【作者】 唐浩东；

【导师】 刘化章；

【作者基本信息】 浙江工业大学 ， 工业催化， 2007， 博士

【摘要】 超临界流体具有类似气相的传质速率和类似液相的溶解能力和热容，是一种理想的反应介质。至今没有人对熔铁催化剂的超临界相费托合成进行研究。本论文目的是引入超临界介质，较好地解决传统气相费托合成中存在的催化剂床层飞温和液相费托合成中合成气传质速率慢的问题，通过研究反应条件和催化剂配方的影响，进一步提高费托合成反应活性，改善产物选择性，延长催化剂寿命。本文在微反-色谱连续流动固定床装置上研究了熔铁催化剂费托合成反应性能，采用XRD、TPH、EDS等实验技术对催化剂进行了表征，得到以下主要结果：1．超临界相费托合成反应具有CO转化率高，甲烷选择性低、C₅₊选择性增加、烯烷比高、单位合成气C₂₊和C₅₊的产率增加、催化剂表面积炭量少、催化剂不易失活等优点。经过48h超临界相费托合成实验，发现CO转化率、甲烷选择性、烯烷比、C₅₊选择性、链增长因子、单位合成气C₅₊产率等主要指标稳定，CO₂选择性下降。催化剂表面积炭略有增加，但仍远小于气相反应。说明超临界相反应催化剂寿命和反应稳定性将远大于气相反应。2．超临界相费托合成反应中合成气在超临界介质中扩散系数更大，使催化剂表面合成气浓度尤其是CO浓度显著提高；由于超临界介质具有类似液体的溶解能力，能及时将反应产物从催化剂表面脱附并传递出催化剂孔道，使催化剂表面活性位效率增加。这是超临界相费托合成反应性能优于气相反应的原因之一。3．通过对反应后催化剂表征，发现超临界相费托合成反应后的催化剂表面积炭明显小于气相反应，尤其是非活性的纤维状碳和石墨碳沉积量较小。说明超临界介质具有良好溶解性能，在反应过程中能及时带走催化剂表面非活性碳沉积的前驱体，有效避免催化剂活性位被积炭覆盖而减少，有利于延长催化剂寿命。这是超临界相费托合成反应性能优于气相反应的另一个原因。4．超临界相费托合成的操作温度宜在介质的临界温度附近，即T／T_c=1.0-1.1之间，过高和过低都不利于超临界相费托合成反应。介质压力低于临界压力反应性能显著变差，而高于临界压力反应性能变化不大。正构烷烃不与反应物和产物反应，不会使催化剂中毒，在合适温度范围内可以作为超临界介质。5．超临界介质循环使用不改变CO转化率和烯烃选择性，但甲烷选择性增加，链增长因子减小。6．电子助剂K和结构助剂Al的含量对超临界相费托合成的影响类似于气相反应。不同母体、不同助剂含量的熔铁催化剂在超临界相费托合成中均表现出优于气相费托合成的反应性能。7．实验对超临界氨合成进行了探索，实验结果表明：在现有氨合成催化剂及其反应条件下（325-425℃，10-15MPa），介质都会发生不同程度的分解，分解产物造成催化剂失活，使反应器出口氨浓度下降。催化剂的活性温度是影响超临界氨合成的关键因素。更多还原

【Abstract】 The conventional FTS reaction has been performed in either gas phase or liquid phase reaction media. Gas phase reactions exhibit higher reaction rates and diffusivities when compared to liquid phase reactions, but are hampered by inadequate heat removal resulting in excessive methane formation. Liquid-phase reactions have superior heat removal capabilities when compared to gas phase reactions and are therefore able to maintain a constant reaction temperature without deactivation. However, liquid-phase FTS suffers from mass transfer limitations, requiring relatively large reactor volumes. The ideal FT synthesis medium would, therefore, be one with gas-like transport properties and liquid-like heat capacity and solubility characteristics. Such a desired combination of fluid properties is possible with supercritical reaction media.The performance of supercritical phase Fischer-Tropsch synthesis over fused iron catalysts was evaluated in the fixed bed reactor. Catalysts were characterized by means of XRD, TPH, EDS and so on to provide better insight into the relationship therein. Main results from this work were as follows.It has been observed that CO conversion, 1-olefin selectivity, and heavy hydrocarbon production can be enhanced in supercritical phase FTS process compared to gas phase FTS. After 48hrs’ continuous running of the reaction in supercritical phase FTS, the catalyst does not show any sign of deactivation and deposition of inactive carbon on catalyst always much lower than that in gas phase FTS.Higher CO conversion in supercritical phase FTS results from: 1) The higher solubility and diffusivity of syngas in the supercritical phase FTS have an important role in the enhancement of concentration of syngas on catalyst active site; 2) The supercritical phase FTS operation results in the enhanced extraction of heavy hydrocarbons from catalyst pores and surfaces thereby enhancing pore diffusivity and creating more active sites; 3) The deposition of inactive carbon on fused iron catalyst in supercritical phase FTS process could be well controlled and this resulted in the creating more active site on catalyst.Compared to gas phase FTS, no significant different effect of temperature, pressure, syngas flow rate and syngas feed ratio on the supercritical phase FTS has been observed. Optimum reaction temperature and pressure are T/T_c=1.0-1.1 and P/P_c=1.0-1.5, respectively. Our results have also shown that paraffins are promising candidates for supercritical solvent because they do not poison the catalysts and are stable under the reaction conditions.Compared to the results without recycle of the solvent, CO conversion and hydrocarbon products distribution is similar to, but CH₄ selectivity is higher than those with recycle of the solvent.Compared to gas phase FTS, no significant different effect of the content of K and Al and the change in Fe²⁺/Fe³⁺ on the supercritical phase FTS has been observed. But higher CO conversion and better products selectivity is achieved in the supercritical phase FTS.we have done supercritical ammonia synthsis research systematically using 17 differenct supercritical media, and investigated the influence of reaction conditions. It has been found that supercritical media is decomposed under reaction conditions when using Fe_1-xO and Ru/AC catalysis. The decomposition products deactivate the catalysts. From experimental results, we conslude that the activation temperature of catalyst is the key factor in supercdtical ammonia synthsis.更多还原