类水滑石中温变压吸附CO2吸附机理及传热传质特性研究

H2/CO2 separation after water-gas-shift process for hydrogen from coal by hydrotalcite-liked CO2 solid adsorbents operating at the incoming stream’s elevated temperature range (200-350oC) takes advantages of simplifying separation process and conserving sensible energy. Surface reaction mechanism of the CO2 adsorption in the present of steam, the effect of heat accumulation effect inside fixed-bed reactor and non-conserved momentum of the flow during pressure swing adsorption process on the separation efficiency have not been well studied yet. This study aims to analyze the competitive adsorption mechanism of between CO2 and steam on the surface of hydrotalcite-liked adsorbents by means of surface enhanced Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature programmed desorption, to manipulate effective adsorption sites on hydrotacite surface and develop novel hydrotalcite-liked adsorbents which enjoy high CO2 capacity but low steam capacity. High pressure thermo-gravimetric analysis and fixed-bed breakthrough tests are deployed to investigate thermodynamic and kinetic characters, reaction heat and flow behavior during pressure swing adsorption process. Coupling mechanism between heat, flow and reactions under real industry pressure swing adsorption operation conditions using novel hydrotalcite-liked adsorbents, and the effect of working conditions on H2/CO2 separation efficiency are obtained through gPROMS metaphysics simulation platform. This study will provide a new energy saving approach for decarbonation after water-gas-shift for industrial hydrogen product from coal.

采用类水滑石固体吸附剂在匹配来流温度的中温区间（200-350oC）实现煤制氢水气变换后H2/CO2分离，具有简化工艺降低能耗优势。但对含水蒸气下吸附CO2机理，变压吸附过程固定床温升效应及流体动量不守恒对分离效果影响规律尚未厘清。本研究通过表面增强拉曼光谱、X射线光电子能谱、程序升温脱附等手段研究CO2与水蒸气在类水滑石表面竞争吸附机理，据此调控类水滑石表面有效吸附位，开发脱碳能力强且吸附水蒸气能力弱的新型类水滑石吸附剂。利用高压热重、固定床突破实验等获取变压吸附过程中热力学、动力学、反应温度及流动特性。通过gPROMS多物理场模拟平台获得新型类水滑石吸附剂实际工业操作工况下传热、流动与反应间的耦合机制以及变压吸附工艺对H2/CO2分离效果的影响规律，为工业煤制氢变换后脱碳净化过程提供节能降耗新思路。

采用固体吸附剂在匹配来流温度的中温区间（150~350℃）实现煤制氢水气变换后H2/CO2分离制氢，具有简化工艺降低能耗优势。本项目研究了CO2与水蒸气在固体吸附剂表面中温下吸附解吸机理，合成了CO2吸附量大且耐受水蒸气的新型类水滑石及疏水活性炭吸附剂，并通过模拟获得了变压吸附实际工况的固定床内传质、热量传递、动量传递规律。针对中温250~350℃区间应用场景，通过插层长碳链阴离子硬脂酸根撑开层间距，增大了钾修饰碱性位在吸附剂表面纳米尺度的分布密度，制备了吸附量1.93mmol/g的新型水滑石吸附剂。针对150~250℃区间，合成了活性炭疏水吸附剂，调控表面含氮基团实现疏水性能以及选择性脱碳，同时揭示了中温下硫化氢可逆吸附机理。建立了多物理场耦合的gPROMS模拟平台，实现了中温变压吸附工艺的模拟及放大。在此基础上设计搭建并运行了中温变压吸附H2/CO2分离系列示范装置。处理量为2~10Nm3/h小试示范装置先后装填了自行开发的水滑石基吸附剂及疏水活性炭吸附剂，采用8塔-6均压-1吸附中温变压吸附工艺，实现煤气化-氢气净化-质子交换膜燃料电池发电全系统累计2500小时运行。5000Nm3/h变换气处理量的中试示范装置装填疏水活性炭吸附剂，于来流变换后温度匹配的170℃实现了工业现场超过100天稳定运行，氢气一次收率大于90%且氢气品质达到国标要求。仅折算电耗，中试净化每标方氢气净化运行成本约为0.051kWh，相比于厂内低温甲醇洗每标方氢气净化电耗0.079kWh可大幅节约运行成本。本项目发展了中温气体吸附分离理论，开发了可工业化使用的新型吸附剂，完成了中温变压吸附分离定向脱除CO2、H2S等杂质工艺优化与技术示范，有望应用于氢能与燃料电池产业，为“双碳目标”的实现提供科学指引及技术支撑。