Effect of sulfation during carbonation on CO_2 capture in calcium looping cycle

Abstract： Two Canadian limestones with different properties were tested to determine the effect of SO2 during the carbonation of sorbent on the CO2 capture performance in Ca- looping. When the reaction gas is mixed with SO2, the carbonation ratio of the sorbent is always lower than that without SO2 for each cycle under the same conditions, and the sulfation ratio increases almost linearly with the increase in the cycle times. At 650 ℃, there is little difference in the carbonation ratio of the sorbent during the first four cycles for the two carbonation time, 5 and 10 rain at 0. 18% SO2. The indirect sulfation reaction that occurs simultaneously with the carbonation of CaO is responsible for the degradation of the sorbent for CO2 capture, and the carbonation duration is not the main factor that affects the ability of the sorbent. 680℃ is the best carbonation temperature among the three tested temperatures and the highest carbonation ratio can be obtained. Also, the sulfation ratio is the highest. The probable cause is the different effects of temperature on the carbonation rate and sulfation rate. A higher SO2 concentration will decrease the carbonation ratio clearly, but the decrease in the carbonation capability of the sorbent is not proportional to the increase of the SO2 concentration in flue gases.

Synthesis of highly reactive sorbent from industrial wastes and its CO_2 capture capacity

A kind of industrial solid waste, i.e., carbide slag, was used as CaO precursor to synthesize CO2 sorbent. The highly reactive synthetic sorbent was prepared from carbide slag, aluminum nitrate hydrate and glycerol water solution by the combustion synthesis method. The results show that the synthetic sorbent exhibits a much higher CO2 capture capacity compared with carbide slag. The CO2 capture capacity and the carbonation conversion of the synthetic sorbent are 0. 38 g/g and 0. 70 after 50 cycles, which are 1.8 and 2. 1 times those of carbide slag. The average carbonation conversion and the CO2 capture efficiency of the synthetic sorbent are higher than those of carbide slag with the same sorbent flow ratios. The required sorbent flow ratios are lower for synthetic sorbent to achieve the same CO2 capture efficiency compared with carbide slag. With the same sorbent flow ratio and CO2 capture efficiency, the energy requirement in calciner for the synthetic sorbent is less than that for carbide slag.

CO_2 capture using dry TiO_2-doped Na_2CO_3/Al_2O_3 sorbents in a fluidized-bed reactor

Abstract： In order to improve the reactivity of Na2CO3/Al2O3 sorbent with CO2, a new sorbent showing high reactivity was developed by doping Na2CO3/Al2O3 with TiO2 using impregnation. Fourteen multi-cycle carbonation/regeneration tests of the sorbent were carried out in a fluidized-bed reactor and the sorbent was characterized by X-ray diffraction and nitrogen adsorption. It is confirmed that TiO2 shows a positive effect on the adsorption process of Na2CO3 and the reaction rate is observed to increase significantly, especially in the first 10 min. Moreover, TiO2 is stable within the temperature range of the process and no other Ti-compounds are detected. The carbonation products are NaHCO3 and Na5H3 （CO3 ）4. The surface area and the pore volume of the sorbent keep stable after 14 cycles. The Fourier transform infrared spectroscopy and the X-ray photoelectron spectroscopy are used to analyze the effect mechanism of TiO2 on CO2 adsorption process of Na2CO3/Al2O3.

CO_2 capture from binary mixture via forming hydrate with the help of tetra-n-butyl ammonium bromide

Hydrate formation rate and separation effect on the capture of CO2 from binary mixture via forming hydrate with 5 wt% tetra-n-butyl ammonium bromide （TBAB） solution were studied. The results showed that the induction time was 5 min, and the hydrate formation process finished in 1 h at 4.5 ℃ and 4.01 MPa. The hydrate formation rate constant reached the maximum of 1.84× 10^-7 molZ/（s.J） with the feed pressure of 7.30 MPa. The CO2 recovery was about 45 % in the feed pressure range from 4.30 to 7.30 MPa. Under the feed pressure of 4.30 MPa, the maximum separation factor and CO2 concentration in hydrate phase were 7.3 and 38.2 mol%, respectively. The results demonstrated that TBAB accelerated hydrate formation and enriched CO2 in hydrate phase under the gentle condition.

Amine-silica composites for CO_2 capture: A short review

Amine-silica composite materials for post-combustion COcapture have attracted considerable attention because of their high COuptake at low COconcentrations, excellent COcapture selectivity in the presence of moisture, and lower energy requirements for sorbent regeneration. This review discusses the recent advances in amine-silica composites for COcapture, including adsorbent preparation and characterization, COcapture under dry and moisture conditions at different COpartial pressures, sorbent regeneration, and stability after many cyclic sorption-desorption runs.

Recent developments and consideration issues in solid adsorbents for CO_2 capture from flue gas

The increase in energy demand caused by industrialization leads to abundant CO_2 emissions into atmosphere and induces abrupt rise in earth temperature. It is vital to acquire relatively simple and cost-effective technologies to separate CO_2 from the flue gas and reduce its environmental impact. Solid adsorption is now considered an economic and least interfering way to capture CO_2, in that it can accomplish the goal of small energy penalty and few modifications to power plants. In this regard, we attempt to review the CO_2 adsorption performances of several types of solid adsorbents, including zeolites, clays, activated carbons, alkali metal oxides and carbonates, silica materials, metal–organic frameworks, covalent organic frameworks, and polymerized high internal phase emulsions. These solid adsorbents have been assessed in their CO_2 adsorption capacities along with other important parameters including adsorption kinetics, effect of water, recycling stability and regenerability. In particular,the superior properties of adsorbents enhanced by impregnating or grafting amine groups have been discussed for developing applicable candidates for industrial CO_2 capture.

Preparation of composite poly(ether block amide)membrane for CO_2 capture

In this study, a poly（ether block amide） （Pebax 1657） composite membrane applied for COa capture was prepared by coating Pebax 1657 solution on polyacrylonitrile （PAN） ultrafiltration membrane. Ethanol/water mixture was used as the solvent of Pebax and the effects of ethanol/water mass ratios and Pebax concentration on the permeation properties of composite membrane were studied. To enhance the com- posite membrane permeance, the gutter layer, made from reactive amino silicone crosslinking with potydimethylsiloxane （PDMS）, was de- signed. The influence of crosslinldng degree of the gutter layer on membrane performance was investigated. As a result, a Pebardamino- PDMS/PAN multilayer membrane with hexane resistance was developed, showing CO2 permeance of 350 GPU and CO2/N2 selectivity over 50. The blend of polyethylene glycol dimethyl ether （PEG-DME） with Pebax as coating material was studied to further improve the membrane performance. After being combined with PEG-DME additive, CO2 permeance of the final Pebax-PEG-DME/amino-PDMS/PAN composite membrane reached 400 GPU above with CO2/Na selectivity over 65.

CO_2 capture by carbonated carbide slag seriflux after drying in calcium looping cycles

A new carbide slag （CS） seriflux utilization was proposed. The flue gas from a coal-fired plant was first bubbled into CS seriflux for CO2 capture. The obtained carbonated carbide slag seriflux （CCSS） was dried and utilized as a CO2 sorbent in the calcium looping cycles. The CO2 capture behavior of the dried CCSS and the raw CS was investigated in a dual fixed-bed reactor and a thermo- gravimetric analyzer. The effects of carbonation time, calcination temperature and carbonation temperature on CO2 capture performance of CCSS in the multiple carbonation/ calcination cycles were studied. The results show that the CO2 capture capacity of CCSS was higher than that of CS. Calcined at 950 ℃, CCSS shows better carbonation reactivity than CS, which benefits CO2 capture under severe calcination conditions. In the range of 700 to 725℃ for the carbonation, CCSS shows the optimal CO2 capture performance. The calcined CCSS shows better porous microstructure than the calcined CS. The calcined CCSS exhibits a larger surface area and pore volume in the cycles, which favors a higher CO2 capture capacity in the multiple cycles.

Resorcinol-formaldehyde resin-based porous carbon spheres with high CO_2 capture capacities

Porous carbon spheres are prepared by direct carbonization of potassium salt of resorcinol-formaldehyde resin spheres, and are investigated as COadsorbents. It is found that the prepared carbon materials still maintain the typical spherical shapes after the activation, and have highly developed ultra-microporosity with uniform pore size, indicating that almost the activation takes place in the interior of the polymer spheres. The narrow-distributed ultra-micropores are attributed to the "in-situ homogeneous activation"effect produced by the mono-dispersed potassium ions as a form of -OK groups in the bulk of polymer spheres. The CS-1 sample prepared under a KOH/resins weight ratio of 1 shows a very high COcapture capacity of 4.83 mmol/g and good CO/Nselectivity of7-45. We believe that the presence of a welldeveloped ultra-microporosity is responsible for excellent COsorption performance at room temperature and ambient pressure.

Modelling of a tubular membrane contactor for pre-combustion CO_2 capture using ionic liquids:Influence of the membrane configuration, absorbent properties and operation parameters

A membrane contactor using ionic liquids(ILs) as solvent for pre-combustion capture CO_2 at elevated temperature(303-393 K) and pressure(20 bar) has been studied using mathematic model in the present work. A comprehensive two-dimensional(2 D) mass-transfer model was developed based on finite element method. The effects of liquid properties, membrane configurations, as well as operation parameters on the CO_2 removal efficiency were systematically studied. The simulation results show that CO_2 can be effectively removed in this process. In addition, it is found that the liquid phase mass transfer dominated the overall mass transfer. Membranes with high porosity and small thickness could apparently reduce the membrane resistance and thus increase the separation efficiency. On the other hand, the membrane diameter and membrane length have a relatively small influence on separation performance within the operation range.

Water-stable ZIF-300/Ultrason? mixed-matrix membranes for selective CO_2 capture from humid post combustion flue gas

Water stable mixed-matrix membranes(MMMs) were developed to help control the global warming by capturing and sequestrating carbon dioxide(CO_2) from post-combustion flue gas originated from burning of fossil fuels.MMMs of different compositions were prepared by doping glassy polymer Ultrason? S 6010(US) with nanocrystals of zeolitic imidazolate frameworks(ZIF-300) in varying degrees. Solution-casting technique was used to fabricate various MMMs to optimize their CO_2 capturing performance from both dry and wet gases. The prepared composite membranes indicated enhanced filler-polymer interfacial adhesion, consistent distribution of nanofiller, and thermally established matrix configuration. CO_2 permeability of the membranes was enhanced as demonstrated by gas sorption and permeation experiments performed under both dry and wet conditions. As compared to neat Ultrason? membrane, CO_2 permeability of the composite membrane doped with 40 wt% ZIF-300 nanocrystals was increased by four times without disturbing CO_2/N_2 ideal selectivity. In contrast to majority of previously reported membranes, key features of the fabricated MMMs include their structural stability under humid conditions coupled with better and unaffected gas separation performance.

CO_2 capture:Challenges and opportunities

Although not everybody wants to admit,climate change has been happening with irreversible consequences.It is getting worse and worse and becoming more and more influential to not only the environment but also to all kinds of beings;our earth is now seriously threatened by climate change.It is a critical issue the whole society must face and actions must

Modification of CaO-based sorbents prepared from calcium acetate for CO_2 capture at high temperature

CaO-based sorbent is considered to be a promising candidate for capturing CO_2 at high temperature. However,the adsorption capacity of CaO decreases sharply with the increase of the carbonation/calcination cycles. In this study, CaO was derived from calcium acetate(CaAc_2), which was doped with different elements(Mg, Al,Ce, Zr and La) to improve the cyclic stability. The carbonation conversion and cyclic stability of sorbents were tested by thermogravimetric analyzer(TGA). The sorbents were characterized by N_2 isothermal adsorption measurements, scanning electron microscopy(SEM) and X-ray diffraction(XRD). The results showed that the cyclic stabilities of all modified sorbents were improved by doping elements, while the carbonation conversions of sorbents in the 1st cycle were not increased by doping different elements. After 22 cycles, the cyclic stabilities of CaO–Al, CaO–Ce and CaO–La were above 96.2%. After 110 cycles, the cyclic stability of CaO–Al was still as high as 87.1%. Furthermore, the carbonation conversion was closely related to the critical time and specific surface area.

Parametric study and effect of calcination and carbonation conditions on the CO_2 capture performance of lithium orthosilicate sorbent

The world is currently facing the challenges of global warming and climate change. Numerous efforts have been taken to mitigate CO2 emission, among which is the use of solid sorbents for CO2 capture. In this work, Li4SiO4 was synthesised via a sol-gel method using lithium nitrate （LiNO3） and tetraethylorthosilicate （SiC8H20O4） as precursors. A parametric study of Li：Si molar ratio （1-5）, calcination temperature （600-800℃） and calcination time （1-8 h） were conducted during sorbent synthesis. Calcination temperature （700-800℃） and carbonation temperature （500-700℃） during CO2 sorption activity were also varied to confirm the optimum operating temperature. Sorbent with the highest CO2 sorption capacity was finally introduced to several cyclic tests to study the durability of the sorbent through 10 cycles of CO2 sorption-desorption test. The results showed that the calcination temperature of 800℃ and carbonation temperature of 700℃ were the best operating temperatures, with CO2 sorption capacity of 7.95 mmol CO2·（g sorbent）^-1 （93% of the theoretical yield）. Throughout the ten cyclic processes, CO2 sorption capacity of the sorbent had dropped approximately 16.2% from the first to the tenth cycle, which was a reasonable decline. Thus, it was concluded that Li4SiO4 is a potential CO2 solid sorbent for high temperature CO2 capture activity.

Study on Absorption and Regeneration Performance of Novel Hybrid Solutions for CO_2 Capture

Recently, a kind of hybrid solution MEA-methanol shows a better CO_2 capture performance over aqueous MEA solution. However, the vaporization of methanol is the biggest disadvantage that hinders its application, so it is necessary to minimize the vaporization of methanol during both the absorption and regeneration processes. In this work, two kinds of hybrid solutions were studied and compared with aqueous MEA solution and MEA-methanol solution, including MEA/TEA/methanol solution and MEA/glycerol/methanol solution. The absorption property of MEA/glycerol/methanol solution is better than aqueous MEA solution within a certain period of time and the absorption property of MEA/TEA/methanol solution is too poor to be used in CO_2 capture. By increasing the concentration of TEA and decreasing the concentration of MEA, the absorption rate, CO_2 capture efficiency and absorption capacity all decreased. Upon adding glycerol, the cyclic capacity decreased and the generation temperature increased, and moreover, the density and viscosity also increased considerably. So after adding TEA and glycerol, the CO_2 capture performance of MEAmethanol solvent cannot be improved.

Designing a green and efficient absorbent for CO_2 capture

Several task-specific ionic liquids（TSILs） with weak alkalinity have been designed based on tetraalkyl-ammonium cation and L-alanine anion([N2222][L-Ala]) for the CO2 absorption.[N2222][L-Ala]has been chosen as a green and efficient activator for methyldiethanolamine（MDEA）.The densities,viscosities and absorption properties of the equimolar[N2222][L-Ala]-MDEA blended absorbents were investigated.Low viscosity and density values support the idea that blended absorbents are preferred in the industrial applications.[N2222][L-Ala]-MDEA behave similarly to the aqueous counterparts but offer more advantages,such as large absorption capacities,fast absorption rate and relatively low damage to the environment.

Fe-substituted Ba-hexaaluminate with enhanced oxygen mobility for CO_2 capture by chemical looping combustion of methane

While Fe-based oxygen carriers(OC) are regarded to be promising for chemical looping combustion(CLC),the decrease of CO_2 selectivity during deep reduction process and the severe agglomeration of Fe_2O_3 often occur after multiple redox cycles due to the low oxygen mobility.Herein,Fe-substituted Bahexaaluminates(Ba Fe_xAl_(12)– xO_(19),denoted as BF_xA-H,x = 1 and 2) prepared by a modified two-step method exhibited not only higher amount of converted oxygen(Ot) and CH_4 conversion(77% and 81% vs.17%and 75%) than those prepared by the traditional co-precipitation method(BF_xA-C,x = 1 and 2) but also high CO_2 selectivity above 92% during the nearly whole reduction from Fe^(3+) to Fe^(2+).Furthermore,the BFxA-H exhibited the excellent recyclability during 50 cycles.The better performance was ascribed to the markedly enhanced oxygen mobility which resulted from dominant occupancy of Fe cations in Al(5) sites(Fe^5: 71% and 70% vs.49% and 41%) in mirror planes of hexaaluminate leading to larger amount of lattice oxygen coordinated with Fe^5(O–Fe^5)(0.45 and 0.85 mmol/g vs.0.31 and 0.50 mmol/g).The improvement of oxygen mobility also favored the preservation of chemical state of Fe cations in hexaaluminate structure in the re-oxidation step,resulting in the excellent recyclability of BF_xA-H.

Experimental Study of the Absorption and Regeneration Performance of Several Candidate Solvents for PostCombustion CO_2 Capture

At present monoethanolamine(MEA) remains as the standard industrial solvent for CO_2 capture processes. But due to the degradation and high energy consumption problems of MEA, new efficient solvents should be found. In the present work, the absorption and regeneration performance of a hybrid solvent MEA-methanol was studied and compared to the aqueous solutions of monoethanolamine(MEA), diethanolamine(DEA) and triethanolamine(TEA) in a bubbling reactor. Also the performance of MEA-methanol solutions(including the absorption performance, regeneration performance,cyclic absorption performance, density and viscosity) was studied with different MEA concentrations. A pilot-plant CO_2 capture test bed was used to study the potential of MEA-methanol to replace aqueous MEA in industrial use. The results showed that the initial absorption rate of MEA-methanol solvent is the fastest compared with other solvents. The 30% MEA-methanol had a faster mass transfer coefficient, a higher CO_2 absorption efficiency and a lower regeneration energy consumption than aqueous MEA. And through the study of the reaction heat of CO_2 into MEA-methanol and aqueous MEA,it can be concluded that the desorption heat of rich MEA-methanol is only about 30% of rich aqueous MEA solvent in the regeneration process which showed that 30% MEA-methanol solvent is a promising candidate for CO_2 capture.

CO_2 Capture by Vacuum Swing Adsorption Using F200 and Sorbead WS as Protective Pre-layers

In order to solve the water issues when 13X zeolite was applied to capture CO 2 from wet flue gas by vacuum swing adsorption process, multi-layered adsorption system was considered regarding activated alumina F200 and silica gel based Sorbead WS as pre-layer materials. LBET (extended Largmuir-BET) model and extended CMMS (cooperative multimolecular sorption) equation were simulated respectively to describe water loading on F200 and Sorbead WS. The two equations can be well added into our in-house simulator to simulate double-layered CO 2 -VSA (vacuum swing adsorption) process. Results indicated that water can be successfully stopped in pre-layers with a good CO 2 capture performance.

Simulation and Comparative Study of CO_2 Capture in Underwater LSS Using HYSYS

Long-duration manned submersible missions require advanced life support systems (LSS) that can regenerate air, water and food. This study presented two CO_2-capture methods used in LSS, CO_2 removal with diethanolamine (DEA) and cryo-freezing with liquid oxygen. Both processes were modeled and simulated with HYSYS simulator. The performance of the two types of module was compared, and the results showed that the latter could be advantageous over the former in specific power, facility scale, operation reliability and safety. Economic evaluation suggested the latter cost only half of the former. Cryo-capture module could be an alternative for underwater LSS because of its efficiency and compactness.