基于阻滞扩散模型估算柴油脱硫吸附剂的适宜孔径分布

Estimation of appropriate pore size distribution for diesel desulfurization adsorbent based on hindered diffusion model

通过GC-PFPD色谱分析国Ⅱ、国Ⅲ、国Ⅳ标准0^#柴油中的主要含硫组分,发现苯并噻吩（BT）、二苯并噻吩（DBT）及其烷基取代衍生物是0^#柴油中的主要含硫化合物,C2-DBT、C3-DBT是国Ⅳ柴油中的主要含硫化合物。以BT、DBT、4,6-DMDBT为模型化合物,计算含硫化合物在不同大小孔道内的扩散阻滞因子,结合氧化铝堆积孔模型,估算氧化铝基柴油脱硫吸附剂的适宜孔径分布。结果表明,当氧化铝的平均孔径为4～10 nm时,含硫化合物的扩散阻滞因子为0.24～0.65,氧化铝的比表面积为100～250 m^2·g^-1,可同时满足较低的扩散阻力和足够大的比表面积。对比分析不同氧化铝的孔分布及其吸附脱硫性能,结果表明氧化铝中4～10 nm范围内的孔面积占总孔面积的百分比与其吸附脱硫性能存在显著的正相关关系,初步推测氧化铝基脱硫吸附剂的适宜孔径分布范围为4～10 nm。

Major sulfur components in 0^# diesel conformed to PRC State Standard Ⅱ, Standard Ⅲ and Standard Ⅳ were identified by a gas chromatograph （GC） equipped with a pulsed flame photometric detector （PFPD）. The PFPD chromatograms illustrated that benzothiophene （BT）, dibenzothiophene （DBT） and their derivatives constitute significant portion of the sulfur species in ORD, majority of which were derivatives of DBT. BT, DBT and 4,6-dimethyldibenzothiophene （4,6-DMDBT） were treated as the characteristic sulfur species in diesel. The hindered diffusion coefficients of characteristic sulfur species in different sizes pore were estimated by a simplified hindered diffusion model. By combining with the stacking pore model of alumina, the appropriate pore size distribution for fuels desulfurization adsorbent was estimated. The results showed that when the average pore diameter of the alumina is 4-10 nm, the hindered diffusion coefficients of characteristic sulfur species were about 0.24 to 0.65 and the specific surface area of the alumina was about 100-250 m^2·g^-1, which can meet the lower diffusion resistance and a sufficiently large specific surface area, simultaneously. There was a significant positive correlation between the desulfurization rate of 0^# diesel conformed to PRC state standard II and the percentage of pore area in the range of 4-10 nm. It was preliminary conjectured that the appropriate pore size distribution of alumina-based adsorbent for fuels desulfurization was in the range of 4-10 nm.