Production of MES by transesterification of castor oil

Abstract

Petroleum based detergents are neither soluble nor biodegradable; they are so stable such that when they flow into the soil, sewer or surface waters, they remain unchanged, resisting conversion into less complex and more soluble substances. In this work methyl ester sulphonate (MES) was produced by transesterification followed by sulphonation of ricinoleic acid, a main constituent of castor oil. A detergent was produced from transesterification followed by sulphonation of castor oil and then compared to another produced by direct saponification of castor oil. The quality of castor oil used was tested and found to be of good quality. The resulting detergents were compared with a local brand on the market and MES produced by transesterification reaction had improved detergency properties compared to that formed by direct saponification of castor oil. The MES detergent had excellent calcium tolerance and ability to cut through grease. Moreover it can be effective in higher pH compared to detergents produced by direct saponification. Castor oil has a linear structure and as such a detergent based on it should be digestible to soil microorganisms.

CHAPTER ONE

1.Introduction

As supply of petroleum derivatives is depleting, energy demand continues to rise, hence use of alternative non edible natural oils have received attention in detergent manufacturing. Transesterification of castor oil is the main way to make methyl ester (biodiesel) and then sulphonation to produce methyl ester sulphonate (MES) (Scholz, 2008).Work has been done in the transesterification of castor oil to produce biodiesel (Deshpande et al.,2012) as means of developing alternative renewable fuels for future utilization. Research carried on the production of detergent from pure castor yielded a directly saponified detergent rather than MES (Lee et.al., 2011). A detergent produced by direct saponification of castor oil is theoretically less effective compared to MES (Harun et al., 2006). A castor oil based detergent is characterized by good biodegradability, nontoxicity, renewability, ease of production and agricultural origin (Efeovbokhan et al., 2012). Castor is amongst the plants with the highest oil yield because of this characteristic it is possible to produce MES detergent at large scale with reduced cultivated land (Scholz, 2008).

A detergent contains an active agent called surfactant that wets the fabric, emulsifies oily matter, solubilizes grime and keeps the soil in suspension (Jarnadhan, 1999). Due to the environmental threats from petrochemical feedstock, considerable attention has been given to non-edible vegetable oils as an alternative source for the production of soaps and detergent. Castor plant in Zimbabwe can be used as an alternative source for petrochemical products Castor oil an extract from castor plant is composed of 90% ricinoleic acid and 10% linoleic and oleic acid (Jarnadhanan, 2006). Transesterification is the process of exchanging the organic R group of an ester with the organic R group of an alcohol to give a different alcohol (glycerol) and a different ester (methyl ester) (Riemennschneider, 2005). Sulphonation of the methyl ester formed produces a surfactant.

CHAPTER TWO

Experimental work

2.1.Oil quality

The quality of oil was determined by testing the saponification value of the oil. In a typical preparation, 2 grams of the extracted oil was placed in a conical flask to which 25 ml of ethanoic potassium hydroxide (0.1M) was added and the mixture allowed to boil gently for about 60 minutes with shaking at regular intervals of 5 minutes. Few drops of phenolphthalein indicator was added to the warm solution and then titrated with 0.5M HCl. The end point was reached when the pink colour of the indicator just disappeared. The same procedure was followed for the blank.

2.2.Preparation of detergent by saponification of castor oil

One molar solution of sodium hydroxide was prepared by adding 40 grams of sodium pellets to 1000 ml of water. In a separate beaker 20 ml of castor oil was added and warmed to 300C. 50 ml of 1M sodium hydroxide was added to the castor oil with rapid stirring after which 20 ml of concentrated sulphuric acid was added drop wise as the reaction is violent. This was carried out in film cardboard. The solution was stirred till a thick creamy paste was formed. The paste was allowed to stand for one hour until it turned to a semi solid. The contents were transferred into an oven. The detergent was allowed to dry at 600C for 20 minutes. After drying the product formed was named Product A and was stored for further tests. The same procedure was repeated by varying acid volume from 20 to 10 ml and from 10 to 5 ml with other conditions kept constant. Products X and Y were formed respectively.