Biodiesel
is a kind of clean and renewable long chain
fatty acid monoester produced from oil crops
(soybean, rapeseed, etc.), oil forest (Oil
Palm, Pistacia chinensis, etc.), oil aquatic
plants (micro-algae, etc.), animal oil, microorganism
oil or waste oils and fats(WOF) through transesterifieation
with short chain alcohol, also known as "green
diesel". It is becoming a promising alternative
to petroleum-based fuels, with its physical
and chemical properties similar to that of
petroleum-based fuels.
Biodiesel
has many advantages over traditional diesel:
⏿Environmental
advantage: reducing the content of hydrocarbons,
CO, particles, sulfide and nitrogenous heterocyclic
compounds in air emission significantly;
biodegradable; suitable to be used in cities,
mines, forestry machinery or tourism vessel.
⏿Produced from
renewable resources, meeting the needs of
sustainable development.
⏿High
kinematic viscosity, easy to form oil film
in cylinder wall-layer, consequently improving
lubricity of kinematic components and reducing
wear of it.
⏿good safety
performance, high flash point (200‿low
volatility, more safe in the process of
transportation and use.
⏿Good
combustion performance, high Cetane Number
(higher than 49), improving performance
of engine, combustion residue is of subacidity,
making the life of catalyst and engine oil
lengthened.
⏿It
can be used directly with no need to change
diesel engine, and refueling equipment,
storage equipment and special technical
training is not necessary neither.
⏿Wide
application area: It can be used alone,
mixed with petroleum-based fuels or as additives
to improve combustion efficiency.
Excellent
performance of biodiesel makes the air emission
index meet with standards of European
more rigorous than EuropeanBiodiesel industry
not only reduces environmental pollution
caused by fossil fuel combustion, bur also
eases pressure of energy shortage to a certain
extent.
The
key of biodiesel process lies in raw material
and production technology. According to
statistics, raw material cost accounts for
75% of preparation cost. Thus, selecting
cheap raw material and increasing convesion
rate is the key to the practicality of biodiesel.
When it comes to production technology,
there are 3 main ways: ①chemical synthesis;
②biological enzyme; ③micro-algae.
Chemical
synthesis: esterification between animal
or plant oil and lower alcohols such as
methanol or ethanol is conducted in the
condition of acid or alkaline catalyst and
high temperature (230-250₿to produce fatty
acid methyl ester or ethyl ester. Then,
biodiesel is obtained after the process
of washing and drying. Thereinto, methanol
or ethanol can be recycled in the production
process; production equipment is the same
as ordinary equipment; about 10% by-product
of glycerin is produced during production
process.
However,
the method of chemical synthesis has following
shortcomings: complicated process, alcohol
must be excessive, follow-up process must
have a corresponding Alcohol Recovery Unit;
high energy consumption, deep color; esterification
product is difficult to be recovered because
that unsaturated fatty acid is metamorphosed
easily, high cost; discharge of waste caustic
liquid during production process.
Facing
above problems, people begin to turn to
biological enzyme (i.e. lipase) to conduct
transesterification. Free fatty acids and
water mixed in reactant has no influence
on enzyme’s catalytic effect. After standing,
fatty acid methyl ester can be separated
from glycerine and cleaner diesel is obtained.
Currently,
bottle-neck of producing biodiesel is its
high cost. According to statistics, raw
material cost accounts for 75% of preparation
cost. Thus, selecting cheap raw material
and increasing convesion rate is the key
to the practicality of biodiesel. Micro-algae
provides a new technical means to produce
diesel.
Producing
biodiesel by the way of micro-algae has
important economic and ecological significance.
Its superiority to other methods lies in
the following: high production capacity
of micro-algae; saving agricultural resources
for its using sea water as natural medium;
oil yield of micro-algae is several times
higher than that of terrestrial plants;
biodiesel produced from micro-algae contain
no sulphur; there’s no poisonous gas emission
when combusted; discharges into the environment
can be degraded by microorganism, with no
environmental pollution.
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