分子筛VP800-5分离氢同位素的动态实验与模型

液氮温度下用分子筛VP800-5在自行设计的单塔变压吸附装置上进行氢同位素气体分离的研究,考察了气体流量、压力与吸附床长度对分离效果的影响;在总压0.40 Mpa、总流量129.79 cm3.min-1与吸附床长度1.0 m时氢氘同位素混合气的分离因子可达到1.63.然而压力为0.0139 Mpa和0.0175 Mpa时D2和H2在分子筛VP800-5上的平衡吸附量比值仅分别为1.14和1.11.结合平衡吸附、动态吸附和分离的结果,低温吸附法能有效分离氧同位素主要是由于两者之间存在显著的动力学吸附速率差异.运用建立的柱动力学模型对氢氘吸附分离过程进行了模拟,结果表明模拟结果与实验结果吻合较好.     

氢同位素气体的新型动力学吸附模型

将氢同位素气体在多孔吸附剂表面上的吸附脱附过程假设为简单对峙反应,提出了一个适用于体积法计算气体动力学吸附速率常数的数学模型。模型可考察温度与初始压力对动力学吸附速率的影响,且能较好地计算不同压力下氢气与氘气在微孔分子筛4A,5A,Y,10X与介孔分子筛CMK-3,SBA-15上的动力学吸附速率常数。当分子筛孔径为0.5 nm时动力学吸附选择性最大,可高达2.48。介孔分子筛的动力学吸附选择性则较小,表明大孔径的吸附剂不利于氢同位素气体混合物的分离。     

多孔材料烷烃/烯烃分离技术的研究

以模拟油品为原料,在小型固定床（200 mL）反应器上考察了硅胶、γ-Al₂O₃、13X分子筛、Y分子筛及ZSM-5分子筛等多孔材料对烷烃/烯烃的吸附分离性能;其中硅胶的烷烃/烯烃分离效果最好,在吸附温度为40 ℃、压力为0.5 MPa、解吸剂为正辛烷/甲基环己烷的条件下,烷烃/烯烃分离度最高达到0.81;与其他类型硅胶相比,平均孔径为4~6 nm的B型硅胶传质效果更好,吸附-脱附过程更易趋于平衡。经过焙烧和溶剂再生的吸附剂,与新鲜剂相比,分离效果没有明显的降低。     

非耦联吸附塔新变压吸附工艺的实验研究

通过提氢实验研究一种新的变压吸附工艺.变压吸附流程的主要特征是通过中间均压罐打开吸附塔之间由均压步骤形成的耦联,从而实现了各塔操作的独立性,并提供了降低吸附压力的可能性.以H₂/N₂/CH₄（60/10/30）混合气模拟石油炼厂干气,进行低吸附压力（≤1 MPa）条件下的提氢操作.针对已有变压吸附工艺的不足和新流程特征,确定了新流程的变压吸附循环时序.分别采用普通活性炭（OAC）和高比表面活性炭（SAC）与5A沸石分子筛（ZMS-5A）的组合吸附剂,研究了不同吸附压力下的变压吸附分离效果,证明此种变压吸附新工艺在1 MPa以下、甚至0.4 MPa的低吸附压力下运行,亦可在较高的回收率下达到99.99%的高氢气纯度,并且显示出更强的对偶然性故障的应变能力.     

13X沸石分子筛对低浓度CO2动态吸附

目前对于吸附分离技术应用于高压、低浓度CO₂脱除的研究还较少,在进行相应吸附脱碳工艺设计时也缺少相关的参考数据。为探究13X沸石分子筛对低浓度CO₂的动态吸附性能,本文利用动态吸附实验的方法,探究不同条件下低浓度（摩尔分数3%）CO₂气体在13X分子筛上的动态吸附性能,得到不同压力、温度、气体流量、填料高度及分子筛规格（尺寸、形状）等因素影响下的13X分子筛对于CO₂气体的动态吸附规律及相应的性能指标参数。结果表明：随着吸附压力的升高,13X分子筛的CO₂吸附量增加但增量逐渐减小;降低吸附温度、减小气体流量和增加填料高度均有利于增强13X分子筛的动态CO₂吸附性能,提高吸附脱碳效果,其中温度及填料高度的变化对于CO₂吸附的影响程度最大;实验还发现小尺寸及条状13X分子筛的动态吸附脱碳性能优于其他规格,并根据其特定条件下的出口CO₂浓度为50mL/m³时的CO₂吸附量指标,给出吸附剂用量与液化天然气（LNG）脱碳工艺处理量的关系系数。     

双柱定容容量法测定气固吸附相平衡

本文提出的方法可用于测量真空及压力下单组分或多组分易达平衡的气固吸附相平衡。对多组分,用安装于柱内的小风机强制气体循环达到均匀吸附。测定了O_2、N_2及其混合物在13X分子筛上298K及308K时的吸附等温线,平衡压力达600kPa。其真空下的吸附量与Cahn 2000电天平的实验结果进行对比,吻合很好。文中对方法的灵敏度进行了分析。     

沼气变压吸附剂吸附性能比较

研究了工程上常用的3种吸附剂CO2吸附剂硅胶、13X分子筛和碳分子筛在高压(0.1~1 MPa)下对CO2和CH4的吸附容量、稳定性和选择性,以确定其在沼气变压吸附分离中应用的可行性. 结果表明,硅胶的吸附稳定性非常好,0.1 MPa时吸附选择性系数为8~10,能有效分离CH4?CO2;13X分子筛对CH4和CO2吸附容量最高、吸附选择性最好,重复使用5次CO2的吸附容量略有下降;以CH4的损失率作为评价标准时,13X分子筛吸附CH4的损失率最低. 降压不能使被碳分子筛吸附的CH4完全解吸,吸附位不能充分释放,不适用于CH4与CO2的分离.     

丝光沸石分子筛催化剂上C_9芳烃脱烷基的研究

将Bi、Ni、Mo、Pt负载在氢型丝光沸石(H/MOR)分子筛上,以异丙苯为模型化合物对分子筛催化剂加氢脱烷基性能进行了评价,考察了不同金属的活性和分子筛催化剂的稳定性。采用Pt/MOR分子筛催化剂时,催化剂的稳定性以及模型化合物的转化率和苯、甲苯、二甲苯(BTX)的产率有显著提高。当反应温度为420℃,压力为0.8MPa,空速为1h-1时,其转化率最高可达89.8%,BTX的产率可高达82.8%。分子筛酸性分布与金属之间的平衡对催化剂的活性至关重要。当w(Pt)=0.5%,总酸为0.825mmol/g时,酸与金属间的平衡协同作用对催化剂的活性和稳定性有明显促进作用。     

读者信箱

<正> 一、问:什么叫变压吸附?答:变压吸附是利用分子筛在不同的压力及温度条件下,对混合气体进行选择性的吸收,并控制压力及温度进行解吸,用以达到分离混合气体的目的。如石油化工、化肥工业以及其它行业中均有应用。如利用分子筛变压吸附分离合成氨厂驰放气中的甲烷及氢;利用分子筛变压吸附分离空气中的氧及氮,利用分子筛变压吸附分离空气中的二氧化碳。这些分子筛有沸石,碳以及 A 型分子筛等。二、问:碳酸氢铵肥料堆放在露天有什么害     

变压吸附的实质

变压吸附是利用分子筛筛分机理的特性来实现气体分离的。由于分子运动自由程的不同,气体分子通过分子筛的孔向孔内扩散时所受阻力不同,导致在孔内扩散速率不同,宏观上这种分离体现为气体被固定于分子筛的孔内部被"吸附"。实际操作时,不断采取"加压吸附-减压脱附"循环方式,因此被形象地称为"变压吸附",其实质是基于分子筛孔本身的筛分机理,并非吸附机理。通过变压吸附的机理分析,我们确定了分子筛孔径的选择方法,同时分析了变压吸附过程的影响因素。     

氢同位素低温吸附分离的平衡吸附模型

1 INTRODUCTION Hydrogen isotope separation has been the com- mon concern for many years, for pure deuterium can be used as a fuel of the nuclear fusion reactor or as a tracer in medical cure, chemical reaction and geo- graphic research. Several methods such as chemical exchange, cryogenic distillation, laser, and thermal diffusion are applied for separating the hydrogen iso- topes, but these methods require great invest and en- ergy consumption. Therefore, other alternative meth- ods need …     

真空变压吸附提纯沼气的实验

以煤基碳分子筛为沼气净化吸附剂,借助扫描电镜观察了碳分子筛的表面形貌,并通过物理化学吸附仪表征了碳分子筛的孔径分布。基于静态容积法测定了CO₂与CH₄在碳分子筛的静态吸附量,并估算了CO₂与CH₄在碳分子筛的动力学扩散系数。单塔穿透实验考察了吸附压力与进料流量对原料气中CO₂穿透曲线的影响,选取吸附压力为0.3 MPa,进料流量为4 L·min-1进行两塔六步真空变压吸附提纯沼气的实验研究,并考察了吸附步骤时长与产品气冲洗率对CH₄富集效果的影响。实验结果表明,吸附步骤时长为140 s,冲洗率为0.05时,产品气中CH₄纯度可达98%,收率可达82%。     

结构化5A分子筛吸附床结构及工艺参数对N2/H2吸附性能的影响

利用吸附等温线获得动力学参数,建立了CFD模型,模拟了氢气/氮气在结构化5A分子筛吸附床中的吸附过程,研究了吸附剂层片间距、吸附剂厚度等结构参数和吸附压力、进气流量等工艺参数对混合气吸附效果的影响。结果表明：减小层片间距和吸附剂厚度可显著提高传质系数和床层利用率。增大吸附压力可提高床层利用率,但会减小传质系数。进气流量对传质系数的影响不明显,但当流量较大时,吸附容量和床层利用率均呈减小趋势。结构化5A分子筛吸附剂吸附性能良好。     

Modelling of the pressure swing air seperation process

A theoretical analysis is given of the separation of oxygen and nitrogen in air by a single column pressure swing gas separation process. The problem treated includes changes in mass flow due to adsorption. The findings are compared with data obtained using molecular sieve adsorbent.     

Air separation by pressure swing adsorption on a carbon molecular sieve

A simplified dynamic model for a PSA air separation process is developed based on linearized mass transfer rate expressions and binary Langmuir equilibrium. Constant pressure is assumed during adsorption and desorption steps but the variation in flow rate through the column due to adsorption is accounted for. The model predictions, using independently measured kinetic and equilibrium data are compared with experimental results obtained in a simple two-bed air separation PSA system packed with a carbon molecular sieve adsorbent. The model is shown to provide a good representation of the experimentally observed behaviour over a wide range of conditions.     

Single and multicomponent adsorption equilibria of carbon dioxide,nitrogen, carbon monoxide and methane in hydrogen purification processes

Single, binary, ternary and quaternary adsorption equilibria of CO₂, CO, CH₄ and N₂ on molecular sieve 5A and activated carbon were experimentally determined over a pressure range from 10^?4 to 10¹ MPa, a temperature range from 303 to 363 K and at various compositions. The adsorption equilibria of steam reformer gases as needed for the hydrogen purification in pressure swing adsorption units were measured by using a circulating volumetric method. For the temperature-dependent correlation of pure gas isotherm fields the Toth equation, which is a favorable model for heterogeneous adsorbents, was extended by two parameters accounting for the temperature-dependencies of the saturation loading and the heterogeneity parameter. Multicomponent equilibria were successfully predicted from single component isotherms by the Ideal Adsorbed Solution Theory based on the accurate representation of the pure component data by this temperature dependent Toth equation. Other thermodynamic models like the HIAS, the MIAS, the SPD or the VS theory and the Statistical Thermodynamics Model were also applied to the prediction of the adsorption equilibrium and the temperature and pressure dependence of the selectivity, with comparable success, which is due to the quasi-ideal adsorption behavior even at a high pressure.     

Kinetic separation of carbon dioxide from hydrocarbons using carbon molecular sieve

Experimental results are reported on a pressure swing adsorption (PSA) process using carbon molecular sieve (CMS) for the separation of a gas mixture containing carbon dioxide, hydrocarbons (methane, ethane, propane, etc.) and nitrogen. This PSA process has direct applications in carbon dioxide removal or purification from landfill gas, natural gas processing plants and tertiary oil recovery effluent streams. The CMS-based PSA process separates the carbon dioxide in a single stage by using the differences in component diffusivities. This approach, therefore, provides a significant advantage compared to conventional equilibrium adsorption processes which require one separation stage for removing components such as ethane and propane that are more strongly adsorbed than carbon dioxide and another separation stage for removing components such as methane and nitrogen that are less strongly adsorbed than carbon dioxide. The CMS-based PSA process operates between a feed pressure of 20 to 40 bars and a regeneration pressure of 1.5 bars at ambient temperature and produces a 98+% carbon dioxide product. The PSA process can be integrated with a liquid carbon dioxide plant to produce food grade product.     

Kinetics of removal of impurities from gases by high pressure adsorption

Among other processes, adsorption is used for the removal of hydrogen sulphide from natural gases. Hereby, competitive adsorption of the different gas components plays an important role, e.g., that of carbon dioxide. Data of equilibrium loading and adsorption kinetics are required for the design of adsorbers, filled with molecular sieve. In order to obtain these data under the prevailing operating conditions, hydrogen sulphide was removed from gas mixtures H₂S/CH₄ and H₂S/CO₂/CH₄, in a pilot plant, by adsorption on molecular sieve 5A. The equilibrium loading, the height of transfer zone, and the length of unused bed were determined from the measured breakthrough curves of H₂S. With these data, the breakthrough time and the optimum process conditions were calculated for a practical example.