Reactor & Impeller Design in Hydrogenation

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GBHE Technical Bulletin CTB #79
Reactor & Impeller Design in
Hydrogenation
Gerard B. Hawkins
Managing Director
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be assumed.

Background
As the topic of reactor types and technologies often comes up in discussions on
hydrogenation, I have collated some information on this. First of all, I have
included a short summary of the main technologies available and my comments
on these technologies. (This is list is not exhaustive, but does cover most of the
common reactor types available today).
I have also included a list of the suppliers of these technologies at the end of the
document and also some information from the websites of these companies
where I think this information is useful. You can view the websites and
information yourselves also.
Hydrogenation Reactors
The hydrogenation reaction usually involves a three-phase slurry – the liquid oil,
the solid catalyst in slurry phase and the hydrogen bubbles as the gas phase. As
there are a number of phase boundaries the mass transfer, and especially the
hydrogen dispersion, is a very important factor. The mixing system that is
employed in the reactor influences the mass transfer coefficient of the gas-liquid
transfer greatly.
The types of mixing systems currently in use can be divided into two broad types:
• Stirred Vessels
• (External) Loop reactors
Stirred Vessels
These are usually batch “dead-end“ (i.e. no external recirculation of hydrogen)
reactors.
In the past recirculation reactors were often used where the hydrogen was
recycled externally from the reactor. This type is no longer widely used.
The main differences between the dead-end stirred reactors are usually with
what type of impeller is used and how the entrainment of hydrogen from the
headspace is enhanced.

The main types can be categorized as follows:
• Flat blade turbine impeller (Rushton):
This is the most common type of impeller in use. It usually has 6 blades -
although this number may vary – bolted to a disc on a rotating shaft. It generates
radial flow patterns. The hydrogen sparger is quite often the ring form just below
the impeller. This is probably the most common impeller in edible oil reactors
(especially older ones) but it is by no means the ideal one for dispersion of the
hydrogen in the oil.
• CD-6/BT-6 impeller (Chemineer):
This is an improvement on the previous impeller with higher mass transfer
coefficients and lower probability of cavitation. There is some information below
on the CD-6 and BT-6 from the Chemineer website.
• Axial impeller (Lightnin):
While the previous two impellers have radial mixing patterns, an axial mixing
pattern is given by the A315 (downward) and A340 (upward) pumping impellers
from Lightnin. The manufacturers claim this has better hydrogen induction from
the headspace and gives better hydrogen dispersion in the bottom half of the
reactor.
• Hydrogen Transport via Shaft (Ekato):
This technology disperses the hydrogen by sucking it from the head space and
passing it through the shaft. The hydrogen is then dispersed in the liquid again
below the liquid surface. This technology is suitable for installation in an existing
reactor.
• Advanced Gas Reactor (Praxair):
This could be considered a type of “loop“reactor, although the hydrogen loop is
inside the reactor. A downward pumping helical screw impeller within a “sleeve“
tube pulls hydrogen in from the headspace and forces it to the bottom of the
reactor from where is recirculates upwards on the other side of the tube. It gives
a high mass transfer rate of hydrogen to oil.

Loop Reactors
These technologies involve the external circulation of unreacted hydrogen and/or
oil. The heating/cooling of the oil-catalyst slurry is also done externally.
• BUSS Loop Reactor:
The reactor mixes the oil-catalyst slurry and the hydrogen in a high shear regime
in a Venturi mixing jet. The oil-catalyst slurry is circulated through an external
heat exchanger and forced through a Venturi mixer at the top of the reactor. The
suction effect here draws in fresh hydrogen.
This type of reactor is advantageous when high pressures, temperatures and
reaction rates occur. It gives a higher mass transfer coefficient and the fact that
there are no heating coils in the reactor is an advantage.
The disadvantages with this system are the higher capital and operation costs.
(More energy - 5kW/m³ - is used to disperse the hydrogen in the liquid than in
traditional stirred vessels where the energy requirement is typically 2 – 3 kW/m³).
Other reactor types
There are also fixed bed continuous and slurry-phase continuous reactor used in
the edible oil industry. However, continuous reactors only really become viable
when there is a large production of a single product.

Appendix A – List of contact details for suppliers
Biazzi SA
Chemin de la Tavallaz 25
CH-1816 CHAILLY s/ MONTREUX (Switzerland)
website: www.biazzi.ch
US agent:
Ambitech Engineering Corporation
1333 Butterfireld Road, Suite 200,
Downers Grove, IL 60515.
Tel: 630-963-5800
Fax: 630-963-8099
Chemineer
P.O. Box 1123 Dayton, Ohio 45401
Phone: (937) 454-3200
Fax: (937) 454-3230
E-mail:
www.chemineer.com
EKATO Rühr- und Mischtechnik GmbH EKATO Corporation
Käppelemattweg 2 700C Lake Street
Germany - 79650 Schopfheim Ramsey NJ 07446 / USA
Tel. +49 - 7622 - 29 – 0 Paul Dwelle
Fax +49 - 7622 - 29 – 213 Phone: +1 201 8 25 46 84
Email: info@ekato.com Fax: +1 201 8 25 97 76
Website: www.ekato.de info.vus@ekato.com
Kvaerner Process Technology (Switzerland) AG
Postal Addr: Buss Industriepark Hohenrainstrasse 10
City: CH-4133 Pratteln 1
Country: Switzerland
Telephone: +41 6182 56668
Telefax: +41 6182 56737
E-Mail: kptch@kvaerner.com
Homepage: http://www.kvaerner.com/kpt/kpt-uk/
LIGHTNIN
135 Mt. Read Blvd.
Rochester, NY 14611 U.S.A.
Tel 1-585-436-5550 (8am-5pm Eastern Time)
Tel 1-888-MIX-BEST (U.S. & Canada)
+1-585-527-1623 (Worldwide)
Fax +1-585-527-1742
www.lightnin-mixers.com

Appendix B – Information from supplier’s websites
(i) Chemineer - Information from website
CD-6 Impeller
Size relative to P-4 0.83
Favorable Applications:
The CD-6 impeller is a second generation gas and immiscible liquid dispersion impeller. The CD-6
can handle about 2.4 times the maximum gas capacity of the D-6 impeller. The CD-6 is similar to the
Smith impeller, but there are substantial power and dispersion capability differences. This impeller
has been used at aeration numbers as high as 2.1.
BT-6 Impeller
Size relative to P-4 0.88
Favorable Applications:
Highest gas dispersing capability available. Can disperse nearly six times the gas handling
capability of the D-6 or Rushton impeller. Unloads less than the CD-6. In fact, the unloading is
nearly all due to the change in effective density of the gassed liquid. The mass transfer capability is
on the order of 10% better than the CD-6. Unlike many other gas-dispersing impellers, the BT-6 is
relatively insensitive to viscosity.

(ii) Ekato - Information from website
Hydrogenation
Requirements:
The reaction of pure gases requires:
• Complete gas consumption
• High productivity
• Uniform suspension of the catalyst
• Safety control of the gases and reaction products
• Recirculation of the reaction gases (picture right)
Typical applications:
Hardening of technical fats: a definite amount of iodine achieved in one hour instead of three. Production
of Sorbitol: With a batch time of 1.5 hours it was possible to reduce the glucose content down to 1000 to
2000 ppm (picture left). Productivity double as high for reduction of aromatic nitro products.

(iii) Kvaerner Buss Loop - Information from website
Loop Reaction Technology Applications
Hydrogenations
Heterogeneous catalytic hydrogenations are the most well-known mass transfer and heat transfer limited
reactions. For this type of reaction many processes have been successfully realised on commercial scale
by KPT-CH based on the Buss Loop Reactor and its latest further development the Advanced Buss Loop
Reactor. A large basis of experience has been created over the years for the following classes of
hydrogenations:
• Double and triple bond hydrogenation
• Ring hydrogenation
• Hydrogenation of aliphatic nitro-compounds
• Hydrogenation of aromatic nitro-compounds
• Hydrogenation of halogenated aromatic nitro-compounds
• Hydrogenation of aldehydes and ketones
• Hydrogenation of nitriles to amines
For all reaction classes we have demonstrated the following advantages:
• Fast heating and cooling
• Short reaction time
• Reduced solvent load
• Reduced catalyst load
• Reduced catalyst consumption
• Higher selectivity
• Higher yield
Higher productivity

(iv) Lightnin - Information from website
A315
Recommended for gas-liquid dispersion and mass transfer-controlled applications
• Can improve mass transfer by 30% compared with Rushton turbines
• Decreases shear rates up to 75%
• Can reduce energy costs up to 45%
• Improves yields in shear-sensitive processes
A340
Recommended for up-pumping applications
• Ideal for multi-phase applications, such as fermentation, polymerization and hydrogenation
• High gas induction from surface
• Controls foaming

(v) Praxair – Information from website
Praxair Advanced Gas Reactor (AGR)
The Advanced Gas Reactor (AGR) is a downward pumping helical impeller that provides extremely
high pumping rates and intimate mixing for catalysed gas/liquid reactions such as hydrogenation.
Headspace gas is drawn into the liquid by either the formation of vortices or by eductor tubes. Praxair
AGR provides faster reaction rates providing increased throughput or lower catalyst consumption and
significant advantages in three phase reactions with oxygen or hydrogen.
The Problem
Many manufacturers of pharmaceuticals and speciality chemicals are experiencing higher costs and
lower productivity than necessary because conventional mixers in stirred tank reactors have long
batch times, catalyst usage is high, power consumption is large, and the gas is inefficiently used.
The Praxair Solution
The Advanced Gas Reactor, when used in place of conventional turbine impeller agitators, can
reduce catalyst usage, increase production, and minimize hydrogen usage. In addition, less power is
required. The system also can handle variable batch sizes and provides uniform, predictable
selectivity.
Process Benefits:
• higher production
• lower catalyst loading
• minimum hydrogen loss
• low power usage
• variable batch size capability
• uniform, predictable selectivity
Customers processing speciality chemicals and edible oils have experienced catalyst savings of 25 to
50 percent, increases in production rates of as much as 35 percent, and up to 60 percent reductions
in power consumption.
Commercial Results
• 25-50% catalyst savings
• 35% faster reaction rates
• 60% power savings
AGR Design Features
The AGR consists of a helical screw impeller enclosed within a draft tube. The impeller pumps the
two or three-phase slurry downward through the draft tube and then upward in the annulus areas
outside the tube. This flow pattern uniformly mixes the entire reactor contents and eliminates dead
spots and localised mixing zones often found in reactors using multiple turbine agitators. Baffles
within the draft tube greatly increase the impeller pumping capacity by preventing liquid rotation.
The AGR, with a power number of 0.84, has the ability to efficiently circulate high flows of liquid
throughout the reactor. Much of the mixing power is used within the draft tube, subjecting the mixture
to the velocity and turbulence needed for maximum mass transfer. The liquid velocities outside the
draft tube are sufficient for keeping the catalyst suspended throughout the liquid phase. The helical
impeller along with special turbulence promoters and a flat blade turbine at the bottom of the shaft
disperse fine hydrogen bubbles into the liquid.
A reactor equipped with an AGR runs as a dead-ended hydrogenator. The hydrogen is fed to the
sparger on pressure demand, and the hydrogen continuously recirculates from the reactor headspace
into the liquid. This continuous recirculation ensures that hydrogen is in contact with the liquid at all
times during the batch run. The means by which headspace hydrogen is recirculated depends on

whether the AGR is designed for processing of fixed or variable batch sizes.
In full batch operations, the draft tube inlet is near the liquid surface and the action of the helical
impeller causes vortices to form at the liquid surface. These vortices feed hydrogen from the
headspace into the draft tube.
For processing smaller batches, the AGR impeller shaft is equipped with eductor tubes located just
above the draft tube inlet. The submerged eductor tubes continuously feed gas into the liquid by
drawing hydrogen from the headspace through a hole in the hollow impeller shaft located above the
liquid level.
The AGR provides the process conditions necessary for optimizing mass transfer rates.
• highly turbulent mixing
• well-dispersed gas and catalyst
• small bubble formation
• well-mixed reactor contents
• high gas holdup
• continuous gas recirculation
Sizing the AGR
Whether selecting an AGR for a new reactor or for retrofitting an existing one, the equipment must be
of an appropriate size and located correctly within the reactor.
The reactor height to diameter ratio should be no greater than 2 to 1 and the AGR nominal diameter
should be approximately 1/3 of the reactor diameter. Standard AGR sizes are 24" (60.96 cm), 30"
(76.2 cm), and 36" (91.44 cm) in diameter; however, special units can also be fabricated.
Reactors to 3000 gallons should have at least 16" (40.64 cm) to 18" (45.72 cm) manways, and larger
reactors should have at least 20" (50.8 cm) manways.
The location of the AGR within the reactor vessel depends on the reactor loading. If varying batch
sizes are to be run, the AGR is located in the bottom half of the vessel. If full batches are run, the unit
is located near the top, reducing driveshaft length and fully using vortex ingestion for recirculating
headspace gas into the reactor. Sizing and selection of an AGR should be done only in consultation
with a Praxair design engineer, and details of reactor internals must be reviewed to ensure that they
will not interfere with AGR operation.
For retrofits, Praxair typically uses the existing drive and seal. For new reactor systems, we can
provide the drive and seal, or work with the customer's vendors to match the AGR to the reactor
vessel.
AGR Drive
Typically, the recommended power level for the AGR is a minimum of 7.5 HP/1000 gallons. When
retrofitting a reactor with the AGR, it may be possible to use the existing drive with minor changes to
the gear box; the AGR usually runs at a higher speed than an flat-blade or pitched-blade turbine.
The generally accepted power correlation for mixers is given in the equation below. The empirically
derived equation gives the dimensionless power number Np.
HP = Np x Sg x N3 x D5
Where: HP = horsepower
Sg = liquid specific gravity
N = impeller speed
D = impeller diameter
Table 1 gives published power numbers for several impeller types.

Impeller Type Power Number
Flat Blade Turbine 5.75
Pitched Blade Turbine 1.27
Marine Propeller 0.87
AGR* 0.84
*AGR power number included for comparison only.
When using equation 1, where D is in inches and N is in RPM, multiply previous equation by 6.566 x
10-14
to obtain HP.
AGR Pumping Rate
The AGR pumping rate must be sufficient to ensure that upward velocity in the annular space is a
minimum of 0.3 ft/sec for catalyst suspension and that the downward velocity in the draft tube is a
minimum of 1 ft/sec to exceed the rise velocity of the gas bubbles. In commercial AGRs the draft tube
exit velocities typically range from 3 to 10 ft/sec.
Heat Transfer
Many hydrogenation and oxidation reactions are exothermic, and internal cooling coils are used to
maintain the temperature. Generally, vessels with internal cooling coils designed for flat-blade
turbines show a 25 to 30 percent reduction in heat transfer with the AGR because the liquid flow is
perpendicular to the cooling coils. An individual experienced in heat transfer should evaluate the
system if there are any questions about cooling capability.
AGR Performance
Comparison tests between the AGR and conventional agitators have been run at the pilot scale level
as well as on a commercial scale. In addition, ongoing programs to better characterize the AGR are
being conducted at universities and research organizations in the United States and around the
world.
Some of the early work in the food hydrogenation area was conducted at the Food Protein Research
Center at Texas A&M University. A series of pilot scale tests were run in a 20-gallon autoclave
comparing the AGR with a flat-blade turbine. The AGR demonstrated 70 percent less time for brush
hydrogenation and 64-68 percent less time for margarine base stock hydrogenation. In the brush
hydrogenation, the AGR selectively hydrogenated the linolenic fats without a significant increase in
stearate. The AGR produced similar solid fat index curves and transisomer contents in margarine
base hydrogenation.
Other pilot scale tests were run in a 20-gallon autoclave. The following results were obtained:
Hydrogenation of Coconut Oil:
• 25% savings in catalyst could be realized at equal batch times
• 10% savings in batch time at equal catalyst loading
• 40% savings in mixing power at equal batch time and catalyst loading
Hydrogenation of Fatty Acids and Fatty Amines:
• 15 to 33% savings on catalyst at equal mixing power and batch times
• 41% reduction in batch time at equal mixing power and catalyst loading
Commercial Experience
For over a decade, Praxair's advanced gas reactors have proven themselves in commercial
hydrogenation and oxidation reactions. Numerous units, both retrofit and new systems, have been
installed around the world.
Pilot AGR Services

Pressure Chemical Co. provides pilot plant, process scale up, and process development services to
chemical, food, and pharmaceutical companies. Pressure Chemical's complement of reactors
includes a 250-gallon, high-pressure stainless steel reactor equipped with an AGR agitation system.
Utilizing this unit and their many years of experience with catalytic processing, Pressure Chemical is
able to help prospective AGR users to evaluate the benefits offered by this agitation technology.
Hydrogen Supply Systems
Praxair offers a complete line of hydrogen supply options, tailored to meet customer needs and
provide cost-effective solutions.
Results of hydrogenated soybean oil in this reactor type were published by Wiese, M., and Delaney, B.,m
“Plants using new hydrogenation agitator design”, Ibid. 3:817 (1992).
(vi) Biazzi - info from website
Main features of the Biazzi hydrogenating system:
The hydrogenation reaction is characterized by being highly exothermic and highly
mass transfer resistant. So in exclusive collaboration with one of the world leaders in
the agitation and mass transfer field, Biazzi has overcome these difficulties and has
been able to develop a high-performance hydrogenation reactor of unique design
(Patented*).
The
reactor:
Pressure : up to 100 bar (special execution up to 200 bar)
Volume : 0.5 to 50 m3
Temperature : up to 350°C
Material : st.steel or other alloy as required
Glass lined : under development
Fitted with:
A special powerful, self aspiring, gas dispersion system
A combination of special elements which provide the required gas-liquid transfer ,
shearing effects, high internal hydrogen recirculation rate and liquid circulation at
moderate power consumption. The agitator is driven by a pratically maintenance
free magnetic coupling system, eliminating sealing problems generally associated
with high pressure equipment.
Cooling /heating elements
High surface area static turbulo-plates of new design to permit practically unlimited
heat transfer.

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