chber 1 (2014) 40-49 200 years in innovation of continuous distillation

200 Years in Innovation of Continuous Distillation

Norbert Kockmann[1]*

www.ChemBioEngRev.de 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ChemBioEng Rev 2014, 1, No. 1, 4049 40

Abstract

Distillation is one of the oldest and most frequentlyused purification methods today. In 1813, Jean-Bap-tiste Cellier-Blumenthal patented the first continu-ously working distillation column, starting an im-pressive development of process equipment. Newproduct areas were discovered as well as improved

equipment installations. 100 years ago, Fritz Raschigpatented his rings as packing material. Current de-velopments are guided by deeper knowledge of heatand mass transfer as well as the integration of var-ious process functions.

Keywords: Alcohol distillation, Coal tar refining, Cryogenic air separation, Continuous distillation, Process intensification,Structured packing

Received: October 31, 2013; accepted: November 19, 2013

DOI: 10.1002/cben.201300003

1 Introduction

The discussion of innovation in technical development mustinclude the social, cultural, and political situation, too. Thepathway often doesnt follow a stringent, engineering-like argu-mentation with precision and reliability; it includes jumps,gaps, or inconsistencies. Innovation in distillation is indeedinfluenced by many technical and nontechnical factors and itshistory gives many illustrative examples guiding also the devel-opments of today. Distillation is a well-defined separation unitconsisting of the partial evaporation of a liquid mixture andsuccessive condensation with a different composition than theoriginal material. The word distillation comes from the Latinverb destillare to drop down or to trickle down. The meaningof rectification origins from Latin, too: rectificare to purify orenhance, but has a broader meaning. In ancient and medievaltimes, nearly all purification and separation operations weresubsumed under the term of distillation, such as filtration, crys-tallization, extraction, sublimation, or mechanical pressing ofoil. Today, distillation is often combined with other processsteps such as extraction or chemical reaction [1], hence it isnow closer to the original meaning.The first civilizations started in Mesopotamia, Egypt, Syria,

and China and spread from there. Conclusions can only bedrawn from excavations in Iraq about the processing of foodsor pharmaceutical products [2] such as perfumes, balsam, tinc-tures, or creams more than 5500 years ago. Chinese activities indistillation are reported from ancient times [3]. Early types ofpots similar to Fig. 1 were found in China around 2000 BC.The equipment from Alexandria during the Hellenic and Ro-man era [4] did not change so much until the 16th centuryAD. With the increased knowledge transfer by printed booksand larger demand of distilled products such as concentrated

alcohol or mineral acids, the development of various stillsthrived and in part already to the extent of mass production.French scientists, English industry and business men as well asGerman engineers brought the equipment to lab and industrialapplication maturity. Important milestones are the patent onthe first continuous distillation column and process 200 yearsago by Jean-Baptiste Cellier-Blumenthal in France [4] and 100years ago the patent of Fritz Raschig on his rings for masstransfer equipment [5].There are many publications on the history of distillation

dealing with the development until the beginning of the lastcentury [4, 611]. This contribution gives after the obligatoryhistorical introduction an overview about the last century in-cluding current distillation innovation. An extensive descrip-tion will be given in a book chapter, which will appear soon[12]. In addition, many old books and further material hasbeen digitalized and is available online to inspire new studies.

2 From Stone to Middle Ages

The development of early distillation devices is illustrated inFig. 1 for the period from early civilizations to the dawn ofmodern ages [3]. The Sumerian began around 3500 BC to ap-ply evaporating and condensing a liquid to refine a substancefor extracting essential oils from herbs. Many of the pots and

[1] Prof. Dr.-Ing. Norbert Kockmann

TU Dortmund, Biochemical and Chemical Engineering Faculty(BCI), Apparatus Design, Emil-Figge-Strae 68, 44227 Dortmund,Germany.E-Mail: [email protected]

English version of DOI: 10.1002/cite.201300092

stills shown on the right side were found in excavations 250 kmnorth of Bagdad, Iraq [2].The liquid in the still evaporates by gentle heating from be-

low and condenses at the colder cap (distillation). Droplets arerunning down to be collected in the ring, where organic materi-al such as leaves and herbs are extracted by the liquid (extrac-tion). Typical dimension of the earthenware pot are approxi-mately 50 cm in diameter and 25 to 50 cm in height. Besidesherbs and perfumes, asphalt and wood tar were distilled, oftenfor spiritual services [13]. Hence, priests and temple servantsused such apparatus and kept their recipes secret. In Egypt,essential oils and elixirs from herbs were distilled depicted onthe papyrus Ebers (1550 BC) on medical issues [13].Pliny and Dioscorides described the top right device to be

used on ships producing drinking water from sea water byheating it up [10] as depicted in Fig. 1 top. Water evaporates bysun radiation and condenses in a wet wool fleece. Similar tothis a Mongolian still works with a collecting cup centrallywithin the still body [3]. Fermented horse milk was heated anddistilled to karakumyss. The amount of cooling water deter-mines the content of alcohol in the product.From 300 BC under the Ptolemaic regime, Alexandria in

Egypt evolved to the scientific center of the antique world. Thecity with university and library served as mediator betweeneastern and western civilization until 600AD. In the 1st cen-tury AD the School of Alchemists formed which systematicallycollected and developed the contemporary chemical knowl-edge.

In the course of developments, the simple earthen ware potswith rim were supplemented with a tubular connectionthrough which the condensate could exit continuously. Capa-city and performance are increased and different fractions canbe taken separately. The rim moves into the lid, hence, the hotstill is thermically separated from the cold dephlegmator andalembic. The elements are connected and sealed by wet lime,clay, wool, and other natural fibers. A beautiful glass distillationhelmet, the alembic, from Alexandria (500800AD) is shownon the top of Fig. 1 [3]. Major products were medical products,herbal essential oils, perfumes, light oils, and also tar as viscousresidue for construction and ship building purposes.The Alexandrian period was followed by the early Arab peri-

od from 7001200AD without any larger disturbances. TheArabs adopted the technology of the Alexandrian and Syrianchemists, mainly for the production of perfume, rose water andoil, and medical substances. Two major centers were importantfor the technology conservation, Bagdad in the east and Cordo-ba in the west. In South Europe, Salerno with its medicalschool, Venice with its trade connections and glass blowing art,and the Moorish cities in Spain played an important role. Here,traditional books were translated from Arabic to Latin. Typicalexamples from the richly illustrated books are shown in Fig. 2,depicting the investigation and teaching in medical schools.Additionally, Eastern knowledge and skills were brought toEurope the Crusades.

In Europe, alcohol was one of the major products due to itsuse for drinking, disinfection, and preparation of medical sub-stances. Albert the Great (Albertus Magnus, 11931280 inCologne) worked on the distillation of wine and other spirits.He considered distillation as the most important method inalchemy: the alchemist requires two or three rooms exclu-sively devoted to sublimations, solutions and distillations [4].Around 1300AD the distillation processes were classified intwo methods: per ascensum (ascending) and per descensum(descending). Both methods and descriptions were kept intothe 18th century, but the latter is now rarely applied. It wasmainly used for the dry distillation of solid substances such aswoods, barks and herbs. The ascending method follows the va-por path and is realized in nearly all current processes.


Figure 1. Development of early distillation equipment fromneolithicum to the beginning of the modern age, according to[3, 8].

Figure 2. Medieval book miniatures from the medical school ofSalerno The Articella. Left: a physician holding a flask with liquid,possibly comparing it to pictures or descriptions in a book; right:a physician displaying a flask to a student. Courtesy of theNational Library of Medicine.

The invention of printed books with movable letters at theend of the 15th century AD led to a wider distribution ofknowledge and further promotion of inventions. Besides effec-tive and rapid multiplication and distribution of knowledge,local languages such as French, English, or German were sup-ported and dominated science and technology. Now, more peo-ple could read and understand the new methods to work onthe equipment and recipes. People with more technical back-ground had the chance to come into contact with the tradi-tional knowledge from monasteries and noble courts. Mainauthors on distillation were Michael Puff von Schrick (1487)[16], Hieronymus Brunschwygk (1500) [17], Philip Ulsted(1526) [18], and Walter Ryff (1545) [19]. In these books equip-ment and design details as well as many recipes were given toproduce a multitude of distilled waters from plants and ani-mals.Apparently, many pharmacists and apothecaries used the ad-

vanced methods of distillation to concentrate herb extracts orto mix alcohol with other ingredients. They placed their appa-ratus directly in the herb gardens, as can be seen on the titlepage from Brunschwygk [17], see Fig. 3.Two different distillation set-ups are shown in the corners: a

Rosenhut still with a man filling an empty flask is depicted in

the top left corner and in the opposite corner another stillalembic and a young man are shown. The Rosenhut, an inven-tion of the medieval ages, is a conical head for the still toimprove cooling and vapor guidance. In the top right corner,a man is drinking from a small bottle, as is the deer in the mid-dle. The lower part of the illustration shows a garden withmany different plants, harvested by two women and a man,probably the farmer with a hoe in his hand. In the lower rightpart the young man with a floral wreath in his hair, similar tothe wreath of young women, harvesting is operating the distil-lation vessel. While heating with his right hand, he is testingthe temperature of the upper part of the cucurbit with the fin-gertips of the left hand. The title page illustrates the two majorproducts of distillation: drinking alcohol and medical applica-tions.As early as 1555, Conrad Gesner described a multistep distil-

lation for higher purity [20]. Georg Agricola described in hisfamous book De Re Metallica [21] in 1556 the distillation andconcentration of mineral acids such as sulfuric or nitric acid.These were used for ore processing and metal separation andpurification. Due to the large amounts needed, the stills werearranged in parallel around the heating source, also calledFauler Heinz (lazy Henry) in German. The first steam heating

was used by Claude Dariot (153394), and nearly200 years later Jean Pissonier (1770) described thefirst counter-current flow cooling [10].The 17th and 18th century were characterized by

the installation of complete laboratories for che-mical studies and the large-scale production ofalcohol, medical substances, perfumes, or mineralacids, see Fig. 4. In 1595, Andreas Libau (Libavius)described in Latin the general setup of a chemicallaboratory [22]. He distinguished the rooms ac-cording to their functions and chemical operationsand already used a tube system for tapped water.He also categorized the distillation equipment ac-cording to the heating, cooling, and the vapor flowdirection, i.e., ascending or descending.Robert Boyle (16261692), often called the father

of modern chemistry, conducted systematic distilla-tion experiments. He distilled alcohol with frag-ments of acetic acid over several days and foundthat the liquid at the end had a higher content inacid than the starting material. He worked undervacuum and elevated pressure conditions. JohannKunckel von Lwenstern, a glassmaker, apothecary,and experimental chemist, described in his bookLaboratorium Chymicum (1716) [25] the currentknowledge of lab chemistry. From his intensiveknowledge of different materials and processes, hepreferred glass equipment in the laboratory, whichis dominant until today.The Industrial Revolution was led by the me-

chanical textile industry with its high demand forsulfuric acid as bleaching agent. The acid was pro-duced with stills from platinum [26]. Concurrently,the production rate of drinking alcohol increaseddriven by sugar cane farming and rum demand. Inthe British colonies The Society of Rectifying Distil-


Figure 3. Title page of Brunschwygks book on the Art of Distillation [17], display-ing an herb garden with two stills.

lers [27] played a major role for the development and spreadingof this technology.

3 Science, Engineers, andIndustrialization

At the end of the 18th century, French scientists leading theway in pure chemistry, but English scientist were ahead incommercial-technical chemistry [28]. At the chemical worldexhibition in 1862, England was indisputable the world leaderin chemical industry, but by 1893 world exhibition in Chicago,Germany had taken over. One reason was the unification ofGermany in 1870/71 that pooled its intellectual forces and al-lowed for easier exchange of goods and information. The ex-change of goods and information got easier. Another reasonwas the strength of German universities in chemical researchand the high standard of engineering schools for science-basedinnovation.At the beginning of the 19th century Napoleon offered a

prize for sugar beet production and fermentation to gain inde-pendence from British imports of sugar and alcohol. A series ofpatents on distillation equipment was issued from 1801 to 1818[4]. Jean-douard Adam developed a discontinuous apparatusfor fractionating distillation, which was further developed toinclude a device for partial condensation by Isaac Brard. Theirwork realized two principles: (i) the enrichment of a low boil-ing component in the rising vapor and (ii) the enrichment ofthe vapor by partial condensation and reflux into the still. Bothprinciples combined led to the continuously working distilla-tion patented by Jean-Baptiste Cellier-Blumenthal (17681840)in 1813, 200 years ago. In Fig. 5, this distillation column is illu-strated. The upper part of the column contains bubble-captrays, while the lower part is structured by conical metal caps,which also serve for contacting vapor and liquid. This setup isbase for all further development in the following 60 years in

France and also influenced the constructions in both Germanyand England.Many details of the Cellier column were improved in the fol-

lowing years. In 1817 Charles Derosne (17801846) also built acontinuously working distillation column and brought it to in-dustrial maturity [4]. His economic and technical success alsorelied on other industrial products, such as sugar plants, loco-motives, and other railway equipment. In 1822 Anthony Per-rier got a patent on baffles as tray construction in a whiskeydistillery to enhance the contact between vapor and liquidphase. They are similar to current bubble-tray caps and inserts.Aeneas Coffey developed perforated trays as sieve structuresfor the vapor-liquid contact in 1830. Sieve plate columns had adistance of 6 in (15 cm) or more [5]. They were primarily de-veloped for higher viscous liquids, which was not successful.Today sieve trays are used for nonfoaming, low viscous liquidssuch as liquefied air separation columns. Higher viscous liquidscould successfully be separated by a bubble-cap trays columnpatented in 1854 by Henri Champonnois.Nearly at the same time as Cellier, Heinrich Pistorius (1777

1858) patented in Germany his distillation plant in 1817 foralcohol from fermented potato mash, see Fig. 6. Brandy fromfermented potatoes became very popular in Germany in thebeginning of the 19th century. The Pistorius still was widelyused in Germany until 1870 and produced liquors with 60 to80% in alcohol content. The unit consists of two stills withmanual stirrer and two conical distributors in the column,which allow only for a low separation performance.


Figure 4. Standardized distillation still with air-cooled alembic.Left: John French (1651) [23]; right: Johann Elsholtz (1674) [24]showing the laboratory setup.

Figure 5. Continuously working distillation column for wine byCellier-Blumenthal, patented 1813 [10]. The arrangement con-sists of two vessels, the stripping region with conical metalsheets, the enrichment section, partial condenser (dephlegma-tor), and water cooled condenser [29].

Pierre Savalle (17911864) was an early co-worker of Cellierand made his first experiments in a sugar refinery. Togetherwith his son Francois Dsir Savalle (born 1838) he designednew equipment and improved many details of the cooling andheating systems [31]. The throughput became 78 times higherthan in the Cellier column [4]. The simple continuously work-ing apparatus from Savalle was especially used for alcohol pro-duction from cane-sugar. In his book from 1873 [31] Savalleobserved that more than 16 000 distilleries are working in Ger-many, but only 700 in France. The production of 100 L alcoholfrom wine needs 40 kg of coal. The Savalle columns contain ty-pically 30 trays and reflux two-thirds of the total distillate. Sa-valle described the rectification of methyl alcohol and the frac-tionation of crude benzene in two columns at BASF [4] inLudwigshafen, Germany. Another pupil of Cellier was Auguste-Pierre Dubrunfaut, who also improved the Cellier column. Hedesigned and built columns with diameter of 80100 cm with adaily yield of 200 to 4800 L alcohol (9294%). His book on dis-tillation [32] is still one of the best sources for the distillationdevelopment [4]. His columns influenced German companiessuch as Heckmann and others [4], and gave input for engineerssuch as Eugen Hausbrand, who will be described later.The second product besides alcohol, by which the innovation

in distillation is guided in the 19th century, was waste from thecoal and coke industry. In the late 18th century dry distilledcoal (coke) was used for the first time for iron production andsmelting. Coke gases were found to burn with a bright flamefor private and public lighting. In 1826 gas lighting was intro-duced in Berlin, after London in 1807 and Paris in 1822. Thegas had to be washed in absorbers before feeding into the pipe-lines. The washing fluid contained ammonia, benzene, phenol,and other aromatic compounds as valuable goods, which hadto be stripped off. Coal tar was the highly viscous byproduct ingas plant for lightening and coke. In 1822, the first industrialtar distillation plant was built in Britain [33]. In 1823, FriedliebRunge discovered phenol and aniline in the coal tar and laidthe foundation of tar chemistry. The valuable side productswere separated by washing, absorption, and distillation at thewhite side of coking plants. The first absorption and distillation

equipment was made from wood withstacked wooden internals [34]. Other mate-rials were dumped and unstructured stonesor lumps of coke and iron or steel forhigher stability of the outer constructionand vessel. Ammonia distillation towersand benzene washers looked similar to al-cohol plants, see Fig. 7.In 1842 the first tar distillation in Ger-

many was started in Offenbach near Frank-furt. Julius Rtgers built a plant in Erknernear Berlin in 1860 [33], followed by otherplants in Dresden, Katowice, Vienna, Mu-nich, and Rauxel. The tar was primarilyused to impregnate and waterproof railwaysleepers, telegraph poles, and other woodenconstruction material. The high boilingfraction or residue was used for streetpavement. In 1867 Georg Lunge wrote acomprehensive book on coal tar distillation

[35], where he described his experience from tar distillationplants in England and Germany. Regarded as the father of tech-nical chemistry, he brought practical knowledge into the aca-


Figure 6. Two-vessel-still by Heinrich Pistorius, German patent of 1817 [30], often usedin small alcohol distilleries.

Figure 7. Ammonia distillation tower with a combination ofdephlegmator and bubble-tray column, tall column with conicalcontactors, and right column with bubble-cap trays [30].

demic circuits as professor in Zrich, discussing quantitativemethods to design distillation plants and related cost calcula-tions. His contribution opened the British technology to con-tinental Europe and inspired for new ideas. Also the youngpetroleum industry benefitted from these developments. Lungealready described the concept of unit operations before it wascoined by Arthur D. Little in 1915. Phenol chemistry needshigh purity components and, hence, tall separation columnswere constructed of up to 60m in height. This development de-manded for better construction material, enhanced gas-liquidcontacting internals, and improved calculation procedures.In the beginning of the 20th century, coal tar distillation was

established for the production of raw materials for the chemicalindustry [36]. Both discontinuous and continuous processeswere developed, although the latter is quite complex due to thehigh viscosity of tar and pitch. The invention of Frederic Len-nard was pathbreaking, with German patents in 1889 and1891, consisting of a long, heated tube for gas generation witha typical throughput of 100150 t d1. In 1913, Fritz Raschigpatented in Germany rings with 25mm height and diametermade from glass, porcelain, copper, iron, or other resistive ma-terial [5]. They exhibited a lower pressure loss and better masstransfer characteristics and could be setup in an arranged pack-ing [28]. In 1914, a Raschig plant was started in Linz am Rheinat Walter Feld GmbH consisting of three tube bundle heatexchangers and two columns. For the medium fraction, the col-umn was equipped with bubble-cap trays, while the vacuumcolumn had a Raschig ring filling for light oil and naphtha se-paration [34].With increasing steel and coal production, the oxygen de-

mand was also increasing, similarly to the increasing nitrogendemand in chemistry. After the liquefaction of air by Carl vonLinde in 1895, the separation of oxygen and nitrogen becameimportant. Raoul Pictet developed his oxygen apparatus in1899 with a special rectifying arrangement [37] and heat recov-ery in the column. The Linde oxygen column from 1902 isfilled with glass beads, wherein nitrogen rich vapor streams up,while the oxygen rich liquid trickles down to the column reboi-ler. The liquid oxygen is partially evaporated and leaves the col-umn over a siphon with a purity of 99%. Distillation columnswith dumped glass beads of 4mm in diameter were alreadytested by Walther Hempel 1881 for lab applications, before in1890 Robert Ilges used porcelain balls with 12 in (2550mm)in diameter in columns [5]. He also developed a temperaturecontrolled apparatus, which was then very popular in small dis-tilleries. In 1903, Georges Claude, founder of the French com-pany lAir Liquide, presented an oxygen column with only onesingle heat exchanger. The column internals were bubble-captrays with downcomers for the liquid on top of the heatexchanger section [37]. In 1907 Linde further improved hisoxygen column with medium and low pressure column andpresumably already sieve trays.

4 Scientific Understanding and ProcessIntegration

At the beginning of the 20th century, the number of productionfrom distillation is increasing together with the multitude ofequipment designs. Devices and internals are built by smalland medium enterprises such as Heckmann [38, 39] or Montz[40] guided by genius engineers. Eugen Hausbrand (18451922) was chief engineer and director at Heckmann and wasalready mentioned in the tradition of Cellier and his pupils. Heis regarded as one of the first process engineers [38], who pub-lished first quantitative calculations for rectification and distil-lation [39]. In his famous monograph [39], he discussed heatand mass flow diagrams in rectification columns similar toSankey-diagrams of today. Hausbrand was director of theHeckmann Company for over 40 years. He practiced the meth-od of discussion to evaluate new technical systems, comparableto HAZOP (hazards and operability studies) methods of today.Further publications of him dealt with heat and mass transferof process equipment, continued later by Wilhelm Nuelt.Simple calculations for batch distillation were performed by

Rayleigh in 1902 [5] with material balance and simplificationof the relative volatility. He applied also Henrys and Raoultslaw and compared his results with test data. Hausbrand in-itiated further work on distillation, e.g. Robinson in 1922 [41],Walker, Lewis, and McAdams in 1923 [42], von Rechenberg in1923 [43], or Mariller in1925 [44]. In 1925 Thiele and McCabe[45] published a simple graphical method to determine theperformance and number of separation steps in columns withbinary mixtures. Thormann already integrated this method inhis textbook [46] from 1927 and described tray columns,dumped packing, binary and ternary mixtures as well as someproperties of binary mixtures. The last chapter of his bookdeals with the equipment of alcohol distillation, the best under-stood system at that time. Other distillation systems were prob-ably still under secrecy (air separation, aromatics, hydrocar-bons etc.) or used equipment comparable to that of alcoholdistillation.To compare the different column types, Thomas Chilton and

Allan Colburn proposed a method of the height equivalent to atheoretical plate reaching vapor-liquid-equilibrium (HETP) forpacked columns in distillation and absorption in the 1935 [47].Later, Colburn defined the Murphree tray efficiency, which in-dicates the relative vapor concentration compared to the equili-brium and is a good measure of the efficacy of the mass trans-fer over a tray. In 1942, the methods of distillation andrectification were standardized in Germany in DIN 7052 [48].In 1929 Emil Kirschbaum started his work at the chair of

process engineering in Karlruhe and later published his famoustextbook on distillation [48]. Based on this work, Reinhard Bil-let in Bochum worked on optimization studies in distillation,especially in vacuum columns [49]. He worked with severalcompanies to optimize structured packing and fluid distribu-tors. Ernst-Ulrich Schlnder in Karlsruhe combined extractionand adsorption with distillation in his textbook [50] andworked on the heat and mass transfer and integration in col-umns. His pupil Jerzy Makowiak wrote the textbook on struc-tured packing [51] and their transport characteristics. In 1960


the textbook on Transport Phenomena by Byron Bird, WarrenStewart, and Edwin Lightfoot [52] was a landmark and shiftedthe view from unit operations to more fundamental processesof mass and heat transfer. Based on the unit operation concept,Schembecker, Gorak and Schmidt-Traub developed the con-ceptual design concept [1] with view on fundamental transportprocesses and their combinations on different levels.Mixtures with close boiling point and isotope separation de-

mand for many separation steps, hence a tall column with in-tensive mass transfer. Internals from wire mesh and structuredmetal sheets were firstly proposed by Walter Podbielnak in1931 [53]. The Atomic Energy Research Establishment in Har-well, UK, developed in the 1930s a special column internalcalled Spraypak filling for heavy water concentration [28]. Thepacking is made from stretched or expanded metal, see Fig. 8.It showed good characteristics for high duty loading for gasand liquid phase and can be operated with two- to threefoldgas velocity compared to bubble-cap trays. Metal mesh couldreach approximately two theoretical stages per meter.The second development line of structured packing was the

Stedman Column in 1935 from Knolls Atomic Power Labora-tory, General Electric Company, for isotope separation [54].The packing is fabricated of Monel wire cloth, which ispunched, embossed, and welded to form a series of cells. An-other type of structured metal sheet packing, the multiple-celltriangular pyramid type, was patented by Stedman in 1936[55]. The triangular packing type exhibits low pressure dropand hold-up and performs with HETP values of 1.52 in (3850mm) and 2.53.3 in (6384mm) for column diameters of1.56 in (38152mm) and 12 in to 11 ft (3003400mm) dia-meter, respectively. Applications were low boiling paraffin hy-drocarbons (C1 to C7 fraction), which were separated in va-cuum columns. The development of structured packing wasguided by smaller companies such as Montz [40], Koch,Glitsch, Khni, or Sulzer [56]. They take up the demand of thelarger industrial companies and developed specialized solutionsin gas-liquid-contacting, which they could offer to further cus-tomers.Further momentum came from the combination of different

separation technology with distillation for complex separationtasks or higher yield and efficiency. In extractive distillationearly work was done from 1945 to 1960 [57] to overcome azeo-tropic limits or to increase the purity. A well-known example isthe separation of toluene and methylcyclohexane [58]. The

selection of the additional solvent is the crucial part duringprocess design [59]. A list of 32 candidates is given in [57] withtheir activity coefficients. The first application of reactive distil-lation was published in 1948 by the Othmer group [60] on theesterification of dibutyl phthalate from butanol and phthalicacid. An illustrative example published in 1984 is the integratedreactive-extractive distillation of methylacetate from methanoland acetic acid, which overcomes the chemical equilibrium aswell as azeotropes [61, 62]. Conceptually, the column can betreated as four heat-integrated distillation columns (one withthe reaction) stacked on top of each other, see Fig. 9. The reac-tive distillation scheme has been widely discussed from 1995 to2003, including [63] or [64]. Catalytic active packing such asKatapak was developed since 1999 and play an important rolein process development.Focusing on energy consumption significant interest was put

on thermally coupled systems and dividing wall columns forternary or more mixtures. A fractionator with vapor sidestream and side-cut rectifier, also known as Petlyuk tower, wasdiscussed by Stupin and Lockhart in 1972 [66]. The dividingwall column is topologically equivalent to the fully thermallycoupled system that was first patented in 1933 to produce threepure products from a single column [67]. One of the first in-dustrial applications was the side rectifier configuration for airseparation and argon production. The fully thermally coupledsystem is 30 to 50% less in energy consumption than any otherternary column configuration [68, 69], depending on the feedcomposition and volatility of the components. Although in-vented long ago, dividing wall columns and fully thermallycoupled distillation systems were not implemented in practiceuntil the late 1980s [70]. All the multicomponent thermallycoupled configurations have a corresponding dividing wall col-umn equivalent. Gerd Kaibel has shown in 1987 [71] severalexamples of columns with multiple dividing walls, separatingthree, four, and six components. In 2005, there were about 60dividing wall columns in operation; 42 are owned by BASF[72], where the first was set up in 1985 in Ludwigshafen, Ger-many.Further improvements in distillation concern the estimation

and determination of vapor-liquid equilibrium properties [73],graphical treatment of separation tasks [74], or the establish-ment of independent research institutes [75, 76], which are out-with the scope of this paper.

5 What Will the Next InnovationCycle Bring?

Due to the long innovation cycle in process indus-tries, owing to high investment costs, innovation isslowly and only partially transferred to practice.The overall goal is the increasing separation powerper unit volume with better understanding of thephysics of mass transfer processes, while decreasingthe equipment cost [56]. Optimization of the gasand liquid flows in future packing geometry will beof high importance assisted by numerical simula-tion, such as computational fluid dynamics, CFD.Distributors will have more streamlined forms to


Figure 8. Left: Spraypak filling of an absorption/distillation column [28]; right:column packing made from metal sheets according to the Stedman patent from1936 [5].

increase capacity and robustness as well as to reduce pluggingand maldistribution. The inlet pressure drop of packing wasminimized and further improvement of mass transfer could bemeasured [56].A general trend is the emerging of multifunctional packing

and their application in combined systems, like catalytic distil-lation. Still, better understanding of the catalytic performanceand reaction together with the distillation process is necessary[1]. Combined processes are often performed in separateequipment, such as hybrid separation processes made fromrectification and melt crystallization to purify close boilingmixtures [77]. Membrane separation was integrated in a distil-lation column [78]. Another interesting combination is the va-cuum distillation with biocatalytic active packing by Li in 2012[79]. Microbial biofilms are grown on the structure surface andemployed for ethylene glycol conversion to aldehydes. Anothertrend is the use of alternative solvents such as ionic liquids.In Fig. 10, the separation performance of dumped and struc-

tured packing is displayed from 1900 with rocks and Raschigrings over Berl and Intalox saddles to more complex structuredNutter rings and Sulzer structured packing in 1990 [80]. Dur-

ing the last 110 years, a doubling in efficiency took nearly50 years. With miniaturized internal structures, an increase ofseparation performance is described with the square symbols.Now, only 15 years are necessary for doubling the separationperformance. Most of the data were obtained in very tinyequipment in the millimeter range [81], from which the resultsare hard to scale up to pilot or even production scale. The com-bination of microchannel flow and a centrifugal field leads tohighest performance in Fig. 10, displayed with circular points.The other two circles represent experimental data from thegroup of Wang in 2011 [82] and Jordan MacInnes and co-workers from rotating spiral microchannel distillation in 2010[83]. The performance values were calculated in comparison toconventional structured packing given in the work.The successful innovation path leads over smart combina-

tion, composition, increasing or diminishing, synthesis of dif-ferent, novel elements as well as application in new areas. Ro-tating internals were already used in absorption and distillationcolumns for better mass transfer in coke tar processing [29].With this multitude of possibilities, the conceptual design ofdistillation systems will become more important [84] and canserve as a guide through topographic methods selecting opti-mum configurations. Large companies as user and small com-panies as flexible suppliers work closely together with academiaand research institutes to push equipment development ontechnology platforms and its applicationsDistillation accompanies mankind since the early civiliza-

tions and distilled products influenced their cultural develop-ment. Today, distillation is the most important separation stepin chemical and biochemical processes. Many brilliant mindsworked on the development of processes and apparatus untiltoday. Nevertheless, new combinations and more advancedequipment still require research and development. This articleillustrates the main development steps over the last centuries,from which new inspirations can be drawn for future innova-tion cycles.

The author has declared no conflict of interests.


Figure 9. Integrated reactive-extractive distillation column to produce methylacetate. Left: column with feed positions, middle: concen-tration profile; right: temperature profile, adapted from [65].

Figure 10. Development of the packing performance (HTU va-lue) over last 110 years, adapted from [80].

Norbert Kockmann studiedmechanical engineering at TUMunich and obtained his PhDon the fouling in heat exchan-gers from the University ofBremen. Starting in 1997, heworked for Messer Griesheim,Krefeld, as project manager inplant construction until join-ing IMTEK at the Universityof Freiburg in 2001, where heestablished the micro processengineering group and habili-tated in 2007. Joining Lonza

AG, Visp, as head of laboratory for continuous reaction en-gineering, he developed micro reactors and processes forpharma production. In April 2011, Norbert Kockmann wasappointed the Bayer endowed chair in Equipment Design atthe TU Dortmund and works on small-scale modular de-vices and process intensification.

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