Biodiesel

Biodiesel is a renewable fuel manufactured from vegetable oils, animal fats, and recycled
cooking oils. Biodiesel offers many advantages:
• It is renewable.
• It is energy efficient.
• It displaces petroleum derived diesel fuel.
• It can be used in most diesel equipment with no or only minor modifications.
• It can reduce global warming gas emissions.
• It can reduce tailpipe emissions, including air toxics.
• It is nontoxic, biodegradable, and suitable for sensitive environments.
• It is made in the United States from either agricultural or recycled resources.
• It can be easy to use if you follow these guidelines.



Biodiesel is a diesel replacement fuel that is manufactured from vegetable oils, recycled cooking greases or oils, or animal fats. Because plants produce oils from sunlight and air, and can do so year after year on cropland, these oils are renewable. Animal fats are produced when the animal consumes plant oils and other fats, and they too are renewable. Used cooking oils are mostly made from vegetable oils, but may also contain animal fats. Used cooking oils are both recycled and renewable.

The biodiesel manufacturing process converts oils and fats into chemicals called long chain mono alkyl esters, or biodiesel. These chemicals are also referred to as fatty acid methyl esters or FAME. In the manufacturing process, 100 pounds of oils or fats are reacted with 10 pounds of a short chain alcohol (usually methanol) in the presence of a catalyst (usually sodium or potassium hydroxide) to form 100 pounds of biodiesel and 10 pounds of glycerine. Glycerine is a sugar, and is a co-product of the biodiesel process.


Benefits of Biodiesel Use
Biodiesel Displaces Imported Petroleum
The fossil fuel energy required to produce biodiesel from soybean oil is only a fraction
(31%) of the energy contained in one gallon of the fuel.
You get 3.2 units of fuel energy from biodiesel for every unit of fossil energy used to produce the fuel. That estimate includes the energy used in diesel farm equipment and transportation equipment (trucks, locomotives), fossil fuels used to produce fertilizers and pesticides, fossil fuels used to produce steam and electricity, and methanol used in the manufacturing process. Because biodiesel is an energy-efficient fuel, it can extend petroleum supplies and makes for
sound state or federal energy policy.


Biodiesel Reduces Emissions

When biodiesel displaces petroleum, it reduces global warming gas emissions such as carbon dioxide (CO2). When plants like soybeans grow they take CO2 from the air to make the stems, roots, leaves, and seeds (soybeans). After the oil is extracted from the soybeans, it is converted into biodiesel and when burned produces CO2 and other emissions, which return to the atmosphere. This cycle does not add to the net CO2 concentration in the air because the next soybean crop will reuse the CO2 in order to grow.


Biodiesel and Human Health
Some PM and HC emissions from diesel fuel combustion are toxic or are suspected of
causing cancer and other life threatening illnesses. Using B100 can eliminate as much as 90% of these “air toxics.” B20 reduces air toxics by 20% to 40%. The effects of biodiese on air toxics are supported by numerous studies, starting with the former Bureau of Mines Center for Diesel Research at the University of Minnesota. The Department of Energy (DOE) conducted similar research through the University of Idaho, Southwest Research Institute, and the Montana Department of Environmental Quality. The National Biodiesel Board conducted Tier I and Tier II Health Effects Studies that also support these claims.

Biodiesel Improves Lubricity
By 2006, all U.S. highway diesel will contain less than 15 ppm sulfur—ultra low sulfur diesel fuel (ULSD). Currently highway diesel contains 500 ppm sulfur (or less). Biodiesel typically contains less than 15 parts per million (ppm) sulfur (sometimes as low as zero). Some biodiesel produced today may exceed 15 ppm sulfur, and those producers will be required to reduce those levels by 2006 if the biodiesel is sold into on-road markets.


Biodiesel is Easy to Use
And last, but maybe not least, the biggest benefit to using biodiesel is that it is easy. In blends of B20 or less, it is literally a “drop in” technology. No new equipment and no equipment modifications are necessary. B20 can be stored in diesel fuel tanks and pumped with diesel equipment.

CHEMICAL REACTION ENGINEERING

Since before recorded history, we have been using chemical processes to prepare food, ferment grain and grapes for beverages, and refine ores into utensils and weapons. Our ancestors used mostly batch processes because scaleup was not an issue when one just wanted to make products for personal consumption.

The throughput for a given equipment size is far superior in continuous reactors, but problems with transients and maintaining quality in continuous equipment mandate serious analysis of reactors to prevent expensive malfunctions. Large equipment also creates hazards that backyard processes do not have to contend with.

Not until the industrial era did people want to make large quantities of products to sell, and only then did the economies of scale create the need for mass production. Not until the twentieth century was continuous processing practiced on a large scale. The first practical considerations of reactor scaleup originated in England and Germany, where the first large-scale chemical plants were constructed and operated, but these were done in a trial-and-error fashion that today would be unacceptable.

The systematic consideration of chemical reactors in the United States originated in the early twentieth century with DuPont in industry and with Walker and his colleagues at MIT, where the idea of reactor “units” arose. The systematic consideration of chemical reactors was begun in the 1930s and 1940s by Damkohler in Germany (reaction and mass transfer), Van Heerden in Holland (temperature variations in reactors), and by Danckwerts and Denbigh in England (mixing, flow patterns, and multiple steady states). However, until the late 1950s the only texts that described chemical reactors considered them through specific industrial examples. Most influential was the series of texts by Hougen and Watson at Wisconsin, which also examined in detail the analysis of kinetic data and its application in reactor design. The notion of mathematical modeling of chemical reactors and the idea that they can be considered in a systematic fashion were developed in the 1950s and 1960s in a series of papers by Amundson and Aris and their students at the University of Minnesota.

In the United States two major textbooks helped define the subject in the early 1960s. The first was a book by Levenspiel that explained the subject pictorially and included a large range of applications, and the second was two short texts by Aris that concisely described the mathematics of chemical reactors. While Levenspiel had fascinating updates in the Omnibook and the Minibook, the most-used chemical reaction engineering texts in the 1980s were those written by Hill and then Fogler, who modified the initial book of Levenspiel, while keeping most of its material and notation.


The major petroleum and chemical companies have been changing rapidly in the 1980s and 1990s to meet the demands of international competition and changing feedstock supplies and prices. These changes have drastically altered the demand for chemical engineers and the skills required of them. Large chemical companies are now looking for people with greater entrepreneurial skills, and the best job opportunities probably lie in smaller, nontraditional companies in which versatility is essential for evaluating and comparing existing processes and designing new processes. The existing and proposed new chemical processes are too complex to be described by existing chemical reaction engineering texts.


The first intent of this text is to update the fundamental principles of the operation of chemical reactors in a brief and logical way. We also intend to keep the text short and cover the fundamentals of reaction engineering as briefly as possible.


Second, we will attempt to describe the chemical reactors and processes in the chemical industry, not by simply adding homework problems with industrially relevant molecules, but by discussing a number of important industrial reaction processes and the reactors being used to carry them out.



Third, we will add brief historical perspectives to the subject so that students can see the context from which ideas arose in the development of modern technology. Further, since the job markets in chemical engineering are changing rapidly, the student may perhaps also be able to see from its history where chemical reaction engineering might be heading and the causes and steps by which it has evolved and will continue to evolve.




Every student who has just read that this course will involve descriptions of industrial process and the history of the chemical process industry is probably already worried about what will be on the tests. Students usually think that problems with numerical answers (5.2 liters and 95% conversion) are somehow easier than anything where memorization is involved. We assure you that most problems will be of the numerical answer type.
However, by the time students become seniors, they usually start to worry (properly) that their jobs will not just involve simple, well-posed problems but rather examination of messy situations where the boss does not know the answer (and sometimes doesn’t understand the problem). You are employed to think about the big picture, and numerical calculations are only occasionally the best way to find solutions. Our major intent in discussing descriptions of processes and history is to help you see the contexts in which we need to consider chemical reactors. Your instructor may ask you to memorize some facts or use facts discussed here to synthesize a process similar to those here. However, even if your instructor is a total wimp, we hope that reading about what makes the world of chemical reaction engineering operate will be both instructive and interesting.

Overview of Chemical Reaction Engineering

Every industrial chemical process is designed to produce economically a desired
product from a variety of starting materials through a succession of treatment
steps. Figure 1.1 shows a typical situation. The raw materials undergo a number
of physical treatment steps to put them in the form in which they can be reacted
chemically. Then they pass through the reactor. The products of the reaction
must then undergo further physical treatment-separations, purifications, etc.-
for the final desired product to be obtained.
Design of equipment for the physical treatment steps is studied in the unit
operations. In this book we are concerned with the chemical treatment step of
a process. Economically this may be an inconsequential unit, perhaps a simple
mixing tank. Frequently, however, the chemical treatment step is the heart of
the process, the thing that makes or breaks the process economically.

Design of the reactor is no routine matter, and many alternatives can be
proposed for a process. In searching for the optimum it is not just the cost of
the reactor that must be minimized. One design may have low reactor cost, but
the materials leaving the unit may be such that their treatment requires a much
higher cost than alternative designs. Hence, the economics of the overall process
must be considered.
Reactor design uses information, knowledge, and experience from a variety
of areas-thermodynamics, chemical kinetics, fluid mechanics, heat transfer,
mass transfer, and economics. Chemical reaction engineering is the synthesis of
all these factors with the aim of properly designing a chemical reactor.
To find what a reactor is able to do we need to know the kinetics, the contacting
pattern and the performance equation. We show this schematically in Fig. 1.2.

Figure 1.1 Typical chemical process.



Figure 1.2 Information needed to predict what a reactor can do.

Much of this book deals with finding the expression to relate input to output
for various kinetics and various contacting patterns, or

output = f [input, kinetics, contacting]

This is called the performance equation. Why is this important? Because with
this expression we can compare different designs and conditions, find which is
best, and then scale up to larger units.



source: Octave Levenspiel