What Is Green Diesel Environmental Sciences Essay

Green Diesel, often called renewable diesel or second generation diesel, refers to petrodiesel-like fuels derived from biological sources fuels derived from biological resources (bio-resources) that are chemically not esters and thus distinct from biodiesel. The green diesel is chemically same as petrodiesel but it is made from bio-resources. Bio-resources refers to the living things (plants, animals, and others aspects of nature). It is important to society for the various services they provide, as well as problems they may create. Biological resources are grouped into those that affect agriculture, such as cultivated plants, pollinators, and pests those that are sources of scientific inputs, such as agricultural plant varieties that provide genetic resources and those that provide natural goods and services, such as wildlife, fish, and scenic beauty. Traditional measures of agricultural productivity do not capture all the benefits of preserving biological resources on private lands. Because of this, private landowners may not have adequate incentives to consider the full range of goods and services produced by the biological resources under their control. Since green diesel is produced by bio-resources, thus it is the eco-friendly and sustainable sources of fuel for vehicles.

Green diesel blends follow the same nomenclature as biodiesel. Green diesel in its pure form is designated R100 while a blend comprised of 20% green diesel and 80% petrodiesel is called R20. Because green diesel is chemically the same as petrodiesel, it can be mixed with petrodiesel in any proportion but users may need to add an additive to address lubricity issue associated with compounds with no oxygen. The characteristic of green diesel compared with other fuel are shown below:

Biodiesel

Diesel

Oxygen, %

Specific gravity

0.78

0.88

0.84

Sulphur, ppm

<10

Heating value, â°C

Cloud point, â°C

-20 to 20

-5 to 15

-5

Cetane

70-90

50-65

Table 1.1(1) : Characteristics of Green Diesel compared with other fuel.

Green diesel can be made from the same feedstock as biodiesel since both are required the tricylglycerol containing material from bio-resources.

Figure 1.1(1) : Brief Renewable Fuel Creation Process Pathway

However the terms green diesels have been further distinguished based on the processing method to create the fuel. The primary differences between green diesel and biodiesel are the technologies used to make the fuel and the molecules that are ultimately produced. Whereas, biodiesel is made using a chemical reaction called transesterfication. There are three different processes for creating green diesel, hydrotreating, thermal depolymerisztion, and biomass-to-liquid (BTL). Green diesel blends follow the same nomenclature as biodiesel. Green diesel in its pure form is designated R100 while a blend comprised of 20% green diesel and 80% petrodiesel is called R20. Because green diesel is chemically the same as petrodiesel, it can be mixed with petrodiesel in any proportion but users may need to add an additive to address lubricity issue associated with compounds with no oxygen. The differences between green diesel and biodiesel are shown below:

Green Diesel

Biodiesel

Pure hydrocarbon

Oxygenated hydrocarbon

Production process:

Hydrotreating

Thermal depolymerisation

Biomass-to liquid (BTL)

Production process:

Tranesterfication

Chemically same with petrodiesel

Chemically different than petrodiesel.

Table 1.1(2): Comparison of Green Diesel and Bio-diesel

The hydrotreating process is a process utilized by petroleum refineries today to remove contaminants such as sulphur, nitrogen, condensed ring aromatics, or metals.

1.1.2 Importance of Green Diesel from Malaysia Chemical Industry Point of View

Diesel oil has good commercial value as it serve many purposes. It has many functions as below:

To move the heavy road vehicles such as buses, lorries and trucks.

To move motors and cars

For overland shipping

To move military vehicles, such as tanks

Can be used in the water transportation as an alternative energy sources to move engines such as in the ships, boats and yacht

As electricity backup energy sources

Power generation

Construction and farming equipment

Removal of tar from bitumen burns

They derived the diesel from crude oil, which is called petrodiesel. With sharply rising use of non-renewable feedstock (crude oil) to derive diesel has a significant impact on the production of biofuels based on the conventional method. A projected future shortage of crude oil coupled with the growing worldwide demand for transportation fuels has raised the interest in the green diesel, which chemically has the same properties as the petrodiesel but with better cetane number, which mean reduce the emission of CO2 and NOx, emission, and thus brings significant improvement on greenhouse effect, global warming and pollutions.

Figure 1.1(2):

Current and Future Trend of Production for Petroleum

For recent studies and development of technologies show that the production of green diesel can be competitive or cost less than petroleum fuels; yield more oil per hectare of land; sequester CO2 from the flue gases emitted from fossil fuel power plants or other resources; able to similar or even outstanding performance than petroleum fuels; improvement of cold flow properties so that it cause least problem to use during winter. The advantages of green diesel compared with others type of diesel can be summarised as below:

Green diesel does appear to have many advantages over the other bio-based diesels. Some of these potential advantages are summarized below:

The process utilizes existing refining operations thereby eliminating the need for the immense capital investment required in the United States to produce a significant amount of biodiesel capable of truly displacing significant amounts of petroleum diesel.

The fuel is produced by refineries with a long track record of safely producing high grade products thereby eliminating the uncertainty of a fuel produced by a large number of independent producers with limited experience in fuels production.

The producers can utilize existing transportation and storage capacity (pipelines, tankage, trucks, etc.) thus eliminating the need for establishing a separate system. It should be noted that due to the detergent character of biodiesel, it cannot be transported or stored in existing petroleum facilities.

This industry places production of a fuel in the hands of companies with significant experience with the marketing and distribution of fuel products.

The process utilizes a high portion of the lipids, such as the glycerin conversion to propane.

Currently green diesel appears to have similar processing cost as biodiesel.

The resulting fuel appears to have more stable fluid and burn properties at low temperatures

Malaysia also has her own biofuel policy. The government has announced the introduction of a National Biofuel Policy on 10 August 2005. The policy is primarily aimed at reducing the country’s fuel import bill, promoting further the demand for palm oil which will be the primary commodity for biofuel production (alongside regular diesel). One of the four strategies in Malaysia’s National Biofuel Policy is to encourage the use of biofuel among the public, which will involve giving out incentives for oil retail companies to provide biodiesel pumps at stations [6]. From this policy, we can conclude that our country started to pay attention to biofuels.

However, with the green diesel stands out to be having more advantages than bio-diesel, the forecast of green diesel in Malaysia would be off the bright one. With all the bio-resources readily available as feedstock in the production of green diesel, definitely green diesel will be one of the most potential alternative energies utilized in the land of Malaysia.

1.1.3 The World Green Diesel Production Plants

Green diesel is a new breed of fats-and-oils based renewable diesel is now increasing its presence in the global biofuels market as major players stared up new production facilities this year. Efforts are being made all over the world to replace fossil fuel. We are belatedly realized that non-renewable energy is causing us serious problems and that is the main cause to develop more alternative energy resources. Green diesel can be produced either by hydrotreating process, BTL reaction or thermal depolymerization processes. Its chemical properties are identical to petroleum diesel as compared with bio-diesel.

The demand of green diesel is so much interesting but also challenging. In Malaysia, the usage of green diesel is not much significant. But, recently, there is new renewable energy pilot plant being launched by Saham Utama Sdn. Bhd. in Sungai Batu Pahat near Kangar, Perlis. The diesel is made from solid waste plastic. This can reduce the amount of plastic wastes, thereby helping to combat the effect of global warming. They have claimed that the added features would be installed to transform plastic bottles into diesel fuel. The goal is to convert any domestic waste including organic waste and liquid into commercial fuels. The engineering method used could be thermal depolymerization which similar to cracking of crude oil.

In Asia, the most nearest country which recently alert about these efforts is Singapore. In November 2010, Finland-based Neste Oil started the world largest renewable diesel plant in Singapore, with a total capacity of 725 760 tonnes per year. The diesel produced is known as NExBTL, a premium-quality product with complex production technology and also more expensive than bio-diesel. It is produced by hydrotreating of the feedstock. The byproducts of the process are bio-gasoline, biogas and water. The feedstock being used is palm oil. However, Neste Oil’s NExBTL can also use rapeseed oil and waste animal fat from food industry. This make the technology becomes more flexible due to availability of feedstocks in the future. Neste Oil also has an intensive research on new materials for future needs.

In Europe, the renewable diesel is experiencing oversupply and Neste Oil exacerbate their plant at Rotterdam in 2011. The renewable plants also could be exacerbated rising fats and oil prices because of the feedstock demand including in US. Researchers claimed that the global renewable diesel capacity totals about 665 million gallon per year today and this will grow up to 2.5 billion gallon per year in 2015, a 33% annual growth.

Below is the summary list of companies that produce green diesel (worldwide):

Technology

Feedstock

Product

Commercial Entity

Commercial Status

Outstanding Commercial Issues

Hydrotreating

Animal fats or vegetable oils co-processed with petroleum diesel

Hydrocarbon mixture- meets ASTM D975

Conoco Philips/ Tyson

Ireland refinery producing since Dec. 2006.

US announced production of 175 million gals/year expected by 2009

EPA registration

Toxicity and biodegradability

Hydrocarbon mixture- meets national fuel quality standards in Australia

Australian refinery producing 5% renewable blend

Animal fats/ vegetable oils

Hydrocarbon mixture- meets ASTM D975

Neste oil

First plant in Finland with capacity of 58 million gals/year

The largest plant available in Singapore with production of 0.8 million tons/year

Also located in US and Netherlands

EPA registration

Toxicity and biodegradability

Marketplace use

Hydrocarbon mixture

Petrobras (Brazil,

H-Bio Technology)

Begin at several refineries since end of 2007

Animal fats

Hydrocarbon mixture

Dynamic fuels (Syntroleum/Tyson)

Commercial pilot started I n 2008

Production start in 2010

Standard development

EPA registration

Economics

Life-cycle analysis

Toxicity and biodegradability

Vegetable oils

UOP Technology

Plant constructed in 2009

Production of 95 million gals/year

Biomass-to-Liquid (BTL) via gasification or Fischer-Trophs

Biomass

Hydrocarbon mixture

JV with Choren/ Daimler-Chrysler/VW

Pilot plant opened in 2007

Production 0f 4.7 million gals/year

Standard development

EPA registration

Economics

Life-cycle analysis

Toxicity and biodegradability

Neste Oil/ Stora Enso

Pre-commercialization

Syntroleum

Pyrolysis-Rapid Thermal Processing

Biomass, municipal and industrial waste

Hydrocarbon mixture

In research stage

Standard development

EPA registration

Economics

Life-cycle analysis

Toxicity and biodegradability

Slaughterhouse waste (animal waste), carbon containing waste

Hydrocarbon mixture- meets ASTM D396, can be refined to ASTM D975

Changing World Technologies

Commercial pilot plant in Missouri

Production of 250 000 gals/moles of slaughterhouse waste

Marketplace use

Table 1.1(3): Summary list of companies in worldwide that produce green diesel

1.1.4 Emerging Energy Demands for next 10 years

Malaysia is currently in the midst of rapid development. One significant sign of rapid development is the increasing trending of energy demands in the future. Not only in Malaysia, the global energy landscape is changing tremendously, but most of it is showing an upward trend. Global energy demands will be about 30 percent higher in 2040 compared to 2010, as economic output more than doubles and prosperity expands across a world whose population will grow by more than 25 percent, reaching to nearly 9 billion people. [1] Global demand for the least carbon-intensive fuels – natural gas, nuclear and renewables – will rise at a faster-than-average rate.

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Figure 1.1(3):

Global energy demand increases by one-third from 2010 to 2035, with China and India accounting for 50 percent of the growth in the New Policies Scenario [2]

In the above graph, the main growth of energy demands more significant in China and Asia due to the increasing population and fast-paced development of the countries. Malaysia falls under the category of “Other developing Asia”. Similarly it also shows an incline trend due to the rapid development of industrial and economic activities in Malaysia.

In order to cope with the high rising of energy, various energy policies and plan were carried out by the government. “Go Green” is one of the most popular concept practice in the world wide, and the term “renewable” and “sustainable” is now related to oil and gas by having renewable diesel (green diesel). Many countries in the world often started on the production of green diesel using various types of technologies such as hydro-treating or thermal depolymerisation.

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Figure 1.1(4): United State production of petroleum and other liquids by source, 2010-2035 (millions barrels per day) [3]

By referring to the graph above, the total production of petroleum and other liquids grows rapidly, from 9.7 million barrels per day in 2010 to 12.1 million barrels per day in 2020. Focusing on renewable sources, prediction shows that the biofuel productions grows by 0.8 million barrels per day from 2010 to 2035 as a result of the EISA2007 RFS (Renewable Fuel Standard Program), with ethanol and biodiesel accounting for 0.7 and 0.1 billion barrels per day, respectively, of the increase in the Reference case. [3] In addition, incline trending of next-generation “xTL” production (including both biomass-to-liquids and CTL) contributes greatly to the growth in total production of petroleum and other liquids in U.S., especially significant after the year 2020. The significant growth of BTL reflects a good potential in the future market, and yet it is a convincing and promising source of renewable diesel.

Not only on the growing capacity of green diesel production giving hopes to mankind, the continuous researches done by scientists also bring upon the increasing quality of green diesel. Before that, economic crisis and technological hurdles delay the start of numerous researches and projects on advanced biofuels, especially on cellulosic biofuel projects. However in the futures, it is expected that, EPA (Environment Protection Agency) will year-to-year evaluate the status of biofuel capacity and also revise on the production mandates for the following year. By the continuous efforts from researchers, it is foresee that BTL will reach the EISA2007 Renewable Fuel Standard after 2030. This providing a better quality or standard of green diesel produced.

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Figure 1.1(5): EISA2007 Renewable Fuel Standard credits earned in selected years, 2010-2035 (billion credits) [3]

However in Malaysia, a sad scenario is that the production of green diesel still in an infant stage. Researches and developments in experimental scales had been carried out so far, but still the production in large industrial scale is still underdeveloped. By taking reference of the forecast on oil and gas field in U.S., rough estimation on the future hope of green diesel production in Malaysia for the next 10 years can be done. The potential of green diesel in the future 10 years of view in Malaysia is consider as a bright one, and to be believed that it will slowly increasing in demands over the next 10 years. Green diesel production in Malaysia is what we are looking for in the future. Scientists and fuel specialists optimistically believe that green or renewable diesel will be one of the future trends in oil and gas production, not only in Malaysia but also in the nationwide.

1.2 PROCESS ALTERNATIVE

Green diesel is being highly looked up to as one of the great hope, with its similar chemical properties similar to diesel. New ways and technologies for improvement in green diesel production are improved as time go by. Of these, three processes of green diesel production will be suggested and discussed from different aspects.

1.2.1 Production of green diesel via biomass to liquid technology and Fisher-Tropsch Process

One of the alternative processes is to produce green diesel is by using Fischer-Tropsch process. It is basically a patent to produce liquid hydrocarbons from mixture of syngas, carbon monoxide gas and hydrogen using metal and cobalt catalysts. The liquid hydrocarbon mentioned here is referred to the paraffin. Normally right before the Fischer-Tropsch process is a series of gasification process of feedstock, to convert the biomass into the biogas that can be utilized to become liquid hydrocarbons, the green diesel.

Let us take a look at the gasification of biomass to syngas. The biomass may undergo low temperature gasification (800 – 1000 °C) to produce product gas which later on converted to bio-syngas through reforming and tar cracking steps. On the other hand, the product gas (CO, H2, CH4, CxHy) may be used to generate electricity. When the organic material inside the biomass burned, it may undergo complete combustion to produce carbon dioxide and water, or it may undergo partial combustion to carbon monoxide and hydrogen. What we need for the feeds of the Fischer-Tropsch process is the carbon monoxide and hydrogen and it can be achieved by control the amount of oxygen during combustion process (gasification). Several reactions are used to control the H2/CO ratio. Most important one is water gas shift reactions, in which the water is reacted with carbon monoxide to produce sources of hydrogen that needed in the Fischer-Tropsch process. The chemical reaction of the Fischer-Tropsch process is shown as below:

http://www.fischer-tropsch.org/primary_documents/presentations/acs2001_chicago/slide03.gif

Figure 1.2(1): Fischer-Tropsch Process [1]

For the Fischer-Tropsch Reaction, it is normally operated with temperature range of 150 – 300°C. Higher temperature will have high rate of conversion but also lead to the production of methane. Thus, the temperature is always maintained at low to middle temperature in order to remain yield of the green diesel. On the other hand, the pressure of the process is ranging from one to several tens atmospheric pressure. Higher pressure will help the reaction faster but also required more costs of operations such as high pressure equipment. We also need to know that too high pressure also can cause the metal or cobalt catalysts that used in the reaction to deactivate due to coke formation. A variety of catalysts can be used for the process such as iron, ruthenium and cobalt, depending on the aims of the operations.

Figure 1.2(2): A simple concept on Fischer-Tropsch Reaction

Green Chemistry and Sustainability

In term of green chemistry, the use of renewable feedstock such as biomass is a sustainable way to overcome the depletion of crude oil. Biomass can be easily obtained from animal fats, agricultural wastes, soybean, woods, etc. The green diesel produced is ultralow sulfur content and the properties of the green diesel produced is very chemically similar with petrodiesel but better than it. The emission of the hazardous pollutant such as carbon dioxide, nitrogen dioxide is also 60-70% lesser.

Besides that, the product off-gas produced from the process can be used in two ways;

1) addition recovery process to recover the chemicals from the byproducts and export them to other company, or 2) generate electricity which is sufficient to supply for some operations in within the plants.

Environmental Impact

Fischer-Tropsch process basically produces ultra clean green diesel which help in reduce the environmental issue such as global warming, greenhouse effect by reduce the emission of carbon dioxide and nitrogen oxide. It seems to be a great potential of alternatives to the non-renewable energy resources, the crude oil.

The side products here are actually light products and also heavy products like waxes which also have high market demand and can be exported out along with the green diesel.

Flexibility of Operation

The production line is actually not only produce green diesel but also heavy products like waxes and also gasoline. By adjusting the operation condition, we may adjust the need to favor the production of desired products

There are two favored reactor types which can be chosen depends on the operator; Multitubular fixed bed reactor with internal cooling and also slurry bubble column reactor with internal cooling tubes.

The process not only limited to the oil as feedstock but also may use the renewable feedstock such as biomass and animal fats.

Energy Consumption

The energy consumption of this technology is mostly depends on the gasification process whereby it consumed 60-70% of the energy of the whole plant.

For high temperature mode (HTFT), the operating temperature is between 300 and 350°C while operating pressure can be ranging from one to several tens of atmospheric pressure.

On the other hand, for low temperature mode (LTFT), the operating temperature is between 200 and 240 °C with operating pressure of 1 to 10atm.

Advantages

No nitrogenous, sulfur compounds formed during the reaction

High cetane number can be obtained (75 – 90% higher than that required for petrochemical derived diesel fuel)

Carbon neutral process

Products off-gas can be used to generate electricity which enough for the operation of the plant.

Disadvantages

FT process is very complex in its reaction mechanism and several studies need to be carry out to maximize the productivity of green diesel from the process

Large number of species involved in the reaction and extra care is needed in the plant design

The present catalyst is not good enough to maximize the yield of the green diesel

Extra process needed to convert the waxes formed from the FT process into green diesel (which mean extra cost!)

The cost of green diesel produced from the process may be more expensive than the diesel produced from the crude oil

Table 1.2 (1): Key Components of Fischer-Tropsch Reaction

1.2.2 Production of green diesel via Thermal Depolymerisation Process

Thermal depolymerisation (TDP) is an industrial process that able to break down and convert various type of biomass or other carbon-containing material into a “bio-oil” product that is then refined into a petrodiesel-like fuel. Thermal depolymerisation involves a depolymerisation process using hydrous pyrolysis for the reduction of complex organic materials (usually waste products of various sorts, often biomass and plastic) into light crude oil. The process is found to be similar to the natural geological processes thought to be involved in the production of fossil fuels. Long chain polymers of hydrogen, oxygen, and carbon decompose into short-chain petroleum hydrocarbons with a maximum length of around 18 carbons under the application of heat and pressure. [1] The list of TDP suitable feedstocks are extensive and flexible, including waste plastic, tires, wood pulp, medical waste, and rather unsavoury byproducts such as turkey offal and sewerage sludge.

Changing World Technologies (CWT) are currently utilizing this method to process slaughterhouse waste and other carbon containing solid waste to create a fuel that can meet the standards of both ASTM D396 and ASTM D975. [2]

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Figure 1.2(3): Thermal depolymerisation process to produce renewable diesel.

In the method used by CWT, the water improves the heating process and contributes hydrogen to the reactions. The feedstock material is first break down into small chunks, and mixed with water (if it is dry). Then it is fed into a pressure vessel reaction chamber, heated to around 250 °C at constant volume (similar principal to a pressure cooker). Steam naturally raises the pressure to 4 MPa (near the point of saturated water) and is held for approximately 15 minutes to heat the mixture completely. After this, the pressure is rapidly released to flash off most of the water content in the feedstock, resulting a mixture of crude hydrocarbons and solid minerals. The minerals are later removed, and the hydrocarbons are channel to a second-stage reactor to heat up to 500 °C in order to further breaking down the longer hydrocarbon chains. The hydrocarbons are then sorted by fractional distillation, in a process similar to conventional oil refining.

CWT claims that 15 to 20% of feedstock energy is used to provide energy for the plant. The remaining energy is available in the converted product. Working with turkey offal as the feedstock, the process proved to have yield efficiencies of approximately 85%; in other words, the energy contained in the end products of the process is 85% of the energy contained in the inputs to the process (most notably the energy content of the feedstock, but also including electricity for pumps and natural gas or woodgas for heating).

The process breaks down almost all materials that are fed into it. TDP even efficiently breaks down many types of hazardous materials, such as poisons and difficult-to-destroy biological agents such as prions. The light hydrocarbons that are produced by TDP can be used fuel sources, filters and fertilizers. It can be used a s a substitute for coal and also in quelling the alarming rise of carbon dioxide concentration in the air. CO2 is one of the chief greenhouse gases that are responsible for global warming.

Green Chemistry and Sustainability

The best part of using thermal depolymerisation (TDP) is that, it can break down substances such as plastic which takes long time to decompose. By using TDP, renewable diesel can be produce from plastic, not only save up waste to be buried, but also getting useful green diesel out of unwanted waste.

Methane in the feedstock is recovered and burned to heat the water, or burned in a combined heat and power plant to sell back electricity to the power grid

Environmental Impact

Emission of foul odors and unpleasant smell to the surrounding area of operating factory, causing nausea and uncomfortable feeling to resident nearby

Flexibility of Operation

Extensive and flexible choice of feedstocks (waste plastic, tires, wood pulp, medical waste, and unsavory byproducts such as turkey offal and sewerage sludge)

Energy Consumption

Require high energy consumption. High energy input requirements to produce green diesel made it not favorable among industry.

Safety Factor and Waste Management

Methane gas produce can be treated by burning to heat up water to produce electricity.

The process not only cleans up wastes but also generate new sources of energy.

Advantages

Able to break down strong chemical bonds of organic poison, making huge benefits to ecosystem balance.

Safely deal on heavy metals by converting them into stable oxides of their original ionized forms.

Recycling the energy content of organic products while retaining the water content. (avoid drying while producing liquid fuel that separates from water in thermal depolymerisation, energy saving).

The vast bulk of waste content can be utilized to produce green diesel. Not only make good use of all the non-bio-degradable waste but also help in producing useful oil. [3]

The light hydrocarbons produced can be used fuel sources, filters and fertilizers.

Disadvantages

Only long molecular chains compound can be broken into shorter ones, so small molecules such as carbon dioxide or methane cannot be converted to oil

If taking biomass as the feedstock, most of the biomass is already being used as animal feed or fertilizers and so are not really available in plenty for TDP

High processing costs, low yield, impurity of yield, high energy input requirements making the process not feasible and viable for large scale production.

Table 1.2(2): Key Components of Thermal Depolymerisation Reaction

1.2.3 Production of green diesel via Hydrotreating Process

Production of renewable energy is expanding at rapid pace worldwide. This phenomenon gives increasing petroleum prices, government regulation and commitment in reducing greenhouse gases. In future, renewable dependent could be increasing as a new technology in producing high quality of renewable energy was invented. These new renewable diesel should be compatible to substitute conventional diesel for transportation. One of the available production processes of green diesel is hydrotreating process. This involves removing of oxygen by using hydrogen gas.

The feedstocks are primarily vegetable oils. This can be getting from soybean, palm, jatropha, or rapeseed oils. Animal fats and grease also can be used as feedstock. Plant oils consist of triglycerides with 1-2% free fatty acids. It contains long, linear aliphatic hydrocarbon chains. The hydrocarbon mainly has even numbers of carbon atoms which generally unsaturated. The carbon number range also is typically found in diesel. In triglyceride molecules are also containing three carbon “backbone”. Volume of diesel produced from vegetable oils is nearly 100%.

Comparison between Feedstock

Feedstock

Price($/bbl)

Diesel Yield, v%

Carbon Number

Olefins, mol%

WTI crude

11-22

Rapeseed oil

16-22

Soy oil

16-18

Palm oil

16-18

Jatropha oil

16-18

Table 1.2(3): Comparison between Feedstock for Hydrotreating Process

Hydrotreating process also called as hydroprocessing. It uses hydrogen in order to remove oxygen from triglyceride’s molecules in two competing reactions:

Decarboxylation giving CO and CO2

Hydrodeoxygenation giving water

The extent of the process is depending on catalyst and process condition. The oxygen from the feed is totally converted to CO, CO2 and water (H2O). The three carbon “backbone” is converted to propane and can be recovered easily into refinery. The resulting product should be consists of only paraffin/diesel.

H2

Green Diesel

Vegetable Oils

HYDROPROCESSING

Hydroprocessing removes the oxygen by reaction with hydrogen producing pure paraffin as product. The volume of yield is about 99% while the main byproducts are propane, CO, CO2 and water. There are some advantages of using this process which are:

Hydrogen required for the production is already available

The product from this process are normal refinery product

The final products from this simple hydroprocessing process (simple paraffins) are the same components as those present in normal fossil diesel.

Does not require any special treatment and equipment

The products can easily blend with conventional refinery products.

Make use of a well-defined procedure that is already in use in the production of convection fossil diesel.

The characteristics of the renewable diesel directly reflect the high amounts of n-paraffins in the product.

This has the beneficial effect of a lower specific gravity and higher cetane index, which are properties both adding to the value to the product. On the other hand, normal paraffins have quite high melting points

There are some precautions that need to be aware in order to maintain the quality of the green diesel.

Depletion of hydrogen combined with high temperatures may lead to accelerated catalyst deactivation and pressure drop build-up

Higher make-up hydrogen and quench gas flows are needed even when co-processing quite small amounts. The refinery hydrogen balance must be checked, and the unit capacity may be lower than when processing fossil diesel only.

CO, which cannot be removed by an amine wash unit, will build up in the treat gas, requiring a high purge rate or another means of treat gas purification.

Operation will typically not be to achieve full conversion but rather to be able to control the very exothermic reactions when using an adiabatic reactor.

Much more reactive than refractory sulphur compounds, which must be removed to produce diesel with less than 10 ppm S.

High amounts of propane, water, carbon monoxide, carbon dioxide and methane are formed and these gases must be removed from the loop. The gases formed will give a decreased hydrogen partial pressure, which will reduce the catalyst activity.

The CO, which cannot be removed by an amine wash unit, will build up in the treat gas, requiring a high purge rate or another means of treat gas purification. In the reactor effluent train, liquid water and CO2 may form carbonic acid, which must be proper handled to avoid increased corrosion rates.

The hydrotreating process is a process that utilized by petroleum refineries today to remove contaminants such as sulfur, nitrogen, condensed ring aromatics, or metals. In this process, feedstock is reacted with hydrogen under elevated temperature and pressure to change the chemical composition of the feedstock. In the case of renewable diesel, hydrogen is introduced to the feedstock in the presence of a catalyst to remove other atoms such as sulfur, oxygen and nitrogen to convert the triglyceride molecules into paraffinic hydrocarbons. In addition to creating a fuel that is very similar to petro-diesel, this process creates propane as a byproduct.

Before feedstocks derived from renewable organic material can be used in conventional automobile engines and distributed using existing fuel infrastructure, it is desirable to convert the material into hydrocarbons similar to those present in petroleum derived transportation fuels. One well-established method for this purpose is the conversion of vegetable oils into normal paraffin in the gasoline or diesel boiling range by employing a hydrotreating process. The renewable organic material is reacted with hydrogen at elevated temperature and pressure in a catalytic reactor.

The same types of catalysts are used in hydrotreating of renewable feeds as presently used for desulphurization of fossil diesel streams to meet environmental specifications. Thus, a co-processing scheme where fossil diesel and renewable feedstocks are mixed and co-processed is possible, producing a clean and green diesel meeting. The hydrotreating may also take place in a dedicated stand-alone unit that processes 100% renewable diesel. In either case, the new feed components mean that completely new reactions occur and new products are formed. This gives rise to a series of challenges relating both to catalyst and process design that need to be addressed.

Process Conditions

The industrial goal of hydrogenating biologically derived (i.e. renewable) feedstocks is to produce hydrocarbon molecules boiling in the diesel range, which are directly compatible with existing fossil-based diesel and meet all current legislative specifications. With the introduction of feedstocks stemming from renewable sources, new types of molecules with a significant content of oxygen are present and must be properly treated by both the hydrotreating process and catalysts. In order to ensure trouble-free operation, it is imperative to understand and control the new types of reactions that occur when higher levels of oxygenates are processed. Overall, the reactions can be characterized as a (hydro-)deoxygenation, i.e. production of a liquid product with no oxygen. However, several reaction pathways exist, and other reactions such as saturation of double bonds and reactions involving carbon monoxide and carbon dioxide complicate the picture. Thus, a fundamental knowledge of the detailed reaction chemistry is needed for catalyst design and evaluation of process design.

Although many different types of renewable feeds exist, the chemistry of vegetable oil or animal fat hydrotreating to produce diesel-type molecules is somewhat simplified by the fact that most of such feedstocks, almost independent of seed type, are supplied as so-called triglycerides (triacylglycerols), an example of which is shown in Figure 1. Triglycerides can be seen as the condensation of glycerol (which may be seen as the C3-backbone of the molecule) and three carboxylic acids (also termed fatty acids). Although the triglyceride form is common to almost all oils and fats, the chain lengths and degree of unsaturation vary significantly.

This affects e.g. the product properties and the hydrogen consumption. Vegetable oils and animal fats may also contain significant amounts of impurities such as alkalis and phosphorus that need to be removed either in a separate process or through carefully designed guard beds. Notably, the content of sulphur and nitrogen species is very low in these feedstocks, and therefore the required HDS conversion is lower when co-processing renewable feeds.

The catalysts must be able to handle the rough conditions inside the reactor caused by the formation of CO, which inhibits the desulphurization, to handle the increased hydrogen consumption and the fast reactions leading to a large temperature increase in the top of the catalyst’s bed. Furthermore, the problem of a high content of n-paraffins in the products with resulting poor cold flow properties also has to be addressed. a choice of catalyst which is not designed or tailor-made to handle co-processing may result in poor desulphurization, hydrogen starvation and pressure drop build-up, and the hydrotreated product may not meet the required targets for cold flow properties.

Byproducts Management

The CO2 can to a large extent be removed in a downstream amine wash, but in order to avoid build-up of CO and CH4 in the loop, a purge can be established and a methanator be applied to remove CO from the purge gas. If the purge gas is simply burnt off, the methanator is obviously not required, but if the purge gas is recovered, CO may be an undesirable component. Inhibition by CO is not a concern when the right catalyst type is selected. It is necessary to remove the CO, since the purge gas is used in another refinery unit, where CO would be a catalyst poison. The existing purge gas recovery unit is a cryogenic unit that cannot remove CO. CO2 formed by the decarboxylation reaction route, which in the presence of liquid water may form carbonic acid downstream the reactor, where the risk of carbonic corrosion in the air cooler and the cold separator is high. The problems with formation of high amounts of CO, CO2 and CH4 are mitigated through a proper purging strategy, methanation of the purge gas and by solving the carbonic acid corrosion issue. This would be discussed in next chapter instead.

Green Chemistry and Sustainability

The feedstock used is renewable since it made up of algae with high growth rates.

The availability of the feedstock is promising as long it is supplied by nutrients and energy.

The CO2 produced from hydrotreating process recycles the CO2 produced into cultavition ponds as carbon source for the algae. Thus, there will be less emission of greenhouse gases into atmosphere

The light gases will be recycled back to the reactor for further reaction forming alkanes.

Environmental Impact

Since there is less emission, there will be less harm to environment

The solid waste can be used as fertilizer since algae containing high potassium content or converted to ethanol since it contained high carbohydrates and cellulose within cell walls.

Flexibility of Operation

The feedstock can be replaced by another source of biological materials that containing triglycerides.

The hydrotreating process can be held either within existing refinery plant or standalone unit

Energy Consumption

This hydrotreating process might involve electricity

High temperature also might be required to convert the triglycerides into n-alkanes. The temperatures might be in range of 300 OC -400OC

The preheated of feedstock might be needed to match with reactor temperature

The fractionation column will require a lot of heat since the separation of fules will be needed to get the green diesel

Safety Factor and Waste Management

The pressure drop should be controlled in order to prevent the fouled bed pressure drop, dead weight of catalyst and support materials, coking of catalyst and liquid holdup

The performance of catalytic hydrotreating is depending on proper loading technique. The ensure of maximum reactor activities and catalyst run length is important to provide maximum performance

Reactor temperature needs to be in proper range to get better conversion as well as maximum performance. The temperature usually based on weighted average bed temperature (WABT)

This hydrotreating process basically produced less emission of waste. This is due to recycle of side product. The water is recycled back to cultivation system. The light hydrocarbon chains are sent back to reactor for further reactions. The CO2 can be acted as carbon source for the algae. The biomass solid then can be sold to another parties to convert it to fertilizer or ethanol to gain extra income

Advantages

Hydrogen required for the production is already available

The product from this process are normal refinery product

The final products from this simple hydroprocessing process (simple paraffins) are the same components as those present in normal fossil diesel.

Does not require any special treatment and equipment

The products can easily blend with conventional refinery products.

Make use of a well-defined procedure that is already in use in the production of convection fossil diesel.

The characteristics of the renewable diesel directly reflect the high amounts of n-paraffins in the product.

Disadvantages

Depletion of hydrogen combined with high temperatures may lead to accelerated catalyst deactivation and pressure drop build-up

CO, which cannot be removed by an amine wash unit, will build up in the treat gas, requiring a high purge rate or another means of treat gas purification.

Operation will typically not be to achieve full conversion but rather to be able to control the very exothermic reactions when using an adiabatic reactor.

Much more reactive than refractory sulphur compounds, which must be removed to produce diesel with less than 10 ppm S.

Table 1.

1.2.4 Comparison between Alternative Processes

Type of Process

BTL technology and Fischer Tropsch Process

Thermal Depolymerisation

Hydrotreating Process

Features

Open system

Chlorella vulgaris undergo photosynthesis to grow

Closed system

Chlorella vulgaris undergo photosynthesis to grow

Closed system

Chlorella vulgaris do not undergo photosynthesis, but is getting carbon, nitrogen and other organic source in order to grow.

Conversion Rate (%)

0.06-0.1

0.2-0.36

4.0-20.0

Green Chemistry and Sustainability

Use free sunlight which is a renewable feedstock.

Can counter-back the carbon dioxide which is released during the combustion as a biofuel by the usage of carbon dioxide during photosynthesis.

Will not depleted.

Do not required catalyst.

Can counter-back the carbon dioxide which is released during the combustion as a biofuel by the usage of carbon dioxide during photosynthesis.

Will not depleted.

Do not required catalyst.

Cannot counter-back the carbon dioxide that is released during the combustion as biofuel. However, since the microalgae is using carbon source from agriculture as one of their substrate, thus, indirectly, the net carbon dioxide balance can be reduced.

Will not depleted.

Do not required catalyst.

Environmental Impact

Other bacteria & fungal might growing in the pond.

No.

Energy Consumption

Low

High

Moderate

Flexibility of Operation

Exposed to open air, get free sunlight and carbon dioxide from atmosphere.

The cultivation rate affected by unpredictable weather condition.

Light penetration is inversely proportional to cell density (Chen 1996) and decreases exponentially with penetration depth.

Need supply of light and carbon dioxide.

The light supply is hard to reach all part of the reactor which is maybe due to the cell attachment on the wall tube.

Light penetration is inversely proportional to cell density (Chen 1996) and decreases exponentially with penetration depth.

Need to supply organic substrate as carbon and energy sources, such as glucose, glycerol and acetate.

Need to provide enough of dissolved oxygen.

Flexible in term of feedstocks choices

Safety Factors

Contamination by other bacterial and fungal in the pond.

The overheating of the photobioreactor due to high light penetration will cause the death of microalgae.

Generally operating at room temperature and pressure. Safe to be handled.

1.2.5 Choice of Process

Among the processes suggested in previous section, hydrotreating is the most applicable and well-established green diesel production in current industry. Many of the green diesel production in worldwide utilizing hydrotreating method as it is a vital part of fuel production.

1.2.5.1 Introduction

Hydrotreating of green diesel provides an excellent opportunity to produce a renewable and sustainable diesel fuel which is fully compatible with existing diesel fuel infrastructure and engine technology. Green diesel technology focuses at achieving highly efficient and environmental friendly fuels production. Hydrotreating process owns the highest conversion rate among the three, giving 4 to 20 percent of high conversion rate. That is why hydrotreating with the high conversion rate is what have been looking into.

Hydrotreated green diesel also offers an improved performance over biodiesel and petroleum-based diesel, including a high cetane value ranging from 70 to 90, as compared with the cetane number range of 40 to 60 found in diesel at the pump today. Cetane number measures the combustion quality of diesel, which means higher cetane number operates better and more effective in engines. [3]

1.2.5.2 Microalgae as Bio-resources Feedstock

In order to produce the green diesel, hydrotreating of microalgae oil is the choice of the process. In order to make the feedstock available in long term perspective, microalgae feedstock (Chlorella vulgaris/Chlorophyta) must be cultivated first. Generally, Chlorella vulgaris can grow either autotropically or heterotrophcally. The selection of cultivation method is very important in order to have a high productivity of algae oil. More detailed information about microalgae cultivation will be enclosed in Section 1.3.

1.2.5.3 Safety and Environmental Issue

Hydrotreating offer a technology solution that supports green diesel production while lessening the environmental impact and issue of fuel production through the use of alternative bio-resources feedstock and the reduction of greenhouse gas emissions. The future of this technology is considered as bright, safe and secure.

Besides, this process basically produced less emission of waste due to the recycle of side product. The water can be recycled back to cultivation system of microalgae. The light hydrocarbon chains are sent back to reactor for further reactions. CO2 can provide a carbon source for the algae for growth.

Some of the products and by-products can be resalable to others, making profits out of the waste. For example, methane can be sold off as fuel. The biomass solid then can be resell to another parties to convert it to fertilizer or ethanol to gain extra income.

1.2.5.4 Economical Indicators and Market Analysis

In the worldwide aspect, people has been seeking alternative for the depleting crude oil supply. Green diesel having various advantages over bio-diesel has been look up with a great hope. A sustainable fuel which is completely compatible with existing diesel fuel engine technology is definitely one of the future trends of the world, ensuring a good market in the coming years.

Scientists and technologies seeking ways of improvement to yield better quality green products. Improving the productivity and efficiency of hydrotreaters has been a topic with great interest currently in today’s economic climate. With the current global economic situation and the uncertainty in the long-term market for crudes, there is a demand for processes that not only with improved productivity, but also increase in the energy efficiency of the unit, leading to a savings in both capital and operating costs. Technologies that prevent catalyst deactivation and the use of advanced process control software are currently being marketed.

The use of better energy efficient boilers and heat exchangers can be employed. More excellent insulation around the whole unit helps to secure the low energy costs. This can be done to improve energy efficiency and effectively meet rising hydrogen demand. Lastly, the use of new separation technologies, for instance membrane separation, which are less energy intense than the traditional separation techniques, may also gain market presence. [2]

1.2.5.5 Flexibility and Controllability

Hydrotreating offers a great flexibility in term of feed type. It allows various processing feedstocks, including animal fats, oil from algae, used oils, jatropha oils, and also other triglyceride feedstocks that might be available in future. This makes the process versatile and favourable among the green diesel production industry. The hydrotreating process can be held either within existing refinery plant or standalone unit, added the flexibility advantage to this process.

However, nothing is perfect. Hydrotreating process requires a greater effort in terms of process controllability. The industrial operation requires better control over the very exothermic reaction when an adiabatic reactor is used. As the reactions also consume large amount of hydrogen (for a 100% renewable feed, a hydrogen consumption of 300-400 Nm3/m3 is not unusual), higher make-up hydrogen and quench gas flows are needed even when co-processing quite small amounts. Hence, the refinery hydrogen balance must be checked.

The depletion of hydrogen combined with high temperatures may lead to accelerated catalyst deactivation and pressure drop build-up. Control of these factors would require the use of tailor-made catalysts and a careful selection of unit layout and reaction conditions. In this way it is possible to achieve a gradual conversion without affecting the cycle length and still meeting product specifications. [4]

However, this hydrotreating process makes use of a well-defined procedure that is already in use in the production of convection fossil diesel. The controllability of the conventional process can be taken as the references for the green diesel production process.

From

1. http://www.ecn.nl/docs/library/report/2004/rx04119.pdf

2. http://www.hydrocarbonpublishing.com/ReportP/ht.php

3. http://www.machinerylubrication.com/Read/28899/emerald-honeywell-diesel

4. https://docs.google.com/viewer?a=v&q=cache:uzipsg49_5sJ:www.topsoe.com/business_areas/refining/~/media/PDF%2520files/Refining/novel_hydrotreating_technology_for_production_of_green_diesel.ashx+&hl=en&gl=my&pid=bl&srcid=ADGEESjB2wNgDZUaIobqoWFoDp6XEwhP-CaipDLWAfZGq04aBzv9GYSmEvvEGwl6PpYOu2n5eIbzMfRvgE9znNid-4uQljxZNcYgJsPM04ezdtvW6oj2UXeUic01l4SjuU-TaSOC600A&sig=AHIEtbQJaXcCzpYPXDCrL4LjqjlmF05jRQ

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