Role of carbon-oxygen complexes on low temperature reduction of NO by coal char

doi:10.11949/0438-1157.20211692

Abstract

Abstract:

The reduction of NO by Shenmu coal char was studied at 450℃, and the relationship between the influencing factors of coal char denitrification and its surface carbon-oxygen functional groups was explored by Raman, FT-IR, XPS and other analytical methods. Combining the results of isothermal experiments and characterizations, close connection between influencing factors and carbon-oxygen complexes was revealed. The effect of coal char preparation temperature, oxygen concentration in flue gas as well as influence of metallic elements could be in connection with carbon-oxygen complexes on coal char surface. More specifically, lowering pyrolysis temperature, increasing oxygen concentration, and loading metals were all conducive to the retention and formation of thermally stable C—O species on coal char surface. Strong linear relationship was discovered via XPS method between thermally stable C—O species and experimental evaluation indexes (R²>0.96). Carbon-oxygen complexes, especially thermally stable C—O compounds, played a key character in NO reduction by coal char.

Key words: coal char, nitric oxide, reduction, multiphase reaction, surface, C(O) complexes

摘要：

在450℃对神木煤制半焦还原NO进行研究，采用Raman、FT-IR、XPS等分析方法探究了半焦脱硝影响因素与其表面碳氧官能团的关系。结果表明：热解制焦温度、烟气中氧气浓度以及负载金属对脱硝效果的影响都与半焦表面碳氧官能团有关，降低热解温度、增大氧气浓度、负载金属均有利于增加C—O官能团。采用XPS表征对金属负载半焦表面的碳氧官能团进行分析，发现热力学相对稳定的C—O官能团含量与脱硝指标之间存在明显的线性关系(R²>0.96)。研究进一步揭示了热力学稳定的C—O官能团在半焦脱硝过程的重要地位。

关键词: 煤焦, 氮氧化物, 还原, 多相反应, 表面, 碳氧官能团

CLC Number:

TQ 536.9

Jiayi WANG, Chuigang FAN, Songgeng LI. Role of carbon-oxygen complexes on low temperature reduction of NO by coal char[J]. CIESC Journal, 2022, 73(5): 2140-2148.

王佳怡, 范垂钢, 李松庚. 碳氧官能团对煤焦低温还原NO的影响[J]. 化工学报, 2022, 73(5): 2140-2148.

Figures/Tables 14

Table 1 Proximate and ultimate analysis of coal char and BET analysis

工业分析/%(质量，ad)						元素分析/%(质量，ad)					BET表征
M	A	V	FC		C		H	N	O^①	S	比表面积/(m²·g^-1)	孔容/(cm³·g^-1)	平均孔径/nm
0.76	6.64	13.95	78.66		85.38		2.34	1.41	3.35	0.13	14.59	0.018	5.026

Table 2 Metallic oxides mass fraction of char ash

Fe₂O₃/%	Al₂O₃/%	CaO/ %	MgO/%	SiO₂/ %	TiO₂/%	SO₃/ %	K₂O/ %	Na₂O/%	合计/%
6.69	17.10	22.92	1.85	38.39	0.88	9.02	0.75	0.67	98.30

Fig.1 Schematic of the experimental system

Fig.2 Effect of pyrolysis temperature on NO-char reduction

Fig.3 Raman spectrum of char pyrolyzed at 450, 550 and 650℃

Fig.4 Effect of oxygen content on NO conversion

Fig.5 FT-IR spectrum of char reacted with simulated flue gas with different oxygen concentration

Fig.6 Curve-fitting FT-IR spectrum of char after reacted with simulated flue gas with 5%(vol) O2

Table 3 Oxygen-containing groups contents of different chars

状态	反应气氛	A_C—O/A_arom	A_C $?$ _O/A_arom
反应前	—	0	0.49
反应后	0%(体积)O₂	0.12	1.76
	1%(体积)O₂	0.43	2.62
	5%(体积)O₂	0.63	2.64

Table 3 Oxygen-containing groups contents of different chars

状态	反应气氛	A_C—O/A_arom	A_C $?$ _O/A_arom
反应前	—	0	0.49
反应后	0%(体积)O₂	0.12	1.76
	1%(体积)O₂	0.43	2.62
	5%(体积)O₂	0.63	2.64

Fig.7 Effect of loading metals on NO-char reaction

Fig.8 Outlet CO x concentration of original SM char and metal loaded chars

Fig.9 C1s and K2p XPS spectra for chars reacted

Table 4 Functionalities of chars estimated by XPS measurement

半焦	C—C, C—H		C—O		R₂C $? ?????$ O		O $? ?????$ C—O		C—K
半焦	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)
SM	284.8	81.92	286.3	12.10	287.5	0.41	289.0	4.61	296.2	0.96
SM-2%MgO	284.8	59.46	286.3	12.14	287.5	23.01	289.0	0.86	296.2	4.53
SM-2%K₂O	284.8	57.42	286.3	17.05	287.5	0.00	289.0	13.96	296.2	11.56
SM-0.5%Na₂O	284.8	74.45	286.3	15.31	287.5	0.49	289.0	8.97	296.2	0.79

Table 4 Functionalities of chars estimated by XPS measurement

半焦	C—C, C—H		C—O		R₂C $? ?????$ O		O $? ?????$ C—O		C—K
半焦	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)	BE/eV	Prop./ %(mol)
SM	284.8	81.92	286.3	12.10	287.5	0.41	289.0	4.61	296.2	0.96
SM-2%MgO	284.8	59.46	286.3	12.14	287.5	23.01	289.0	0.86	296.2	4.53
SM-2%K₂O	284.8	57.42	286.3	17.05	287.5	0.00	289.0	13.96	296.2	11.56
SM-0.5%Na₂O	284.8	74.45	286.3	15.31	287.5	0.49	289.0	8.97	296.2	0.79

Table 5 Correlation coefficients of C（O） complexes with NO-char evaluating indexes

评价指标	C—O	R₂C $? ?????$ O	O $? ?????$ C—O
X	0.9989	0.2921	0.9115
S	0.9999	0.1025	0.6096
CO/CO _x	0.9662	0.1923	0.7920

Table 5 Correlation coefficients of C（O） complexes with NO-char evaluating indexes

评价指标	C—O	R₂C $? ?????$ O	O $? ?????$ C—O
X	0.9989	0.2921	0.9115
S	0.9999	0.1025	0.6096
CO/CO _x	0.9662	0.1923	0.7920

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