(34e) H.E.N.C.I. Dispersed-Particle Bed Technology and the Advent of High Mass- and Momentum- Transport Efficiency Nanocatalytic Reaction Processes

When employed in-situ, many new nano- (and micro-) sized catalyst particles/structures have been shown to effect extremely favorable (rapid) extrinsic kinetics, largely due to their great surface-area/mass ratios. This effect is extreme in catalytic scenarios in which the rate-limiting step(s) include mass transport to/from the catalytic surfaces (such as a packed-bed reactor being fed with an ultra-dilute-solute reactant), and has extremely positive economic ramifications for applications requiring high-throughput, high-conversion and high-mass- (& momentum-, & often heat-) transport efficiencies to achieve cost-effective operation (hereafter acronymed HTCT3 applications). Rapid overall kinetics hold the potential to greatly increase process efficiencies of niche catalytic CPI processes as well, and the desire to use these highly effective catalysts for various CPI as well as large-scale GWR applications has been a natural consequence. Catalytic nanoparticles themselves, often toxic, are however, rarely desirable in any product stream, thus their in-situ use usually necessitates that they be completely removed prior to product use, which is generally difficult in high linear-velocity processing: Because these particles are so small (and numerous), very robust (e.g. N.F or R.O.) operations would often be required to assure such removal, rendering most in-situ HTCT3 nanocatalytic operations extremely cost-prohibitive. Conversely, ex-situ use of nanocatalysts (immobilizing them in such a way as to thoroughly exploit their advantages in a flow-through reactor both safely and cost effectively) has been stymied as well. Why? Until the advent of High-Efficiency Nano-Catalyst Immobilization (H.E.N.C.I.) technology, the following seven engineering criteria inherent to immobilizing nano-sized particles for cost-effective ex-situ HTCT3 catalysis had proven insurmountable: 1. Complete Immobilization ? nano-catalytic particles are held 'fast' in place and never become part of the reactant matrix phase as they effect reaction(s): The particles never actually enter into the reactant solution, and thus never have to be removed via subsequent expensive and elaborate unit operations such as R.O., NF.& mag. filtering. The process can be validated to emit zero nano- /micro- particles in the effluent. 2. Ultra High Immobilization Density: At ~1010 to 1013 particles per gram, many nanocatalysts must indeed be immobilized per unit reactor volume in order for the technology to be truly valuable for HTCT3 applications. In preliminary tests using ~80mn Zero-Valent Iron Fe/Pd nanocatalyst particles HENCI reactors easily be immobilized over 25 x 1015 particles - 3.7 million ft2 of available catalytic surface area per cubic foot of reactor volume, without significant pressure drop through the reactor, at linear velocities in excess of 60 FPM. 3. High Mass Transport Efficiency: When micro-or nano-sized structures are employed for catalysis, boundary layers are virtually eliminated, and nearly 100% of the surface area of each catalytic particle is directly exposed to the bulk-composition reactant matrix (low-transport-rate pore-wall volume is negligible or non-existent on nano-structures ? all surface area is on the particle perimeter). Moreover, HENCI technology overcomes the natural tendency for small-particle agglomeration so that the particles are immobilized within the HENCI reactor in a micro-homogeneous three-dimensional mono-disperse array of individual particles within the column, eliminating flow-channeling and maximizing overall reaction rates. The static micro-mixing effect of HENCI facilitates overall rates equal to or greater than those achievable via in-situ agitation, and 'plug' flow often occurs at superficial Nre under 300. 4. High Momentum Transport Efficiency: HENCI columns exhibit extremely low pressure-drop per unit reactant matrix flux: linear velocities of hundreds of ft/second can be achieved with extremely small pressure drops per unit reactor length, and hence with small, inexpensive pumps. For GWR, the head available at the source is usually more than adequate, eliminating the need for additional pumps altogether 5. The Technology is Readily Scalable & Configurable: Any combination of throughput & conversion can be addressed with HENCI. System modularity is easily accomplished, minimizing system capital costs. 6. The Technology is Inexpensive to Build and Operate: On the basis of mass of nanocatalyst immobilized, HENCI facilitated systems are roughly 1 to 2 orders of magnitude less expensive to manufacture, operate, and maintain than any other immobilization technology known by the author. 7. Potential for quick regulatory-agency acceptance: HENCI usually exposes the reactant matrix to no additional contact materials (beyond those in the catalyst particles themselves)

HENCI technology alone meets these criteria, thus comprising the ?last piece in the puzzle' of unleashing the true power of nanocatalysis outside the lab by safely exploiting it's highly favorable kinetic and transport rates, especially in HTCT3 applications such as large-scale remediation of our now-carcinogenic groundwater supplies (see below). The micro-homogeneous, ultra-high-density, ultra-low pressure-drop dispersion accomplished within the tubular HENCI reactor has come to be known also as the Dispersed Nano/Micro-Particle Reactor Bed, or HENCI DNP reactor for short. Dr. Mamadou Diallo at the Beckman Institute, Cal Tech; Dr. Michael Wong et. al. at CBEN / CNST, Rice University, and Dr. Peter Rony et. al. of Virginia Tech's Ch.E. department are currently evaluating and developing new GWR and CPI applications and process scenarios using HENCI DNP units. Several other universities are also in the process of obtaining HENCI DNP systems as of December 2006. One application deserves note: Groundwater Remediation. Though CHC levels in ground water basins may be but a few ppm, Many of these ubiquitous carcinogenics have EPA limits under 15 ppb for potability, and hence often require 99.9% (or higher) conversion to achieve regulatory compliance. Thus, heretofore, large-scale (High throughput x High conversion )catalytic groundwater remediation (GWR) has remained infeasible due to the mass-transport limitations inherent to trace pollutants competing for reaction-sites when ?outnumbered' by the H2O matrix ( for every billion catalyst-surface sorption events only a few actually involve the reactant). However, today, when the right nano-particle catalyst composition is charged to an HENCI DNP system, rapid and complete catalytic destruction (cleavage/breakdown to benign species) of these toxins can be effected with unprecedented process efficiencies: Per unit throughput of remediated water, Catalytic groundwater remediation-plant sizes, operating, and capital cost are reduced by several orders of magnitude, and thus brought, for the first time ever, well into the realm of feasibility.