Tiny Reactors - Aim for big role
Process Intensification (PI) has promised many things but has it fulfilled its promises? When looking at reactor technology, the answer is a definite - Yes.
Rocky Costello, R. C. Costello & Associates, Inc In this article the author emphasizes on how process intensification has improved the reactor technology with different examples.
The heart of chemical processing has always been the reactor, with the Continuous Stirred Tank Reactor (CSTR) long dominating continuous production. The CSTR was first used more than 300 years ago in the processing of gold ore, but maybe its time is up. PI is entering the scene in a big way; a number of new specialty reactors have appeared, bringing both technological advances and additional manufacturers into the market.
The term Process Intensification was originally coined at Imperial Chemical Industries in the U.K. in the 1970s. Put simply, PI involves the miniaturization of unit operations. This miniaturization should bring:
• reduced energy use;
• decreased capital expenditure;
• lower plant profile (height);
• smaller plant footprint (area);
• environmental advantages; and
• safety benefits.
Biodiesel gives process intensification a push
Recent interest in alternative energy sources such as biodiesel has helped fuel attention on PI. Why? The biodiesel reaction typically is a transesterification of soybean oil, canola oil or palm oil (triglycerides) and methanol, producing fatty acid methyl esters or biodiesel and a glycerol byproduct. This reaction isn’t very exothermic and methanol isn’t very soluble in the soybean oil. The micromixing produced by PI reactors dramatically overcomes the insolubility issue and increases reaction rates. This ultimately leads to very small reactors because the residence time can be dramatically reduced. Kreido Laboratories has produced biodiesel at residence times of 0.5 sec.
The Hydro Dynamics SPR also speeds up the continuous transesterification reaction time and allows existing batch reaction processes to more than double production rates or, because the reaction occurs instantaneously, to achieve true continuous processing. The SPR reportedly has demonstrated significant yield increases and an improvement in product quality, hold-
ing total glycerin to less than 0.05%. The reactor also enables use of lower-priced oil feed stocks. Hydro Dynamics has produced biodiesel with residences times of less than 2 sec.
When building a new plant, process equipment typically represents approximately 20% of the capital costs, with structural steel, piping, conduit, wire and instrumentation accounting for much of the balance. Smaller unit operations made possible by PI translate into a more-compact plant, lower weight, and less structural steel, piping, conduit and wire. The reduced weight of the equipment may even allow savings on concrete foundations. Overall, PI means less-expensive plants with smaller footprints. In addition, many process-intensified plants are amenable to construction on skids, which can lower costs even further.
Decreased costs aren’t enough, though, to guarantee acceptance of units so different from conventional ones. With reactors typically considered the heart of the plant, companies also want increased reactor performance. Here, the new PI reactors provide a number of advantages. They cut residence times, boost reaction rates, minimize side reactions, and reduce energy-intensive downstream processing steps such as distillation and extraction. In addition, the units can dramatically decrease the volumes of explosive, hazardous or toxic compounds in the process.
With many reactions, heat-transfer, mass-transfer or mixing limitations control the reaction rate rather than the fundamental kinetics, explains Protensive, Newcastle upon Tyne, U.K., a developer of PI units. An exothermic reaction may require a couple of hours to carry out in a batch reactor not because of any kinetic constraint, but because of the time necessary to remove the heat of reaction, adds the company. PI reactors offer a way to overcome such limitations.
Now let’s look at five commercially available PI reaction systems to see how they work and the benefits they offer. We’ll also touch upon two established PI technologies reactive distillation and static mixing.
Kreido Laboratories, Camarillo, Calif., offers the Spinning Tube in a Tube (STT) reactor. This unit induces so-called Couette Flow by mixing reactants in a narrow annular gap between a stationary stator and a rapidly rotating, concentric, internal rotor (Figure 1) so that the reactants move as a coherent thin film in a high shear field, says the company.
This very high shear field extends over the total length of the tube. Flow through the annular space is actually in the laminar range. This unit is very compact (Figure 2) and can easily perform gas/liquid and liquid/liquid reactions.
The STT reactor accelerates the rates of chemical reactions by up to three orders of magnitude, increases conversions and yields, controls the quality of production in real-time, lowers costs, and dramatically decreases the time required for manufacturing scale-up, claims the company.
Some applications include: selective oxidation, selective hydrogenation, esterification, transesterification, saponification, hydrosilylation, condensation reactions and preparation of ionic liquids.
The transesterification reaction of soybean oil and methanol for biodiesel production is being done at a residence time of 0.5 seconds. Kreido offers what it calls a complete pipe-to-pipe biodiesel production unit, the STT 30G.
Scaleup involves holding shear constant: D1πω1/d1 = D2πω2/d2
where D is the diameter of the rotor in millimeters, ω is the revolutions per second of the rotor, and d is the gap millimeters. If d1 = d2 then, for any change in diameter, the new ω can be calculated.
Protensive makes the Spinning Disk Reactor (SDR), which provides plug flow and intense mixing while resisting fouling. The SDR relies on high centrifugal acceleration over a disk surface to overcome interfacial mass-transfer limitations that thwart conventional processes (Figure 3).
The generation of very thin films, typically fractions of a millimeter down to a few microns thick, through controlled flow rate and disc speed or RPM can deliver surface-to-volume ratios tailored to processing require- ments, ranging from 1,000s of m2/m3 for high viscosity materials such as polymer melts, down to 100,000s m2/ m3 for low viscosity systems typical of a wide range of chemical synthesis routes.
The SDR boasts an overall heat transfer coefficient typically five to 10 times greater than achieved by most heat-transfer devices, says the company, enabling small discs with low process fluid inventory to handle significant thermal duties. Figure 4 shows a laboratory unit.
Fast exothermic reactions can be conducted in the thin turbulent film on a spinning disc reactor using much higher temperatures than could be contemplated in stirred tanks. This is because the superior heattransfer performance of the unit carefully controls temperatures, and completes reactions in a residence time of just 1-2 sec.
The reaction to produce CaCO via CO absorption
3 2 is completed within 1 sec., says the company. The high surface-to-volume ratio can be used both to allow rapid transport between gas and liquids for simple operations such as stripping liquids of volatiles, scrubbing gases or for more-complex gas/liquid reactions.
For crystallization and precipitation, the vaporstripping characteristics of the SDR, arising from the thin turbulent liquid film on the disk surface, combined with the reactor’s plug flow characteristics, are said to allow excellent control over particle size selection and attainment of a relatively narrow particle-size distribution.
The reactor also reportedly can remove solvents or monomers left trapped in bundled polymer chains after polymer production to very low levels difficult to achieve in traditional equipment even with the use of vacuum and temperature.
Hydro Dynamics, Inc., Rome, Ga., harnesses cavitation in its ShockWave Power Reactor (SPR) to provide increased mass transfer and scale-free heating. Basically, the shockwaves and resulting microscopic bubbles cause intense mixing as well as a cleaning action. Because heating takes place in the material, not by conduction through metal, there are no hot and cold spots.
The heart of the SPR technology is a specialized spinning rotor with cavities. The spinning action generates hydrodynamic cavitation within the cavities away from the metal surfaces. This cavitation is controlled by RPM. Thus, there is no damage to the equip-
ment. Eight different parameters determine optimum hole location, depth, angle, layout, etc. The SPR looks like a pump from a casual observation (Figure 5); however, that is where the similarity ends.
The SPR can provide: reduced reaction time, uniform temperature with no solid scale build-up, fewer side reactions, and improved yield and quality.
The reactor suits both batch and continuous processes, and can provide up to 150-million-gal/yr processing capacity in a single unit. In addition, the unit can be easily retrofitted into existing operations.
The device already is used in numerous commercial applications, including the mixing of consumer products, food pasteurization/homogenization, gel and gum hydration, scale-free heating of chemicals, and concentration of solvents.
The unit also can serve as a superior gas/liquid mixer, handling gas-to-liquid volume ratios as high as 5 to 1.
Velocys, Plain City, Ohio, uses microchannel technology to dramatically reduce heat and mass transport distances commonly found in conventional systems, thus increasing the rate of heat and mass transfer and, in turn, greatly accelerating reaction rates. Further, as the efficiency of converting feedstock material to products is strongly governed by the ability to control these chemical reactions, which depends upon the ability to control reaction temperature, which in turn is governed by the ability to move heat quickly, the technology often can increase product yield.
Velocys’ chemical processors feature parallel arrays of microchannels, with typical dimensions in the 0.010in. to 0.200-in. range (Figure 6).
This structure is said to allow use of much more active catalysts than conventional systems, greatly boosting the throughput per unit volume. A catalyst can be tethered to the reaction wall or coated inside the channels. Overall system volumes reportedly can be reduced by 10 to 100 fold compared to conventional hardware. Figure 7 shows a large-scale, prototype microchannel reactor that will begin operating in 2007.
Some of the applications under development include:
• hydrogen production using steam methane reforming;
• high intensity oxidation and partial-oxidation reactions with improved process selectivity and yield;
• high-performance emulsification processes; and
• synthetic-fuel production and methanol synthesis in compact units suitable for land or offshore installation.
Steam reforming highlights the power of the approach. About 95% of the hydrogen produced today in the U.S. is made by reforming a methane source such as natural gas using high-temperature (700°C to 1,000°C) steam. Refineries are major producers of hydrogen, using it primarily for their hydrotreaters and hydrocrackers. In the reforming process, methane endothermically reacts with steam under 3 25-bar pressure in the presence of a catalyst to produce hydrogen, carbon monoxide and a relatively small amount of carbon dioxide.
With the microchannel technology, hot combustion gases push the reaction forward, with the hot gases flowing in channel layers alternating with the reactor channel layers. The hydrogen is then purified in a pressure swing adsorption unit. Plant size is reduced by 90% compared to conventional reformers, and the approach boasts a 30% savings in capital cost, higher thermal efficiency and lower emissions, according to the company.
Scale-up is easily accomplished by adding more layers of channels. Once a plant is in operation, its capacity can be increased simply by installing additional layers of channels.
Cambridge Reactor Design, Cottenham, U.K., offers the Oscillating Flow Reactor, which takes advantage of the company’s Oscillating Flow Mixing (OFM) technology (Figure 8).
OFM combines fluid oscillations with baffle inserts to provide highly effective mixing in tube reactors. Mixing behavior is controlled dynamically by oscillation intensity or geometrically by baffle design. While the technology can be applied to batch operations, it is said to be particularly suited to continuous processing.
The standard reactor consists of an oscillator base and a reactor tube top section (Figure 9). A nutating cam mechanism driven by an electric motor and linear actuator controls the amplitude and frequency of operation. A pair of pistons driven off the two cams provides oscillations in an inverted “U” arrangement of reactor tubes. All of the variations are achieved by electronic control of the motors.
Process tubes are added via top plate extensions, each of which takes two reactor tubes. In this manner, the unit can be operated as four-pass, six-pass, etc., as required to increase reactor volume or residence time.
Typical applications include biodiesel, suspension polymerizations and liquid/liquid dispersions.
PI doesn’t necessarily have to involve cutting-edge mechanical developments. Another, long-established form of PI is reactive distillation, which combines a reactor and distillation column. The technique typically is used with reversible, liquid-phase reactions. For many such reactions, including esterifications, transesterifications, hydrolyses, acetalizations and aminations’ byproduct formation limits the amount of product made. Reactive distillation allows removal of the byproduct, thus shifting reaction equilibrium and leading to more product. Other types of reactions that could benefit from reactive distillation include: alkylation/transalkylation/dealkylation, isomerization and chlorination.
Reaction components are fed countercurrent into a distillation column. Then, the product and byproduct can be separated by distillation. Some reactions require placement of catalysts inside the column e.g., via structured packing coated with the appropriate catalyst, trays containing pillows filled with catalyst particles or pillows filled with catalyst particles rolled into bales.
Figure 10 shows an esterification reaction for a highboiling carboxylic acid being added at the top of the reactive distillation column and a lower-boiling point alcohol being added at the bottom. Byproduct water comes off the top of the column and the product ester comes off the bottom.
We expect installations using reactive distillation to continue to grow at a moderate pace in this decade.
Another traditional form of PI also garnering increasing interest relies on the use of so-called static or motionless mixers as reactors either as single units or in bundles with a jacket.
Chemical reactions in the laminar fluid-flow range (below a Reynolds number of 2,000) are possible with a Continuous Flow Reactor (CFR) developed by R. C. Costello & Associates (Figure 11).
The Model CFR-T consists of a 3/8-in.-diameter Type-316 stainless steel tube with mixing elements that divide the flow at the beginning of each element. Subsequent stretching and folding produces a radial motion of the high-velocity core regions outward toward the wall of the reactor, which has an inside diameter of about 0.20 in. Without the elements, flow clearly would be laminar but with them intense mixing occurs, enabling liquid/liquid and gas/liquid reactions to occur.
A bench-scale device is offered with 34 mixing elements, which means the liquid contents is split and folded 234 (or more than 17 billion) times after passing through the CFR.
For multiple units in series, BHR Group, Cranfield, U.K., offers the FlexReactor, which looks similar to a heat exchanger with static mixers in each tube. The unit can be re-piped with simple U-tube connections to have multiple passes in series or parallel operation. Heating or cooling is easily achieved with the FlexReactor.
Variable Inlet Vane Damper
Variable Inlet Vane (VIV) Dampers are designed with mechanical principle of adjustment. Inlet guide vanes are synchronously adjustable in the same angular position by a connecting element. Adjustment can be made either automatically via an adjusting element from pulse generator by hand.
• Energy Savings with fans utilizing variable inlet vanes.
• VIV Dampers are often used for capacity modulation. They give accurate modulation and power savings over other styles of dampers at reduced air flow.
• When an inlet vane is partially closed, each blade directs the air into the wheel in the direction of rotation and so the air is prespun. This brings about a reduction in the Capacity, Static Pressure and BHP. The amount of BHP savings at reduced capacity is determined by the type of system and type of fanvane combination.
• For every inlet vane position there is different Capacity V/s Static curve and Capacity V/s Brake Horsepower (BHP) curve generated by the fan.
• VIV Dampers are designed with mechanical principle of adjustment.
• Inlet Guide vanes are Sychronously adjustable in the same angular postion by a connecting element.
• Adjustment can be made either automatically via an adjusting element from pulse generator or by hand.
For more details contact: Vacunair Engineering Co Pvt Ltd Ahmedabad Phone: +91792290771-2-3 Email: email@example.com Website: vacunair.com
GKD: process belts for phosphoric acid production
Whether phosphorous gypsum or FGDP gypsum dewatering, cooling lubricant filtration, or process water treatment: the filtration efficiency, productivity, and process reliability of continuous vacuum belt filter systems represent key success parameters in increasingly discerning markets. With its VACUBELT® filter belts developed for specific processes, GKD offers products that have been proven worldwide for these applications. Their special mesh design combines high filtration efficiency with optimum cake discharge and excellent cleaning properties. High air permeability and a low clogging tendency underline the performance. The rugged belts made of polyester monofilaments are capable of handling the high mechanical, thermal, and chemical stresses that occur during the process and also excel through their high degree of lateral stability. Tracking stability and a long service life are the keys to the success of this product range.
Tailored specifically for phosphorous gypsum dewatering
A special production method qualifies the highperformance VACUBELT® filter belts for phosphorous gypsum dewatering, whereby each belt is thermally matched individually to the respective gypsum and process conditions. Manufactured individually and assembled on parallel rollers, the belts guarantee 100% directional stability. Thanks to this optimum controllability, this belt type is characterized by a reduced tendency to form creases. The particularly flat seam also contributes to a hasslefree process, as its very low aperture reduces significantly particle penetration.
Proven for FGDP gypsum dewatering
The VACUBELT® filter belt 2015 has already proven its worth in the field of FGDP gypsum dewatering over many years. Whether in new systems or retrofitting existing power plants, the belt made of pure polyester monofilaments meets the strictest requirements. Fast dewatering and robust transverse stability are the main factors contributing to its superiority. During the FILTECH fair, it became clear that the need for more efficient gypsum dewatering in the field of flue gas desulfurization, and thereby interest in this belt type, is still on the rise - particularly in South Africa and India.
Numerous users and well-known equipment manufacturers discussed concrete issues regarding the design and range of potential applications of the horizontal filter belts with the GKD experts. Process Belt Division Manager, Michael Seelert, therefore reflects on the trade fair appearance with a sense of satisfaction: “FILTECH was a real success for us.” He also believes that the excellent networking opportunities are one of the most important aspects of this trade fair. “We were able to make new and promising contacts and also welcome back visitors looking for more indepth information.”
Phenomenex introduced bioZen™ Series for characterization of biotherapeutics
Phenomenex Inc., a global leader in the research and manufacture of advanced technologies for the separation sciences, introduced bioZen – a new series of LC solutions for bioseparations in pharmaceutical, biopharmaceutical and academic research. The series encompasses both proven and entirely new media spanning two particle platforms – core-shell and thermally modified fully porous – along with new biocompatible titanium hardware. The initial product line featured seven chemistries for the UHPLC and HPLC characterization of biotherapeutics such as monoclonal antibodies, antibody-drug conjugates and biosimilars. The offering included specific LC chemistries for the analysis of aggregates and total mAb, intact mass and fragments, peptide mapping and quantitation, and glycan mapping.
As an added benefit, all bioZen media, particle sizes and phases are available in Phenomenex’s new biocompatible titanium hardware, which minimizes secondary reactions, carryover and other recovery issues to provide better overall reproducibility than stainless steel hardware. It also minimizes the amount of time typically spent on column priming and does not interfere with protein or peptide integrity.
The bioZen thermally modified fully porous media is produced with Phenomenex’s proprietary postsynthetic thermal treatment process, which improves particle mechanical strength and inertness, providing significantly better peak shape and fewer unwanted secondary interactions than traditional LC media. The thermally modified media pairs well with highefficiency Core-Shell Technology media which delivers increased resolution and sensitivity in shorter retention time windows. Both particle platforms undergo stringent QC testing to ensure consistent high quality, while all individual columns have QC protocols for specific biologic applications to confirm product performance and reproducibility.
Simon Lomas, Senior Manager of Global Product Marketing for Phenomenex, said “The bioZen series springs from our close work with customers who wanted a comprehensive product offering to cover all of their bioseparations needs. This is an exciting and growing portfolio of novel particles, chemistries and biocompatible hardware, supported by our industry gurus, that all combine to help our customers overcome the many challenges associated with the characterization of biologics.”
Figure 1. This design produces high shear along entire length of tube, accelerating reaction rate.
Figure 2. Compact unit can handle liquid/liquid and liquid/gas
Figure 3. This small Spinning Disk Reactor can serve as a complete mini-development plant.
Figure 4. High centrifugal acceleration overcomes conventional interfacial mass-transfer limitations.
Figure 7. Large-scale demonstration unit is slated for operation in the first quarter of 2007.
Figure 6. Microchannels permit use of much more active catalysts, which greatly boosts throughput.
Figure 5. Purposely generated cavitation enhances mass trans
fer and produces uniform heating.
Figure 9. Standard design includes an oscillator base and a reactor tube top section.
Figure 8. Baffle geometry coupled with intensity of oscillation produced by pistons control mixing behavior.
Figure 10. This unit produces an ester as bottoms product, while byproduct water goes overhead.
Figure 11. Internal elements fold streams billions of times, providing intense mixing.
A special production method qualifies the high- Picture 3 © GKD performance VACUBELT® filter belts from GKD for phosphorous gypsum dewatering.