Application of the hottest near infrared spectrosc

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The application of near infrared spectroscopy in pulp and paper industry

near infrared spectroscopy has been paid more and more attention and recognized by more and more people because of its rapid rise. It plays a particularly prominent role in analysis and detection, and has also achieved extensive success in control. In this paper, the development status of near-infrared light technology and the needs of the development of pulp and paper industry are introduced, and the application of near-infrared spectroscopy technology in pulp and paper industry is introduced

1. Development status of near infrared spectroscopy

in recent years, near infrared spectroscopy (NIR), as a rapidly rising spectral analysis technology, has attracted more and more attention in the field of analysis and testing. At the Pittsburgh Conference on Analytical Chemistry and applied spectroscopy (Pittcon 97) in 1997, there were 25 articles on near infrared spectroscopy There are 178 automatic control instruments in the curing room, and NIR reflection spectrum is still an important topic at this meeting. It can be seen that near infrared spectroscopy, as a kind of rapid analysis and testing instrument, is being recognized and used by more and more analysts, as it does not need to be processed in sample analysis, does not destroy and consume samples, and has no environmental pollution itself. At the same time, it is also concerned by the field of industrial control. At the Pittsburgh Conference on Analytical Chemistry and applied spectroscopy (Pittcon 98) in 1998, acoustooptic tunable filters (AOTF) and near-infrared probes have been successfully used in near-infrared process monitoring instruments to monitor polymer viscosity, acid number, additives, degree of polymerization, etc. Since the 1990s, NIR, as a modern testing technology, has been basically mature, and its application field has expanded rapidly. From the initial food industry, NIR has rapidly penetrated into the petroleum, chemical, environmental and biochemical industries. NIR has played a prominent role in process control, product quality analysis and detection, created huge economic benefits, and achieved extensive success in process control

2. Application of near infrared spectroscopy in pulp and paper industry

at present, the output and quality of pulp and paper are increasing all over the world. If it is not enough to only rely on providing high-quality fiber raw materials and improving pulp and paper technology to promote production, it is also necessary to develop and use some new process analysis instruments and sensors. With the development of near infrared spectroscopy technology and spectral data processing software, a new way to develop new process analysis instruments is provided. The application of NIR in the process of pulp and paper production with a capacity of more than 40000 tons is introduced below. Although most of the application is still limited to the laboratory at present, the future development trend must be on-site analysis and measurement and control, so as to realize the transformation from laboratory to production site

2.1 detect the moisture content in the paper coating

in the range of 400 ~ 1100nm, use the transmission mode to analyze the moisture content in the coating mixture. Although the reproducibility of measurement is affected by the existence of suspended particles in the coating, this problem can be avoided for continuous flow coating, so as to realize measurement

2.2 determine the content of coniferous wood in pulp

in the range of 1100 ~ 2500nm. Adopt the reflection mode, and take two samples to calibrate the laboratory measured value and the measured value respectively. Although the error of the measured value is larger than expected, the measurement results still show that NIR can be used to determine the coniferous content in pulp

2.3 measure the kappa number of mixed wood pulp

adopt the reflection mode, take 27 samples at 2180nm for the calibration curve, 9 samples as the test set, and the measurement error is 5.6%. Although the measurement results show that NIR may be used to measure the kappa number of mixed wood pulp, whether the measurement error can be accepted by the industrial process remains to be studied

2.4 measure the kno (logarithm of kappa number) of the pulp in the spray pipeline of the cooking pot.

within the range of 1100 ~ 2500nm, use the reflection mode to measure the kno of the pulp. Univariate linear regression was carried out at 1672nm, and the measurement error was 1.0%; Due to the influence of wavelength fluctuation, 1436nm is introduced for multiple linear regression, and the measurement error is reduced to 0.5%

2.5 measure the moisture of the paper and the weight of the paperboard

adopt the reflection mode, and use the characteristic absorption of water at 1940nm to measure the moisture in the paper; The change of paperboard weight is obvious in the range of 2100 ~ 2500nm, and univariate linear regression is carried out at 2346nm. The results show that NIR is very sensitive to the moisture of paper and the weight of paperboard. Due to the nonuniformity of the sample itself, the area of the sample should be larger when measuring and scanning, so as to take the average value

2.6 monitor the resin layer of the paper

analyze the samples in the range of 1100 ~ 2500nm using the reflection mode. The results show that the uncoated paper has no characteristic absorption at 1688nm, 1766nm and 2160nm, so the influence of the paper can be avoided. At 2160nm, the calibration curve has an error of 0.7%

2.7 monitor the kappa number of pulp cotton linter mixture

use the reflection mode, analyze the sample in the range of 1100 ~ 2500nm, and carry out univariate linear regression at 1680nm. The error is 1.2 kappa numbers, and the effective range of calibration is 3.4 ~ 33.9 kappa numbers. This result is applicable to both dry and wet pulp cotton linter mixtures

2.8 detect the content of polysilicon layer on tissue paper

scan 8 tissue paper samples with polysilicon concentration of 0.69% ~ 5.67% in the range of 1100 ~ 2500nm, and carry out univariate linear regression at 1744nm, with an error of 0.2%

2.9 detect the content of wax and phenol resin in wood fibers

use reflection mode to scan wood fiber samples with wax concentration of 0.3% - 2.4% and phenol resin concentration of 1.3% - 4.3% in the range of 1100 ~ 2500nm, respectively. The phenol resin was calibrated at 2158nm with an error of 0.4%; The wax was calibrated at 1728nm with an error of 0.1%

2.10 detect the lignin content in dry wood pulp

use reflection mode to scan the wood pulp with lignin concentration of 5.7% - 33.6% in the range of 1100 ~ 2500nm. Multiple linear regression was carried out at 2172nm and 1556nm, and the error was 1%

2.11 detect the content of wax and phenol formaldehyde resin in wood fiber

using reflection mode, scan wood fiber, pure wax, freeze-dried phenol formaldehyde resin and wood fiber containing wax and phenol formaldehyde resin in the range of 1100 ~ 2500nm, and find that the wax in the fiber has characteristic absorption at 2250nm, 2310nm and 1725nm, while the resin has characteristic absorption at 1980nm

2.12 detect the content of water absorbent in fluff pulp

using reflection mode, scan fluff pulp samples with water absorbent concentration of 0.00% - 44.9% in the range of 1100 ~ 2500nm, and calibrate at 1752nm, with an error of 6%

2.13 detect the coating layer of coated paper

within the range of 1100 ~ 2500nm. For coated paper with coating concentration of 0 ~ 12%, use optical fiber to measure NIR reflection spectrum, and calibrate it at 2316nm, with an error of 0.1%. However, the influence of inorganic substances in the paper cannot be ruled out

3. Outlook

it can be seen from the above that near infrared spectroscopy is widely used in the pulp and paper industry and has a good application prospect. In particular, near-infrared spectroscopy has become a hot topic in the field of analysis and testing of pulp and paper industry in the world in recent years. However, the problems that should be paid attention to are: (1) for different pulp species, the curves and equations must be recalibrated; (2) The main component of pulp is carbohydrate, which is hygroscopic. Therefore, when measuring its spectrum, it should be carried out in the same surrounding environment to reduce moisture interference, so as to reduce errors; (3) Considering the complexity of supporting policies for the introduction of pulp components, it is best to use derivative spectrum and multiple regression method of multi characteristic absorption peak to determine the lignin content in pulp by using near-infrared spectroscopy for quantitative analysis of pulp

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