基于拉曼光谱解析的对二甲苯装置吸附塔循环液成分分析

Component Analysis of the Circulating Fluid in an Adsorption Tower in a P-Xylene Unit Based on Raman Spectral Decomposition

采用拉曼光谱分析法实现PX（对二甲苯）装置中吸附塔循环液快速、准确的在线分析。由于循环液中各组分的拉曼谱峰相互重叠,且各组分的含量变化范围很大,需要收集大量的训练样本。为此,提出了基于拉曼光谱解析的循环液成分分析方法。首先,要获得循环液所含各组分纯物质的拉曼光谱,以及少量训练样本的拉曼光谱,对这些拉曼光谱进行基线扣除和均值归一化;其次,选取特征波段680~880cm-1,对每一个训练样本预处理后的拉曼光谱在特征波段进行光谱分解,得到该训练样本中各组分的分解系数;然后,基于全部训练样本各组分的分解系数与对应的浓度数据,建立分解系数与浓度之间的定量分析模型。而对于某一测试样本,先获取其拉曼光谱,进行上述相同的光谱预处理,并在相同的特征波段基于纯组分的拉曼光谱对其进行谱分解,以获得该样本的光谱分解系数;再根据得到的分解系数和上述定量分析的模型,预测出该测试样本中各组分的含量。实验结果表明,一方面,由各纯组分混合得到的训练样本的拉曼光谱可以较精确地分解成各组分的拉曼光谱的线性加权和;另一方面,基于拉曼光谱分解系数建立的定量分析模型可以准确地预测出循环液中各组分的含量,对测试样本中甲苯、乙苯、对二甲苯、间二甲苯、邻二甲苯和对二乙基苯含量的标准预测误差分别为0.301%,0.088%,0.563%,0.384%,0.366%和0.536%。为PX装置中吸附塔循环液的在线分析提供了改进方法。

In order to achieve fast and accurate online analysis of the circulating fluid in an adsorption tower in a p-xylene unit, the Raman spectral analysis method is adopted.However,the Raman spectra of the pure components included in the circulating fluid overlap together,and the concentration of each component varies obviously,the present Raman analysis technology needs a large amount of training samples.Therefore,this paper applies Raman spectral decomposition method in component analysis of the circulating fluid.First of all,the Raman spectra of the pure components and the spectra of a few training samples must be measured,and baseline subtraction and mean normalization are applied to obtain pretreated Raman spectra.Then the characteris-tic wave number range,680~880cm-1 ,is chosen,and the Raman spectral decomposition method is adopted,to get decomposi-tion coefficients of each component for each training sample.Next,the mathematical model between coefficients and concentra-tions of each component are built based on all training samples.For a testing sample,the above spectral pretreatment and the spectral decomposition for the same wave number range is adopted,then the decomposition coefficients of each component can be obtained.Based on the built mathematical model,the concentrations of all components can be predicted.Experimental results show that the standard prediction errors for the concentration of toluene,ethylbenzene,p-xylene,m-xylene,o-xylene and p-di-ethylbenzene are 0. 301%,0. 088%,0. 563%,0. 384%,0. 366%and 0. 536% respectively.The above method provides a meth-odological basis for the online analysis of the circulating fluid in adsorption towers.