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A critical aspect of the design of a biodiesel process is the object
of having the final product perform with well-defined specificity.
The ignition properties of the fuel, an alkyl ester, requires
well-defined set conditions depending the type of use to which it is
being put such as
implosive combustion, compressive combustion as in the case of
an automotive fuel, and simply as a
burner fuel.
In general, the set of properties required for optimal performance
in each of these case should depend on the length of the carbon
chain of the biodiesel molecule. The fact is that, in general, the
thermophysical properties of substances are related to the atomic
constituents and configuration within the molecule. The lowest flash
temperature of biodiesel fuel is known to be 200C. Obviously the
higher temperature must correspond to higher carbon chain length
alkyl esters.
Evidently then, there exists
the need to design any biodiesel process to produce biodiesel that
is targeted at the use-purpose of production. In this regard, there
is the need to ensure that process bio-oil feed is of virtually
constant carbon chain length.
However, currently, the technology development for
biodiesel production has focused mostly on the
transesterification of waste vegetable
oil with respect to hobbyists, and other nonspecific vegetable oil.
In particular for waste vegetable oil which has free fatty acids of
varying carbon chain length, the esters produced from the reaction
are also of varying length, and therefore are not suitable for
use-purposes requiring precise performance- conditions. This
situation has to some extent resulted in the operating of the reactors,
Laming
Process reactors based on use of weight ratios
rather than molar-ratios as necessarily required by stoichiometric
relations. The empirical data change widely with operating
conditions including variation of mixer/stirrer speed, loading of
catalysts, etc. Consequent on this is also the empirical
observation, however, that reproducibility is not always assured,
and so quality control is particularly unreliable or is assured only
over a wide range of variations.
A more reasoned approach for
designing any biodiesel process therefore would be to preprocess the
feed vegetable oil before feeding the same to the process
transesterification reactor: The waste vegetable oil must be such
that even the free fatty acids in the oil are of the same
carbon chain length, before being fed into the process whether the |
process is operated with a
dual-reactor system or a single waste vegetable oil
transesterification reactor; The algal vegetable oil - though likely
to be of the same carbon chain length - should have very narrow band
in any form statistical distribution in chain length.
Property-Specificity
Separator
Several approaches may be adopted for the design of the feed
preprocessor separator, which is being termed in this case
Property-Specificity Separator. Further, the separator design
approach is for preprocessing the feed before the
transesterification reaction although one could also perform
post-reaction separation depending on the adopted production
criteria. However, the focus here is on the preprocessing, so in
designing for properties-specificity the technical approach
processes the feed oils instead of the biodiesel.
Depending on the proximity
of the thermophysical properties of the target feed oil and the oil
for removal, the technical approach for adoption may be one of two
chemical separation processes: A Distillation Process or a
composite of Chromatography Separators together with Distillation
Processes corresponding to the several categories of oils aimed to
be recovered. For oils which widely varying boiling points then the
use of Distillation process is suggested. However, for oils with
very close boiling points, then the use of the Chromatographic
Separators-cum-Distillation Processes is suggested.
In effect, the feed oils to
be separated must first be assayed with liquid chromatography , or
mass-spectrometer, or some other suitable method of identification
of the contents. Next the proximity of the properties are evaluated
to enable choosing a method. The case of widely varying boiling
points and the consequential use of Distillation Processes does not
require much discussion as any process designer can effectively
incorporate the distillation Process into the Biodiesel process.
However, the separator for the case of proximate boiling points oils
requires some analysis.
In implementing the
alternative method, the oils have to be pulsed through the
Chromatographic Separators, and then flushed into a storage tank.
The configuration of these separators depends on the number of oil
streams that will be generated with the separation operation. In
general, the separators may be arranged in parallel, in multi-stage
or a mix of parallel and multi-stage as per the design rationale of
the process designer. |
Each liquid is pumped into a
corresponding distillation Process for the extraction of the oil
that is then feed into the operating reactor preset at the optimal
operating conditions for the particular oil feed.
Properties-Specificity Process Advantages
Designing for
properties specificity undoubtedly enables the production of a
product that has nearly a constant properties instead of a set of median
values for the users of the product to operate by, given the
remediation of the effect of carbon chain length variation of the
final biodiesel product. Although the primary motivation for
property specificity, designing for properties specificity also
affords the process design and the production operation some other
advantages.
The one of the process
design advantages is the ease of design of the
Continuous
Water Washing Biodiesel Separator: The properties-specificity
derivative of the design approach also makes uniform the time-to
micelle formations inside the separator and thereby making the
mathematical design much simpler than otherwise. Of course,
consequent on the properties-specificity is also optimal
performance that previously was lacking.
Another advantage is a
more precise design of the transesterification reactor, because of
the expected elimination of the dependence of the reaction rate
equations on the derivative properties-specificity. The rate
equation can give more precise results as the dependence would not
be based on a statistical median of the properties but rather on the
actual value characteristic of the feed-oil. Moreover, the
reactor design
can be based on molar ratios as should be under the dictates of
stoichiometric analysis, instead of the mass ratios currently used
in most reactor designs and operations.
Finally, the design can
also become more flexible as specific reaction-quench substances
can now be opted for in undertaking the
transesterification reactions quenching as is essential
for continuous biodiesel
production processes.
One advantage in the operation of the process is prediction of the
reactor dynamics which should become fairly reliable as a result of
the molecular uniqueness of the feed-oil. |
