Browsing by Subject "Piperazine"
Now showing 1 - 18 of 18
- Results Per Page
- Sort Options
Item Absorber performance and configurations for CO2 capture using aqueous piperazine(2016-05) Sachde, Darshan Jitendra; Rochelle, Gary T.; Baldea, Michael; Bhown, Abhoyjit; Chen, Eric; Hwang, GyeongAbsorber design for CO2 capture with amine solvents is complicated by the presence of temperature gradients and multiple rate controlling mechanisms (chemical reaction and convective mass transfer). The development of rigorous rate-based models has created the opportunity to study the performance limiting mechanisms in detail. A structured approach was developed to validate absorber models, identify limiting phenomena, and develop configurations that specifically address limiting mechanisms. A rate-based model utilizing concentrated aqueous piperazine (PZ) was the focus of model validation and process development. The model was validated using pilot plant data, matching the number of transfer units (NTU) within + 1% while identifying a systematic bias (loading measurement) between the model and pilot plant data. The validated model was used to define limiting cases (isothermal and adiabatic absorbers) to study the effects of operating conditions on the formation of temperature-induced mass transfer pinches. The method allowed for screening of intercooling benefits – high CO2 applications (15% - 27% CO2) require intercooling over the entire practical loading range for PZ and benefit significantly from simple in-and-out intercooling with limited additional benefit expected from advanced design. Low CO2 (4% CO2) applications are expected to benefit the most from improved intercooling, but also have the largest operating window without the need for intercooling (< 0.22 mol CO2/mol alkalinity for 8 m PZ). An analogous approach was developed to study rate mechanisms. A mass transfer parameter sensitivity analysis approach was developed to identify the relative contribution to overall mass transfer resistance of each mechanism as a function of operating conditions and position in the absorber column. The pseudo-first order and instantaneous reaction asymptotic solutions to the reaction-diffusion problem were used to define a dimensionless parameter that quantifies the approach of the modeling results to the limiting conditions and was found to be predictive of the relative liquid film resistance (diffusion vs. reaction) at all conditions. The results of the analysis indicated that the absorber is strongly diffusion controlled, has limited gas-film resistance, and that equilibrium constraints at the rich end of the absorber (depletion of free amine) significantly increase diffusion limitations. Finally, the validation and mechanistic studies provided the basis for four new absorber configurations: 1) integration of a spray nozzle in the intercooling loop, 2) solvent recycle intercooling, 3) integrated flue gas and solvent cooling functions, 4) hybrid intercooling (high intensity contacting with intercooling). Each approach coupled mass transfer enhancement with intercooling and provided new degrees of freedom for operation and design of absorbers for CO2 capture.Item Amine aerosol in aqueous scrubbing for CO₂ capture(2021-10-01) Akinpelumi, Korede Fiyinfoluwa; Rochelle, Gary T.; Hildebrandt Ruiz, Lea; Bonnecaze, Roger T; Knuutila, Hanna; Chen, EricSustained amine emissions above one ppm are prohibitive to amine scrubbing and prevalent with aerosol in the flue gas. The development, demonstration, and quantification of mitigation strategies for amine aerosol will ensure sustainable CO₂ capture operations. This work supports that goal by conducting systematic aerosol tests and developing aerosol models for 2nd and 3rd generation CO₂ capture solvents. SO₃ generation by catalytic conversion and plasma oxidation of SO₂ were compared and adapted for aerosol tests. The catalytic bed was proven highly effective at pilot scale with the demonstration of 97% conversion and 8 ppm SO₃ injection into 4000 lb/hr flue gas. Plasma oxidation had a much lower conversion but showed great promise due to its relative cost and ease of start-up/shut down. Amine aerosol can be sustainably mitigated upstream of CO₂ capture or within the absorber and water wash and are reduced at NGCC conditions. The hydrated lime addition rate is the critical indicator for upstream SO₃ reduction and inlet aerosol mitigation in baghouse operations. The threshold for SO₃ slippage is at half the normal lime rate. As inlet flue gas SO₃ increases, amine emissions increase, and the water wash performance decreases. There exists a tradeoff between capital or energy costs and amine aerosol control. A 98% reduction in PZ aerosol was demonstrated for flue gas with 2 ppm SO₃ by increasing the lean solvent to 58 °C and using a 2-stage water wash. Particulate measurements showed that PZ aerosol grows and gets collected at higher lean solvent temperatures. The growth of amine aerosol in the absorber is driven by amine-limited diffusion, and the aerosol is in equilibrium with water in the bulk gas phase. More volatile solvents grow bigger drops due to the larger driving force for amine transfer, and the effect of aerosol concentration on drop size is diminished. Therefore, aerosol mitigation with mist eliminators should be feasible for highly volatile solvents. As the volatility of the amine in a solvent system increases, vapor emissions will become more significant than aerosol emissions.Item Amine oxidation in carbon dioxide capture by aqueous scrubbing(2013-05) Voice, Alexander Karl; Rochelle, Gary T.; Sexton, Andrew J; Reible, Danny D; Willson, Carlton G; Anslyn, Eric VAmine degradation in aqueous amine scrubbing systems for capturing CO₂ from coal fired power plants is a major problem. Oxygen in the flue gas is the major cause of solvent deterioration, which increases the cost of CO₂ capture due to reduced capacity, reduced rates, increased corrosion, solvent makeup, foaming, and reclaiming. Degradation also produces environmentally hazardous materials: ammonia, amides, aldehydes, nitramines, and nitrosamines. Thus it is important to understand and mitigate amine oxidation in industrial CO₂ capture systems. A series of lab-scale experiments was conducted to better understand the causes of and solutions to amine oxidation. This work included determination of rates, products, catalysts, and inhibitors for various amines at various conditions. Special attention was paid to understanding monoethanolamine (MEA) oxidation, whereas oxidation of piperazine (PZ) and other amines was less thorough. The most important scientific contribution of this work has been to show that amine oxidation in real CO₂ capture systems is much more complex than previously believed, and cannot be explained by mass transfer or reaction kinetics in the absorber by itself, or by dissolved oxygen kinetics in the cross exchanger. An accurate representation of MEA oxidation in real systems must take into account catalysts present (especially Mn and Fe), enhanced oxygen mass transfer in the absorber as a function of various process conditions, and possibly oxygen carriers other than dissolved oxygen in the cross exchanger and stripper. Strategies for mitigating oxidative degradation at low temperature, proposed in this and previous work are less effective or ineffective with high temperature cycling, which is more representative of real systems. In order of effectiveness, these strategies are: selecting an amine resistant to oxidation, reduction of dissolved metals in the system, reduction of the stripper temperature, reduction of the absorber temperature, and addition of a chemical inhibitor to the system. Intercooling in the absorber can reduce amine oxidation and improve energy efficiency, whereas amine oxidation should be considered in choosing the optimal stripper temperature. In real systems, 2-amino-2-methyl-1-propanol (AMP) is expected to be the most resistant to oxidation, followed by PZ and PZ derivatives, then methyldiethanolamine (MDEA), and then MEA. MEA oxidation with high temperature cycling is increased 70% by raising the cycling temperature from 100 to 120 °C, the proposed operational temperature range of the stripper. PZ oxidation is increased 100% by cycling to 150 °C as opposed to 120 °C. Metals are expected to increase oxidation in MEA and PZ with high temperature cycling by 40 - 80%. Inhibitor A is not expected to be effective in real systems with MEA or with PZ. MDEA is also not effective as an inhibitor in MEA, and chelating agents diethylenetriamine penta (acetic acid) (DTPA) and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) are only mildly effective in MEA. Although MEA oxidation in real systems cannot be significantly reduced by any known additives, it can be accurately monitored on a continuous basis by measuring ammonia production from the absorber. Ammonia production was shown to account for two-thirds of nitrogen in degraded MEA at low temperature and with high temperature cycling, suggesting that it is a reliable indicator of MEA oxidation under a variety of process conditions. A proposed system, which minimizes amine oxidation while maintaining excellent rate and thermodynamic properties for CO₂ capture would involve use of 4 m AMP + 2 m PZ as a capture solvent with the stripper at 135 °C, intercooling in the absorber, and use of a corrosion inhibitor or continuous metals removal system. Reducing (anaerobic) conditions should be avoided to prevent excessive corrosion from occurring and minimize the amount of dissolved metals. This system is expected to reduce amine oxidation by 90-95% compared with the base case 7 m MEA with the stripper at 120 °C.Item Amine solvent development for carbon dioxide capture(2016-05) Du, Yang; Rochelle, Gary T.; Sanchez, Isaac; Critchfield, James; Hwang, Gyeong; Chen, Eric36 novel aqueous piperazine (PZ)-based amine blends for CO2 capture from flue gas were screened for their thermal degradation, amine volatility, CO2 cyclic capacity, and CO2 absorption rate at normal operating conditions. These amines include 7 imidazoles, 8 cyclic and long-chain diamines, 12 tertiary amines, 4 hindered amines, 3 hindered and tertiary amino acids, and 2 ether amines that were selected based on known amine structure-property relationships and their potential for industrial application. 18 thermally stable PZ-based amine blends were identified with proposed degradation mechanisms. 14 novel tertiary and hindered amines were found to have a lower volatility than 2-amino-2-methyl-1-propanol (AMP). A group contribution model to predict amine volatility was developed. In a PZ/tertiary amine, the optimum pKa of the tertiary amine was around 9.1 to give the highest CO2 cyclic capacity. A generic model for PZ/tertiary amines was developed in Aspen Plus®, which can predict the CO2 vapor-liquid-equilibrium based on the pKa of the tertiary amine in blend. To a lesser degree than pKa, the polarity of the tertiary amine also affects the CO2 solubility of the blend. CO2 absorption rates of most 2.5 m PZ/2.5 m tertiary amines are slightly lower than 2.5 m PZ itself, due to the higher viscosity of the blends, but they still absorb CO2 much faster than 7 m monoethanolamine (MEA). 2 m PZ/3 m 4-hydroxy-1-methylpiperidine (HMPD) is the blend that shows the best overall properties for thermal stability, amine volatility, CO2 cyclic capacity, and CO2 absorption rate. 2 m PZ/3 m HMPD also has a much better solid solubility than 5 m PZ. The capital and energy cost for flue gas CO2 capture using 2 m PZ/3 m HMPD is expected to be much lower than that using 7 m MEA, while comparable to that using 5 m PZ. Thermally degraded diglycolamine® (DGA®)/dimethylaminoethoxyethanol (DMAEE) was found to have a better performance for CO2 capture than the original solvent. At high temperature, DGA®/DMAEE reaches equilibrium with its major degradation product, methylaminoethoxyethanol (MAEE). The production of MAEE enhances the CO2 absorption rate, while maintaining the CO2 capacity of the original solvent.Item Corrosion of stainless and carbon steel in aqueous amine for CO₂ capture(2019-05-09) Fischer, Kent Billington; Rochelle, Gary T.; Hwang, Gyeong S; Keitz, Benjamin K; Wheat, Harovel GPost-combustion carbon capture and storage with amine absorbents is a key technology needed to provide low-cost decarbonized electricity. Improving understanding of corrosion by amines may reveal a solvent system compatible with carbon steel, which would reduce plant capital costs. Corrosion of stainless and carbon steel in aqueous monoethanolamine (MEA) and piperazine (PZ) has been measured. High temperature amine corrosion was measured in a bench-scale pressure vessel and iron solubility in amines was screened in stirred reactors. Corrosion was measured at two PZ pilot plants and one MEA pilot plant, using coupons and electrical resistance probes. Corrosion products were characterized by SEM and powder X-ray diffraction. Carbon steel (C1010) often performs well in 5 molal PZ up to 150 °C due to the formation of a passivating FeCO₃ layer. This layer is promoted at high temperature, high CO₂ loading, low solution velocity, and in amines with low Fe²⁺ solubility. FeCO₃ formation is favorable at high temperature because Fe²⁺ solubility decreases and the kinetics of FeCO₃ formation are faster. This also means that FeCO₃ is not observed at low temperature. Despite this, carbon steel performs well at low temperature due to slower kinetics of metal oxidation. Depassivation and high corrosion of stainless steel (316L) can occur in amine solutions at high temperature (150 °C) when conditions are relatively anoxic and reducing. Performance of stainless at high temperature in PZ suggests that it can be pushed into and out of the passive state by small process changes, such as different flue gas O₂ concentrations. However, stainless performs well in both MEA and PZ in pilot plants at ≈120 °C. Fe³⁺ corrosion products are generated in the absorber, then reduced to Fe²⁺ in the high temperature, anoxic conditions of the stripper. In this way, carried-over Fe³⁺ is responsible for oxidation of amine and corrosion at high temperature. Certain highly corrosive amines also have high Fe²⁺ solubility. Ethylamines like MEA are likely the correct chain length to form stable complexes with Fe²⁺ in solution. Stable Fe²⁺-amine complexes cause high Fe²⁺ solubility, which prevents FeCO₃ formation and leads to high corrosion.Item Formation and decomposition of 1-nitrosopiperazine in the CO2 capture process(2012-12) Ashouripashaki, Mandana; Rochelle, Gary T.Piperazine (PZ) is a cyclic diamine, which means it can absorb two moles of CO2 per mole of amine and potentially has a higher capacity for CO2 capture than monoethanolamine, the current solvent of choice for flue gas treatment. Nitrosamines are formed from the reaction between secondary or tertiary amines and nitrites or nitrogen oxides. Over 80% of nitrosamines are carcinogenic. The reaction of PZ and nitrite can form 1-nitrosopiperazine (also mononitrosopiperazine, MNPZ) and N-N,dinitrosopiperazine (DNPZ). Carcinogenicity of DNPZ is almost 20 times as that of MNPZ. There is also a possibility of nitrosamine formation of PZ in the CO2 capture process because of NOx in input flue gas, with the oxidative and thermal degradation products of PZ. Analytical methods were developed in order to perform kinetic studies of the reaction between a nitrite solution and PZ over a range of temperature from 20 to 150 °C at two different PZ concentrations, 8 and 2 mol/kg of solution, and three levels of CO2 loading, 0.3, 0.2, and 0.1 mole CO2/mole of alkalinity. At less than 75 °C, nitrite reacts with PZ and disappears during the reaction to an equilibrium concentration while at the higher temperature; the concentration of nitrite quickly decreases to a very low value. There is no evidence of DNPZ as a reaction product in all reaction conditions, but MNPZ is formed at the temperature greater than 75 °C. The MNPZ concentration approaches a maximum value consistent with the material balance and nitrite disappearance. By developing the time of reaction at the higher temperature a decomposition of MNPZ has been observed, by either the reverse of the formation reaction or decomposition to other compounds. By increasing the temperature, the maximum value of MNPZ concentration is achieved more quickly and the rate of MNPZ decomposition increases. Reactions follow the same trend at both PZ concentration and at the three different degrees of CO2 loading. A model has been established considering temperature, PZ concentration, and CO2 loading. The calculated activation energies of MNPZ production and decomposition were determined. MNPZ decomposition is more rapid than PZ degradation.Item Mitigation methods for piperazine oxidation in post-combustion carbon capture(2022-08-12) Wu, Yuying, Ph. D.; Rochelle, Gary T.; Allen, Dave; Hwang, Gyeong; Goff, George SPiperazine is a promising second-generation solvent for amine scrubbing in post-combustion CO₂ capture. However, the oxidative degradation of PZ can cause environmental problems and economic loss. This work presents the effects of two mitigation methods: carbon treating and N₂ sparging, on the PZ oxidation in long-term operations. The species and their respective quantities adsorbed by the activated carbon were tested in a bench-scale device. The carbon was then tested in the High Temperature Oxidation Reactor (HTOR), where the solvent oxidizes at a reasonably fast rate. Pilot plant campaigns were also performed at the UT Austin SRP and the National Carbon Capture Center (NCCC) and the effects were verified. When dissolved Fe is removed by carbon treating or other methods, available soluble Fe in the system dissolves and replaces the dissolved Fe. Therefore, all available Fe and ligands need to be removed for the mitigation to be effective. The sources of soluble Fe include fly ash and the corrosion of stainless steel, and the ligands are degradation products. All PZ degraded solvents have two absorbance peaks at 320 nm and 538 nm. The 320 nm peak is caused by dissolved metals, especially Fe, complexed by degradation products. The 320 nm peak is related to the amine degradation level and can be used as a simple and efficient method to estimate the amine degradation rate. The pilot plant data suggest that NO₂ can oxidize PZ significantly, possibly through radical reactions. 0.01 mmol/kg-hr absorption of NO₂ increased the PZ oxidation rate from 1.2 mmol/kg-hr to 2.5 mmol/kg-hr.Item Modeling advanced strippers for CO₂ capture from gas-fired power plants using aqueous piperazine(2023-08-08) Suresh Babu, Athreya; Rochelle, Gary T.; Baldea, Michael; Bonnecaze, Roger; Lin, Yu-Jeng; Tsai, RobertEnergy performance of 5 m piperazine was evaluated with an advanced stripper at the pilot scale, accounting for heat loss. Modeling studies indicated that heat loss at locations other than the heat source impacted the heat duty. For strippers with excess packing, the column was the most important source of heat loss, and values as low as 0.03 GJ/hr can cause pinch and reabsorption of CO₂. Solvents like 5 m PZ are more affected by heat loss in the column due to a top-side temperature pinch at high lean loading. Heat loss impacts NGCC CO₂ capture more than coal-based CO₂ capture. Surface temperature measurements pilot plants showed that heat loss was 50-75% controlled by natural convection. Measured heat loss was correlated with steam flowrate and wind speed and ranged from 8126 to 219668 Btu/hr, representing 35% of the measured heat rate on average. Net heat duty linearly varied with CO₂ removal at low lean loading and was similar for coal and NGCC conditions at fixed removal. At 90% removal, net heat duty was about 2.5 GJ/t with 4 and 12% CO₂ in the flue gas. At NGCC conditions, strippers with finite packing can benefit from a flashing feed to the top of the column by using a hot bypass. A flashing feed was linked to a reduction in irreversibility of the stripper from temperature driving forces. It also reduces heat duty by up to 6% at fixed packing height and reduces packing requirement for a fixed steam heater size compared to a warm bypass. Lean loading and lean solvent rate were effective handles to maximize profitability of a fixed stripper design at low gas price. High ambient temperature operation can benefit from low pressure stripping to about 0.18 lean loading at 150 ℃ to maintain the cyclic capacity at reduced rich loading. At low gas price, the capture plant was able to maximize profitability even with a high heat duty of 2.7-3.1 GJ/t at a lean loading of 0.2-0.22 mol/mol. Heat recovery by partial water vapor condensation in a gas-liquid exchanger can be replaced by a direct contact condenser (DCC). The DCC improved gas cooling and reduced heat duty compared to the CO₂ exchanger at 0.2 lean loading. The DCC when used with a 150 ℃/5.5 bar stripper can reduce the cost of capture compared to the base case by $3- 4/tonne at 15 ft of packing (optimum) but increases cost of capture by $6/tonne with a 120 ℃/2 bar stripper and 10 ft of packing (optimum). The DCC can work effectively with a solvent with a high heat of absorption and thermal stability.Item Modeling of carbon dioxide absorption using aqueous monoethanolamine, piperazine and promoted potassium carbonate(2012-05) Plaza, Jorge Mario; Rochelle, Gary T.; Chen, Chau-Chyun; Edgar, Thomas; Eldridge, Bruce; Freeman, Benny D.Rigorous CO₂ absorption models were developed for aqueous 4.5 m K+/4.5 m PZ, monoethanolamine (7m - 9m), and piperazine (8m) in Aspen Plus® RateSepTM. The 4.5 m K+/4.5 m PZ model uses the Hilliard thermodynamic representation and kinetics based on work by Chen. The MEA (Phoenix) and PZ (5deMayo) models incorporate new data for partial pressure of CO₂ vs. loading and kinetics from wetted wall column data. They use reduced reaction sets based on the more relevant species present at the expected operating loading. Kinetics were regressed to match reported carbon dioxide flux data using a wetted wall column (WWC). Density and viscosity were satisfactorily regressed to match newly obtained experimental data. The activity coefficient of CO₂ was also regressed to include newly obtained CO₂ solvent solubility data. The models were reconciled and validated using pilot plant data obtained from five campaigns conducted at the Pickle Research Center. Performance was matched within 10% of NTU for most runs. Temperature profiles are adequately represented in all campaigns. The calculated temperature profiles showed the effect of the L/G on the location and magnitude of the temperature bulge. As the L/G is increased the temperature bulge moves from near the top of the column towards the bottom and its magnitude decreases. Performance improvement due to intercooling was validated across the campaigns that evaluated this process option. Absorber intercooling was studied using various solvent rates (Lmin, 1.1 Lmin and 1.2 Lmin). It is most effective at the critical L/G where the temperature bulge without intercooling is in the middle of the column. In this case it will allow for higher absorption by reducing the magnitude of the bulge temperature. The volume of packing to get 90% removal with L/Lmin =1.1 at the critical L/G is reduced by 30% for 8m PZ. For MEA and a solvent flow rate of 1.1 Lmin packing volume is increased with intercooling at constant L/G. This increase is compensated by higher solvent loadings that suggest lower stripping energy requirements. The critical L/G is 4.3 for 8m PZ, 6.9 for 9m MEA and 4.1 for K+/PZ.Item Modeling of stripper configurations for CO₂ capture using aqueous piperazine(2013-05) Madan, Tarun; Rochelle, Gary T.This thesis seeks to improve the economic viability of carbon capture process by reducing the energy requirement of amine scrubbing technology. High steam requirement for solvent regeneration in this technology can be reduced by improvements in the regeneration process. Solvent models based on experimental results have been created by previous researchers and are available for simulation and process modeling in Aspen Plus®. Standard process modeling specifications are developed and multiple regeneration processes are compared for piperazine (a cyclic diamine) in Chapter 2. The configurations were optimized to identify optimal operating conditions for energy performance. These processes utilize methods of better heat recovery and effective separation and show 2 to 8% improvement in energy requirement as compared to conventional absorber-stripper configuration. The best configuration is the interheated stripper which requires equivalent work of 29.9 kJ/mol CO₂ compared to 32.6 kJ/mol CO₂ for the simple stripper. The Fawkes and Independence solvent models were used for modeling and simulation. A new regeneration configuration called the advanced flash stripper (patent pending) was developed and simulated using the Independence model. Multiple complex levels of the process were simulated and results show more than 10% improvement in energy performance. Multiple cases of operating conditions and process specifications were simulated and the best case requires equivalent work of 29 kJ/mol CO₂. This work also includes modeling and simulation of pilot plant campaigns carried out for demonstration of a piperazine with a 2-stage flash on at 1 tpd CO₂. Reconciliation of data was done in Aspen Plus for solvent model validation. The solvent model predicted results consistent with the measured values. A systematic error of approximately +5% was found in the rich CO₂, that can be attributed to laboratory measurement errors, instrument measurement errors, and standard deviation in solvent model data. Stripper Modeling for CO₂ capture from natural gas combustion was done under a project by TOTAL through the Process Science and Technology Center. Two configurations were simulated for each of three flue gas conditions (corresponding to 3%, 6% and 9% CO₂). Best cases for the three conditions of flue gas require 34.9, 33.1 and 31.6 kJ/mol CO₂.Item Oxidation of piperazine in post-combustion carbon capture(2018-05-07) Nielsen, Paul Thomas, III; Rochelle, Gary T.; Ekerdt, John G; Willson, Grant; Chen, Eric; Sexton, Andrew JSolvent oxidation in amine scrubbing systems for post-combustion CO₂ capture is a significant issue. Piperazine (PZ) is a promising solvent due to its relative stability and performance. PZ oxidation rates and products were thoroughly characterized in the High Temperature Oxidation Reactor (HTOR) bench-scale cyclic degradation apparatus and compared to observed PZ oxidation from campaigns at the UT Austin SRP, CSIRO Tarong, and "Pilot Plant 2" (PP2) pilot-scale facilities. The HTOR simulated solvent conditions cycling between a 40-55 °C absorber and a 120-150 °C stripper. In both the bench and pilot-scale the intermediary degradation products piperazinol, piperazinone, and ethylenediamine were initially the most significant degradation products before reaching steady-state concentrations, with ammonia and formate the most significant final products produced from the decomposition of the intermediates. PZ oxidation increased as the solvent degraded due to the cycling of dissolved iron, aldehydes, and hydroperoxide contaminants, which could be oxidized in the absorber and subsequently oxidize PZ at high temperature. An N₂ sparger was used to selectively remove dissolved oxygen (DO) in the HTOR before heating while still allowing for oxidation due to contaminant cycling. Ammonia was correlated to dissolved iron at 0.72 mmol NH₃/kg PZ/hr/(mmol/kg Fe) [superscript 0.5]. An additional 0.4 mmol NH₃/kg/hr was produced due to direct reaction of PZ with DO regardless of the level of contamination. Dissolved iron was solubility-limited in both the HTOR and pilot plants, but increased as the solvent degraded, resulting in the autocatalytic effect of PZ oxidation. HTOR data was used to model oxidation and solvent management costs for a full-scale amine scrubber. The model matched observed oxidation at SRP and Tarong. Maintaining 0.1 to 0.5 wt % contaminant accumulation optimized amine make-up, solvent reclaiming, and increased energy costs due to changes in solvent viscosity, at a minimum of $2.6/MT CO₂ for PZ treating coal flue gas with a thermal reclaimer to remove contaminants. Feed rate and amine recovery in the reclaimer were the most impactful design variables, followed by operating temperature and hold-up in the stripper, prescrubbing of flue gas contaminants SO₂ and NO₂, and least significantly N₂ sparging to remove DO.Item Oxidative degradation of piperazine in the absorption of carbon dioxide(2005-05-21) Alawode, Akinleye Olaolu; Rochelle, Gary T.Oxidative degradation of piperazine was quantified by using Gas and Ion Chromatography. The GC analysis involved the direct analysis of the piperazine using calibration standards, while the IC analysis was based on quantifying acetate, a degradation product which is an indication of piperazine loss. This study used an agitated reactor maintained at 55̊C, with conditions similar to those in absorber/stripper configurations for CO₂ removal from flue gas. The problems encountered with the apparatus by the previous investigator were eliminated and the effect of varying some process parameters such as catalyst concentration, duration and agitation on degradation was studied. The rate of acetate production ranged from 0.08 to 0.4mM/hr while actual piperazine loss ranged from 1mM/hr to 5mM/hr. The degradation rate was found to be dependent on agitation rate and catalyst concentrationItem Pilot plant modeling of Advanced Flash Stripper with piperazine(2018-12-07) Selinger, Joseph Leo; Rochelle, Gary T.Implementation of carbon capture using amine scrubbing is limited by the large energy penalty of CO₂ capture and compression. Alternative stripper designs can reduce lost work in the stripper by implementing heat recovery unit operations and reducing opportunities for solvent degradation. The advanced flash stripper (AFS) has reduced the required equivalent work by 12-15% compared to the simple stripper by using multiple solvent bypasses to equalize heat capacity across cross exchangers and minimizing lost latent heat of water vapor in the condenser. The Advanced Flash Stripper using 5 m piperazine was studied at the National Carbon Capture Center (NCCC) pilot plant, which presented the novel opportunity to test the solvent and design configuration with coal-fired power plant flue gas. Piperazine (PZ) solvent was stripped of CO₂ with an average stripper operating temperature of 150 °C The energy cost averaged 2.2 GJ/MT CO₂ for the AFS and 3.8 GJ/MT CO₂ for the simple stripper (SS). A temperature-control heuristic for controlling bypass flowrates was evaluated using five AFS test cases. Using bypass temperature differences of 7 °C, the bypass rates were automatically controlled to within 5% of the optimal bypass configuration. While the method was successful in simulations, unexpected heat loss in the NCCC plant limited the accuracy of the temperature-control heuristic due to the heat loss reducing the benefits of heat recovery unit operations. Overall energy balances of the AFS using the Independence model showed a positive heat gain of 65000 Btu/hr. The unexpected heat gain was attributed to an overestimated heat of absorption in the Independence model, as well as an underestimation of the total heat transferred from the process steam. A test AFS run was analyzed using three different assumption methods, with energy requirements varying from 2.1 – 3.0 GJ/MT CO₂.Item Solvent reclaiming by sulfate precipitation for CO2 capture(2011-12) Rafique, Humera Abdul; Rochelle, Gary T.; Sanchez, Issac C.Sulfate accumulates in the post-combustion CO₂ capture system and must be removed to re-use amine efficiently. Removal of sulfate from the amine-based postcombustion CO₂ capture system through a solvent reclaiming process may reduce CO₂ capture costs. This work determines the solubility of K₂SO₄ and Na₂SO₄ in 2 to 8 m PZ loaded with CO₂ and develops a thermodynamic and process model for the reclaiming process. At 40°C the solubility of Na2SO₄ in 8 m PZ with a CO₂ loading of 0.3 is 0.3 m Na2SO₄ and that of K₂SO₄ is 0.1 m K₂SO₄. Sulfate solubility in PZ solutions is represented by the empirical models: K₂SO₄: ln(Ksp) = 10.53I[superscript 0.3] - 0.98[PZ][subscript T] -3440/T - 2.42 ; Na₂SO₄: ln(Ksp) = 2.137I[superscript0.3] - .6505[PZ][subscript T] -826/T + 265 where [PZ][subscript T] = 2*(molality of PZ). A K₂SO₄ and Na₂SO₄ solubility thermodynamic model was developed in the eNRTL framework in the Fawkes model for PZ/CO₂/H₂O in Aspen Plus[trademark]. The energy cost of the Na process when removing the equivalent of 100 ppm SO₂ from the flue gas, ranging from $0.1-0.5/ton CO₂, was practically the same as the K process(ranging from $0.1-0.8/ton CO₂). The K₂SO₄ recovered in the process can be used as fertilizer. However, the KOH will still cost $0.6/tonne CO₂. If it is not possible to sell the K₂SO₄ as fertilizer because of the impurities that may be present on the K₂SO₄crystals, the chemical cost of the process would increase to $2/tonne CO₂. The chemical cost for the Na case is $0.7/tonne of CO₂.Item Thermal degradation and oxidation of aqueous piperazine for carbon dioxide capture(2011-05) Freeman, Stephanie Anne; Rochelle, Gary T.; Maynard, Jennifer A.; Reible, Danny D.; Katz, Lynn E.; Critchfield, JamesAbsorption-stripping with aqueous, concentrated piperazine (PZ) is a viable retrofit technology for post-combustion CO2 capture from coal-fired power plants. The rate of thermal degradation and oxidation of PZ was investigated over a range of temperature, CO2 loading, and PZ concentration. At 135 to 175 °C, degradation is first order in PZ with an activation energy of 183.5 kJ/mole. At 150 °C, the first order rate constant, k1, for thermal degradation of 8 m PZ with 0.3 mol CO2/mol alkalinity is 6.12 × 10-9 s-1. After 20 weeks of degradation at 165 °C, 74% and 63%, respectively, of the nitrogen and carbon lost in the form of PZ and CO2 was recovered in quantifiable degradation products. N-formylpiperazine, ammonium, and N-(2-aminoethyl) piperazine account for 57% and 45% of nitrogen and carbon lost, respectively. Thermal degradation of PZ likely proceeds through SN2 substitution reactions. In the suspected first step of the mechanism, 1-[2-[(2-aminoethyl) amino]ethyl] PZ is formed from a ring opening SN2 reaction of PZ with H+PZ. Formate was found to be generated during thermal degradation from CO2 or CO2-containing molecules. An analysis of k1 values was applied to a variety of amines screened for thermal stability in order to predict a maximum recommended stripper temperature. Morpholine, piperidine, PZ, and PZ derivatives were found to be the most stable with an allowable stripper temperature above 160 °C. Long-chain alkyl amines or alkanolamines such as N-(2-hydroxyethyl)ethylenediamine and diethanolamine were found to be the most unstable with an allowable stripper temperature below 120 °C. Iron (Fe2+) and stainless steel metals (Fe2+, Ni2+, and Cr3+) were found to be only weak catalysts for oxidation of PZ, while oxidation was rapidly catalyzed by copper (Cu2+). In a system with Fe2+ or SSM, 5 kPa O2 in the inlet flue gas, a 55 °C absorber, and one-third residence time with O2, the maximum loss rate of PZ is expected to 0.23 mol PZ/kg solvent in one year of operation. Under the same conditions but with Cu2+ present, the loss rate of PZ is predicted to be 1.23 mole PZ/kg solvent in one year of operation. Inhibitor A was found to be effective at decreasing PZ loss catalyzed by Cu2+. Ethylenediamine, carboxylate ions, and amides were the only identified oxidation products. Total organic carbon analysis and overall mass balances indicate a large concentration of unidentified oxidation products.Item Thermodynamics and kinetics of aqueous piperazine with potassium carbonate for carbon dioxide absorption(2005) Cullinane, John Timothy; Rochelle, Gary T.This work proposes an innovative blend of potassium carbonate (K2CO3) and piperazine (PZ) as a solvent for CO2 removal from combustion flue gas in an absorber/stripper. The equilibrium partial pressure and the rate of absorption of CO2 were measured in a wetted-wall column in 0.0 to 6.2 m K+ and 0.6 to 3.6 m PZ at 25 to 110o C. The equilibrium speciation of the solution was determined by 1 H NMR under similar conditions. A rigorous thermodynamic model, based on electrolyte non-random two-liquid (ENRTL) theory, was developed to represent equilibrium behavior. A rate model was developed to describe the absorption rate by integration of eddy diffusivity theory with complex kinetics. Both models were used to explain behavior in terms of equilibrium constants, activity coefficients, and rate constants. The addition of potassium to the amine increases the concentration of CO3 2- /HCO3 - in solution. The buffer reduces protonation of the amine, but increases the amount of carbamate species, yielding a maximum reactive species concentration at a K+ :PZ ratio of 2:1. The carbamate stability of piperazine carbamate and dicarbamate resembles that of primary amines and has approximately equal values for the heats of reaction, ∆Hrxn (18.3 and 16.5 kJ/mol). The heat of CO2 absorption is lowered by K+ from -75 to -40 kJ/mol. The capacity increases as total solute concentration increases, comparing favorably with 5 M monoethanolamine (MEA). The rate approaches second-order behavior with PZ and is highly dependent on other strong bases. In 1 M PZ, the overall rate constant is 102,000 s-1, 20 times higher than in MEA. The activation energy is 35 kJ/kmol. In K+ /PZ, the most significant reactions are PZ and piperazine carbamate with CO2 catalyzed by carbonate. Neutral salts in aqueous PZ increase the apparent rate constant, by a factor of 8 at 3 M ionic strength. The absorption rate in 5 m K+ /2.5 m PZ is 3 times faster than 30 wt% MEA. A pseudo-first order approximation represents the absorption rate under limited conditions. At high loadings, the reaction approaches instantaneous behavior. Under industrial conditions, gas film resistance may account for >80% of the total mass transfer resistance at low loadings.Item Thermodynamics of aqueous piperazine/aminoethylpiperazine for CO₂ capture(2014-05) Du, Yang, active 21st century; Rochelle, Gary T.Aqueous piperazine (PZ) blended with N-(2-aminoethyl) piperazine (AEP) is an attractive solvent for CO₂ capture from coal-fired power plants. Blending PZ with AEP can remediate the precipitation issue of concentrated PZ while maintaining its high CO₂ absorption rate, and high resistance to degradation. 5 m PZ/2 m AEP also shows a milder nitrosamine issue than concentrated piperazine. A rigorous thermodynamic model was developed in Aspen Plus® to predict properties of PZ/AEP/H₂O/CO₂, using the electrolyte-Nonrandom Two-Liquid (eNRTL) activity coefficient model. A sequential regression was performed to represent CO₂ solubility, speciation, and amine volatility data over operationally significant loading and temperature ranges. The model predicts a CO₂ cyclic capacity of 0.78 mol/kg (PZ + AEP + water) for 5 m PZ/2 m AEP, compared to 0.50 mol/kg for 7 m MEA and 0.86 mol/kg for 8 m PZ. The predicted heat of absorption is 75 to 80 kJ/mol CO₂ at the operating loading range (0.290-0.371 mol CO₂/mol alkalinity). Although 5 m PZ/2 m AEP has a slightly lower CO₂ capacity than 8 m piperazine, its higher heat of absorption may offset the negative effect on energy consumption. Speciation for PZ/AEP/H₂O at various CO₂ loading and temperature was also predicted, from which behavior of CO₂ in the amine system was proposed.Item Vapor-liquid equilibrium of monoethanolamine/piperazine/water at 35-70°C(2006-05) McLees, John Arthur; Rochelle, Gary T.The equilibrium partial pressures of monoethanolamine (MEA), piperazine (PZ), and water were measured in a stirred reactor with a recirculating vapor phase by FTIR analysis at 35 - 70 Celsius degrees. MEA and PZ volatility were measured in two separate pilot plant campaigns to capture CO₂ from flue gas under a range of absorber conditions. The laboratory data were regressed to determine NRTL binary interaction parameters that predicted the experimental points within 10 - 20%. It was proven that MEA volatility (0.45