Study on the reaction characteristics of tar model compounds with an Fe-based oxygen carrier
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摘要: 本研究以生物质/煤的焦油模型化合物（TMCs）为研究对象，在两阶段固定床实验上探究了铁基氧载体（70%Fe2O3/30%Al2O3）对TMCs的转化特性，考察了不同TMCs的反应性及其转化的影响因素。研究发现，TMCs与氧载体的反应活性为：苯酚>蒽>萘，且苯酚转化生成积炭的比例最多（64%），而萘转化生成积炭的比例最少（40%）；氧载体与萘的反应程度相对较高，但容易导致氧载体的烧结。此外，积炭表征显示萘生成的积炭在三种TMCs中具有最高的稳定性。增加氧载体的用量和提高反应温度不仅有利于萘和蒽的进一步转化，而且能够增加气相产物中CO2的分率。由于苯酚分子具有较高的反应活性及较强的裂解效果导致其转化率随氧载体用量和反应温度的增加变化较小，然而，较高的反应温度（1000 ℃）导致焦油发生严重的裂解现象并产生大量积炭。三次循环实验结果表明与萘反应的氧载体失活最为严重。Abstract: This work investigated the conversion characteristics of iron-based oxygen carrier (70%Fe2O3/30% Al2O3) with TMCs in a two-stage fixed-bed reactor using tar model compounds (TMCs) of biomass/coal, and evaluated the reactivity of different TMCs and the factors affecting their conversion. It was found that the reaction degree of TMCs with oxygen carrier was phenol>anthracene>naphthalene, and the conversion of phenol to carbon deposition was the highest (64%), while the conversion of naphthalene to carbon deposition was the lowest (40%); the degree of reaction between oxygen carriers and naphthalene is relatively high, but easily led to the sintering of oxygen carrier. Besides, activity characterization of the carbon deposition showed that the carbon deposition generated from naphthalene had the highest stability among the three TMCs. Increasing the amount of oxygen carrier and reaction temperature is beneficial to the further conversion of naphthalene and anthracene, and can also can increase the fraction of CO2 in gaseous products.The high reaction activity and strong cracking effect of phenol lead to a small change in the conversion rate with increasing the amount of oxygen carrier and reaction temperature, however, higher reaction temperature (1000 ℃) can lead to severe cracking of the tar to generate a large amount of carbon deposition. The results of the cycle experiment showed that the oxygen carriers reacting with naphthalene was most severely deactivated.
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图 2 不同TMCs的转化率及产物分布
Figure 2 Conversion and product distribution of different TCMs (t=800 ℃，φ=0.75)
图 3 与相关TMCs反应后氧载体的XRD谱图
Figure 3 XRD diagram of oxygen carrier after reaction with relevant TMCs (t=800 ℃, φ=0.75)
图 4 与相关TMCs反应前后氧载体的SEM照片
Figure 4 SEM images of the oxygen carrier before and after reaction with relevant TMCs: (a) Fresh oxygen carriers; (b) Reacted with phenol; (c) Reacted with naphthalene; (d) Reacted with anthracene
图 5 与不同TMCs反应后氧载体的拉曼光谱谱图
Figure 5 Raman spectra of oxygen carrier reacted with different TMCs
图 6 与不同TMCs反应后氧载体的（a）升温曲线和（b）失重速率
Figure 6 Temperature ramping curve (a) and weight loss rate (b) of oxygen carrier after reaction with different TMCs
图 8 不同反应条件下TCMs的产物分布
Figure 8 Product distribution of TCMs under different reaction conditions: (a) Phenol; (b) Naphthalene; (c) Anthracene
图 9 不同反应条件下晶格氧的利用率
Figure 9 Utilization rate of lattice oxygen under different reaction conditions
图 10 不同循环次数下相关TMCs的转化率和产物分布
Figure 10 Conversion and product distribution of related TMCs for different cycle times (t=900 ℃, φ=1.5)
表 1 在两阶段固定床反应器中进行的实验操作参数
Table 1 Summary of experimental operating parameters carried out in the 2-stage fixed bed reactor
Operating condition 1st stage 2st stage Feedstock TMCs OC: 70% Fe2O3/30% Al2O3
(0.3−0.8 mm)Temperature /℃ 200 800, 900, 1000 Oxygen/carbon ratio (φ) φ= 0.75, 1.5
(Corresponding weight of OC = 1.25, 2.5 g)
(Corresponding bed height of OC = 0.25, 0.5 cm)Superficial velocity
Weight hourly space velocity (WHSV)0.007 m/s
0.047–0.093 h−1
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表 2 与相关TMCs反应前后氧载体的比表面积及孔分布
Table 2 Specific surface area and pore distribution of oxygen carriers before and after reaction with relevant TMCs
Sample Specific surface area
/(m2·g−1)Total pore volume
/(cm3·g−1)Pore size distribution micropore
(<2 nm,%)mesopore
(2–50 nm,%)macropore
(>50 nm,%)Fresh oxygen carrier 11.3 0.062 0.75 74.71 24.54 Reacted with phenol 12.5 0.055 1.34 75.38 23.28 Reacted with naphthalene 9.7 0.050 0.65 75.28 24.07 Reacted with anthracene 10.4 0.058 0.70 73.86 25.44
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表 3 热重实验前后氧载体样品中碳的定量分析
Table 3 Quantitative analysis of carbon in oxygen carrier before and after thermogravimetric test
Phenol w/% Naphthalene w/% Anthracene w/% Before reaction 2.37 0.79 1.89 After reaction 0.37 0.22 0.29
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表 4 TMCs在不同反应条件下的焦油产物
Table 4 Tar products of TMCs under different reaction conditions
TMCs Reaction products Peak area of various tar component ( × 106） φ = 0.75 (t=800 ℃) φ = 1.5 (t=800 ℃) φ = 1.5 (t=900 ℃) φ = 1.5 (t=1000 ℃) Phenol benzene 14.4 5.01 0.23 0.11 toluene 0.15 0.09 − − styrene 0.14 0.10 − − naphthalene 2.95 2.48 1.23 − Naphthalene benzene 7.79 7.76 3.31 0.26 toluene 0.15 0.09 − − styrene − 0.21 0.45 − naphthalene 258 224 121 0.03 1,1'-binaphthalene 3.33 5.58 3.34 − Anthracene benzene 3.08 3.96 4.65 − toluene 0.17 0.64 0.93 − styrene 0.12 0.41 0.52 − naphthalene 2.97 3.67 4.21 − anthracene 67.7 46.5 17.4 −
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