Cellulose
Source
Cellulose is found in plants as microfibrils (2-20 nm diameter and 100 - 40 000 nm long). These form the structurally strong framework in the cell walls. Cellulose (E460) is mostly prepared from wood pulp.

Cellulose is a linear polymer of β-D-glucopyranose units in 4C1 conformation. The fully equatorial conformation of β-linked glucopyranose residues stabilizes the chair structure, minimizing its flexibility (for example, relative to the slightly more flexible α-linked glucopyranose residues in amylose). Cellulose preparations may contain trace amounts (~0.3%) of arabinoxylans.

Molecular structure
Cellulose is an insoluble molecule consisting of between 2000 - 14000 residues with some preparations being somewhat shorter. It forms crystals (cellulose Iα) where intra-molecular and intra-strand hydrogen bonds holds the network flat allowing the more hydrophobic ribbon faces to stack. Each residue is oriented 180° to the next with the chain synthesized two residues at a time. Although individual strand of cellulose are intrinsically no less hydrophilic, or no more hydrophobic, than some other soluble polysaccharides (such as amylose) this tendency to form crystals utilizing extensive intra- and intermolecular hydrogen bonding makes it completely insoluble in normal aqueous solutions (although it is soluble in more exotic solvents such as aqueous N-methylmorpholine-N-oxide (NMNO, , ~0.8 mol water/mol, then up to 30% by wt cellulose at 100°C [1060]), CdO/ethylenediamine (cadoxen), LiCl/N,N'-dimethylacetamide or near-supercritical water [1070]). It is thought that water molecules catalyze the formation of the natural cellulose crystals by helping to align the chains through hydrogen-bonded bridging.

Part of a cellulose preparation is amorphous between these crystalline sections. The overall structure is of aggregated particles with extensive pores capable of holding relatively large amounts of water by capillarity.
The natural crystal is made up from metastable Cellulose I with all the cellulose strands parallel and no inter-sheet hydrogen bonding. This cellulose I (that is, natural cellulose) contains two coexisting phases cellulose Iα (triclinic) and cellulose Iβ (monoclinic) in varying proportions dependent on its origin; Iα being found more in algae and bacteria whilst Iβ is the major form in higher plants.

Cellulose Iα and cellulose Iβ have the same fibre repeat distance (1.043 nm for the repeat dimer interior to the crystal, 1.029 nm on the surface [721]) but differing displacements of the sheets relative to one another. The neighboring sheets of cellulose Iα (consisting of identical chains with two alternating glucose conformers) are regularly displaced from each other in the same direction whereas sheets of cellulose Iβ (consisting of two conformationally distinct alternating sheets, (as shown right where the 2-OH and 6-OH groups both change orientations so altering the hydrogen bonding pattern) each made up of crystallographically identical glucose conformers) are staggered [559]. It has been found that cellulose (Iβ) significantly alters the water structuring at its surface out to about 10 Å, which may affect its enzymatic digestion [905].
Cellulose Iα and cellulose Iβ are interconverted by bending during microfibril formation [418] and metastable cellulose Iα converts to cellulose Iβ on annealing.

Penghasilan Bioethanol (Secara Ringkas)

Perkara paling asas didalam penghasilan produk bio-ethanol adalah bahan mentah. Pelbagai bahan mentah digunakan didalam penghasilan bio-ethanol seperti gula, sugar baggase dan lain2. Selulosa didalam batang padi tadi di hidrolisiskan menggunakn asid sulfurik cair, atau pun pemanasan reflux, pemanasan stim (low temperature pyrolisis), dan teknik yang lain. Tumbuhan mempunyai 3 struktur pembina yang berlainan iaitu lignin, hemiselulosa, selulosa. Kebiasannya lignin ini merupakan bahagian yang memberi warna kepada tumbuhan, dan struktur ini juga memeningkan kepala para saintis untuk memboleh kan semua selulosa terhidrolisis, kerana struktur ini bagaikan 'kulit' kepada tumbuhan dan memberikan perlindungan. Ia bertindak seperti 'gam' yang menyatukan struktur selulosa dan hemiselulosa. Setelah proses hidrolisis, proses kawalan pH dimulakan untuk memastikan sel yis dapat hidup iaitu sekitar pH 6.0. Proses respirasi anaerobic yis akan menghasilkan ATP(adenosina trifosfat) dan ethanol sebagai 'side product'. Kebiasaannya tumbuhan akan menghasilkan ethanol ketika proses anaerobik dan haiwan pula menghasilkan asid laktik. Apabila kepekatan ethanol didalam medium penapaian mencapai kepekatan 12%-20% v/v yis tadi akan memasuki peringkat dorman dan tiada proses kehidupan berjalan. Pemisahan ethanol daripada medium menggunakan kaedah penyulingan, tetapi masalah azeotropik akan timbul kerana air akan disuling sekali dan amat sukar unutk memperoleh 100% ethanol. Penggunaan agen azeotropik seperti benzena akan memutuskan ikatan hidrogen antara molekul air dan ethanol. ethanol akan disuling keluar bersama benzena. Ethanol yang disuling keluar akan dikenal pasti melalui keadah spektroskopi sinar infra merah dan GC-MS.

by: Muhammad Aizuddin Bin Zali

Posted from en.wikipedia.org

'First-generation fuels' refer to biofuels made from sugar, starch, vegetable oil, or animal fats using conventional technology.[12]
The most common first generation biofuels are listed below.

Vegetable oil
Main article: Vegetable oil used as fuel
Vegetable oil can be used for either food or fuel; the quality of the oil may be lower for fuel use. Vegetable oil can be used in many older diesel engines (equipped with indirect injection systems), but only in warm climates. In most cases, vegetable oil is used to manufacture biodiesel, which is compatible with most diesel engines when blended with conventional diesel fuel. MAN B&W Diesel, Wartsila and Deutz AG offer engines that are compatible with straight vegetable oil. Used vegetable oil is increasingly being processed into biodiesel, and at a smaller scale, cleaned of water and particulates and used as a fuel.

Biodiesel
Main articles: Biodiesel and Biodiesel around the world
Biodiesel is the most common biofuel in Europe. It is produced from oils or fats using transesterification and is a liquid similar in composition to mineral diesel. Its chemical name is fatty acid methyl (or ethyl) ester (FAME). Oils are mixed with sodium hydroxide and methanol (or ethanol) and the chemical reaction produces biodiesel (FAME) and glycerol. 1 part glycerol is produced for every 10 parts biodiesel.
Biodiesel can be used in any diesel engine when mixed with mineral diesel. In some countries manufacturers cover their diesel engines under warranty for 100% biodiesel use, although Volkswagen Germany, for example, asks drivers to make a telephone check with the VW environmental services department before switching to 100% biodiesel (see biodiesel use). Many people have run their vehicles on biodiesel without problems. However, the majority of vehicle manufacturers limit their recommendations to 15% biodiesel blended with mineral diesel. In many European countries, a 5% biodiesel blend is widely used and is available at thousands of gas stations.[13][14]
In the USA, more than 80% of commercial trucks and city buses run on diesel. Therefore "the nascent U.S. market for biodiesel is growing at a staggering rate—from 25 million gallons per year in 2004 to 78 million gallons by the beginning of 2005. By the end of 2006 biodiesel production was estimated to increase fourfold to more than 1 billion gallons," energy expert Will Thurmond writes in an article for the July-August 2007 issue of THE FUTURIST magazine.

Bioalcohols
Main article: Alcohol fuel
Biologically produced alcohols, most commonly ethanol, and less commonly propanol and butanol, are produced by the action of microorganisms and enzymes through fermentation of sugars or starches (easiest), or celulose (which is more difficult). Biobutanol (also called biogasoline) is often claimed to provide a direct replacement for gasoline, because it can be used directly in a gasoline engine (in a similar way to biodiesel in diesel engines).
Butanol is formed by ABE fermentation (acetone, butanol, ethanol) and experimental modifications of the process show potentially high net energy gains with butanol as the only liquid product. Butanol will produce more energy and allegedly can be burned "straight" in existing gasoline engines (without modification to the engine or car),[15] and is less corrosive and less water soluble than ethanol, and could be distributed via existing infrastructures. DuPont and BP are working together to help develop Butanol.
Ethanol fuel is the most common biofuel worldwide, particularly ethanol fuel in Brazil. Alcohol fuels are produced by fermentation of sugars derived from wheat, corn, sugar beets, sugar cane, molasses and any sugar or starch that alcoholic beverages can be made from (like potato and fruit waste, etc.). The ethanol production methods used are enzyme digestion (to release sugars from stored starches, fermentation of the sugars, distillation and drying. The process requires significant energy input for heat (often unsustainable natural gas fossil fuel).
Cellulosic ethanol production uses non food crops or inedible waste products, which has less of an impact on food. Lignocellulose is the "woody" structural material of plants. This feedstock is abundant and diverse, and in some cases (like citrus peels or sawdust) it is a significant industry-specific disposal problem.
Producing ethanol from cellulose is a more difficult-and-expensive additional-step technical problem to solve. Ruminant livestock (like cattle) eat grass and then use slow enzymatic digestive processes to break it into glucose (sugar). In cellulosic ethanol laboratories, various experimental processes are being used to do the same thing, and then do the above process to make ethanol fuel.
Some scientists have expressed concern that if experimental recombinant DNA genetic engineering continues to be used to develop unprecedented enzymes that break down wood much faster than in nature, such microscopic life forms may accidentally be released into nature, grow exponentially, be distributed by the wind, and eventually destroy the structure of all trees, ending all Earthly life that breathes oxygen released by photosynthesis in trees[citation needed].
Ethanol can be used in petrol engines as a replacement for gasoline; it can be mixed with gasoline to any percentage. Most existing automobile petrol engines can run on blends of up to 15% bioethanol with petroleum/gasoline. Gasoline with ethanol added has higher octane, which means that your engine can typically burn hotter and more efficiently. In high altitude (thin air) locations, some states mandate a mix of gasoline and ethanol as a winter oxidizer to reduce atmospheric polloution emissions.
Ethanol fuel has less BTU energy content, which means it takes more fuel (volume and mass) to go the same distance. More-expensive premium fuels contain less, or no, ethanol. In high-compression engines, less ethanol, slower-burning premium fuel is required to avoid harmful pre-ignition (knocking). Very-expensive aviation gasoline (Avgas) is 100 octane made from 100% petroleum. The high price of zero-ethanol Avgas does not include federal-and-state road-use taxes.
Ethanol is very corrosive to fuel systems, rubber hoses-and-gaskets, aluminum, and combustion chambers. It is therefore illegal to use fuels containing alcohol in aircraft. Ethanol is incompatible with marine fiberglass fuel tanks (it makes them leak). For higher ethanol percentage blends, and 100% ethanol vehicles, engine modifications are required.
Corrosive ethanol cannot be transported in petroleum pipelines, so more-expensive over-the-road stainless-steel tank trucks increase the cost and energy consumption required to deliver ethanol to the customer at the pump.
When considering the total energy consumed by farm equipment, cultivation, planting, fertilizers, pesticides, herbicides, and fungicides made from petroleum, irrigation systems, harvesting, transport of feedstock to processing plants, fermentation, distillation, drying, transport to fuel terminals and retail pumps, and lower ethanol fuel energy content, the net energy content value added and delivered to consumers is very small. And, the net benefit (all things considered) does little to reduce un-sustainable imported oil and fossil fuels required to produce the ethanol.[16]
Many car manufacturers are now producing flexible-fuel vehicles (FFV's), which can safely run on any combination of bioethanol and petrol, up to 100% bioethanol. They dynamically sense exhaust oxygen content, and adjust the engine's computer systems, spark, and fuel injection accordingly. This adds initial cost and ongoing increased vehicle maintenance. Efficiency falls and pollution emissions increase when FFV system maintenance is needed (regardless of the 0%-to-100% ethanol mix being used), but not performed (as with all vehicles). FFV internal combustion engines are becoming increasingly complex, as are multiple-propulsion-system FFV hybrid vehicles, which impacts cost, maintenance, reliability, and useful lifetime longevity.
Alcohol mixes with both petroleum and with water, so ethanol fuels are often diluted after the drying process by absorbing environmental moisture from the atmosphere. Water in alcohol-mix fuels reduces efficiency, makes engines harder to start, causes intermittent operation (sputtering), and oxidizes aluminum (carburetors) and steel components (rust).
Even dry ethanol has roughly one-third lower energy content per unit of volume compared to gasoline, so larger / heavier fuel tanks are required to travel the same distance, or more fuel stops are required. With large current un-sustainable, non-scalable subsidies, ethanol fuel still costs much more per unit of distance traveled than current high gasoline prices.[17]
Methanol is currently produced from natural gas, a non-renewable fossil fuel. It can also be produced from biomass as biomethanol. The methanol economy is an interesting alternative to the hydrogen economy, compared to today's hydrogen produced from natural gas, but not hydrogen production directly from water and state-of-the-art clean solar thermal energy processes.[18]

Biofuel: An alternative renewable fuel

Nowadays, oil demands are raising high, therefore the price of nymex crude oil per barrel are up to $108.67 and the nymex heating oil reaching 307.98 cents per gallon (according to http://www.bloomberg.com/energy/ on 8th of April 2008). Saudi Arabia will last their oil reserve in 50 years. So it is very important for the scientist community to search the best solutions for the matters. Therefore we from the Chemistry Department, University of Malaya, Kuala Lumpur, Malaysia under supervision of Assoc. Prof. Dr. Zainudin Ariffin, initiating our research toward Cellulosic bioethanol from paddy straw. Dr. Teoh as the post-doc in the research while Mr. Muhammad Aizuddin as the final year project student. Anyone can post their comment, ideas, criticism, questions, or others that related to this field.