Abstract:
The experimental studies of tanning extraction from rambutan peel were devided into 3 main parts. The first part was the batch extraction without mixing. The extraction units were 250 ml. Erlenmeyer flasks. It was found that the optimum size of rambutan peel was 1-2 mm.. For the temperature 30-70℃, 50% ethanol, 1% and 3% Na2SO3 should be used. When the extraction temperature raised up to 90℃, pure water should be used. The optimum ratio of rambutan peel to solvent was about 1:10.The optimum extraction time was 9 and 3 hours at 70℃ and 90℃, respectively. The second study was to determine the tannin equilibrium curve and the diffusion coefficients (kˊA/b) at different temperatures by using a mixing vessel. It was found that the term of kˊA/b was linear function of the extraction temperature ( K) kˊA/b = 0.192 t 56.09 for pure water and kˊA/b = 0.203 T 59.37 for 50% ethanol under the studied conditions : size = 1-2 mm., the ratio of rambutan peel to solvent = 1:10, temperature = 30°-70℃ and mixing speed of the magnetic stirrer = 500 rpm. The third study was the semi continuous counter current extraction. Six units of 3 litres stainless steel cylinders were used. Each extracter cylinder had a porous cylinder filled up with rambutan peel inside. These six units were partially immersed in the water bath. It was reveaed that for the extraction time of 1/2 hours, the 3% Na2SO3 solvent yielded a better efficiency than using 1% Na2SO3, 50% ethanol and pure water at 70℃. Therefore, Na2SO3 addition is appropriate and does not cause any harm in using since Na2SO3 is a common chemical used in tanning industry. It is concluded that the semi-continuous counter-current extraction system could improve significantly the tannin extraction efficiency in comparision with the batch with mixing system. Meanwhile, the batch without mixing system had the lowest extraction efficiency.