【作者】 陈五花；

【导师】 赵宗昌；

【作者基本信息】 大连理工大学 ， 化学工程， 2009， 博士

【摘要】 含蜡油输送时,低温下蜡晶的析出会阻塞输油管道,从而严重影响原油的输送和生产。目前采用了许多物理或者化学方法来解决这一问题。添加化学降凝剂的方法以其操作简单、设备投资少,且不需要后处理等优点而被广泛采用,因此研究降凝剂对石蜡沉积的影响有非常重要的意义。本文以模拟油为研究对象,从实验和模型化两个方面研究了降凝剂对石蜡沉积的影响。采用高速离心分离法和气相色谱法测定了模拟含蜡油添加降凝剂前后不同温度下的析蜡量以及析出蜡晶的组成。结果表明添加降凝剂后,一定温度范围内的析蜡量减少,随着温度的不断降低,析蜡量降低的幅度逐渐减小,当温度降低至某一温度时,加剂前后的析蜡量趋于相等;在同一温度下,加剂后析出的蜡晶中高碳数烷烃所占比例增加,析出蜡晶的摩尔质量增大。差示扫描量热法（DSC）测定了添加降凝剂前后蜡晶的热谱图,结果表明加剂后蜡晶的整个DSC曲线向低温方向移动,根据DSC分析程序得出,加剂后蜡晶的熔点和固-固转换温度降低,但是蜡晶的熔解焓和固-固转换焓变化很小,特别是熔解焓和固-固转换焓的和几乎没有变化。采用X射线衍射仪和偏光显微镜对添加降凝剂前后蜡晶的晶格结构和晶形进行了研究。X射线结果表明降凝剂的加入促进了蜡晶形成旋转晶型,减弱了正交晶型的蜡晶生成。正交晶为蜡晶低温有序固相,旋转晶为蜡晶高温无序固相,降凝剂的加入使得蜡晶以一种类似于液态的非有序固相存在,这意味着在某一温度下从加剂溶液中析出的蜡晶结构与在更高的温度下从未加剂溶液中析出的蜡晶结构相同,降凝剂的加入,有效地降低了蜡晶的熔点。蜡晶的偏光显微图像表明添加降凝剂后蜡晶颗粒尺寸变大,蜡晶界面轮廓更清晰、形状更规整,单位体积内蜡晶颗粒的数量大大降低。加剂后由于单位体积浓度的降低、蜡晶聚集颗粒形状的准球形化和蜡晶聚集体絮凝能力的减弱,含蜡油开始呈现非牛顿流体特性的温度降低。从正规溶液理论和聚合物溶液理论两个角度出发,结合液-固两相热力学平衡理论,在前人的基础上分别建立了加剂前后石蜡沉积的正规溶液模型和UNIQUAC局部组成活度系数模型,并且比较了两个模型的预测性能。（1）正规溶液理论模型:在该模型中组分i在固相和液相中的非理想性均采用正规溶液理论来描述。（2） UNIQUAC局部组成活度系数模型:在该模型中,液相的相态描述采用了G^E-EOS模型,其中状态方程为改进的PR状态方程,混合规则采用LCVM模型;固相的非理想性则采用改进的UNIQUAC局部组成活度系数模型来描述。研究表明,当石蜡的碳链大于9时,其固相至少存在着四种晶体结构,即旋转晶（α_H）、三斜晶（β_T）、单斜晶（β_M）和正交晶（β_O）,旋转的α晶体在许多情况下类似于液体,它在C₉～C₄₃的奇碳数烷烃和C₂₂～C₄₂的偶碳数烷烃的熔点下是稳定的。当温度低于旋转化温度时,烷烃成为低能量不可转化的β晶体,其间不同碳原子数的正构烷烃都经历了固-固转换。基于这种现象,本文两个热力学模型在组分i的标准态逸度比公式中考虑了固-固转换对石蜡沉积的影响,并且根据文献实验数据,对于正构烷烃的熔解焓、固-固转换焓以及固-固转换温度建立了新的关系式。差示扫描量热仪实验显示添加降凝剂后蜡晶的熔点和固-固转换温度降低,本文采用了这一实验结果对添加降凝剂后蜡晶的熔点和固-固转换温度也进行了新的关联。基于新建立的正构烷烃的熔解焓、固-固转换焓以及固-固转换温度的关系式,采用本文两个模型对文献中含蜡原油体系的析蜡点以及不同温度下的析蜡量进行了计算并与文献中模型的预测结果进行了比较,结果表明本文所建立的模型,特别是UNIQUAC局部组成模型的模拟结果更加接近于实验值,从而验证了本文模型的可靠性和正确性。将所建立的热力学模型对本文含蜡油体系添加降凝剂前后的析蜡点、不同温度下的析蜡量以及析出蜡晶的组成进行了模拟计算,模型计算值与实验值吻合较好。模型计算结果表明,烷烃的熔点和固.固转换温度等热力学性质对于石蜡沉积的计算有很大的影响,添加降凝剂后,在一定温度范围内,含蜡油的析蜡量降低,析出蜡晶中高碳数烷烃所占比例增加,析出蜡晶的摩尔质量增大,与降凝剂对石蜡沉积影响的实验现象一致。更多还原

【Abstract】 When waxy oils are transported at low temperature,the plug of pipeline caused by wax precipitation has important influence on the transportation and production of crude oils.At present,many physical and chemical means have been used to solve this problem.Adding chemical pour point depressant(PPD) to the oils have been applied extensively because of its simple operation,low investment and non-after treatment.It is important to study the influence of pour point depressant(PPD) on wax precipitation.This research works on the effect of PPD on the thermodynamic properties of wax precipitation from the point of view of experimental and thermodynamic models.The amount and composition of wax precipitated from simulated oils with and without PPD at different temperatures were measured by high speed centrifuge and gas chromatography(GC),respectively.It can be concluded that the amounts of wax precipitated from oils treated with PPD in the experimental range are lower than that from untreated oils. However,the amounts of wax precipitated from oils treated and untreated with PPD are the same when the temperature drops to a certain temperature.At the same temperature,the wax precipitated from treated oils is richer in paraffins with higher melting point than that from untreated oils,so the wax formed from the treated oil mixture has a higher molecular weight than the wax formed from the untreated oil mixture.The thermograms of waxes with and without PPD were measured by differential scanning calorimetry(DSC).After the waxes were treated with additives,the DSC curves of waxes are all shifted to lower temperature.The experimental data show that the melting points and the solid-solid transition temperatures of paraffin mixtures are both decreased while they were being treated with PPD.However,the transition enthalpies have little changes especially the sum of solid-solid transition enthalpy and melting enthalpy.The lattice structure and morpholopy of wax crystals were studied by X-ray diffraction and the polarized light micsoscope,respectively.The X-ray diffraction results indicated that after adding PPD,the structure of wax is partly transformed from orthorhombic into hexagonal lattice.The orthorhombic lattice is an ordered phase at lower temperature and the hexagonal lattice is a disordered phase at higher temperature.The wax with PPD will prefer to crystallize in a less ordered state which is more akin to the liquid phase.This means that the wax precipitated from treated oils at a given temperature is corresponds to the wax precipitated from untreated oils at a higher temperature.The polarized light micsoscope results indicated that the function of PPD on the crystal morpholopy is increasing the size of paraffin particles,improving their symmetry,reducing their dispersivity,depressing their interaction and connection,so the characteristic temperature of non-Newton waxy oils is lowered.Based on the regular solution theory and polymer solution theory as well as the liquid-solid phase thermodynamic equilibrium,the regular solution model and the UNIQUAC local composition model were established in this work to predict the wax precipitated from oils with and without PPD,the prediction performance of these two models were also compared in this work.(1) Regular solution model:The activity coefficient based on a regular solution theory approach was used to account for the non-ideality of liquid and solid phases.(2) UNIQUAC local composition model:The fluid phase behavior was described by the modified LCVM,PR equation of state-G~E model and the solid phase non-ideality was represented by the UNIQUAC equation using the local composition concept.It is well known that the solid phases of all n-paraffins with more than nine carbon atoms in the chain consist of four distinct crystal structures,hexagonal(α_H),triclinic(β_T), monoclinic(β_M) and orthorhombic(β_O),respectively.When the temperature is slightly lower than the wax appearance temperature,the paraffin will precipitate with a disorderedα_H crystal structure,with the further decrease of temperature,and all of the solid paraffins become orderedβphase.The influence of solid-solid transition on the wax precipitation was considered in the correlation of standard fugacity ratio.From the point of view of the close relation between the crystal lattice structure and the thermal properties of paraffins,new correlations for fusion enthalpy,solid-solid transition enthalpy and solid-solid transition temperature of paraffins were established in this work based on the data from literatures.New correlations for the melting point and solid-solid transition temperature of treated paraffins were also established based on experimental results with differential scanning calorimeter (DSC),which show that these properties are both decreased after being treated with PPD.Based on the new correlations for fusion enthalpy,solid-solid transition enthalpy and solid-solid transition temperature of paraffins established in this work,a good calculation results as well as the reliability and precision of the models are demonstrated through a comparison calculation for three examples in the literature.The calculation results by these two models for the wax appearance temperature,the amount and composition of wax precipitated from oil with and without PPD at different temperatures have been compared with experimental observations.The predictions of the models agree well with the present experimental data.The calculation results indicated that the performance of wax precipitation models is strongly influenced by the thermodynamic properties of paraffins such as the fusion temperature and the solid-solid transition temperature etc.The results presented show that after adding PPD,the amount of wax precipitated from oils treated with PPD in the experimental range is lower than that from untreated oils,the wax precipitated from treated oils is richer in paraffins with higher melting point than that from untreated oils,which is consistent with the experimental phenomena of effect of pour point depressant on wax precipitaton.更多还原