Enhanced formation of α-olefins by the pulse process between Fischer-Tropsch synthesis and N2 purging
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摘要: 费托合成可以将煤炭或者生物质气化得到的合成气转化为α-烯烃等重要的化工产品。研究将费托合成和氮气吹扫操作组合成一脉冲过程, 在稳定的操作状态下保证费托合成和氮气吹扫交替进行。在传统的费托合成条件下(反应气速为2 000 h-1, 温度为497 K, 压力为2.0 MPa, 氢碳体积比为2.0) 考察了Fe-Co催化剂在脉冲过程中费托合成的活性和选择性。结果表明, N2吹扫温度和压力分别为517 K和0.2 MPa下的费托合成的C3烯烷比是未脉冲的相同反应条件下的九倍左右。同时, 反应过程中CH4的选择性和CO的转化率有所下降。在此基础上, 通过间歇反应在固定床反应器中进行该脉冲过程, 实验结果表明, 利用脉冲操作在费托反应中可以获得更高的烯烃选择性。Abstract: The Fischer-Tropsch synthesis has offered an alternative way to convert coal and biomass into chemicals such as α-olefins via sygas comprised of H2 and CO. A pulse process switching between Fischer-Tropsch synthesis and N2 purging was carried out when the Fischer-Tropsch synthesis became stable in the fixed bed reactor. The activity and selectivity over Fe-Co catalyst for α-olefins in Fischer-Tropsch synthesis reaction were measured under the normal conditions of 2.0 MPa, 497 K, 2 000 h-1 and H2/CO volume ratio of 2.0. It was found that the olefin to paraffin ratio of C3 for Fe-Co catalyst purged at 517 K and 0.2 MPa was almost nine times higher than that of the fresh one without purging under the same reaction conditions, and the CH4 selectivity and CO conversion decreased after purging. Two possible reasons were proposed to explain these phenomena. Moreover, a batch experiment by the pulse process in fixed bed reactor was performed. Notably, a high olefins yield was obtained via the pulse process during the Fischer-Tropsch synthesis.
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Key words:
- alpha olefins /
- pulse process /
- N2 purging /
- Fischer-Tropsch synthesis
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Figure 1 Experiment setup of the FTS
①: H2 cylinder; ②: N2 cylinder; ③: syngas cylinder; ④: regulators; ⑤: mass flow controllers; ⑥: shut-off valves; ⑦: fixed bed reactor; ⑧: hot trap; ⑨: cold trap; ⑩: gas chromatograph
Figure 2 Dependences of the O/P for C3 on the reaction time during FTS after different purging process
(a): 0.2 MPa; (b): 1.0 MPa; (c): 2.0 MPa
▲: 517 K; ○: 507 K; ■: 497 K; ▽: without purging
Figure 3 Dependences of the CO conversion on the reaction time during FTS after different purging process
(a): 497 K; (b): 507 K; (c): 517 K
■: without purging; ○: 2.0 MPa; ▲: 0.2 MPa
Figure 4 Dependences of the CH4 selectivity on the reaction time during FTS after different purging process
(a): 497 K; (b): 507 K; (c): 517 K
■: without purging; ○: 2.0 MPa; ▲: 0.2 MPa
Figure 5 Comparison of the time dependence of production in propylene after purging during FTS among different purging process
■: 0.2 MPa, 517 K; ○: 1.0 MPa, 517 K; ▲: 0.2 MPa, 507 K; ▽: 1.0 MPa, 507 K; ◆: without purging
Figure 6 Dependence of the O/P for C3 on the reaction time during FTS after only one purging with purging temperature of 517 K and purging pressure of 0.2 MPa
Figure 7 Time dependence of CO conversion during FTS after only one purging at the purging temperature of 517 K and the purging pressure of 0.2 MPa
Table 1 Comparison of amount of propylene for different batch
Reaction time t/h Amount of propylene /mmol first batch second batch third batch 48 1.443 1.452 1.435 96 5.557 1.452 1.435 144 9.518 12.878 12.959 192 13.290 16.995 12.959 240 17.599 21.122 25.548 288 21.762 25.224 25.548 336 25.739 29.376 37.423 384 29.711 33.573 37.423 432 33.672 37.748 50.297 
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