Extracting Bio Crude From Algae And Other Biomass Through Hydro-thermal Liquefaction.

There are a lot of process involve in the extraction of  bio crude from algae; these process became when the idea of obtaining a high oil content from the feed stock or biomass present.

Algae provide many potential routes for the conversion into biofuels, including hydrothermal liquefaction. During hydrothermal liquefaction, high moisture biomass is subjected to elevated temperatures (250-350 deg C) and pressures (10-20 MPa) in order to break down and reform the chemical building blocks into a bio-crude oil. [University of Illinois, Dept. of Agriculture]

At these temperatures and pressures, water becomes a highly reactive medium promoting the breakdown and cleavage of chemical bonds, allowing for the reformation of biological molecules. The conversion mimics the natural geological processes which produced our current fossil fuel reserves and allows for the conversion of a wide range of feed stocks. Tested feedstocks include low lipid algae, swine manure, sawdust, garbage, and even sewage sludge. [University of Illinois, Dept. of Agriculture]

Hydro-thermal liquefaction, other wise known as HTL is also called hydrous pyrolysis, is a process for the reduction of complex organic materials such as bio - waste or biomass into crude oil and other chemicals. It mimics the natural geological processes thought to be involved in the production of fossil fuels.

HTL is one of the processes of a general term of TCC which includes gasification, liquefaction, HTL, and hydrous pyrolysis. 

There is a general consensus that all fossil fuels found in nature — petroleum, natural gas, and coal, based on biogenic hypothesis — are formed through processes of TCC from biomass buried beneath the ground and subjected to millions of years of high temperature and pressure. In particular, existing theories attribute that petroleum is from diatoms (algae) and deceased creatures and coal is from deposited plants. Gasification of biomass produces a mixture of hydrogen and carbon monoxide, commonly called syngas. 

The syngas is then reformed into liquid oil with the presence of a catalyst. Pyrolysis is a heating process of dried biomass to directly produce syngas and oil. Both gasifi cation and pyrolysis require dried biomass as feedstock, and the processes occur in an environment higher than 600C.

HTL involves direct liquefaction of biomass, with the presence of water and perhaps some catalysts, to directly convert biomass into liquid oil, with a reacting temperature of less than 400C. 

HTL has different pathways for the biomass feedstock. Unlike biological treatment such as anaerobic digestion, HTL converts feedstock into oil rather than gases or alcohol. There are some unique features of the HTL process and its product compared with other biological processes. First, the end product is crude oil which has a much higher energy content than syngas or alcohol.

And second, if the feedstock contains a lot of water, HTL does not require drying as gasifi cation or pyrolysis. The drying process typically takes large quantities of energy and time. The energy used to heat up the feedstock in the HTL process could be recovered effectively with the existing technology. HTL may have two pathways from biomass to biofuel: (1) direct conversion of biomass or (2) pretreatment of biomass and then fermentation.

For the biomass with little lignocellulosic fraction — such as waste streams from animal, human, and food
processing — it can be directly converted into biofuel thermochemically. Pretreatment is currently a bottleneck in the conversion of cellulosic feedstock. HTL may hold a substantially greater potential to shorten the fermentation time of lignocellulose.

Traditionally,acid hydrolysis was commonly used to convert lignocellulosic materials to monosaccharides, but the high concentration of acids used in hydrolysis requires extensive waste treatment or recovery costs.

The Role of Water in HTL

Water plays an essential role in HTL. It is therefore critical to understand the fundamentals of water chemistry when subjected to high temperature conditions. Water is rather benign and will not likely react with organic molecules under standard environmental conditions (20 ° C and 101,325 kPa). However, when the temperature increases, two properties of water molecules change substantially.

First, the relative permittivity (dielectric constant), of water decreases quickly when the temperature increases. When the thermal energy increases, the shared electron by oxygen and hydrogen atoms tends to circulate more evenly and the electronegativity of the oxygen molecule is reduced (less polar). For example, when temperature increases from 25 ° C to 300 ° C, the relative permittivity decreases from 78.85 to 19.66, resulting in water molecules from very polar to fairly nonpolar, in a relative term.

Chemistry During Hydrothermal Liquefaction

The ability to convert such a wide range of feedstocks under hydrothermal conditions is due to the fundamental biological building blocks that are broken down and reformed during the process. Depending on the feedstock, waste biomass is composed of varying ratios of macromolecules including carbohydrates (cellulose and starch), lignin, lipids, and proteins. Initially, these macromolecules are broken down into their monomer units.

As the hydrothermal liquefaction process continues, the monomer units are further cleaved and broken into smaller fragment molecules. During fragmentation, the goal is to remove oxygen and other heteroatoms (e.g. nitrogen, sulphur, phosphorous), leaving behind the initial carbon and hydrogen atoms in the form of low molecular weight compounds. This process maximizes the energy content of the biocrude oil and increases the value and ability to refine the final product.

Synergistic Waste-water Treatment and BioEnergy Production 

The robust reaction conditions and aqueous environment make hydrothermal liquefaction well suited for the conversion of low-lipid, fast-growing algae that proliferate in wastewater treatment facilities. Additionally, integrating algae cultivation into a wastewater treatment plant offers the synergetic benefit of providing nutrient remediation. Algae capture and utilize dissolved nitrogen and phosphorous present in wastewater to support growth. These plentiful nutrients would otherwise be released into the environment, creating harmful eutrophic zones as a result of prolific algal growth. By converting nutrient waste into a resource, we can reduce environmental pollution, produce bioenergy, and preserve our water resources.