MIX AND MATCH This model of the FlexReactor shows a core of static mixer tubes in a baffled shell for effective heat transfer and linked by reconfigurable U-bends on the head. BHRSOLUTIONS

One innovation, FlexReactor, is a flexible reactor for continuous processing being developed by engineering consultant firm BHRSolutions. The core of the reactor is a bundle of static mixer tubes in a reconfigurable package, according to Andrew Green, the company's technical director. Detachable U-bends connect the tubes in a wide range of configurations.

The operator can decide whether to run all the static mixer tubes together or use just one or two, adjust the length of the flow path, introduce instrumentation along the reactor, and add accessories for heat transfer or separation, for example. The bundle can be retrofitted as part of an external loop to a conventional reactor. Or it can run between two batch vessels or as part of a completely continuous process.

Green says people looking for alternatives to stirred-tank reactors are interested in the FlexReactor. Development units are being tested in a customer site for a high-value product, and one unit is available for people to rent so they can try the technology, he adds. A mobile version is being developed.

Such a unit alongside existing stirred tanks could carry out the parts of a process that are suited to continuous operation--for example, reactions that are highly exothermic. "In the short term, it will not completely replace stirred tanks, but it's an opportunity to revolutionize one or two steps," Green says.

Meanwhile, Air Products & Chemicals has developed a new fixed-bed technology for stirred-tank reactors, called the monolith loop reactor. The core of the invention is a monolithic catalyst consisting of a magnesium aluminum silicate support coated with a proprietary formulation of metal oxides in which precious-metal catalysts are deposited.

The monolithic catalyst is assembled like a honeycomb with long parallel channels. The number of cells per unit area--and consequently the catalytic surface area--can be varied. The coat formulation can be tailored to modify catalyst behavior.

The invention is aimed at eliminating use of catalyst slurries in stirred-tank operations. According to Brian P. Roy, business development manager at Air Products, loss of precious metal is a major problem with catalyst slurries. Also, another unit operation is needed to separate the catalyst. In a monolith configuration, the catalyst is in a fixed structure. Achieving product quality standards for catalyst carryover is vastly simpler, he says.

The innovation targets reactions involving gases and liquids. In the monolith loop reactor, the monolithic catalyst is combined with Air Products' technology for flowing gases and liquids over the catalyst. The reactor has been designed to be retrofitted to existing infrastructure, so the risk associated with implementation is limited, Roy says.

The flow technology includes a gas ejector that draws gas into the liquid stream, which moves through the channels of the honeycomb. In effect, Roy says, the reactor intensifies the catalytic reaction while simultaneously achieving mass-transfer rates that are up to 100 times greater than is typical for stirred-tank reactors. Retrofitted to existing infrastructure, the reactor will do the chemistry and the batch vessel will act as a holding vessel. In an all-continuous-flow system, the technology offers shorter cycle times or smaller reactors, he says.

Various hydrogenations have been run using the new reactor, including conversion of nitroaromatic compounds to aromatic amines, hydrogenation of aromatic compounds to aliphatic compounds, and reduction of alkynes, nitriles, and unsaturated esters. Up to 50% reductions in the cost of goods can be achieved, Roy says.

The possibilities for the technology are wide, Roy says. The honeycomb catalysts can be made available in canisters--much like the oil filter in a car. "You put it in place, operate for a time, and then replace," he says. Canisters of various types can be stacked in one reactor for sequential reactions mediated by different catalysts. And because what comes out of the reactor typically is water-clear material, he adds, the material can go directly to postprocessing, bypassing filtration. "The potential now exists for alternative postreaction operations--for example, distillation."

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