【作者】 蔡晨波；

【导师】 俞汝勤； 沈国励；

【作者基本信息】 湖南大学 ， 分析化学， 2008， 博士

【摘要】 本论文的研究主题为近红外光谱分析中的一些基础性问题,包括用漫反射光谱在线非接触监测气-固吸附过程以研究其平衡、动力学和吸附状态,以小规模校正集定量分析多组份或多元体系,以及笔者从实验中观察到的近红外光谱的空间效应。其具体内容如下:一、通过设计实验硬件(包括吸附床的设计、光谱分析的工作方式的选择、测样装置的设计等),使近红外漫反射光谱在线非接触监测氧化铝吸附气相苯胺的全过程成为可能,并得到了平衡、动力学和吸附剂与吸附质相互作用的信息。更为重要的是该吸附床为微分吸附床,所得这些信息又是同步的,这就能更全面深入地了解该吸附过程。该研究还表明:该法发挥了近红外光谱的几乎所有优点,提供的信息直观,无需复杂的数学处理和传质理论假设就能建立可信的传质模型以供工程设计和操作之用。二、用近红外漫反射光谱在线非接触监测邻二甲苯、异戊醇对硅胶的竞争吸附过程,以得到平衡、动力学信息。该研究是第一部分工作的继续与深化,将其推广到更为常见的多元竞争吸附情形,从而进一步展示了近红外光谱在气-固吸附领域的应用前景。三、将离散小波变换、随机样本设计与相关系数判断相结合试图解决近红外光谱定量分析多组份体系中的一个难题,即如何减少校正样本的数量,而同时不损害预测的准确性。在这一方法中,先按随机样本法设计一小规模校正集,然后用离散正交小波分解这些样本的近红外光谱,依相关系数判别法选择合适的变量,最后建立偏最小二乘多元校正模型。研究结果表明,当所测体系的近红外信息丰富时,上述策略是有效的。但在诸如水溶液那样近红外信息匮乏的体系中,上述策略虽有一定作用,误差仍然偏大,有待改进。四、将小波包变换、最小相关样本设计与相关系数判断相结合,以期对第三部分的工作做进一步改善。在这一方法中,先按最小相关样本法设计一小规模校正集,然后用离散小波包按最佳小波树分解这些样本的近红外光谱,依相关系数判别法选择合适的变量,最后建立偏最小二乘多元校正模型。研究结果表明,与离散小波变换相比,小波包变换更能从近红外光谱中提取各组份相应的特征,尤其是在水体系中时。同时,最小相关样本设计能进一步减少所需的校正样本数,且能提供更多合适变量以建立多元校正模型。这两方面的改进使模型的预测能力得以提高,其预测精度即使在水体系中也有明显的改善。五、近红外漫反射光谱在线非接触监测气-固吸附过程中出现了一个意外现象,即在近红外光谱上,被13X分子筛吸附的苯胺的二级倍频几乎完全消失了。这促使笔者深入探讨了近红外光谱的空间效应(当一分子被一足够小的刚性空间限制时,其振动的受限导致一级倍频和二级倍频强度均减少,并且后者减少的程度比前者更大)。虽然这似乎是理论上的当然推论,但从未有人明确提出过,更没有用实验予以严格证实的报道。此外,还以超分子体MCA为例说明了这一效应在超分子体结构研究中的潜在价值。本章的研究表明:近红外光谱比中红外对外界空间大小更为敏感应该是未来近红外理论和应用中的特色之一。当然,本章的研究是非常初步的,离实际应用还相距甚远,但无疑为近红外光谱的理论和应用提供了一条全新的思路。更多还原

【Abstract】 The presented thesis focuses on some fundamental issues of near-infrared spectroscooy (NIR), including studies on themodynamics, kinetics, and adsorption state of a gas-solid adsorption process through non-invasive monitoring the process, quantitatively analyzing a multi-component system with a small-scale calibration set, as well as the spatial effect of NIR that was experimentally observed by the author. They can be concisely described as follows:1) Through non-invasive monitoring the uptake of aniline vapor by active alumina in a differential adsorption bed (DAB) with near-infrared diffuse reflectance spectroscopy (NIR-DRS), we have studied several features of the adsorption, including isotherm, kinetics and the chemical state of aniline molecules in aniline-alumina system. What is perhaps more important, since the information above is obtained synchronously, the proposed methodology could provide information about the type of adsorption (chemical or physical adsorption), the change of chemical state of aniline in the system during the adsorption process, whether the chemical adsorption and physical adsorption took place simultaneously, the rate of the chemical and physical adsorption, and so on.2) We have studied the uptake of orthoxylene / isoamyl alcohol on silica gel as an example to demonstrate a novel methodology for studying multicomponent gas adsorption on solid adsorbent. In the method, the solid adsorbent was filled into a differential adsorption bed, and the bed was in-line monitored with near-infrared diffuse reflectance spectroscopy continuously when the adsorption process was taking place. The spectral data recorded during the process were treated with algorithm of locally weighted regression, which constructed a series of partial least squares models to more accurately predict concentrations of each adsorbates on the adsorbent. These efforts made the method feasible to obtain more thermodynamic and kinetic information about the adsorption process in a more convenient, rapid, economical as well as straightforward way.3) Through randomly arranging samples of a calibration set, treating their NIR spectra with orthogonal discrete wavelet transform, and selecting suitable variables in terms of correlation coefficient test (r-test), it is possible to extract features of each component in a multi-component system respectively, and partial least squares (PLS) models based on these features are capable of predicting the concentration of each component. What is perhaps more important, with the proposed strategy, the predictive ability of the model is at least not impaired while the size of the calibration set can be substaintially reduced. Therefore, it provides a more economical, rapid, as well as convenient approach of NIR quantitative analysis for multi-component system. In addition, all important factors and parameters related to the proposed strategy are discussed in detail.4) The paper focuses on solving a common problem of NIR quantitative analysis for a multi-component system: how to significantly reduce the size of the calibration set. To cope with the problem orthogonal discrete wavelet packet transform, least correlation design and correlation coefficient test (r-test) have been combined. A two-component carbon tetrachloride system and a two-component aqueous system have been treated with the proposed strategy where only 21 calibration samples are needed, and the result showed that the predictive ability was not obviously impaired for the former system while being clearly strengthened for the latter one in comparison with a conventional way that required a calibration set of 100 samples.5) An unlooked-for experimental observation that in near-infrared spectroscopy (NIR) the second overtone of aniline adsorbed by 13X molecular sieve nearly disappeared led us investigate a fundamental problem: the behavior of NIR when the outside space surrounding a molecule is too small to allow the molecule to vibrate freely. Through NIR of various organic compounds adsorbed by different porous inorganic materials like 13X molecular sieve, silica gel and active aluminium oxide, and NIR of supramolecular cyanuric acid-melamine, we can reasonably conclude that in the micro-environment above, all intensities of NIR absorbance decrease, and the second overtone decreases more than the first overtone does. Furthermore, one distinct feature of NIR, higher sensitivity to the size of micro-environment space as compared with mid-infrared (MIR), and its application to the study of supramolecular structures are outlined by our experiments.更多还原