Refining Process Handbook

[Marsilius Boa]

Petroleumrefining involves refining crude petroleum as well as producing raw materials for the petrochemical industry. This book covers current refinery processes and process-types that are likely to come on-stream during the next three to five decades. The book includes (1) comparisons of conventional feedstocks with heavy oil, tar sand bitumen, and bio-feedstocks; (2) properties and refinability of the various feedstocks; (3) thermal processes versus hydroprocesses; and (4) the influence of refining on the environment.

There is a renaissance that is occurring in chemical and process engineering, and it is crucial for today's scientists, engineers, technicians, and operators to stay current. With so many changes over the last few decades in equipment and processes, petroleum refining is almost a living document, constantly needing updating. With no new refineries being built, companies are spending their capital re-tooling and adding on to existing plants. Refineries are like small cities, today, as they grow bigger and bigger and more and more complex. A huge percentage of a refinery can be changed, literally, from year to year, to account for the type of crude being refined or to integrate new equipment or processes.

This book is the most up-to-date and comprehensive coverage of the most significant and recent changes to petroleum refining, presenting the state-of-the-art to the engineer, scientist, or student. Useful as a textbook, this is also an excellent, handy go-to reference for the veteran engineer, a volume no chemical or process engineering library should be without. Written by one of the world's foremost authorities, this book sets the standard for the industry and is an integral part of the petroleum refining renaissance. It is truly a must-have for any practicing engineer or student in this area.

Kayode Coker PhD, is Engineering Consultant for AKC Technology, an Honorary Research Fellow at the University of Wolverhampton, U.K., a former Engineering Coordinator at Saudi Aramco Shell Refinery Company and Chairman of the department of Chemical Engineering Technology at Jubail Industrial College, Saudi Arabia. He has been a chartered chemical engineer for more than 30 years. He is a Fellow of the Institution of Chemical Engineers, U.K. and a senior member of the American Institute of Chemical Engineers. He holds a B.Sc. honors degree in Chemical Engineering, a Master of Science degree in Process Analysis and Development and Ph.D. in Chemical Engineering, all from Aston University, Birmingham, U.K. and a Teacher's Certificate in Education at the University of London, U.K. He has directed and conducted short courses extensively throughout the world and has been a lecturer at the university level. His articles have been published in several international journals. He is an author of five books in chemical engineering, a contributor to the Encyclopedia of Chemical Processing and Design. Vol 61. He was named as one of the International Biographical Centre's Leading Engineers of the World for 2008. Also, he is a member of International Who's Who of ProfessionalsTM and Madison Who's Who in the U.S.

Whey is very often diluted with water. The figures above relate to undiluted whey. As to the composition of the NPN fraction, about 30 % consists of urea. The rest is amino acids and peptides (glycomacropeptide from renneting action on casein). Table 15.2 lists some fields of application for whey and whey products.

Advances in membrane filtration and chromatography have underpinned economically viable commercial processes for the fractionation of whey into highly purified protein and lactose products that allow end users to take advantage of the various functional properties of individual whey components. This is a trend that is expected to continue as research uncovers new bioactive properties and consumers become more educated about the nutritional value of whey.

The block diagram in Figure 15.1 summarizes various processes used in the treatment of whey and its end products. The first stage is filtering the curd particles left in the whey, followed by separation of casein fines and fat (Figure 15.2), partly to increase the economic yield and partly because these constituents interfere with subsequent treatment.

Production of whey powder, delactosed whey and lactose has traditionally dominated processing of whey solids. However, the increased demand for whey proteins results in approximately 40 % of processed whey solids being directed to associated products WPC35-80, whey protein isolate (WPI), lactose and permeate. The shift in the image of whey from an unwanted by-product to a highly-valuable nutritional source is complete. Some of the products now in use are described in this chapter.

Whey must be processed as soon as possible after it is drawn from the cheese curd as its temperature and composition promote the growth of bacteria that lead to protein degradation and lactic acid formation.

It is recommended that whey is drawn directly from the cheese process into short duration buffer storage then clarified, separated, pasteurized and cooled into storage to await further processing. If transporting the whey it can be concentrated by membrane filtration to reduct transport costs.

Casein fines are always present in whey. They have an adverse effect on fat separation and should therefore be removed first. Various types of separation devices can be utilized, such as cyclones, centrifugal separators or vibrating/rotating screens, Figure 15.2.

Whey that is to be stored before processing must be either chilled or pasteurized and chilled as soon as the fat and fines have been removed. For short-time storage (The use of drum dryers involves a problem: it is difficult to scrape the layer of dried whey from the drum surface. A filler, such as wheat or rye bran, is therefore mixed into the whey before drying, to make the dried product easier to scrape off.

Spray drying of whey, is at present, the most widely used method of drying. Before being dried, the whey concentrate is usually treated as mentioned above to form small lactose crystals, as this results in a non-hygroscopic product which does not go lumpy when it absorbs moisture.

Acid whey from cottage cheese and casein production is difficult to dry due to its high lactic acid content. It agglomerates and forms lumps in the spray dryer. Drying can be facilitated by neutralization and additives, such as skim milk and cereal products. Increasingly it is preferred that lactic acid is removed by a combination of nanofiltration and electrodialysis improving flavour, nutritional profile, drying and handling. Salt is also removed and typically a demineralisation level of > 60% corresponds to a level of acid reduction that is acceptable.

Whey proteins were originally isolated through the use of various precipitation techniques, but nowadays membrane separation (fractionation) and chromatographic processes are used in addition to both precipitation and complexing techniques.

Fink and Kessler (1988) state that a maximum whey protein denaturation rate of 90 % is possible for all denaturable fractions. Proteose peptone, comprising some 10 % of the fraction, is considered undenaturable.

Whey proteins, as constituents of whey powders, can easily be produced by careful drying of whey. Isolation of whey proteins has therefore been developed. The whey proteins obtained by membrane separation or ion exchange possess good functional properties, i.e. solubility, foaming, emulsion formation and gelling, can be highly nutritional and in the case of WPI produce a very clear beverage enhancing it's healthy image.

Protein concentrates have a very good amino acid profile, with high proportions of available lysine and cysteine.

Whey protein concentrates (WPC) are powders made by drying the retentates from ultrafiltration of whey. They are described in terms of their protein content, (percentage protein in dry matter), ranging from 35 % to 80 %. To make a 35 % protein product, the liquid whey is concentrated about six-fold to an approximate total dry solids content of 9 %.

Example: 100 kg of whey yields approximately 17 kg of retentate and 83 kg of permeate at close to six-fold (5.88) concentration. Table 15.3 shows the compositions of the feed (whey) and the resulting retentate and permeate.

Percentage protein in dry matter according to the values in Table 15.3:

In concentration, most of the true protein, typically > 99 %, is retained, together with almost 100 % of the fat. The concentrations of lactose, NPN and ash are generally the same in the retentate serum and permeate as in the original whey, but a slight retention of these components is reported.

To obtain a more than 80 % protein concentrate, the liquid whey is first concentrated 20- to 30-fold by direct ultrafiltration to a solids content of approximatively 25 %; this is regarded as the maximum for economic operation. It is then necessary to diafilter the concentrate to remove more of the lactose and ash and raise the concentration of protein relative to the total dry matter. Diafiltration is a procedure in which water is added to the feed as filtration proceeds, in order to wash out low molecular components which will pass through the membranes, basically lactose and minerals.

Table 15.4 shows the compositions of some typical whey protein concentrate (WPC) powders.

A process line for the production of drier whey protein concentrate using UF is shown in Figure 15.3. Up to 95 % of the whey is collected as permeate and protein concentrations as high as 80-85 % (calculated on the dry matter content) can be obtained in the dried product. Typically, the evaporator is not used for protein concentrations above 60 % dry matter so as to minimize heat damage to the proteins. Advances in high-concentration nanofiltration allows these products to be concentrated to > 35 % dry matter prior to drying. For further details about UF, see Chapter 6.4, Membrane filters.

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