Supporting Information
TiO(OH)
2Nanoparticle Composite Membranes for Enhancing the
Hot Potash Process
Ebrahim Ataeivarjovi1, Yubing Liu2, Zhigang Tang 1*, Hao Ding1, Dong Guo1, Xiaofei Song2, Guoxun Ben1, Mengyue Zhou1
1State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua
University, Beijing 100084, China
2School of Chemical & Environmental Engineering, China University of Mining & Technology,
Beijing 100083, China
Figure S1. Schematic diagram for traditional thermal desorption (a) and catalytic membrane desorption (b)
Table S1. Membrane Parameters used in this work
Materials
PTFE-
PVDF/PET Width (mm) 520
aperture (μm) 0.22 thickness (μm) 160-180
99.5% ethanol bubble pressure (MPa) 0.11 length (m) 2
air flux (m3/m2·hr, Δp=0.01MPa) 2 color white
Table S2. Experimental equipment decomposition of KHCO3 aqueous solution
enhanced by membrane
No.
Experimental
Apparatus
Apparatus
Specifications
Manufacturer
1 Feed liquid bottle 2500mL Beijing Glass Instrument Factory
2 Constant flow pump BT-200M Hebei Baoding Lange Constant-Flow Pump Co., Ltd.
3 Heat Exchanger 0.2m2 Beijing Glass Instrument Factory
4 water bath DC-0506 Shanghai Precision Science Instrument Co., Ltd.
5 Membrane contactor 23.75cm2 Hebei Yinzhou Zefan Intelligent Technology Co., Ltd.
6 Alkali absorber 1000mL Beijing Glass Instrument Factory
7 Vacuum pump 2ZX-2 Beijing Yi Decheng Experimental Equipment Co., Ltd.
Table S3. Experimental equipment for catalytic decomposition of KHCO3 aqueous
solution
No. Experimental Apparatus
Apparatus
Specifications
Manufacturer
1 N2 Gas cylinder 40L Beijing Beiwen Gas Co., Ltd.
2 Gas flowmeter LF485-SM Beijing Star Instrument Sensor Technology Co., Ltd.
3 Decomposition reactor YTFYQ-4L Yantai Zhaoyuan Chemical Equipment Co., Ltd.
4 water bath DC-0506 Shanghai Precision Science Instrument Co., Ltd.
5 Dry column 500mL Beijing Glass Instrument Factory
6 Gas analyzer QGS-08C Beijing Beifen Ruili Analytical Instrument Co., Ltd.
Fig S2. Verification of the second –order reaction
○ 250 ml H2O + 27.8 g KHCO3 (10 wt %) + 27.8 g TiO(OH)2, 95°C.
□ 250 ml H2O + 27.8 g KHCO3 (10 wt %) + 27.8 g TiO(OH)2, 85°C.
◇250ml H2O +27.8g KHCO3 (10 wt %) + 27.8g TiO(OH)2, 80°C
▲ 250ml H2O + 27.8g KHCO3 (10 wt %), 95°C.
■ 250 ml H2O + 27.8 g KHCO3 (10 wt %), 90°C.
250ml H2O + 27.8g KHCO3 (10 wt %), 85°C..
Derivation of Eq. 3.2
𝟐𝑲𝑯𝑪𝑶𝟑 ⇌ 𝑲𝟐𝑪𝑶𝟑 + 𝑪𝑶𝟐 + 𝑯𝟐𝑶
Feed/mol n
Reacting/mol 𝐧 ⋅ 𝛂 𝐧 ⋅ 𝛂/𝟐 𝐧 ⋅ 𝛂/𝟐 𝐧 ⋅ 𝛂/𝟐
Remaining/mol 𝐧 ― 𝐧 𝛂 𝐧 ⋅ 𝛂/𝟐 𝐧 ⋅ 𝛂/𝟐 𝐧 ⋅ 𝛂/𝟐
Herein, n is the amount (mol) of the material of the KHCO3 raw material, α is the conversion rate of the KHCO3. It can be derived that when the reaction reaches equilibrium, 𝒄(𝑲𝟐𝑪𝑶𝟑)=
𝒏(𝑲𝟐𝑪𝑶𝟑)
𝑽 =
𝐧 ⋅ 𝛂 𝟐𝐕
𝒄(𝑲𝑯𝑪𝑶𝟑)=𝒏(𝑲𝑯𝑪𝑶𝟑)
𝑽 =
𝐧 ― 𝐧 𝛂 𝐕 As defined, equilibrium constant is
𝐊 =𝒄(𝑲𝟐𝑪𝑶𝟑)× 𝒄(𝑪𝑶𝟐) 𝒄𝟐(𝑲𝑯𝑪𝑶𝟑)
So that the equilibrium constant can be written as
𝐊 = 𝒄(𝑪𝑶𝟐) 𝒄(𝑲𝟐𝑪𝑶𝟑)
𝒄𝟐(𝑲𝑯𝑪𝑶𝟑)= 𝒄(𝑪𝑶𝟐)
𝐧 ⋅ 𝛂 𝟐𝐕 (𝐧 ― 𝐧 𝛂
𝐕 )
𝟐= 𝒄(𝑪𝑶𝟐)
𝛂𝐕 𝟐𝒏(𝟏 ― 𝛂)𝟐
Fig.S3 Comparison of NaHCO3 aqueous solution decomposition and KHCO3
aqueous solution decomposition
●10 wt.% NaHCO3 aqueous solution decomposition using PDMS membrane loading 1wt% catalyst.
○10 wt.% KHCO3 aqueous solution decomposition using PDMS membrane loaded 1wt% catalyst.
Demonstration of No Significant Adsorption in TiO(OH)2’s Function
If we assume that adsorption plays an important role in the function of TiO(OH)2, then it should be chemical adsorption but not physical adsorption, since no apparent holes or channels exist in our membrane, otherwise the solution will leak. Based on this assumption, the first step reaction between TiO(OH)2 and HCO3- is suggested by Eq.1.2 in main file. One molecule of TiO(OH)2 is corresponded to one molecule of CO2. However, if we calculate CO2 desorption amount based on this assumption, then the desorption amount is too low (only 0.0022 mol, calculation process is shown below), we impose that even the adsorption amount could reach 2 molecules of CO2 per molecule of TiO(OH)2, then the desorption amount (0.0043 mol) is still much lower than the actual desorption amount in experiments (0.0556 mol). Calculation process is shown as below.
6 g of PDMS, 14 g of n-heptane solution, 1.2 g of TEOS and 0.5 g of dibutyltin dilaurate are used, so 1 wt % sample contains 0.217 g TiO(OH)2, which is equal to 0.0022 mol. If we assume that one molecule of TiO(OH)2 is corresponded to one molecule of CO2, then the desorption amount should be 0.0022 mol in maximum. If we assume that one molecule of TiO(OH)2 is corresponded to two molecule of CO2, then the desorption amount should be 0.0043 mol in maximum. Both values are much lower than the desorption amount in experiments (0.0556 mol), so adsorption is not significant
Fig.S4 Effect of catalyst concentration on decomposition conversion rate.
Fig.S5 Effect of temperature on decomposition conversion rate
Fig.S6 Decomposition conversion rate (a) and CO2 flux at different temperatures and concentrations of KHCO3 materials (b)
● Decomposition of 20 wt.% KHCO3 aqueous solution was desorbed by PDMS membrane loaded 1wt% catalyst.
○ Decomposition of 15 wt.% KHCO3 solution was desorbed with PDMS membrane loaded 1wt% catalyst.
♦ Decomposition of 10 wt.% KHCO3 aqueous solution using PDMS membrane loading 1wt% catalyst.
Table S4. Energy consumption of different desorption methods
Energy consumption
CO2 energy consumption
Method Equipment
（watt） （kJ/kg）
Proportion
Absorption tower 0.00 0.00 0.0%
Desorption tower -1.56×104 5.16×103 34.8% Heat exchanger A 2.25×104 7.44×103 50.2% Heat Exchanger B -3.21×103 1.06×103 7.2%
Pump 1.98×102 6.55×101 0.4%
Condenser -3.27×103 1.08×103 7.3%
Thermal desorption
total 1.48×104 100.0%
Absorption tower 0.00 0.00 0.0%
Membrane disrober 8.22×103 2.72×103 42.6% Heat exchanger A -4.81×103 1.59×103 24.9% Heat exchanger B -4.77×103 1.58×103 24.7%
Pump 6.81×102 2.25×102 3.5%
Vacuum pump 8.27×102 2.73×102 4.3%
PDMS membrane without catalyst
total 6.38×103 100.0%
Absorption tower 0.00 0.00 0.0%
Membrane disrober 8.22×103 2.72×103 52.8% Heat exchanger A -3.06×103 1.01×103 19.6% Heat exchanger B -3.04×103 1.00×103 19.5%
Pump 4.34×102 1.43×102 2.8%
1wt.% catalyst -PDMS membrane
Calculation Process of Table S4
Data in Table.S4 is collected by simulation software Aspen. As suggested in main file, the calculation is based on Fig.10 (main file). Table.S5 shows specific parameters in simulation. Processing and materials flow in different desorption methods are kept same, which is exhibited in Table.S6.
Table S5. Process and Equipment Parameters of Process Simulation
Table S6. Material Flow
Mixed Gas Purified Gas Recycled Gas
Temperature (℃) 80 87.6 45
Pressure (bar) 20.265 20.265 1
Flux (kg/h) 24.209 13.41 11.379
Component
H2O 0 0.353 0.48
CO2 12.384 1.239 10.893
N2 11.824 11.818 0.006
K+ 0 0 0
HCO3- 0 0 0
Brief Calculation of Reaction Activation Energy
The effect of TiO(OH)2 on the activation energy of KHCO3 decomposition reaction was calculated . The changes in CO2 concentration over time were analyzed with a gas analyzer.
CO2 concentration in the decomposed gas was analyzed in real time with a gas analyzer. The relationship between volume fraction and time is demonstrated in Fig.S7. The reaction rate rapidly increased with temperature along with the concentration curve. After reaching the set temperature, the reaction rate started to decrease as the concentration decreased. Finally, owing to CO2 diffusion limitation, the reverse reaction rate gradually increased, so that the concentration curve gradually decreased and eventually became flat. Thus, the highest peak in the graph could approximately represent the reaction rate under a certain temperature at this concentration (subtracting the concentration change caused by the initial temperature increasing process).
As illustrated in main file, thermal decomposition of KHCO3 aqueous solution belongs to the second-order reaction. Eq.S1 shows the kinetic equation.
𝐫 = 𝐤[𝐂𝐊𝐇𝐂𝐎𝟑]𝟐 (S1)
could be calculated from . According to the reaction rate and
𝐂𝐊𝐇𝐂𝐎𝟑 𝐂𝐂𝐎𝟐
concentration at different temperatures from Fig.S7 (concentration value has subtracted the change caused by the temperature rising process at beginning), the k value in Eq.S1 under each temperature could be obtained as Eq.S1 suggests. So that the activation energy (E) of the decomposition reaction can be calculated by a linear fitting using Arrhenius Formula as Eq.S2.
𝐥𝐧𝐤 = ―𝐑𝐓𝐄 +𝐥𝐧𝐀 (S2)
The effect of TiO(OH)2 on the reaction activation energy can be determined. The activation energy without TiO(OH)2 was E=76.8 kJ·mol−1, and the deviation from the literature value (reference [15] in main file) is 14.22%. When TiO(OH)2 was added, the activation energy (Ecat) was 11.5 kJ·mol−1, and the activation energy was reduced by about 85%. Results showed that the catalyst (TiO(OH)2) ) has a significant catalytic effect on the thermal decomposition of KHCO3 aqueous solution
Fig.S8 Comparison of capture energy consumption by different desorption methods
