Hydrate-based CO2 capture from IGCC syngas with TBAB and nano

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Hydrate-based CO2 capture from IGCC syngas with TBAB and nano Al2O3 Ze-Yu Li, Zhi-Ming Xia, Xiao-Sen Li, Zhao-Yang Chen, Jing Cai, Gang Li, and Tao Lv Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03605 • Publication Date (Web): 09 Jan 2018 Downloaded from http://pubs.acs.org on January 13, 2018

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Energy & Fuels

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Hydrate-based CO2 capture from IGCC syngas with TBAB and nano

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Al2O3

3 4 5 6 7 8 9 10 11 12 13 14 15 16

Ze-Yu Lia,b,c,d,e, Zhi-Ming Xiaa,b,c,d, Xiao-Sen Lia,b,c,d*, Zhao-Yang Chena,b,c,d, Jing Caia,b,c,d, Gang Lia,b,c,d, Tao Lva,b,c,d a

Guangzhou institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, 510640,

People’s Republic of China b

CAS Key laboratory of gas hydrate, Guangzhou, 510640, People’s Republic of China

c

Guangdong Provincial Key laboratory of New and Renewable Energy Research and Development,

Guangzhou, 510640, People’s Republic of China d

Guangzhou Center for Gas Hydrate Research, Chinese Academy of Sciences, Guangzhou, 510640,

People’s Republic of China e

University of Science and Technology of China, Nano Science and Technology Institute, Suzhou

215123, People’s Republic of China

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ABSTRACT: Hydrate-based CO2 capture and/or H2 purification from IGCC syngas has been

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more and more attractive technology in both environmental and clean energy fields. This

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work focused on both microcosmic and macroscopic studies for the CO2/H2 hydrate formation

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process with synergic additives comprised Tetra-n-butyl Ammonium Bromide (TBAB) and

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nano Al2O3. The experiments were carried out with 0.5 wt % nano Al2O3 and 1, 5, 10 and 11

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wt % TBAB, respectively. The microcosmic study shows that, with the synergic additives, the

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CO2/H2 mixture hydrate formed mainly on the nano Al2O3 surface and formed semiclathrate

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structure. Additionally, the macroscopic study shows that the synergic additives could

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remarkably promote the gas uptake and separation efficiency. Noteworthy, compared with

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unitary TBAB, THF and CP, the synergic additives could increase the gas uptake for the

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CO2/H2 hydrate formation process by approximate 43.62%, 230.56% and 173.27%,

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*

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E-mail: [email protected].

To whom correspondence should be addressed: Telephone: +86 20 87057037. Fax: +86 20 87057037.

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respectively. The experimental results indicate that the synergic effect of TBAB and nano

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Al2O3 is helpful for hydrate-based CO2 capture from IGCC syngas.

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1. INTRODUCTION

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Global warming resulted by the increasing emission of greenhouse gas is widely

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considered to be the urgent problem in the 21st century.

1

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cycle (IGCC), as one of new clean energy technologies, has prominent contribution on

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retarding the climate change. The essential of this approach, in fact, is that the CO2 capture

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from CO2/H2 mixture gas. Removal of CO2 from mixture gas can be achieved by a serious of

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technologies such as physical absorption, chemical adsorption, membranes, cryogenic

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distillation, and so on. 2-5 However, these methods have the individual issues of large energy

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consumption, apparatus corrosion, easily caused second pollution or low capacity, and so

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forth. Hence, it is necessary to develop a cost-effective and environment-friendly

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capture/separation technology for CO2 capture and separation.

Integrated gasification combined

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Hydrate-based CO2 capture from IGCC is one of the new technologies which based on gas

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hydrate formation process to capture CO2 and purify H2. Gas hydrates are nonstoichiometric

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compounds existing in lattice structures which are made up by host molecules and guest

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molecules.

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component between hydrate phase and gaseous phase. For instance, the hydrate formation

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pressure of H2 is 300 MPa while that of CO2 is 2.91 MPa at 280 K. 7 Spencer et al. 8 made an

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economic assessment, and reported that the cost for capturing CO2 from CO2/H2 syngas by the

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hydrate methods is about 10 dollars per ton CO2, which is pretty cost-effective.

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6

The basis for the hydrate-based CO2 capture is the selective partition of CO2

However, for industrial utilization, hydrate-based CO2 capture still need further study to 2

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enhance the gas storage and to accelerate the gas hydrate formation rate. 9, 10 In order to lower

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the hydrate formation pressure and improve the hydrate formation rate, some additives such

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as TBAB, 11-13 THF (Tetrahydrofuran), 14-16 and CP (Cyclopentane) etc. 17-19 were proposed to

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enhance the gas hydrate formation process. Kamata et al.

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semiclathrate hydrate with water molecules, and it was suitable for small guest gas molecules

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separation. Li et al.

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pure system of TBAB, the experimental results indicated that it has better gas storage and

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separation efficiency for TBAB system than pure water system. Duc et al.

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0.29 mol % TBAB was the optimum concentration for reducing CO2 composition from

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CO2/N2 mixture. What else, THF hydrates have pretty well cavity structure which are suitable

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for guest gas molecules storage. Lee et al.

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concentration

from

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non-environmental-protection chemical and easily cause environment pollution. As for the

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study on CP by Zhang et al. 23, they found that the hydrate formation and dissociation could

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significantly enrich CO2 from 40 to 98 mol % at 282 K for pure CP system. Furthermore, Li

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et al.

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capture from IGCC syngas with 5 vol% CP is 3 mmol gas/mol.

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24

11

for

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reported the TBAB could form

studied on hydrate-based CO2 separation from CO2/H2 syngas in the

the

CO2

capture

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presented that

reported that 1 mol %THF was the optimum CO2/H2

syngas.

Whereas,

THF

is

reported that, at 4.5 MPa and 273.15 K, the gas uptake for the hydrate-based CO2

However, besides the above additives, heat and mass transfer is demonstrated to be the 25-27

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most difficult and significant for the gas hydrate formation process.

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researchers proposed the idea that using nano fluid to enhance the heat and mass transfer

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processes. Park et al.

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the gas uptake of methane hydrate by 300 %. And then the effect of the MWCNTs was

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Recently, some

reported that the muti-carbon nanotubes (MWCNTs) could increase

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compared with the oxide muti-walled carbon nanotubes (OWMCNTs) on the methane hydrate

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formation process in terms of gas uptake, they found that the OMCNTs had a better

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performance in gas uptake. 29 Kakati et al. 30 used the nano Al2O3 and Sodium dodecyl sulfate

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(SDS) to enhance the CH4 gas hydrate formation process, and demonstrated that the gas

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uptake of 0.8 wt % nano Al2O3 and 0.03 wt % SDS was 2.5 times more than that of pure water.

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Choi et al. 31 found that the gas uptake of the 0.2 wt % nano Al2O3 and 0.6 wt % SDS system

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was 3.74 times higher than that of 10 wt % THF system, they explained that the nano Al2O3

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promoted the solution system thermal conductivity, while SDS reduced the surface tension of

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CO2 and water molecules. Indeed, the research for hydrate-based CO2 capture from IGCC

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syngas with nano fluid is still faultiness, and need further study. As a porous medium, nano

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Al2O3 has pretty performance on heat and mass transfer feature. Also, as a well-known

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thermodynamic promoter, TBAB could relieve the gas hydrate formation condition. Therefore,

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this work focused on the kinetic, separation efficiency and microcosmic study for CO2

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removal from CO2/H2 syngas with TBAB and nano Al2O3.

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2. EXPERIMENTAL SECTION

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2.1. Material. Table 1 summarizes all the materials for this work. In pre-combustion IGCC

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power station, the treated syngas mainly consists 60 mol % H2. Hence, the 40 mol % CO2 and

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60 mol % H2 mixture gas was simulated as the syngas in this work. The de-ionized water was

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prepared in the laboratory by DZG-303A, EPED. What else, all the chemicals including

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TBAB and nano Al2O3 were provided directly by purchasing without further treatment.

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The particle size distributions of the nano Al2O3 were measured by the Mastersizer 2000

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particle size analyzer (Malvern Instruments. Ltd., Britain). As shown in Figure 1, the average 4

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particle size of the nano Al2O3 sample is about 550 nm, which could mix with water and form

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homogeneous colloidal dispersion in relatively lower concentration (99.99

BEST-REAGENT,CHENGDU

Nano Al2O3

200-600 nm

XFNANO,NANJING

624

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625 626 627 628 629 630 631 632 633

Table 2. Summary of the experimental conditions and results Texpa

Pexpb

RTc

Pfinald

CCRe

CCHf

S.Fr.g

(K)

(MPa)

(min)

(MPa)

(%)

(%)

(%)

0.1 wt % Nano Al2O3

279.65

3.00

49

2.62

-

-

-

2

0.5 wt % Nano Al2O3

279.65

3.00

105

2.46

-

-

-

3

0.8 wt % Nano Al2O3

279.65

3.00

220

2.44

-

-

-

281.25

3.08

122

2.61

28.65

78.71

39.86

281.25

3.09

120

2.56

26.62

88.97

45.49

281.25

3.07

123

2.23

27.38

80.22

50.31

281.25

3.00

125

2.37

25.01

81.97

55.71

Exp. No.

System

1

4 5 6 7

634 635 636

a.

0.5 wt % Nano Al2O3+1wt%TBAB 0.5 wt % Nano Al2O3+ 5 wt %TBAB 0.5 wt % Nano Al2O3+10 wt %TBAB 0.5 wt % Nano Al2O3+11 wt %TBAB

Experimental temperature;

reaction completed;

e.

b.

Original pressure;

c.

Reaction time; (tconstant-t0); f.

d.

Final pressure when

CO2 composition in the Residual gas; CO2 composition in the hydrate phase; g.

Split fraction.

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