Chemical & Process Technology: Process Intensification

Sunday, May 16, 2010

Process Intensification

Process Intensification (PI) is a revolutionary approach to process and plant design, development and implementation. It presents significant scientific challenges to chemists, biologists and chemical engineers while developing innovative systems and practices which can offer drastic reduction in chemical and energy consumptions, improvements in process safety, decreased equipment volume and waste formation and increased conversions and selectivity towards desired product(s). In addition they can offer relatively cheaper and sustainable process option.

Here one must note that development of a new chemical route or a change in composition of a catalyst, no matter how dramatic the improvements they bring to existing technology, do not qualify as process intensification.

Process Intensification can be broadly divided into two areas:

Process Intensifying Equipment
Process Intensifying Methods (Unit Operations)

Process Intensifying Equipment

Monolythic Catalytic Reactor
Monolithic substrate used today for catalytic applications are metallic or non metallic bodies providing a multitude of straight narrow channels of defined uniform cross sectional shapes To ensure sufficient porosity and enhance the catalytically active surface, the inner walls of the monolith channels usually are covered with a thin layer of wash coat, which acts as the support for the catalytically active species.

The advantages of Monolithic Reactors are as follow.

Low pressure drop
High mass transfer area
Low space requirement
Low cost
Better Selectivity
Better Safety
Less Environmental problems

Micro-Reactors
Micro-reactors are chemical reactors of extremely small dimensions that usually have a sandwich-like structure consisting of a number of slices (layers) with micro-machined channels (10-100 micron in dia.). The layers perform various functions, from mixing to catalytic reaction, heat exchange, or separation

Higher values of heat transfer coefficient values upto 20000 W/m2K are reported. Hence highly exothermic reactions can be easily carried out .This is very useful for toxic or explosive reactants / products. The chan¬nels in the plates of micro-channel heat exchangers are usually around 1 mm or less wide, and are fabricated via silicon micromachining, deep X-ray lithography, or non-lithographic micromachining

Spinning Disk Reactors (SDR)
For fast and very fast liquid-liquid reactions like sulphonation, nitration , polymerization (styrene) involving high heat of reactions, this type of reactor is developed by Newcastle University. In SDRs, a very thin (typically 100 micron) layer of liquid moves on the surface of a disk spinning at up to approximately 1,000 rpm. At very short residence times (typically 0.1 s), heat is efficiently removed from the reacting liquid at heat-transfer rates reaching 10,000 W/m2K. SDRs currently are being commercialized.

Static Mixer Reactors

Static Mixers are not only used for physical mixing of Gas-Gas, Liquid –Liquid and Gas –Liquid applications but used in reactions also. Use of structured packing reduce the pressure drop considerably. When static mixers are placed in heat exchanger tubes better mixing as well as heat transfer can be achieved. A Norwegian company has intensified manufacturing of Hydrogen Peroxide by using static mixers extensively to combine oxidation and extraction.

Supersonic Gas-Liquid Reactor
Praxair Inc. developed this type of reactor for fast and very fast processes for gas/liquid systems and it employs a supersonic shockwave to disperse gas into very tiny bubbles in a supersonic in-line mixing device.

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The Jet Impingement Reactor
An apparatus to allow reaction in liquid phase. The apparatus is a vessel having a baffle. There are openings in the baffle through each of which liquid passes as jet. Neighboring openings are sufficiently close to allow impingement of the jet thereby allowing for the reaction of liquids. This is useful for immiscible liquids. e.g. Nitration of aromatic compound with aqueous solution , manufacture of Nitroglycerine etc.

NORAM Engineering and Constructors (Vancouver, BC) uses this system of specially configured jets and baffles to divide and remix liquid streams with high intensity.

Buss Loop Reactor

This type of reactor is suitable for gas – liquid system and can be used for Amination, Alkylation, Carbonylation, Chlorination, Ethoxylation, Hydrogenation, Nitrilation, Oxidation , Phosgenation etc. The Buss loop reactor has been successfully used for hydrogenation, amination and sulphonation.

Rotary Pump Reactor

Rotor/stator mixers, which are aimed at processes requiring very fast mixing on a micro scale, contain a high-speed rotor spinning close to a motionless stator. Fluid passes through the region where rotor and stator interact and experiences highly pulsating flow and shear. In-line rotor/stator mixers resemble centrifugal pumps and, therefore, may simultaneously contribute to pumping the liquids.

HIGEE Reactors / Separations / Stripper

HIGEE technology intensifies mass-transfer operations by carrying them out in rotating packed beds in which high centrifugal forces (typically 1,000 g) occur. This way, heat and momentum transfer as well as mass transfer can be intensified. The rotating-bed equipment can be used in absorption, extraction, distillation and also can be utilized for reacting systems (especially, those that are mass-transfer limited). It potentially can be applied to other phase combinations including three-phase gas/liquid/solid systems. e.g. Absorption of CO2, H2S using Di-ethanol Amine

Another example is the filtering centrifuge-cum-dryer. The centrifuge combines these operations for a pesticide/herbicide/pharmaceutical product with recycle of the solvent used for crystallization. This saves on floor area, operators, conveying, drying equipment, etc. Centrifuge for liquid- liquid separation are already in use.

HIGEE packed bed replaces towers up to 50-60 ft tall and can process up to 250 tons of water per hour. The size of the equipment is about 6 ft tall.. The deoxygenated water is required for oil well injection to enhance oil well production. This could also be used for boiler water deaeration Dow Chemicals have used these columns for stripping of hypochlorous acid from brines

LOGEE Concept

Lower value of g will affect the convection currents. This in turn may affect growth of the crystals in crystallization. Lowering effect of g can be obtained by providing bottom entry in the crystallization vessel.

Compact Heat Exchangers Reactors

Plate Heat Exchangers, Spiral Plate Heat Exchangers, Capillary Tube Type Shell and Tube type heat exchangers are already used as reactors .

There are several other type of reactors such as Biofilm Annular Reactor , Oscillating Flow Reactors, Drip Flow reactor etc can be used to improve the performance

Process Intensifying Methods (Unit Operations)

Several Process Intensifying methods listed as follows :

a)   Multifunctional Reactors
b)   Hybrid Separators
c)   Alternative source of energy
d)   Other methods

MULTIFUNCTIONAL REACTORS

Reverse Flow Reactor

The reactor concept aims to achieve an indirect coupling of energy necessary for endothermic reactions and energy released by exothermic reactions, without mixing of the endothermic and exothermic reactants, in closed-loop reverse flow operation. Periodic gas flow reversal incorporates regenerative heat exchange inside the reactor. This reactor is used for SO2 oxidation, total oxidation of hydrocarbons in off-gases, and NOx reduction.

Reactive Distillation

It is a distillation column filled with catalytically active packing. In the column, chemicals are converted on the catalyst while reaction products are continuously separated by fractionation (thus overcoming equilibrium limitations). The catalyst used for reactive distillation usually is incorporated into a fiberglass and wire-mesh sup¬porting structure, which also provides liquid redistribution and disengagement of vapor. Structured catalysts, such as Sulzer's KATAPAK,

The advantages of catalytic distillation units, besides the continuous removal of reaction products and higher yields due to the equilibrium shift, consist mainly of reduced energy requirements and lower capital investment The number of processes in which reactive distillation has been implemented on a commercial scale is still quite limited - but the potential of this technique definitely goes far beyond today's applications.

Membrane Reactor

The membrane enable in-situ separation of catalyst particles from reaction products. thus itself becoming a highly selective reaction-separator It also can be applied for a controlled distributed feed of some of the reacting species, either to increase overall yield or selectivity of a process (e.g., in fixed-bed or fluidized-bed membrane reactors or to facilitate mass transfer (e.g., direct bubble-free oxygen sup¬ply or dissolution in the liquid phase via hollow-fiber membranes ).

Heat- and mass-integrated combination of hydrogenation and dehydrogenation processes can be carried out in a single membrane unit. Yet, practically no large-scale industrial applications have been reported so far due to high price

Catalytic Reactors

Reactive extruders used in the polymer industries enable reactive processing of highly viscous materials without re¬quiring the large amounts of solvents. Popular twin-screw extrud¬ers offer effective mixing, can operate at high pres¬sures and temperatures, plug-flow characteristics, and capability of multi-staging. New types of extruders with catalyst immobilized on the surface of the screws may allow carrying out three-phase catalytic reactions.

Methyl Acetate

Eastman Chemicals successfully changed the methyl acetate plant. The process involves the esterification of methanol with acetic acid in presence of catalyst, removal of water of reaction, distillation of product and recovery and recycle of excess reactants. There are as many as six distillation columns that have been replaced by single multifunctional distillation column. Imagine the reduction of number of reboilers, condensers, pumps, etc. The heat input and rejection is practically only at two points.

Fuel Cell

Here, integration of chemical reaction and electric power generation takes place (Simultaneous gas/solid reaction and comminution in a multifunctional reactor also has been investigated).

Isothermal Reactor Process

Isothermal reactor crystallizer cooler operation gives higher P2O5 recovery efficiency, superior sulfate control. The P2O5 content of gypsum is 0.7%, phosphoric acid concentration 28%. This gigantic single vessel, combining, reactor, crystallizer and cooler, (12 meter dia, 1300 M3 volume) occupies less space, requires fewer moving parts and is substantially less expensive to build, operate, clean and maintain than conventional installations, thereby substantially reducing capital and operating costs.

HYBRID SEPARATION

Membrane Absorption and Stripping

Here the membrane serves as a permeable barrier between the gas and liquid phases. By using hollow-fiber membrane modules, large mass-transfer areas can be created,

Membrane Distillation

This offers operation independent of gas and liquid flow rates, without entrainment, flooding, channeling, or foaming The technique is widely considered as an alternative to reverse osmosis and evaporation. Membrane distillation basically consists of bringing a volatile component of a liquid feed stream through a porous membrane as a vapor and condensing it on the other side into a permeate liquid. Temperature difference is the driving force of the process. Main advantages of membrane distillation are

100% rejection of ions, macro-molecules, colloids, cells, and other non-volatiles;
lower operating pressure ,hence lower risk and low equipment cost
less membrane fouling, due to larger pore size;
lower operating tem¬peratures en¬able processing of temperature-sensitive materials.

Adsorptive Distillation

Here a selective adsorbent is added to a distillation mixture. This increases separation ability and may present an attractive option in the separation of azeotropes or close-boiling components. Adsorptive distillation can be used, for the removal of trace impurities in the manufacturing of fine chemicals; it may allow switching some fine-chemical processes from batch wise to continuous operation.

ALTERNATIVE FORMS AND SOURCE OF ENERGY

Ultrasound

Ultrasound is used as a source of energy for formation of micro- bubbles in the liquid medium of reaction. These cavities can be thought of as high energy micro-reactors. Their collapse creates micro-implosions with very high local energy release (temperature rises of up to 5,000 K and negative pressures of up to 10,000 atm are reported ). This may have various effects on the reacting species, from homolytic bond breakage with free radicals formation, to fragmentation of polymer chains by the shockwave in the liquid surrounding the collapsing bubble. This is still at development stage.

Solar Energy

A novel high-temperature reactor in which solar energy is absorbed by a cloud of reacting particles to supply heat directly to the reaction site has been studied. Experiments with two small-scale solar chemical reactors in which thermal reduction of MnO2 took place also are reported. Other studies describe, the cyclo-addition reaction of a carbonyl compound to an olefin carried out in a solar furnace reactor and oxidation of 4-chlorophenol in a solar-powered fiber-optic cable reactor.

Microwave

Microwave heating can make some organic syntheses proceed up to 1,240 times faster than by conventional techniques. Microwave heating also can enable energy-efficient in-situ desorption of hydrocarbons from zeolites used to remove volatile organic compounds.

Electric Field

Electric fields can augment process rates and control droplet size for a range of processes, including painting, coating, and crop spraying. In these processes, the electrically charged droplets exhibit much better adhesion properties. In boiling heat transfer, electric fields have been successfully used to control nucleation rates. Electric fields also can enhance processes involving liquid/liquid mixtures, in particular liquid/liquid extraction where rate enhancements of 200-300% have been reported.

Plasma Technology

Gliding Arc technology, that is, plasma generated by formation of gliding electric discharges. These discharges are produced between electrodes placed in fast gas flow, and offer a low-energy alternative for conventional high-energy-consumption high-temperature processes. Example include: methane transformation to acetylene and hydrogen, destruction of N2O, reforming of heavy petroleum residues, CO2 dissociation, activation of organic fibers, destruction of volatile organic compounds in air, natural gas conversion to synthesis gas, and SO2 reduction to elemental sulfur.

OTHER METHODS

Supercritical Fluid (SCF)

SCF is any substance at a temperature and pressure above its critical point. It can diffuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned".

Many of the physical and transport properties of a SCF are intermediate between those of a liquid and a gas. Diffusivity in an SCF, falls between that in a liquid and a gas; this suggests that reactions that are diffusion limited in the liquid phase could become faster in a SCF phase. Also Compounds that are largely insoluble in a fluid at ambient conditions can become soluble in the fluid at supercritical conditions. Conversely, some compounds that are soluble at ambient conditions can become less soluble at supercritical conditions. SCFs have been investigated for systems, including enzyme reactions, Diels-Alder reactions, organo-metallic reactions, heterogeneously catalyzed re¬actions, oxidations, and polymerizations.

Cryogenic Techniques

Cryogenic techniques involving distillation or distillation combined with adsorption, today are used almost exclusively for production of industrial gases, may in the future prove attractive for some specific separations in manufacturing bulk or fine chemicals.

Dynamic Reactor Operations
The inten¬tional pulsing of flows or concentra¬tions has led to a clear improvement of product yields or selectivities at lab scale. Yet, commercial-scale applications are scarce.

Continuous Processes
There are several examples in which continuous process is more economical than batch processes e.g

Oxy chloride from Phosphorous Trichloride using air or oxygen
Monobromo benzaldehyde required for Meta Phenoxy Benzaldehyde (Pesticide intermediate)

Vapour Absorption Refrigeration

This is a well known example where several equipment are put together to make compact ,energy efficient equipment.

Advantages /benefits of Process Intensification

Safety - As per Cell for Industrial Safety and Risk Analysis (CISRA) the major cause of accident is STORAGE. When size of the process equipment is reduced , operating inventory will be reduced.
Health - The fugitive emissions will be reduced due to smaller equipment size. This will improve the health of the society in general. Environment Better efficiency /yield leads to less rejection to environment hence less pollution.
Quality - It is possible to get desired quality of products
Energy - Due to higher energy efficiency, leads to enhanced production
Cost - Less due to less raw material, catalyst, labour, utility and space requirement

Following photos indicate how old plant (above) will look like after Process Intesification implementation (below) .This is how more production, better quality can be obtained from less energy, less space, less cost

Implementation of Process Intensification (PI)
May consider following actions for PI implementation.

Utilise existing facilities / human resources efficiently
Develop new modern facilities
Connect all scientific research institutes
Allocate separate funds for R&D
Provide favorable environment for R&D
Develop platform for Industry –Academy interaction
Develop patent laws in accordance with global practices.
Create awareness
Provide incentives in the form of awards

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Guess post by P.J. Lakhapate

P.J. Lakhapate is a Chemical Engineer from UDCT, Mumbai (1975) & has completed a Post Graduation in systems management from J. Bajaj Institute, Mumbai. He is a lead assessor for ISO-9000. He received Quality Award from Chemtex Engg of India Ltd,Powai. He has travelled U.S.A., Brazil, Russia, Kuwait, Saudi Arabia. He has written more than 40 articles & published in national & international magazines. He is distinguished member of expert committee group (for PUMPS & VALVES ) of NATIONAL ADVISORY COUNCIL. He has to his credit a work experience of more than 35 years. He is working as a consultant

Email : plakhapate@rediffmail.com

Thanks to P.J. Lakhapate.
by JoeWong

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2 Comments:

Chemical Engineering Net said...: I must admit that this article from Lakhapate is very good and helpful for me especially as I'm involve very much in REaction engineering.

Did Dr. Lakhapate contact you to publish this article?; June 25, 2010 at 7:55 AM
JoeWong said...: CE NET,

Yeap...Dr. Lakhapate contacted us...; June 27, 2010 at 7:08 AM