the sample. Rayleigh and Raman scattering are sent back to the analyzer through different optical fibers, and optical filters are used to filter out unknown wavelengths. The Raman-scattered light is dispersed into a spectrum, which is recorded by a highly sensitive CCD camera. The end of the Rayleigh fiber is at a photodiode, as part of the laser safety function for the analyte. The geometric arrangement of the laser, controller, and detectors (spectrograph and camera) allows the Raman analyzer to use a spectrograph and CCD camera to simultaneously measure four industrial process streams (while recording internal reference spectra). The inter-phase correction process of the patented technology generates a standard spectrum to enable comparability among the internal channels. Its advantage is that the calibration can be transferred to multiple monitoring points, avoiding the need for re-calibration when replacing optical components. Furthermore, factor-based standardization can help eliminate variations in bulk samples, such as bubbles. A combination of standardized procedures and internal references can ensure good reproducibility of spectral results. For quantitative analysis, spectral data is converted into the contents of components by using multivariate correction methods (such as Partial Least Squares regression). Data processing is carried out by the analyzer, allowing accurate data on component contents to be obtained within a one-minute update time. The Rosemount Analytical Raman service team works on both sides of Atlanta, providing early-stage project guidance and consultation, as well as engineering applications and calibration, in collaboration with engineers from Huntsman Petrochemicals. Emerson’s engineers remotely monitored the Rosemount Raman analyzer in Ohio to carry out online tuning and remote optimization of the calibration mode. (end)