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:
Heating value, â°C
Cloud point, â°C
-20 to 20
-5 to 15
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:
Biomass-to liquid (BTL)
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
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.
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 . 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):
Outstanding Commercial Issues
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
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
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
Toxicity and biodegradability
Begin at several refineries since end of 2007
Dynamic fuels (Syntroleum/Tyson)
Commercial pilot started I n 2008
Production start in 2010
Toxicity and biodegradability
Plant constructed in 2009
Production of 95 million gals/year
Biomass-to-Liquid (BTL) via gasification or Fischer-Trophs
JV with Choren/ Daimler-Chrysler/VW
Pilot plant opened in 2007
Production 0f 4.7 million gals/year
Toxicity and biodegradability
Neste Oil/ Stora Enso
Pyrolysis-Rapid Thermal Processing
Biomass, municipal and industrial waste
In research stage
In research stage
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
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.  Global demand for the least carbon-intensive fuels – natural gas, nuclear and renewables – will rise at a faster-than-average rate.
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 
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.
Figure 1.1(4): United State production of petroleum and other liquids by source, 2010-2035 (millions barrels per day) 
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.  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.
Figure 1.1(5): EISA2007 Renewable Fuel Standard credits earned in selected years, 2010-2035 (billion credits) 
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:
Figure 1.2(1): Fischer-Tropsch Process 
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.
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.
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.
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.
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.  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. 
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
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)
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.
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. 
The light hydrocarbons produced can be used fuel sources, filters and fertilizers.
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
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