Category Archives: Chemical & Engineering News

Synthetic Stones Capture Carbon

While scrubbers in smokestacks at coal plants can pull out toxic gases like sulfur dioxide, scientists haven’t yet developed a cost-effective technology to remove carbon dioxide from industrial exhaust. Now European researchers have tinkered with the chemical composition of limestone to produce a material that absorbs almost twice as much CO2 as the natural mineral can (Environ. Sci. Technol., DOI: 10.1021/es2034697).

Small-scale carbon-scrubbing operations currently rely on amine-based materials. But these materials lose some of their absorbency after repeated use. Dolomitic limestone, CaMg(CO3)2, is an alternative. As early as the 1970s, scientists noticed that when they heated it, the mineral could absorb CO2 from the mixture of gases emitted by coal power plants and later release it as a purified gas, ready to compress and store. It doesn’t absorb as much CO2 as amine-based materials, but it can survive more absorption-release cycles.

To improve on dolomitic limestone’s carbon-absorbing properties, Christoph Müller of the Swiss Federal Institute of Technology, Zurich (ETH), and his colleagues wanted to minimize the amount of magnesium in the material. Magnesium helps form microscopic pores in the mineral, which expose more surface area of the calcium component to CO2. But magnesium doesn’t react with CO2. With more of the element, the limestone becomes heavier and requires more heat to drive the calcium to react with CO2.

So Müller and his colleagues created a series of synthetic limestones by mixing different ratios of calcium and magnesium, precipitating the mineral with different bases, and using different crystallization times. They found that a calcium-to-magnesium ratio of about 7:3, precipitation with a nitrate base, and 14 days of crystallization produced the best-performing material.

Per gram of material, the material absorbed about 0.56 g of CO2, while natural dolomitic limestone absorbs 0.38 g CO2. The synthetic material also performed better after repeated cycles of absorption and release. After 15 such cycles, a gram of the synthetic limestone could still grab about 0.51 g of CO2, while the natural mineral could absorb only 0.26 g.

When the scientists studied the best-performing synthetic mineral’s crystal structure using a scanning electron microscope, they found that the magnesium and calcium atoms were mixed evenly throughout the crystal lattice, similar to dolomitic limestone’s structure. Meanwhile, in the poor-performing materials, the two elements formed separate mini-crystals. The team speculates that the precipitation technique and crystallization time allowed the material to form more pores despite the low amount of magnesium.

Carlos Abanades, a chemical engineer at the National Coal Institute in Oviedo, Spain, says that the material is promising and adds that the researchers next should test whether a scaled-up version of the material will cost less than existing amine technologies.

Edward J. Anthony, a chemical engineer at the University of Ottawa, calls the study “very intriguing work.” He says the next step will be to test whether the new material performs as well after even more cycles and in the hot conditions found in industrial settings. Müller says his team plans to test the material under those conditions.

First published by Chemical & Engineering News: [html] [pdf]

Greening Mortar With Olive Waste

The cement industry is one of the world’s largest producers of atmospheric carbon dioxide. The reason is that cement’s calcium carbonate releases the greenhouse gas. Now researchers have shown that they can replace up to 10% of the cement in mortar mixtures without harming the strength of the widely used masonry paste. The cement’s replacement is environmentally friendly, to boot: a waste product from olive oil production (Environ. Sci. Technol., DOI: 10.1021/es200968a).

For decades, cement makers have substituted fly ash, a fine residue from coal-burning power plants, for part of the cement in mortar. The ash contains silicon and aluminum, which react with the cement to form a strong mortar. Over the past few years researchers have experimented with supplementing mortars with other sources of fly ash, including tire rubber and some forms of biomass.

Luis Sánchez Granados at the University of Córdoba, in Spain, and his colleagues decided to experiment with olive fly ash, which also contains silicon, calcium, and aluminum. This ash comes from factories that generate heat or electricity by burning plant material left over from pressing olive oil.

The researchers replaced different fractions of cement with olive fly ash and measured the strength of the resulting mortars. The mortar grew weaker as the percentage of the olive ash in it rose, but it met industry strength standards with up to about 10% of the cement replaced. Used in mortars in the right proportion, Sánchez says, olive biomass would be low cost, produce little carbon dioxide, and help olive-oil-producing countries dispose of a major waste product.

This Concentrate first appeared in Chemical & Engineering News: [html] [pdf]

Sewer Sampling Reveals Patterns Of Drug Use

While high school graduates in Oslo, Norway, partied hard for two weeks last spring during the so-called Russ graduation festivities, levels of the drug ecstasy spiked about 10-fold in the city’s sewer system, according to new research. In the past few years, water quality specialists have monitored such illicit drug use through sewage sampling there and in other cities, including London and San Diego, to observe the effects of drug control policies.

However, current analytical methods require expensive equipment to collect water samples and don’t allow for continuous sampling of wastewater. Now researchers demonstrate that so-called passive filters provide an efficient and inexpensive means to measure drug use over weeks in municipal wastewater. With the samplers, they studied the ebbs and flows of 11 drugs in Oslo’s sewers for a year, including during the Russ celebrations (Environ. Sci. Technol., DOI: 10.1021/es201124j).

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