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催化提质原位煤热解焦油的研究
Alternative TitleCatalytic upgrading of in-situ coal pyrolysis tar
韩江则
Subtype博士
Thesis Advisor许光文
2014-05
Degree Grantor中国科学院研究生院
Degree Discipline化学工艺
Keyword热解   催化裂解   焦油品质   半焦基催化剂   催化剂载体
Abstract煤焦油是煤炭在热解,焦化,气化过程中产生的液体物质,其主要组分为脂肪烃,芳香族化合物及其他有机化合物的混合物。目前运行的热解工艺所得焦油中沸点高于360 ℃的重质组分的质量分数高达50 wt.%。焦油中的重质组分不仅降低了焦油的品质,而且容易冷凝造成后续管路的堵塞,影响系统的正常运行。采用催化裂解的方法可将焦油中的重质组分在特定催化剂的作用下裂解为沸点低于360 ℃的轻质组分。 焦油的二次催化裂解是将原料的热解反应和焦油的催化裂解反应分别在不同的装置内或者在同一装置的不同部位进行。这可以单独控制各段的反应温度和气氛保证热解反应和催化裂解反应均在各自最佳的操作条件下进行,使更换和回收催化剂可以更方便地进行,反应结束后热解半焦和催化剂可直接处理,不再需要进行催化剂和半焦的分离操作。 本论文的主要研究内容是对煤热解产生的焦油进行原位二次催化裂解以获得高品质热解焦油。在两段反应装置中首先研究了半焦的表面积及灰分对煤热解产物的催化裂解作用。在此基础上,以半焦和γ-Al2O3为催化剂载体,负载一定量的金属制备相应的催化剂并考察其对煤热解焦油催化裂解的效果。最后在两段流化床内进行连续性实验,验证我们所开发催化剂的催化裂解效果。获得如下主要结果: (1) 采用半焦为催化剂对煤热解产物进行二次催化裂解,与煤直接热解相比热解焦油的总收率下降,热解气体收率提高,但焦油中的轻质组分含量有明显提高,轻质焦油收率基本保持不变或略有增加。其反应的总体效果是将焦油中重质组分裂解为轻质焦油和燃气。 (2) 半焦的比表面积和灰分都对煤热解产物的催化裂解有一定影响。在比表面积较低时,半焦中的灰分对煤热解产物的催化裂解作用比较明显;随着比表面积的增加,灰分的影响越来越弱,半焦比表面积的影响越来越明显。过高的比表面积使半焦的裂解能力增强,过高的催化裂解能力不但可以将焦油中的重质组分裂解为轻质焦油和气体,同时也会使更多的轻质组分被裂解,使得焦油中的轻质组分含量大幅上升,但轻质焦油的收率明显下降。半焦的比表面积越大,在焦油裂解过程中产生的积碳越多。 (3) 以半焦作为催化剂载体负载一定量的金属时,其催化裂解活性有所增强,负载不同金属的半焦催化剂具有不同的催化活性。当Ni-char催化剂添加助剂Ce时,催化裂解效果最好,可使焦油中更多的重质组分转化为轻质焦油组分。在最佳实验条件下,轻质焦油(沸点低于360 ℃的馏分)的含量可由直接热解所得焦油的52 wt.% 提高至75 wt.%,轻质焦油的收率提高了10.1%。焦油中的H/C摩尔比提高了61.7%,N、S等污染元素的含量分别下降50.5%和45.8%。 (4) 当以γ-Al2O3作为催化剂载体时所制备的催化剂对焦油的催化裂解能力远高于半焦载体,最终使大量的焦油组分裂解为气体和少量轻质焦油,轻质焦油的收率大幅下降。γ-Al2O3作为载体时其较强的催化裂解性能归因于载体表面发达的孔道结构和载体本身所具有的较强酸性。但是,γ-Al2O3表面发达的孔道结构使其更容易产生积碳,造成催化剂易失活。不同催化剂使用寿命的考察表明:添加助剂Ce后的催化剂抗积碳能力有所增强,催化剂的使用寿命有所增加,但相对于Ce-Ni-char催化剂,Ce-Ni-Al2O3催化剂更容易失活,主要由于后者催化剂更容易积碳所造成的。 (5) 采用NH3-TPD对催化剂的酸性分析表明,Ni-char 催化剂上存在的两个峰分别代表较弱的L酸和较强的B酸,而半焦本身并没有酸性。助剂Ce的添加使Ni-char催化剂上的酸性位分布发生改变,在Ce-Ni-char催化剂上仅仅存在一个L酸峰位,但其酸性位的数量明显高于Ni-char催化剂。对于Ce-Ni-Al2O3催化剂,其酸性位数量明显高于Ce-Ni-char催化剂,这是由于γ-Al2O3本身就具有一定的酸性,致使该催化剂的裂解能力较强。催化剂的XRD分析结果表明金属Ni在催化剂上以单质形式存在,助剂Ce以CeO2形式存在。催化剂表面形貌分析表明Ce的添加可以使催化剂上负载的金属分布更加均匀,避免了Ni颗粒聚集而产生强的酸性位。 (6) 在两段流化床反应器中,采用不同催化剂对煤热解焦油进行了二次催化裂解的连续性实验,对不同催化剂的催化裂解效果进行验证。结果表明,随着质量空速(煤加料速率与催化剂加入量的比)的增加,焦油的收率逐渐增加,所得焦油中轻质组分的含量逐渐下降。当煤在下段流化床中的热解温度为600 ℃,上段流化床中催化剂层的裂解温度为500 ℃,质量空速为5 h-1时,采用Ce-Ni-char催化剂可使轻质焦油的含量由直接热解所得焦油的55 wt.%提升至72 wt.%,轻质焦油的收率提高了4.5%。相同实验条件下,采用Ce-Ni-Al2O3催化剂作用后焦油中轻质焦油的含量由直接热解所得焦油的55 wt.%提升至77 wt.%,但轻质焦油的收率却降低了18.0%。相对于Ce-Ni-char催化剂,Ce-Ni-Al2O3催化剂对焦油的裂解能力更强,虽然可以使焦油中的轻质组分含量显著增加,但轻质焦油收率下降明显。两段流化床的连续性实验结果表明,采用Ce-Ni-char催化剂的催化裂解效果最好,这与前述的两段固定床小试实验结果一致。
Other AbstractCoal tar derived from coal pyrolysis, coking, gasification and many other technologies is a complex mixture of hydrocarbons such as aliphatics, aromatics and other organic chemicals. The coal tar usually has high content of heavy components with boiling points above 360 ℃ (pitch in fact), for example, it may account for above 50 wt.% of the total tar mass. The heavy components in tar are difficult to be treated and it may lead to operational troubles by blocking and fouling the downstream equipment such as engines and turbines. On the other hand, the heavy components in tar can be cracked into valuable desired oil components over selected catalysts. The secondary catalytic cracking of tar is conducted in different reactor or the different parts of the same equipment, in which the coal pyrolysis and tar catalytic cracking reactions occurre separately. So the reaction temperatures and atmospheres for coal pyrolysis and tar cracking can be controlled independently, and the replacement and recovery of the catalyst can be handled more conveniently. After the coal pyrolysis and tar catalytic cracking the resulted char and spent catalyst have no need for separation and can be treated directly. In this study the in-situ coal tar catalytic upgrading was conducted to get high quality tar. Firstly, the catalytic cracking of coal pyrolysis tar was investigated in a dual-stage fixed bed reactor over char with different surface area and the catalytic cracking effect of ash in char was also studied. And then the metal supported on char or γ-Al2O3 were adopted asthe catalysts. Finally, a continuous two-stage fluidized bed was used to verify the catalytic effects of the catalysts developed by ourselves. The following summarizes the major research results. (1) In comparison with the direct pyrolysis of coal, the coal pyrolysis with a secondary catalytic upgrading over char catalyst resulted in lower total tar yield and higher non-condensable gas yield, but the fraction of light tar (boiling point < 360 ℃) obviously increased, led to the yield of light tar remained constantly or increased slightly. The catalytic secondary cracking in coal pyrolysis works mainly to convert heavy oil components into light oil and pyrolysis gas. (2) Both of the surface area and ash in char have catalytic effects on the coal pyrolysis products. The catalytic effect of the ash in char was obvious when the char surface area was small, as the surface area increasing the catalytic effect of ash became weaker. The char owned larger surface area had stronger catalytic ability, under the effect of which not only the pitch was cracked into light tar and gas, but also some light tar was cracked, all of which led to the light tar yield decreased obviously and more coke deposited on the char. (3) When the metal-impregnated char was adopted as catalyst, the catalytic activity increased and varied with different impregnated metals. The best results were obtained over the Ni-char catalyst doped with Ce additive, which can convert more pitch into light tar. At the optimal operating conditions, the realized light tar fraction elevated from 52 wt.% to 75 wt.% and its yield increased by 10.1% in comparison with direct coal pyrolysis without catalyst. The corresponding increase in the H/C molar ratio of the tar was 61.7%. The upgrading effect also lowered the contents of element N and S in the resulting tar by 50.5% and 45.8%, respectively. (4) When the γ-Al2O3 was chosen as the catalyst support the catalytic ability was much higher than the char support, which resulted in lots of tar fractions were cracked into gas and light tar. The high catalytic ability attributed to the developed pore structure and stronger acidity on the γ-Al2O3support. However, the developed pore structure made coke deposition easily, which may lead to the catalyst deactivation easily. The service lives of different catalyst declared that the Ce additive could enhance the anti-coke ability and m
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15526
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
韩江则. 催化提质原位煤热解焦油的研究[D]. 中国科学院研究生院,2014.
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