Substantia. An International Journal of the History of Chemistry 3(1): 101-111, 2019 Firenze University Press www.fupress.com/substantia ISSN 1827-9635 (print) | ISSN 1827-9643 (online) | DOI: 10.13128/Substantia-69 Citation: F. Barzagli, F. Mani (2019) The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature: are there actions to mitigate the global warming?. Substantia 3(1): 101-111. doi: 10.13128/Substantia-69 Copyright: © 2019 F. Barzagli, F. Mani. This is an open access, peer- reviewed article published by Firenze University Press (http://www.fupress. com/substantia) and distribuited under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All rel- evant data are within the paper and its Supporting Information files. Competing Interests: The Author(s) declare(s) no conflict of interest. Feature Article The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature: are there actions to mitigate the global warming? Francesco Barzagli1,2, Fabrizio Mani2 1 University of Florence, Department of Chemistry, via della Lastruccia 3, 50019 Sesto Fiorentino, Italy 2 ICCOM CNR, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy E-mail: fabrizio.mani@iccom.cnr.it Abstract. Some frozen bodies have been recently discovered in the Alp glaciers because the global warming is forcing the ice to retreat. Many years have passed since the first perception of a strong link between the temperature of the Earth and the amount of some gases in the atmosphere, the so called greenhouse gases. Today there is a general consensus among the governments, the scientists and industrial organi- zations of most countries in recognizing the relationship between the increase of the atmospheric CO2 concentration resulting from over a century of combustion of fossil fuels and the observed global warming. The development of technologies to reduce the anthropogenic emissions should not be further delayed, in accordance with the Paris Agreement that recommended keeping the global mean temperature well below 2 °C above pre-industrial levels to reduce the risks and impacts of climate change. This paper gives an overview of the different greenhouse gases, their emissions by eco- nomic sectors and the international treaties that require the most developed countries to pursue the objective of reducing their greenhouse gas emissions. Amongst the dif- ferent actions directed towards a low-carbon economy, the chemical capture of CO2 from large stationary emission points is the most efficient and widespread option. Additionally, new technologies are currently exploited to capture CO2 directly from air and to convert CO2 into fuels and valuable chemicals. Keywords. Global warming, climate changes, greenhouse gas emissions, CO2 capture, CO2 utilization. THE GLOBAL WARMING AND THE POLICIES FOR ITS MITIGATION It is very likely the relationship between the Earth’s temperature, climate and the concentration of some gases, the so called greenhouse gases (GHGs), in the atmosphere. As a matter of fact, the greenhouse effect made our planet habitable with an average temperature of 18 °C, otherwise it would be – 19 °C. 102 Francesco Barzagli, Fabrizio Mani If we look back to hundreds of thousands years ago, cooler glacial and warmer interglacial cycles occurred with periods of about 100,000 years (Figure 1). They are related to the variation of the amount of solar radiation with time, caused by the precession of the equinoxes (the rotation of the Earth’s direction axis), the varia- tion of the obliquity of the Earth’s axis with respect to the perpendicular to the plane of the orbit around the sun, and the variation of the eccentricity of the orbit that varies the Earth-Sun distance. It must be noted that the variation of CO2 concentration over time was a conse- quence of the variation of the temperature: the increas- ing temperature released more dissolved CO2 from the oceans and permafrost, thus increasing the greenhouse effect that accelerated the global warming. The opposite effect occurred when the temperature decreased. The last glacial period ended about 21,000 years ago, and currently we are in an interglacial period of very low increasing Earth’s temperature that has been accel- erated in the last century, most likely by the increasing GHG emissions from human activities. The anthropo- genic GHG emissions, predominantly carbon dioxide, add to the “natural” greenhouse effect and could result in Earth’s temperature rising and subsequent climate change. The “greenhouse effect” and the global warming have a long history, that started two centuries ago. The famous French mathematician and natural philosopher Jean-Baptiste Fourier (Auxerre, 1768 – Paris, 1830), sug- gested in the late 1820 that the atmosphere limits the heat loss from the Earth’s surface, that is warmer than it would be in the absence of this effect. In 1860 John Tyn- dall (Leighlinbridge, 1820 – Haslemere (UK), 1893), an Irish scientist, measured the absorptive power of some gases and discovered that water vapour and “carbonic acid” (carbon dioxide) absorb the re-emitted heat from the Earth’s surface that cools overnight. He realised that climate changes could be related to the concentration of these gases. Svante Arrhenius (Vik, 1859 – Stockholm, 1927), a Swedish physicist and chemist, Nobel laure- ate for Chemistry in 1903, in 1896 calculated that 50% increase of CO2 concentration in the atmosphere would take thousands of years and would increase the Earth’s temperature of 2.5-3 °C. Arrhenius concluded that the world population would benefit in the future from a warmer climate that would prevent new glacial ages, thus affording more land for harvesting. Contrary to the Arrhenius’ belief, the 50% of CO2 concentration has increased in the last two centuries, because of the fossil fuel combustion to sustain the continuously increasing demand of energy of the industrial revolution and the economic growth of the population that, additionally, rose from about 1 billion in 1800 to today 7.6 billion. Now, there is a general consensus among the gov- ernments, the scientists, and industrial organisations of most countries about the correlation (95-100% prob- ability) between the GHG emissions in the atmosphere originating from the human activities, the rise of the Earth’s temperature and the climate change (Figure 2).3-5 It has become a worldwide priority to reduce the anthro- pogenic GHG emissions, particularly those of CO2, the main component of GHGs, together with the techniques for the adaptation to climate change. Afterwards the first stations at South Pole and Mauna Loa, Hawaii, in 1950 began measuring the CO2 concentration in the atmosphere, accurate data were available. In 1988 the Intergovernmental Panel on Cli- mate Change (IPCC) was established by the World Mete- orological Organization (WMO) and the United Nations Environmental Programme (UNEP) to provide “policy- Figure 1. Correlation between CO2 concentration1 in the atmos- phere and Earth’s temperature2 over the last 800,000 years. Tem- perature change is the difference from the average of the last 1000 years. Figure 2. Correlation between the change in the mean annual temperature records and the CO2 concentration. Temperature data from NASA/GISS;3 CO2 concentration data from Mauna Loa, Hawaii,4 and from ice cores from Law Dome, Antarctica.5 103The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature makers with regular assessments of the scientific basis of climate change, its impacts and future risks, and options for adaptation and mitigation”. Until now IPCC has released f ive Assessment Reports,6,7 and the sixth will be completed in 2021. The fifth Assessment Report (IPCC AR5)8 is referred to 2014 and is based on the work of 831 worldwide experts on physics, engineering, chemistry, meteorology, ocean- ography, ecology, economics. The scenarios provided on the GHG emissions by human activities and global warming are indisputable. The CO2 concentration in the atmosphere, largely the main component of GHGs, increased from 280 ppm (0,028 % v/v) of the pre-industrial level (the beginning of the industrial society is conventionally fixed to 1750) to today 410 ppm (0,041%; April 2017). In the same time the Earth’s temperature increased approximately of 1.0÷1.2 °C, most of which in the last century. Before 1750 the mean temperature, even if with ± 0.3 °C vari- ations, and GHG concentration remained roughly con- stant for hundreds of years. Carbon dioxide emissions from fossil fuel combus- tion and industrial processes account for about 76% of the current total GHG emissions. The percentage of the other GHGs is reported in Table 1 as CO2-equivalent (CO2eq), that takes into account for the relative amount of emissions and for the global warming potential (GWP) relative to CO2.9 GWP100 measures the warming effect of a mass of a GHG relative to that of the same mass of CO2, over a period of 100 years. The lifetime of each GHG in the atmosphere, and consequently its GWP, is different to each other, because of the different reactivity with the other components of the atmosphere and with solar radiation. About 75% of overall anthropogenic CO2 emissions between 1750 and 2010 occurred in the last 60 years, because of the unrestrainable growth of the population (from 2.5 billion in 1950 to 7.6 billion in 2018), the ener- gy intensive lifestyle of the population and the economic activities of the developed countries, and the socio- economic growth of rapidly developing countries (cur- rently, China, India, Brazil), that require more and more energy production. Total anthropogenic GHG emissions increased over 1970 to 2012 of 91% from 24 to 47 Gtonne CO2eq/y, the highest in human history. Also the rate of warming of the atmosphere and ocean since 1950 is the greatest ever recorded.10 The Kyoto Protocol (December 1997) is an interna- tional treaty that commits the 39 most industrialised countries to tackle the global warming by reducing their GHG emissions in the atmosphere to a level that “would prevent dangerous anthropogenic interference with the cli- mate system”. The six greenhouse gases taken into con- sideration by the Kyoto Protocol were carbon dioxide (CO2), methane (CH4), dinitrogen oxide (N2O), sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs) and per- fluorocarbons (PFCs) (Table 1). The treaty was signed and ratified by 187 countries and entered into effect on 2005, after being ratified by at least 55 of the most indus- trialised countries which accounted in total for at least 55% of the total CO2 emissions for 1990 (“55%” clause). USA and Australia did not ratify the treaty; China, India and Brazil had no targets of reduction. By 2012 the sig- natory countries should have fulfilled the cut of GHG emissions of 5.2% below the 1990 level (–8% for Euro- pean Union); the reduction target 2013-2020 should be –18%. European Union met the objective of Kyoto Pro- tocol by 2011. In the 21st Paris Climate Conference (COP21, 2015), an agreement was signed by 195 countries and entered in force in 2016. For the first time the countries signato- ries agree to carry out actions to limit the increase of the Earth’s temperature in the range 1.5 - 2 °C above pre- industrial levels; the increase of temperature from today should be comprised between 0.65 °C and 1.15 °C. Each country is committed to provides the GHG inventories every five years, starting from 2023. However, it must be pointed out that the Paris Protocol is not a legally binding treaty, and, additionally, a country that did not accomplish its reduction target may purchase carbon credits (GHG certificates) from other countries that have no reduction obligation or are below their reduction tar- get. In 2017 Donald Trump declared he is going to with- draw US from the Paris Agreement, which was previ- ously signed by the former US President Barack Obama. To keep the temperature increase below 2 °C rela- tive to pre-industrial level, the CO2 concentration in the atmosphere by 2100 should be about 450 ppm, com- pared to current 410 ppm. The fulfilment of that objec- tive relies on some strategies, namely reducing fossil fuel Table 1. Contribution of each gas to global GHG emissions, rela- tive to CO2, based on the amount of gas emitted and on the relative global warming potential (GWP100). GWP100 emissions (CO2eq) CO2 1 76% CH4 21 16% N2O 310 6% HFC/PFCa 650 ÷ 11,700 2%b SF6 23,900 a hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs); b summed fluorides. 104 Francesco Barzagli, Fabrizio Mani combustion increasingly substituted by renewable energy sources, improving the efficiency of energy production and use, enhancing the CO2 capture from large-point sources, the so called Carbon Capture and Sequestration (CCS) technology. Without mitigation scenarios, by 2100 the CO2 concentration in the atmosphere is expected to increase up to 750 ppm and the Earth’s surface tem- perature between 3.7 to 4.8 °C. Obviously, the mitigation objectives cannot be an obstacle to the increasing food production and to the socio-economic development of the world population that is expected to grow to at least 9 billion over the next 35 years. From the data reported in Table 1 it is clear that the greatest contribution to the overall GHG effect comes from CO2 emissions, mainly originating from fossil fuel combustion in power plants, transportation and build- ing heating. Livestock farming, agricultural and other land use, waste management, account for most of non- CO2 (CH4 and N2O) GHG emissions. Due to their sparse point sources, most of the non-CO2 emissions cannot be abated. Consequently, the strategies aimed at reduc- ing the overall GHG emissions should be focused on the abatement and capture of CO2 emissions from the energy sectors (fossil fuel power generation without CCS tech- nology should phase out by 2100),8 industry and trans- port. In summary, most of the sectors of the human activities must be redirected towards a sustainable low– carbon economy. Replacing coal and oil by less carbon containing fuels in all of the sectors of energy produc- tion, are feasible objectives. For instance, an immediate great contribution to the CO2 emission abatement from combustion (between 11% and 25%) should be gained by replacing carbon rich fossil fuels with natural gas (CH4). The global GHG emissions by economic sector are reported in Table 2. Low carbon electricity must play a crucial role in accelerating the global transformation to a low-carbon society, by substantially increasing the use of renewable technologies: photovoltaic cells, wind farm, solar energy, will continue to grow and to become cheaper and more competitive compared to fossil fuel combustion. How- ever, it must be pointed out that wind and solar are intermittent energy sources, and their transformation and storage in the form of chemical energy would be a feasible solution. Nuclear energy also cannot be omit- ted, even though in Europe its contribution is decreas- ing; however, contrary to popular belief and mass media information, 59 new nuclear reactors are under con- struction around the world. In Europe, the production of electricity by renew- able sources (wind, solar, biomass) should increase from the current 32% to 80% by 2050. Afforestation, reduced deforestation and bioenergy production are natural sinks of CO2. To date, the decarbonisation of energy genera- tion occurs at a greater rate than in industry, building and transport sectors. As worldwide transportation sec- tor accounts for about 20% of CO2 emissions from fos- sil fuel combustion, it is expected a substantially reduc- tion of the CO2 emissions attained from technological innovations that include more efficient thermal engines, cleaner fuels (natural gas, biofuels produced by biomass and regenerated fuels), light materials and electric pro- pulsion systems. Hybrid, plug-in-hybrid and full electric vehicles (powered by improved batteries or fuel cells) should eventually replace those equipped with thermal engines. By 2025, it is expected that the electric cars equipped with more efficient batteries will have cruising range over 600 km and substantial reduction of charge time. Sustainable biofuels should replace kerosene in avi- ation and diesel fuel in heavy duty trucks. The building conditioning should reduce their CO2 emissions by about 90% by 2050: this objective can be achieved by the new zero-energy buildings, and by refurbishing as much as possible the yet existing build- ings, in particular the commercial and tertiary ones. The industrial sector, especially the cement and steel production, could reduce their GHG emissions (mostly CO2) by about 80% with more energy efficient processes and increased recycling of the wastes and by-products. Also, CCS technology should be applied to reduce CO2 emissions of the industrial sector. The agricultural sector is expected to have a less impact in the GHG reduction with a non-CO2 GHG emission (CH4 and N2O) reduced by 45-50%, thanks to an improved land and fertiliser use, improved livestock farming, and bio-gas recovery from organic manure. Moreover, improved agricultural and forestry activities can increase CO2 sink and can provide feedstock for energy and industry. It must be considered that the bio- sphere (land and oceans) takes part to the global cycle of CO2 through photosynthesis of green plants and phyto- plankton, that represent a natural 50% sink of the global anthropogenic emissions of CO2. Table 2. The global GHG emissions percentage by economic sector.a Power plants 38% Agriculture and forestry 22% Transport 20% Buildings 10%b Industry 10%b a there is poor agreement amongst different sources on the share of individual sector: the data are adapted from references 8 and 11; b doesn’t comprise the consumption of electricity. 105The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature It is hard to believe that hydrogen could be a substi- tute of fossil fuels in a short-term (hydrogen economy), even if it could have a crucial role in the conversion of CO2 into liquid fuels. Hydrogen is currently produced by fossil fuels (mostly from methane), because its produc- tion from water electrolysis is not cost-effective. Finally, an appreciable contribution to the mitiga- tion scenarios could be given by a less energy consuming lifestyle of the population of the most developed coun- tries, for instance less mobility demand, less energy use in households, choice of longer-lasting products, less disposable items, reduction in food wastes; moreover, it would be highly beneficial recycling wastes into indus- trial new products (Italy is a European leader in this field). Noticeable, thanks to the policies of low-carbon technologies, yet worldwide adopted mostly for energy production, the global emissions of CO2 remained stable to 35.8 Gton CO2/year in the last three years (2014-2016). On the contrary, the GHG emissions increased in 2017 because of the growing industrial emissions that weren’t compensated by the increased energy production by renewables and by the reduction of coal use. Benefiting from low-carbon energy sources and energetic efficiency, European Union has set up the ambitious objective of the following reductions com- pared to 1990, to be completed before 2020 (before 2030 in parenthesis):11 1) 20% (40%) reduction of GHG emissions; 2) 20% (27%) of the overall energy from renewable sources; 3) 20% (27%) of the increase of energetic efficiency. Currently the 26% reduction of CO2 emissions has been attained in Italy. By 2050 the reductions of GHGs in the 28 countries of the European Union should be: CO2 – 63%; CH4 – 60%; N2O – 26%. Nevertheless, it must be pointed out that Europe accounts for only 9.6% of the worldwide CO2 emissions (compared to 14.0% of US and 29.2% of China; 2016 data),10 and once these objectives were reached, they would not sufficient for the 2 °C target. Last but not least scenarios are the technologies of CO2 capture from large point sources (the CO2 concen- tration in the exhaust gases may be comprised between 5% and 40% v/v), such as fossil fuelled power plants and some industrial processes, and the safe CO2 stor- age underground (CCS technology). Notwithstanding its low concentration (0,04% v/v), CO2 can be also cap- tured directly from air (DAC technology). Contrary to the CO2 storage, in the carbon capture and utilization option (CCU technology), pure CO2 could be used as a feedstock for producing chemicals and fuels. TECHNOLOGIES OF CO2 SEPARATION FROM GAS MIXTURES The CO2 separation from gas mixtures is a technol- ogy applied at industrial scale in hydrogen and ammo- nia production, natural gas processing and sweetening. These methodologies can be also applied to large fixed- point sources, such as cement and steel production, and to post combustion gases from fossil fuelled power plants, the main sources of GHG emissions (Table 2). Chemical capture of CO2 by a liquid alkaline solution (the absorbent) is recognized as the most efficient tech- nology for dilute CO2 (low partial pressure) removal from a gas mixture. Different technologies for CO2 capture have been also proposed, based on physical methods, cryogenic and membrane separation processes, biological fixation, but none of them went into application to large scale separation of CO2 from exhaust gases because of the low efficiency or high costs. In this section, an overview of the chemical capture of CO2 with possible application to power plants is pre- sented.12,13 Combustion of fossil fuels with air produces exhaust gases containing 4-15% (v/v) CO2, N2 (from air), with residual O2, water vapour, and variable amount of sul- fur and nitrogen oxides as well as particulate matter. The CO2 percentage depends on the carbon content of the fossil fuel and the technology employed: the lowest value refers to a gas turbine combined cycle, where the com- bustion is accomplished with a large excess of air. A typical coal-fired power plant of 1000 MW can emit about 3·106 m3/h of exhaust gases containing 15% (v/v) of CO2.14 The storage underground of that huge amount of combustion gases is not a feasible option, because of the high compression costs and of the very large geologic reservoirs where the gas mixture should be stored. On the other hand, the storage in the deep sea is not safe, and would increase the water acidity which is harmful for sea life. Therefore, it is firstly necessary to remove CO2 from the gas mixture, afterwards the nearly pure CO2 is compressed and injected underground (car- bon capture and storage, CCS technology). An accurate geological investigation must be performed to select the site of CO2 storage, that should reduce as most as pos- sible leakage in time of sequestered CO2 from the reser- voirs.15 The employed technologies for the chemical capture of CO2 are substantially similar to each other and differ, at most, in the liquid absorbents. To be a cost-effective process and to avoid millions of tons of wastes per year (the carbonated absorbent), the CO2-loaded absorbent 106 Francesco Barzagli, Fabrizio Mani must be regenerated and recycled: the reactions of CO2 with the absorbent must be reversible. The equipment for CO2 capture comprises the stainless-steel absorber (the scrubber) and desorber (the stripper) units connected to each other through a heat exchanger (Figure 3). The absorber and the desorber are packed columns that maximize the gas-liquid exchange surface, thereby enhancing the reaction rate. The absor- bent circulates continuously between the two devices in a continuous cyclic process. The gas stream (12-15 % CO2 v/v) is injected to the absorber (kept at about 40-50 °C) and the carbonated solution exiting from the absorb- er is preheated by the cross-heat exchanger and sent to the desorber where it is heated to 110-130 °C (at pressure of 1-2 bar) by steam. The regenerated solution is cooled and then it is circulated back to the absorber and reused for further CO2 capture. Finally, the nearly pure CO2 released from the top of the stripper can be compressed at 100-200 bar and transported to the storage site by a pipeline. The size of the equipment to be fitted in a power plant is proportional to the flow rate of the exhaust gas i.e. to the amount of CO2 to be captured. The height/ diameter of the packed columns may be 15 m/7 m for the absorber and 10 m/4.5 m for the desorber; the plants have a capacity of CO2 capture in the range of 3-4·106 tonne/year. Most of the absorbents for CO2 removal from gas mixtures are based on aqueous solutions of primary and secondary alkanolamines;12-17 a few examples are: MEA (monoethanolamine) 2-aminoethanol NH2 HO DEA (diethanolamine) 2,2’-iminodiethanol H N HO OH AMP (aminomethylpropanol) 2-amino-2-methyl-1-pro- panol NH2 HO The hydroxyl functionality of the amines provides their sufficient solubility in water and substantially low- ers their vapour pressure, to reduce as much as possible the amine loss by evaporation. In the continuous search of more efficient absorbents, blends of amines and non- aqueous absorbents have been also investigated.18-21 The concentration of the aqueous absorbents is usually lim- ited to 30% (wt/wt), to reduce corrosion of the equip- ment and amine loss by heating, yet pursuing the target of 90% (v/v) of CO2 removal from the gas stream. The main reactions of CO2 with aqueous primary and secondary alkanolamines are: AmH + CO2 + H2O ⇄ HCO3– + AmH2+ (1) 2AmH + CO2 ⇄ AmCO2– + AmH2+ (2) where AmH denotes the free amine; AmCO2– and AmH2+ indicate, respectively, the amine carbamate and the protonated amine. Equation (2) doesn’t apply to tertiary amines that are unable to form carbamate, as well as to amines featuring steric hindrance around the amine functionality (AMP) because the carbamate is less stable than bicarbonate in aqueous solution. The forward reactions (1) and (2) are exothermic and the reverse endothermic reactions account for CO2 release and amine regeneration in the desorber. Whatever the technolog y and absorbent may be used, the overall process of CO2 separation from gas mixtures is energy intensive, therefore the CO2 cap- ture from a fossil fuelled power plants reduces the output electric power by 20% up to 40%, depending on the process configuration and fuel used; the cost of CO2 capture from a power plant can be as high as 50-60 $/tonne CO2. As a result, more fuel is consumed (additional 15-45%), more CO2 is emitted that must be captured, for a given output of electric power.22-26 The main operating cost of any process of CO2 removal is the heat for absorbent regeneration, namely to reverse the exothermic absorption reactions (1) and (2). Addi- tional energy is required to pump the absorbent within the entire apparatus and for final CO2 compression. Moreover, the thermal and oxidative degradation of the alkanolamines may be another serious concern in the CCS technology.27 Figure 3. A simplified flow sheet for the CO2 removal process 107The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature Compared to organic absorbents, very few inor- ganic solvents have been investigated, mainly aqueous Na2CO3, K2CO3 and NH3. Aqueous alkali carbonates do not suffer of thermal degradation and loss of the absorbent, have low regen- eration energy and high absorption capacity (mass CO2/ mass absorbent), but have low rate of reaction with CO2.28 CO32– + CO2 + H2O ⇄ 2HCO3– (3) Absorbents based on aqueous NH3 display fast absorption rate, significantly lower regeneration energy and thermal and oxidative stability compared to alkan- olamines, but entail a major concern related to its high volatility.29-31 The reactions of aqueous ammonia with CO2 are: NH3 + CO2 + H2O ⇄ HCO3– + NH4+ (4) NH3 + HCO3– ⇄ CO32– + NH4+ (5) In the absence of water, ammonium carbamate is the sole reaction product 2NH3 + CO2 ⇄ NH2CO2– + NH4+ (6) With the purpose of substantially reducing the ener- gy penalty of absorbent regeneration, new absorbents based on “ionic liquids” and “demixing solvents” have been recently developed. Both methodologies avoid the heat wasted to bring the diluent to the desorption tem- perature (sensible heat), a significant share of the over- all desorption energy; it must be pointed out that water account for 70 wt% of the aqueous absorbents. Addition- al cost saving and advantages come from the reduced size of the equipment and from the negligibly vapour pressure and high thermal stability of ionic liquids. Ionic liquids are organic salts in the liquid phase at room temperature (RTILs): as an example of a common ionic liquid, the chemical structure of 1-butyl-3-methyl- imidazolium hexafluorophosphate ([BMIM]PF6), a com- mon ionic liquid is reported. N N P F F F F F F One-component RTILs containing an amine func- tionality or mixtures of RTILs and alkanolamines have been exploited for the CO2 capture.32-34 Because those absorbents are liquid before and after the CO2 capture, no added diluent is necessary. To overcome the intracta- ble viscosity of most of the carbonated absorbents based on RTILs, commercially available and inexpensive sec- ondary amines (2-(butylamino)ethanol, for example) have been recently formulated35,36 that reversibly react with CO2 at room temperature and pressure to form liq- uid carbonated species without any aqueous or organic diluent. Demixing solvents are based on two liquid-liquid phase separation. Upon CO2 capture, some aqueous or non-aqueous amines split into two separate, immiscible, liquid phases (Figure 4) which separate by virtue of their different density.37,38 Only the lower phase that contains the carbamate and the protonated amine must be ther- mally regenerated, thus avoiding to heat the diluent in the upper phase. DIRECT CO2 CAPTURE FROM THE ATMOSPHERE The objective of zero-emission energy should be ful- filled by 2100 in most of the developed countries. Mean- while, the lifetime of CO2 in the atmosphere and the inertia of the climate change, strongly suggest to reduce Figure 4. Two liquid phase recovered from CO2 capture: the lower phase is the carbonated absorbent and the upper phase is predomi- nantly the diluent with a small amount of the amine carbamate. 108 Francesco Barzagli, Fabrizio Mani the CO2 concentration in the atmosphere. Moreover, the direct CO2 capture from air (DAC technology) is the only method to contrast the dispersed emissions from transport, heating systems of buildings and biomass burning, that cannot be captured at their sparse sources. A comprehensive overview of DAC is provided by the American Physical Society report (June 2011).39 The DAC method is at the early stage of investiga- tion and no proposed process is today suitable for large scale application because of the low efficiency and high costs. Because of the very low concentration of CO2 in the air (0,04% v/v), large air-absorbent contactors are necessary equipped with many fans to blow air to the absorber (Figure 5). The absorbents so far used are concentrated aqueous solutions of NaOH or KOH (2–3 mol dm–3) which cap- ture CO2 as soluble Na2CO3 or K2CO3; the efficiency of CO2 capture is usually no more than 50%.40 To be a fea- sible process, the hydroxide regeneration is accomplished with lime 2Na+ + CO32– + Ca(OH)2 → CaCO3 + 2Na+ + 2OH– (7) Once separated from the solution, calcium carbon- ate is calcinated at 900-1000 °C to restore quicklime (CaO) and to release CO2 CaCO3 → CaO + CO2 (8) The entire energy requirement of the process has been estimated 17 GJ/tonne CO2 captured (4.7·106 kWh/ tonne CO2 captured) and about half is due to the cal- cium carbonate calcination.41 The production of the same amount of energy (thermal and electric) from coal combustion, releases in the atmosphere 1.89 ton of CO2: more CO2 is emitted than captured! The CH4 combus- tion produces less CO2 but it doesn’t compensate the investment, maintenance and overall operational costs. To make the DAC technology attractive, it is mandatory to produce the energy to run the process (thermal and electrical) with photovoltaic cells and solar heat concen- tration. Benefiting of the advantage of the DAC technol- ogy that can be placed everywhere, areas with higher solar radiation should be preferred. Moreover, the aque- ous NaOH or KOH solutions must be replaced by new absorbents that require less regeneration energy, yet maintaining sustainable efficiency. If that method will be successfully implemented at a pilot-scale, CO2 will be captured from air by using the solar radiation, as green plants are used to do. FROM CO2 TO VALUABLE PRODUCTS At present, the carbon capture and utilisation (CCU) technologies are non-profit options, because of their high costs. Notwithstanding, the CCU technol- ogy is more and more studied, because it has the poten- tial of converting CO2 into value-added chemicals and synthetic fuels, combined with the mitigation of CO2 emissions, yet at a low extent.42-48 In other words, the energy depleted CO2 is captured and converted into reusable chemical energy, contrary to the CO2 storage underground of CCS technology. It must be pointed out that CCS technology can store underground billions of tonnes CO2 per year (about six million per year from a single 1000 MW power plant), whereas CCU relies on different products that overall could capture millions of tonnes of CO2 per year. The very high stability of CO2 (ΔG° = –395 kJ mol–1) is a great advantage in the energy production from the combustion of carbon containing fuels [equation (9), for example], but has an adverse effect on its reactivity. For instance, the reverse of reaction (9) is thermodynami- cally disfavoured, whereas the reduction of CO2 with hydrogen, [reaction (10)], features a severe kinetic obsta- cle; much energy together with catalysts therefore are necessary to convert CO2 into useful chemicals. CH4 + 2O2 → CO2 + 2H2O(g) (9) ΔH° = –803 kJ mol–1 ΔG° = –801 kJ mol–1 CO2 + 3H2 → CH3OH + H2O (10) ΔH° = –131 kJ mol–1 ΔG° = –9 kJ mol–1 Europe is leader in the study of the CCU technology, in particular Germany, thanks to its long-lasting tradi- tional leadership in the chemical industry. The first com- pany that has demonstrated (2015) the feasibility of the production of a liquid fuel from CO2, H2O and renew- able energy is based in Dresden. Figure 5. Proposed design to capture 1 million tonnes of CO2 per year. Photo-illustration: courtesy of Carbon Engineering Ltd. 109The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature Without any doubt, the most challenging option of CCU is the conversion of CO2 into liquid fuels (power to liquid technology, PtL), to reduce the dependence from the fossil fuels and to address the progressive decar- bonisation of the fuels for the transportation sector (an example of the so called circular economy). The most promising PtL technology is the methanol production,49 obtained by reacting CO2 with hydrogen [equation (10)]. To increase its rate, the reaction is accomplished at 200 °C with copper-based catalysts; notwithstanding, the yield of reaction is no more than 40%, based on today technologies. The cost, mainly due to the cost of electric- ity, is estimated to be about 600-700 euro/tonne CH3OH, which is not competitive with the standard produc- tion of methanol from methane, and with the methane itself as a fuel. To be sustainable, the reaction (10) must be accomplished with solar and wind energy, so that intermittent and fluctuating energy is stored as dispos- able chemical energy of methanol. Methanol, directly or in blends, can be used as fuel for thermal engines in transportation, or converted into gasoline (methanol to gasoline, MtG, process) or into dimethyl ether, a possible substitute of propane, a liquefied petroleum gas (LPG). Liquified DME has been also proposed as an alternative fuel to diesel for compression ignition engines. Combus- tion of DME eliminates particulate and greatly reduces nitrogen oxides from exhaust emissions, compared to conventional diesel fuel, but at the expense of about half energy density.50 Biofuels as alternative to the fossil fuels are cur- rently produced at industrial scale (millions of tonnes every year), mainly in Brazil and USA. Gasoline blend- ed with 25% up to 85% of ethanol is delivered in USA, and ten million of vehicles in Brazil are fuelled by 100% ethanol.51 All the efforts to imitate the photosynthesis of the green plants that converts sunlight into chemical ener- gy are failed because the energy costs to produce useful chemicals from artificial photosynthesis by far overcome the energy output of the combustion of those artificial fuels. Consequently, it is much more advantageous to allow the nature make most of the work. Based on that strategy, ethanol is produced in Brazil from sugarcane, whereas corn is the main feedstock in USA. Biodiesel as alternative fuel for diesel engines is produced with the alkaly-catalyzed transesterification process which con- verts vegetal oils into methyl or ethyl esters, featuring a reduced viscosity compared to the natural sources.52 The production of biofuels points out some prob- lems.51 The cost of the raw material (planting, irrigation, fertilization, harvesting and transportation) accounts for 60% to 75% of the cost of biodiesel producing. If the life cycle assessment of the process is taken into account, the biofuels are still not a viable alternative to fossil fuels, in the absence of the government support. As a final con- sideration, it should be a better option to use farmland for food production instead of crop-based biofuels. In the search of nonedible sources of biofuels, any form of biomass can be converted into a liquid fuel by means of a thermochemical process, but at unsustain- able costs. In that contest, algae-based biodiesel has emerged as a promising option, because it doesn’t entail a reduction of food production and features a substan- tially higher photosynthetic efficiency compared to land crops.53,54 Using CO2 for the manufacture of plastics and spe- ciality chemicals is a further option to store and re-use CO2. However, the estimated worldwide production of such products is about 180 million tonnes every year, that corresponds to less than 1% of the anthropogenic CO2 emissions. Compared to the production of fuels, the production of chemicals doesn’t have an appreciable impact on the reduction of CO2 emissions. Taking the advantage of the thermodynamically favoured and fast acid-base reactions between CO2 and NH3, it has been recently developed an innovative pro- cess that integrates the CO2 capture with the produc- tion of urea, the most worldwide used nitrogen fertilizer, more than 108 tonne/year. The CO2 capture (15% v/v in air) in water-ethanol produces solid mixtures of ammo- nium bicarbonate and carbamate [reactions (4), (6)]. By heating the solid mixtures at 165 °C in a closed vessel without any external pressure, both ammonium carba- mate, and bicarbonate are converted into urea.55,56 NH2CO2NH4 ⇄ NH2CONH2 + H2O (11) 2NH4HCO3 ⇄ NH2CONH2 + CO2 + 3H2O (12) The industrial production of urea is carried out with NH3 and purified CO2 in the gas phase at high temper- ature (180 –230 °C) and pressure (150 – 250 bar). Pure CO2 is obtained by the conventional aqueous amine scrubbing and thermal stripping. The advantage of pro- cess based on the solid ammonium salts compared to the industrial process, is the potential energy saving because both the CO2 purification step with aqueous amine scrubbing and the high pressure working are avoided, yet with efficiency (about 47% with respect to NH3) and reaction time (60 min at most) comparable with the industrial process. As a final consideration, 60 million tonnes of CO2 are employed in different commercial sectors every year, and are currently extracted from natural sources under- 110 Francesco Barzagli, Fabrizio Mani ground. A cheap capture technology from exhaust gases yet recovering high purity CO2, could replace the cur- rent CO2 production that is re-emitted in the atmos- phere and the end of its utilization cycle. CONCLUSIONS The increased greenhouse effect originating from human activities is most likely responsible of the increase of Earth’s temperature in the last century, and possibly of the climate change. The climate change has, and will have to a greater extent in the future, adverse impacts on the society development and world economy, because of the increasing extreme weather events such as storms, floods, drought and heat waves. The frequency of snowfall and rain is reduced in the recent years, but they are heavier. 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Juan Manuel García-Ruiz Similarities and contrasts in the structure and function of the calcium transporter ATP2A1 and the copper transporter ATP7B Giuseppe Inesi Finding Na,K-ATPase II - From fluxes to ion movements Hans-Jürgen Apell Range separation: the divide between local structures and field theories David M. Rogers Hydration of silica and its role in the formation of quartz veins - Part 2 John Elliston Chuckles and Wacky Ideas Carl Safina The increased anthropogenic gas emissions in the atmosphere and the rising of the Earth’s temperature: are there actions to mitigate the global warming? Francesco Barzagli1,2, Fabrizio Mani2 The ‘Consciousness-Brain’ relationship Jean-Pierre Gerbaulet1, Pr. Marc Henry2 Dmitry I. Mendeleev and his time Dmitry Pushcharovsky Early contributions of crystallography to the atomic theory of matter Giovanni Ferraris Bringing Together Academic and Industrial Chemistry: Edmund Ronalds’ Contribution Beverley F. Ronalds