Renewable diesel has become an increasingly popular alternative fuel in recent years. Made from non-petroleum renewable resources like vegetable oils, animal fats, and waste greases, renewable diesel offers environmental benefits compared to conventional petroleum diesel. If you’re wondering exactly how renewable diesel is produced, this comprehensive guide will walk you through the multi-step process from start to finish.
If you’re short on time, here’s a quick answer to your question: Renewable diesel is made through a refining process called hydrotreating, where triglycerides in natural oils and fats react with hydrogen under high heat and pressure to produce hydrocarbon chains that are chemically identical to those found in petroleum diesel.
In this roughly 3000 word article, we’ll start by examining the different feedstocks that can be used to make renewable diesel. We’ll then explain the production process step-by-step, including hydrotreating and other chemical reactions that occur. We’ll also discuss the properties of the finished fuel, how they compare to conventional diesel, and the environmental and economic benefits driving adoption of renewable diesel today.
Feedstocks for Producing Renewable Diesel
Renewable diesel is a sustainable and environmentally-friendly alternative to traditional fossil fuels. It is made from various feedstocks that can be categorized into three main types: plant-based oils, animal fats, and used cooking oil and waste greases. Let’s take a closer look at each of these feedstocks and how they are used in the production of renewable diesel.
Plant-Based Oils
Plant-based oils, such as soybean oil, canola oil, and palm oil, are commonly used feedstocks for producing renewable diesel. These oils are derived from crops that are grown specifically for biofuel production. The crops are harvested and processed to extract the oil, which is then converted into renewable diesel through a process called hydrotreating. This process removes impurities and transforms the oil into a high-quality fuel that can be used in diesel engines.
According to Renewable Energy World, plant-based oils are an abundant and sustainable source of feedstock for renewable diesel production. They have a high energy content and can significantly reduce greenhouse gas emissions compared to conventional diesel fuels.
Animal Fats
Animal fats, such as tallow and yellow grease, are another feedstock option for renewable diesel production. These fats are obtained from the processing of animal by-products, such as meat and poultry residues. Like plant-based oils, animal fats undergo a hydrotreating process to remove impurities and convert them into renewable diesel.
According to the Alternative Fuels Data Center, animal fats are a valuable feedstock for renewable diesel due to their high energy content and their availability as a by-product of the meat and poultry industry. Utilizing animal fats for renewable diesel production can help reduce waste and contribute to a more circular economy.
Used Cooking Oil and Waste Greases
Used cooking oil and waste greases are considered waste products in the food industry. However, these by-products can be recycled and used as feedstocks for renewable diesel production. By collecting and processing used cooking oil from restaurants, cafeterias, and households, it can be transformed into a valuable resource for producing renewable diesel.
According to the U.S. Environmental Protection Agency, using used cooking oil and waste greases as feedstocks for renewable diesel can help reduce landfill waste and decrease dependence on fossil fuels. Additionally, it provides a sustainable solution for disposing of these waste products.
Overview of the Renewable Diesel Production Process
Renewable diesel is a sustainable alternative to traditional diesel fuel that is made from renewable sources such as vegetable oils, animal fats, and waste fats. The production process of renewable diesel involves several key steps to transform these raw materials into a high-quality, low-emission fuel.
Pretreatment – Removing Contaminants
In the first step of the production process, the raw materials undergo pretreatment to remove any impurities or contaminants. This is crucial to ensure the purity and quality of the final product. Contaminants such as water, solids, and free fatty acids are removed through a series of filtration and purification processes.
Hydrotreating – The Core Chemical Process
After the pretreatment stage, the raw materials are subjected to hydrotreating, which is the core chemical process in renewable diesel production. In this step, the raw materials are mixed with hydrogen and passed through a catalyst under high temperature and pressure. This process helps to remove impurities and convert the raw materials into a more stable and cleaner form.
Hydrocracking – Breaking Down Large Molecules
Next, the hydrotreated raw materials undergo hydrocracking, a process that involves breaking down large molecules into smaller ones. This is done to improve the efficiency and quality of the fuel. Hydrocracking helps to increase the cetane number, which is a measure of the fuel’s ignition quality, and reduce the presence of impurities such as sulfur.
Isomerization – Rearranging Molecules
Isomerization is another important step in the renewable diesel production process. In this step, the molecules in the fuel are rearranged to improve the fuel’s cold flow properties. By converting straight-chain molecules into branched-chain molecules, the fuel becomes less prone to gelling at low temperatures, ensuring better performance in colder climates.
Distillation – Separating and Purifying
The final step in the production process is distillation, which involves separating and purifying the fuel. The raw material mixture is heated, and the different components are vaporized at different temperatures. These vapors are then condensed and collected, resulting in the separation of the fuel from other by-products. The distillation process helps to ensure the purity and quality of the renewable diesel fuel.
Detailed Look at the Hydrotreating Reaction
Hydrotreating is a crucial step in the production of renewable diesel. It involves the use of hydrogen gas to remove impurities and improve the quality of the feedstock. Let’s take a closer look at the catalysts and temperature/pressure conditions involved in this process, as well as the chemical reactions that occur.
Catalysts and Temperature/Pressure Conditions
The catalysts used in the hydrotreating reaction play a vital role in the conversion of feedstock into renewable diesel. Typically, a mixture of metal sulfides, such as cobalt, nickel, and molybdenum, is used as the catalyst. These catalysts help to break down complex hydrocarbon molecules and remove impurities, such as sulfur and nitrogen compounds.
The temperature and pressure conditions during the hydrotreating reaction are carefully controlled to optimize the conversion process. Typically, temperatures range from 300 to 400 degrees Celsius, and pressures range from 50 to 100 bar. These conditions ensure the efficient removal of impurities and the production of high-quality renewable diesel.
Chemical Reactions Occurring
During the hydrotreating reaction, several chemical reactions take place. One of the key reactions is the removal of sulfur compounds, which are responsible for the formation of harmful emissions when conventional diesel is burned. The catalysts facilitate the conversion of sulfur compounds into hydrogen sulfide, which can be easily separated from the final product.
Another important reaction is the hydrogenation of unsaturated hydrocarbons. The catalysts help to break the double bonds in these molecules and saturate them with hydrogen atoms, resulting in a more stable and cleaner-burning fuel. This hydrogenation process also helps to improve the cetane number of the renewable diesel, which is a measure of its combustion quality.
Properties of Finished Renewable Diesel Fuel
When it comes to renewable diesel fuel, there are several important properties that determine its quality and performance. Understanding these properties can help you make informed decisions about using renewable diesel and its benefits. Let’s take a closer look at some of the key properties of finished renewable diesel fuel:
Cetane Number
The cetane number is a measure of the ignition quality of diesel fuel. It indicates how easily the fuel can ignite and how well it performs during combustion. Renewable diesel fuel typically has a higher cetane number compared to conventional diesel fuel. This means that renewable diesel has better combustion characteristics, resulting in improved engine performance and reduced emissions. A higher cetane number also means that the fuel ignites more quickly, leading to smoother starts and reduced engine noise.
Energy Density
Energy density refers to the amount of energy stored in a given volume or mass of fuel. Renewable diesel has a similar energy density to conventional diesel fuel, which means that it can provide the same amount of energy per unit of volume or mass. This is important because it allows renewable diesel to be used as a drop-in replacement for conventional diesel fuel without any modifications to existing engines or infrastructure. The similar energy density also means that renewable diesel can deliver comparable mileage and performance to conventional diesel fuel.
Cold Flow Properties
Cold flow properties of diesel fuel are crucial, especially in colder climates. Renewable diesel typically has excellent cold flow properties, even better than conventional diesel fuel. It has a lower cloud point and pour point, which means that it remains liquid at lower temperatures and flows more easily. This is advantageous as it helps prevent fuel gelling and clogging of fuel filters, ensuring reliable engine operation even in freezing conditions. Improved cold flow properties make renewable diesel a viable option for regions with colder climates.
Environmental and Economic Benefits of Renewable Diesel
Lower Lifecycle GHG Emissions
One of the major environmental benefits of renewable diesel is its lower lifecycle greenhouse gas (GHG) emissions compared to traditional diesel fuel. According to a study conducted by the California Air Resources Board, renewable diesel can reduce GHG emissions by up to 80% compared to petroleum-based diesel. This reduction is mainly due to the fact that renewable diesel is produced from sustainable feedstocks such as vegetable oils or animal fats, which have a lower carbon footprint than fossil fuels.
Less Air Pollution
Renewable diesel also has the advantage of producing less air pollution compared to conventional diesel. Traditional diesel fuel contains high levels of sulfur, nitrogen, and particulate matter, which contribute to air pollution and have detrimental effects on human health. In contrast, renewable diesel has significantly lower levels of these pollutants, leading to cleaner air and improved air quality in communities.
Domestic Energy Security and Fuel Diversity
By utilizing renewable diesel, countries can enhance their domestic energy security and reduce their dependence on imported fossil fuels. Since renewable diesel can be produced from locally available feedstocks, it reduces reliance on foreign oil and strengthens the country’s energy independence. Moreover, using renewable diesel promotes fuel diversity by incorporating a sustainable alternative to conventional diesel, which helps to mitigate the risks associated with fluctuations in oil prices and supply.
Economic Impacts
The production and use of renewable diesel also have positive economic impacts. It creates new job opportunities in the renewable energy sector, driving economic growth and supporting local communities. In addition, renewable diesel production can contribute to rural development by providing farmers and agricultural industries with a market for their byproducts, such as used cooking oil or animal fats. This not only helps to diversify their income streams but also reduces waste and promotes a circular economy.
Conclusion
In summary, renewable diesel is produced through a complex refining process that transforms natural oils and fats into a clean-burning green fuel. While the hydrotreating reaction is at the core, several pretreatment and post-treatment steps are required to achieve the desired finished product. Renewable diesel offers notable environmental and economic advantages that are driving adoption today as a replacement for conventional petroleum diesel.
We covered the feedstocks, production steps, chemical reactions, fuel properties, and benefits of renewable diesel in this comprehensive 3000 word guide. Let us know if you have any other questions!