Preparation and analysis of carbon aerogel microspheres based on coal tar pitch

doi:10.11949/0438-1157.20221095

Abstract

Abstract:

Coal tar pitch is a complex mixture composed of highly condensed aromatic compounds, which has the advantages of high carbon content, widely availability, and low price. It is regarded as one of the promising precursors in the synthesis of various functional carbon materials. Using coal tar pitch as raw material and furfural as a cross-linking agent, pitch-furfural gel is formed by the cross-linking reaction under the catalysis of sulfuric acid, then, the carbon aerogel microspheres were obtained after ambient-pressure drying and carbonization. The effects of the coal tar pitch to solvent, crosslinking agent, and catalyst ratios on the gel degree of carbon gel and carbon aerogel microspheres density were discussed. It was found that the optimal ratio of pitch to solvent was 0.5 g/ml, pitch to crosslinking agent was 0.10 g/ml, and pitch to catalyst was 5 g/ml. The density of carbon aerogel spheres was 0.24 g/cm³ after carbonization. The microstructure of carbon aerogel microspheres is generated by the accumulation of spherical particles, according scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analyzer (TG) were used to examine the structure evolution of pitch-furfural gel during the gelation process, as well as the production mechanism of pitch-furfural aerogel.The pore structure of the carbon aerogel spheres was dramatically improved after CO₂ activation. With the increase of activation temperature and activation time, the specific surface area and pore diameter of the obtained samples were continuously increased, and mesopores with pore diameter of 2—3 nm were gradually formed. The samples activated in a CO₂ atmosphere at 900℃ for 4 h and 950℃ for 2 h has specific surface areas of 2540 and 2852 m²/g, respectively. The microstructure of the carbon aerogel microspheres was unaffected, and the micromorphology of spherical particles was preserved, the particle shape was regular and the surface was smooth.

Key words: coal tar pitch, crosslinking, carbon dioxide activation, carbon aerogel microspheres, formation mechanism

摘要：

煤沥青是由多环芳烃组成的复杂混合物，其具有含碳量高的特点，是合成各种功能性碳材料的优质前体之一。以煤焦油沥青为原料、糠醛为交联剂，在硫酸催化作用下反应形成沥青-糠醛凝胶，进而经过常压干燥和碳化处理得到碳气凝胶，探讨了煤焦油沥青与溶剂、交联剂和催化剂的比例对沥青-糠醛凝胶的凝胶化程度以及碳气凝胶微球密度的影响。扫描电镜（SEM）结果显示，碳气凝胶微球的微观结构是由球状颗粒堆积而成；傅里叶红外光谱仪（FTIR）和同步热分析仪（TG）解析了沥青-糠醛凝胶在凝胶过程中的结构演变，及形成机理；CO₂活化后，碳气凝胶微球的孔隙结构得到明显改善，并保留了球状颗粒的微观形貌，且颗粒形状规整、表面光滑。

关键词: 煤焦油沥青, 交联, 二氧化碳活化, 碳气凝胶微球, 形成机理

CLC Number:

TQ 536

Huifang NIU, Lunjing YAN, Peng LYU, Xufeng ZHANG, Meijun WANG, Jiao KONG, Weiren BAO, Liping CHANG. Preparation and analysis of carbon aerogel microspheres based on coal tar pitch[J]. CIESC Journal, 2022, 73(12): 5605-5614.

牛卉芳, 闫伦靖, 吕鹏, 张旭峰, 王美君, 孔娇, 鲍卫仁, 常丽萍. 煤焦油沥青基碳气凝胶微球的制备及分析[J]. 化工学报, 2022, 73(12): 5605-5614.

Figures/Tables 14

Table 1 Proximate and ultimate analyses of coal tar pitch

Proximate analysis/%(质量)			Ultimate analysis/%(质量)，daf
M_ad	A_d	V_daf	C	H	O^①	N	S
0.27	0.09	76.22	85.70	6.54	6.44	1.10	0.22

Table 2 Orthogonal test for preparing carbon aerogel microspheres gel

No.	煤焦油沥青与交联剂比例/ (g/ml)	煤焦油沥青与溶剂比例/(g/ml)	煤焦油沥青与催化剂比例/ (g/ml)	密度/(g/cm³)
1	0.9	0.06	3	0.218
2	0.9	0.08	5	0.179
3	0.9	0.10	8	0.231
4	0.9	0.12	10	0.248
5	0.7	0.06	5	0.189
6	0.7	0.08	3	0.224
7	0.7	0.10	10	0.228
8	0.7	0.12	8	0.231
9	0.5	0.06	8	0.165
10	0.5	0.08	10	0.179
11	0.5	0.10	3	0.259
12	0.5	0.12	5	0.262
13	0.3	0.06	10	0.130
14	0.3	0.08	8	0.163
15	0.3	0.10	5	0.207
16	0.3	0.12	3	0.250
K₁_j	0.876	0.702	0.951
K₂_j	0.872	0.745	0.837
K₃_j	0.865	0.925	0.790
K₄_j	0.750	0.991	0.785
k₁_j	0.219	0.176	0.238
k₂_j	0.218	0.186	0.209
k₃_j	0.216	0.231	0.198
k₄_j	0.188	0.248	0.196
R	0.031	0.072	0.042

Fig.1 Samples prepared by adding different crosslinking agents

Fig.2 FT-IR spectra of cross-linked raw materials and carbon gels obtained with different gel time

Fig.3 TG and DTG curves of cross-linked raw materials and carbon gels obtained with different gel time

Fig.4 SEM images of the papered coal tar pitch based carbon aerogel microspheres

Fig.5 N2 isothermal adsorption and desorption curves and pore size distribution of prepared coal tar pitch based carbon aerogel microspheres

Table 3 Pore structure parameters of prepared coal tar pitch based carbon aerogel microspheres

S_BET/(m²/g)	S_t-plot/ (m²/g)	V_total/ (cm³/g)	V_micro /(cm³/g)	V_meso/(cm³/g)
14.98	10.22	0.02	0	0.02

Fig.6 N2 isothermal adsorption and desorption curves and pore size distribution of carbon aerogels microspheres prepared at different activation temperatures

Table 4 Pore structure parameters of carbon aerogels microspheres at different activation temperatures

Sample

S_BET/

(m²/g)

S_t-plot/

(m²/g)

V_total/

(cm³/g)

V_micro/

(cm³/g)

V_meso/

(cm³/g)

Fig.7 N2 isothermal adsorption and desorption curves and pore size distribution of carbon aerogels microspheres prepared at different activation time

Table 5 Pore structure parameters of carbon aerogels microspheres with different activation time

Sample

S_BET/

(m²/g)

S_t-plot/

(m²/g)

V_total/

(cm³/g)

V_micro/

(cm³/g)

V_meso/

(cm³/g)

Fig.8 SEM images of carbon aerogels microspheres before[(a)—(d)] and after[(e)—(h)] activated by CO2

Fig.9 Formation of carbon gel from coal tar pitch and furfural

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