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(2l) Application Number:    KE/P/2010/ 001092       
       
(22) Filing Date: 1211moo8       
       
(30) Priority data: 08154310.0  10/04/2008  EP andm2456/MUM/2007    14/12/2007  1N   
       
(86)  PCT data    PCT/EP08/0 10836 12/12/2008 W02009/077189 25/06/2009   

(73) Owner: UNILEVER PLC of Unilever House, 100 Victoria Embankment, London EC4Y ODY, Great Britain

(72) Inventors: SINGH, Gunneet of Hindustan Lever Ltd Research Centre 64 Main Road, Whitefield P.O. Bangalore 560 066, India; ISRANI, Sameer Harnam ofTulip Building, Flat No. 10. Plot No. 389 16th Road Bandra (W), Mumbai 400 050, India; NAIK, Vijay Mukund of House No.2, Nandadeep Cooperative Housing Society, Jayaprakash Nagar, Goregaon East, Mumbai 400 063, lndia and SlRCAR, SURANJAN of P-66, Lakeview Road, Kolkata, West Bengal 700 029, India

(74) Agent/address for correspondence: Kaplan & Stratton Advocates, P.O. Box 40111-00100, Nairobi

(54) Title: PROCESS FOR RECOVERlNG VOLATILE TEA COMPOUNDS.

(57) Abstract: Disclosed is a process for recovering volatile compounds from an aqueous tea extract by distilling the said extract by fractional distillation comprising condensing of vapours, separating the oil phase condensate from the aqueous phase and refluxing the substantially oil-free aqueous phase.


PROCESS FOR RECOVERING VOLATILE TEA COMPOUNDS

TECHNICAL FIELD

The invention relates to a process for recovering volatile compounds from an aqueous tea extract The invention particularly relates to a process for recovering and concentrating tea volatile compounds e.g. aroma compounds from dilute aqueous tea condensate streams

and other waste steams.

BACKGROUND OF THE INVENTION

10    Tea is one of the most widely consumed beverage in tile world. Tea is available in many forms e.g as green tea, black tea, hot instant tea, iced tea etc.

Green tea is generally preparad by heat treating (e.g. by steaming or pan-frying) freshly

picked leaves to anest enzyme action and tilen subjecting the leaves to a series of drying

15    and rolling steps.

Black tea is generally preparad by subjecting freshly picked tea leaves to a series of

pror.essing conditions including withering and macerating the fresh tea \eaves, followed by fermentation which mainly contributes to the characteristic colour, flavour and aroma of

20    black tea. The tea is dried at high temperature aRer fermentation to arrest the enzyme action and to bring down tile moisture to a low level.

Green tea and black tea are products which are brewed in hot water to produce tea infusions in tile hot water wherefrcm tile tea leaf insolubles have to be fitterad before the

25    infusions are consumed. Hot instant tea is a product which contains no water insolubles. This hot instant tea product is fully soluble in hot water and this solubilized product can be consumed as such wtthout any fittration. Iced tea is a product made frcm tea where tile fully water-soluble fractions of tea are dissolved in water with or without additional Havou10 and tile dissolved tea solution is kept chilled in a refrigerator before it is consumed.
30

The process for tile preparation of hot instant tea and iced tea are described in ltterature. One such description can be found in the reference book 'Tea - Cuttlvation to


Consumption'edned by K. C. Wilson & M. N. Clifford & published by Chapman & Hall

(1992).

Many tea manufacturing processes produce by-product streams that conlain aroma volatile compounds. In the leaf tea manufacture process, lhe dl}'erexhaust conlaining aroma volatiles can be cooled to oblain an aqueous condensate containing aroma volati~ compounds. The evaporator condensate stream in instant tea manufacturing
processes also contains aroma volatile compounds.  However, the aroma in these

condensate  streams  is  usually  present  at  very  low  levels.  Typically  the

10    concentration of aroma volatiles in the condensate streams is below 500 mg/1, and often less than 50 mg/1 and can be as low as 10 mg/1. This dilute nature of the aroma in the condensate streams restricts their application as a source of aroma for add-back. These condensate steams are often not utilized or are limned in their
use due to the extremely low concentrations.  In many cases these streams are even

15 discarded, leading to loss of precious aroma bearing compounds, This is because lhe known processes for recovel]l of these compounds are enher not technically and/or commercially viable or are very inefficient Tea aroma is one of the most important factors for determining tea qualny. Hence tea wnh good aroma profile fetches a premium in the market Recovery of aroma volatile compounds from the condensate streams can provide
20    a source of natural tea aroma that can be used for add-back and improving the aroma of the tea.

Many processes to recover and concentrate volatile compounds from dilute streams have been known and practised. These processes include reverse osmosis, distillation,

25    cryoconoentration, freeze drying, staged/partial condensation and pressure swing adsorption. Distillation has always been one preferred process, GB 1061009 (Salada Foods, 1967) describes a process for recovery of aroma from aqueous tea streams using
distillation earned out in an inert atmosphere. The present inventors have determined that using the method descnbed in the GB publication, the quality of the tea aroma recaptured 3 o   improves to a small extent but a large percenlage of the aroma present in the tea aqueaus
extract can not be recovered using this process and there are high losses.

It is thus an object of the present invention to overcome or ameliorate at least one of the disadvanlages of the prior art.

It is an object of the present invention to provide for a process for the enhanced recovery of volatile compounds from aqueous tea extract streams like oondensate slreams from hot instant tea and ice tea manufacture.

It is another object of the present invention to provide for a process for the reoovery of volatile oompounds like aroma oompounds in more concentrated fonns as compared to
10    known processes of the prior art

SUMMARY OF THE INVENTION

Accorrling to the first aspect of the present invention there is provided a  process for

recovering volatile oompounds from an aqueous tea extract by distilling the said extract by

15    fractional distillation oomprising oondensing of vapou•rs, separating the oil phase condensale from the aqueous phase and refluxing the substantially oil-free aqueous phase.

It is particularly preferred that that the dislilling is earned out at not less than 0.7 bar

2 o    absolute pressure.

It is further particularly preferred that the fractional dis@ation is carried out in a distillation assembly that contains less than 5 volume percent of non-rondensable gasas prior commencing the distillation operation.

25

It is even further particularly preferably that the dislillation assembly is filled with steam before commencing the distillation operation.

Accorrling to a seoond aspect of the present invention there Is provided a process for 3 o producing tea with enhanced aroma comprising mixing tea with the volatile compounds
recovered by the first aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Tea

11Tean for the purposes of the present invention means material from Camellia sthensis var.

sinensis or Camellia sinensis var. assamica.  It also includes rooibos tea obtained from

Aspalathus linearis. "Tea" is also intended to include the product of blending two or more of any of these materials.

The aqueous tea extract of this invention could be from any of the following tea sourres: fermented tea (i.e. black tea), semi-fermented tea Q.e. oolong tea) andlor substantially
10    .unfermented tea Q.e. green tea). "Fermentation" refers to the oxidative and hydrolytic process that tea undergoes when certain endogenous enzymes and substrates are brought together, e.g., by mechanical disiuption of the cells by maceration of the leaves. Duling this process colourless catechins in the leaves are converted to a complex mixture
of yellow and orange to dark-brown polyphenolic substances.  Attemately and preferably

15    the aqueous tea extract could be spent or waste condensate streams from processes for preparing hot instant teal iced tea.

Many volatile compounds confnbute to the aroma of tea. A list of most of the aroma volatile compounds is reported in 'Tea- Cultivation to Consumption'edtted by K. C.

20    Wilson & M. N. Clifford &published by Chapman & Hall(1992). Some of the important tea aroma compounds from this list are acetaldehyde, benzaldehyde, benzyl alcohol, t,t-2,4-decedienal, b-damascenone, diacetyl, g_eraniol, c-4-hep!enal, t,t-2,4-heptadienal, t-2-heptanal, 2,4-hexadienol, 1-hexanal, 1-hexanol, hexanoic acid, c-:>-hexenol, t-2-hexenal, b
-ionone, linalool & tts oxides, methional, 2-methyl butanal, 3-methyl butanal, 2-methyl 2 5   propanal, methyl sulphide, methyl salicylate, nero!, t-2,c-6-nonadienal, t,t-2,4-nonadienal, nonanal,  octanal,  t-2-<>ctenal,  1-<Jdene-3-<JI,  1-pentanol,  t-2-jlentenal,  1-penten-3-<ll,
phenylacetaldehyde, 2-phenylethanol, a-terpenial, and vanillin.

A number of aqueous condensate streams containing aroma volatiles are available or

30    potentially available from tea manufacturing processes. The concentration of aroma volaUies in these aqueous condensate streams range from 10 mgn to 500 mgn. Such streams include the one from aroma capture from the dryer exhaust in leaf tea

manufacture described In WO 2007/039018. Aroma stripping from tea extraction processes before ~s ooncentration has been desolibed in patents GB 855 423, GB 1490 370 and US 3,717,472. All these processes resutl in aqueous aroma oondensates. Similarly, the oondensate oollected in the evaporation stage for ooncentration of soluble solids also has aroma volatiles, though at very low levels.

In the present Invention, the volatile compounds can be recovered from waste streams which would otherwise have fetched no value. The invention has the advantage in that the volatile oompounds are recovered and concentrated to a low water content The invention

10    also provides for concentrating the aroma oompounds to a form of nearly pure oil. The concentration of the volatile compounds by the process of the invention provides far improved economy when they are added back to tea to prepare aroma enriched tea. Since the concentrate has low water oontent, tea to which ~ is added requires very little or no subsequent drying to prepare an aroma enriched tea product Hence the process

15    preferably comprises simply spraying the concentrate on to tea and packing the sprayed tea.

The first aspect of the present invention provides for a process for recovering volatile

compounds tram an aqueous tea extract comprising tractional distillation of said extract in

20    a distillation assembly wherein the vapours are substantially condensed, the oil phase in the condensate is separated from the aqueous phase and the substantially oil-free aqueous phase is refluxed. The tractional distillation is preferably a mutli-stage batch distiflation.

2 5 The process preferably comprises substantial condensation of the overhead/rectified vapours. This may be achieved using cold traps, cold fingers or any other known oondensation methods.

A preferred aspect of the invention provides for a process wherein the assembly contains

30    less than 5 volume percent of non-a>lldensable gases prior to chal!)ing the aqueous tea extract to said assembly.

A further preferred aspect provides for the distillation assembly to be substantially free of air or any other non-rondensable gases before commencing the distillation operation. Most preferably the distillation assembly is filled with steam before commencing the distillation operation. By the phrase 'non-<:ondensablegas'is meant to include those gases having a vapour pressure greater than 1 bar (absolute) at O'C. Examples of commonly used non-<:ondensable gases are air, oxygen, n~rogen, carbon dioxide, and helium.

The process of the invention is capable of recovering and concen!Iating aqueous tea 1 D    extract which generally has 10 to 500 ppm of volatile compounds.  Starting with such a concentration, the distillation process of the invention recovers and concentrates the aroma compounds to a concentration higher than 20000 ppm. It is also possible to concentrate ~ to nearly pure  oil.   The inventors have used all the recovery and concentration equipments known to them and available in the art for concentrating

15    aqueous tea extracts and found that with known equipments, the extract could be concentrated by a factor of at most 40. Using the process of the invention, a concentration factor of greater than 80, sometimes greater than 100 could be obtained. It has also been found that out of the total amount of the volatile compounds in an aqueous tea extract , nearty 70 to 85 percent of the volatile compounds can be recovered by the process of the

2D    invention. Thus the losses are at most 30%.

The distillation assembly is preferably operated at substantially atmospheric pressure.

The distillation assembly used for the process of the invention generally comprtses a 2 5   reboiler, a distillation column, a condenser and a liquid-liquid separator. The process is optimally operated when the volume ratio of the total feed to the reboiler to the total condensate hold up in the condenser and liquid-liquid separator at the conclusion of the distillation operation is higher than 100, preferably in the range of 100 to 2000, more
preferably in the range of100to 500.

30

A very important advantage of the present invention is that the process can be canied out at close to ambient conditions of pressure i.e. pressures close to atmospheric. The

distillation is generally earned out with reboiler temperatures near 100'C,preferably in the temperature range of 80 to 1DO'C. The reboiler is heated to this temperature using any known heating means e.g. using a electrically heated resistance coils, or the reboiler could be jacketed and hot water or steam could be passed through the jacket to heat the material being distilled.

A suitable method of ensuring that the distillation assembly does not comprise more than 5% no~ndensable gases before commencing the distillation operation, is to fill it up with steam while purging the air out of the assembly. Steam may be tapped form an external

10    source e.g a boiler and piped into the assembly. Allemately, a small amount of water is initially taken in the reb oiler and all of the water is boiled off to steam to fill up the distillation assembly while the air is purged out of the assembly.

A preferrnd method of ensuring high recovel)l and minimizing loss. of volatiles is by

15    following a practice wherein the aqueous tea extract desired to be concentrated is not

added to the reboiler at the start of the process. Initially, water, which comprises a small percentage e.g. 5 to 10 wt% of the total aqueous tea extract feed to be distilled, is added. to the reboiler. The distillation operation is started with this feed and a total reflux is established. The operation is carried out till the air is purged from the column. Thereafter

20    the aqueous tea extract is gradually added to the reboiler while ensuring that a reflux is maintained as the distillation process is earned oul It has been found that in a typical batch of 100 kg of aqueous tea extract, the distillation operation can generally be completed in a Ume of 4to 6 hour,;.

2 5 The distillation assembly has a distillation column which is preferably filled with packings which preferably provides a low hold up in the range of 10 to 20%. To achieve this end, packings are generally chosen from structured packings, wire mesh packings, saddles or Raschig rings. The packed column for the process of the invention is generally kept short and usually does not require more than 10 equilibrium stages, preferably 3 to 5 equilibrium

3 o stages. Having such short columns also ensures lower equipment cost and thereby improves the commercial viability of the process. A preferrncl condition for carrying out the process of the invention comprises carrying out the distillation at a low boi~up rate,

preferably in the range of 30 to 40% of Hooding. The distillation is preferably canied•out under near total reffux conditions.

The distillation assembly preferably has a condenser that is a shell and tube condenser, preferably ver1ically mounted. The vapotS are preferably be fed to the verucal condenser from the top. The vapors are preferably be fed to the tube side of the condenser.

The distillation assembly is preferably operated at conditions that ensure minimal or substantially no internal reffux. This is ensured, for example, by providing good Insulation 10   on all the unlls and pipelines where ffow of vapours occurs. Ensuring minimal or substantially no internal reftux is especially important during the start-up stage to ensure minimal loss and maximum recovery of volatile compounds.  This is achieved, for example, by ensuring that the distillation column is externally heated during start-up. The heating may be by known method e.g. by providing steam in a jacket around the distillation
15    column.

It has also been determined that the pipelines for transporting the vapours in the distillation assembly are preferably of a small diameter. It is especially preferred that the ratio of the

diameter of the liquid-liquid separator to the diameter of the pipeline downstraam of it is

20    greater than 2, preferably in the range of2 to 20, more preferably in the range of10to 20.

The invention will now be illustrated with the help of the rol/owing non-limiting drawings and examples.

25    BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic of an embodiment of the distillation assembly as per an aspect of the invention.

DETAILED DESCRIPTION OFTHE DRAWINGS

As shown in Figure-11he distillation assembly comprises a reboiler (E1) equipped with a jacket (J1) to which aqueous tea extract can be added through valve (V1) and residue can be drained using valve (V2). The assembly is equipped with a packed column (E2) filled with Raschig ring packings. A vertical shell and lube heat exchanger (E3) is provided to condense the volatiles. A valve (V3) is• provided on condenser (E3) to drain any condensate. A liquid-liquid separator (E4) is provided downstream of the condenser to collect the concentrated volatile compounds. Various liquid-liquid separators may be used. Prefened ratio of the volume of the reboiler to that of the liquid-liquid separator is in the
10    range of 50 to 2000, more preferably in the range of 100to 500. A valve (V4) is provided al the top of the liquid-liquid separator as an oil avertlqw valve. A product discharge valve (V6) as shown is provided to collect the concentrated volatile compounds. A reflux valve (VS) is provided to control the reflux ratio at which the distlllation is carried out

15    When in use, calculated amount of water is first added to the reboiler (E1), the water in the reboiler is heated by passing steam in the jacket (J1). k. the water in the reboiler boils to form steam, the steam is allowed to fill up all parts of the distillation assembly, and the air is purged from the assembly using the various vent valves. When the distillation assembly is substantially filled up with the condensable gas viz steam, the aqueous tea extract is

2 o added to the reboiler to begin the distillation. lnnially a part of the total amount of tea extract is added to the reboiler. The overhead vapours are condensed in the condenser, the ail• phase in the condensate is separated firom the aqueous phase and the substantially oil-free aqueous phase is ratiuxed. The reflux valve is adjusted to the desired position to get the desired reflux ratio. As the prooass attains close to steady state operation, the rest of

2 5 the tea extract is added intermittently to the reboiler. The reb oiler is usually kept filled to 5 to 70 volume percent filling. k. the distillation proceeds, the concentrated volafile compounds collect in the liquid-liquid separator (E4). At the end of the prooass, the concentrated volatile compounds are drained through valve (V6) and collected as desired.

Examples

Example-1

A batch of 20 L of aqueous tea extract having 200 mgll of volatile aroma compounds was distilled using lhe process of the invention using the distillation assembly as shown in Figure-1. In lhe distillation assembly, lhe volume of lhe reboiler was 40 Jitres. A two meter tall glass column filled with Sulzer BX packing was used. The volume of condensate collected was 1000 mi. About 31ttres of water was used initially to purge lhe air out of the assembly and to saturate it with steam prior to addition of lhe tea extract A two-phase condensate appears almost at lhe start of distillation- the lighter phase being lhe oil phase

10    while the heavier phase being lhe aqueous phase. Care was taken to separate lhe two phases and only lhe aqueous phase was refluxed to lhe distillation column during the entire operation. The resuns in tenns of (a) percent of volatile compounds lost, (b) lhe concentration ratio and (c) lhe% recovery were detennined and are summarized in Table

-1.

15

Example-2

A batch at exactly lhe same conditions as in Example-1 was carried out except lhat no water was used to saturate lhe assembly prior to adding lhe tea extract . The distillation was started with air filled in lhe void spaces of lhe distillation assembly. The corresponding
2 o   results are summarized in Table - 1.

Example3

A batch of 144 L of aqueous tea extract having 346 mgn of volatile aroma compounds was distilled using lhe process of the invention using the distillation assembly as shown in

25    Rgure-1. About 6 Jttres of water was used initially to purge lhe air out of the assembly and to saturate it with steam prior to addition of lhe tea extract • A two-phase condensate appears almost at the start of distillation - the lighter phase being the oil phase while the heavier phase being the aqueous phase. Care was taken to separate the two phases and only the aqueous phase was reffuxed to lhe distillation column during lhe entire operation.

3 o The distillation was carried out by gradually adding the tea extract to the reboiler over a period of 8 hours. The total time of distillation was 10 hours. In the distillation assembly the volume of the reboiler was 200 lttres. About 335 ml of total distillate product rich in

aroma was recovered from the liquid-liquid separator of which 30 ml was aroma in pure oil phase. The corresponding resuHs are summarized in Table -1.

Example-4:

A batch of 100 L of aqueous tea extract having 302 mg/1 of volatile aroma compounds was distilled using the process of the invention using the distillation assembly and the process similar to Example- 3. About BOO ml of condensate rich in aroma was recovered from the liquid-liquid separator. The corresponding results are summarized in Table- 1.

10    Example- 5:

A batch distillation run similar to Example4 was carried out except that the reffux comprised of a mix of oil and aqueous phases. The corresponding resuHs are summarized in Table -1.

15    lnTable-1,

Concentration Ratio = Concentration of aroma compound in producV Concentration of aroma compound in feed
The material balance of the aroma compounds is given by;

F=P+B+L

20    Where F is the amount of aroma compound in the feed, P is the amount of aroma compound in the product, B is the amount of aroma compound in the residue and L is the amount of aroma compound lost in the process.
%    recove!)l = P/F • 100

%    losses = UP •1 00

25
    
Table-1                           
                           
Exam ole        %losses            Concentration ratio        %Recovery
Example -1    5        19        95
                       
Example-2    30        12        40
                       
Example -3    0        270        62
                           
Example    4    0        97        76
                           
Example    5    56            39        31
                           

The data in Table -1 indicates that the Joss of volatile aroma compounds in the examples as per the invention (Examples 1 to4) is much Jess as comparad to process of the prior art (Example 5) . Also the %recovery in the examples as per the invention is significantly better then the example cri the prior art. Further, with the process of the present invention, product having higher concentration of aroma compounds can be preparad as comparad to the prior art.

10

Example 4 to 11:

Experiments were conducted in a distillation assembly similar to that shown in Figure -1 except that (0 the volume of the reboiler was 10 J~res; 00 the volume of the condenser was 43 ml and (iii) the column was 1 m long pecked and had a diameter of 38 mm. It was

15    packed with glass Raschig rings of diameter 12mm and length 12mm. Experiments were done to concentrate aqueous solutions of two model aroma compounds present in tea extract solution. The two model compounds used were 2-methyl propanal (which is a Jaw boiling compound) and Unalool (which is a relatively high boiling compound). The experiments were conducted similar to Example - 1 except that the following condnions

2 o   were used:

In Experiments 6, a and 9 about three Jnres of feed were fed to the reboiler over the course of distillation. In Expemnents 7, 10 and 11, abcut 5 Jnres of feed were fed to the reboiler over the ocurse of distillation. In all the experiments 30% of the feed was boiled

25    over.

Example - 6, 7: The distillation was conducted after purging the assembly of air and filling with steam prior to the start of distillation. The feed was added gradually over a period of 3 hours and the total time of distillation was 4 hours.

Example - 8, 10: The disbllation was conducted starting with air present in the assembly. The reb oiler was filled with all of the feed at the beginning of the experiment The total time of distillation was 4 hours.

Example- 9, 11: The distillation was conducted after purging the assembly of air and filling

10    with nttrogen prior to start of distillation. Nitrogen flow was stopped gradually once the system filled up with the vapours of the feed. The total time of distillation was 4 hours.

The resu~s on %recovery and %losses are summarized in Table- 2.

15    Table-2

Example        Model    Concentration    Concentration    Concentration    %        %
        compouncj    in feed, mg!L    in    product,    ratio    recovery    losses
                    mg!L                       
6        2-methyl    97        4905    51        54.8    15.0
        orooanal                               
8        2-methyl    133        950    7.2    6.6    92.4
        orooanal                               
9        2-methyl    96        721    7.5        7.3        91.4
        propanal                               
7        Linalool    186        18900    101        88        4
10        Una loci    193        17515    91        78        15
11    •    Linalool    190        17195    91        79        15

The data in Table- 2 indicates that superior recovery can be obtained using a preferred aspect of the invention (Examples 6 and 7). Further, the losses using the preferred
process of the invention are much lower.
 
1.    A process for recovering volatile compounds from an aqueous tea extract by distilling the

said extract by fraclional dislillation comprising condensing of vapours, separaling lhe oil phase condensate from the aqueous phase and reftuxing the substanlially oil-free aqueous phase.

2.    A process as claimed in claim 1 comprising distiHing at not less than 0. 7 bar absolute pressure.

3.    A process as claimed in claim 1 or claim 2 comprising distilling in a distillalion assembly that contains less than 5 vdume percent of non-condensable gases prior to commencing the dislillation operation.

4.    A process as claimed in claim 3 wherein the disfillalion assembly is substantially free of air or any other non-condensable gas before commencing the dislillalion operation.

5.    A process as claimed in any one of the preceding claims 3 or 4 wherein the distillalion

assembly  is  filled  with  steam  before  commencing  the  dislillation  operation.

6.    A process as claimed in any one of the preceding claims 3 to 5 wherein the dislillalion assembly comprises a reboiler, a distillation column, a condenser and a liquid-liquid separator wherein the volume ratio of the total feed to the reboiler to the total condensate hold up in the condenser and liquid~iquid separator at the conclusion of the distillalion operalion, is more than 100.

7.    A process as claimed indaim6wherein said volume ratio is in the range of 100to2000.

8.    A process as claimed in claim 6 or 7 wherein said distillation column has packings which provide a low hold up in the range of10 to20%.
9.    A process as claimed in any one of the preceding claims 6 to 8 wherein the ratio of lhe diameter of the condensate receiver to the diameter of the pipeline downsteam of it is in lhe range of 2 to 20.

10.    A process as claimed in any one of the preceding claims 6 to 9 comprising a relatively short packed column of 3 to 5 ecuilibrium stages.

11.    A process as claimed in any one of the preceding claims 6 to 10 wherein said condenser is a vertically mounted shell and tube condenser.

12.    A process as claimed in any one of lhe preceding claims comprising distilling at a low boil-up rate in lhe range of 30 to 40% of flooding.

13.    A process as claimed in any one of the preceding claims comprising fractional distillation at near total reflux conditions.

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