Glycerine Recovery From Spent Soap Lye 2

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The recovery of glycerine from spent soap lye has been done using soap lye samples obtained from the hot process of soap production using palm kernel oil (P.K.O). The main advantage of hot process is that exact concentration of the lye solution is not known, but to perform this with adequate success, the lye and fat are boiled together at 80 – 1000C at times above 1000C until saponification occurs. The overall weight of glycerine recovered per 100g of oil used was 9.0g. The quantity of spent soap lye obtained was 250ml, Acid value was 555.39, percentage free acid value was 5.6%, total fatty acid = 7.131, percentage free caustic acid = 0.14%, percentage free  fatty acid obtained was 0.07131%, the specific gravity was 1.059, purity of glycerine was 92%. These parameters obtained were measured relatively to international standards with negligible error due to the type of equipment used. From the result, it is evident that the amount of glycerine recovered depends largely on the quantity of spent soap lye. Other processes the spend soap lye and the glycerine undergo as may be seen in other chapters includes, salting out, filtration, splitting and others. 





Title page                                                                        i

Letter of Transmittal                                                      ii

Approval page/certification                                            iii

Approval page                                                                 iv

Dedication                                                                       v

Acknowledgement                                                           vi

Abstract                                                                          vii

Table of Contents                                                            viii

List of Figures/Tables                                                    xii

Definition of Terms/Nomenclature                                        xiii


1.0      Introduction                                                          1

1.1 Background of the study                                          1

1.2 Statement of the problem                                         4

1.3 Scope and limitation of the study                            6

1.4 Purpose/aim/objectives of the study                       6

1.5 Method of Research                                                  7

1.6 Significance of the study                                          8


2.0              Literature Review                                           10

2.01          History of glycerine                                         13

2.02          Lye clarification                                              16

2.03          Recovery of glycerine from spent lye              25

2.04          Twitchel process                                             38

2.05          Autoclave saponification                                48

2.06          Lime saponification                                         49

2.07          Acid saponification                                 52

2.08          Aqueous saponifictaion                                  54

2.09          Splitting fats with ferments                            55

2.10          Krebitz porcess                                               59

2.11          Distillation of fatty acids                                62

2.12          Glycerol detection and estimation                 66

2.13          Glycerine as a by-product of soap

manufacture                                                    75

2.14          Process description of soap production 78

2.15          Process summary                                            79

2.16          Step 1:     oil preparation                                79

2.17          Ion exchange                                                  81

2.18          Soap removal                                                  82

2.19          Composition of glycerine production              83

2.20          Physical properties of glycerine                      87

2.21          Chemical properties of glycerine                    88

2.22          Sources and types of lipids                             90

2.23          Distinction between fats and oils                   91

2.24          Uses of glycerine                                             93

2.25          Major types of saponification                          95

2.26          Separation of glycerine and free fatty acid    99

2.27          Quantifying the phosphoric acid to be used 100

2.28          Metabolism                                                     102

2.29          Application of glycerine in food                      103

2.30          Application of glycerine in urethane polymers 104

2.31            Application of glycerine in drugs and cosmetics 104

2.32          Application of glycerine as a lubricant.          106

2.33          Application of glycerine in snuffs                   106

2.34          Other uses of glycerine                                   107

2.35          Hyper osmotic effects                                      108

2.36          Basic raw material for flycerine production.  108


3.0      Experimental Procedure                                         111

3.01 The Saponification Process                                     112

3.02 Splitting Method                                                     115

3.03 Determination of the viscosity of Glycerine           116

3.04 Titration                                                                  117

3.05 Percentage Free Alkaline (FCA)                             118

3.06 Bleaching of Crude Glycerine                                119


4.0      Experimental Result and Analysis                         121


5.0      Discussion                                                              128

5.1 Conclusion                                                                128

5.2 Recommendation                                                      129

References                                                              131

Appendices                                                              132


Table 2.0:        Properties of glycerine                            87

Table 2.1:        Physical properties of glycerine              86

Table 4A:         Glycerine producer association standard for Glycerine recovery                                  121

Table 4B:         Estimation consumption of glycerol in various industries                                    122

Table 4C:         Order of increment of the amount of % glycerine in all the samples.                  124

Table 4D:         Standard deviation table for percentage (%) salt and percentage glycerine              127








%     =      Percentage

N/4  =      Quarter normal

Lbs  =      Pounds

C.C  =      Cubic centimeter

PZ    =      Paterson Zochonis

IEA  =      International Equitable Association

KSI  =      Kitchen Soap Industries

SSL  =      Laboratory Stimulated sample

V      =      Volume of Acid

FFA=      Free fatty Acid

AV   =      Acid Value

SD   =      Standard Deviation

FCA=      Free Caustic Alkali

CA   =      Percentage Concentration of Glycerol

Vs    =      Volume of NaOH added to the sample

Vb    =      Volume of NaOH

 Added to the bank

Ws   =      Weight of Sample

% FAV = Percentage free Acid Value




Glycerine, (otherwise known as propan 1, 2, 3 triol) is found dissolved in the soap lye and also as an impurity in the crude soap during the saponification of fats and oils with caustic soda. Customarily, the process of soap manufacture, from fats and oil yields glycerol to about 10% of the value of the soap formed and due to its varied uses, its recovery is pertinent to the manufacturing cost analysis for any soap making business. Glycerol being an important bye product of soap manufacture, many small scale and medium scale soap manufacturers normally discards the lye as an unwanted product.

Glycerol occurs in nature combined in the form of triglycerides (fats and oil) and is obtained during the saponification of these triglycerides. This process was the only means of producing glycerol commercially, until 1949 when synthetic glycerol was produced as the compound recovered as by-product from the soap manufacture was sufficient for the world consumption. Alternatively, glycerol is synthesized from propene by the alternate chlorination and hydroxylation process. It is also obtained from the fermentation of various sugars. Glycerine is also produced by various routes from propylene. The epichlorohydrin process is the most important; it involves the chlorination of propylene to give ally chloride which is oxidized with a strong base to give epichlorohydrin. This epichlorohydrin is then oxidized to give glycerine.

In biodiesel, glycerine is a waste, as a result, the market for glycerol is depressed and the old epichlorohydrin process for glycerol synthesis is no more economically viable.

Fats and oils are esters of glycerine with long-chain fatty acid such as stearic acid (C17H35COOH) Palmitic acid (C15H31COOH) and oleic acid (C17H33COOH). Since glycerine contains three –OH groups, it can form three series of esters thus;

Mono-ester              di-ester            and tri-esters

CH2.OH                   CH2.OH           CH2.O.OC.R

CH.OH                     CH.O.OC.R      CH.O.OC.R

CH2.O.OC.R            CH2.O.OC.R    CH2.O.OC.R

Mono=-ester            di-ester            tri-ester

Some of the major industrial applications of glycerol include the manufacture of alkyd resins and flexible polyurethane for the plastic industry. It is also an important ingredient in cosmetics and adhesive manufacture. Many pharmaceutical preparations such as glycerol phenol mixture which serves as tranquilizers utilize glycerol.

Glycerol residue has been reported to contain 20.2% glycerol, 6.6% fatty acids (as soap) and 64.3% salt. Thus 91.1% of it is potentially useful. It is obviously advantageous, both environmentally and economically, to recover the glycerol in the waste material from soap industries as a potential alternative for the production of glycerol using chemical methods.



The method of analyzing glycerine is greatly varied due to the fact that glycerine contained impurities which acted so much like glycerine as to introduce serious errors in the determination of crude glycerine. This however led to the appointment of committees in the United States and Europe to investigate the method of glycerine analysis. It was concluded in the meeting of the International Committee set for this purpose, that acetin method should control the buying and selling of glycerine, but the more convenient bichromate method in a standardized form might be used in factory control and other technical purposes.

The quantity of recovered residual salt is dependent on the point of recovery and nature of lye treatment. Neutralizes of the acid and alkaline content of the soap lye helps to reduce the amount of salt originally combined with soap by precipitation, coagulation and flocculation. This is done through their pH adjustments.

The whole process becomes entirely cumbersome as absolute care is taken to ensure that glycerine passes through all the stages required to obtain pure glycerine devoid of impurities.




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Glycerine Recovery From Spent Soap Lye 2