Prakash D. Vaidya

Kinetics of removal of carbon dioxide by aqueous solutions of N,N-diethylethanolamine and piperazine.

N,N-Diethylethanolamine (DEEA) is a very promising absorbent for CO(2) removal from gaseous streams, as it can be prepared from renewable resources. Aqueous mixtures of DEEA and piperazine (PZ) are attractive for the enhancement of CO(2) capture, due to the high CO(2) loading capacity of DEEA and high reactivity of PZ. In the present work, for the first time, the equilibrium and kinetic characteristics of the CO(2) reaction with such mixtures were considered. Kinetic data were obtained experimentally, by using a stirred cell reactor. These data were interpreted using a homogeneous activation mechanism, by which the investigated reaction was considered as a reaction between CO(2) and DEEA in parallel with the reaction of CO(2) with PZ. It is found that, in the studied range of temperatures, 298-308 K, and overall amine concentrations, 2.1-2.5 kmol/m(3), this reaction system belongs to the fast pseudo-first-order reaction regime systems. The second-order rate constant for the CO0 reaction with PZ was determined from the absorption rate measurements in the activated DEEA solutions, and its value at 303 K was found to be 24,450 m(3)/(kmol s).

Insight into sub-critical wet oxidation of phenol

Abstract Low molecular weight organic acids, especially acetic acid, are often formed during wet oxidation. The role of mass transfer in the formation of acetic acid in wet oxidation was studied. For this purpose, phenol was considered as a model substrate. Acetic acid formed was maximum when mass transfer limitations existed. The waste may contain free radical initiators or scavengers. Therefore, the model compound hydroquinone was used as a free radical generator. It accelerated degradation but acetic acid formation increased. On the other hand, t -butanol as a free radical scavenger suppressed both phenol degradation and acetic acid formation. The strongly alkaline pH resulted in more acetic acid formation, though rates of phenol degradation increased. Wet oxidation of phenol was also studied in the presence of the homogeneous catalysts cupric sulfate and ferrous sulfate. The effects of these catalysts on the rates of oxidation and the acetic acid formation were studied. The amount of acetic acid formed in the presence of ferrous sulfate was relatively higher.

GAS–LIQUID REACTION KINETICS: A REVIEW OF DETERMINATION METHODS

The aim of this article is to provide comprehensive insight into the determination and interpretation of reaction kinetics of two-phase (gas–liquid) systems. Various aspects of the methodologies used for the measurements of kinetic parameters (such as equipment design, corresponding theoretical background, main steps, advantages, and limitations) are discussed in detail. In addition, an illustrating example is provided based on an industrially relevant absorption system.

Sorption‐Enhanced Steam Reforming of Glycerol over Ni–hydrotalcite: Effect of Promotion with Pt

Sorption‐enhanced steam reforming of glycerol (SESRG) is a promising method for the sustainable production of hydrogen (H2). In this work, composites of Ni and cationic‐modified hydrotalcite (HTlc) were promoted with Pt, thus resulting in two novel hybrid materials Pt‐NiMgHTlc and Pt‐NiCuHTlc. Activity trials for SESRG were performed in a fixed‐bed reactor in the range 673–873 K and it was found that the promotion with Pt improved H2 purity and multi‐cycle durability. The best results were achieved when Pt‐NiCuHTlc was employed at T=823 K: a H2 concentration of 98.7 mol % and adsorption capacity of 1.34 mol CO2/kg sorbent was achieved. When the multi‐cycle performance was tested for 20 cycles, it was found that NiMgHTlc, NiCuHTlc, Pt‐NiMgHTlc, and Pt‐NiCuHTlc were stable for 5, 8, 13, and 18 cycles. Finally, a likely reaction pathway for SESRG over the investigated multifunctional materials was proposed.

ACCELERATION OF THE WET OXIDATION REACTION OF PIPERAZINE BY HETEROGENEOUS Ru/TiO2 CATALYST

Wet air oxidation is a candidate technique for the effective treatment of wastewater contaminated by nitrogenous organic pollutants. Piperazine (PZ) is a cyclic diamine representing this class of compounds. In the present work, the wet oxidation reaction of PZ was studied for the first time. It was found that, in the studied range of temperatures of 180°–230°C and O2 partial pressures of 0.69–2.07 MPa, the oxidation process was slow. Total organic carbon (TOC) conversion at 230°C and 0.69 MPa O2 partial pressure was just 52% after 2 h. The investigated reaction was accelerated by a heterogeneous Ru/TiO2 catalyst. Maximum TOC conversion (91%) was achieved during catalytic wet oxidation at 210°C and 1.38 MPa O2 pressure. Kinetic data were collected over the range of temperatures 180°–210°C, O2 partial pressures 0.34–1.38 MPa, and catalyst loading 0.11–0.66 kg/m3. The lumped TOC concentration decay was a two-step first-order process.

Activated DEEA Process for CO2 Capture

Publisher Summary CO 2 represents an undesirable component in a variety of industrial gases and it has to be removed down to very low concentrations to meet the required specifications. Although a number of different CO 2 separation technologies are available by now, chemisorption with alkanolamines represents the most feasible option, and it is commonly used in the gas processing industry. Industrially important alkanolamines for CO 2 removal are the primary amine, monoethanolamine (MEA), the secondary amine, diethanolamine (DEA), and the tertiary amine, methyldiethanolamine (MDEA). N,N-Diethylethanolamine (DEEA), which can be prepared from renewable resources, represents a candidate alkanolamine having good potential for the bulk removal of CO 2 from gaseous streams. A blend comprising DEEA, piperazine (PZ), and H2O, which combines the high CO 2 loading capacity of DEEA with the high reactivity of PZ, is attractive for the enhancement of CO 2 capture. The investigated reaction is considered as a reaction between CO 2 and DEEA in parallel with the reaction of CO 2 with PZ. The CO 2 –DEEA–PZ system belongs to the fast pseudo-first-order reaction systems.

New Amine Blends for Improved CO2 Separation: A Study on Reaction Kinetics and Vapor–Liquid Equilibrium

Gas cleaning will be more eco-friendly if the absorbents used for CO2 capture are prepared from renewable supplies such as ethanol. Ethylene diamine (EDA), N-ethylmonoethanolamine (EMEA), N-ethyldiethanolamine (EDEA), and N,N′-diethylmonoethanolamine (DEMEA) represent this class of solvents. We selected two new blends from this group: EDEA + EMEA and DEMEA + EDA. Thus, a high-capacity tertiary amine (EDEA or DEMEA) was mixed with a very reactive amine (EMEA or EDA). Using a stirred cell, we analyzed kinetics of the CO2 reaction with these blends in aqueous solutions (2–3 M) at 308 K. On the whole, two reactions ensued in parallel: one, between CO2 and EDEA (or DEMEA), and the other, between CO2 and EMEA (or EDA). We evidenced that DEMEA and DEMEA + EDA were more reactive than EDEA and EDEA + EMEA. We reported the rate constant for EMEA and EDA (4700 and 28,300 M−1 s−1). Finally, we presented vapor–liquid equilibrium data for the DEMEA + EDA blend.

On the Production of Hydrogen from Bio-Oil: A Representative Study Using Propylene Glycol

In a bio-refinery focused on fast pyrolysis, hydrogen (H2) producible from reforming of the aqueous fraction of bio-oil with steam can be utilized for upgrading pyrolytic lignin into fuels by hydrotreatment. In this work, propylene glycol (PG) was chosen as a typical compound symbolizing higher polyols in the bio-oil aqueous fraction. Catalytic processing of PG into H2 at low temperature (T = 500°C) was investigated using several commercial catalysts such as Ni/Al2O3, Ru/Al2O3, Ru/C, Pt/C, and Pd/C in a laboratory-scale fixed-bed reactor. The efficiencies of the catalysts were presented as selectivity to CO, CO2, CH4 and H2, and PG conversion into gaseous phase. Wide ranges of temperature (300–500°C), W/FO (18.6–92.9 g h/mol), and S/C ratio (5.6–12.7 mol/mol) were examined using Ni/Al2O3. At T = 500°C, H2 selectivity (73.7%) and PG conversion (66.2%) were maximized using ratios of catalyst mass to molar flow rate of PG (W/FO) = 18.6 g h/mol and steam to carbon (S/C) = 12.7 (10 wt% PG solution). It was found that Ni/Al2O3 demonstrates stable operation for at least 6 h of time-on-stream. Finally, a plausible reaction pathway for PG reforming was proposed.

On the Efficacy of Ru/Al2O3 Catalyst for Steam Reforming of Ethylene Glycol

This work describes hydrogen (H2) production via steam reforming of ethylene glycol (EG) over a supported ruthenium catalyst. EG is chosen as a model compound for the alcohols contained in the aqueous phase of bio-oil. Using a fixed-bed reactor, experimental runs are carried out over Ru/Al2O3 at various temperatures (350–500°C), ratios of the mass of the catalyst (W) to the molar flow rate (FO) of EG at the inlet (W/FO = 0.37 − 2.38 g h/mol), and feed concentrations (22.3–53.4 wt.% EG in water). The role of Ru in conversion of EG, production of H2, and product distribution of the carbonaceous species is studied. Reaction pathways previously described in the literature are used to elucidate our results.

Aqueous-phase hydrodechlorination of model chlorinated organic compounds over Ru/C catalyst

ABSTRACT Effluents from the pharmaceutical and dye industries contain chlorinated organic pollutants. The effective treatment of such effluents constitutes a challenging task. In this work, 4-chlororesorcinol (PCRE) and 4-chloro-2-aminophenol (PCAP) were selected as model chloro-organic compounds. Catalytic hydrodechlorination (HDC) of PCRE and PCAP in the aqueous phase was investigated in a slurry reactor using commercial carbon supported ruthenium catalyst. HDC reactions of PCRE and PCAP were studied over the ranges in temperature, 313–353 K, H2 partial pressure, 0.69–2.76 MPa, and catalyst loading, 0.2–1.2 kg/m3. The performance of Ru/C catalyst for hydrodechlorination and ring saturation was promising. The kinetic data were modeled using Langmuir–Hinshelwood–Hougen–Watson kinetics. The HDC reaction of PCRE and PCAP using Ru/C catalyst proceeds via a dual-site mechanism, wherein atomic H2 reacts with the adsorbed organic substrate. The activation energy for the hydrodechlorination reactions of PCRE and PCAP was 41.6 and 49.4 kJ/mol, respectively.