The aim of intensification is to optimize capital, energy, environmental and safety benefits by radical reduction in the physical size of the plant.
Process intensification in the chemical process
industry is very recent subject in the field of chemical engineering. The
concept is hardly a decade old. It is a highly innovative concept
in the design of chemical process plants.
The aim of intensification is to optimize capital, energy, environmental and
safety benefits by radical reduction in the physical size of the plant. Thus
the concept is intimately connected
with the physical nature of the plant and not some thing which will take
a long time to move from theory to final commercial application using existing
and available hardware.
In other words process
intensification consists of the development of novel apparatuses and
techniques, as compared to the present state-of-art, to bring dramatic improvements
in manufacturing and processing, substantially decreasing equipment
size/production-capacity ratio, energy consumption, or waste production.
Perhaps a simpler definition could be; any chemical engineering development
that leads to a substantially smaller, cleaner, and more energy-efficient
technology is process intensification.
There is a caveat to the definition: 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
This concept has started a revolution and already 5-6
international conferences have been held. It could change the way chemical
engineering curriculum iscurrently
structured in the universities. Already some universities
in the west have started offering courses.
is some discussion as to the meaning of dramatic improvement,
Prof. Colin Ramshaw, of University of New
Castle, a pioneer of this concept, talks of 100 times reduction in
equipmentvolume, however many would be
happy with volume decrease by half or more. Prof Ramshaw's assertion is not
some thing airy-fairy but a very achievable target at least for some
What is in the chemical engineers arsenal to attack
the problem of process intensification? Broadly they could be divided into
hardware and methodologies.
It should be noted that many of the equipments
(hardware)are of type never known
before but there are quite few equipments which have been available to the
chemical engineer but their potential was never fully exploited. Examples are
compact heat exchangers, structured packed columns, static mixers, etc.
Examples of new developments are the HIGEE column, spinning disc reactor,
oscillating flow reactor, loop reactors, spinning tube in tube
reactor, Heat exchange reactor, supersonic gas liquid reactor,
static mixing catalysts, microchannel reactors, microchannel heat
The methodologies which are available are, reactive
distillation, reactive extraction, membrane separations, oscillating flows in
reactors, membrane reactions, fuel cells, etc. Use of ultrasound, microwave,
centrifugal fields, etc. supercritical fluids, etc
reactors, including simple plug-flow pipe units, tubular models containing
static or other mixing devices, and various jet devices have been used to
efficiently produce toxic materials for immediate consumption in downstream
processing with little or no inventory.
here are examples of process intensification from the industry indicating vast
gains in capital and operating expenses.
Many years ago,
nitrated products such as nitroglycerine were manufactured in large
batch reactors. Now, modern nitration plants use either small continuous
stirred tank reactors that provide intense mixing and large heat
transfer areas, or jet reactors to deliver
the intense mixing and rapid contacting of reactants.
small intensely stirred reactors are used to produce TNT in a inherently
safe mode. A Canadian company has built jet impingement reactors for producing
nitrobenzene, with a ten fold increase in reaction rate.
The Buss loop reactor known for quite some time has been successfully applied to hydrogenation,
amination and sulphonation.
capacities are the order of day for phosphoric acid manufacture. For a plant of
2000 tons P2O5/day, a US based company reduced the volume
by half, power consumption was reduced by 1/3, number of equipments reduced
from 30 to 9 and the number of motors from 15 to 3. The other advantages
1. Lower Environmental Emissions
The system is simpler to operate and control than
Obnoxious fluorine gases produced in the reactions
of the wet process are condensed by, and removed with, the condenser water. The
usual fluorine scrubber system with its ductwork, dampers and fans, normally
required to prevent atmospheric pollution, are unnecessary.
2. Process Advantages of the Isothermal Reactor Process
Simplicity of isothermal reactor crystallizer cooler operation. Higher P2O5 recovery efficiency, superior sulfate control, high operating factor. The P2O5 content of gypsum is 0.7%, phosphoric acid concentration 28%.
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.
Packed Catalytic Reactor
bed three phase catalytic reactor. The problem was that the catalyst was
getting fouled up and required opening up of the column every 2-3 weeks. There
were local hot spots in the reactor. If production had to be increased a new
plant costing $5 million would be required. The other solution was to increase
productivity. A $ 20,000 retrofit of static mixer for the gas-liquid feed with
some other changes increased the productivity by 42%. This saved the company
nearly $0.3 million per year and the investment of $ 5 million was avoided.
conventional method phosphorus trichloride is reacted with oxygen or air in
batch reactors. About 500 tons per month can be produced in 3 reactors
aggregating to 34 M3 volume. In a continuous process with a radical
change inreactor design the reacting
volume was only 0.5 M3 and it is possible to produce 700 tons per
month. The productivity goes up by a factor of 95. It also results in only 5%
excess oxygen consumption compared about 15-25% excess by batch process.
are other benefits like more uniform loading of utilities such as chilled
water, cooling water, etc. The size of utility plants become smaller as they do
not have to meet peak loads.
Monobromo-benzaldehyde is required for the
manufacture of meta-phenoxy benzaldehyde, a pesticide intermediate,
typically it is produced in batch reactors.
There are also side reactions and therefore the conversion has to be limited.
The batch process has productivity of
about 15.5 kg/M3/hr. The same process if made continuous has
a productivity about 34.5 kg/M3/hr. A large amount of
infrastructural facilities get downsized.
Eastman Chemicals successfully changed the methyl
acetate process. 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.
Sulzer has similarly changed the
process of hydrogen peroxide distillation. A Norwegian Company has intensified
the process of manufacturing hydrogen peroxide which uses static mixers
extensively to combine oxidation and extraction, etc. The company feels that it
may be possible to set up on site plants to meet local consumer demand.
The developments, by a Spanish company,
in workhorse of chemical industry,
the shell-tube heat exchangers have led to
considerable savings examples are reduction in heat transfer area by 55% in sugar
cane juice heater, the volume of the HE was reduced to 16% of the
shell-tube HE volume. In another case the area was reduced by half and the
volume of HE to 6.5% of the shell-tube HE volume. There are similar reductions
specially where viscous liquids are involved.
Chlorination using Thionyl chloride has been mainly
practiced as batch process. The process can be made continuous using a loop
type reactor with a heat exchanger in the loop. The productivity would vary
with the organic product being chlorinated however for a tonnage product the
productivity is 340 kg/hr/M3 of reactor volume.
This is compared to the productivity of
about 10 kg/hr/M3 in a batch reactor. 18M3
ofglass lined reactor capacity could
be replaced by a reactor ofabout 0.5M3
a volume a reduction of 36 times.The
equipment can be literally fixed to a side wall. A lab. bench model would have
throughput of about 10 kg /hr sufficient to produce 5-6 tons of product per
Caro's acid, used in metal processing
is made by reacting concentrated sulphuric
acid with hydrogen peroxide. This acid is a powerful oxidizing agent and
decomposes readily. A process was developed
to manufacture 1000 kg/day of Caro's acid in a tubular reactor with a
volume of only 20 ml and a residence time of less than 1 sec, with a product
being mixed immediately with the
solution to be treated.
Process intensification can take the route
of combining two or more operation s in one equipment. An 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
Elastomers like Styrene-Butadiene Rubber are produced
by coagulation of latex, washing, extrusion, dewatering and drying to
give crumbs. Usually all these operations are carried out in separate
equipments, however these operation have been combined in a single equipment,
by a US based company. A typical 2000 kg/hr main equipment occupies a floor
area of 25 sq meters, comparedto a
building ofabout 400 sq. meters or
more that such plants occupy. The plant has been used for ABS, SBR, NBR and
CR to date. The other advantages are less water usage, less waste
treatment, recycle of solids and water, monomer recovery, lower energy,
utilities, manpower, environment friendliness. Plants have been built with
capacities of 100 kg/hr to 7000 kg/hr
The HIGEE Reactor
HIGEE packed columns have been there since its invention in
1980's, however the most successful development has been done very recently in
China in deareation of flooding waters for oil wells, and another by Dow
Chemicals of stripping of hypochlorous acid from brines.
HIGEEreactor 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. They are small enough to be located on oil well
platforms. The deoxygenated water is required for oil well injection to
enhance oil well production. This could also be used for boiler water
Phosgene on Demand Technology
Phosgene on demand technology: Phosgene a
very toxic chemical yet a very useful chemical presented the problem of large
quantities to be stored for keeping the continuity of production. A continuous
tubular reactor was developed to make this chemical for immediate consumption
by a group of batch processing vessels. One plant using the new design contains
70 kg of gaseous phosgene, compared to an inventory of 25,000 kg of the liquid
in equipment and storage in the old facility.
Avoiding A Bhopal
(MIC), the infamous chemical that was released at Bhopal, can be
generated and immediately converted to final product (a pesticide) in a process
that contains a total inventory of less than 10 kg of MIC.
The expansion and exfoliation of crude
vermiculite ore produces the basic material used in the manufacture of fire
protection and industrial insulation products. The usual process is to have
rotary furnaces for heating and reaction. A UK based company replaced set of 3
rotary furnaces of 1.5 tons/hr capacity with a single Toroidal fluidized
bed (Torbed) furnace of 1 meter dia. with a capacity of 2 tons/hr.
reduces overall energy consumption and vermiculite wastage. Other benefits
included lower maintenance costs and much improved environmental conditions.
The savings achieved by this project resulted in a pay back period of 16 months.
11 plants are operational in Europe
This Torbed is being
commercialized to produce silica from rice husk. A task more easily
performed than by conventional methods. There are other areas like food
processing, roasting of sulphide ores, etc.
Milling and Grinding
Grinding is another area where the
traditional ball mill, roll mill etc. in case of fine grinding some times
combined with dispersion has been replaced by dispersed media mills. The mills
operate in liquid media with small size steel, ceramic or glass balls (beads)
which are circulated in a vessel having rotating members inside. There is vast
reduction in power consumption and civil infrastructure. These have been
applied to paint and ink industry, red phosphorus, ferrite powder, pigments,
Solid- Solid Mixing
An interesting example in batch
solid-solid mixing is an invention by a Norwegian company that gives an almost
perfect mix with in a matter of minutes. A 250 - 500 kg batch is mixed in 3-5
minutes. Compare this with a traditional ribbon or cone blender which can take
hours. There are numerous installations.
Micro-reactor systems are coming of age as
illustrated by CYTOS micro reactor system for 6 stage synthesis of Ciprofloxacin
. The reactors are of the size of book 100 mm x 150
mm. These reactors are now commercially available. Reactions which are
difficult to carry out in ordinary reactors have shown to be safe and feasible
such as (a) Nitration of toluene with highly explosive acetyl nitrate,
Nitration of pyridine-N-oxide at
high temperature(c) Nitration of 2-methylindole
, emphasizing safe handling and the very short
contact time. Potential of such reaction systems could perhaps be realized in
the possibility of obtaining kilogram quantities of new molecules for testing
purposes in a very short time.
A miniplant customized by it, is able to handle the suspension formed in the
synthesis of a dye. With the equivalent of six CYTOS microreactors running in
parallel, the mini-plant has a capacity of 30 tons per year on a footprint no
larger than that of an office table.
Micro-heat-exchanger, absorption systems, evaporators, etc are now
moving away from laboratory curiosities to commercial evaluation for such
diverse applications as absorption refrigeration systems, man cooling systems,
are employed to derivatize and protect various
substrates during synthetic sequences. This has been done in continuous
reaction system also.
Continuous synthesis reaction for ethylalkoxysilanes
has been done.
Reduction in Capital Cost
One international chemical giant proposed a $ 6
million plant for a product. The strategy of process intensification cut the
capital cost down to $ 2.5 million.
A process developed by Hitachi for production of PET
from EG and PTA by esterification and polycondensation
accomplishes it in three reactors compared to requirement two reactors and four
mixers for the esterification reaction process and three reactors and three
mixers for the polycondensation reaction process. In the Hitachi process
compared to conventional systems, the cost per unit power of the main reactor
is approximately one-sixth, and there are only one-seventh as many places
requiring maintenance. This is a highly energy-efficient process.
While cost reduction was the original target for
process intensification, it quickly became apparent that there were other
important benefits, particularly in respect of improved intrinsic safety,
reduced environmental impact and energy consumption. Given the anticipated
plant volume reductions, the toxic and flammable inventories of intensified
correspondingly reduced, thereby making a major
contribution to intrinsic safety. It can be inferred that the Dow hazard
index and Dow toxicity index could be drastically reduced.
above are some examples of successful process intensification projects in
operation taken from literature as well as personal knowledge. However it is
difficult to come by examples as in most cases the benefits are so large that a
high level of secrecy is kept in many cases the product name is not revealed.
examples indicate application of PI to a wide variety chemistry's, processes
and across many industries. There are very large number of laboratory
initiatives at present. Some of them are like the use of Spin disc
reactors(SDR), Oscillating flow reactor(OFR), Heat exchange reactor(HEX), which
are being actively being considered for various processes.
other equipmentssuch Sonochemical
reactor, Microwave reactors, ceramic cross flow heat exchangers and reactors,
gas lift reactors, membrane reactors, are also available.
are many chemical processes where these methods could be used. However the
strategies have to be carefully crafted, because in most cases the existing information
may not be suitable. The actual kinetic data for reaction could be camouflaged
by flow, mass and heat transfer effects. The intensity of mixing could be more
than magnitude or two over conventional mixing. It would be necessary to run
bench scale and pilot plant to understand the operations and gather information
for design and scale up. Initially it may appear that benefits would be their
if the reactions are fast, slow reactions may not give the desired benefits.
However innovations such as oscillating flow reactor could be a pointer.
chemical process industries or chemical processes where process intensification
could give large benefits are mentioned below. The basic idea is the possible
use of well proven technologies that already exist that can be used in an
intensification strategy as also some of the newer equipment which are coming
- Red phosphorus -
changing from batch to continuous process. The problems associated with
the change over are known and require fine tuning using the latest
developments in process intensification.
- Production of precipitated
calcium carbonate by reaction of CO2 with milk of lime to
produce very small particle size.
- Production of HEDP-
(hydroxy ethylene diphosphonic acid) this product has a simple chemistry
but there are problems of recycle and recovery and therefore quite a few
variations in processing are practiced. Continuous production with
innovative reactor strategies can lead to vast improvements in
productivity and reduction in energy and improved recycling.
Emulsion polymerizationor co-polymerization of acrylates, styrene, butadiene, vinyl
Low temp. chlorination -
a pesticide intermediate is prepared by chlorination at -40o C.
Considerable heat is evolved. The process could be carried out in novel
types of mixers heat exchanger and coolant system to make it more
efficient, with excellent temp. controls and other benefits.
production of trioxane and the
polymer polyacetal. The polymerization is almost instantaneous with
Process intensification methodologies can be used to produce
products of xylenes in small sized
equipments. The high heat transfer rates would possibly eliminate the use
of inert diluent and thus simplifying post processing. As a corollary one
could think of dinitration of derivatives of xylidines,
(intermediate for Pendimethalin) using these methods. It is likely
the by-product formation would be reduced.
- Another area where it can
be applied is the dilution of acids and alkali such as sulphuric
acid, caustic soda, etc
Combinations of static mixers and heat exchangers can make
equipment with very small foot print, even for capacities of many tons per
- Another potential area of
these methods for reactions with high heats of reaction such as neutralization,
nitration, sulphonation, etc.
- These methods could be
extensively applied to dye chemistry, reducing by-product formations,
reducing utility costs,reducing
solvent requirements, etc.
- Production of aromatic
isocyanates by continuous reaction.
- Catalytic nitration of
aromatics without the use of mixed acid.
- Dehydration of organic
solvents more specifically solvent mixtures by membrane processes in
contrast to azeotropic and extractive distillation.
- Continuous hydrolysis of nitriles
- Surface catalytic
reactions combined with heat transfer such as in KATAPAC.
- Continuous production of phosphorus
penta sulphide - this reaction has a very high heat of reaction, reacts
with almost explosive violence. Many methods have been devised earlier to
- Reaction of
alkali phenate with
aromatic acetal is normally carried
out batch wise with an inert diluent. This has a very high heat of
reaction and it appears that heat transfer may be the limiting factor,
therefore process intensification strategies may turn out to be very
- Hydrolysis of phenoxy
acetal can use process intensification methods to reduce reactor
volumes as well as to produce more concentrated recycle streams.
- Roasting of minerals
in reducing or oxidizing atmosphere.
This is a very limited illustrative list, there could be
hundreds of other potential applications of process intensification.
A word of caution
read about the benefits one may be tempted to leap into process
intensification, however there are certain cautionary signals.
In words of Prof. Ramshaw,
"A strategy of process intensification requires a
step change in the philosophy of plant and process design. If effectively
implemented it will lead to major improvements in environmental acceptability,
energy efficiency, intrinsic safety and capital cost. A major cultural change
is required on behalf of chemists, engineers
and managers and it is this, rather than technical difficulty which represents
the main obstacle to progress".
To paraphrase Prof Ramshaw's observations, in
general it is perceived "that the biggest obstacle to the adoption of process
intensification technology will be business process issues rather than technology.
In particular, chemists involved in process development have both a lack of
awareness of concept of process intensification and a fear of `mechanical`
This attitude is not only about chemists but most
chemical engineers brought up upon a diet of conventional batch processing.
What could also be called the 5 liter flask syndrome.
strategy would be to use continuous systems at the outset because once beakers
and flasks areused in the initial
development process it is very difficult to gain the acceptance of the chemist
for a continuous operation and we will end up with the same old pots and pans."