1. Introduction

In recent years, bioenergy has become a sustainable power source for modern industrial economies, domestic energy security, concerns over global warming from greenhouse gases (GHG) emissions and instability of fuel prices, provide income to poor farmers and rural communities, create jobs and additional markets for agricultural commodities and waste biomass around the globe, besides growing energy demand, and increased openness to renewable energy resources, and the push for expansion into new markets for plantation crops, wastes and biomass are all factors driving interest in expanding biofuels, bioenergy and biorefineries (^{Koutinas et al. 2014}).

The novel processes of biofuels production have been oriented towards the use of biomass (carbohydrates, fats, and lignin); all of them are found in roots, stems, leaves, seeds and waste fruits and vegetables. They can be exploited directly by being the plant cultivated or indirectly using the residues of agro-industrial or forestry processes. Besides, livestock residues or even organic matter from sewage treatment plants can also be used as a source in agro-industrial facilities (^{Abdulkareem-Alsultan et al. 2020}).

In this regard, it is necessary adequate political and regulatory conditions that allow in a general way the use of wastes towards biofuels evolution. Most of countries that are involved in obtaining biofuels have established regulations that guide their production processes considering technological and socioeconomic aspects that permit generating the necessary infrastructure and optimal comparative and competitive advantages for the production of biofuel and bioenergy. At the global level, there are countries that have established laws to encourage the generation of internal markets that allow the production of biofuels in an integral manner, considering incentives for the establishment of crops or the use of waste to generate the raw material (^{Arnold et al. 2019}; ^{Gregg et al. 2017})

^{Lin et al. (2014}) and ^{Arancon et al. (2013)} discuss various approaches related to current valorization strategies and alternatives for wastes from food production to be developed to maximize the value as source for biofuels and biochemical.

There is a growing multidisciplinary campaign related to biofuels, which has been primarily addressed with issues as public policy instruments, environmental impact and greenhouse gas emission reductions, food and poverty interactions and countless scientific papers on technological advances in ethanol manufacturing (^{Gaurav et al. 2017}; ^{Ji et al. 2016}).

^{Sukumara et al. (2014)} and ^{Pérez et al (2017)} presented overall frameworks and multidisciplinary methodologies to estimate various factors for sustainable biorefining encompassing feedstock assessment, supply chain optimization, and process systems engineering can be implemented to estimate the total production cost of energy, fuel, and inputs from various renewable resources in a specific geographic region.

Several studies indicate that biofuels have the capacity to reduce GHG; nevertheless, the environmental impact analysis in the production of biofuels production, the development of different production technologies and potential impacts has become controversial. Indicators should be developed to evaluate the effects of each of the processes and steps carried out to produce biofuels from the generation of crops or their biomass sources, the production or refining processes, the cogeneration systems, the conversion of their waste and the compounds that are released into the atmosphere according to each geographic region (^{Callegari et al. 2020}; ^{Venturini et al. 2020}; ^{Ziolkowska, 2014})

On the one hand, there is uncertainty about the current and future availability of suitable biomass for bioenergy use with dynamic physical, technological, economic, politics and social constraints because they are strongly interrelated with other economic sectors and sustainability, and ultimately depend of political-normative decisions (^{Leibensperger et al., 2021}).

The main barriers to bioenergy and biofuels deployment are:

^{Ziolkowska, (2014)} concluded the design of biofuels policy, multiple economic, environmental and social goals and stakeholders perceptions need to be considered to be sustainable in three ways simultaneously:

The objective of this review is to analyze the Mexican context, opportunities, barriers and political, socioeconomic and technological challenges for the establishment of a national sugar cane ethanol program based in sugarcane

2. Literature Review

2.1 Worldwide biofuel production and management

The 1G (first-generation biofuels) are largely associated to ethanol produced from sugar- and starch-based feedstocks derived from food crops such as sugarcane (Saccharum spp.), sugar beet (Beta vulgaris subsp. vulgaris), cassava (Manihot esculanta), corn (Zea mays) and other food grains.

^{Kumar et al (2020)}; ^{Meneghin (2016)} and ^{Organization for Economic Co-operation and Development (OECD) - FAO (2020)} reported that forty-five countries are ethanol producers. As the main biofuel, ethanol production is undergoing exponential growth and is a mature market with three large geographic areas currently dominating the value chain: the United States, Brazil and European Union. Demand for fuel ethanol in the United States is expected to remain strong. The world leaders in ethanol production in 2020 were United States produced from corn (53 %), followed by Brazil from sugarcane (molasses, juice and syrup) (30 %), European Union (5 %), China (3 %), India (2 %), Canada (2 %), Thailand (2 %), Argentina (1 %) and accounting for the rest of world production (2 %) using wheat or sugar beet.

Beet or cane molasses are the most established carbon source for ethanol production, equivalent to around 70% of world production. Other countries, growers of maize, cane or beet, are planning to implement competitive domestic biofuel programs (https://ethanolrfa.org/statistics/annual-ethanol-production/) Biofuel ethanol as a mixture with gasoline vary between regions depending on the geopolitics of oil and the availability of raw materials from agroindustries, public policies, industrialists and automobile companies and at 2020 because of COVID-19 pandemic (Figure 1 and 2).

Figure 1 Ethanol producing countries (^{OECD-FAO, 2020}  

Source: Data from https://ethanolrfa.org/statistics/annual-ethanol-production/

Figure 2 World ethanol production  

The bioethanol-based motor biofuels and programs most popular are E5 (UK), E10 (EU), E15 (United States of America), and E25-100 (Brazil). ^{Meneghin (2016)} reported that the main blend mandates of ethanol are Brazil (27 %), Paraguay (24 %), Argentina (12 %), the United States, China, and India (10 %), whereas for the rest of the world (approximately 60 countries) it ranges from 2 to 10%.

The biofuel ethanol value chain is generically divided into three different stages: Processing of carbon sources (sugarcane, cereals, beet, agro-industrial by-products or energy plantations), anhydrous ethanol production technology, and transportation logistics, distribution, mixed and retail to users. Derived from these stages, there are three forces that shape the evolution of the biofuel ethanol chain structure: (i) permeable industrial borders, (ii) security in the supply of inputs, and (iii) access to the retail market. These forces structure vertical integration in the development of the biofuels biorefinery (^{Banerjee et al. 2019}).

Therefore, worldwide some countries and regions have introduced ethanol biofuel programs and mandates over the last 30 years, the main goals are:

1. Rising or decreasing oil, petrochemical, fuel (gasoline and diesel) and fuel additive prices (MTBE etc)

2. Concern about fuel emissions (COx, SOx, NOx, ozone) and other potentially carcinogenic chemicals, etc.

3. The Kyoto Protocol of industrialized nations and Paris Agreement about carbon emissions (GHGs)

4. The generation of alternative jobs and income for growers and industrialization in developing countries (^{Chen and Chao 2020}; ^{Azad et al. 2016}).

Thus, the increasing use of bioethanol, as a replacement for fossil fuels, has already been pushed for years, based on competitive core technology models from Brazil and the USA, which, despite being competitive and sustainable, consist of several controversial issues such as: anhydrous and hydrous ethanol prices and end uses, taxes, bioethanol policies and regulatory framework, world markets and drivers, use of different feedstocks, trade policies, flex-fuel vehicle production, market prospects, economic and energetic ethanol balances (inputs/outputs) shares of fuel and energetic balance & gasoline, industrial and beverage ethanol production, byproduct output of wet and dry milling from corn and sugarcane vinasses and development of ethanol byproduct value chain, future ethanol plants and projects as ethanolchemistry, impacts of the gasoline price and additives such as MTBE (Methyl-Tert Butyl Ether), ETBE (Ethyl-Tert Butyl Ether), or TAME (tert-Amyl methyl ether) etc, the total cost of producing ethanol biofuel (capital-related or fixed, variable operating, feedstock costs and byproduct and wastes prices), change of agricultural land use for food, feed, destruction of native vegetation, pollution by additional agricultural practices, methodological frameworks and approaches to evaluate the sustainability and environmental impacts such as life cycle assessment (LCA), eMergy, ecological footprint (carbon and water), and Energy Return on Investment (EROI), among many other socio-economic, political, technological and environmental issues (^{Yang et al. 2020}).

Besides, there are other key economic factors:

• Ethanol is more expensive than gasoline and additives mainly in developing countries oil producers, except for Brazil, due to multiple factors influence the biofuels final costs such as the carbon source, crop type, production efficiency, technology among others

• Faces an unfavorable opportunity cost structure in relation to the replacement of gasoline and additives without a holistic program with stakeholder agreements.

• Feedstock price support by government with investments, tax incentives, infrastructure and research available land with high suitability to increase the productivity of current or energy crops such as sugar cane, maize etc. and increase the current agricultural frontier.

• Capital cost support.

• Income tax concessions.

• Excise tax concessions.

• Diversify markets and move gradually towards a flexible sugar mill or integrated biorefinery.

• Guaranteed (captive) markets, such as late model car owners.

• Price guarantees.

• Direct price support from government.

• The recent worldwide increase in flex-fuel automobiles, which that can use gasoline, ethanol fuel or any mixture of them

About 46% of the world’s sugar (beet or cane) producing countries and 40% of the corn producers are also ethanol producers. In this regard, ^{Balat and Balat (2009)}, ^{Sorda et al. (2010)}; ^{Ji et al (2016)}; and ^{Ghoddusi, (2017)} reviewed the world's fuel ethanol programs, public policies, and mandates. ^{Manochio et al. (2017)} provided an extensive overview of ethanol biofuel production processes as 1G and 2G from cane, corn and beet related to energy, carbon emissions and economic indicators.

Moreover, the possibility to increase production capacity in starch- and sugar-based ethanol (first generation, 1 G) and lignocelulosic ethanol (second generation, 2G) through the use of agro-industrial residues, wastes and byproducts as feedstocks in developing countries is a sustainable option because the materials are abundant and have negligible production costs, and labor is qualified and inexpensive. As a result, these regions have great comparative advantages and great potential for competitive advantages for ethanol biofuel and non-fuel production (^{Alalwan et al. 2019}; ^{Chang et al 2017})

The technologies used in current ethanol biofuel production are fairly mature and new advances are coming with the promise of sustainability and competitiveness, because biofuel use can provide air quality benefits in terms of lower emissions of key pollutants, such as carbon monoxide and sulfur dioxide, which leads to several questions: How “Green” is ethanol biofuel?, How large is the world and domestic potential for production?, With ethanol, is there a new future for rural communities as suppliers of raw materials?, What will be the impact on energy security and trade? These questions have been answered by stakeholders in several articles, publications and reports with three fundamental aspects of ethanol fuel (^{Bian & Liu, 2021}; ^{Berchi et al. 2018})

Moreover, the key components of future success for ethanol biofuel are:

1. Feedstocks (ethanol yields per ha, ethanol yields per ton of feedstock, gross feedstock costs per liter of ethanol, energy balance by feedstock)

2. Technology

3. Policy

4. World production will continue to grow strongly

Based in advantages and disadvantages the conclusions drawn by ^{Goldstein, (2016)} are:

1. Ethanol produced by biological means is commercially viable and profitable for farmers and producers.

2. Ethanol is another valued entity in the mix of viable energy alternatives, any of which can apply depending on specific circumstances of countries.

3. The ethanol industry is de facto a valued partner of the petroleum industry by helping to preserve our energy supply that provides fuel for automobiles.

4. The ethanol industry can be a primary pathfinder, seeking ways via research to show how fuel blends can be more efficient.

5. The industry can serve as a primary resource to lead research to improve the environment based on its actions and the products it can develop and refine.

6. The ethanol industry can provide ways to introduce health benefits to the animal feed industry using byproducts.

7. The industry covers all facets involving the production and use of ethanol.

8. Topics include the optimization of raw materials, energy, capital, software, and human resources to produce ethanol.

3. Data and Methodology

This review was carried out to study the challenges and potential to produce ethanol from sugarcane in Mexico with the analysis of scientific literature proposed by ^{Koutsos et al. (2019)} during the last years and to understand their impact on the overall performance of the Mexican sugar mills before the objective of the productive reconversion to ethanol and electric cogeneration plants. These primary data along with secondary data from the sugar industry (technological and socioeconomic statistics) formed the basis for the analysis.

4. Mexican ethanol biorefinery from sugarcane

Sugarcane in Mexico is an agroindustry with 500 years of history that has created producing regions, popular culture and traditions related to sugarcane plantations, trapiches and sugar mills which have been studied by various disciplines such as chemical and agronomic engineering, economy, anthropology, sociology, geography, history, and others by Mexican and foreign researchers.

However, although there are various technological developments and management practices that would increase productivity by reducing pollution, production costs and expanding the value chain beyond the production of sucrose (raw, standard, refined, muscovado etc.), the low level of coordination and holistic solutions among stakeholders mainly farmers, ethanol producers, traders, sugar mill owners, technology and agrochemical companies, government, universities, researchers, shipping firms, logistics companies, PEMEX, CFE, and users of cane derivatives, industrial and beverage ethanol is the main characteristic of this agribusiness.

Furthermore, the political, socio-economic, environmental, business and academic debate of stakeholders, as well as the technologies employed for cogeneration, as a necessary complement for the joint production of ethanol, sugar, steam and electric energy under the concept of biorefining in sugar mills, remain largely unchanged since the establishing of last Decretos cañeros (1991) and the current legislation of 2005 (Law of sustainable development of sugar cane) and the national program of sugar agroindustry (PRONAC) of each presidential sexennium by the National Sustainable Development Commission of Sugarcane (CONADESUCA).

In this regard, only the production of ethanol derived from molasses is considered in the annual statistical reports. Moreover, the ethanol in turn is imported, for the needs of the domestic food, beverages, chemical and pharmaceutical industries, as non-fuel ethanol or denatured and undenatured ethanol, of at least 80 degrees GL, from countries such as Brazil, the United States, Canada, the United Kingdom, Colombia, Guatemala, and Australia, among others (^{García-Chávez, 2014}).

In the entire sugarcane value chain: raw material production, industrial processes, fermentations, distillation, vinasses uses and several environmental and socioeconomic impacts of the current low production of ethanol (as bioproduct) and low sugarcane yield (t ha^-1) (as raw material) with a high harvested area and sucrose monoproduction (Figures 3 and 4) are constraints of high controversy among stakeholders for future prospects in the use of this renewable feedstock to biofuel and its integration with sugar production in Mexico that have not been resolved.

Source: Data from ^{CONADESUCA, 2021} and ^{INEGI, 1994}

Figure 3 Ethanol and sugar production 1970-2021 

Source: Data from ^{CNPR, 2021} and ^{CONADESUCA, 2021}

Figure 4 Historical ethanol production from sugarcane 

The indicators show that the sugar industry has displaced ethanol production for several decades, and the sugar mills have a productive structure based on producing exclusively sugar with the increase in the area planted with stagnant or low yields, consequently an underutilization of the technological potential of sugarcane (Figures 5 and 6)

Source: Data from ^{CONADESUCA, 2021}

Figure 5 sugar production harvest season 2019/2020 

Source: Data from ^{CONADESUCA, 2021} and ^{INEGI, 1994}

Figure 6 Harvested area and cane yield 1970-2021 

This situation was seen directly during the harvest season 2020/2021 an area of 789,996 ha was industrialized with a cane production of 51,292,545 t with a field yield of 64,93 t ha^-1. The sugar production was 5'715,448 t, factory yield 11.14% and agroindustrial yield 7,23 t/ sucrose/ha. The sucrose production was classified by sugar qualities: Refined sugar 1'348,267 t, standard sugar 3'410,438 t, special white sugar 182,721 t, muscovado 35,876 t and raw 738,146 t. and ethanol production of 15'248.167,00 L.

Therefore, the production of ethanol under current conditions is not viable, mainly due to the lack of demand for automobiles, the low productivity of the field without determining a differentiated price of the sugarcane destined for this purpose. There is no program or public policy that allows directing the sugar agribusiness towards improving productivity and/or taking advantage of the opportunities that ethanol represents (^{Carrillo-Nieves et al. 2019}).

Changes are required in the policies that currently support the sugar industry such as the establishment of a free market for sugar cane outside the context of the Sustainable Development Law of Sugar Cane (LDSCA), or linking the price of ethanol to the payment of cane. Encourage investment projects related to the diversification of the uses of sugarcane to transfer technology and capital. The labor-management relations, outside the contract, the related Sugar Industry Laws, and the Sugarcane Production Committee.

The attainment of these targets, to move to a new competitive model of the sugar industry and use of byproducts such as biorefineries and ethanol biofuel, requires major policy decisions which should be taken as soon as possible.

In relation to the above,

Additionally, its necessary to make better decisions on technological and socioeconomic issues, agricultural land management, agroindustrial byproducts disposal, stakeholder opinions and formulation, monitoring and implementation of public policies under uncertain conditions and domestic needs of cane regions

Notwithstanding, the lack of efficient public policies for Mexican sugarcane agroindustry makes it difficult for stakeholders such as growers, and investors of sugar mill owners to make informed decisions about the economic viability of entire cane biomass utilization for ethanol biofuel. Besides the price paid for sugar cane in Mexico is high and there is no value addition with the production of biofuels, cogeneration and other bioproducts (Figure 7)

Source: Data from ^{CONADESUCA, 2021}

Figure 7 Cane price paid for sugar cane in Mexico by sugar mills (USD / t) 

Therefore, the high price of cane as a raw material for sugar has created a productive inertia and is a factor that, together with stagnant productivity, limits the diversification of cane stalks and harvest residue towards other business options or is marginal such as piloncillo and livestock production.

In the particular case of the ethanol, the global trend has been driven mainly by environmental pollution and the reduction of oil reserves. Efforts have focused by Mexican researchers on the development of several technologies to achieve greater efficiency and performance in yield of ethanol with high profits. However, it is necessary to analyze the implications of ethanol biofuel from a perspective that allows to approach the factors complexity involved in the context of each region or sugar mill to obtain ethanol biofuels and bioproducts from byproducts (vinasse, yeast, CO₂) by observing the socio-economic generation and use of raw materials, available and future technologies, political, spatial, technological and environmental implications of the transition to a biofuel economy (^{Islas-Samperio et al. 2020}; ^{Aguilar-Rivera et al. 2019}; ^{Carrillo-Nieves, et al. 2019}).

In Mexico, according to ^{Islas-Samperio et al. (2020)} and ^{Aburto and Hernandez, (2020)}, there are technological, environmental and social conditions (soil, raw materials, qualified labor, etc.) through multidisciplinary research, carried out by researchers at universities and research centers. Consequently, there are comparative and competitive advantages for the production of ethanol from sugarcane to improve the performance of gasoline and mainly reduce Volatile organic compounds (VOCs) from gasoline evaporation (^{Mugica-Alvarez et al. 2020}). However, to date there are no concrete agreements so that national ethanol producers (sugar mills) can sell a potential production to Petroleos Mexicanos (PEMEX) and the parastatal company carry out the logistical and technological operations for the mixture and distribution of gasoline and ethanol as established by the official Mexican standard NOM-016-CRE-2016, about the maximum content of ethanol in gasoline at the national level with reductions of ozone (O₃), especially the Metropolitan Zones of the Valley of Mexico, Guadalajara and Monterrey based in research results of the use of ethanol in gasoline (^{Koupal and Palacios, 2019}) and other pollutants not derived from the combustion of ethanol

In relation to the above, it is required a national ethanol program developed by the stakeholders of the sugar industry that allows: Revalue the inertial cultivation of sugar cane so that the sale price does not depend exclusively on the volatility and geopolitics of sugar in the national and international market, which each year loses profitability and competitiveness due to the incorporation of other sweeteners such as corn syrup of high fructose (HFCS) and stagnant sugarcane productivity or affected by environmental factors, the burning of cane fields, conventional management practices, the impact of climate change and others and the marginal reconversion or productive diversification.

Self-sufficiency of ethanol for all industrial uses, pharmaceuticals, perfumery beverages and currently for the production of antibacterial gel and reduce imports

Installation of new distilleries in the face of uncertainty in current public policies and future prospects in renewable energies

Therefore, if the complexity generated by the lack of agreements between the stakeholders for a national ethanol program is resolved, the following scenarios should be considered:

The self-sufficiency of ethanol in its anhydrous or hydrated type to satisfy the current needs of the food and beverage, pharmaceutical, perfumery industries, and as a biofuel or oxygenate for gasoline requires the transition of the current sugar agribusiness in three options.

In all three cases, it is essential to consider the gradual reduction of the harvest with the burning of cane fields, agroecological cultivation, optimization of inputs and technical irrigation and good management practices to increase productivity with the same area and therefore the increasing availability of the residue of harvest as an energy source in the own distillery, sugar mill and a cogeneration system and other derivatives (^{Klein et al. 2019}; ^{Cardoso et al. 2019}).

Besides is fundamentally necessary to establish a constant link with universities and research centers to optimize the processes of sustainable production of sugarcane, sugar, anhydrous and hydrated ethanol, handling of by-products, and logistics, administrative, financial and environmental management processes and looking for ISO certifications and BONSUCRO.

In a national sugarcane biofuel ethanol program, entrepreneurs and owners of sugar mills must strongly consider various aspects such as strategic relationships with stakeholders, conflicting goals and participation of the automotive industry, economic valuation, finance and business strategy, carbon, capitals, and futures markets, climate change risk management and corporate social responsibility (CSR) (Figure 8) because ethanol projects are highly strategic, therefore their valuation should not be based solely on technological or market analysis, but on real options and other industry-specific methodologies.

Source: Data from ^{Sawaengsak et al. 2019}; ^{De Rosa, 2018}; ^{Souza et al. 2018}

Figure 8 corporate social responsibility (CSR) for ethanol industry 

The ethanol program in the state of Veracruz should consider several stages to resolve multidimensional limiting factors step by step according to ^{López-Ortega et al. (2021)}) and ^{Klein et al. (2019)} employ some of the expertise acquired by Brazil during its transition from typical sugar mills into advanced biorefineries or integrated sugar-agro-complex to retrofit the Mexican sugar industry (Figure 9)

Figure 9 National program of ethanol biofuel from sugarcane 

6. Veracruz Mexico and the challenges for the production of sugar, ethanol and energy

The state of Veracruz covers an area of ​​71,826 km² in northeast Mexico. The climate is warm subhumid and warm humid, with an average annual temperature of 23 ° C and average annual rainfall of 1,500 mm. It is Mexico’s third most populous state with 8,112,505 inhabitants. In addition, 38,9 % of the population in the state lives in towns with less than 2,500 inhabitants, making it the state with the largest rural population in the country. The state is made up of 212 municipalities,

Veracruz is the third state of 32 with the largest population in poverty with where the 33 % are indigenous. Today, Veracruz residents are subject to increasing insecurity due to the rise in organized crime activity, including drug trafficking. Nationally, Veracruz is the state with the fourth lowest Human Development Index (HDI), just after Chiapas, Oaxaca and Guerrero. At the same time, state residents suffered the greatest decrease in real labor income in the period 2010 to 2020 and a considerable number of people live in extreme poverty (Table 1).

In contrast, it has the geographical, climate and soil conditions conducive to carrying out competitive agricultural activities as agriculture, livestock farming, forestry, hunting or fishing; however, low returns are obtained. There are several product systems operating in the state that cover the most economically important crops in Mexico. However, most of these crops require a larger acreage to reach these indicators, one of the most important being sugarcane (Figure 10).

Figure 10 Crop area of Veracruz, Mexico 

In this context, the agricultural sector has two major challenges. On the one hand, the productive performance of crops such as sugarcane, fruit species and other crops with potential must be improved through the accumulation of capital by small producers, because the 10 most important crops represent 88% of the planted area of the state of Veracruz and their conversion to more productive crops and the use of byproducts with a firm basis in sustainability and the circular bioeconomy is a priority. Moreover, the great variety of crops that are cultivated should use sustainable technologies to increase productivity and the value chain by exploiting the state’s comparative advantages.

In this sense, in the state of Veracruz there are 173 municipalities where sugar cane is grown for delivery to sugar mills, trapiches, livestock farmers as survival food and other uses of which 92 are the most significant for the sugar agroindustry having the indicators presented in Table 2 and Figure 11

Figure 11 Sugar cane producing municipalities for sugar mills 

In the 2020/2021 harvest season there was a planted area of 302,297.75 ha, 294,777.75 ha harvested with an average productivity of 65,083 tha^-1 distributed in 18 supply areas to sugar mills (Table 3)

The cultivation and processing of sugarcane, according to its indicators in 20 years and the las harvest season (2020/2021) represents an inertial and stagnant agribusiness, without growth options that are reflected in a decrease in the production of superior quality sucrose such as refined and muscovado, an increase in the production of low quality sugar as standard and raw, the disastrous reduction of 95.6% in the production of ethanol in addition to a reduction in the field and agro-industrial yield with increase in the harvested area, generation of by-products and the price of sugarcane on the rise due to an increase in production costs and low profitability. Among the indicators, the almost total reduction in oil consumption is important, but agribusiness is still dependent on external electricity. Some of the causes are:

Therefore, significant changes are required in monoculture, the productive structure, energy self-sufficiency, production costs and profitability and in general the revaluation of sugarcane and by-products within the approaches of circular bioeconomy and sustainable development in the face of changes in the global sugar consumption patterns that will necessarily imply a reduction in the demand for this sweetener and the potential projects to diversify the use of sugarcane (sucrochemical, ethanolchemical, lignochemical, etc.).

7. Agroecological zoning of sugarcane cultivation

The regionalization or agroecological zoning of the sugarcane crop is a tool that would allow the evaluation and determination of the productive surface susceptible to the implementation of bioenergetic projects for the production of anhydrous ethanol and the cogeneration of electrical energy, defining the zones and the potential in tons of sugarcane per hectare and the agro-industrial yield, in liters of ethanol and KWH per ton of sugarcane that allows a profitable and synergistic sharing. That is, to produce raw material, with the current surface area, reducing inputs mainly fuels, agrochemicals, land and water and consequently reducing production costs, environmental impacts and optimizing inputs, variety replacement, reducing the harvest with burning and generating new productions of harvest waste, management of impacts of climate change, direction of management practices, mechanization and harvest, minimizing restrictions or limiting factors to the possible expansion of crop in the future.

For the agroecological zoning modeling, the MaxEnt software (^{Gao et al. 2021}; ^{Kogo et al. 2019}) was used, which is based on the maximum entropy theory, whose mathematical foundation determines the environmental variables that intersect at the georeference point of the presence of the crop to be analyzed generating zoning as a spatial decision-making instrument generating cartography in a Geographical Information System (ESRI ArcMap 10.1), (Figure 12)

Figure 12 Agroecological zoning of cane areas in Veracruz, México 

Of the total of the Veracruz area currently destined to the cultivation of sugarcane, 4.186% presented an average aptitude or high agroecological potential, 57, 114% medium 38.643% low and 0.057% very low. As a result, sugarcane production in different regions of sugar mills needs different use of new crop varieties, environmental management techniques and stakeholders participation to increase productivity reducing cost.

Sugarcane regions of high potential are located in the Higo Sugar Mill, medium potential areas are grouped around El Modelo, La Gloria, Central El Potrero, San José de Abajo, Central San Miguelito, San Pedro, Panuco, Central Progreso, La Constancia, San Nicolás, Central Motzorongo, Central La Providencia and El Carmen sugar mills. Most of the area with low potential is in the region of Mahuixtlan, CIASA Cuatotolapan, San Cristobal and Tres Valles areas

8. Strategies to produce ethanol in sugar mills

Evaluate the distance and strategic location to mixing and distribution centers and in the future to PEMEX refineries.

Incorporate cogeneration schemes in the mills for the steam and energy needs of the sugar and ethanol production processes and the surplus can be offered to CFE and / or associated companies or nearby cities.

Employ adequate technology and infrastructure for the treatment of stillage to agricultural irrigation and considering the recovery of yeast as livestock feed.

For sugar groups, it may be envisaged that one or two sugar mills in the group displace the equivalent of excess cane or molasses in ethanol production, in addition to their sugar production.

Increase competitiveness by reducing production costs and establish technological strategies for the flexibility of ethanol processes based on the fermentation of molasses A, B, C, cane juice or any combination of them according to the demand of the national or international market for ethanol, molasses and sugar

Therefore, the sugar mills must evaluate the infrastructure required for the production of sugar, ethanol and electrical energy such as: process equipment, civil infrastructure, electrical installations, instrumentation / automation, detailed engineering, environmental control and water treatment, generation of steam, batey and extraction (increased milling capacity), distillery, modifications in the sugar factory, turbines and power generation, industrial inputs, by-product management, professional services for administration and operation, among others.

9. Conclusions and prospects

The problems related to generation of greenhouse gases, have become more pronounced in recent years due to the rapid pace of development towards modernization throughout the world. Therefore, the sustainable production of biofuels is a priority in Mexico in terms of improving energy security, environmental protection, and the well-being of the population. The state of Veracruz, Mexico, an impoverished region with social conflicts and an economy heavily oriented towards agricultural and livestock activities with comparative and competitive advantages for the production of sugar cane presents a real potential for the production of biofuel ethanol. This work showed that even with conventional technologies, cane stalks, molasses and trash can be successfully transformed into ethanol and new value chains can be started to reduce rural poverty and dependence on gasoline additives. At the same time, it is necessary a program with stakeholders for the use of cane and agro-industrial by-products in bioproducts