نوع مقاله : مقاله پژوهشی

نویسندگان

• محمود کریمی ¹
• رضا محمدی گل ¹
• روح اله رحیمی ²

¹ استادیار گروه مهندسی مکانیک بیوسیستم، دانشگاه اراک، اراک، ایران

² استادیار پژوهشی، مؤسسه تحقیقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران

چکیده

برای کاهش مصرف مواد و انرژی و ارتقای استفاده از منابع تجدیدپذیر مانند سوخت های زیستی، نیاز به اندازه گیری جریان مواد و انرژی اهمیت بیشتری پیدا می کند. تحلیل جریان اکسرژی به عنوان یک ابزار ارزیابی زیست محیطی برای محاسبه پسماندها، تعیین بازده اکسرژی، ارزیابی جایگزین ها و منابع انرژی مختلف، در تعیین سیاست های اقتصادی و زیست محیطی بسیار موثر است. این پژوهش فرآیند ترانس استریفیکاسیون پسماند روغن خوراکی را برای تولید بیودیزل با تمرکز بر کاهش مصرف مواد و انرژی و ارتقای بازده انرژی و اکسرژی بررسی می کند. اجرای واکنش ترانس استریفیکاسیون در شرایط مختلف جرم و انرژی انجام شد و تجزیه و تحلیل ترمودینامیکی برای اندازه گیری ورودی و خروجی اکسرژی فرایند تولید مورد استفاده قرار گرفت. ارزیابی تأثیر متغیرهای آزمایشی از جمله نسبت مولی متانول به روغن، غلظت هیدروکسید پتاسیم و دمای واکنش بر بازده اکسرژی و اتلاف اکسرژی در ترانس استریفیکاسیون صورت گرفت. بیشترین بازده اکسرژی (7/91 درصد) و حداقل اتلاف اکسرژی (MJ 32/4 به ازای یک کیلوگرم تولید بیودیزل) با نسبت مولی متانول به روغن 8:1، غلظت هیدروکسید پتاسیم 1 درصد وزنی و دمای واکنش ℃55  حاصل شد. تحلیل اکسرژی واکنش ترانس استریفیکاسیون نشان داد که استفاده بیش از حد بهینه متانول و کاتالیست در فرآیند تولید بیودیزل باعث افزایش اتلاف اکسرژی به دلیل تولید و هدررفت مواد پسماند شده که این امر باعث کاهش بازده اکسرژی شده است.

کلیدواژه‌ها

• اکسرژی
• بیودیزل
• ترانس استریفیکاسیون
• پسماند
• روغن گیاهی
• تحلیل ترمودینامیکی

موضوعات

• انرژی و انرژیهای تجدیدپذیر

عنوان مقاله [English]

Analyzing the efficiency of biodiesel production through exergy analysis of transesterification

نویسندگان [English]

• Mahmoud Karimi ¹
• Reza Mohammadigol ¹
• roohollah rahimi ²

¹ Assistant Professor, Department of Biosystem Mechanics Engineering, Arak University, Arak, Iran

² Assistant Professor, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

چکیده [English]

Introduction: Biodiesel is viewed as a promising alternative to fossil fuels due to its favorable chemical properties and environmental benefits. Research has shifted towards producing biodiesel from non-edible oils and waste cooking oils to avoid food scarcity issues. The high cost of production is a major challenge, with raw materials accounting for 75% of the total cost. Sustainability depends on low-cost feedstocks like waste cooking oil. Exergy analysis is a useful tool for optimizing biodiesel production by reducing energy and resource consumption and increasing production yield. The study focuses on the exergy flow of transesterification of waste cooking canola oil, with parameters like methanol:oil ratio, catalyst concentration, and temperature being evaluated.
Materials and Methods: Waste cooking oil (WCO) was used in the present study, with physicochemical properties including density, viscosity, free fatty acid content, and acid value measured. Biodiesel production using a two-step catalyzed method was carried out, with the first step being esterification to remove high water and FFA content in the waste cooking oil. The second step involved transesterification using different methanol:oil ratios, catalyst concentrations, and reaction temperatures. The FAME content of the samples was analyzed using gas chromatography and an equation was provided to calculate the FAME content of the biodiesel samples. In the process of transesterification of WCO, four balance equations were used to analyze exergy. Mass, energy, and entropy input and output must be balanced, with a portion of exergy input being destroyed. The mass exergy component is divided into physical, chemical, potential, and kinetic exergy. The overall exergy of a mixture of substances was calculated by considering physical and chemical exergy. Mixing in the transesterification process is irreversible, with potential work being wasted. Exergy transfer by heat flow and workflow was calculated using specific equations. An exergy conversion coefficient was used to estimate the chemical exergy content of fuels. Dead state conditions were considered for calculating exergy efficiency in the transesterification process.
Results and Discussion: The GC analysis of transesterification conversion products from a standard sample showed that the main components in WCO-derived biodiesel were methyl salicylate, methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, and methyl oleate. The efficiency of the transesterification process under specific conditions was determined to be 90.23% with an exergy efficiency of 91.73%. Exergy analysis revealed that the exergy embodied in biodiesel was higher than that in WCO, but a portion of WCO's exergy was consumed in the production of biodiesel. The study also highlighted ways to reduce energy loss and material waste in the transesterification process, emphasizing the importance of recycling and reusing waste materials to improve overall resource efficiency. The experiment variables of methanol:oil molar ratio, KOH concentration, and reaction temperature were investigated in the transesterification process for biodiesel production. A higher methanol:oil molar ratio of 6:1 was recommended for maximum yield when using pure oil with low FFA and water content. Increasing the ratio from 4:1 to 8:1 resulted in higher biodiesel yield and exergy efficiency. However, further increasing the ratio to 12:1 led to decreased efficiency. The KOH concentration and reaction temperature also had significant impacts on biodiesel yield and exergy efficiency. Higher catalyst concentration and reaction temperature increased exergy destruction, while a temperature increase from 45℃ to 55℃ improved efficiency and yield. The study suggested that careful optimization of these variables is essential for maximizing biodiesel production and minimizing exergy losses.
Conclusions: Exergy analysis is a valuable tool for assessing the environmental impacts of products, processes, or activities by quantifying energy and material usage and waste generation within a comprehensive framework. It also allows for estimating the resource requirements for processes such as transesterification in the production of renewable resources like biodiesel. In this study, the exergy flow in the transesterification of waste cooking oil was evaluated, with a focus on the impact of variables such as methanol:oil ratio, potassium hydroxide concentration, and reaction temperature on biodiesel yield, exergy efficiency, and exergy destruction. Experimental data was collected and used for exergy calculations, revealing that maximum biodiesel yield and exergy efficiency were achieved at specific conditions. Excess methanol or potassium hydroxide led to decreased efficiency and increased exergy loss in the process. Lower temperatures also resulted in higher exergy loss due to reduced conversion efficiency. Understanding the effects of these variables can help improve exergy efficiency and economic performance in commercial biodiesel production. Exergy analysis can also be used to evaluate environmental performance and aid in the development of environmental policies and resource management strategies.

کلیدواژه‌ها [English]

• Exergy
• Biodiesel
• Transesterification
• Waste
• Vegetable oil
• Thermodynamic analysis