Hydrothermal liquefaction of animal by product waste using zeolite catalyst: A Mini-review

In view of the worldwide challenges posed by rising pollution and fossil fuel usage, it is imperative that we adopt a new energy strategy that makes use of all available refuse and vegetation to generate electricity. This is the safest and most effective way to address this worldwide issue. The process of hydrothermal liquefaction converting dry and moist material, such as (agricultural and animal waste, algae, and foodstock waste) into bio-crude in the presence of high temps and pressure in a watery medium is a potential technology in the area of renewable energy. When producing bio-crude, it is better to use solvents and catalysts to improve biomass liquefaction and boost output. As such, this review provided a brief overview of the research into the mechanism of HTL processes and biomass represented by animal by-products, their transformation, and the production of bio-crude; the effect and effectiveness of zeolite used as a catalyst in the hydrothermal liquefaction process; the energy efficiency of the process; and the effect of parameters such as heat, pressure, and process residence time; all with the goal of developing better pathways.


Introduction
Developing renewable energy sources is of great interest due to the non-renewability of natural fuels, rising energy consumption, and expanding environmental worries regarding development.A future energy system that is more viable will rely heavily on biomass, one of the most plentiful forms of green energy.Growing interest is being paid to the processing of vegetation into liquid energy sources in addition to direct burning.Petroleum and petrochemical sectors have developed millions of petroleum-based goods because fossil fuels have historically been the lowest source of energy.Unfortunately, variables such as the loss of readily available reserves and the ever-increasing demand from developing countries have contributed to high increases in the price of gasoline in recent years.As energy consumption rises, it will be necessary to switch to alternative energy sources and advance related technologies [1].However, during its treatment, these renewable energy sources eventually caused many issues related to waste management and radioactive IOP Publishing doi:10.1088/1755-1315/1232/1/012012 2 emissions from biomass and nuclear energy.Biomass energy has therefore been known as the most promising source of renewables in the transport sector.
Biomass is a renewable resource and carbon neutral in principle [2].Researchers have been looking for renewable energy and chemical sources as hydrocarbon supplies have steadily dwindled in the face of rising demand.It's possible that biomass is the key to ending the quest.For economic growth, people have been using more and more nonrenewable fossil fuel resources, which scientists have discovered to be steadily dwindling.As a sustainable resource that can be used for the production of energy and compounds, biomass such as agricultural, woodland, urban refuse waste, animal wastes, wastes from food preparation, and marine leftovers offers a viable option to depleting petroleum resources.Since there are running out of natural fuels and increasing temperatures are due to manmade carbon dioxide pollution, scientists all over the world have begun looking into renewable energy alternatives [3].Major environmental issues linked to global warming are exacerbated by the use of petroleum compounds derived from old crude oil because of the release of greenhouse gases.Hydrothermal liquefaction is a thermochemical process that uses water at low to high pressure (5-30 MPa) in a decomposition process to create solid, liquid biocrude, and gas.For the purpose of producing compounds with great added value, hydrothermal liquefaction is an exciting new.The worldwide search for renewable energy has been sparked by the dwindling reserves of fossil fuels and the increasing levels of pollution [4].To convert various feedstock kinds into a sustainable, CO2-neutral oil biocrude suitable for co-raffination at current crude oil plants, Hydrothermal liquefaction (HTL) is a promising possibility.On the other hand, the bio-crude oil made from HTL has superior characteristics, including a higher heating value (HHV) of around 35 MJ/kg and a low oxygen/carbon ratio.Water's special characteristics "high ionic product and low dielectric constant" allow it to depolymerize and repolymerize hemicellulose, cellulose, and lignin into biocrude oil, watery phase, solid waste, and gas under subcritical and supercritical circumstances [5].Since hydrothermal liquefaction technology is the most effective means of converting wet mass, the goal of this work is to determine the optimum operating conditions for converting wet biomass represented by animal by-products to give the best productivity of biocrude, as well as to understand the impact of the catalyst on the process and the efficiency of the process in the presence of zeolite.

Hydrothermal liquefaction process
Inside the reactor, the biomass mixture, solvent, and catalyst are all introduced together.In order to remove any trace of air from the autoclave, an inertgas such as nitrogen or hydrogen is added and allowed to circulate for a few minutes.The reactor is first preheated to a certain temperature, after which nitrogen or hydrogen is used to pressurize it to the required pressure.It's worth noting that as temperatures rise, pressure is also likely to climb steadily.All the way up to the reaction temperature, the churning is maintained at a steady rate.After the reactor has reached the desired temperature, it will remain at that setting for a predetermined amount of time, which will vary based on the parameters of the experiment.When the holding time is up, the autoclave is chilled to room temperature using an electric air blower, an ice tank, the removal of the heating garment, or an interior cooling coil system.Most studies simply discharge the gaseous product once the reactor reaches room temperature, but there are a few exceptions in which the gaseous product is gathered in a gas-collecting receptacle inside the reactor.[6].

Animal by product
Carcass, feet, viscera, cranium, blood, bones, and feathers are all examples of biological by-products produced in significant quantities as a result of the cattle and chicken industry.High protein and fat leftovers (like those found in animal corpses and animal products) have been found to be desirable sources for biogas generation.Disposing of dead animals in a humane and secure manner is a global concern.Animal carcasses may harbor diseases, many of which are of infectious significance, necessitating precautions to ensure the safety of the surrounding ecosystem, domesticated animals, and the general public [7].The biocrude is primarily produced by lipids and fatty acids in roughly a 90:10 ratio, and hydrothermal liquefaction of Animal By-Products is a potential method for their reprocessing and discharge.Increases in temperature boost the output of free fatty acids, as well as those of amides and heterocyclic chemicals produced from processes involving lipids and proteins.[4].There are several major biological waste sources, including blood from the hemorrhage process, paunch from the elimination of the rumen and digestive fluid, intestinal leftovers from the evisceration processes, fat from the flesh trim phase, and the head and extremities (mostly composed of bone).Sludge is also produced at the slaughterhouse's effluent purification facility.There is a lot of biological material in these residues, mostly from livestock products.Animal leftovers are described by SJVFS 2000:166 (3) as any animal or animal product that is not meant for direct human sustenance.Animal by-products are categorized as (1) high-risk material if they pose a significant risk of disseminating infectious illnesses to animals or humans, or (2) low-risk material if they are obtained from healthy animals killed in an abattoir that has passed health certification.After the discovery of BSE, it became clear that the animal by-products that might spread spongiform encephalopathy needed to be culled from circulation.This portion constitutes SRM, which requires special handling during disposal (either burning, coincineration, or dumping).Animal leftovers do not include rumen, stomach, and digestive material, or excrement from barns and vehicles.About a quarter of the overall animal weight killed goes to waste.[8].

HTL catalysis using zeolite
HTL processes work best with heterogeneous catalysts because they are easy to isolate, reclaim, and dispose of.Biocrude oil made with heterogeneous catalysts, as mentioned above, is of better grade and the method is seen as more environmentally benign than that made with uniform catalysts.Catalysts used in the petrochemical business for hydrocarbon processes appear to be applicable in the HTL process as well.Important catalyst reactions in hydrocarbon processing, pollution control, and industrial operations rely heavily on zeolitic materials.For instance, ZSM-5 zeolite acts as a powerful catalyst and/or supports a wide variety of crucial reactions.ZSM-5 has a wide specified area thanks to its ion exchange properties and distinctive pore creation, such as the micro three-dimensional porosity structure [9].Lewis sites are often the surface basic sites of the zeolite.Density of negative charge on a specific oxygen atom is related to Lewis basicity since it is a measure of how strongly the oxygen atoms in a certain framework are negatively charged.It is common practice to use zeolites, which are alumino-silicate minerals, as catalysts and supports in chemical synthesis reactions.While several other types of zeolites have been investigated for use in hydrothermal biomass liquefaction, the greatest conversion rates from biomass to liquid have been found for ZSM-5.Because their acidity and shape selectivity, zeolites are commonly used in bio-crude upgrading approaches for the HTL process [10].They are utilized as heterogeneous catalysts in industry for a variety of processes such as catalysis, adsorption, separation, and ion exchange [11].A variety of zeolite catalyst applications are listed in table 1.

Loading of zeolite
Typically, traditional ion-exchange and impregnation were used to modify HZSM-5 by loading transition metals.While the impregnation method seems to be less time-consuming to produce, the metal-support integration is poor, and bigger metal particles are often obtained.In reality, most metals do not function as compensatory ions inside the framework but rather are dispersed over the surface.Conversely, the ionexchange technique reveals robust contact between metal and support.When it comes to Ni-and Pd/Hmordenite, Canizares et al. looked at how the loading procedures impacted the material.When Ni was used as a metal site, the findings revealed that loading by ion exchange or impregnation made little impact.In contrast, Pd/H-mordenite had notably different results.Although Pd atoms were dispersed throughout the ion-exchange catalysts, they clustered together in the impregnated ones.This study by Maia et al. compares the effects of two methods of nickel loading preparation (dry impregnation and ionic exchange) on HZSM-5 support.In the event of an ionic exchange being prepared, nickel tended to spread as compensating cations in the zeolite framework.The synthesis of light olefins was also enhanced by a Ni-ZSM-5 catalyst that was made using the ionic exchange approach.Table 2 shows that zeolite modified by loading transition metals for upgrading technologies is seldom documented.[12]

Parameter effecting on hydrothermal liquefaction
Table 3 shows the results of an evaluation of the impacts of process factors on bio oil output and quality.These variables include biomass composition "pressure", "temperature", "biomass heating rate", etc.This article, however, briefly covered such topics as the bio-elemental crude's composition after HTL, the various feedstocks used in HTL, the mechanism of hydrothermal processes, and the energy efficiency of the process.In addition, this work provided a prospective future focus of the study for researchers to think about [14].[22]

Mechanism of the hydrothermal liquefaction Process
The literature provides little insight into the mechanism of hydrothermal liquefaction.Depolymerization, followed by breakdown and recombination, are the three primary processes in the HTL route.The following sections elaborate on these points in further depth.Decomposing and depolymerizing biomass into smaller molecules is a simplified explanation.In order to deal with the potential reactivity of these compounds, it is necessary to polymerize and create bio crude, gas, and solid compounds.In addition, the repolymerization, condensation, and breakdown of the components from the distinct phases may occur under varied conditions, depending on crucial process factors like temperature and residence time.Since biomass is a heterogeneous blend of components such carbohydrates, lignin, proteins, and lipids, the reaction chemistry and processes involved in biomass liquefaction are equally intricate.The steps of the reaction HTL process are shown in a simplified form in Fig1.[14].The hydrothermal liquefaction method is currently the best method for converting wet dry biomass in particular, as it is an environmentally friendly method.
2. Temperature and residence time have a major role in affecting the productivity of bio-crude.
3. Solid catalysts are preferred for hydrothermal liquefaction due to their ability to withstand higher temperatures and process pressures and it is important to note that the use of a catalyst can significantly increase the efficiency of hydrothermal liquefaction.
4. Common types of solid catalysts include minerals such as zeolites.These catalysts are often loaded with metals to improve their stability and activity.
5. While reusing the aqueous phase is essential for the achievement of the process, it increases the amount of dissolved organics in the aqueous medium with each cycle until the saturation threshold is reached after around three or four recycling passes.
6. Altering the metal loading type and percentages applied to the zeolite surface alters the selectiveness, stability, and activity of the zeolite, The extreme temperatures and pressures experienced during hydrothermal liquefaction make solid catalysts the material of choice.

Table 2 :
Zeolite modified by loading transition metals.

Table 1 :
the use of zeolite catalysts in catalytic HTL

Table 3 :
Summary of literature pertained to hydrothermal liquefaction of biomass (both wet and dry).