By C. P . Wilson
Rb s b a r c h La b o r a t o r y, Ca l i f o r n i a Fr u i t Gr o w e r s Ex c h a n g b, Co r o n a, Ca l i f o r n i a
The first serious a tte m p t to convert th e low er grades of C alifornia lemons into b y -products was m ade in 1898 a t N ational C ity, San Diego C ounty.
O ther factories for th e production of various pro d u cts from citrus fru its have been s ta rte d a t various tim es a t P asadena, R edlands, S an ta A na, R iverside, and other places. An excellent account of these has been given b y Will.®
W ork along sim ilar lines in connection w ith F lorida oranges has been published by M c D e rm o tt3 an d by W alker.4
T he U nited S tates D e p a rtm e n t of A griculture becam e in terested in th e possibility of developing a citrus by-p ro d u cts in d u stry in th is co u n try , and in 1907 sent M r. E. M. Chace to Ita ly to stu d y sim ilar industries th e re .6
M r. C hace m ade a survey of th e lem on in d u stry in C alifornia in 1908, an d as a resu lt of his w ork th e D e p artm en t established th e C itrus B y -p ro d u cts L a b o rato ry in 1911 a t Los Angeles.
T he early w ork of th is lab o rato ry was done by M r. H.
S. Bailey and th e a u th o r u nder th e direction of M r.
Chace, who has been in charge of th e la b o ra to ry since its beginning. T he C itru s B y-products L ab o rato ry secured accu rate d a ta on th e m ethods applicable to th e m an u factu re of citric acid, and th e yield to be ex
pected from lemons.
I t m ust be rem em bered th a t th e average haul by which citrus fru it raised in California reaches its m ark et is ab o u t 2500 miles. This precludes th e shipm ent of a n y th in g b u t sound fru it of good appearance and keeping q u ality . T here is necessarily left a large q u a n tity of fru it th a t is n o t fit to pack an d ship. This is culled o u t for reasons such as: irregular shape, oversize, undersize, fro st dam age, h e a t dam age, clipper cuts caused by careless picking, th o rn pricks, -wind scars, th rip m arks, excessive scale, or an y so rt of m echanical in ju ry or indication of decay or infection of a n y kind.
T he steps in th e process of m an u factu re of citric acid m ay be readily followed by m eans of th e accom panying sketch.
E X T R A C T IO N OF J U IC E
All th e citric acid in a lem on is contained in th e
1 R e a d before th e S o u th e rn C alifornia Section of th e A m erican C hem i
cal Society, Los Angeles, C al., D ecem ber 1920,
* Th i s Jo u r n a l, 8(1 9 1 6 ), 78.
* Ib id ., 8 (1 9 1 6 ), 136.
« F lo rid a A g ricu ltu ral E x p erim en t S ta tio n , Bulletin 135.
»Bureau of P la n t In d u s try , U. S. D e p a rtm e n t of A g ricu ltu re, Bulletin
1*0,
juice, so th a t th e sep aratio n of juice from th e pulp m ay be considered th e first step in th e recovery of the acid.
T he fru it is shoveled or dum ped on to a b road belt conveyer and, if o th er p ro d u cts th a n acid are to be m ade, is graded to give th e kind of fru it needed for such a p ro d u ct. A ny lem on can be used to make citric acid, th o u g h , of course, th e yield varies enor
m ously from as low as 15 lbs. per to n from badly frozen lem ons to 50 lbs. or m ore from th e thin -sk in n ed juicy lem onettes. I t is in terestin g to n o te th a t th e effect of frost is to decrease th e am o u n t of juice in th e fru it and also th e percentage of acid in th e juice which rem ains.
T he fru it passes from th e grading belt by w ay of a b ucket elevator to a pair of cu ttin g knives which te a r th e lem ons coarsely and drop th e m into a set of wood roller crushers which tho ro u g h ly bruise th e fru it and press o u t some juice. T he crushed fru it drops into th e hopper of a continuous screw press where m ost of th e juice is rem oved. T he continuous presses are sim ilar to those used for pressing m oisture, fat, or oils from garbage, fish scraps, copra, vegetable seeds, etc.
From th e first press th e juice ru n s to th e m easuring ta n k , while th e pulp is passed th ro u g h a soaking box where it is s a tu ra te d w ith w ater. F rom th is box th e wet pulp is dum ped in to an o th er continuous press an d th e juice goes to th e sam e m easuring ta n k as did th e first juice. Pulp from th e second press is ele
v a te d to th e hopper of a th ird press, receiving a spray of w ater as it ascends th e elevator. Juice from the th ird press serves as m aceration w ater for th e first soaking, while th e pulp passes o u t an d is used as fer
tilizer.
One to n of lem ons contains on th e average about 70 lbs. of to ta l acid (calculated as crystallized citric acid). U sing th e ex tractio n process described above, 85 p er cent or m ore of th is acid is obtain ed in th e juice.
P u re pressed lem on juice contains from 6 to 7 per cen t citric acid, b u t on account of th e dilution by m aceration w ater th e mixed juice obtain ed in factory practice averages ab o u t 4 per cent acid an d contains ab o u t 5 to 5.5 per cent of to ta l solids. T he juice contains ab o u t 0.5 per cen t of insoluble solids an d is ra th e r th ick an d pulpy. I t is stored in wooden ta n k s of a b o u t 57,000 liters capacity, in which it is allowed to undergo ferm en tatio n for a b o u t 4 or 5 days in w arm
June, 1921 T E E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C E E M I S T R Y 555 weather, or a b o u t 10 days in cold w eather. T his
ferm entation seems to liquefy som e of th e m ucilagi
nous, slim y co n stitu en ts an d to coagulate others. T he sugars are com pletely rem oved. T h e chem istry of this change has n o t been w orked o u t in detail, b u t it has been show n th a t th e loss of citric acid b y ferm en
tation is negligible for th e first few days. F a cto ry experience has tho ro u g h ly d em o n stra te d th a t fresh
juice is very difficult to filter, while properly ferm ented juice filters easily an d requires a m inim um of filter-cel.
After proper ferm en tatio n , th e juice is thoroughly agitated so as to reincorporate th e pulp, which during ferm entation has p a rtly sunk to th e b o tto m an d p a rtly risen to th e to p , leaving a clear lay er in th e m iddle.
In earlier p ractice th is m iddle p ortion was draw n off and used w ith o u t filtration, and th e pulp was w ashed by agitation w ith w ater an d subsequent settlin g and d é cantation. T his was a slow, w asteful process an d left in th e ta n k s a slim y volum inous residue th a t was very troublesom e to handle. T h e p resent p ractice is to filter th e whole juice a fter boiling w ith filter-cel.
The well-mixed ferm ented juice is p um ped in to pine tanks 2.4 m eters deep an d 2.4 m eters in d iam eter, equipped w ith copper h eatin g coils an d m echanical agitators. A bout 7500 liters are h andled a t a charge, and enough filter-cel is ad d ed to clarify th e juice on boiling. T he o p erato r adds th e a m o u n t of filter-cel he deems necessary, as in d icated b y experience, and brings th e juice to a boil. A sam ple is w ithdraw n, and if it clears quickly b y settlin g it is read y to filter. If it does n o t clear readily, m ore filter-cel is added. T he juice is again boiled an d th e te s t re p eated u n til th e juice is read y to filter. On th e average, ab o u t 12 to 20 kilos of filter-cel are required for each 1000 liters of juice.
F iltra tio n is carried o u t by m eans of a copper-lined Sw eetland press. A 30-in. wood p la te an d fram e, open delivery, w ashing ty p e press is used w hen g reater c ap acity is necessary. T he cake is th o ro u g h ly washed w ith h o t w ater. T he filter-cel m ay be recovered from th e press cake by b u rn in g o u t th e organic m a tte r, or i t m ay be used for th e p ro d u ctio n of decolorizing carbon, as m entioned later.
P R E C IP IT A T IO N O P C A L C IU M C IT R A T E
T he filtered juice is a b rillian t, lig h t am ber liquid, averaging ab o u t 4 per cen t acid. I t is pum ped in to wooden ta n k s 2.4 m eters in d iam eter by 1.5 m eters high, w ith staves m ade of Oregon pine 7.6 cm. th ic k . E ach ta n k is equipped w ith copper heatin g coil a n d m echanical a g itato r. A charge consists of a b o u t 3700 liters of juice, an d from a la b o rato ry assay th e am o u n t of calcium required to p recip itate th e citric acid is calculated. In practice, sufficient h y d ra te d lim e of. high p u rity is add ed to p re c ip ita te 90 per cent of th e to ta l acid, calculated as citric. Sufficient calcium carb o n ate is th e n added to neutralize th e rem aining 10 per cen t of acid, and an excess of 7 kg. of calcium c arb o n ate is added.
E xperience has show n th a t if th e juice is com pletely n eutralized w ith calcium hydroxide, dark-colored com pounds are form ed. T hese com pounds are diffi
cult, if n o t im possible, to wash out, an d if n o t rem oved cause th e liquor produced by th e decom position of th e c itra te to be very d ark colored. T his increases th e difficulty of securing satisfacto ry crystals.
I t has also been show n th a t, how ever g reat th e excess of calcium carb o n ate add ed to th e juice, th ere is alw ays a sm all residual acid ity , v ary in g from 0.08 to 0.20 per cent, depending on th e acid ity of th e original juice.
T he resistance to corrosion of th e copper coils placed in these ta n k s is notew orthy. For 2 yrs. th e ta n k s containing these coils were used for decom posing th e c itra te as well as p recip itatin g it from th e juice. T he coils were therefore su b jected to th e action of liquors containing 10 to 20 per cen t of citric acid an d ab o u t 0.2 per cen t of sulfuric acid for a g reat m an y days.
D uring th e la st tw o years th e ta n k s were used only for p recip itatin g citrate. A p p aren tly th e coils were w orn th in by th e swirling calcium c itrate, ra th e r th a n b y reaction betw een th e copper an d th e acids.
T h e p recip itated c itra te is pum ped in to an iron p late a n d fram e filter press and th o ro u g h ly washed w ith w ater a t as near 100° C. as possible, an d th e n p a rtly dried by blowing air th ro u g h th e cake. The c itra te is dum ped by w ay of a convenient chute directly in to one of a series of pine ta n k s exactly like those used for p recip itatin g th e citra te , except th a t it has no h eatin g coil.
D E C O M P O S IT IO N O F C IT R A T E
T he c itra te is suspended in dilute liquor obtained in w ashing th e previous b a tc h of gypsum , and th e am o u n t of 66° Be. sulfuric acid needed for th e com plete decom position is added. T he accuracy of th is reaction is checked by filtering off a sam ple of th e acid liquor, a fter th orough ag itatio n for 30 m in., and adding ab o u t 5 cc. of 45 per cen t C aC l2 solution to an equal
556 T E E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C E E M I S T R Y Vol. 13, No. 6 volum e of th e filtered liquor. A fain t precipitate of
calcium sulfate should be noticeable after holding in th e steam b a th 5 m in., in dicating an excess of not more th a n 0.2 per cent sulfuric acid.
If to o m uch sulfuric acid has been added it is nec
essary to add calcium c itrate, th e am o u n t of which is ascertained as follows: T o tal acid ity of th e liquor is determ ined by titra tio n of a 10-cc. sam ple, using phenol- phthalein. A solution is th e n m ade up which is exactly 10 cc. in volum e an d 10 per cent acid (as citric) in stren g th . As th e liquor alw ays contains over 10 per cent citric acid, th is is a sim ple dilution. A sta n d a rd solution is m ade containing 10 per cent citric acid, w ith a drop or tw o of ferric chloride solution added to give a d ep th of color equal to th a t of th e solution to be tested . T his is for th e purpose of over
coming th e difficulty in com paring dep th s of color which are n o t th e sam e shade, an d in practice has been very successful. T hree drops of a 1:1000 solution of thym olsulfonephthalein and 1.5 cc. 0.5 N sodium hydroxide are added to each solution. The pure citric acid solution assum es a ch aracteristic yellow tin t, while th e sam ple containing sulfuric acid con
tin u es to display th e red color due to th e more highly ionized m ineral acid. T he la tte r is titra te d w ith 0.5 N sodium hydroxide until th e color m atches th a t of th e sta n d a rd . T he num ber of cc. of 0.5 N alkali used in th e last titra tio n m easures th e excess of sulfuric acid, and hence the am o u n t of calcium c itra te which will be decomposed by it. T his m ethod has been found very practical in facto ry control work.
T he decom position of th e c itrate is usually com pleted in a b o u t 3 hrs. T he p recip itated calcium sulfate is allowed to settle by g rav ity and th e acid liquor draw n off. T he p recipitate is w ashed free from acid by d ecan tatio n by th e co u n tercu rren t principle, using a five-step cycle. T he calcium su lfate residue is sun-dried and sold as fertilizer.
T he acid liquor th u s obtain ed is a light am b er solu
tion containing ab o u t 12 to 15 per cent acid. I t has a density of a b o u t 5° to 6° Be., contains ab o u t 0.2 per cen t sulfuric acid, an d has a p u rity of ab o u t 95 to 98 per cent.
C O N C E N T R A T IO N O F L IQ U O R S
T he acid liquor from th e decom position of citrate is ru n into lead-lined open evaporators of ab o u t 17,000 liters capacity, equipped w ith lead steam coils, and in these evap o rato rs th e liquor is co n cen trated to 20° to 25° Be. T he liquor is k ep t a t incipient boiling an d never boiled hard . A gitation is m ain tain ed by air jets.
The concentration is com pleted in lead-lined vacuum pans of a b o u t 7000 liters capacity. T he co n centrated liquor is delivered to th e lead-lined crystallizers a t 37° to 38° B6. In 3 to 5 days a good crop of crystals is set, and th e m other liquor is draw n off and reboiled to produce an o th er crop. T he crystals are washed w ith cold w ater in a b asket centrifugal. These cen
trifugals are sta n d a rd 30-in. W eston ty p e machines w ith bronze baskets. T he inner lining is perforated sheet monel m etal. T h e curbs are lined w ith lead.
T he crude crystals are usually m ade by th e granu
la tio n process in which th e crystallizing liquor is kept in gentle ag itatio n . A heav y crop of sm all crystals is th u s produced.
T h e crude crystals are dissolved in w arm w ater in a lead-lined ta n k by dum ping th em in a perforated lead b ask et suspended a t th e to p of th e ta n k , utilizing th e well-known principle of th e h eav y solution going to th e b o tto m while th e m ost dilute solution is always a t th e surface where th e crystals are continually dis
solved.
P U R IF I C A T IO N O F C R U D E A CID
T he solution of crude acid is subjected to laboratory te sts an d purifying tre a tm e n t prescribed and carried o u t u nder stric t la b o ra to ry control.
T he im purities to be rem oved are m ainly: (1) or
ganic color, (2) lead, (3) copper, tin , an d antim ony, (4) iron an d nickel, (5) sulfuric acid, and (6) calcium sulfate. All of these, except organic color,would appear in th e ash on incineration, an d th e ir elim ination au
to m atically brings th e ash to a negligible quantity.
o r g a n i c c o l o r— Organic coloring m a tte rs are
present in th e raw juice, others are form ed on heating and rem ain in th e filtered juice, and to som e extent are held by th e c itra te th ro u g h o u t th e washing, and ap p ear in th e liquors. Some color is added by de
com position of th e citric acid and organic im purities on h eatin g in th e evaporators. If n o t rem oved this color appears in th e final crystals, bringing th em below sta n d a rd as to color an d translucency.
In our early work bone-black was used, b u t it had to be tho ro u g h ly w ashed w ith hydrochloric acid to rem ove th e calcium phosphate, an d th e n w ith water to rem ove th e acid and soluble salts. T his was ex
pensive and laborious. E xperim ents w ith a num ber of decolorizing carbons soon showed th e p ro d u ct known as filtchar 5B to be well suited to th e work, and as com pared w ith th e bone-black to be cheaper in first cost, and in operating cost. Since th e n an o th er carbon has been applied very successfully.
F iltch ar is added to th e liquor in th e p roportion of a b o u t 1 to 2 per cent of the w eight of th e liquor, about 6000 to 7000 kilos of liquor being tre a te d in a batch.
The liquor is slowly w arm ed to ab o u t 70° C. Other corrective tre a tm e n ts are given a t th e sam e time.
T he com pletion of th e decolorization is te ste d by filtering a sam ple of th e liquor, tre a tin g a portion of th e filtered liquor w ith more filtchar, h eatin g and filtering, and com paring th e color of th e tw o filtrates.
M ore filtchar is added or not, as in d icated by this te st. T he final decolorized filtrate is a very pale straw color in layers several inches deep, an d appears practically w ater-w hite w hen seen th ro u g h a three- fourths-inch te s t tube.
l e a d— A p a rt of th e lead is rem oved as sulfate by
th e sulfuric acid, a sm all am o u n t of which is norm ally present in this liquor. The rem ainder of th e lead is rem oved by p recip itatio n as lead sulfide.
c o p p e r, t i n, a n d a n t i m o n y— C opper and tin are ta k e n up from pipe lines, pum ps, an d valves, an d an
tim o n y from th e lead pipe lines and containers, which are alloyed w ith 2 to 4 per cent of an tim o n y for stiffen
June, 1921 T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 557 ing. All th ree m etals are p recip itated as sulfides
at the sam e tim e th a t th e lead is rem oved.
i r o n a n d n i c k e l— Iro n enters th e process as a
slight im p u rity in th e filter-cel, calcium hydroxide, calcium carbonate, an d sulfuric acid, an d is dissolved from certain p a rts of th e presses and other m achinery with which th e liquor comes in to co ntact.
Iro n in th e ferric s ta te im p a rts a d irty brow nish color to th e acid crystals. In th e ferrous s ta te iron gives no noticeable color, b u t it slowly oxidizes and causes th e crystals to become d istin ctly yellow on standing, even in closed containers. T he color due to iron strikes th e eye im m ediately, an d from a com m er
cial p oint of view is one of th e m ost undesirable defects the crystals can possess. •
Nickel is ta k e n up from monel m etal containers and conducting lines, etc., and, th o u g h present in sm all am ounts, it im p a rts a brow nish tin t to th e crystals.
In some cases th e re seems to be deposited a very fine precipitate of oxide of nickel which gives th e crystals
In some cases th e re seems to be deposited a very fine precipitate of oxide of nickel which gives th e crystals