生物质乙醇在Fe-HZSM-5分子筛催化剂上脱水制乙烯（英文）

发布时间：2018-02-28 20:07

  本文关键词： 铁 ZSM- 脱水 乙醇 乙烯　出处：《催化学报》2016年11期 　论文类型：期刊论文

【摘要】：乙烯是一种重要的大宗化工原料.目前国内外乙烯的生产方法主要是石脑油裂解法.但是,随着全球性石油资源供求关系日趋紧张,以及该生产过程存在较大环境污染,该工艺面临严峻挑战.生物乙醇是一种可以通过生物质发酵获得的可再生资源.因此,生物质乙醇催化脱水制乙烯工艺受到越来越多研究者关注.该技术的关键在于高性能乙醇脱水制乙烯催化剂的开发.研究发现,Si/Al比大于40的Fe改性ZSM-5分子筛在乙醇转换制碳氢化合物的催化反应中具有较高活性,当反应温度大于400 ℃时,可生成C_1-C_9的烷烃、烯烃和芳香烃,其中以C_3产物和芳香烃产物为主.本文研究了Si/Al比为25-300的Fe离子交换ZSM-5分子筛在乙醇脱水制乙烯反应中的催化活性,并利用XRD,NH_3-TPD,吡啶吸附FT-IR和DRS UV-VIS等表征手段,研究了催化剂的晶相结构、表面组成及酸性位点等,进而探究了该催化反应的反应机理.我们首先考察了Si/Al比为25-300的HZSM-5分子筛.随着分子筛Si/Al比增大,乙醇转化率先增加后降低,在Si/Al比为100时获得最高值;但是乙烯收率随着Si/Al比的增加而持续下降,Si/Al比为25时有其最高值47%.经产物分析,HZSM-5(25)和HZSM-5(300)虽具有相似的乙醇转化率,但前者产生大量C_(3+)产物,而后者产物只有乙烯和乙醚.据文献报道,乙醚是乙醇脱水制乙烯的中间产物,它的进一步脱水产生乙烯,而乙烯可进一步转化生成C_(3+)产物.因此,由于HZSM-5(300)表面酸性较弱,主要生成反应中间体,而HZSM-5(25)较强的表面酸性又导致乙烯进一步转化,生成C_(3+)产物.然后我们考察了经过3次离子交换处理的Fe-ZSM-5催化剂.随着Si/Al比上升(25-300),乙醇转化率和乙烯收率下降,Si/Al比为25时为其最高值;随着反应温度上升,乙醇转化率在260 ℃时达到近100%,之后维持不变,乙烯收率也在260℃时为其峰值,温度继续上升造成乙烯收率再次下降;催化剂空速增大降低乙醇转化率和乙烯收率.经产物分析,温度较低和空速较大时产生大量的反应中间体乙醚,而温度较高时导致乙烯进一步转化生成C_(3+)产物.在反应温度为260 ℃、空速为0.81 h~(-1)时,Fe-HZSM-5(25)催化剂上乙醇转化率为98%-99%、乙烯收率为97%-99%,并可实现长达1440 h的单程使用寿命,该值是HZSM-5(25)催化剂的20余倍,具有很好的工业应用前景.为探究Fe-ZSM-5(25)催化剂高催化活性和长催化寿命的原因,我们表征了催化剂.从XRD结果可以看出,离子交换没有损坏HZSM-5的晶体结构,也没有新的可检测到的物相产生.从NH3-TPD结果看,HZSM-5(25)的CH/CL(强酸/弱酸)比为0.7,Fe-ZSM-5(25)的CH/CL比为0.29,可知Fe离子交换降低了分子筛的表面酸性,特别是强酸性位.从吡啶吸附FT-IR结果看,HZSM-5(25)的B/L(Br?nsted酸性位/Lewis酸性位)比为1.42,Fe-ZSM-5(25)的B/L比为0.25,可知Fe离子交换主要减少的是分子筛表面的Br?nsted酸性位.文献报道,乙醇脱水制乙烯主要发生在弱酸性位上,而乙烯进一步转化为C_(3+)产物发生在强酸性位上.所以,催化剂上强酸性位的减少有利于乙烯的生成反应.另据文献报道,Br?nsted酸性位是乙烯聚合、迅速覆盖催化活性位点产生积炭的催化活性中心.因此,Br?nsted酸性的降低可认为是Fe-HZSM-5(25)催化剂单程使用寿命长较HZSM-5(25)分子筛显著延长的原因.从UV-VIS结果得知,Fe-ZSM-5上的Fe物种主要以骨架内和骨架外Fe~(3+)为主,此外含有少量低聚合的Fe_xO_y,但几乎没有Fe_2O_3颗粒存在.文献记载,Fe~(3+)物种是乙烯形成的活性物种,而FeO_x催化产生乙烯和乙醛.因此,催化剂中大量骨架内和骨架外Fe~(3+)物种的存在也可认为是该催化剂具有较强乙醇脱水制乙烯催化活性的原因之一.
[Abstract]:Ethylene is a kind of important chemical raw materials. At present the main method of domestic production of ethylene is naphtha pyrolysis method. However, with the increasingly tense relationship between supply and demand of global oil resources, environmental pollution and the large production process, the process is facing severe challenges. Bio ethanol is a kind of can be obtained by fermentation of biomass renewable resources. Therefore, the biomass catalytic dehydration of ethanol to ethylene process has attracted more and more attention of researchers. The key of this technology lies in the development of high performance catalyst for preparing ethylene by ethanol dehydration. The study found that the Si/Al ratio is greater than 40 Fe modified ZSM-5 molecular sieve with high activity in the catalytic reaction of ethanol conversion for hydrocarbons, when the reaction temperature is greater than 400 C, can generate C_1-C_9 alkanes, olefins and aromatics, which C_3 products and aromatic hydrocarbon product. This paper studies the Si/Al ratio of 25-300 F E ion exchange ZSM-5 molecular sieve catalytic activity in the reaction of ethanol dehydration to ethylene, and the use of XRD, NH_3-TPD, FT-IR and DRS UV-VIS pyridine adsorption characterization methods, investigated the crystal structure, surface composition and acidic sites, and then explore the reaction mechanism of the catalytic reaction. We first examined the Si/Al ratio for the 25-300 HZSM-5 molecular sieve with molecular sieve Si/Al ratio increases, ethanol conversion increased first and then decreased, the Si/Al ratio of 100 was the highest value; but the ethylene yield increases with the Si/Al ratio continued to decline, the Si/Al ratio of 25 has the highest value of 47%. by product analysis, HZSM-5 (25) and HZSM-5 (300) is similar to the conversion of ethanol, but the large amount of C_ (3+) product, the latter only product of ethylene and ether. It is reported that ether is the intermediate product of ethanol dehydration to ethylene, it further dehydration to produce ethylene, and Ethylene can be further transformed into C_ (3+) product. Therefore, the HZSM-5 (300) surface acidity is weak, the main reaction intermediates, and HZSM-5 (25) surface strong acid and ethylene resulted in further transformed to generate C_ (3+) product. Then we investigated the effect of Fe-ZSM-5 catalyst after 3 ion exchange treatment with. Si/Al Rose (25-300), ethanol conversion and ethylene yield decreased, Si/Al ratio was 25 for the highest value; as the temperature increases, the conversion rate of ethanol reached nearly 100% at 260 DEG C, then remain unchanged, the ethylene yield also at 260 DEG C for its peak value, the temperature continues to rise caused by ethylene yield decreased again the increase of space velocity of catalyst; ethanol conversion and ethylene yield decreased. By product analysis, resulting in a large number of ether reaction intermediates of low temperature and high space velocity, and higher temperature leads to ethylene was further transformed into C_ (3+) in the product. 鍙嶅簲娓╁害涓，

本文编号：1548756