chemical engineers"who changed the world"-part2

                                                             Rubber, PVC and bubblegum

                                           Waldo Semon

           Like so many innovations, the success of PVC – the world’s second most-used plastic, after polyethylene – is down to an accidental discovery. Waldo Semon, a young chemical engineer a few months into his first proper job with rubber producer BF Goodrich, had meant to find an adhesive that would bond rubber to metal. Semon decided to work with polyvinyl chloride, a brittle polymer universally thought to be totally useless. In an attempt to remove the chlorine, Semon solvated the PVC with a high-boiling solvent before treating it with zinc or a strong organic amine. “Imagine my surprise when I found that the solvated PVC was flexible, resilient and would bounce!,” he later said. “When I later found that the plasticised PVC would resist alkaline, strong acids and most solvents it seemed to me that it would have quite a range of commercial possibility.”

Convincing the management of this potential would prove a challenge in its own right, solved through a canny combination of PVC-coated (and therefore waterproofed) curtains, a vice president fond of camping (but tired of leaking tents) and an ad-hoc demonstration involving a bulging in-try and a decanter of water.

Today, PVC is the material of choice for two out of three water pipes and three quarters of the world’s sanitary sewers, with other applications ranging all the way from credit cards and window frames to electrical insulation tape.

Semon, meanwhile, didn’t rest on his laurels: he went on to develop a process and formula for synthetic rubber – a highly sought-after commodity during World War II, considering that the war had cut off supplies of natural rubber from Asia and Germany would not reveal the secret of producing “Buna-S”, the only other known synthetic rubber at the time. Through hard work and determination, Semon and his team developed the Ameripol rubber process, which by 1944 saw the US produce twice as much synthetic rubber as the world’s production of natural rubber had totaled before the war.

                       Engineering the sexual revolution

      George Rosenkranz, Luis Miramontes and Carl Djerassi

                  Not all of chemical engineering’s contributions revolve around heavy industry, chemicals and refining. In pharmaceuticals, too, they have made their mark – and one of their contributions to the pharma industry has had social consequences that could hardly have been more profound.

If you’re a modern woman, who takes it for granted that women can expect the same sort of career path as men and who revels in the liberty of being able to choose if and when to have children, then you, too, owe a debt to George Rosenkranz, Luis Miramontes and Carl Djerassi. The three – two chemical engineers and one chemist, two Jewish refugees from Europe and one local Mexican – were responsible for synthesising the first synthetic progesterone, which would go on to be used in the contraceptive pill.

Building on a process discovered by the maverick chemist Russel Marker, who synthesised progesterone from sapogenins, natural steroids found in Mexican yams, Rosenkranz, Miramontes and Djerassi created a synthetic variant that not only was a lot more active, but would also survive absorption through the digestive tract.

Not that anyone thought of using it as a contraceptive, at least to begin with; initial target indications were menstrual disorders and, ironically, infertility. Even once its contraceptive effect became known, fear of religiously-motivated boycotts caused companies to veer away from the drug. Rosenkranz says: “I went around Europe and the world offering the contraceptive, but nobody wanted it.”

A sustained campaign by women’s rights campaigners Margaret Sanger and Katharine Dexter McCormick, backed up by deep pockets and research funding, changed all that. Today, the Pill is used by over 100m women ever day. The freedom to choose and time when to have children has allowed women to claim equality in the workplace, and the sharp drop in birth rates in countries wherever the Pill is easy to obtain is arguably chemical engineering’s greatest-ever contribution to sustainability.

                                           From fuel hero to climate zero

                                        Thomas Midgley

                   Not everyone who changed the world did so in a way we’d celebrate. And sometimes, it takes the benefit of hindsight to realise the true impact of an apparently beneficial innovation. That certainly is the case for Thomas Midgley – mechanical engineer, chemist and chemical engineer – who during his lifetime was celebrated as a prolific inventor with a can-do attitude who had solved the longstanding and damaging problem of engine knock and gifted the world affordable and safe coolants for refrigerators and air conditioning units, as well as a universal safe propellant for aerosols.

Today, he is described, in a much less reverential tones, as the man who “had more impact on the atmosphere than any other single organism in Earth’s history.” Midgley’s innovations? Tetraethyl lead and chlorofluorocarbons (CFCs).

Midgley had, by all accounts, a brilliantly inventive mind, untroubled by received wisdom and undaunted by even the most complex tasks. When his scientific reasoning sent him in the wrong direction, strokes of sheer luck would deliver the unexpected breakthrough, such as in the discovery of TEL. Though his hands-on pragmatic attitude makes for chilling reading for today’s engineers, especially when it comes to the conditions found in the early TEL production plants and Midgley’s cheerful dismissal of the warnings he received about TEL’s poisonous side-effects.

While there were some early indications of the dangers of TEL (even if they were downplayed and dismissed at the time), it would take much longer for the side effects of Midley’s second innovation to become known. For thirty years, CFCs – particularly Midgley’s innovation, Freon – were the workhorse of the refrigeration industry and the propellant of choice in just about any hairspray, deodorant or insecticide spray. Unlike the available alternatives, Freon was neither toxic, flammable nor explosive.

At the time of Midgley’s untimely death at the age of 55, he was highly celebrated and decorated, holder of numerous awards and prestigious offices. His legacy stayed with us for many years more, though perhaps not in the way he and his contemporaries might have anticipated.

                                          Cool inventions

                           Carl von Linde and William Hampson

                    The liquefaction and separation of air is one of those processes that many engineers worked on over the years, but only one – or rather two – would succeed at. Two very similar processes for the liquefaction of air were independently developed in Germany and the UK and patented within weeks of each other; the first by the mechanical engineer Carl von Linde, the second by a hitherto unknown, classics graduate and barrister William Hampson.

Both used air itself as a refrigerant, exploiting the Joule Thompson effect, which describes how gas gets colder as it expands. The effect is even more pronounced if the gas was previously compressed and chilled. Harnessing the effect in a virtuous cycle, by allowing compressed cooled air to expand in a counter-current heat exchanger so it cools the incoming compressed air to ever-lower temperatures, both inventors eventually cooled the air to -190ºC: the point at which it turns liquid.

It might have taken von Linde three days of running increasingly cold air through an incredibly long steel tube which he’d packed in wool for insulation, but on 29 May 1895, he eventually got there: “With clouds rising all around it, the pretty bluish liquid was poured into a large metal bucket,” he writes in his autobiography. “The hourly yield was about three litres. For the first time on such a scale air had been liquefied, and using tools of amazing simplicity compared to what had been used before.”

Where von Linde was an engineer, industrialist and already an expert in refrigeration before he started, Hampson was a complete unknown, with no relevant training and no record of what might have perked his interest in sciences and engineering. Nevertheless, his process was both simpler and more efficient than von Linde’s, liquefying air in a mere 20 minutes compared with the three days of von Linde’s early attempts.

The Hampson-Linde cycle gave rise to the modern industrial gases industry, provided pure gases for countless industrial processes and paved the way for  the discovery of several rare gases.

                                    Degrees of separation

                                       Csaba Horváth

There are those who have hailed chromatography as one of the most significant developments of the 20^th century, and yet few people outside a chemistry lab would have any understanding of what chromatography is, or what it is used for. A classic ‘behind the scenes’ technology, chromatography is the workhorse of analytical chemistry, and finds extensive use in healthcare, quality control, and drug discovery to name but a few fields.

Pharmaceutical companies use it to isolate active ingredients and ensure accurate dosing, hospitals use it to identify poisons or drugs in patients’ blood; environmental laboratories rely on it to check for contaminants; forensic scientists apply it to analyse samples from a crime scene; industrial chemists rely on it to determine the composition of petroleum oil, check the level of additives in foods, monitor pesticide contamination, and so on.

Key to making the process widely applicable was the adaptation of gas chromatography to liquids. This opened up its use for the separation of organic and biological molecules, many of which are involatile and too fragile for vaporization.

That achievement goes to the Hungarian born chemical engineer, Csaba Horváth, the father of modern high performance liquid chromatography. Horwath took an early interest in separation sciences and – unusually for a chemical engineer during the 1960s – in biochemical engineering. Adapting recent advances in gas chromatography to the nascent science of liquid chromatography, Horváth dramatically speeded up throughput and ramped up sensitivity while reducing the size of the equipment.

Today, HPLC is so sensitive that the characteristic patterns of peaks not only identify different molecules in a sample, but – thanks to very subtle differences in production processes and batch chemistry that give chemicals a very unique “fingerprint” also the production plant they came from.

Csaba Horváth may not be a household name, but without him, the world would be a much scarier place.

                                             Man of steel

                                          Henry Bessemer

If the industrial revolution was built on steel, then the father of the industrial revolution was Henry Bessemer. It was the Bessemer process that made steel available in industrial quantities at an affordable price.

Patented in 1855, the Bessemer process reduced the cost of steel from £50–60/t to £6–7/t and was accompanied by vast increases in scale and speed of steel production. Steel girders for bridges, buildings, railroads, skyscrapers – all were unimaginable before Bessemer. The same goes for modern steel ships, steel wire, high-pressure boilers (and with them, the steam engine), not to mention turbines for power generation.

Bessemer was a prolific inventor. Despite no university education, he patented innovations in fields as diverse as pigment production and ship building.

During his experiments with steelmaking, he discovered that contact with hot air would turn pig iron into steel, prompting Bessemer to take the – at the time highly counter-intuitive – step of forcing air directly through the molten iron. He was lucky that the resulting reaction, which was extremely violent, did not permanently damage to his workshop. But at least after just 20 minutes of mild explosions, violent eruptions and showes of red-hot slag, Bessemer was left with a converter full of steel.

Once he had convinced himself that there was no way of toning down the violence of the reaction, Bessemer channelled his efforts into developing a reactor vessel designed to contain the violent inferno with some degree of reliability and safety. The result: the Bessemer Converter.

This in turn prompted the rise of steel as a ubiquitous construction material, driving the second industrial revolution, and made Henry Bessemer a very, very wealthy man indeed.

                                     Power Stores

                                     Yoshio Nishi

Handheld electronics and gadgets – from mobile phones to laptops – have transformed the way we live over the past decade or so. But the revolution led by Steve Jobs and his slightly less famous compatriot, Adam Osborne (the inventor of the laptop), would not have been possible without high-power rechargeable batteries, and they were brought to market thanks to a chemical engineer. Like many engineers, Yoshio Nishi is not a household name but frankly he should be, for he led the team that turned the lithium ion battery from a research concept into practical, commercially viable reality.

Nishi, who studied solid physical chemistry at the engineering department of Keio University in Tokyo, spent a lifetime working for Sony. In the mid-1980s he was appointed general manager of the lithium ion battery development team.

Lithium ion batteries promised to overcome the environmental problems associated with nickel-cadmium batteries, and also had a much greater energy density. Even so in the early stages of development many thought that lithium was too dangerous, the technology too risky and the whole concept premature.

One of the biggest challenges was making the battery safe even when subjected to serious abuse.

The team devised vents to prevent overpressure, introduced a porous membrane separating anode and cathode that would become impermeable in the event of a temperature spike, added elements with a positive temperature coefficient to prevent thermal runaway, and designed a mechanical link that would disconnect the cathode lead if pressure built up inside the battery.

Even so, lithium ion batteries have caused many phones and laptops to spontaneously combust over the years, triggering huge product recalls. Nishi blames price competition putting pressure on engineers to use cheaper materials and other shortcuts, and device designers ignoring the battery’s usage specifications.

His advice: Engineers have a duty to ensure management understands the safety implications of cost cuts, and not to compromise easily on what they believe is important.

                                Driving units and progress

                                        Arthur D Little

If chemical engineering is the application of science to industry, then one of its most influential pioneers was Arthur D Little. Founder of the international consultancy that bears his name, Little’s achievements stretch much further: he developed the concept of unit operations – still a cornerstone of the profession – and used it to define the role of chemical engineering in industrial chemistry. He was also one of six founding members of the American Institute of Chemical Engineers and the driving force behind the creation of the chemical engineering practice school at the Massachusetts Institute of Technology in 1920.

Little was far ahead of his time in recognising the importance of long-term industrial research. The turn of the century saw rapid industrial development and process design, but corporate R&D remained an intermittent and hap-hazard affair, stopping and starting on a project-by-project basis. Little was an early and vociferous proponent of organised, longterm R&D, both within companies and at universities, which he lambasted for failing to provide adequate equipment for industrial research.

The consultancy he set up was one way of filling this gap. Little and the people he hired applied themselves tirelessly to improving processes and perfecting products. Their tenacity paid off: within five years of its foundation in 1905, the Arthur D Little consultancy had made a name for itself and ran specialised departments covering fuel engineering, forest products, textiles and more.

To the profession, his most lasting legacy is the concept of unit operations. He explained: “Any chemical process, on whatever scale conducted, may be resolved into a coordinate series of what may be termed ‘unit operations’, as pulverising, dyeing, roasting, crystallising, filtering, evaporation, electrolysing and so on.” He added that the number of different unit operations is quite finite – the great complexity of chemical engineering is the result of the variety of conditions under which these unit operations are carried out.

Almost 100 years later, his analysis remains as accurate as ever.

         

                                              

chemical engineers" who changed the world"-part1

                                                         Upping the octane 
                                  Vladimir Haensel

To many an engineer the phrase “It cannot be done”  is like a red rag to a bull. Vladimir Haensel, process research coordinator with UOP, was no exception. Haensel was working on petroleum cracking and looking for ways of increasing the octane rating of the resulting fuels – at the time, in 1941, an octane rating of 65 RON was the norm. Such a low octane rating makes a fuel very likely to combust prematurely, causing serious engine knock – which in turn makes it impossible to use efficient high-compression engines.

Haensel was looking for a suitable catalyst for the cracking process and was convinced that platinum would be perfect for the job. Except, of course, that platinum was extremely rare and prohibitively expensive – “it cannot be done” was the received wisdom.

But what, thought Haensel, if he could make do with a vanishingly small quantity of platinum? What if on top of that he could regenerate any fouled catalyst in situ, allowing him to – in theory at least – run the process indefinitely?

His refusal to accept conventional wisdom led to the creation of a heterogeneous alumina-supported platinum catalyst that would very effectively dehydrogenate the hydrocarbons in the C6–C10 paraffins and transform the resulting unsaturated hydrocarbons into nice aromatic rings. By working with a highly-dispersed catalyst with extremely small platinum particles, Haensel managed to reduce the platinum content in the catalyst to as little as 0.01%. The so-called ‘platforming’ (platinum reforming) process was born.

The first platforming unit started up in 1949 and is still very much with us – some minor improvements aside. Today the vast majority of our fuels are produced through a platforming process. Without Haensel’s determination, we could say goodbye to today’s supercars and hello to the backfiring smoke-belching cars of the 1930s.

                              Plastic fantastic

         Reginald Gibson, Eric Fawcett, Michael Perrin                                                                                                                       

Polyethylene (PE) is everywhere. From shopping bags to Tupperware boxes, from plastic toys to water pipes and even hip replacements, it’s PE’s versatility that makes it the world’s most common plastic.

Its commercial success came courtesy of two ICI chemists, Reginald Gibson and Eric Fawcett, who in 1933 experimented with ethylene and benzaldehyde at high pressure. The reaction yielded a mysterious waxy solid but the reaction was fickle – attempts to reproduce it would as often as not result in a very loud bang and a mixture of hydrogen and carbon. Nobody could work out initially why the experiment would result in these quite spectacular failures, and ICI eventually decided to stop the research before someone came to serious grief.

It later transpired that the key to making the experiment work was oxygen: if there’s too little, nothing happens, too much and the mixture explodes. It had been pure luck that some of the ethylene bottles used in the early experiments had been contaminated with just the right amount of oxygen. 

With high-pressure chemistry still in its infancy, there was little off-the-shelf equipment, and it fell to the team’s resident engineer, Dermot Manning, to design and build most of the reaction vessels. A key problem was sealing the vessels, as the standard lens ring would not hold gas at pressures above 300 atm – and ICI wase working at well over 1,000 atm here. Manning devised a self-sealing wave ring, which used the rising internal pressure to seal the wavy circumference of the ring into its seat, which overcame the problem.

Full-scale production of PE started the very day Germany invaded Poland, and a polymer that had been destined for telecommunications cable was used to insulate airborne radar instead. This proved to be an important advantage, as it enabled the British forces to create a radar system that was light enough to place on fighter planes, which helped their supply ships avoid German submarines.

                                                 Fuelling a way of life 

Donald Campbell, Homer Martin, Eger Murphree                                                                                                      and charles Tyson

        Modern life runs – quite literally – on the products of a fluid catalytic cracking unit. Our cars run on petrol, the planes on jet fuel, we pick up our food from the supermarket (or bring it from home) wrapped in polyethylene film and wash it down with drinks from a polycarbonate bottle, while standing on a polypropylene carpet.

Yet this ubiquitous feedstock of modern life in all its aspects would be a lot rarer – not to mention a great deal more expensive – if it wasn’t for the workhorse of the refining industry, the fluid catalytic cracking (FCC) unit.

Some 400 FCC units are in operation around the world today. And each and every one of them can trace its ancestry back to one such unit, the Model I FCC, which started up in Baton Rouge, Louisiana, on 25 May 1942.

The 17,000 bbl/d unit was largely the brainchild of four chemical engineers, known as “the four horsemen”, working for the New Jersey company Standard Oil. They were Donald Campbell, Homer Martin, Eger Murphree and Charles Tyson.

The four developed today’s modern  FCC process largely because their employer (and several other companies) did not want to pay the hefty $50m licensing fee for another early catalytic cracking process, developed by the French engineer Eugene Houdry and the pharmacist EA Prudhomme. But while the Houdry process was a semi-batch process using a fixed-bed catalyst, the real breakthrough for the “four horsemen” (and their advisors at MIT) was to realise that under certain circumstances, a powdered catalyst could behave like a liquid. This paved the way for the continuous process that was so efficient that it not only rapidly outcompeted the Houdry process, but remains in continuous use 60 years on.

                        Pfizer’s penicillin pioneers

                     Jasper Kane and John McKeen

Sometimes it’s not the innovation itself that matters – it’s making it available in quantity and at the right time. Scale-up, in other words.

Ensuring that there was sufficient penicillin to treat the hundreds of thousands of soldiers that took part in the D-Day landings during World War II was not the work of Alexander Fleming; it was chemical engineers who made that happen. While many worked on scaling up production of penicillin, it was Pfizer chemist Jasper Kane and chemical engineer John McKeen who arguably made the biggest contribution.

The two cracked the problem of production via deep-tank fermentation. Since penicillin requires air to grow, the biggest problem was designing an aerated, stirred tank that would reliably and efficiently produce quantities of the notoriously fickle drug.

War-time materials shortages forced Pfizer to take a huge commercial gamble on producing the drug: with no means of acquiring extra reactors, Pfizer had to re-configure units producing tried and tested cash products.

Factory manager John Smith was reluctant. “The mould is as temperamental as an opera singer, the yields are low, the isolation is difficult, the extraction is murder, the purification invites disaster and the assay is unsatisfactory. Think of the risks and then think of the expensive investment in big tanks – think of what it means if you lose a 2000-gallon tank against what you lose if a flask goes bad. Is it worth it?”

It is to the credit of Kane that he did not back down, and convinced his bosses to do the right thing and take the commercial gamble. And it is to the credit of McKeen and his team, who worked sixteen hours a day, seven days a week, to complete the scale-up in just six months. The D-day landings alone saw 150,000 soldiers treated with penicillin, and 90% of the doses supplied were supplied by Pfizer.

                               

opportunities in chemical engineering

cpcl report ..part3

REFINING PROCESS IN CPCL:

Every refinery begins with the separation of crude oil into different fractions by distillation.

The fractions are further treated to convert them into mixtures of more useful saleable products by various methods such as cracking, reforming, alkylation, polymerisation and isomerisation. These mixtures of new compounds are then separated using methods such as fractionation and solvent extraction. Impurities are removed by various methods, e.g. dehydration, desalting, sulphur removal and hydrotreating.

Refinery processes have developed in response to changing market demands for certain products. With the advent of the internal combustion engine the main task of refineries became the production of petrol. The quantities of petrol available from distillation alone was insufficient to satisfy consumer demand. Refineries began to look for ways to produce more and better quality petrol. Two types of processes have been developed:

• breaking down large, heavy hydrocarbon molecules
• reshaping or rebuilding hydrocarbon molecules
• Distillation (Fractionation)

                      Crude oil is a mixture of hydrocarbons with different boiling temperatures, it can be separated by distillation into groups of hydrocarbons that boil between two specified boiling points. Two types of distillation are performed: atmospheric and vacuum.
Atmospheric distillation takes place in a distilling column at or near atmospheric pressure. The crude oil is heated to 350 - 400^oC and the vapour and liquid are piped into the distilling column. The liquid falls to the bottom and the vapour rises, passing through a series of perforated trays (sieve trays). Heavier hydrocarbons condense more quickly and settle on lower trays and lighter hydrocarbons remain as a vapour longer and condense on higher trays.
Liquid fractions are drawn from the trays and removed. In this way the light gases, methane, ethane, propane and butane pass out the top of the column, petrol is formed in the top trays, kerosene and gas oils in the middle, and fuel oils at the bottom. Residue drawn of the bottom may be burned as fuel, processed into lubricating oils, waxes and bitumen or used as feedstock for cracking units.
To recover additional heavy distillates from this residue, it may be piped to a second distillation column where the process is repeated under vacuum, called vacuum distillation.This allows heavy hydrocarbons with boiling points of 450^oC and higher to be separated without them partly cracking into unwanted products such as coke and gas.
The heavy distillates recovered by vacuum distillation can be converted into lubricating oils by a variety of processes. The most common of these is called solvent extraction. In one version of this process the heavy distillate is washed with a liquid which does not dissolve in it but which dissolves (and so extracts) the non-lubricating oil components out of it. Another version uses a liquid which does not dissolve in it but which causes the non-lubricating oil components to precipitate (as an extract) from it. Other processes exist which remove impurities by adsorption onto a highly porous solid or which remove any waxes that may be present by causing them to crystallise and precipitate out.

Reforming

Reforming is a process which uses heat, pressure and a catalyst (usually containing platinum) to bring about chemical reactions which upgrade naphthas into high octane petrol and petrochemical feedstock. The naphthas are hydrocarbon mixtures containing many paraffins and naphthenes. In Australia, this naphtha feedstock comes from the crudes oil distillation or catalytic cracking processes, but overseas it also comes from thermal cracking and hydrocracking processes. Reforming converts a portion of these compounds to isoparaffins and aromatics, which are used to blend higher octane petrol.

• paraffins are converted to isoparaffins
• paraffins are converted to naphthenes
• naphthenes are converted to aromatics

e.g.

	catalyst
heptane	->	toluene	+	hydrogen
	C7H16	->	C7H8	+	4H2

	catalyst
cyclohexane	->	benzene	+	hydrogen
	C6H12	->	C6H6	+	3H2

Cracking

Cracking processes break down heavier hydrocarbon molecules (high boiling point oils) into lighter products such as petrol and diesel. These processes include catalytic cracking, thermal cracking and hydrocracking.

e.g.

A typical reaction:

	catalyst
	C16H34	->	C8H18	+	C8H16

Catalytic cracking is used to convert heavy hydrocarbon fractions obtained by vacuum distillation into a mixture of more useful products such as petrol and light fuel oil. In this process, the feedstock undergoes a chemical breakdown, under controlled heat (450 - 500^oC) and pressure, in the presence of a catalyst - a substance which promotes the reaction without itself being chemically changed. Small pellets of silica - alumina or silica - magnesia have proved to be the most effective catalysts.

The cracking reaction yields petrol, LPG, unsaturated olefin compounds, cracked gas oils, a liquid residue called cycle oil, light gases and a solid coke residue. Cycle oil is recycled to cause further breakdown and the coke, which forms a layer on the catalyst, is removed by burning. The other products are passed through a fractionator to be separated and separately processed.

Fluid catalytic cracking uses a catalyst in the form of a very fine powder which flows like a liquid when agitated by steam, air or vapour. Feedstock entering the process immediately meets a stream of very hot catalyst and vaporises. The resulting vapours keep the catalyst fluidised as it passes into the reactor, where the cracking takes place and where it is fluidised by the hydrocarbon vapour. The catalyst next passes to a steam stripping section where most of the volatile hydrocarbons are removed. It then passes to a regenerator vessel where it is fluidised by a mixture of air and the products of combustion which are produced as the coke on the catalyst is burnt off. The catalyst then flows back to the reactor. The catalyst thus undergoes a continuous circulation between the reactor, stripper and regenerator sections.

The catalyst is usually a mixture of aluminium oxide and silica. Most recently, the introduction of synthetic zeolite catalysts has allowed much shorter reaction times and improved yields and octane numbers of the cracked gasolines.

Thermal cracking uses heat to break down the residue from vacuum distillation. The lighter elements produced from this process can be made into distillate fuels and petrol. Cracked gases are converted to petrol blending components by alkylation or polymerisation. Naphtha is upgraded to high quality petrol by reforming. Gas oil can be used as diesel fuel or can be converted to petrol by hydrocracking. The heavy residue is converted into residual oil or coke which is used in the manufacture of electrodes, graphite and carbides.

This process is the oldest technology and is not used in Australia.

Hydrocracking can increase the yield of petrol components, as well as being used to produce light distillates. It produces no residues, only light oils. Hydrocracking is catalytic cracking in the presence of hydrogen. The extra hydrogen saturates, or hydrogenates, the chemical bonds of the cracked hydrocarbons and creates isomers with the desired characteristics. Hydrocracking is also a treating process, because the hydrogen combines with contaminants such as sulphur and nitrogen, allowing them to be removed.

Gas oil feed is mixed with hydrogen, heated, and sent to a reactor vessel with a fixed bed catalyst, where cracking and hydrogenation take place. Products are sent to a fractionator to be separated. The hydrogen is recycled. Residue from this reaction is mixed again with hydrogen, reheated, and sent to a second reactor for further cracking under higher temperatures and pressures.

In addition to cracked naphtha for making petrol, hydrocracking yields light gases useful for refinery fuel, or alkylation as well as components for high quality fuel oils, lube oils and petrochemical feedstocks.

Following the cracking processes it is necessary to build or rearrange some of the lighter hydrocarbon molecules into high quality petrol or jet fuel blending components or into petrochemicals. The former can be achieved by several chemical process such as alkylation and isomerisation.

Alkylation

Olefins such as propylene and butylene are produced by catalytic and thermal cracking. Alkylation refers to the chemical bonding of these light molecules with isobutane to form larger branched-chain molecules (isoparaffins) that make high octane petrol.

Olefins and isobutane are mixed with an acid catalyst and cooled. They react to form alkylate, plus some normal butane, isobutane and propane. The resulting liquid is neutralised and separated in a series of distillation columns. Isobutane is recycled as feed and butane and propane sold as liquid petroleum gas (LPG).

e.g.

			catalyst
isobutane	+	butylene	->	isooctane
	C4H10	+	C4H8	->	C8H18

Isomerisation

Isomerisation refers to chemical rearrangement of straight-chain hydrocarbons (paraffins), so that they contain branches attached to the main chain (isoparaffins). This is done for two reasons:

• they create extra isobutane feed for alkylation
• they improve the octane of straight run pentanes and hexanes and hence make them into better petrol blending components.

Isomerisation is achieved by mixing normal butane with a little hydrogen and chloride and allowed to react in the presence of a catalyst to form isobutane, plus a small amount of normal butane and some lighter gases. Products are separated in a fractionator. The lighter gases are used as refinery fuel and the butane recycled as feed.

Pentanes and hexanes are the lighter components of petrol. Isomerisation can be used to improve petrol quality by converting these hydrocarbons to higher octane isomers. The process is the same as for butane isomerisation.

Polymerisation
Under pressure and temperature, over an acidic catalyst, light unsaturated hydrocarbon molecules react and combine with each other to form larger hydrocarbon molecules. Such process can be used to react butenes (olefin molecules with four carbon atoms) with iso-butane (branched paraffin molecules, or isoparaffins, with four carbon atoms) to obtain a high octane olefinic petrol blending component called polymer gasoline.

Hydrotreating and sulphur plants

A number of contaminants are found in crude oil. As the fractions travel through the refinery processing units, these impurities can damage the equipment, the catalysts and the quality of the products. There are also legal limits on the contents of some impurities, like sulphur, in products.

Hydrotreating is one way of removing many of the contaminants from many of the intermediate or final products. In the hydrotreating process, the entering feedstock is mixed with hydrogen and heated to 300 - 380^oC. The oil combined with the hydrogen then enters a reactor loaded with a catalyst which promotes several reactions:

• hydrogen combines with sulphur to form hydrogen sulphide (H₂S)
• nitrogen compounds are converted to ammonia
• any metals contained in the oil are deposited on the catalyst
• some of the olefins, aromatics or naphthenes become saturated with hydrogen to become paraffins and some cracking takes place, causing the creation of some methane, ethane, propane and butanes.

Sulphur recovery plants

The hydrogen sulphide created from hydrotreating is a toxic gas that needs further treatment. The usual process involves two steps:

• the removal of the hydrogen sulphide gas from the hydrocarbon stream
• the conversion of hydrogen sulphide to elemental sulphur, a non-toxic and useful chemical.

Solvent extraction, using a solution of diethanolamine (DEA) dissolved in water, is applied to separate the hydrogen sulphide gas from the process stream. The hydrocarbon gas stream containing the hydrogen sulphide is bubbled through a solution of diethanolamine solution (DEA) under high pressure, such that the hydrogen sulphide gas dissolves in the DEA. The DEA and hydrogen mixture is the heated at a low pressure and the dissolved hydrogen sulphide is released as a concentrated gas stream which is sent to another plant for conversion into sulphur.

Conversion of the concentrated hydrogen sulphide gas into sulphur occurs in two stages.

1. Combustion of part of the H₂S stream in a furnace, producing sulphur dioxide (SO₂) water (H₂O) and sulphur (S).

2H2S

+

2O2

->

SO2

+

S

+

2H2O

2. Reaction of the remainder of the H₂S with the combustion products in the presence of a catalyst. The H₂S reacts with the SO₂ to form sulphur.

2H2S

+

2O2

->

3S

+

2H2O

As the reaction products are cooled the sulphur drops out of the reaction vessel in a molten state. Sulphur can be stored and shipped in either a molten or solid state.

CRUDE  OIL  ATMOSPHERIC  DISTILLATION  PROCESS:

              The crude oil distillation unit (CDU) is the first processing unit in virtually all petroleum refineries. The CDU distills the incoming crude oil into various fractions of different boiling ranges, each of which are then processed further in the other refinery processing units. The CDU is often referred to as the atmospheric distillation unit because it operates at slightly above atmospheric pressure.

Below is a schematic flow diagram of a typical crude oil distillation unit. The incoming crude oil is preheated by exchanging heat with some of the hot, distilled fractions and other streams. It is then desalted to remove inorganic salts (primarily sodium chloride).

Following the desalter, the crude oil is further heated by exchanging heat with some of the hot, distilled fractions and other streams. It is then heated in a fuel-fired furnace (fired heater) to a temperature of about 398 °C and routed into the bottom of the distillation unit.

The cooling and condensing of the distillation tower overhead is provided partially by exchanging heat with the incoming crude oil and partially by either an air-cooled or water-cooled condenser. Additional heat is removed from the distillation column by a pumparound system as shown in the diagram below.

VACCUM  DISTILLATION  UNIT:

                            Vacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapor pressure (usually less than atmospheric pressure) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points). This distillation method works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure. Vacuum distillation is used with or without heating the mixture.

Petroleum crude oil is a complex mixture of hundreds of different hydrocarbon compounds generally having from 3 to 60carbon atoms per molecule, although there may be small amounts of hydrocarbons outside that range. The refining of crude oil begins with distilling the incoming crude oil in a so-called atmospheric distillation column operating at pressures slightly above atmospheric pressure.

In distilling the crude oil, it is important not to subject the crude oil to temperatures above 370 to 380 °C because the high molecular weight components in the crude oil will undergo thermal cracking and form petroleum coke at temperatures above that. Formation of coke would result in plugging the tubes in the furnace that heats the feed stream to the crude oil distillation column. Plugging would also occur in the piping from the furnace to the distillation column as well as in the column itself.

The constraint imposed by limiting the column inlet crude oil to a temperature of more than 370 to 380 °C yields a residual oil from the bottom of the atmospheric distillation column consisting entirely of hydrocarbons that boil above 370 to 380 °C.

To further distill the residual oil from the atmospheric distillation column, the distillation must be performed at absolute pressures as low as 10 to 40 mmHg (also referred to as Torr) so as to limit the operating temperature to less than 370 to 380 °C.

Image 1 is a photograph of a large vacuum distillation column in a petroleum refinery and Image 2 is a process diagram of a petroleum refinery vacuum distillation column that depicts the internals of the column.

The 10 to 40 mmHg absolute pressure in a vacuum distillation column increases the volume of vapor formed per volume of liquid distilled. The result is that such columns have very large diameters.

Distillation columns such those in Images 1 and 2, may have diameters of 15 meters or more, heights ranging up to about 50 meters, and feed rates ranging up to about 25,400 cubic meters per day (160,000 barrels per day).

The vacuum distillation column internals must provide good vapor-liquid contacting while, at the same time, maintaining a very low pressure increase from the top of the column top to the bottom. Therefore, the vacuum column uses distillation trays only where withdrawing products from the side of the column (referred to as side draws). Most of the column uses packing material for the vapor-liquid contacting because such packing has a lower pressure drop than distillation trays. This packing material can be either structured sheet metal or randomly dumped packing such as Raschig rings.

The absolute pressure of 10 to 40 mmHg in the vacuum column is most often achieved by using multiple stages of steam jet ejectors. 

HYDRO CRACKING:

The hydrocracking process is used to convert waxy distillate and deasphalted oil (DAO) into kerosine and gasoil by breaking down some of their constituents. The process is carried out in two stages, the first to reduce the amount of nitrogen, sulfur and oxygen impurities that may Long-chain alkanes of more than twenty carbon atoms each the second stage catalyst, and the second to continue the process of cracking, hydrogenating and isomerising the compounds in the oil. The reactions occurring are denitrogenation, desulfurisation, deoxygenation, hydrogenation, hydrocracking, isomerisation, all of which are exothermic and all of which, except for isomerisation, consume hydrogen. The heat released is absorbed by injecting cold hydrogen quench gas between the catalyst beds. Without the quench the heat released would generate high temperatures and rapid reactions leading to greater heat release and an eventual runaway.

 FLUID  CATALYTIC  CRACKING  UNIT:

                            Fluid catalytic cracking (FCC) is the most important conversion process used in petroleum refineries. It is widely used to convert the high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases, and other products. Cracking of petroleum hydrocarbons was originally done by thermal cracking, which has been almost completely replaced by catalytic cracking because it produces more gasoline with a higher octane rating. It also produces byproduct gases that are more olefinic, and hence more valuable, than those produced by thermal cracking.

The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from about 200 to 600 or higher. This portion of crude oil is often referred to as heavy gas oil. The FCC process vaporizes and breaks the long-chain molecules of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.

In effect, refineries use fluid catalytic cracking to correct the imbalance between the market demand for gasoline and the excess of heavy, high boiling range products resulting from the distillation of crude oil.

As of 2006, FCC units were in operation at 400 petroleum refineries worldwide and about one-third of the crude oil refined in those refineries is processed in an FCC to produce high-octane gasoline and fuel oils.  During  2007, the FCC units in the United States processed a total of 5,300,000 barrels (834,300,000 litres) per day of feedstock and FCC units worldwide processed about twice that amount.

The modern FCC units are all continuous processes which operate 24 hours a day for as much as 2 to 3 years between shutdowns for routine maintenance.

There are a number of different proprietary designs that have been developed for modern FCC units. Each design is available under a license that must be purchased from the design developer by any petroleum refining company desiring to construct and operate an FCC of a given design.

Basically, there are two different configurations for an FCC unit: the "stacked" type where the reactor and the catalyst regenerator are contained in a single vessel with the reactor above the catalyst regenerator and the "side-by-side" type where the reactor and catalyst regenerator are in two separate vessels. These are the major FCC designers and licensors:

Side-by-side configuration:

§  CB&I

§  ExxonMobil Research and Engineering (EMRE)

§  Shell Global Solutions International

§  Stone & Webster Engineering Corporation (The Shaw Group) / Institut Francais Petrole (IFP)

§  Universal Oil Products (UOP) — currently fully owned subsidiary of Honeywell

Stacked configuration:

§  Kellogg Brown & Root (KBR)

Each of the proprietary design licensors claims to have unique features and advantages. A complete discussion of the relative advantages of each of the processes is well beyond the scope of this article. Suffice it to say that all of the licensors have designed and constructed FCC units that have operated quite satisfactorily.

Reactor and Regenerator

The reactor and regenerator is considered to be the heart of the Fluid Catalytic Cracking Unit. The schematic flow diagram of a typical modern FCC unit in Figure 1 below is based upon the "side-by-side" configuration. The preheated high-boiling petroleum feedstock (at about 315 to 430 °C) consisting of long-chain hydrocarbon molecules is combined with recycle slurry oil from the bottom of the distillation column and injected into the catalyst riser where it is vaporized and cracked into smaller molecules of vapor by contact and mixing with the very hot powdered catalyst from the regenerator. All of the cracking reactions take place in the catalyst riser within a period of 2-4 seconds. The hydrocarbon vapors "fluidize" the powdered catalyst and the mixture of hydrocarbon vapors and catalyst flows upward to enter the reactor at a temperature of about 535 °C and a pressure of about 1.72barg.

The reactor is in fact merely a vessel in which the cracked product vapors are: (a) separated from the so-called spent catalyst by flowing through a set of two-stage cyclones within the reactor and (b) the spent catalyst flows downward through a steam stripping section to remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator. The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst line.

Since the cracking reactions produce some carbonaceous material (referred to as coke) that deposits on the catalyst and very quickly reduces the catalyst reactivity, the catalyst is regenerated by burning off the deposited coke with air blown into the regenerator. The regenerator operates at a temperature of about 715 °C and a pressure of about 2.41 barg. The combustion of the coke is exothermic and it produces a large amount of heat that is partially absorbed by the regenerated catalyst and provides the heat required for the vaporization of the feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that reason, FCC units are often referred to as being 'heat balanced'.

The hot catalyst (at about 715 °C) leaving the regenerator flows into a catalyst withdrawal well where any entrained combustion flue gases are allowed to escape and flow back into the upper part to the regenerator. The flow of regenerated catalyst to the feedstock injection point below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot flue gas exits the regenerator after passing through multiple sets of two-stage cyclones that remove entrained catalyst from the flue gas,

The amount of catalyst circulating between the regenerator and the reactor amounts to about 5 kg per kg of feedstock, which is equivalent to about 4.66 kg per litre of feedstock. Thus, an FCC unit processing 75,000 barrels per day (11,900 m³/d) will circulate about 55,900 metric tons per day of catalyst.

CATALYSTS

Modern FCC catalysts are fine powders with a bulk density of 0.80 to 0.96 g/cc and having a particle size distribution ranging from 10 to 150 μm and an average particle size of 60 to 100 μm. The design and operation of an FCC unit is largely dependent upon the chemical and physical properties of the catalyst. The desirable properties of an FCC catalyst are:

§  Good stability to high temperature and to steam

§  High activity

§  Large pore sizes

§  Good resistance to attrition

§  Low coke production

Regenerator flue gas

Depending on the choice of FCC design, the combustion in the regenerator of the coke on the spent catalyst may or may not be complete combustion to carbon dioxide CO₂. The combustion air flow is controlled so as to provide the desired ratio of carbon monoxide (CO) to carbon dioxide for each specific FCC design.

In the design shown in Figure 1, the coke has only been partially combusted to CO₂. The combustion flue gas (containing CO and CO₂) at 715 °C and at a pressure of 2.41 barg is routed through a secondary catalyst separator containing swirl tubes designed to remove 70 to 90 percent of the particulates in the flue gas leaving the regenerator. This is required to prevent erosion damage to the blades in the turbo-expander that the flue gas is next routed through.

The expansion of flue gas through a turbo-expander provides sufficient power to drive the regenerator's combustion air compressor. The electrical motor-generator can consume or produce electrical power. If the expansion of the flue gas does not provide enough power to drive the air compressor, the electric motor/generator provides the needed additional power. If the flue gas expansion provides more power than needed to drive the air compressor, than the electric motor/generator converts the excess power into electric power and exports it to the refinery's electrical system.

The expanded flue gas is then routed through a steam-generating boiler (referred to as a CO boiler) where the carbon monoxide in the flue gas is burned as fuel to provide steam for use in the refinery as well as to comply with any applicable environmental regulatory limits on carbon monoxide emissions.

The flue gas is finally processed through an electrostatic precipitator (ESP) to remove residual particulate matter to comply with any applicable environmental regulations regarding particulate emissions. The ESP removes particulates in the size range of 2 to 20 microns from the flue gas.

The steam turbine in the flue gas processing system (shown in the above diagram) is used to drive the regenerator's combustion air compressor during start-ups of the FCC unit until there is sufficient combustion flue gas to take over that task.

EMISSION CONTROL IN CPCL:

                       Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles (motor cars) and other powered vehicles but they can also regulate emissions from industry, power plants, small equipment such as lawn mowers and diesel generators. Frequent policy alternatives to emissions standards are technology standards (which mandate Standards generally regulate the emissions of nitrogen oxides (NO_x), sulfur oxides, particulate matter (PM) or soot, carbon monoxide (CO), or volatile hydrocarbons (see carbon dioxide equivalent).

The first Indian emission regulations were idle emission limits which became effective in 1989. These idle emission regulations were soon replaced by mass emission limits for both petrol (1991) and diesel (1992) vehicles, which were gradually tightened during the 1990s. Since the year 2000, India started adopting European emission and fuel regulations for four-wheeled light-duty and for heavy-dc. Indian own emission regulations still apply to two- and three-wheeled vehicles.

Current requirement is that all transport vehicles carry a fitness certificate that is renewed each year after the first two years of new vehicle registration.

On October 6, 2003, the National Auto Fuel Policy has been announced, which envisages a phased program for introducing Euro 2 - 4 emission and fuel regulations by 2010. The implementation schedule of EU emission standards in India is summarized in Table 1.

Table 1: Indian Emission Standards (4-Wheel Vehicles)
Standard	Reference	Date	Region
India 2000	Euro 1	2000	Nationwide
Bharat Stage II	Euro 2	2001	NCR*, Mumbai, Kolkata, Chennai
		2003.04	NCR*, 12 Cities†
		2005.04	Nationwide
Bharat Stage III	Euro 3	2005.04	NCR*, 12 Cities†
		2010.04	Nationwide
Bharat Stage IV	Euro 4	2010.04	NCR*, 12 Cities†
* National Capital Region (Delhi) † Mumbai, Kolkata, Chennai, Bengaluru, Hyderabad, Ahmedabad, Pune, Surat, Kanpur, Lucknow, Sholapur, and Agra

The above standards apply to all new 4-wheel vehicles sold and registered in the respective regions. In addition, the National Auto Fuel Policy introduces certain emission requirements for interstate buses with routes originating or terminating in Delhi or the other 10 cities.

For 2-and 3-wheelers, Bharat Stage II (Euro 2) will be applicable from April 1, 2005 and Stage III (Euro 3) standards would come in force preferably from April 1, 2008, but not later than April 1, 2010.

CONCLUSION:

Refiners have several options to fulfill higher industrial gas needs. Of course, gas production plants can be bought from competent suppliers. That necessarily means that the complete investment shows up in the balance sheet of the refinery. In addition, operation and maintenance costs have to be borne by the refinery.

All this is conventional procedure with advantages and disadvantages. The main disadvantage certainly is that refiners are not specialized in gas plant operation. Therefore reliability of the plants tends to be lower than optimum and the cost higher. But there is an alternative which gains more and more friends among the refining community: "on site supply."

The basic idea behind on site supply is that a gas company builds, owns, and operates the gas production plant for the refinery and the refiner receives the gas as a utility so that it can concentrate on its core business, making fuel.