1 - IMPACT OF RENEWABLE ENERGY INTIGRATION IN CHEMICAL PROCESS

OPTIMIZATION
There is a demand for new chemical reaction technologies and associated engineering aspects due to on-
going transition in energy and chemistry associated to moving out progressively from the use of fossil fuels.
Focus is given in this review on two main aspects

i) the development of alternative carbon sources and ii) the integration of renewable energy in the
chemical production. It is shown how addressing properly these aspects requires to develop new
tools for chemical engineering assessment and innovative methodologies for the development of the
materials, reactors and processes. This review evidences the need to accelerate studies on these
directions, being a crucial element to catalyse the transition to a more sustainable use of energy and
chemistry. It is remarked, however, the need to go beyond the traditional approaches, with some
examples given. In fact, the presence of radical changes in the way of production is underlined,
requiring thus novel fundamentals and applied engineering approaches

“The life-cycle environmental and

economic impacts of integrating
hydrogen fuel and biofuels into chemical
processes optimisation to minimize costs
and environmental harm while
promoting sustainability”

The statement highlights a specific focus on hydrogen fuel and bio fuel within the broader renewable energy
landscape, particularly in the context of chemical process optimization.

1.1– HYDROGEN FUEL:

The energy carrier hydrogen is an alternative to fossil fuels with the potential to achieve these
goals. Hydrogen is abundant in chemical compounds such as water and the organic compounds of
biomass, and its combustion produces only heat and water with no offensive pollutants or carbon
dioxide. Hydrogen can be combined with oxygen in the electrochemical reactions of a fuel cell to
produce electricity, a clean, versatile carrier of energy enabling many end uses including lighting,
refrigeration, communication, information processing, and transportation. The intimate connection
between hydrogen and electricity through fuel cells makes hydrogen much more than simply a clean
substitute for fossil fuel combustion.

Achieving the promise of hydrogen as an efficient, sustainable, and environmentally friendly fuel
requires widespread innovation and development of the means for its production, storage, and use. The
energy-chain and technical challenges for creating a viable hydrogen economy are shown in Figure 1.
The most effective use for hydrogen is conversion of its chemical energy to electrical energy in fuel
cells. The high conversion efficiency of fuel cells, up to 60%, makes them attractive compared to other
electrical generation alternatives based on fossil fuels, which are about 34% efficient on average. The
high efficiency of electric motors (typically well above 90%) makes the fuel cell–motor combination
 attractive for transportation compared to gasoline engines, typically about 25% efficient. This potential
for high-efficiency end use adds additional appeal to the environmental argument for hydrogen: not
only is it free of pollutants and greenhouse gases, but it also uses considerably less primary energy for
a energy use.

1.1.1 – HYDROGEN PRODUCTION :

Hydrogen could replace fossil fuel for transportation in cars and light trucks, produce electricity for
distribution through the grid, and provide portable electricity for personal electronics and other applications.
Transportation now consumes about 20% of the world’s energy and electricity about 12.5%. About 600
megaton/year of hydrogen will be needed worldwide to power all cars and light trucks in 2030, compared to
about 50 megaton/year now produced. About half of the global supply of hydrogen is produced by reforming
natural gas. The reforming of natural gas, however, is not an attractive production route for a mature
hydrogen economy, because the order-of magnitude increase in demand would deplete our finite reserves
and the concentration of gas reserves in a relatively few regions of the world could lead to unstable supplies.
Environmental impact is also a major concern, as reforming natural gas to hydrogen produces as much
pollution and CO2 as burning the natural gas directly.

Progress toward a mature hydrogen economy depends on breakthroughs in finding new materials and basic
understanding of the nanoscale phenomena that govern the interactions of hydrogen with materials. The
ultimate evolution of a hydrogen economy, however, depends on much more than technical feasibility. As
with all new technologies, comparisons of hydrogen with a developing mix of alternatives for performance,
cost, efficiency, convenience, reliability, and safety will determine its future course. The outcomes of these
comparisons are themselves developing, as the costs of fossil fuels and environmental mitigation of their use
increase and as engineering and scientific discoveries alter the mix of competing alternatives.

As a highly storable carrier of energy, hydrogen offers remarkable versatility, enhanced by its compatibility
with electricity, the less-storable energy carrier that forms the backbone of our energy distribution system.
Splitting water renewably, that is, using only renewable energy inputs, is an attractive production route for
hydrogen as a fuel of the future. Water is abundant on the surface of the earth and more widely distributed
geographically than fossil fuels. The water–hydrogen cycle (see Figure-2).

1.1.2 – HYDROGEN AS A FUEL CELL:

Fuel Cells Fuel cells converting hydrogen and oxygen to electricity and water are an appealing
alternative to fossil fuel combustion engines for their efficiency, versatility, and environmental
friendliness. The basic operation of a fuel cell is depicted in Figure 3. Fuel cells produce electricity
with a potential efficiency of 60%; the electricity can be used directly or converted to motion, light,
and heat.

FIGURE 3 - Basic operation of a fuel cell.

Hydrogen enters at the anode (red), where it
is catalytically dissociated and ionized to
protons and electrons. The protons enter the
polymer electrolyte membrane (green) where
they migrate by ionic conduction to the
cathode (blue). Electrons travel through an
external circuit where they do electrical work
before arriving at the cathode. The cathode
reacts electrons, protons, and oxygen
molecules to produce water. The net input of
the fuel cell is hydrogen and oxygen; its net
output is water, electricity and heat.
 Polymer electrolyte membrane (PEM) fuel cells for transportation rely on dispersed Pt nanoparticle
catalysts supported on carbon substrates for promoting the reaction of protons, electrons, and oxygen
molecules to water. Although Pt is the best-known catalyst for this reaction, it cannot meet the demands of a
mature hydrogen economy because of its high cost and relative scarcity. Orders-of-magnitude increases in
its catalytic activity are needed to reduce the required quantities, or it must be replaced by an alternate
catalyst that is active, abundant, and inexpensive.

A recent breakthrough increasing the catalytic activity of Pt by a factor 10 for the oxygen reduction
reaction at the fuel cell cathode reveals a promising new research direction for tuning catalytic activity, as
shown in figure 4,

Figure 5 - Factor-of-10 improvement in catalytic

activity of Pt with subsurface alloying. (a) Near-
surface structure of single crystal alloys of nominal
composition Pt3Ni produced by surface
segregation. The top layer is a pure Pt-skin
covering a Ni-rich subsurface layer and Pt-rich
layers beneath. The Pt skin composition and crystal
structure are identical to those of a pure Pt crystal.
(b) The specific activity of the Pt-skin is enhanced
over the pure Pt surface for the oxygen reduction
reaction. For the (111) Pt-skin surface, the
enhancement is a factor of 10, as a result of subtle
changes in the Pt-skin electronic structure. Theory
plays a major role in subsurface alloying, predicting
and describing experimental outcomes.

1.1.3 – EVOLUTION OF HYDROGEN ECONOMY :

Widespread hydrogen-powered chemical processes requires the simultaneous solution of
challenges in production, storage, and use, a much more difficult task than solving any of the
three alone. We are far from practical solutions in fossil-free production and in solid-state
storage, and the path to these outcomes will not be based on incremental innovations in
today’s technologies of reforming natural gas or coal, or storage in compressed gases and
liquids. Fuel cells are qualitatively different, however: a competitive technology can arise
from innovations on today’s approaches and designs. Like the internal combustion engine of
a century ago, today’s fuel cells can spawn a long line of progeny based on successive
innovation of their electrodes, membranes and catalysts.
The requirement of disruptive innovation for the success of fossil-free production and solid-
state storage makes the entrepreneurial approach difficult to launch for chemical processes.
The value of a hydrogen economy, however, extends well beyond chemical process
hydrogen is remarkably attractive in many applications as an energy carrier. Once produced,
it is environmentally friendly, and it is flexibly convertible to other forms of chemical,
thermal, or electrical energy at high efficiency. In these respects, hydrogen shares the
appealing attributes of electricity, the world’s most versatile and fastest-growing energy
carrier. Hydrogen and electricity are natural partners, as they can be interchanged at high
efficiency through electrochemistry in fuel cells and electrolysers. Their compatibility is
enhanced by their complementary storage characteristics: hydrogen stores energy
indefinitely and at high density in chemical form, whereas electricity is typically used at the
moment it is produced and lacks a convenient high-density form of storage. The intermittent
character of renewable electricity and the diurnal and seasonal fluctuations in demand make
local hydrogen storage and interconversion to electricity a powerful and natural option.

1.1.4 – HYDROGEN STORAGE :

The use of hydrogen for chemical processes requires an effective hydrogen storage medium.
Existing technology for hydrogen storage is limited to compressed gas and liquefaction, both
of which are used now. Compressed gas, even at the highest practical pressure of 10,000 psi,
is still a bulky way to store hydrogen that requires a significant fraction of the trunk space
Liquid hydrogen takes up slightly more than half the volume of 10,000 psi compressed gas,
but it loses 30–40% of its energy in liquefaction. Although gas and liquid storage are useful
as temporary options in a provisional hydrogen economy, more compact and efficient storage
media are needed for a mature hydrogen economy. The most promising hydrogen storage
routes are in solid materials that chemically bind or physically adsorb hydrogen at volume
densities greater than that of liquid hydrogen.
The challenge is to find a storage material that satisfies three competing requirements: high
hydrogen density, reversibility of the release/charge cycle at moderate temperature in the
range of 70–100°C to be compatible with the present generation of fuel cells, and fast
release/charge kinetics with minimum energy barriers to hydrogen release and charge. The
first requires strong chemical bonds and close atomic packing; the second requires weak
bonds that are breakable at moderate temperature; and the third requires loose atomic
packing to facilitate fast diffusion of hydrogen between the bulk and the surface, as well as
adequate thermal conductivity to prevent decomposition by the heat released upon hydrating.
Although several materials have been found that satisfy one or more of the requirements,
none has proven to satisfy all three. In addition to these basic technical criteria, viable
storage media must satisfy cost, weight, lifetime, and safety requirements as well.
Hydrogen storage materials employ two complementary strategies for releasing hydrogen
for use: thermalization and destabilization. In thermalization, hydrogen is released from the
storage media by heating to the decomposition temperature, where some or all of the
hydrogen is driven off. This traditional approach emphasizes hydrides with light elements
from the first and second rows of the periodic table, to maximize the mass percentage of
hydrogen.The ternary and quaternary hydrides of these elements have high storage
capacities, notably the borohydrides M+ BH4 − (where M is Li, Na, or K and B can be
replaced by Al),26 and the boranes NHnBHn , where n ranges from 1 to 4.
 The borohydrides have significant storage capacities, up to 19% of the mass of the
molecule for LiBH4, but they suffer from high decomposition temperatures and large
activation barriers to rehydrogenation. Catalysts such as Ti reduce the barriers for both the
decomposition and rehydrogenation of borohydrides and alanates, offering a practical route
to their use as hydrogen storage materials.30 NH4BH4 substitutes the ammonium ion for a
simple metal cation in the borohydride structure, packing four more hydrogens into the
molecule. The hydrogen mass ratio is an impressive 24%, but not all of the hydrogen can be
easily removed thermally. The hydrogen comes off in stages, with about 6% of the mass
released for each decrease of n by one, as shown in Table I ;

1.1.4.1 – METHODS OF STORING HYDROGEN :

A) Compressed Hydrogen Storage:
The advancement of hydrogen technology is driven by factors such as climate change,
population growth, and the depletion of fossil fuels. Rather than focusing on the
controversy surrounding the environmental friendliness of hydrogen production, the
primary goal of the hydrogen economy is to introduce hydrogen as an energy carrier
alongside electricity. Water electrolysis is currently gaining popularity because of the
rising demand for environmentally friendly hydrogen production.

B) Liquid Hydrogen Storage:

Liquid hydrogen storage plays an essential part enabling companies to use this element.
Throughout many industries, hydrogen is being used to enable different processes: Helps
storing energy produced by renewables, which is often intermittent Works as rocket fuel for
combustion in the space industry, including nuclear-powered rocket Provides decarbonized
alternatives for domestic heating Plays a part in the metallurgical industry, where it prevents
oxidation and reduces metal oxides. Raw material for chemical processes, including the
manufacture of plastics .All these processes can only take place once safe and optimized
liquid hydrogen storage is achieved.
1.2 – BIO FUELS :

Biofuels are a kind of energy fuels derived from the organic sources (comprehensively
depicted as biomass) created by the plants and living things, which can be grown and
harvested over and over again. Biofuels used to replace non-renewable energy fuels are
sourced chiefly from agricultural and vital harvesting, woodlands, and residue streams
Biofuels are typical forms of either biodiesel (produced from vegetable oils, re-used wax, or
creature fats) or bioethanol (alcohol produced by fermenting sugar and starch crops such as
corn) or biogas. Petroleum oil is one of the world’s most important energy sources. The
transport sector utilizes more than 70% of all petroleum fuel. As petroleum usage is rising
significantly, it is estimated that by 2070–2080, the world will fall short of petroleum oil . Its
overuse has given rise to concerns about well-being and global warming due to greenhouse
gas emissions (GHG), consisting of CO2 and other toxic gases such as methane, carbon
monoxide, and chlorofluorocarbons. Greenhouse gases are predicted to rise to approximately
43 billion metric tonnes by 2040. Thus, complementary power resources that are easily
accessible, renewable, and readily obtainable are necessary . Biofuels are developed as a
substitute for petroleum because of their nontoxic, sulphur-free, biodegradable nature,
originating from the renewable sources.
Depending upon the feedstock, biofuels are categorized into four types: 1st, 2nd, 3rd, and
4th generation biofuels :
1.1.5 – METHODS OF EXTRACTION AND BASIC KNOWLEDGE ON BIO FUELS :

1.1.5.1 - Main techniques to manufacture biofuels:

Modern technology for biofuels continues to evolve, improving the quality of output and decreasing power
use and CO2 pollution. The major popular techniques include fermentation of compounds from sugar or starch
towards ethanol with trans-esterification of components of waste kitchen oil or fat of an animal to produce
biodiesel. There is continuous innovation in the manufacture of fluid biofuels compared to the manufacture of
solid biofuels or gaseous biofuels. Fluid biofuel manufacturing methods reveal a capacity for greater
transformations, lower waste production, and usage of low area and water compared with gas-based biofuel
manufacturing methods. Essential criteria, including feedstock rates, manufacturing infrastructure, quality of
the commodity, and market demand, decide the commercial sustainability of the growth of biofuels. While the
use of organic trash feedstocks shows promise in biofuel generation, an efficient approach must be followed
to maintain a substantial supply of natural deposit for uninterrupted growth.

1.2.1.2 - Organic trash feedstock capacity for the manufacture of biofuels:

Organic trash covers food, farming, forestry, lignocellulosic trash, livestock, animals, waste
paper, wastewater, and corporate garbage, comprising mostly chemical- free trash. Feedstock
composed of organic corporate waste fragments is inexpensive and easy to access in city
regions. In contrast, agrarian, rustic crop materials, and other leafy trash, are proper to rural
biofuel generation. In areas where timber-based products are widespread due to ease of access,
and fair price, forestry, and other lignocellulose remnants are unified alternatives. Including
the price of feedstock, is thus a key component in the manufacture of biofuels across the globe.
Fig. shows a comparison between crude oil and biofuel formation, usage, and their effects on
the nature.
Biofuels have gained a great deal of interest because of their environmentally-friendly
and nontoxic nature. Biofuels are an intriguing subject and incorporate financial matters,
nature, agronomy, ecological sciences, microbiology, chemical engineering, science,
mechanical, and plant science. Original biofuels are presently economically accessible,
and crops that are not currently generally utilized for biofuel creation or are not
monetarily developed, can become appealing feedstocks for original fuels. With regard
to the third-age biofuels, they are still in the beginning phase of advancement. The
financial attainability of these cycles will be sought out after an objective.
Commercialization requires propelling lab-scale cycles to improve yields and
productivities. Specific biomass feedstocks and techniques are used to generate biofuels.
Biofuel production uses human foodstuffs such as maize, peanuts, sugarcane,
soya,increasingly criticized for creating competition between crops as food and as raw
material for biofuels. The present study covers all aspects of biofuel production, and the
different types of feedstock employed the benefits and drawbacks. Further techniques
are also systematically assessed as are the feedstocks of various generations, their future
performance, and the related greenhouse gas release. The increasing need for non-
renewable energy prompted scientists and analysts worldwide to take biofuel into
account, for it is a potential renewable energy alternative. It is environmentally friendly
and less polluting, rendering it a more appealing power source. These findings are based
on biofuel development studies, different outlets, new manufacturing techniques, and a
wide variety of feedstocks used during biofuel manufacturing.
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