46

Chapter 3

Soap alld DEIEI~4EI1Is

The washing industry, usually known as the soap industry, has roots over 2CXXl years in the past, a soap factory having been found in the Pompeii excavations. However, among the many chemical process industries, none has experienced such a fundamental change in chem-ical ra'w materials as have the washing industries. It has been generally a~pted that the per capita use of toilet soap is a reliable guide to the standard of living for any country.

HISTORICAL. Soap itself was never actually "discovered," but instead gradually evolved from crude mixtures of alkaline and fatty materials. Pliny the Elder described the manufac-ture of both hard and soft soap in the first century, but it was not until the thirteenth century that soap was produced in sufficient quantities to call it an industry. Up to the early 1800s soap was believed to be a mechanical mixture of fat and alkali; then CheVTeul, a French chemist, showed that soap formation was actually a chemical reaction. Domeier completed his research on the recovery of glycerin from saponification mixtures in this period. Until Leblanc's important discovery producing lower-priced sodium carbonate from sodium chler ride, the alkali required was obtained by the crude leaching of wood ashes or from the evap-oration of naturally occurring alkaline waters, e.g., the Nile River.

The raw material shortages of World War I led the Germans to develop "synthetic soaps" or detergents. These were composed of short-chain alkyl naphthalene sulfonates, which were good wetting agents but only fair in detergent action. This sparked the interest worldwide in developing detergents, and new developments are continuing to the present time. From the original short-chain compounds the development has progressed through long chain alcohol sulfates in the 1920s and 19305, through alkyl-aryl long chain sulfonates in the 1 940s, to branched chain com pounds in the 1950s and 1960s. During the 19605 the requirement of biodegradability became important and caused the return to linear long chains, becatL

47

trial uses accounted for the difference. Figure. 3'.1 and Tables 3.1 and 3 .3 show the gradual replacement of soap by detergents in the household market.

Laundry products, toilet soaps, shampoos, dish washing products, and cleaning products are the chief household uses of these materials. Industrial uses include cleaning compounds, spe-cialty surfactants for hospital germicides, fabric conditioners, emulsifiers for cosmetics, flow-ing and wetting agents for agricultural chemicals, and rubber processing aids. A potentially large use is for enhanced oil recovery from presently "worked-out" oil wells.

DETERGENTS2

Detergents differ from soap in their action in hard water. Soaps form insoluble compounds with the calcium and magnesium ions present in hard water. These insoluble compounds precipitate out and reduce foaming and cleaning action. Dett:~gents may react with the hard water ions, but the resulting products are either soluble or remain colloidally dispersed in the water. Table 3.2 illustrates the differences between soaps and detergents in composition and manufacture. Table 3 1.3 shows the consumption of surfactants in detergents.

Detergents have been divided into four main groups: anionic, cationic, nonionic, and amphoteric. The largest group consists of the anionics which are usually the sodium salts of

~cientifically, the term detergent covers both soap and synthetic detergents. or "syndets." but it is widely used to indicate synthetic cleaning compounds. as distingUished from soap. It is so used in this book. The U.S. Tariff Commission reports on detergents under the name surface-active agents or surfactants under the broader class of synthetic organic chemicals.

0

E '0 C Q) u

~ Q)

0...

100

80

60 Soaps

40

Detergents

20

~~30~t-=~~~-'--1~9~50~----lC~~(-50------19~7~0~--~1980 Dreff

introduced Tide

Introduced

Fig. 3.1. Relative production of detergents and soap.

48

Table 31.1 Production and Sales of Soaps and Sur'factants

Soap Surfactallt~ Total ~-- ---------~

106$ kt 10$ kt 106S

1940 :313 145,5 1 ,~ ,) ,20 1945 527 11'1'7 :3.S f5h ,)h2 1950 540 l:"301:i 294 ri55 ':5:14 1960 376 '551) q53 [7(\9 [ :3:2Y J970 42, .s()' 1 :3,~J 251),) J ,~()h 19HO 10:30 ,')4,,) K4:30 2f1fj:3 Y4h(J

kt

t-H';,', 1 -:- ').5 196) 2:3-1-:-3132 3:20,~

VJUHCE CPI 4, chap, 29: (':"; Industnat Outlook, 19h2, l'S Dept of Commerce

an organic sulfatp or sulfonate, Detergents can be formulated to produce do prrJCluc:t (i ~:-:t desired characteristics rUflf2;ing fr(lnl rrJaxirnllfTJ clf'a1JJrl~ pmq-"r rn2..\lrTJllm clf-dnin~ 'lr,:' , cost, to maximum hi()dt'graciahilll\ l alt, Sodium salts + bllilclers, etc - deterg(:,I1t~

1'0 Make Soap Tallow + hydrolysis (splitting fats) - tallow fatty acid Tallow fatty acid + NaOH - sodium salt of fatty acid Salt of fatty acid + builder, etc, - soap

:\ nlUIllCS

:\Ih Ibenztl,e sulfonate :\ic(Jho! etho,x: sulfates

,~lcohol sulfates !\onionics

Alcohol ethoxylates .~Ikyl phenol ethox;lates :\mines. amine o\lde~ 5

SOI,ReF. Chem Week127203-3 19VJ

L

49

gents may contribute to the eutrophication of lakes, so the use of phosphates in detergents was banned. in some areas of the country. Many different substitutes were formulated into detergents, but some of these were found to be unsafe and were then banned. The position taken by the detergent industry has been that phosphates in wastewater can be removed by special treatment in sewage plants and, in view of the proved lack of toxicity of phosphates, their replacement may not be the most desirable solution. The soap and detergent industry and its suppliers face an enormous task in testing new materials for all possible effects on the environment, and extensive research will be needed before this complex problem can be solved..

Raw Materials

A large volume of active organic compounds, or surfactants,S for both detergents and soap are manufactured in final form by soap and detergent companies. Examples are linear alkyl-benzene sulfonate (LAS) and fatty alcohol sulfate, which these companies manufacture in hundreds of millions of pounds. The same is true for fatty acids, the basic materials for soaps. Most of the inorganic materials, such as oleum, caustic soda, and various sodium phosphates and a large number of additives, the last mentioned amouilting to 3% or l'ess of the total product weight are purchased.

SURP.4CTANTS. These embrace "any compound that affects (usually reduces) surface tension when dissolved in water or water solutions, or which Similarly affects interfacial tension between two liquids. Soap is such a material, but the term is most frequently applied to organic derivatives such as sodium salts of high molecular weight alkyl sulfates or sulfo-nates. 6 The surfactants of both soap and synthetic detergents perform the primary cleaning and sudsing of the washing action in the same way through the reduction of surface tension. The cleaning process consists of (1) thoroughly wetting the dirt and the surface of the article being washed with the soap or detergent solution, (2) removing the dirt from the surface, and (3) maintaining the dirt in a stable solution or suspension (detergentcy). In wash water, soaps or detergents increase the wetting ability of the water so that it can more easily penetrate the fabrics and reach the soil. Then soil removal begins. Each molecule of the cleaning solution may be considered a long chain. One end of the chain is hydrophilic (water-loving); the other is hydrophobic (water-hating, or SOil-loving). The SOil-loving ends of some of these molecules are attracted to a soil particle and surround it. At the same time the water-loving ends pull the molecules and the soil particles away from the fabric and into the wash water. This is the action which, when combined with the mechanical agitation of the washing machine, enables a soap or detergent to remove soil, suspend it, and keep it from redepositing on clothes.

Classification. In most cases the hydrophobic portion is a hydrocarbon containing 8 to 18 carbon atoms in a straight or slightly branched chain. In certain cases, a benzene ring may replace some of the carbon atoms in the chain, for exam pIe, C lZH25 -, C9H 19' C6H4 -. The hydrophilic functional group may vary widely and may be anionic, e.g., - OS04 or SO~-; cationic, e.g., - N(CH3)t or CsHsN+; or nonionic, e.g., - (OCHzCH2)nOH. I In the anionic class one finds the most used compounds, namely linear alkylbenzene sul-fonates from petroleum and alkyl sulfates from animal and vegetable fats (Fig. 3.2). Soap is

5 Abbreviation for surface-active agents. 6Rose, The Condensed Chemical Dictionary, 6th ed., Reinhold, New York, 1961.

50

Straight-chain alcohols Sulfation ~ Alcohol sulfates

Polymerization E t hy len e -""Z~ie:"'g~1 e;":;r':":c'::"a;:';t a':":l;';'y s""r-

a-Olefins

Straight-chain benzene alkylotes

Alkane sulfonates

Reaction with benzene Straight-chain ~ benzene alkyJates

c,\\o~~ ... e~e ~eo ~e

Purification by ~\\'" Petroleum __ ~-.,-_,...-:._~~_ n- Paraffins ~------~- a-Olefins fraction molecular sieves

or urea adduction S"ll"o I)Q/'

101)

Alkane sulfonates

Straight-chain benzene alkylates

Alkane sulfonates

Fig. 3.2. Some possible paths to soft-detergent components. [Chern. Eng. 70 (18) 25 (1963).]

also anionic in character. Quaternary ammonium compounds comprise the cationic class. Three general types are used, mainly for fabric softeners. Type A is a dialkyl dimethyl qua-ternary ammonium compound

TH~ .. R-N+-CH2 x-

I R

where X- is either CI- or CH3S04. Type B is a diamido alkoxylated. quaterIl?ry ammonium compound, where X- is CH3S04

o (CH2CH20)nH 0 II I II

R-C-NH-(CH2)z-N+-(CH2)2-NHC-R X-I CHs

Type C7 is an amido imidazolinium compound where X- is CH3S04.

CHs I

N-CH /1 I 2 R-C:+ \\ N-CH I 2 CH2--CH2-NHC==O

R

7Williams, How to Choose Cationics for Fabric Softeners, Soap Cosmet .. Chem. Spec. 58 (8)28,(1982).:, '.' r~ .. h

,,"

51

Being generally weak in detergent power, although they have good lubricating, antistatic. and germicidal properties, they are not usually used as household detergents. Anionics and cationics are not compatible with soap.

Ethylene oxide condensates of fatty alcohols illustrate the molecular structure of nonionic surfactants. There are many excellent soil-removing types that are low sudsers and hence are useful in drum-type automatic clothes washers. Nonionics are more effective than anionics in removing soil at the lower temperatures necessary for laundering synthetic fibers. They are also more effective at removing body oils.

Biodegradability.8 In view of the attention being given to water pollution control and abatement, product-development chemists and chemical engineers have realized that sllrfac-tants being developed for use in household and industrial detergents that go down the drain to the sewer must be readily decomposable to inorganic compounds by the microbial action of sewage treatment and in surface streams. This nev'! parameter has been added to the per-formance, efficiency, and cost factors the detergent industry must consider in developing: new products. Some surfactants, like tetra propylene-derived alkylbenzene sulfonate, degrade slowly, leaving a persistent residue. Others are more readily decomposablE' b\ microorganisms and leave practically no persistent residues. The easE' with which a surfactant is decomposed by microbial action has been defined as its biodl:gradability. Tests are being developed and standards are being established for biodegradability. To have broad application, such stan-dards must recognize the breadth of variation in environmental conditions. ?'v1aterials which may be only partly degraded in inefficient treatment processes can be completely decom-p(lsed hy mort- ~(jphlstiC'at,:cl biological trt'atrnent '>\~kIll:-' \lethlld:-, uf tnting radiobllt'lt>d ~urfactant~ of anionic, caticll1ic. and l]()ni()nic t~;l)(-':-' dIlll huilc1t'l'\ kl \,' [,t'\'11 de\ c'lup,-d t~ determine the rate of biodegradation in parts per billion in natural waters and also to decer-mine if threshold concentrations, below which degradation is not observed, exist. 9

STRAIGHT-CHAIN ALKYLBENZENES. Biodegradable detergents are made primarily from phenyl-substituted n-alka:Jes of 1] to 14 carbon atoms. The straight-chain paraffins or olefins needed are produced from petroleum as shown in Fig. 3.2. In 1981, 233 kt were produced in the United States.

n-Alkanes are separated from kerosene by adsorption using molecular sieves. Branched chain and cyclic alkanes have larger cross-sectional diameters than do the linear molecules, thus making sieve separation possible. The other common method of separation of the normal paraffin compounds from the branched and cyclic ones is by reaction v-;ith urea or thiourea erea will react with linear chain hydrocarbons having at least seven carbon atoms to give a crY'stalline adduct which is separable by filtration. :\0 such adduct is formed with the hranched ckiin Cor (,'yclic compounds ThE' adduct can theTl \If.' deC-nnlpi)sf>d by hf>ating widl hot water at bO to '::lUc. Conversely, thiourea will react with the branched chain hydrocar-bons but will not form adducts with straight-chain or aromatic ones. The separated n-paraf-fins are converted to benzene alkylates or are cracked to yield a-olefins.

Linear olefins are prepared by dehydrogenation of paraffins, by polymerization of ethvlene to a-olefins using an aluminum triethyl catalyst (Ziegler-type catalyst), by cracking pa~affin wax, or by dehydrohalogenation of alkyl halides.

8Larson, "Role of 'Biodegradation Kinetics in Predicting Environmental Fate," in Maki, DicksoI}., and Cairns (ed.), Biotransformation and Fate of Chemicals in the Aquatic Ent-'i-ronment, Am. Soc. for MicrobioL Pub!., Washington, D.C., 1980.

I ~arson and Wentler, Biodegradation of Detergent Materials, Soap Cosmet. Chern. Spec.

58 (5) 53 (1982).

52

a-Olefins or alkane halides can be used to alkylate benzene through the Friedel-Crafts reaction, employing hydrofluoric acid or aluminum fluoride as a catalyst.

FATTY ACIDS AND FATTY ALCOHOLS

Economics. Fatty alcohols and fatty acids are mainly consumed in the manufacture of detergents and soaps. Fatty acids, both saturated (e.g., stearic acid) and unsaturated (e.g., oleic), have long been employed in many industries as both free acids, and, more frequently,

. as salts. Examples are:

M~gnesium stearates in face powders. Calcium or aluminum soaps (insoluble) employed as water repellents in waterproofing tex-

tiles and walls. Triethanolamine oleate in dry cleaning and cosmetics. Lithium stearate as a component of greases. Rosin soap consumed as a sizing for paper.

Manufacture of Fatty Acids. 10 Basic raw materials, such as oils and fats, which have been used for a long time (Chap. 2), have, since about 1955, been very extensively supple-mented by improved chemical proc~ssing and by synthetic petrochemicals. A selection from these processes is given here. Table 3!.4 compares three processes for splitting fats that have been used for many years. Figure 3'.3 illustrates the high-pressure hydrolysis, catalyzed by zinc oxide, which is used in the soap industry. Fatty acids are drawn off from the distillate receiver for sale or for further conversion to fatty acid salts (calcium, magnesium, zinc, etc.). Several older and less used separation methods for purifying fatty acids are panning and pressing, fractional distillation, and solvent crystallization.

Manufacture of Fatty Alcohols. Th~ Ziegler catalytic procedure for converting a-ole-fins to fatty alcohols and the methyl ester hydrogenation process are the important methods for preparing fatty alcohols. See also the flowchart in Fig. 3.4 and the text presented under soap for the continuous hydrolysis of fats to furnish fatty acids which may be hydrogenated to fatty alcohols.

The Ziegler ll procedure is an important one for manufactUring C12 to CI8 a-olefins and fatty even-numbered straight-chain alcohols for detergents. See Fig. 3.4. Gaseous ethylene is converted to higher, linear aluminum trialkyls and a-olefins by the action of aluminum triethyI which takes part in the reactions.

CHz = CHz + CHz = CHz - CHsCHzCH = CHz + CHz = CHz -- CHsCHzCHzCHzCH = CHz etc.

CHAIN GROWTH REACTION

CH 2CH 3 / lOO130C Al-CH2 CH3 \

CH2 CH 3

+ CHz=CH2 :> 115 MPa

IOECT, 3d ed., vol..4, 1978, p. 837. llSittig, Detergent Manufacturing, Noyes, Park Ridge, N.J., 1979; ECf, 3d ed., voL 1,

1978, p. 740.

53

Table 3'-4 Tabular Comparison of the Various Fat-Splitting Processes

Tern perature, C

Pressure, MPag Catalyst

Time, h Operation Equipment

Hydrolyzed

Advantages

Disadvantages

Twitchell

100-105

Alkyl-aryl sulfonic acids or cycloaliphatic sulfonic acids, hath used with sulfuric acid 0.75-1.25% of the charge

12-48 Batch Lead-lined, copper-

lined, Monel-lined, or wooden tanks

85-98% hydrolyzed 5-15% glycerol solution obtained, depending on number of stages and type of fat

Low temperature and pressure; adaptable to small scale; low first cost because of relatively simple and inexpensive equipment

Catalyst handling; long reaction time; fat stocks of poor quality must often be acid-refined to avoid catalyst poisoning; high steam consumption; tendency to form dark-colored acids; need more than one stage for good yield and high glycerin concentration; not adaptable to automatic control; high labor cost

Batch autoclave

150-175 240

5.2-10.0 2.9-3.1 Zinc, No catalyst

calcium, or mag-nesium oxides, 1-2%

5-10 2-4 Batch Copper or stainless-steel autoclave

85-98% hydrolyzed 10-15% glycerol, depending on number of stages and type of fat

Adaptable to sma'll scale; lower first cost for small scale than continuous process; faster than Twitchell

High first cost; catalyst handling; longer reaction time than continuous processes; not so adaptable to automatic control as continuous; high labor cost; need more than one stage for good yield and high glycerin concentration

Continuous Countercurrent

250 4.1-4.9

Optional

2-3 Continuous Type 316 stainless tower

97-99% 10-25% glycerol, dependent on type of fat

Small !loor space; uniform product quality; high yield of acids; high glycerin concentration; low labor cost; more accurate and automatic control; lower annual costs

High first cost; high temperature and pressure; greater operating skill

SOURCE: Mostly from Marsel and Allen, Fatty Acid Processing, Chem. Eng. 54 (6) 104 (1947). Modified in 1982. "See Fig. 29.8.

Steam

Flash Fattyacids tonk

Hydrolyzer 250C,4 MPa

Blend tonk

Steam

/,' , , '

Steam

54

High vacuum still

Bottoms, to storage and

recovery

Distillote receiver

Conven tionol soap finishing: bar, flake or

power

Fallyacids

Soap blender Steam

Fig. 3 .3. Continuous process for the production of fatty acids and soap. (Procter & Gamble Co.)

Air

Aluminum powder

Oxidation

Activation

Hydrogen

Solvent

Aluminum olkyls

Solvent and by- products

Sulfuric acid

Recycle aluminum triethyl

Sodium hydroxide

Froctionation 'Alfoi" clcoOOls

Fig. 3 A. The aHol process. Fatty alcohols made by means of the organometallic route have carbon chain lengths ranging from 6 to 20 carbons. The aHol process used by Conoco commences by reacting alumi-num metal, hydrogen, and ethylene, all under high pressure, to produce aluminum triethyl. Thi.5 com-pound is then polymerized with ethylene to form aluminum alkyls. These are oxidi.z.ed with air to form aluminum alkoxides. Following purification, the alkoxides are hydrolyzed with 23 to 26% sulfuric acid to produce crude, primary, straight-chain alcohols. These are neutralized with caustic, washed with water, and sepa'rated by fractionation. Basic patents covering the process have been licensed. (DuPont-Conoeo.) .. ~.~

55

Each ethyl group on the aluminum triethyl can add ethylene to form aluminum trialkyls of 4 to 16 or more carbons per alkyl group.

DISPLACEMENT REACTIONS

Thermal decomposition

Regeneration of ethyl group

/CH ZCH 2 )b CH 3 /CH 2 CHz)b CH 3 Al-H + CHz=CHz --~) Al-CHzCH 3 \ \ (CH zCH z)dCH3 (CH zCHz)d CH3

The growth and displacement reactions take place concurrently, but the thermal decompo-sition reaction is much slower than the regeneration reaction and thus is the rate-determining step for the overall reactions. These reactions take place repeatedly as long as unreacted eth-ylene is present. They are run in an inert hydrocarbon solvent such as heptane or benzene. In these solvents aluminum "trialkyl" is not pyrophoric at less than 40% concentration. It takes approximately 140 min to build up to a C 12 average chain length when reacting 5 mol of ethylene for each ~ mol of aluminum triethyl The tri,dkyl aluminum is oxidized to vield an aluminum trialkoxide, which in turn is treated with sulfuric acid to give alkyl or fatty alcohols.

OXIDATION REACTION

~H is exothermic, liberating about 2.5 MJ /kg of oxidized alkyl. Its conversion is 98 percent at 32C in about 2 h.

HYDROLYSIS (ACIDOLYSIS)

Figure 3.4 gives a flow diagram of the production of alcohols using these reactions.

Fatty Alcohols from Methyl Esters. Fats have long been basic raw materials for soaps and detergents. Such fats as are available are glyceryl esters of fatty acids (C6 to C24 ) and

56

have been hydrolyzed to the acids for soaps and reduced to the alcohols by catalytic hydro genation for detergents. The methyl esters of fatty acids12 are also hydrogenated to fali; alcohols. These esters are prepared by reacting methanol with coconut or tallow triglyceride catalyzed by a small amount of sodium methylate. [he refined oil is first dried by flashing a ISOC under a vacuum of 16.6 kPa, as otherwise it will consume relatively expensive sodiun methylate and also form soap. The methyl exchange esterification takes place in about al hour; then the reaction mix is settled and separated into an upper layer rich in ester an( methanol and a lower layer rich in glycerin and methanol. The ester layer is washed coun tercurrently to remove excess methanol, to recover glycerin, and to remove the catalyst which would poison the hydrogenation. Yields of fatty alcohols are 90 to 9S percent.

Hydrogenation of methyl esters is catalyzed by a complex catalyst of copper II and coppe III chromite (made from copper nitrate, chromic oxide, and ammonia, with final roasting and is carried out at approximately 21 MPag and 260 to 31SC. The continuous equipmen used is outlined in Fig. 3.S and consists of three vertical reactors 12 m high using 30 mol 0 heated hydrogen per mole of ester; the hydrogen serves not only for reducing but also fo: heating and agitation. The crude alcohols are fractionated to the specified chain length.

SUDS REGULATORS. Suds regulation is often necessary for surfactants to do an efficient jot of cleaning in a washing machine. This is often achieved by combining different types sud as anionics with nonionics, or anionics with soap. For soaps, foam inhibition increases ..... id the amount of saturation and the number of carbons in the fatty acid residue. Soaps of satu rated CZO-Z4 fatty acids are good foam inhibitors.13 Other foam inhibitors are higher fatty acic

1ZECT, 3d ed., vol. 1, 1978, p. 732. 13Sittig, op cit., p. 446.

Fresh catalyst

Dried methyl esters or fatty acids

FEED TANK

Steam:::~~2) HEATER

H2 and overheads

UNDERFLOW SEPARATOR

HYDROGEN HEATER

FILTER FEED

Fuel

UNDERFLOW FILTER

OVERHEADS SEPARATOR

HZ COMPRESSC

HZ RECYCLE COMPRESSOR

Water or methanol

j

~ __ Spent catalyst to disposal and recyCle

Fig. 3.5. Flowchart for the hydrogenolysis of methyl esters to obtain fatty alcohols and gJycerin from natural fats. (ECT, 3d ed., vol. 4, 1978, p. 837.)

57

amides, aliphatic carboxylic acid esters containing at least 18 carbons in one or preferabl~ both acid and alcohol chains, and N-alkylated aminotriazines.

BUILDERS. Builpers boost detergent power. Complex phosphates, such as sodium tripoly-phosphate, have been used most extensively. These are more than water softeners which sequester water-hardening calcium and magnesium ions. They prevent redeposition of soil from the wash water on fabrics. Proper formulation with complex phosphates has been the key to good cleaning with surfactants and made possible the tremendous development of detergents. Polyphosphates (e.g., sodium tripolyphosphate and tetrasodium pyrophosphate; have a synergistic action with the surfactant together with an enhanced effectiveness and hence reduce the overall cost. The rapid rise in the acceptance of detergents stemmed from the building action of the polyphosphates. During the 1960s the growth of algae and eutro-phication in lakes became linked to the presence of phosphates in detergents. Several states restricted phosphate use so that substitutes had to be found. The first compound suggested was nitrilotriacetic acid (NTA), but it was declared a carcinogen in 1970. But new research results have vindicated its safety; in 1980 the EPA said it saw no reason to regulate i\TA. This has not freed NT A for use because various congressional and environmental groups have challenged the EPA decision. There are no restrictions on its use in Canada.

Other builders are citrates, carbonates, and silicates. The newest, and seemingly most promising, substitute for phosphates is the use of zeolites. 14 By 1982 about 136 kt/year of zeolites were being used as detergent builders. The builder market is large and amounts to over 1000 kt annually. In 1980 phosphates accounted for 50 percent, zeolites 12 percent, silicates 13 percent, carbonates 12 percent, and NT A and citrates 2 percent each.

ADDITIVES. Corrosion inhibitors, such as sodium silicate, protect metal and washer parts, utensils, and dishes from the action of detergents and water. Carboxymethyl cellulose has been used as an antiredeposition agent. Tarnish inhibitors carryon the work of the corrosion inhibitor and extend protection to metals such as German silver. Benzotriazole has been used for this purpose. Fabric brighteners are fluorescent dyes which make fabrics look brighter because of their ability to convert ultraviolet light to visible light. Two dyes thus used are 4(2H -naphtho[1 ,2-d]triazol-2-yl)stilbene-2-sulfonate and disodium 4,4/-bis( 4-anilino-6-mor-pholino-S-triazin-2-ylamino )-2,2/-stilbene disulfonate.

Bluings improve the whiteness of fabrics by counteracting the natural yellowing tendency. The ingredients used for this purpose can vary from the long-used ultramarine blue (bluing) to new dye materials. Antimicrobial agents include carbanilides, salicylanilides, and cationics. Peroxygen-type bleaches are also employed in laundry products. The use of enzyme-contain-ing detergents has been common in Europe for several years and recently has been introduced into the United States. The enzymes decompose or alter the composition of soil and render the particles more easily removable. They are particularly useful in removing stains, partic-ularly those of a protein nature.

Manufacture of Detergents Table 31.5 compares three types of detergents. The most widely used detergent, a heavy-duty granule, is presented in Fig. 29.6, with the quantities of materials required. The reac-tions are:

14Layman, Detergents Shift Focus of Zeolites Market, Chern. Eng. News 60 (39) 10 (1982).

58

Table 3.5 Basic Composition of Three Types of Dry Phosphate-Based Detergents (Granules)

Ingr~ient on Dry-Solids Basis, wt %

Light-Duty Heavy-Duty High ControlJed

Ingredient Function Sudsers Sudsers

Surfactants Organic active, with suds Removal of oily soil, cleaning 25-40 8-20

regulators Builders

Sodium tripolyphosphate Removal of inorganic soil. 2--30 30-50 and/or tetrasoditlffi detergent-building pyrophosphate

Sodium sulfate Filler with building action in 30-70 0-30 soft water

Soda ash Filler v~th some building 0 0-20 action

Additives Sodium silicate having 2.0 Corrosion inhibitor with 0-4 6-9

;S Si02/Na20 ;S 3.2 slight building action Carboxymethyl cellulose Antiredeposition of soil 0-0.5 0.5-1.3 Fluorescent dye Optical brightening 0-0.05 0.05-0.1 Tarnish inhibitors Prevention of silverware 0 0-0.02

tarnish Perfume and sometimes Aesthetic, improved product 0.1 0.1 dye or pigment characteristics

Water Filler and binder 1-5 2-10

SOURCE: Van Wazer. Phosphorus and Its Compounds. vol. 2. Interscience, New York. 1961. p. 1760 . ..

LINEAR ALKYLBENZENE SULFONA TION

1. Main reaction:

DoH = -420 kJlkg

Alkylbenzene Oleum

2. Secondary reactions:

Alk:lbenzene sulronale

Sulruric acid

S03H

R(O)SO'H + H,so.so,-R(O)S03H + H,SO, Alkylbenzene

sulronale

Alhlbenzene "ulronalf'

Oleum

Alkylben7.ene

Disulronate

Sulrone 10/,

Sulruric acid

Heavy-Duty High

Sud.sers

20-35

10-20

0-5

4-8

0.5-1.3 -0.1 0-0.02

0.1

3-10

59

STACK

Silicate ---~! lDry scrap Phospha~

Surfactant storage t ~ SULFONATOR SULFATOR NEUTRAlIZ.ER CRUTCHER

SPRAY TOwEP

In order to produce 1 t of finished product, the following materials (in kilograms) are required:

Surfactant Materials Alkylbenzene (petrochemical) Fatty alcohol (from tallow) Oleum NaOH solution

75 75

150 200

Corrosion Inhibitor Sodium silicate

Builder Sodium tripolyphosphate

Miscellaneous additives Water

125

500 30

500

Fig. 3 .6. Simplified continuous flowchart for the production of heavy-duty detergent granules. (Procter & Gamble Co.)

FATTY ALCOHOL SULFATION

1. Main reaction:

.6.H = -325 to -350 kJ/kg

2. Secondary reactions:

R-CH20H + R'-CH2-OSOsH -+ R-CHz-0-CH2-R' + H2S04 R'-CH2-CHzOH + SOs -+ R'-CH=CH2 + H2S04 R-CHzOH + S03 -+ RCHO + H20 + S02 R-CH20H + 2503 -+ RCOOH + H20 + 2502

This presentation is supplemented by Table 3.5, which gives the basic constituents in more detail for the three types of detergent granules. The continuous flowchart in Fig. 3.6 can be broken down into the following coordinated sequences:

,60

Sulfonation-sulfation. The alkylbenzene (AB) is introduced continuously into the suI-fonator with the requisite amount of oleum, using the dominant bath principle shown in Fig. 29.8 to control the heat of sulfonation conversion and maintain the temperature at about 55C. Into the sulfonated mixture is fed the fatty tallow alcohol and more of the oleum. All are pumped through the sulfater, also operating on the dominant bath principle, to maintain the temperature at 50 to 55C, thus manufacturing a mixture of surfactants.

Neutralization. The sulfonated~sulfated product is neutralized with NaOH solution under controlled temperature to maintain fluidity of the surfactant slurry. The surfactant slurry is conducted to storage.

The surfactaht slurry, the sodium tripolyphosphate, and most of the miscellaneous addi-tives are introduced into the crutcher. A considerable amount of the water is removed, and the paste is thickened by the tripolyphosphate hydration reaction:

Sodium Sodium tripolyphosphate tripolyphosphate _____ hexahydrate

Th~s mixture is pumped to an upper story, where it is sprayed under high pressure into the 24-m-high spray tower, counter to hot air from the furnace. Dried granules of acceptable shape and size and suitable density are formed. The dried granules are transferred to an upper story again by an air lift which cools them from 115C and stabilizes the granules. The granules are separated in a cyclone, screened, perfumed, and packed.

The sulfonation conversion is shown in Fig. 3.7 to be extremely fast. The reactions also need 10 have the hig~ heats of reaction kept under control, as shown in more detail in Fig. 29.8, depicting the circulating heat exchanger, or dominant baths, for both these chemical conversions and for neutralization. The use of oleum in both cases reduces the sodium sulfate in the finished product. However, the oleum increases the importance of control to prevent oversulfonation. In par-ticular, alkylbenzene sulfonation is irreversible and results in about 96 percent conversion in less than a minute when run at 55C with 1 to 4% excess S03 in the oleum. A cer-tain minimum concentration of S03 in the oleum is nec-essary before the sulforyation reaction will start, which in this case is about 78.5% S03 (equivalent to 96% sulfuric acid). As both these reactions are highly exothermic and rapid, efficient heat removal is required to prevent over-sulfonation and darkening. Agitation is provided by a cen-trifugatpump, to which the oleum is admitted. The recir-culation ratio (volume of recirculating material divided by the volume of throughput) is at least 20: 1 to give a favorable system. To provide the sulfonation time to reach the desired high conversion, more time is allowed by con-ducting the mixture .through a coil, where time is given for the sulfonation reaction to go to completion. '

Neutralization of the acid slurry releases six to eight times as much heat as the sulfonation reaction. Here a

100

'" '" C1.> C

80

~ 60 C1.> 0.. E o u

C 40 C1.> u '-

C1.> a..

20

OL~--~2--L-~4--~~6 Minutes

Fig. 31.7. AIkyIbenzene sulfooation completeness versus time at 55C. (Procter & Gamble Co.) i

Cooling water

Alkyl benzene

SULFONATiON

61

Cooling water

SULFATION

. ! ~: \0

Cooling woter- ' LJ-----{

NEUTRALIZATION

Fig. 3.8. Continuous series sulfonation-sulfation, ending with neutralization, in the circulating heat-e?:changing dominant bath to control heat. (Procter & Gamble Co.)

dominant bath (Fig. 3.8) is employed which quickly effects the neutralization, since a partly neutralized acid mix is very viscous,

SOAP

Soap comprises the sodium or potassium salts of various fatty acids, but chiefly of oleic, stearic, palmitic, lauric, and myristic acids. For generations its use has increased until its manufacture has become an industry essential to the comfort and health of civilized human beings. The relative and overall pr!::kluction of soap and detergents is shown by the curve in Fig. 3.1. History and industrial statistics are discussed in the first part of this chapter (Table 3.1).

Raw Materials

Tallow is the principal fatty material in soapmaking; the quantities used represent about three-fourths of the total oils and fats consumed by the soap industry, as shown in Fig. 3.1. It contains the mixed glycerides obtained from the solid fat of cattle by steam rendering. This solid fat is digested with steam; the tallow forms a layer above the water, so that it can easily be removed. Tallow is usually mixed with coconut oil in the soap kettle or hydrolyzer in order to increase the solubility of the soap, Greases (about 20 percent) are the second most impor-tant raw material in soapmaking. They are obtained from hogs and smaller domestic animals and are an important source of glycerides of fatty acids. They are refined by steam rendering or by solvent extraction and are seldom used without being blended with other fats. In some

62

cases, they are treated so as to free their .fatty acids, which are used in soap instead of the grease itself. Coconut oil has long been important. The soap from coconut oil is firm and lathers well. It contains large proportions of the very desirable glycerides of lauric and myr-istic acids. Free fatty acids are utilized in soap, detergent, cosmetic, paint, textile, and many other industries. The acidification of "foots," or stock resulting from alkaline refining of oils, also produces fatty acids. The important general methods of splitting are outlined in Table 3.4. The Twitchell process is the oldest. IS Continuous countercurrent processes are no'\\' most

commonly used. I The soap maker is also a large consumer of chemicals, especially caustic soda, salt, soda ash,

and caustic patash, as well as sodium silicate, sodium bicarbonate, and trisodium phosphate. Inorganic chemicals added to the soap are the so-called builders. Important work by Harris of Monsanto and his coworkers I6 demonstrated conclusively that, in particular, tetrasodiurn pyrophosphate and sodium tripolyphosphate were unusually effective synergistic soap build-ers. Of considerable economic importance was the demonstration that combinations of inex-pensive builders, such as soda ash, with the more effective (and expensive) tetrasodium pyro-phosphate or sodiunl tripolyphosphate, were sometimes superior to the phosphate used alone. It was further shown that less soap could be used in these mixtures to attain the same or more effective soil removal.

Manufacture

The manufacture of soap is presented in Fig. 3'.3. The long-established kettleI7 process, how-ever, is mainly used by smaller factories or for special and limited production. As soap tech-nology changed, continuous alkaline saponification was introduced. Computer control allows an automated plant for continuous saponification by NaOH of oils and fats to produce in 2 h the same amount of soap (more than 300 t/day) made in 2 to 5 days by traditional batch methods.

The present procedure involves continuous splitting, or hydrolysis, as outlined in Table 3.2 and detailed in Fig. 3 .3. After separation of the glycerin, the fatty acids ate neutralized to soap.

The basic. chemical reaction in the making of soap is saponification. I8

3NaOH' + (C17H35COO)3C3HS - 3C17H35COONa + C:3Hs(OHb Caustic Glyceryl Sodium stearate Glycerin

soda stearate

lSThis process is described in more detail in CPI 2, p. 619. I60il Soap 193 (1942); Cobbs et aI., Oil Soap 17 4 (1940); Wan Wazer,' "Phosphorus and

Its Compounds," chap. 27, in Detergent Building, Interscience, New York, 1958. 17Full descriptions with flowcharts for the kettle process full-boiled' (several days), semi-

boiled, and cold are available on pp. 623-625 of CPI 2. 18 Although stearic acid is written in these reactions, oleic, lauric, or other constituent acids

of the fats could be substituted. See.Table 28.1 for fatty acid composition of various fats and oils.

63

The procedure is to split, or hydrolyze, the fat, and then, after separation from the valuable glycerin, to neutralize the fatty acids with a caustic soda solution:

(CJ7 H35COOhC3Hs + 3HzO - 3C17 H35COOH + C3Hs\OH)j Glyceryl Stearic acid Glycerin stearate

CJ7H35COOH + NaOH - C17H3.'5COONa + H20 Stearic Caustic Sodium

acid soda stearate

The usual fats and oils of commerce are not composed of the glyceride of anyone fatty acid. but of a mixture. However, some individual fatty acids of 90% purity or better are available from special processing. Since the solubility and hardness of the sodium salts (Table 3.6) of the various fatty acids differ considerably, the soapmaker chooses the raw material according to the properties desired, with due consideration of the market price.

In continuous, countercurrent splitting the fatty oil is deaerated under a vacuum to prevent darkening by oxidation during processing. It is charged at a controlled rate to the bottom of the hydrolyzing tower through a sparge ring, which breaks the fat into droplets. These towers, about 20 m high and 60 cm in diameter, are built of Type 316 stainless steel (see Fig. 3.5) The oil in the bottom contacting section rises because of its lower density and extracts the small amount of fatty material dissolved in the aqueous glycerin phase. At the same time (laerated, demineralized water is fed to the top contacting section, where it extracts the glyc-erin dissolved in the fatty phase. After leaving the contacting sections, the two streams enter the reaction zone. 19 Here they are brought to reaction temperature by the direct injection of high-pressure steam, and then the final phases of splitting occur. The fatty acids are dis-charged from the top of the splitter or hydrolyzer to a decanter, where the entrained water is separated or flashed off. The glycerin-water solution is then discharged from the bottom of an ~utomatic interface controller to a settling tank. See Fig .. 3.10 for glycerin processing.

Although the crude mixtures of fatty acids resulting from any of the above methods may be used as such, usually a separation into more useful components is made. The composition of the fatty acids from the splitter depends upon the fat or oil from which they were derived.

19A1len et aI., Continuous HydrolYSiS of Fats, Chem. Eng. Frog., 43 459 (1947); Fatty Acids, Chern. Eng. 57 (11), 118 (1950); Ladyn, Fat Splitting, Chem. Eng. 71 (17) 106 (1964) (con-tinuous flowcharts).

Table 3'.6 Solubilities of Various Pure Soaps (in grams per 100 g of water at 250

Stearate Oleate

Sodium 0.1" IB.l Potassium 25.0 Calcium 0.004t 0.04 Magnesium 0.004 0.024 Aluminum

Approximate. tSolubility given at 15C only. NOTE: i indicates that the compound decomposition.

Palmitate Laurate

0.8" 2.75 70.0"

0.003 0.004t 0,008 0.007 d

is insdluble:- d indicates

-

64

Those most commonly used for fatty acid production include beef tallow and coconut, palm, cottonseed, and soybean oil. Probably the most used of the older processes is panning and pressing. This fractional crystallization process is limited to those fatty acid mixtures which solidify readily, such as tallow fatty acid. The molten fatty acid is run into pans, chilled, wrapped in burlap bags, and pressed. This expression extracts the liquid red oil (mainly oleic

J

acid), leaving the solid stearic acid. The total number of pressings indicates the purity of the product. To separate fatty acids of different chain lengths, distillationZO is employed, vacuum distillation being the most widely used. Three fractionating towers of the conventional tray type are operated under a vacuum. Preheated, crude fatty acid stock is charged to the top of a stripping tower. While it is flowing downward, the air, moisture, and low-boiling fatty acids are -,:wept out of the top of the tank. The condensate, with part of it redrawn as a reflux, passes into the main fractionating tower, where a high vacuum is maintained at the top. A liquid side stream, also near the top, removes the main cut (low-boiling acids), while over-heads and noncondensables are withdrawn. The liquid condensate (high-boiling acids) is pumped to a final flash tower, where the overhead distillate is condensed and represents the second fatty acid fraction. The bottoms are returned to the stripping tower, reworked, and removed as pitch. The fatty acids may be sold as such or converted into many new chemicals.

The energy requirements that enter into the cost of producing soap are relatively unim-portant in comparison with the cost of raw materials, packaging, and distribution. The energy required to transport some fats and oils to the soap factory is occasionally considerable. The reaction that goes on in the soap reactor is exothermic.

The following are the principal sequences into which the making of bar soap by water splitting and neutralization can be divided, as shown by the flowchart in Fig. 3.3.

Transportation of fats and oils. Transportation and manufacture of caustic soda. Blending of the catalyst, zinc oxide, with melted fats and heating with steam takes place

in the blend tank. Hot melted fats and catalysts are introduced into the bottom of the hydrolyzer. Splitting of fats takes place countercurrently in the hydrolyzer at 250C and 4.1 MFa,

continuously, the fat' globules rising against a descending aqueous phase: The aqueous phase, having dissolved the split glycerin (about 12%), falls and is separated The glycerin water phase is evaporated and purified. See Glycerin. . The fatty acids phase at the top of the hydrolyzer is dried by flas~g off the water and

further heated. In a high-vacuum still the fatty acids are distilled from the bottoms and rectified. The soap is formed by continuous neutralization with 50% caustic soda in high-speed

mixer-neutralizer. The neat soap is discharged at 93C into a slowly agitated blending tank to even out any

inequalities of neutralization. At this point the neat soap analyzes: 0.002 to 0.10% NaOH, 0.3 to 0.6% NaCl, and approximately 30% H20. This neat soap may be extruded, milled, flaked, or spray-dried, depending upon the product desired. The flowchart in Fig. 29.3 depicts the finishing operations for floating bar soap.

2Fatty Acid Distillation, Chern. Eng. ,55 146 (1948). Pictured flowcharts of both straight and fractional distillation; Marsel and AI'len, Fatty Acid Processing, Chern. Eng. 54 (6) 104 (1947); ECT, 3d ed., vol. 4, 1978, p. 839.

65

These finishing operations are detailed: The pressure on the neat soap is raised to :3.5 ~lPa, and the soap is heated to about 200C in a high-pressure steam exchanger. This heated soap is released to a flash tank at atmospheric pressure, where a partial drying (to about 20%) takes place because the soap solution is well above its boiling point at atmospheric pressure. This viscous, pasty soap is mixed with the desired amount of air in a mechanical scraped-wall heat exchanger, where the soap is also cooled by brine circulation in the outer shell from lOsoe to about 65C. At this temperature the soap is continuously extruded in strip form and is cut into bar lengths. Further cooling, stamping, and wrapping complete the operation. This entire procedure requires only 6 h, as compared with over a week for the kettle process. The main advantages of soap manufactured by this process as compared with the kettle process are (1) improved soap color from a crude fat without extensive pretreatment. (2) improved glycerin recovery, (3) flexibility in control, and (4) less space and labor. Intimate molecular control is the key to the success of this continuous process, as, for example, in the hydrolyzer, where the desired mutual solubility of the different phases is attained by appropriate process conditions.

Typical Soaps

The main classes of soap are toilet soaps and industrial soaps. These different soaps can fre-quently be made by one or more of the procedures described. The bar soapZl market consists of regular and superfatted toilet soaps, deodorant and/or antimicrobial soaps, floating soaps. transparent/translucent, marbelized, and hard water soaps. Some overlapping occurs as some deodorant bars have a superfatted base. Toilet soap is usually made from mixtures of tallo\\. and coconut oil in ratios of 80/20 or 90/10, and superfatted soaps have ratios of 50/50 or 60,' 40 and some have 7 to 10% free fatty acid added as well. Deodorant soaps contain an agent such as 3,4',5-tribromosalicylanilide (TBS) which prevents the decomposition of perspiration into odorous compounds.

Practically all soa p merchandised contains from 10 to about 30% water. If soap were anhy-drous, it would be too hard to dissolve easily. See Table 3.6. Almost all soaps contain per-fume, even though it is not apparent, serving merely to disguise the original soapy odor. Toilet soaps are made from selected materials and usually contain only 10 to 15% moisture; they have very little added material, except for perfume and perhaps a fraction of a percent of titanium dioxide as a whitening agent. Shaving soaps contain a considerable proportion of potassium soap and an excess of stearic acid, the combination giving a slower-drying lather. "Brushless" shaving creams contain stearic acid and fats with much less soap.

Another type of bar soap (in comparison wi~h the floating type in Fig. 3.3) is milled toilet soap. The word milled refers to the fact that, during processing, the soap goes through several sets of heavy rolls, or mills, which mix and knead it. Because of the milling operation, the finished soap lathers better and has a generally improved performance, especially in cool water. The milling operation is also the way in which fragrant perfumes are incorporated int(l, cold soap. If perfume were mixed with warm soap, many of the volatile scents would evaporate. After the milling operation, the soap is pressed into a smooth cylinder and is extruded continuously. It is then cut into bars, stamped, and wrapped as depicted in Fig. 3.9.

21Jungerman, New Trends in Bar Soap Technology, Soap Cosrnet. Chern. Spec. 58 (1) 31 (1982).

66

',' .:. ; :~".

Fig. 3.9. Making soap in milled bars. Another type of bar soap (in comparison with the floating type shown in Fig. 3'.3) is milled toilet soap, The word "milled" refers to the fact that, during processing, the soap goes through several sets of heavy rolls or mills which mix and knead it. A much more uniform product is obta:'ned, and much direct labor is saved.

Crystal Phases in Bar Soap. The physical properties of bar soap are dependent upon the crystalline soap phases present lnd the condition of these phases. Any of three or more phases may exist in sodium soaps, depending upon the fat used, the moisture and electrolyte composition of the system, and the processing conditions. Milled toilet soaps are mechanically worked to transform the omega phase, at least partially, to the translucent beta phase pro-ducing a harder, more readily soluble bar, Extruded floating soaps contain both crystals [ornled in the freezer and crystals that grow from the melt after it leaves the freezer. Pro-cessing conditions are adjusted for an optimum proportion of crystallized matrix, which adds strength and rigidity to the bar. If necessary, the bar may be tempered by reheating to strengthen it.

GLYCERIN

HISTORICAL. Glycerin22 is a clear, nearly colorless liquid having a sweet taste but no odor. Scheele first prepared glycerin in 1779 by heating a mixture of olive oil and litharge. On washing with water, a sweet solution was obtained, giving, on evaporation of the water, a viscous heavy liquid, which the discoverer called "the sweet principle of fats." In 1846 Sobrero produced the explosive nitroglycerin for the first time, and in 1868 Nobel, by absorb-ing it in kieselguhr, made it safe to handle as dynamite. These discoveries increased the demand for glycerin. This was in part satisfied by the development in 1870 of a method for recovering glycerin and salt from spent soap lyes, Since about 1948, glycerol has been pro-duced from petrochemical raw materials by synthetic processes.

22The term glycerin is chosen for the technical product containing the pure trihydroxy alcohol glycerol. The spelling of glycerin is that employed by the USP.

67

USES AND ECONOMICS. The production of crude glycerin is approximately 158 kt/year. Syn-thetic glycerin furnishes about 40 percent of the market. Glycerin is supplied in several grades, including USP and CP, grades which are chemically pure, contain not less than 95% glycerol, and are suitable for resins and other industrial products. Yellow distilled is used for certain processes \,,'here higher-purity types are not essential, e.g., as a lubricant in tire molds. Glycerin is employed in making, preserving, softening, and mOistening a great many prod-ucts, as shown in Table 3'.7.

Manufacture Glycerin may be produced by a number of different methods, of which the following are important: (1) the saponification of glycerides (oils and fats) to produce soap, (2) the recovery of glycerin from the hydrolysis, or splitting, of fats and oils to produce fatty acids, and (3) the chlorination and hydrolysis of propylene and other reactions from petrochemical hydrocarbons.

In recovering glycerin from soap plants, the energy requirements are mostly concerned with heat consumption involved in the unit operations of evaporation and distillation, as can be seen by the steam requirements on the flowchart in Fig. 29.10. The breakdown of natural and synthetic procedures for glycerin is:

Glycerin from Sweet Water from Hydrolyzer

E~aporation (multiple effect) for concentration Purification with settling Steam vacuum distillation

P~rtial condensation Decoloration (bleaching) Filtration or ion-exchange purification

Glycerin from Petroleum

Purification of propylene Chlorination to allyl chloride Purification and distillation Chlorination with HOCl Hydrolysis to glycerin Distilla tion

RECOVERY FROM FATTY ACIDS. Practically all natural glycerin is now produced as a coproduct of the direct hydrolysis of triglycerides from natural fats and oils. Hydrolysis is

Table. 3'.7 Glycerin Consumption (metric kilotons)

1978 1980

Alkyd resins Cellophane Tobacco Explosives Drugs and cosmetics Urethane foams Foods and beverages Miscellaneous

21.5 6.4

14.2 2.9

24.1 13.8 14.8 15.8

27 8

25 3

38 18 24 16

SOURCE:' ECT, 3d ed., vol. II, 1980, p. 927; Chem. Mar. Rep, May 25, 1981.

FLASH TANK I

"Sweetwater" \ from hydrolyzer (12% glycerol)

To ejectors

EVAPORATORS

Refined glycerin (95-99~o glycerol)

HG=high gravity; YD=yeliow distilled

FILTER

68

CRUDE GLYCERIN SETTLING

TANK

Fat skimmings

To ejecrQ('j

S T -;:::j::=======> CONDENSERS Steam NW CW DR

Crude glycerin (78 % glycerol)

Caustic

STILL FEED TANK

GLYCERIN STILL

HP steamJ]~~

Distillation roots

B c

PRODUCT TANKS ~I

CP HG yo glycerol glycerin glycerin

BLEACHING TANK

Fig. 3.1.0. Flowchart for glycerin manufacture from hydrolysis of sweet water (Procter & Gamble Co.)

carried out in large continuous reactors at elevated temperatures and pressures with a cata-lyst. Water flows countercurrent to the fatty acid and extracts glycerol from the fatty phase. The sweet water from the hydrolyzer column contains about 12% glycerol. Evaporation of the sweet water from the hydrolyzer is a much easier operatiop compared with evaporation of spent soap lye glycerin in the kettle process. The high salt content of soap lye glycerin requires frequent soap removal from the evaporators. Hydrolyzer glycerin cont~ins practi-cally no salt and is readily concentrated. The sweet water is fed to a triple-effect evaporator, as depicted by the flowchart in Fig. 3.10, where the concentration is increased froITf 12% to 75 to 80% glycerol. Usually, no additional heat (other than that present in the sweet-water effluent from the hydrolyzer) is required to accomplish the evaporation. After concentration of the sweet water to hydrolyzer crude, the crude is settled for 48 h at elevated temperatures to reduce fatty impurities that could interfere with subsequent processing. Settled hydrolyzer crude contains approximately 78% glycerol, 0.2% total fatty acids, and 22% water. The settled crude is distilled under a vacuum (8 kPa) at approximately 200C. A small amount of caustic is usually added to the still feed to saponify fatty impurities and reduce the possibility of codistillation with the glycerol. The distilled glycerin is condensed in three stages at decreas-ing temperatures. The first stage yields the purest glycerin, usually 99% glycerol, meeting CP specifications. Lower-quality grades of glycerin are collected in the second and third con-densers. Final purification of glycerin is accomplished by carbon bleaching, followed by fil-tration or ion exchange.

69

SYNTHETIC GLYCERIN.23 The growing market for glycerin, and the fact that it was a coproduct of soap and dependent upon the latter's production, were the incentives for research into methods for producing this trihydroxy alcohol. The process of making glycerin from propylene procured for the Shell Development Co. the 1948 Chemical Engineering achievement award.24 The propylene is chlorinated at 51O'oC at 101 kPa to produce allyl chloride in seconds in amounts greater than 85 percent of theory (based on the propylene). Vinyl chloride, some disubstituted olefins, and some 1, 2 and 1, 3-dichloropropanes are also formed. (The reaction producing allyl chloride was new to organic synthesis, involving the chlorination of an olefin by substitution instead of addition.) Treatment of the allyl chloride with hypochlorous acid at 38C produces glycerin dichlorohydrin (CHzCl CHCI CHzOH), which can be hydrolyzed by caustic soda in a 6% NazC03 solution at 96C. The glycerin dichlorohydrin can be hydrolyzed directly to glycerin, but this takes two molecules of caustic soda; hence a more economical procedure is to react with the cheaper calcium hydroxide, taking off the epichlorohydrin as an overhead in a stripping column. The epichlorohydrin is

23ECT, 3d ed., vol. 11, 1980, p. 923; McGraw-Hill Encyclopedia of Science and Technol-ogy, 5th ed., vol. 16, McGraw-Hill, New York, 1982, p. 310.

24Hightower, Glycerin from Petroleum, Chern. Eng. 55 (9) 96 (1948); Synthetic Glycerin, Chern. Eng. 55 (10) 100 (1948).

Acetone

I 2 I

AC~\ GIY""\ldehYde ALLYL

ALCOHOL.:

H20 02 // \ H2\ 1/ /prOP'ylene /NOOH HO\Cl ~OXlde / ALLYL Glycerol

PROPYLENE Ct2 CHLORIDE M,noChr'hY~N'OH--.-GLYCEROL

H2 0 '" i HOtCl I No OH "" ~ H20

NoOH

~ Glycidol GLYCEROL DICHLOROHYDRIN NoOH

~ / EPICHLOROHYDRIN

Fig. 3.11. Routes for the synthesis of glycerin.

70

easily hydrated to monochlorohydrin and then hydrated to glycerin with caustic soda. The reactions are:

CH3 CH: CH2 + Cl2 - CH2CI CH: CHz + HCI (85 percent yield) CH2CI CH: CH2 + HOCI - CH2CI CHCl CH20H (95 percent yield) CH2CI CHCl CH20H + 2NaOH - CHzOH' CHOH CHzOH + 2NaCI

The overall yield of glycerin from allyl chloride is above 90 percent. Another process for obtaining glycerin from propylene involves the following reactions,

where isopropyl alcohol and propylene furnish acetone and glycerin (through acrolein) in good yields.

CH3 CHOHCH3 + air - CH3 'CO'CH3 + HzOz CH3 CH:CHz + air -+ CHO'CH:CHz + H20 CHO'CH:CHz + HzOz - CHOCHOHCHzOH - CHzOH'CHOH'CHzOH

Figure 29.11 illustrates the various methods of synthetic glycerin production. In 1982 only Dow Chemical Co. was producing synthetic glycerin the the United. States

because of rising energy costs and the increase in supplies from soapmakers and imports of low-priced glycerin from Europe.

SELEC1'ED REFERENCES

. DiStasio, r I.: Surfactants, Detergents and Sequestrants, Noyes, Park Ridge, N.J., 1981. Garrett,H. E.: Surface Active Chemicals, Pergamon, Oxford, 1974. Gutcho, 5.: Surface. Acttve Agents, Noyes, Park Ridge, N.J., 1977. Jungerman, E.: Cationic Surfactants, Marcel Dekker, New York, 1976. Linfield, M.: Anionic Surfactants, Marcel Dekker, New York, 1976 .. Longman, G. F.: The Analysis of Detergents and Detergent Products, Wiley, New York, 1976. Sittig, M. Detergent Manufacture Including Zeolite Builders, Noyes, Park Ridge, N.J., 1979.

Chemical Technology III (3rd Year)3: Soap and Detergents