Monday, February 8, 2010
Exploring Atom Recovery
In exploring the atom recovery link, I was disappointed. I read, "Theoretical yield = (moles of limiting reagent)(stoichiometric ratio; desired product/limiting reagent)(MW of desired product)". That was enough! That's a language I don't speak and don't understand, and even worse: it's a mathematical equation. And I've never been good at those. The tables and the illustrations were simply frightening. While I appreciate that good mathematicians and chemists might really get excited about working out atom recovery equations, I want to run far, far away.
Catalyst of the Week: Chromium
Name: Chromium
Symbol: Cr
Type: Transition Metal Atomic weight: 51.996
Density @ 293 K: 7.19 g/cm3 Atomic volume: 7.23 cm3/mol
Melting point: 2180 K (1907 oC) Boiling point: 2943 K (2670 oC)
Shells: 2,8,13,1 Electron configuration: [Ar] 3d5 4s1
Minimum oxidation number: -2 Maximum oxidation number: 6
Minimum common oxidation no.: 0 Max. common oxidation no.: 3
Electronegativity (Pauling Scale): 1.66 Polarizability volume: 11.6 Å3
Chromium is a solid; its hardness is 8.5 mohs. It was was discovered in 1780 by Nicolas-Louis Vanquelin. He isolated chromium by heating the oxide in a charcoal oven. Vanquelin also identified small amounts of chromium in ruby and emerald stones. Chromium is not found as a free element in nature but is found in the form of ores. The main ore of chromium is chromite (FeCr2O4). To isolate the metal commercially, chromite ore is oxidized to chromium(III) oxide (Cr2O3). The metal is then obtained by heating the oxide in the presence of aluminum or silicon. The metal is widely used as a catalyst.
Chromium metal is an essential trace element, but hexavalent chromium (Cr(VI)) is very toxic and carcinogenic. Chromium is odorless, tasteless, and malleable. Chromium is a silver, lustrous, very hard metal that can take a high mirror polish. Chromium is used in stainless steel, and other alloys. Chromium plating on cars and bicyles produces a smooth, silver finish that is highly resistant to corrosion.
Chromium was named from the Greek word 'chroma', meaning color because it forms a variety of colorful compounds. The metal forms a thin protective oxide coating in air, and burns when heated to form green chromium oxide(Cr2O3). Chromium compounds are valued as pigments for their vivid green, yellow, red and orange colors.
Plastic that grows in the field
Posted by Chemist as General Science on Jun 14, 2007
A chromium catalyst is the key to efficiently converting glucose to a chemical feedstock with potential to replace many uses of crude oil including pharmaceuticals, cosmetics and plastics, scientists from Pacific Northwest National Laboratory report. As the world tries to emancipate itself from its oil addiction, researchers are seeking a clean, efficient and cost effective process that uses renewable biomass.
Hydroxymethylfurfural, or “HMF,” is a promising compound which is conventionally prepared from fructose using acid catalysts which, unfortunately, causes various side reactions, significantly increasing the cost of product purification.
Haibo Zhao and coauthors converted fructose and glucose to HMF in acid-free conditions by experimenting with 19 different metal halide catalysts such as CrCl2 (chromium (II) chloride), CuCl2 (copper (II) chloride), VCl2 (vanadium (II) chloride) in a sugar-solubilizing ionic liquid solvent - 1-alkyl-3-methylimidazolium chloride.
Twelve of the metal halides tested showed 40% conversion of glucose, but only one catalyst, CrCl2 (chromium (II) chloride), gave HMF in high yield and produced very little byproduct of levulinic acid.
Reference: “Metal Chlorides in Ionic Liquid Solvents Convert Sugars to 5-Hydroxymethylfurfural,” by H. Zhao, J.E. Holladay, H. Brown and Z. Conrad Zhang at Pacific Northwest National Laboratory in Richland, WA
Here is the press-release from Northwest National Laboratory in Richland:
It has been an elusive goal for the legion of chemists trying to pull it off: Replace crude oil as the root source for plastic, fuels and scores of other industrial and household chemicals with inexpensive, nonpolluting renewable plant matter.
Scientists took a giant step closer to the biorefinery this week, reporting in the June 15 issue of the Journal Science that they have directly converted sugars ubiquitous in nature to an alternative source for those products that make oil so valuable, with very little of the residual impurities that have made the quest so daunting.
"What we have done that no one else has been able to do is convert glucose directly in high yields to a primary building block for fuel and polyesters," said Z. Conrad Zhang, senior author who led the research and a scientist with the PNNL-based Institute for Interfacial Catalysis, or IIC.
That building block is called HMF, which stands for hydroxymethylfurfural. It is a chemical derived from carbohydrates such as glucose and fructose and is viewed as a promising surrogate for petroleum-based chemicals.
Glucose, in plant starch and cellulose, is nature's most abundant sugar. "But getting a commercially viable yield of HMF from glucose has been very challenging," Zhang said. "In addition to low yield until now, we always generate many different byproducts, including levulinic acid, making product purification expensive and uncompetitive with petroleum-based chemicals."
Zhang, lead author and former post doc Haibo Zhao, and colleagues John Holladay and Heather Brown, all from PNNL, were able to coax HMF yields upward of 70 percent from glucose and nearly 90 percent from fructose while leaving only traces of acid impurities. To achieve this, they experimented with a novel non-acidic catalytic system containing metal chloride catalysts in a solvent capable of dissolving cellulose.
The solvent, called an ionic liquid, enabled the metal chlorides to convert the sugars to HMF. Ionic liquids provide an additional benefit: It is reusable, thus produces none of the wastewater in other methods that convert fructose to HMF.
Metal chlorides belong to a class of ionic-liquid-soluble materials called halides, which "in general work well for converting fructose to HMF," Zhang said, "but not so well when glucose is the initial stock." In fact, attempts at direct glucose conversion created so many impurities that it was simpler to start with the fructose, less common in nature than glucose.
Zhang and his team, working with a high-throughput reactor capable of testing 96 metal halide catalysts at various temperatures, discovered that a particular metal "chromium chloride" was by far the most effective at converting glucose to HMF with few impurities and, as such reactions go, at low temperature, 100 degrees centigrade.
"This, in my view, is breakthrough science in the renewable energy arena," said J.M. White, IIC director and Robert A. Welch chair in materials chemistry at the University of Texas. "This work opens the way for fundamental catalysis science in a novel solvent."
The chemistry at work remains largely a mystery, Zhang said, but he suspects that metal chloride catalysts work during an atom-swapping phase that sugar molecules go through called mutarotation, in which an H (hydrogen) and OH (hydroxyl group) trade places.
The hydrogen-hydroxyl position-switch that allows the catalytic conversion was verified by nuclear magnetic resonance performed at the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at PNNL. During the swap, the molecule opens, Zhang said. "The key is to take advantage of the open form to perform a hydride transfer through which glucose is converted to fructose."
Zhang's next step is to tinker with ionic solvents and metal halides combinations to see if he can increase HMF yield from glucose while reducing separation and purification cost. "The opportunities are endless," Zhang said, "and the chemistry is starting to get interesting.
Symbol: Cr
Type: Transition Metal Atomic weight: 51.996
Density @ 293 K: 7.19 g/cm3 Atomic volume: 7.23 cm3/mol
Melting point: 2180 K (1907 oC) Boiling point: 2943 K (2670 oC)
Shells: 2,8,13,1 Electron configuration: [Ar] 3d5 4s1
Minimum oxidation number: -2 Maximum oxidation number: 6
Minimum common oxidation no.: 0 Max. common oxidation no.: 3
Electronegativity (Pauling Scale): 1.66 Polarizability volume: 11.6 Å3
Chromium is a solid; its hardness is 8.5 mohs. It was was discovered in 1780 by Nicolas-Louis Vanquelin. He isolated chromium by heating the oxide in a charcoal oven. Vanquelin also identified small amounts of chromium in ruby and emerald stones. Chromium is not found as a free element in nature but is found in the form of ores. The main ore of chromium is chromite (FeCr2O4). To isolate the metal commercially, chromite ore is oxidized to chromium(III) oxide (Cr2O3). The metal is then obtained by heating the oxide in the presence of aluminum or silicon. The metal is widely used as a catalyst.
Chromium metal is an essential trace element, but hexavalent chromium (Cr(VI)) is very toxic and carcinogenic. Chromium is odorless, tasteless, and malleable. Chromium is a silver, lustrous, very hard metal that can take a high mirror polish. Chromium is used in stainless steel, and other alloys. Chromium plating on cars and bicyles produces a smooth, silver finish that is highly resistant to corrosion.
Chromium was named from the Greek word 'chroma', meaning color because it forms a variety of colorful compounds. The metal forms a thin protective oxide coating in air, and burns when heated to form green chromium oxide(Cr2O3). Chromium compounds are valued as pigments for their vivid green, yellow, red and orange colors.
Plastic that grows in the field
Posted by Chemist as General Science on Jun 14, 2007
A chromium catalyst is the key to efficiently converting glucose to a chemical feedstock with potential to replace many uses of crude oil including pharmaceuticals, cosmetics and plastics, scientists from Pacific Northwest National Laboratory report. As the world tries to emancipate itself from its oil addiction, researchers are seeking a clean, efficient and cost effective process that uses renewable biomass.
Hydroxymethylfurfural, or “HMF,” is a promising compound which is conventionally prepared from fructose using acid catalysts which, unfortunately, causes various side reactions, significantly increasing the cost of product purification.
Haibo Zhao and coauthors converted fructose and glucose to HMF in acid-free conditions by experimenting with 19 different metal halide catalysts such as CrCl2 (chromium (II) chloride), CuCl2 (copper (II) chloride), VCl2 (vanadium (II) chloride) in a sugar-solubilizing ionic liquid solvent - 1-alkyl-3-methylimidazolium chloride.
Twelve of the metal halides tested showed 40% conversion of glucose, but only one catalyst, CrCl2 (chromium (II) chloride), gave HMF in high yield and produced very little byproduct of levulinic acid.
Reference: “Metal Chlorides in Ionic Liquid Solvents Convert Sugars to 5-Hydroxymethylfurfural,” by H. Zhao, J.E. Holladay, H. Brown and Z. Conrad Zhang at Pacific Northwest National Laboratory in Richland, WA
Here is the press-release from Northwest National Laboratory in Richland:
It has been an elusive goal for the legion of chemists trying to pull it off: Replace crude oil as the root source for plastic, fuels and scores of other industrial and household chemicals with inexpensive, nonpolluting renewable plant matter.
Scientists took a giant step closer to the biorefinery this week, reporting in the June 15 issue of the Journal Science that they have directly converted sugars ubiquitous in nature to an alternative source for those products that make oil so valuable, with very little of the residual impurities that have made the quest so daunting.
"What we have done that no one else has been able to do is convert glucose directly in high yields to a primary building block for fuel and polyesters," said Z. Conrad Zhang, senior author who led the research and a scientist with the PNNL-based Institute for Interfacial Catalysis, or IIC.
That building block is called HMF, which stands for hydroxymethylfurfural. It is a chemical derived from carbohydrates such as glucose and fructose and is viewed as a promising surrogate for petroleum-based chemicals.
Glucose, in plant starch and cellulose, is nature's most abundant sugar. "But getting a commercially viable yield of HMF from glucose has been very challenging," Zhang said. "In addition to low yield until now, we always generate many different byproducts, including levulinic acid, making product purification expensive and uncompetitive with petroleum-based chemicals."
Zhang, lead author and former post doc Haibo Zhao, and colleagues John Holladay and Heather Brown, all from PNNL, were able to coax HMF yields upward of 70 percent from glucose and nearly 90 percent from fructose while leaving only traces of acid impurities. To achieve this, they experimented with a novel non-acidic catalytic system containing metal chloride catalysts in a solvent capable of dissolving cellulose.
The solvent, called an ionic liquid, enabled the metal chlorides to convert the sugars to HMF. Ionic liquids provide an additional benefit: It is reusable, thus produces none of the wastewater in other methods that convert fructose to HMF.
Metal chlorides belong to a class of ionic-liquid-soluble materials called halides, which "in general work well for converting fructose to HMF," Zhang said, "but not so well when glucose is the initial stock." In fact, attempts at direct glucose conversion created so many impurities that it was simpler to start with the fructose, less common in nature than glucose.
Zhang and his team, working with a high-throughput reactor capable of testing 96 metal halide catalysts at various temperatures, discovered that a particular metal "chromium chloride" was by far the most effective at converting glucose to HMF with few impurities and, as such reactions go, at low temperature, 100 degrees centigrade.
"This, in my view, is breakthrough science in the renewable energy arena," said J.M. White, IIC director and Robert A. Welch chair in materials chemistry at the University of Texas. "This work opens the way for fundamental catalysis science in a novel solvent."
The chemistry at work remains largely a mystery, Zhang said, but he suspects that metal chloride catalysts work during an atom-swapping phase that sugar molecules go through called mutarotation, in which an H (hydrogen) and OH (hydroxyl group) trade places.
The hydrogen-hydroxyl position-switch that allows the catalytic conversion was verified by nuclear magnetic resonance performed at the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at PNNL. During the swap, the molecule opens, Zhang said. "The key is to take advantage of the open form to perform a hydride transfer through which glucose is converted to fructose."
Zhang's next step is to tinker with ionic solvents and metal halides combinations to see if he can increase HMF yield from glucose while reducing separation and purification cost. "The opportunities are endless," Zhang said, "and the chemistry is starting to get interesting.
Tuesday, February 2, 2010
Chemistry Bonding Images
The images on this site are interesting and colorful, but I had to read through the color-coding descriptions a few times and am still not sure that I understand the concept. If I understand correctly, positive electrostatic potential is created by high electron density (a high negative charge); therefore, both positive electrostatic potential and high electron density are depicted in blue. Red is supposed to depict negative electrostatic potential and low electron density. But low electron density does not necessarily mean negative electrostatic potential, does it?
Covalent Bond Types are Like Eating in a Restaurant
I love the analogy. It makes the concept of electron-sharing really easy to remember and to understand. In my mind, I have converted "non-polar" to "no pickles" because I would be more willing to give half of my cheeseburger to my son if the cheeseburger had no pickles. If it has pickles/"polar" my son would take my whole cheeseburger and give me little in return. Coordinate covalent bonds are different, you just give it up to another in need with no expectation of sharing.
Monday, February 1, 2010
Palladium
Palladium is a soft, ductile, steel-white, tarnish-resistant, metallic element occurring naturally with platinum, especially in gold, nickel, and copper ores. Its atomic number is 46; atomic weight 106.4; melting point 1,552°C; boiling point 3,140°C; specific gravity 12.02 (20°C); valence 2, 3, 4. Along with platinum, rhodium, ruthenium, iridium and osmium, palladium is one of the elements in the "platinum group metals" (PGMs). Palladium has the lowest melting point among this group and is the least dense.
Palladium was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas, which was discovered about the same time.
Because it can absorb large amounts of hydrogen, palladium is used as a purification filter for hydrogen and a catalyst in hydrogenation. Over half of the supply of palladium goes into catalytic converters, which convert up to 90% of harmful gases from auto exhaust (hydrocarbons, carbon monoxide and nitrogen oxide) into less harmful substances (nitrogen, carbon dioxide and water vapor). Palladium is used in fuel cells and in many electronics including computers, mobile phones, low voltage electrical contacts, and SED/OLED/LCD televisions. It is alloyed for use in electric contacts, jewelry, nonmagnetic watch parts, and surgical instruments.
Ore deposits of palladium and other platinum group metals are rare, and the most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex in the Transvaal in South Africa, the Stillwater Complex in Montana, United States, the Sudbury District of Ontario, Canada, and the Norilsk Complex in Russia. Palladium is also obtained by recycling scrapped catalytic converters.
All palladium compounds should be regarded as highly toxic and as carcinogenic. However palladium chloride was formerly prescribed as a treatment for tuberculosis at the rate of 0.065 g per day (approximately 1 mg kg-1) "without too many bad side effects".
Sources: Answers.com; WebElements.com and Wikipedia.com
Palladium was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas, which was discovered about the same time.
Because it can absorb large amounts of hydrogen, palladium is used as a purification filter for hydrogen and a catalyst in hydrogenation. Over half of the supply of palladium goes into catalytic converters, which convert up to 90% of harmful gases from auto exhaust (hydrocarbons, carbon monoxide and nitrogen oxide) into less harmful substances (nitrogen, carbon dioxide and water vapor). Palladium is used in fuel cells and in many electronics including computers, mobile phones, low voltage electrical contacts, and SED/OLED/LCD televisions. It is alloyed for use in electric contacts, jewelry, nonmagnetic watch parts, and surgical instruments.
Ore deposits of palladium and other platinum group metals are rare, and the most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex in the Transvaal in South Africa, the Stillwater Complex in Montana, United States, the Sudbury District of Ontario, Canada, and the Norilsk Complex in Russia. Palladium is also obtained by recycling scrapped catalytic converters.
All palladium compounds should be regarded as highly toxic and as carcinogenic. However palladium chloride was formerly prescribed as a treatment for tuberculosis at the rate of 0.065 g per day (approximately 1 mg kg-1) "without too many bad side effects".
Sources: Answers.com; WebElements.com and Wikipedia.com
Sunday, January 24, 2010
Transition Metal: Rhenium
Did you know that rhenium (pronounced ri-neum) was the next-to-last naturally occurring element to be discovered?
Its name derives from the Latin term rhemus meaning Rhine. Those who know their world geography will deduce from its name that it was discovered in . . . Germany, in the year 1925.
Rhenium is clingy and reclusive. It is not found free; rather, it is detected in ores, like platinum and porphyry copper, and minerals, like columbite. It's favorite companion is molybdenum. Rhenium is recovered as a byproduct from roasting molybdenum concentrates.
Recovering rhenium is an expensive process, which lends to rhenium's distinction of making the list of the top 10 most expensive transition metals. During 2006, average rhenium metal price was a whopping $1,170 per kilogram, but it rose as high as $5,000 per kilogram when Kazakhstan refused to supply it to the U.S. for several months!
Rhenium is a component of platinum-rhenium catalysts that are used primarily in producing lead-free, high-octane gasoline and in high-temperature superalloys used for jet engine components.
The largest producer of rhenium has always been Chile. Kazakhstan has become the second largest producer. The United States relies heavily on rhenium imports, as it produces rhenium from only six mines in the U.S.: Two in Arizona and one each in Montana, Nevada, New Mexico and Utah.
Its name derives from the Latin term rhemus meaning Rhine. Those who know their world geography will deduce from its name that it was discovered in . . . Germany, in the year 1925.
Rhenium is clingy and reclusive. It is not found free; rather, it is detected in ores, like platinum and porphyry copper, and minerals, like columbite. It's favorite companion is molybdenum. Rhenium is recovered as a byproduct from roasting molybdenum concentrates.
Recovering rhenium is an expensive process, which lends to rhenium's distinction of making the list of the top 10 most expensive transition metals. During 2006, average rhenium metal price was a whopping $1,170 per kilogram, but it rose as high as $5,000 per kilogram when Kazakhstan refused to supply it to the U.S. for several months!
Rhenium is a component of platinum-rhenium catalysts that are used primarily in producing lead-free, high-octane gasoline and in high-temperature superalloys used for jet engine components.
The largest producer of rhenium has always been Chile. Kazakhstan has become the second largest producer. The United States relies heavily on rhenium imports, as it produces rhenium from only six mines in the U.S.: Two in Arizona and one each in Montana, Nevada, New Mexico and Utah.
Sunday, January 17, 2010
Speaking of Carbon, Carbon-Neutral, Carbon Dioxide . . .
Check out coffee ground firelogs by Java Log. The Java-Log fireplace log ($22 for a case of 6) is made with 100-percent recycled coffee grounds. The manufacturers claim that these logs give off 25 percent more heat and 14 percent less carbon dioxide than wood fires. Plus, they help divert coffee grounds from landfills, if you don't already use them to fortify your acid-loving plants.
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