Tag Archives: greener process

Nano research leads to a greener lubricating oil.

Synopsis by Wim Thielemans, Sep 15, 2011

Majano, G, E-P Ng, L Lakiss and S Mintova, 2011. Nanosized molecular sieves utilized as an environmentally friendly alternative to antioxidants for lubricant oilsGreen Chemistry http://dx.doi.org/10.1039/c1gc15367f.

An environmentally-friendly, sieve-like nanomaterial can reduce the chemical fallout from the breakdown of lubricants better than the chemical additives now used.

Looking to solve an old problem in a new way, green chemists find that a special porous material can better reduce levels of dangerous breakdown byproducts in oil lubricants than the long-used but harmful chemicals now added. The team of researchers report their findings about the material – called zeolites – in a recent issue of Green Chemistry.

Lubricant oils reduce friction between moving parts in machines and motors in every part of society, including factory conveyor belts, cars and sewing machines. Synthetic mineral oils are used most often because they are more stable than other types. About 32 million tons of the lubricant oils leak and enter the environment every year.

To reduce human health impacts and meet new European regulatory standards, chemists are trying to find ways to make the oils both functional and environmentally benign.

One big problem with lubricants is they break down and form byproducts when exposed to oxygen – a process known as oxidation. Oxidation generates water, reactive alcohols and acids that increase corrosion and rust, thicken the lubricant, form sludge and sediment, break down the oil and create foam.

Chemical additives prevent or reduce the oxidative reactions. Unfortunately, most additives are dangerous and can impact human health and the environment. Some also affect the machine’s function, such as deactivating the catalyst converters in cars.

In this work, researchers from France, Belgium and Malaysia tested how a highly porous inorganic nanomaterial called zeolites absorb the initial oxidation products in an effort to reduce the harmful chemical byproducts that form. They did not try to stop oxidation like the current crop of chemical additives do. In theory, since oxidative reactions naturally speed up over time, removing the reaction products would reduce further oxidation, slow the process and create less harmful byproduct.

One of the three zeolites compared in the study worked surprisingly well. The researchers found the zeolite cleans up the process in two ways. First, it slowed the inherent oxidation reactions and reduced the amount of chemical byproduct produced. Second, it also absorbed the byproducts that formed. In the end, very little sludge was produced.

The zeolites used have no known adverse environmental effects and can even work together with existing oxidation-preventing chemical additives. The zeolites – when combined with perhaps a next generation of more benign additives – would then give added protection.

Future laboratory studies will need to test the performance of the numerous other zeolites available. From there, they must be tested and assessed in a real working environment. Even though this is not the final word on the technology, it looks to be very promising.

Read more science at Environmental Health News.

Bacteria rejoice: study identifies safe solvents.

Bacteria rejoice: study identifies safe solvents.

Synopsis by Wim Thielemans and Wendy Hessler, August 2, 2011

Wood, N, JL Ferguson, HQ Nimal Gunaratne, KR Seddon, R Goodacre and GM Stephens. 2011. Screening ionic liquids for use in biotransformations with whole microbial cells. Green Chemistry http://dx.doi.org/10.1039/c0gc00579g.

Chemists took a first step towards designing a more environmentally-friendly solvent known as ionic liquids by identifying those that won’t kill the bacteria used to transform raw materials into useable products.

For the first time, a large number of the new type of solvents were tested on the E. coli bacteria strains that are widely used in industry. Many of them did not harm the bacteria and may be hopeful candidates for industry.

Ionic liquids’ popularity is growing as researchers eye them to replace toxic, smelly and polluting organic solvents currently used to produce all manner of chemicals and consumer products.

 

Context

To make chemicals, solvents are commonly required.Solvents dissolve gases, solids or liquids into a solution. They can help to bring the reacting chemicals in contact, separate the products from reactants and sometimes even speed up the chemical reaction. Unfortunately, many solvents are toxic, volatile – they evaporate quickly and/or flammable. It is therefore important to perform reactions without solvents, if possible, or use more benign solvents.

Ionic liquids are a relatively new class of solvents. They are salts – a designation for chemicals made up of both a positively and a negatively charged component– that are liquid at low temperatures, unlike common salts such as kitchen salt. Bulky positive and negative groups that make up the ionic salts hinder their packing into a solid crystal. Thus, they stay liquid to much lower temperatures – even room temperature.

People are interested in using ionic liquids because they have extremely low volatility resulting in virtually no vapor emissions. The properties of these ionic liquids (solvating power, melting point, water solubility) can also be easily varied by changing the positive and negative groups.

Researchers wish to use ionic liquids for industrial biotransformation – a process in which bacteria produce chemical products. The most commonly known biotransformation is sugar fermenting into ethanol – the way beer and wine are produced. However, fuel from renewable resources – i.e. biofuel – and even valuable chemicals can also be made this way.

Biotransformation has the potential to have a much lower impact on the environment than pure chemical reactions.

What did they do?

In this work by researchers from the United Kingdom, the toxicity of 90 different ionic liquids was tested in the laboratory using the bacterium Escheria coli (E. coli).

E. coli regularly receives negative press attention because it can cause food poisoning in people. However, it is also used frequently in industrial biotransformation

The major problem in biotransformations is that the produced chemicals are sometimes toxic to the bacteria. So as the bacteria become more efficient at producing the wanted product, they become less efficient because they die. And this is where ionic liquids can play an important role. By using an ionic liquid in which the reaction product, which is toxic to the bacteria, is soluble, the product could be extracted from the aqueous broth of bacteria before it accumulates too much, becomes too toxic and kills the bacteria.

This plan requires ionic liquids that are not toxic to the bacteria. The work described here begins to identify the nontoxic varieties by looking at the effect of the different ionic liquids on cell viability and growth rates. The researchers examined in high throughput tests ionic fluids that can dissolve (miscible) or remain undissolved (immiscible) in water.

What did they find?

Various ionic liquids were found to be non-toxic towards E. coli. There were both water miscible and immiscible ionic liquids that did not show toxicity. Importantly, the ionic liquids displayed similar toxic behavior based on their specific negative and positive chemical groups.

With this information, it is possible to start to predict the toxicity of ionic liquids towards E. coli if they contain the same charged groups as those used in this study. Surprisingly, it was also possible to prepare a type of ionic liquid called quaternary ammonium salt ionic liquids that were non-toxic to E. coli by changing the negative ion attached to it. This is a remarkable result since quaternary ammonium salts are being widely investigated for use as antibacterial agents on hard surfaces.

What does it mean?

Many types of ionic liquids were compatible with the bacteria E. coli and could be candidates for industrial uses that transform starting materials into products.

The results are very important because the toxicity trends prove that it is possible to start to rationally design ionic liquids.

The study shows it is possible to make a certain ionic liquid that has the toxicity effect that is required by choosing the positive and negative ions that it is made from. It is already possible to adjust physical parameters, such as melting point, freezing point and solvating power, i.e. the amount of a specific chemical that can be dissolved. This work thus adds another parameter that can be manipulated, adding another benefit to the use of ionic liquids.

This work is the first in a range of studies that will need to be performed to isolate which ionic liquids will perform the best. While 90 ionic liquids is a large number, more ionic liquids will need to be studied to help form a much better idea of their toxicity towards E. coli and other bacteria useful to industry.

See more science at Environmental Health News.

 

 

Gold, palladium team up to clean up chemical-making process.

 

Kesavan, L, R Tiruvalam, MH Ab Rahim, MI bin Saiman, DI Enache, RL Jenkins, N Dimitratos, JA Lopez-Sanchez, SH Taylor, DW Knight, CJ Kiely and GJ Hutchings. 2011. Solvent-free oxidation of primary carbon-hydrogen bonds in toluene using Au-Pd alloy nanoparticles. Science http://dx.doi.org/10.1126/science.1198458.

 


Jun 07, 2011

 

2011-0606audreyshand
Audrey Moores
Chemists report a cleaner way to produce a much-used compound called benzylbenzoate.

A team of researchers have cleaned up the process to produce a versatile compound – called benzylbenzoate – that kills disease-causing mites, stabilizes fragrances and is a building block for pharmaceuticals. Benzylbenzoate is made from toluene – a cheap and readily available chemical in crude oil. The new process applies oxygen gas and toluene to a material made of carbon and tiny particles of metals gold and palladium. No solvents are used, and no waste byproducts are generated. The finding is also important because it is a stepping stone to a method to convert natural gas into a useful fuel like methanol.

 

 

Context

Adding an oxygen atom to a molecule – called oxidation – in a controlled fashion is a long sought but challenging goal of chemistry. The procedure is important because most molecules used in industrial and consumer applications have unique properties due to the exact position on the molecule of specific groups of atoms – their chemical functional groups. Many of these functional groups are oxygen based.

For example, introducing one oxygen atom would convert methane – the main component of natural gas and an abundant resource – into methanol, which could be used as a liquid fuel. While simple on paper, the actual transformation is challenging. It often leads to more than one oxygen attaching and ultimately, to the complete burning of methane into carbon dioxide.

More generally, the chemical industry heavily relies on molecules that contain oxygen at key positions. They are used as bulding blocks to make other chemicals. Among them, benzyl alcohol, benzaldehyde, benzoic acid and benzylbenzoate have important economical impacts. They constitute starting points in the manufacture of important products, such as pharmaceuticals, dyes, solvents, perfumes, plasticizers, preservatives and flame retardants.

But, harmful chemicals are needed to make this family of molecules. The process starts with a simple, carbon-based molecule called toluene. Toluene is a component of crude oil. Its transformation currently requires harsh processes involving chlorinated chemicals, acidic solvents or toxic metals. The process has very poor yields (around 15 percent) and generates copious quantities of waste.

Alternatives starting with biomass are desirable and intensely researched, but to date, no alternative process exists to create this important family of compounds.

Current research on oxidation reactions focuses on three key points. First, any required additive needs to be solid to ease separation. Second, the oxygen atom introduced should preferably come from oxygen gas present in air, as opposed to more wasteful or toxic sources. Third, the process must be very efficient – that is, yield a lot of material– and selective – create only one molecular product and thus limit separating the wheat – what’s wanted – from the chaff – what’s not – after the reaction.

What did they do?

The research team from the United Kingdom and the United States exposed toluene to oxygen at 160 degrees Celcius and 10 bars of oxygen – equivalent to 10 times normal atmospheric pressure – for two days. Under these conditions, a very small fraction – 2.9 percent – of toluene was converted into a mixture of benzaldehyde, benzoic acid and a small quantity of the desired benzylbenzoate.

Then, they tested several materials for their ability to improve the reaction. One was gold nanoparticles deposited onto titania, because it actively promotes oxidation of alcohols and carbon monoxide.

Gold nanoparticles deposited onto carbon – similar to porous charcoal – was also tested.

In another approach, they deposited tiny particles of gold and palladium inside the carbon pores. In this setting, gold and palladium form an alloy that has unique properties, different from both pure gold and pure palladium.

They also varied the proportion of gold and palladium in the system and measured how it was impacting the chemical process.

Each system was analyzed using two criteria: 1) conversion – the number of toluene molecules transformed – and 2) selectivity – Did one toluene transform into one or several kinds of molecules?

What did they find?

The gold and palladium nanoparticles on the porous carbon offered the best materials to spur the difficult reaction that transforms toluene to benzylbenzoate.

About half of the toluene was converted with this media. The process was very selective – 94.3 percent of the product was benzylbenzoate. This process required 6,500 times less metal than toluene.

The authors then tried to improve toluene conversion by altering the amount of metal. By adding more metal – 1,650 times less metal than toluene – they reached a conversion of 94.4 percent.

Researchers found that the other materials were not as good. Gold nanoparticles on titania did not perform well despite its other successes. Gold alone on carbon was not very active, either.

The mixture of the gold with palladium inside each nanoparticle proved essential to activity. The optimum proportion was 1 gold atom for 1.85 palladium atoms. Size mattered too, and a small size particle was critical to obtaining high conversion.

What does it mean?

In this work, researchers developed a novel material that takes oxygen from the air to transform toluene into the valuable benzyl benzoate. The material is composed of carbon, gold and palladium at specific ratios for optimum performance.

This research is very important because it brings chemists closer to defining the reaction that could convert methane from natural gas to methanol. Such a  process could allow two important developments.

First, methane is a flammable gas and is thus impractical and dangerous to use as a fuel for vehicles. Methanol, on the other side, is a liquid similar in properties to ethanol. Ethanol currently makes up a small fraction of automobile fuel sold in the United States.

Second, methanol has other important applications in the chemical industry. It is used as a solvent, as an antifreeze and as a building block for a host of commodity chemicals.

The new reaction is also remarkable because of its high yield, chemical selectivity, low waste and use of available resources. The use of a very simply reagent – oxygen gas from air – generated no waste.

The material was very convenient to use. After the reaction, the ending product separated completely from the starting material and was simply filtered off. This allows for two good things: 1) no metal or carbon ended up in the product and 2) the material can be reused in subsequent reactions. The materials was reused four times without measuring any alteration of reactivity.

The porous carbon support played an important role in the success of the reaction. The same material based on porous titania was less active. The researchers suggest the improved performance originates from the difference in surface structure between the carbon and titania based nanoparticles. They believe carbon causes the metal particles to be rougher and thus more reactive with the oxygen.

In all cases, the chemists did not detect any carbon dioxide waste. This means that the oxidation reaction – that is, adding an oxygen atom to the starting carbon, gold and palladium materials – proceeds well. Only one atom of oxygen is added, not several, which happens during complete combustion. This process affords a valuable chemical from toluene without burning toluene itself.

More development and studies are needed to turn this discovery into an industrial process.

Resources

Edwards, JK, B Solsona,E Ntainjua, AF Carley, AA Herzing, CJ Kiely, and GJ Hutchings. 2009. Switching Off Hydrogen Peroxide Hydrogenation in the Direct Synthesis Process. Science 323(5917):1037-1041.

Enache, DI, JK Edwards, P Landon, B Solsona-Espriu, AF Carley, AA Herzing, M Watanabe, CJ Kiely, DW Knight and GJ Hutchings. 2006. Solvent-Free Oxidation of Primary Alcohols to Aldehydes Using Au-Pd/TiO2 Catalysts. Science 311(5759):362-365.

Konietzni, F, U Kolb, U Dingerdissen, WF Maier. 1998. AMM-MnxSi-catalyzed selective oxidation of toluene. Journal of Catalysis 176(2):527-535.

Partenheimer, W. 1995. Methodology and scope of metal/bromide autoxidation of hydrocarbons. Catalysis Today 23(2): 69-158.

Saravanamurugan, S, M Palanichany, V Murugesan. 2004. Oxyfunctionalisation of toluene with activated t-butyl hydroperoxide. Applied Catalysis A General 273(1-2), 143-149.

Sheldon, RA, and JK Kochi. 1981. Metal-catalyzed oxidations of organic compounds. Academic Press:New York.

Homing in on a cheaper Haber-Bosch process.

Read Original Article in Chemistry World (RSC)

Simon Hadlington
23 May 2011

A cheaper alternative to the Haber-Bosch process could have moved a step closer thanks to a new ruthenium-based catalyst complex developed by chemists in Germany.

Each year the Haber-Bosch process produces millions of tonnes of ammonia for the fertiliser industry by direct hydrogenation of nitrogen with hydrogen gas over a catalyst. However, this process needs temperatures of around 450°C and pressures of 300 bar, consuming vast amounts of energy.

Synthetic cycle

Synthetic cycle of the formation of ammonia from azide and hydrogen with x-ray crystal structure of the ruthenium(IV) nitrido intermediate in the centre
© Bjorn Askevold

Now, a team led by Sven Schneider at the University of Erlangen-Nürnberg and Max Holthausen at the University of Frankfurt have shown how a ruthenium complex with a nitrogen-metal triple-bond can split molecular hydrogen to produce high yields of ammonia at atmospheric pressure and temperatures of only around 50°C. The finding could point the way to solving the ‘second half’ of the Haber-Bosch process, the activation of hydrogen and hydrogenation of a nitrogen atom to create ammonia.

The German researchers synthesised a planar molecule with a ruthenium centre clamped by a nitrogen and two bulky flanking phosphine groups – known as a PNP pincer ligand. A nitrido ligand triply bonded to the ruthenium can then be introduced with an azide. This ligand combine with the hydrogen to form ammonia.

The mechanism of H-H bond cleavage that the team proposes has the first hydrogen atom moving to the nitrogen of the pincer with the other remaining on the ruthenium. This latter hydrogen is then transferred to the terminal nitrido ligand. This reaction repeats twice more to produce ammonia.

‘A key aspect of the system is the cooperative nature of the metal-pincer ligand fragment,’ says Schneider. ‘Both the transition metal centre and the ligand are crucial for the reaction to proceed. We have essentially modelled the second half of a Haber-Bosch type hydrogenation of nitrogen in solution.’ The next step is to try to find a way of splitting dinitrogen to obtain the single nitrogen attached to the ruthenium complex.

Commenting on the work, Christopher Cummins, an expert in nitrogen chemistry at the Massachusetts Institute of Technology in the US, says: ‘This work gives a clear demonstration of nitride ligand hydrogenolysis yielding ammonia. Now, if a nitride ligand with such reactivity could be obtained via N2 splitting then a homogeneous analogue of the Haber-Bosch ammonia synthesis would be at hand. The authors’ choice of robust pincer ancillary ligands to support the hydrogenolysis reactivity is probably crucial.’