GREEN CHEMISTRY
Another aspect is to find means of CO2 recycling reconverting the CO2 to usable forms of energy. The technique adopted is the Reverse water gas shift reaction. Yet another technique is substituting the fossil fuel by renewable sources of fuels like biomass by converting the bio mass to liquid fuels like Bio ethanol, or Bio diesel that can be fed to transport vehicles or by converting the bio mass to liquid hydrocarbon products by the famous Fischer-Tropsch synthesis to produce feed stocks to fertilizer plants or converting bio mass into Hydrogen, a clean fuel by steam reforming bio ethanol. All these techniques are classified as Green Chemistry and Researches are being conducted with utmost urgency to achieve break through in this field. Physical Chemistry, especially, Catalytic Chemistry plays an important role in this Pioneering fielding finding out the suitable and economically viable catalyst for the various processes. This paper enumerates a few research Papers presented in the Green Chemistry conference held in Green Chemistry in Energy Production Symposium.
Global warming poses a severe threat to survival of future generations, and the chief cause is the continuous and ever increasing ingress of CO2 in the earths atmosphere. The present main reason source of CO2 ingress is the humanitys need of energy being met by fossil fuels. So Scientists of various disciplines are contributing their mite by frantically working for finding alternate routes of energy for mitigating this problem. This essay deals with the recent work done by Physical Chemist in the field of Catalyst chemistry, relevant for the field of Green chemistry.
222 Catalytic Steam Reforming of ethanol
Producing clean fuel is the current need in view of the impending disastrous consequences of Global warming due to the accrual of Green house gases especially, CO2. Hydrogen is the most promising clean fuel for power generation as well as fuel for transport vehicles. The current source of Hydrogen is from steam reforming of natural gas which again produces CO2 as a by product. The eco friendly source is the Bio mass derived feed stocks like ethanol.
Current Status of the technology.
Steam reforming of ethanol currently uses costly Noble metal catalysts. In the present scenario of mass requirement of Hydrogen it is imperative to employ cost effective and efficient catalysts. Cobalt based catalysts are being employed for this purpose. Cerium Oxide (CeO2) having high oxygen storage capacity, high oxygen mobility, higher selectivity for H2 and CO2 and better stability is used as a supporting medium to the Cobalt Catalyst.
Focus of the present study.
Catalyst doping is a unique technique in catalyst Chemistry. Hua Song and Umit S. Ozkan have attempted to study doping the Co CeO2 Catalyst with Calcium in the Steam reforming of Ethanol process with success.
Catalyst preparation.
A solution of Cerium Nitrate hexa hydrate and Calcium Nitrate tetra hydrate in molar ratio of CeCa 91 in de ionized water is precipitated with Sodium carbonate solution with constant stirring for 1 hour, maintaining a pH of 9 to 10. The precipitates of the calcium and cerium carbonates are allowed to age at room temperature for 24 hrs, then filtered, washed thoroughly and dried at 95 OC overnight and calcined at 550 OC for 3 hrs. Then this Ca doped CeO2 is impregnated with Cobalt nitrate solution mixed with ethanol to a cobalt loading of 10 , and dried at 95 OC. Impregnating and drying steps were repeated many times as needed and then calcined at 450 OC and used for the experiments.
Experimental part.
The catalyst placed in tubular reactor is heated at 400 OC for 30 minutes in an atmosphere of Helium and reduced with 5 H2 in He medium at 400 OC for 2 Hours. Then a mixture of Ethanol and water at a mol ratio of 1 10 is vaporized and superheated to 200 OC and the vapor is carried with Helium Gas to the tubular reactor containing the catalyst. The experiment is continued for various temperature ranges, ranging from 300 to 550OC and data collected for every 50 OC increments holding the temperature constant for 2 Hrs. At the end of each experiment, the ethanol flow is stopped, the gaseous products are analyzed for the product Hydrogen, and un reacted Ethanol.
Catalyst performance.
The above experiments are repeated with different combinations of catalyst CeO2, Ca CeO2, Co CeO2, and Co Ca CeO2 .The performance of the catalysts are evaluated in the following terms, Oxygen uptake, CO uptake, H2 yield , EtOH conversion , and Turnover frequency (TOF). Of the four combinations of catalysts - CeO2, Ca CeO2, Co
CeO2, and Co Ca CeO2, the Co Ca CeO2 has shown the highest performance in all respects of Oxygen uptake, CO uptake, H2 yield , EtOH conversion , and Turnover frequency (TOF) and lower yield of other liquid byproducts. Hua Song and Umit S. Ozkan assert, calcium in the CeO2 lattice structure leads to cell expansion and the creation of Oxygen vacancies because of the lower oxidation state of Ca (2) compared with that of Ce (4). The creation of oxygen vacancies facilitates improved of oxygen mobility in the ceria-supported Co catalysts which results in better catalytic performance - higher H2 and CO2 yields, higher turnover frequencies, and lower yield to liquid byproduct such as acetone in ethanol steam reforming.
Comment.
Steam reforming the ethanol also produces CO2. But since the Ethanol source is Biomass, the CO2 is neutral, in the sense it is only recycled CO2 rather than CO2 produced from fossil fuels
444 Catalytic Steam reforming of Ethanol with Electric Field
Hydrogen is emerging as a clean fuel as against the fossil fuel based feed stocks. The current Technology of Steam reforming of Ethanol for producing Hydrogen is based on Catalytic process which requires high temperature, posing problems like selection of MOC, Heat loss, Catalyst degradation etc. Yasushi Sekine et al have attempted to steam reform ethanol in an electric field with considerable success. The salient feature is the low Catalyst bed temperature requirement say 200 OC (473K), thus promising a cost effective and energy efficient process. The electric field applied is not Plasma but milder than plasma.
Current Status of the technology
Catalytic Steam reforming of Ethanol proceeds in four different steps- 1). Ethanol to acetaldehyde and Hydrogen, 2). Acetaldehyde to CO and Hydrogen, and Acetaldehyde to Methane and CO 3). Methane to CO and Hydrogen, 4). Water gas shift reaction Co to CO2 and Hydrogen. Of these the third reaction, methane reforming is highly endothermic, having positive Gibbs free energy of 18.9KJmol at 573 K and 13.0 KJmol at 673 K. The thermodynamic Equilibrium constant is 6.5 x 10-8 at 573 K, 5.9 x 10-5 at 673 K. It could be seen a temperature of around 500 OC in the catalyst bed is to be maintained to effect the methane reforming.
Focus of the present study.
The reactions- ethanol decomposition, water gas shift reaction, and steam reforming of methane are studied both by conventional Catalytic method and by the electroforming method at an electric field of 0.39 to 2 W. The Catalyst used is PT, Rh, and Pd with CeO2 support.
Catalyst preparation.
Three different Catalysts are prepared by impregnating CeO2 with aqueous solutions of Platinum Ammonium Nitrate, Rhodium Nitrate and Palladium Acetate to a composition of 1 Pt CeO2, 1 Rh CeO2, and 1 Pd CeO2. CeO2 was soaked in distilled water, stirred and de aerated for 2 hrs at room temperature, and the aqueous solution of (Pt(NH3)4(NO3)2,
Pd(OCOCH3)2, and Rh(NO3)3) are added, stirred for 2 h, evaporated to dryness, then calcined at 973 K and crushed into particles with sizes of 355-500 m.
Experimental part.
The catalyst is loaded in a quartz tubular reactor of 6 mm OD to a depth of 4 mm and SS electrodes of 2 mm OD placed at each end of the catalyst bed with a clearance of 0.5 mm between the catalyst bed and the tip of the electrode. The catalyst is pretreated in situ with 5 Hydrogen in Argon medium at 723 to 823K before the reaction to reduce the catalyst. Ethanol vapor with steam at a ratio of 1 2 is preheated to 423 K, passed over the bed with Argon maintaining the temperature in the range of at 423 to 523K, simultaneously supplying a high voltage (130 to 600V) DC power supply to the electrodes with a fixed current of 3mA. The reaction products are analyzed by Gas Chromatography for the various products CH3 CHO, CH4, CO, H2. The experiment is carried out for the three Catalysts. Another set of experiments are conducted with out the supply of electric field, keeping all other parameters same. The results of both sets are compared.
Performance.
The ultimate performance is evaluated in terms of Conversion i.e. Carbon atoms of the out put of products Carbon atoms of the input Ethanol. Another criteria is yield of Hydrogen i.e. Moles of product HydrogenInput ethanol mols.
Observations.
1). On an overall assessment, it seems , Rhodium catalyst with electro reforming at 473 K gives the highest performance of around 70. 2). 473 K seems to be ideal for Rh while Pd catalyst gives its better performance at 523K with electro reforming. 3). Hydrogen yield is highest with Rh Catalyst at 473 K. 4). Pt catalyst comes third in all criteria.
5). Steam reforming with out electric field gives a conversion of less than 10 with all the three Catalysts.
Comment.
Hitherto Hydrogen is derived from fossil based fuels like natural gas or Coal. But Hydrogen to be CO2 Neutral, it has to be derived from Biomass derived feed stocks like Ethanol.
666 Study of Mechanism of Steam Reforming of Ethanol
Hydrogen, especially from Bio mass source has got enormous potential and is expected to play a crucial role in mitigating global warming. The current technology of Hydrogen production is by catalytic Steam reforming. Lot of research is being carried out to update the technology. In this context a theoretical study to elucidate the reaction mechanism of the process is needed to augment the other efforts of updating the Technology.
Current Status of the technology.
The Steam reforming of ethanol is carried out in the presence of Catalyst systems of Ni, Co, NiCu and noble metals like Pt, Rh, and Pd. The supports for these may be Oxides like Al2O3, MgO, La2O3, ZnO etc. Each supports have their advantages and disadvantages. Al2 O3 has Mechanical strength and Chemical resistance, but because of its acidic nature yields ethylene which leads to coke formation. Nickel catalyst also has a tendency to form coke. Addition of Noble metals improves the performance.
Focus of the present study.
The catalytic Steam reforming of ethanol may proceed by two pathways, 1). Dehydration of ethanol to yield Ethylene, 2). Dehydrogenation of ethanol to yield Acetaldehyde. Both
Ethylene and Acetaldehyde can react with water to yield H2. But, because of catalyst deactivation other Carbon by products are also produced. The formation of the other Carbon by products are to be minimized in order to increase the yield of H2 and thus the conversion efficiency. So studying the mechanism of catalyst deactivation assumes importance. Maria Cruz Sanchez-Sanchez et al have studied the Mechanism of catalytic Steam reforming of ethanol with PtNi Al2 O3 system and the mechanism of deactivation of the catalyst. .
Catalyst preparation.
Mono metallic catalysts of Ni (13by Wt) and Pt (2.5 by Wt) are prepared by impregnating calcined (at 923 K) Al2 O3 with aqueous solutions of Nickel Nitrate and Platinum Ammonium Nitrate respectively. The impregnated samples are dried (at 393 K for Ni and 383K for Pt) and calcined at 773K in air for Ni catalyst and 573K in Vacuum for Pt catalyst. Bi metallic catalyst is prepared by wet impregnation of calcined Ni Al2 O3 catalyst with Platinum Ammonium Nitrate solution, dried at 383 K and calcined at 573 K under Vacuum.
Experimental part
The three catalysts were activated under 10 H2 at 623K for PtAl2O3, at 823K for PtNiAl2O3 and at 923K for NiAl2O3. 30 mg of each catalyst were placed in three U-shape quartz reactor (4 mm ID), further pre treatments carried out in situ and then ethanol vapor, 3 in Helium media at 300K is admitted to the reactor and Temperature-programmed desorption (TPD) studies were carried out and the products are analyzed by Gas chromatography and the results are compared.
Catalyst performance
It is observed that all catalysts showed a first desorption peak at temperatures lower than 400 K, and small amounts of C2 products (acetaldehyde and ethylene).The main desorption peaks were observed at 473 K for Pt catalyst, at 523 K for Ni catalyst, and at 463 K for PtNi catalyst. In this temperature range, desorbed species are CH4, CO, H2, and small amounts of acetaldehyde. The formation of these products is probably related to the dehydrogenation of ethanol and the subsequent decomposition on metal particles of the produced acetaldehyde into CO and CH4. It is elucidated from the study that, 1). The main reaction proceeds by ethanol dehydrogenation and subsequent acetaldehyde decomposition. 2. The active sites responsible for acetaldehyde decomposition are easily deactivated by carbon deposits formed from dehydrogenation of CxHy intermediates. 3. Bimetallic PtNiAl2O3 catalyst possesses a higher activity and stability in converting ethanol into hydrogen and C1 products than monometallic counterparts. At 673 K the yield of Hydrogen was at its maximum at 20 minutes of reaction time
4). The PtNi bimetallic catalyst showed the lowest desorption temperature (463 K,), followed by Pt monometallic catalyst (473 K,) and finally, Ni catalyst (523 K,).
Comment
The study indicates bi metallic catalyst, say PtNi on the support Al2O3 performs better than either Pt or Ni catalyst supported on Al2O3
aaa Catalytic Steam reforming of Ethanol using CuO- CeO2 Catalyst
Introduction. Hydrogen from Ethanol is tipped as major substitute for petroleum fuels. Scientists are looking for economic routes to produce Hydrogen from Biomass derived ethanol.
Current Status of the technology
Steam reforming of Ethanol is currently carried out employing Noble metal catalysts. Efforts are taken to substitute the noble metal catalysts with commonly available and low cost catalysts. Cobalt based catalysts have been proved to have good reforming performance, but they have the limitation of sintering of the metal at high temperatures and deposition of carbonaceous materials on the Catalyst surface thus deactivating the catalyst. Catalyst supports like Al2 O3, having acidic properties accelerates dehydration of ethanol to produce ethylene which may polymerize and form carbon deposits. Supports like MgO exhibits improved coking resistance, but no additional catalyst activity.
Focus of the present study.
Supports like CeO2, ZrO2 have coking resistance and high Oxygen Mobility. Copper posses high activity in C-C bond cleavage. Considering these facts, Petar Djinovic et al have carried out studies to find out the efficacy of CuOCeO2 catalyst system for Steam reforming of Ethanol and also for dry reforming of Methane with CO2.
Catalyst preparation.
CuO-CeO2 catalysts with a nominal 10, 15, and 20 mol
CuO content were synthesized by hard template method using KIT 6 Template and impregnating with Copper nitrate and Cerium Nitrate solutions, drying and calcining.
Experimental part.
The catalyst is placed in a u tube type hastelloy C fixed bed reactor of 9 mm ID and reduced with 20 CO in Helium medium at 400 OC. Reforming experiment is carried out at temperature of 400 to 600 OC at an increment of 25 OC for a period of 75 Hrs with feeding ethanol vapor and steam at a mol ratio of 13. The ensuing products are analyzed in a gas chromatograph and the performance is evaluated.
Performance.
Increased conversion is obtained for CuO- CeO2 Catalyst than for CeO2 Catalyst. But beyond 500 OC the conversion drops in the case of CuO CeO2 system But CeO2 catalyst proved more stable. This shows CuO poses problem of sintering which leads to deactivation.
Observations.
1). Surface area of CuO CeO2 catalyst decreased with increase in temperature. 2) Addition of CuO enhanced the surface area. 3). Pure CeO2 showed less morphological change compared to CuO-CeO2 catalyst thus proving disadvantage of CuO. 4) But Oxygen mobility with in CeO 2 Structure is greatly enhanced when CuO is added.
888 CO-Free Hydrogen Production for Fuel Cell Applications over AuCeO2 Catalysts
Global warming has catalyzed research in the efficient utilization of fuels. The thermal route for extracting energy, whether mechanical or Electrical is a low efficient method. One promising route of energy extraction from fuel is the Fuel cell Technology, where in the Fuel is oxidized by atmospheric Oxygen, releasing a major part of the Heat of reaction as electrical Energy, much efficiently, and eco friendly than the conventional process. The catalysts used in fuel cells are noble metals and highly sensitive to catalyst poisons like CO. So it is imperative to supply Hydrogen free of CO Researches are being conducted in this sphere for developing technology for producing very high Pure Hydrogen suitable for Fuel cell Technology.
Current Status of the technology
Hydrogen is currently produced from Steam reforming of Methane or ethanol, followed by water gas shift reaction to convert the CO to again CO2 and Hydrogen Stoichiometrically (CO H2O CO2 H2). But the ensuing Gas contains around 1 CO. In order to use it in Fuel cells the CO content should be brought down to less than 10 PPM. The PROX reaction, preferential Oxidation of CO, subsequent to reforming of the fuel and Water Gas shift (WGS) reaction is a potential, promising proposal for achieving the required purity of Hydrogen. Researches are conducted presently to find out the efficacy of GoldCeria, for the PROX reaction. But the presence of CO2 and H2O in the reformed gas slows down its catalytic activity. Doping the GoldCeria catalyst by Sm, La, or Zn is said to increase the Catalytic activity.
Focus of the present study.
Ms Tatyana Tabakova, Maela Manzoli, Floriana Vindigni, Vasko Idakiev, and Flora Boccuzzi have attempted to study the efficacy of doping the AuCeO2 catalyst with Zinc.
Catalyst preparation.
Both doped and un doped AuCeO2 Catalyst systems were prepared for comparative study. For doped catalyst, aqueous Zinc Nitrate and Cerium Nitrate solutions at an atomic ratio of 0.5 for Zinc is precipitated with Potassium carbonate, keeping the pH at 9.0 and Temperature at 333K, filtered, washed free of Ions, dried under vacuum at 353K and calcined in air at 673K for 2 Hrs. This support catalyst is immersed in a solution of Gold chloride and the Gold is precipitated with K2 CO3 at a constant pH of 7.0 maintaining a temp of 333Kand washed, dried and calcined as previously. The un doped catalyst is prepared similarly, but avoiding the addition of Zinc Nitrate.
Experimental part.
The Catalyst, after suitable pretreatment, Oxidative or reductive as the case may be, is loaded into a flow reactor of 0.5 cm 3 bed volume. The reactant gas containing 4.4 of CO in Argon is passed through the catalyst bed at a space velocity of 4000 Hr and a Partial pressure of 31kPa. The Product gas is analyzed for CO content and degree of CO conversion is estimated.
Performance.
The experiment shows lower WGS activity for the doped catalyst and for the PROX reaction it is reverse.
Observations.
1). AuCeO2 demonstrated superior WGS activity. 2). Au Zn-CeO2 is more active for the PROX
Comment
777 Methanol Synthesis from Hydrogen and CO2
Developing liquid fuels to substitute petroleum fuels is of urgent need today. Direct production of Alcohol from Bio mass is uneconomical as its yield is low and cannot cater to the global need. Recycling CO2 to Methanol by catalytic Hydrogenation has attracted the attention of Scientists. The overall pathway is the Reverse water gas shift reaction, CO2 H2 CO H2O followed by Hydrogenation of CO, CO 2H2 CH3OH.
Current Status of the technology.
Finding out the suitable catalyst having the required activity is the urgent need. MoS2 is known to exhibit catalytic activity for syn gas to alcohols. MoS2 exhibit better sulfur and coke resistance and better selectivity than other Rh and Cu based catalysts. But MoS2 need to be promoted by alkali and transition metals, other wise it will yield hydrocarbons rather than Methanol. But Mo6 O8 is predicted to be a promising catalyst.
Focus of the present study.
Ms Ping Liu, YongMan Choi, Yixiong Yang, and Michael G. White have attempted to study the efficacy of Mo6 S8 . They have employed Density Functional Theory to investigate Methanol Synthesis from CO2 an H2 using Mo6 S8 . It is ascertained that M6S8 clusters have the highest CO binding energy. So a stronger Mo-CO bond could facilitate the reaction by weakening the C-O bond to yield an intermediate and finally Methanol.
Observations.
The Mo6S8 cluster behaves differently than MoS2 . The reaction follows reverse water gas synthesis and then Hydrogenation of CO to HCO radical and then to Methanol. The Co to HCO is the limiting criteria for the formation of Methanol.
MoS2 is active for syn gas conversion . It promotes C-O bond cleavage to form Methane. It is observed that both Mo and S sites participate in the reaction . Mo adsorbs CO2 , CO and HCO radical . The S facilitates H-H bond cleavage.
The Mo6 S8 is a sub stoichiometric entity, having lower SMo ratio and has low activity as against MoS2, which, because of its strong affinity with adsorbates, shows poor sensitivity to Methanol synthesis. But the Mo6 S8 , having moderate interactions with reactants and intermediates, C-O bond cleavage is not prominent, thus Hydrocarbon formation is not favored and hence more selective than MoS2 for methanol production.
Comment.
Though this process seems to be promising to recycle CO2 , one has to ponder the following questions.1). Though CO2 emission is tremendous globally, it is not available in concentrated form for the economic utilization . 2). To make CO2 usable as Methanol, one need the stoichiometric quantum of Hydrogen. 3). To make Hydrogen we need ethanol or methanol. Thus the whole exercise seems to be a vicious cycle.
111 Synthesis of Carbon Nanofibers by Catalytic Hydrogenation of CO2
CO2 is the main cause for Global warming and efforts are being taken to reduce its emission as well as to find means of recycling it. Catalytic conversion of CO2 back to carbon is recognized as one of the potential option.
Current Status of the technology.
Current research reports point out the possibility of Reverse Water Gas Shift (RWGS) reaction capable of producing CO from CO2, by employing suitable catalysts. Similarly the CAMERE process, (carbon dioxide hydrogenation to form methanol via a reverse-water-gas shift reaction) is capable of producing Methanol from CO2. The CAMERE process needs only simple equipments, and easy to operate and maintain.
Focus of the present study.
The technology of producing Carbon nano Fibers and tubes, (CNF CNT) is an established one and CO is being used as a feed for this process. But direct production of CNF and CNT from CO2 is not yet established. If it can be established to produce carbon directly from CO2, then this will go a long way in recycling CO2. Ms Ching S. Chen, Jarrn H. Lin, Jiann H. You, and Kuo H. Yang have found that the Ni catalyst with K (Ni-KAl2O3) allows for the formation of CNF from CO2. The Nickel catalyst (Ni-KAl2O3) is efficient for reduction up to CO. But addition of K enhances the reduction up to Carbon formation. The factors influencing the formation of Carbon are established in their work.
Catalyst preparation.
The commercially available NiAl2O3 catalyst (17wt Ni) is impregnated with required KNO3 aqueous solution to have a potassium concentration of 0.0, 1.2, 2.0, and 2.7, dried at 353K, calcined in air at 773K and reduced at 773K under Hydrogen prior to use in the experiment.
Experimental part.
30 mg of catalyst is placed in a 9.5 mm OD fixed bed reactor with Temperature controller. A stream of 11 mixture of Hydrogen and CO2 at atmospheric pressure is passed through the reactor and the temperature increased at a rate of 10OC minute from 25 OC to 800 OC and the TPD (Temperature Programmed Desorption) study is conducted. The ensuing gas is analyzed for its CO2 content by a Gas Chromatograph and the CO2 signal is measured by a Mass Spectrometer.
Performance.
Rate of carbon formation, gm Cgm Catalyst per hr increases with increasing Potassium, say, 0 K 0 gm Carbon, 1.2 K 0.19 gm Carbon, 2.0 K 0.23 gm Carbon, 2.7K 0.29gm Carbon
Observations.
1). The Potassium addend induces the formation of carbon or CNF on the NiAl2O3 catalyst. 2). The impregnated K ions partially cover the active sites and strongly adsorb the CO2 on the catalyst. 3). The addition of K to the NiAl2 O3 catalyst weakens the interaction between Ni- Al2O3 and creates a K related active phase that enables carbon deposition. 4). The carbon formed is directly from the CO2
Thermal Decomposition of Bio Diesel
Petroleum products emit net stoichiometric quantum of CO2 a green house gas, while combustion in the engine of Vehicles. Substituting Biomass derived Fuels, though emit CO2, the CO2 is neutral and hence, is a favored option. Vegetable oils can not be directly used in Diesel Engines. But the vegetable oils Trans etherified with Methanol, known as fatty acid methyl esters (FAME) are reliable addends to the petroleum fuels. The abundant supply of rapeseed oil and Soya bean oil has opened the way for using them as Bio diesel. These oils can not be used as such, but their methyl esters- rape seed methyl ester (RME) and Soya bean oil methyl ester (SME) find use in the diesel Engines.
Composition of the Bio diesel (RME) Methyl Palmitate 4.8, methyl stearate 1.5 methyl oleate 60 methyl linoleate 21.5, methyl linolenate 7.6 eicosenoic acid methyl ester 2 SME also has these compounds but in different composition. The combustion Chemistry of these Bio diesels can be studied by simulating the combustion of the different methyl esters of the corresponding fatty acids. The modeling of Engine combustion needs the Thermo chemical data. Ms Antoine Osmont, Laurent Catoire, and Philippe Dagaut have attempted to study the combustion mechanism of these Methyl esters, focusing on the high temperature decomposition chemistry. They have provided the computed thermo chemical data in the CHEMKIN-NASA format and this will be of use to engine designers.
555 Dehydrogenation of Ethyl benzene under a Carbon Dioxide Atmosphere
CO2 is the problematic byproduct of the societys energy consumption. Scientists are looking into ways of putting it to use. One such option is the utilization of CO2 for the manufacture of Styrene, one of the high volume basic chemical in the petroleum Industry. It is currently manufactured by Catalytic dehydration of Ethyl Benzene at a temperature of 873K in the presence of excess steam used, say 10 to 15 times that of the raw material, as a diluent. The reaction is highly endothermic and the heat is supplied by the sensible heat of the steam, while the latent heat of the steam is lost while quenching the reaction mixture. The Potassium promoted iron oxide catalyst gets deactivated during the prolonged run due to the loss of potassium. In this circumstance use of CO2 as the diluent provides an economic alternative.
Current Status of the technology.
Recent studies have shown that Iron activated carbon catalyst gives a higher yield and selectivity under CO2 rather than without CO2. similarly Vanadium Magnesium Oxide catalyst gives a yield 2.5 times more in CO2 medium than with out CO2. Other Catalysts like vanadium Oxide, iron Oxide , Chromium Oxide are also reported to be effective in the presence of CO2 for the production of Styrene by dehydrogenation of Ethyl Benzene. Use of CO2 for the dehydrogenation of Ethane Iso propyl Benzene and Iso butane are also reported.
Focus of the present study.
The reaction mechanism of the dehydrogenation is studied . Badstube et al have asserts the role of CO2 in a FeAC catalyst as the participation in the reverse Water gas Reaction n process. Ms Kazuhiro Saito, Kazumi Okuda, Na-oki Ikenaga, Takanori Miyake, and Toshimitsu Suzuki have studied the role of lattice Oxygen in Metal Oxides by Transient response technique. They have studied the behavior of vanadium, Chromium and Iron Oxide loaded Catalyst in the de hydrogenation of Ethyl Benzene. The supports used are MgO, Al2 O3, Activated carbon and Oxidized diamond.
Catalyst preparation.
The supports as mentioned are impregnated with aqueous solutions of Ammonium Vanadate, Chromium Nitrate, and ferric Nitrate, dried under Vacuum to evaporate water and calcined, - MgO and Al2 O3 supported catalyst are calcined at 873K, Oxidized diamond supported catalyst at 723K and Activated carbon supported catalyst at 973K.
Experimental part.
The experiments are carried out in fixed bed flow Quartz reactor with 50 mg Catalyst in place. CO2 is bubbled through Ethyl benzene kept at 315 K and passed through the Catalyst bed kept at 823K and the products are condensed and the liquid ( Styrene, Ethyl Benzene, Benzene and Toluene ) and the un condensable ( CO, CO2, H2) are analyzed by suitable Gas Chromatographs.
Performance.
Vanadium Catalyst supported by Activated carbon has given the highest performance.
Observations.
Kazuhiro Saito et al claims, transient response method shows that under CO2, the transferred lattice oxygen was supplied partly from CO2 to keep vanadium or iron oxides at higher valence state oxides. Thus a promoting effect of CO2 could be exhibited. But Cr2O3-loaded catalysts, shows no significant oxygen transfer from the lattice oxygen and hence no promoting effect.
333 Liquid Phase Catalytic Hydrogenation of Dicyclopentadiene over PdC Catalyst
Coal tar is the low value end product of Coal processing. Deriving value added products from Coal Tar instead of simply burning it for fuel purpose is a good idea of Green Chemistry.
Focus of the present study.
Di Cyclo Penta Diene (DCPD) can be obtained from Coal tar and the worlds potential is around a million Ton annually. Endo Tetra Hydro Dicyclo Penta Diene (endo THDCPD) can be synthesized from DCPD by Catalytic hydrogenation process and this on isomerization will yield exo THDCPD, a high volumetric energy density fuel being used in modern Aircrafts and cruise missiles. Miaoli Hao et al and Jianming Yang et al have studied the reaction mechanism of Catalytic Hydrogenation of DCPD to endo THDCPD with PdC catalyst in Ethanol medium with the aim of providing useful data for scaling up to commercial projects for producing High performance Fuel from a low value by product of the coal industry.
Selection of Catalyst and solvent.
Hydrogenation can be carried with PdC or Raney Nickel. But the life of Raney Nickel is short and can not be reused or regenerated. So PdC catalyst is favored. Alcohols like Methanol, Ethanol and Iso propanol can be used for Hydrogenation. But the yield of the product was low with Iso propanol. Methanol is toxic and has a low boiling point. So ethanol id considered for this experiment.
Experimental part.
A one liter stainless steel autoclave with heating and cooling facility is used as a batch reactor. The DCPD, Solvent and the catalyst are placed in the reactor and the reactor is tested for its holdability at 20 ATA with Nitrogen. Then Nitrogen is thoroughly purged out and replaced by Hydrogen. Then the reaction is started by heating it to the set Temperature, keeping the required pressure constant. Samples were collected intermittently and after the reaction is over the set up is allowed to cool and the reaction mixture is centrifuged to separate the catalyst from the liquid reaction mixture. The liquid reaction mixture is evaporated in a water bath to distill out the solvent and the product is analyzed with a gas chromatograph. The experiments are repeated for Different temperature like 323,333,343, and 353 K, for different pressures like 5, 10 and 15ATA, for different catalyst loading like 0.25, 0.5, 0.75, and 1.0 and data collected at different reaction time. The composition of the reaction mixture DCPD (the raw material), DiHydroDCPD (the intermediate) and THDCPD (the desired product) are analyzed and tabulated against the reaction conditions mentioned above.
Performance.
The concentration of DCPD decreased constantly with reaction time. The concentration of DHDCPD increased initially and then drops. The concentration of THDCPD increased steadily. This shows the reaction proceeds through an intermediate step of forming DHDCPD. The Increase in Hydrogen pressure, increase in catalyst loading and the increase in temperature , all these shortens the time of reaching the equilibrium stage and enhances the reaction for the production of THDCPD.
Observations.
The absence of compounds like C5H6, C5H8, C5H10, or C10H18 shows that there are no side reactions of these types.
Surface and Catalytic Elucidation of Rh-Al2O3 Catalysts during NO Reduction by C3H8 in the Presence of Excess O2, H2O, and SO2
In any combustion process, highly polluting chemical species like COX, NOX and SOX are emitted causing environmental degradation, photo chemical smog, and acid rain, affecting human health and other living beings- flora and fauna. This essay deals with the reduction of NO from combustion gases.
Current Status of the Technology.
Both the stationary sources like Boilers and furnaces and mobile sources like automobiles emit NO in their combustion gases. But their conditions are different. Combustion in automobile engines is done at near stoichiometric proportions of air and there is a slight reducing atmosphere. Under these conditions, the Three way Catalytic Converters (TWC) perform well. In Stationary applications, excess Oxygen is admitted for effecting complete combustion and better fuel economy. But TWC can not reduce NO to N2 under the oxidizing condition. In this condition Selective Catalytic Reduction (SCR) of NO by NH3 is successfully practiced. But, storage of NH3 and its high vapor pressure poses problems and hence other catalytic routes are being g probed for the removal of NO from combustion gases.
Focus of the present study.
Selective Catalytic Reduction of NO under oxidizing condition by hydro carbon is currently under investigation. Normally the combustion gases contain small amount of hydrocarbons which can be utilized there by reducing both the pollutants NO and HC by a single catalytic converter. Zeolite catalysts show good activity for NO reduction, but they exhibit poor thermal stability and lose their activity in the presence of SO2 and H2O, which are normally present in combustion products. Metal oxide catalysts show good activity and do have better hydrothermal stability, but easily get poisoned by the SO2 present in the combustion gases. Rh based Catalysts show good catalytic activity, thermal stability, and SO2 tolerance. Ms G. Pekridis, N. Kaklidis, V. Komvokis, C. Athanasiou, M. Konsolakis, I.V. Yentekakis, and G. E. Marnellos have selected Rh Catalyst supported over Al2O3 for studying its SCR performance with Hydrocarbon (C3H8) in the presence of SO2, H2O and excess Oxygen. TPD measurements and DRIFTS studies were conducted.
Catalyst preparation.
Commercial Al2O3 is crushed and the fraction of 180 to 355 m sizes is impregnated with aqueous Rhodium Chloride Solution to a catalyst loading of 1, dried at 120OC and calcined in atmospheric air at 600OC at a rate of 10 OC min.
Experimental part.
The experiment is carried out in a 8 mm ID Quarts fixed bed reactor up to a temperature of 600 OC at a rate of 10 OC min, while passing the gas mixtures - one or more of 0.13 NO, 5 O2, 0.17 C3H8, 100 ppm SO2, 3 H2O diluted in He. The reaction product gases are analyzed with Gas chromatograph.
Observations.
1). The SO2 has a clear negative effect on both NO and C3H8 conversions as evidenced by the lower NO conversions in SO2-containing mixtures and the reduction of catalytic activity at increased SO2 concentration. This is because of the poisoning of the catalyst due to formation of irreversible SO4 ion. But for the oxidation of C3H8 the inhibition of the catalyst by SO2 is milder, because SO4 ion participates in the Oxidation of C3H8.
2). Water also suppresses the reduction of NO by the oxidation of Rh site.
3). In the absence of SO2 and H2O, the reaction between NO and C3H8 is a typical reduction reaction, with active intermediates of NOx, Carboxylates and iso cyanates yielding the final products of N2 and CO2.
4). The formation of carboxylate is the rate determining step.
Hydrolysis of Tetrafluoroborate and Hexafluorophosphate Counter Ions in
Imidazolium-Based Ionic Liquids
Room Temperature Ionic liquids are a special class of chemical compounds known as liquid salts. Since they exhibit a very low vapor pressure, they are thought of as environmentally friendly and considered as a sort of green Chemicals which may replace other conventional organic solvents, thus reducing ingress of organic vapors into atmosphere. The Ionic liquid salts are composed of asymmetric Nitrogen containing cations like imidazole, pyrrole, piperidine and pyridine, and a variety of anions ranging simple halides to very complex Organic anions. Imidazole based tetra fluoro borate and hexa fluoro Phosphate are very popular ionic liquids.
Ms Mara G. Freire, Catarina M. S. S. Neves, Isabel M. Marrucho, Joao A. P. Coutinho, and Ana M. Fernandes have studied the hydrolysis rate of Imidazolium - based Ionic Liquids with tetrafluoroborate and hexafluorophosphate anions .
The aim of the study is to high light the environmental impact of wide spread industrial use of these liquids under unfavorable conditions like thermal and hydrolytic influence, under which these may undergo decomposition Hydrolysis to yield highly toxic by- products like Hydrofluoric acid etc.
They have studied the Chemical and thermal stability of hexafluorophosphate-
and tetrafluoroborate-based ILs by studying their Hydrolysis under various field conditions pH and Temperature, by Electro spray ionization mass spectroscopy, NMR Spectroscopy, and pH measurements to arrive at their conclusions.
Observations
1). Hydrolysis occurs affects the anions - PF6 and BF4 but not the imidazolium cation. 2). Hydrolysis of BF4 occurred under all conditions, even at room temperature. 3) PF6 is more stable than BF4 in that, it is stable in moderate conditions, but, decomposition is significant at temperature above 343K or pH less than 3.
Effect of the Previous Composting on Volatiles Production during Biomass Pyrolysis
The organic material derived from the plants is known as Bio mass. The main components of bio mass are cellulose, hemi cellulose, extractable liquids, and lignin. Their composition varies from source to source. Bio mass contributes around 9 to 13 to the total energy requirement in the Industrialized countries. There are further opportunities to increase the availability of bio mass by cultivating certain fast growing species like, leucaena and tagasaste which can be even grown in semi arid conditions economically.
Bio mass applications.
The utilization of Bio mass takes different routes, say, Incineration, Pyrolysis, gasification, and the Integrated Gas Steam combined Cycle (IGCC) processes.
By incineration, all the organic materials are burnt and the heat of combustion is used for producing energy, be it thermal, mechanical or electrical as per the requirement.
By pyrolysis, the bio mass is heated in the absence of air to degrade it into gaseous products like CO, CO2, H2O, H2, HC , liquid product- bio oil and solid product - Char which is mainly carbon. Slow pyrolysis yields more of Char and rapid pyrolysis yields more of Bio oil. Both Char and Bio oil can be used as renewable fuels.
By Gasification, Bio mass is reacted with gasification agents like Steam , air , Oxygen, H2 , CO2 or their mixtures at high temperatures to produce Syn Gas, a gaseous fuels comprising predominantly CO, and H2. The syn gas can be further processed to petroleum products by Fischer - Tropsch synthesis or fuels like Methanol which can be used for making Bio diesel. Syn gas can also be fed into Gas Engines to produce Power.
Pretreatments of Bio mass like drying, size reduction, composting enhances the down stream processing. One of the important pretreatment is composting where in chemical changes occur which is favorably disposed towards the further processing by gasification. It is known, the composted Bio mass has more of lignin and yields more Hydrogen while gasification.
Focus of the present study.
Ms. Agust1n G. Barneto, Jos Ariza Carmona, and M. Jess Daz Blanco has studied the yield of Hydrogen in both Composted Bio mass and ordinary bio mass to assess the benefit of composting Bio mass prior to further down stream processing.
Experimental set up.
For the experiments the bio mass of Leucaena and Tagasaste are used. 2 Kgs of bio mass are taken, chipped, moistened to 60 moisture content, and composted in a Poly ethylene container at 24 OC for about 40 days, continuously aerating the sample and changing the container every four days. The resultant composted bio mass is further crushed and analyzed for its contents like Cellulose , Hemi cellulose, Lignin and ethanol- benzene extractables. Also the Bio mass is analyzed by thermo gravimetric method, by heating at a rate of 10 OCmin from 25 to 900 OC under Helium atmosphere. The gaseous products are analyzed by mass spectrometer. The experiment is repeated for both composted and uncomposted bio mass and the results are compared.
Observations.
1). Composting increases volatilization rate of Cellulose and Hemi cellulose. The mass loss rate is higher for the compost than that for the biomass. 2). The carbohydrates present in biomass undergo a degradative process, which reduces its proportion in compost and produces volatiles (mainly H2O and CO2).
3). When composting is finished, in about 35 days, a part of the initial hemi cellulose and cellulose (close to 12 wt ) remains in the compost as a humic fraction. 4). In biomass pyrolysis, the lignin fraction has a very important contribution on the total char production. This effect is increased during compost pyrolysis (close to 75 wt ).
5). Lignin, mainly in compost, produces a higher amount of volatiles. The compost of leucaena produces 12 more hydrogen than Biomass.
999 Combining Homogeneous Catalysis with Heterogeneous Separation using Tunable Solvent Systems
Tunable Solvent systems are a unique catalytic system wherein both homogenous catalytic reaction and the separation of products in different heterogeneous phases are carried out simultaneously, thereby avoiding unnecessary mass transfer operation like distillation to separate the phases thus saving energy and improving economics. Two examples of solvent systems, tunable by CO2 are Poly ethylene glycol (PEG) Organic tunable solvents (POTS) and Organic aqueous Tunable solvents (OATS). The reaction is carried in homogenous phase and CO2 or Propane is added to induce a phase split between the polar and non polar solvents, say, in the case of POTS, PEG and an organic solvent respectively. By depressurizing the CO2 the phase separation can be reversed. By this process many pharmaceutical products can be catalytically synthesized and separated from the reaction mixture easily.
Ms. Vittoria M. Blasucci, Zainul A. Husain, Ali Z. Fadhel, Megan E. Donaldson, Eduardo Vyhmeister, Pamela Pollet, Charles L. Liotta, and Charles A. Eckert have studied the palladium-catalyzed coupling of 1-bromo- 3,5-dimethylbenzene and o-cresol to potassium hydroxide to produce o-tolyl-3,5-xylyl ether and 1-bromo-3,5-di-tert-butylbenzene to potassium hydroxide to produce 3,5-di-tert-butylphenol in PEG 4001,4-dioxanewater, (2) the rhodium-catalyzed hydroformylation of p-methyl styrene in wateracetonitrile to form 2-(p-tolyl) propanal, and (3) the phase behavior of a propane-induced tetrahydrofuran.
Observations.
1). PEG increases the rate of reaction as it can complex cations and activate anions for the reaction. 2). PEG has the advantages of low cost, thermal stability, very low vapor pressure, bio degradability and non toxicity. 3). PEG is superior to water as a polar solvent for tunable solvent systems as it is compatible with many organic co solvents, unlike water. 4). Use of propane as an anti solvent may provide many advantages over CO2, like elimination of formation of carbonic acid for pH sensitive reactions, lowering phase shift operating pressure, avoiding buffers and the consequent solid separation. 5). Tunable solvent systems offer easy solution for homogenous catalytic reaction and heterogeneous separation
Suggestions and Comments
There a lot of enthusiasm among scientists regarding Green Chemistry and a lot of researches are in pipe line. But most of the Research works are of laboratory type or at the maximum bench scale type. If the Academic research is to be fruitful, these have to be scaled up to pilot plant semi commercial and commercial scale. Pilot plant study is essential to assess the efficacy of the process in terms of
Mass balance,
Energy balance,
Overall economics taking into account all aspects of manufacturing like
Raw material landed cost,
Processing cost,
Utilities Energy cost, and
Fixed expenses as against the other alternate routes.
Safety of the process with respect to personnel, machinery and environment impact.
There is an optimism of replacing fossil fuel with Hydrogen. People do have hopes of producing and using Hydrogen in order to avoid CO2 emission. They even pin hopes on reverse water gas shift reaction to produce carbon from CO2 and H2. But one has to ponder the following points.
Hydrogen, being a first group element in the periodical Table, is highly reactive and as such is not available in nature as an element and so it is not available as a source material for industrial exploitation.
We can only produce H2 from other source materials containing H2, like water, Hydrocarbon or other carbonaceous materials by spending energy.
If we produce H2 from Hydrocarbons or carbonaceous materials like Coal by steam reforming or by Coal gasification route, we cant say it is a green source as we will generate equivalent quantities of CO2 at the site of manufacturing H2 and emitting it to the atmosphere.
If we produce H2 from water by electrolysis we put more electric energy to produce H2 rather than the energy derived from the H2 thus produced, because of the thermodynamic considerations. We have to remember that Electric energy from thermal power plants is not green energy as it produces CO2 during combustion of fossil fuels.
If we are contemplating use of nuclear energy to produce H2 by Thermo chemical or electro chemical route and take all the pain to store and transport H2, would it not be worth while to directly use the power from Nuclear energy for the Transportation and other purposes.
In all these cases Hydrogen is not an energy source rather an intermediate for energy conversions.
If we are to derive H2 from CO2 neutral sources like Bio mass, we have to ponder whether Bio mass production can substitute all fossil fuels, and if so how much land area and human efforts are required to produce, transport and utilize them.
An overall economic study has to be done for these processes.
The redeeming fact of these emerging researches is the inventions of new avenues for improving the overall efficiencies and alternate route of energy manufacture and utilization. One example is the research focus on Fuel cell technology.
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