What does ‘drop in fuel’ mean?
A drop in fuel is a liquid hydrocarbon fuel with physicochemical properties very similar to fossil fuels. It is capable of replacing the traditional gasoline, diesel and jet fuels up to any extent. The existing automobile engines and fuel storage and distribution infrastructure cannot make out any difference between a drop in fuel and its traditional fossil fuel counterpart. This means that the use of drop in fuels makes it redundant to go for engine modifications typically required when we use first generation and second generation biofuels beyond a certain limit. The article intend to provide a preview of technologies under investigation to produce drop in fuels from lignocellulosic biomass.
Lignocellulosic biomass feedstock
Wide range of biomass can be used to produce drop in fuels. It could be grasses, forest thinning, wood chips, agriculture waste like corn stalks and rice husk, industrial waste such as bagasse, bark from paper and pulp production and waste paper, dedicated energy plants or algae.
Technology for production of drop in fuels
The synthesis of replacement fuels for traditional fossil fuels like gasoline, diesel and jet fuels is being attempted by taking various routes. The most sought after are following:
(A) Via Syngas
This is one of the most preferred routes because it utilizes almost all types of biomass and do not require pretreatment of the biomass except minor adjustments in its moisture level. The first step in the production of liquid transportation fuel is the gasification at high temperature (1200 °C to 1600 °C) in the presence of limited supply of oxygen. This leads to the conversion of carbonaceous biomass into syngas which is primarily a mixture of carbon mono oxide and hydrogen. The syngas can be converted into the transportation fuel leveraging from the established technological pathways.
The two most developed routes to convert syngas into drop in fuel are given below. Both of these come under the thermochemical route of drop in fuel production.
(i) Fischer Tropsch synthesis
In general cobalt or iron based catalysts are used to catalyze the reaction to convert syngas into drop in replacements of diesel.
(ii) Mobil process in the first step syngas is converted into methanol which is converted into dimethyl ether in the second step. Dimethyl ether in turn is converted into hydrocarbons of different chain lengths. The presence of catalyst is required in different steps.
(B) Via bio oil
(i) Hydrothermal liquefaction Water usually works as a medium in hydrothermal liquefaction. It is kept at or below its critical temperature (374 °C). Under high pressure of around 2500-3000 psi the heated biomass is cooked. The temperature is subsequently brought down. The process results in the conversion of biomass into bio oil.
(ii) Catalytic fast pyrolysis In an air tight chamber dried biomass is heated at a temperature around 500 °C in the presence of a catalyst. Its subsequent cooling results in a kind of tar known as bio oil. Rich in oxygen it is different in chemical composition from the bio oil generated by hydrothermal liquefaction of biomass.
The bio oil obtained by following either of the two procedures needs to undergo hydroprocessing so as to become infrastructure compatible drop in fuel.
Cool Planet Energy systems (http://biofueluptodate.com/biomass-cool-planet-energy-systems/) and Avello Bioenergy (http://biofueluptodate.com/biomass-fast-pyrolysis-avello-bioenergy/) work on the same lines.
(C) Via lignocellulosic sugars
The acid pretreatment of the lignocellulosic biomass is followed by its enzymatic hydrolysis to yield solubilized sugars which are then utilized to produce drop in fuels. Given below are the two routes mostly followed in order to get drop in fuels from these sugars:
(i) Leveraging from synthetic biology Through modifying the metabolic pathways of the microorganisms it is possible to feed them the solubilized sugars (Amyris) or other ingredients (Joules Unlimited) and make them produce the precursor chemicals from which the fossil fuels equivalent can be synthesized.
(ii) Catalytic conversion of lignocellulosic sugars to hydrocarbon fuels This is one of the promising technologies which attempts catalytic conversion of glucose, xylose and other solubilized components of lignocelluloses to hydrocarbon fuels. Virent Inc. utilizes this approach to make drop in fuels (http://biofueluptodate.com/sugars-to-drop-in-fuels-virent-inc/)
All these routes lead to the synthesis of drop in fuels which are still under research and development phase. Many pilot and demonstration plants are under construction around the world. Apart from these methods there are many other methods (developed by Joules Unlimited) as well which leads to drop-in fuel
You may also like to know about
First Generation Biofuels click http://biofueluptodate.com/first-generation-biofuels/
Second Generation Biofuels click http://biofueluptodate.com/second-generation-biofuels-bioethanol/
Third Generation Biofuels click http://biofueluptodate.com/algae-biofuel/