Study On A Special Ethylene Absorbent And The Related Absorbing System

Ethylene(C₂H₄) acts as a plant hormone which increases the ripening process of fruits and vegetables.It is widely reported that the postharvest life of many fresh produce items can be considerably prolonged by removing the ethylene in time.In practice,ethylene could be produced by plants or from the outside circumstance.Using ethylene absorbent is an economical option to exclude the ethylene efficiently.And at present,most of the commercialized absorbents are on the base of oxidizing ethylene by potassium permanganate(KMnO₄).Despite its efficiency,the absorbing capacity of these absorbents is rather limited and only lasts in a very short time because of the great oxidizing ability of KMnO₄.What's more,the toxicity of potassium permanganate brings about forgivable concerns from the general public about food safety.There are also many other commercial products which are based on physical absorption.Most of these materials are of porous structure,e.g.activated carbon,activated clay and zeolites,etc.And these materials can also be finely dispersed in polymer films.The main flaws of these absorbents are their much limited absorbability,unselective absorption and the vulnerability to the moisture which exists in the storaging circumstance.In recent years,some research using microorganisms(most of them are isolated from soil,like Xanthobacter,Nocardia, Mycobacterium,Rhodococcus,Bacillus,and Pseudomonas) and Light-sensitive material TiO₂ to degrade ethylene have also been reported.But at present they are still only used on laboratory scale.Overall,the main problem about most of these studies is that the exact ethylene adsorbing capacity of the absorbents have rarely been studied and documented scientifically,therefore the absorbing efficiency of the materials is difficult to substantiate.Due to the special characteristic of formingÏ€-complexation with ethylene,Ag(I) is generally known as an efficient ethylene-absorbing material in the field of natural gas conditioning and industrial off-gas purifying.Since Ag(I) Only complexates with ethylene,the absorption is of high selectivity.Actually,the strength ofÏ€-complexation is relatively weaker than covalent bond and electrovalent bond.However,it is considerably stronger than Van Der Waals Force,which contributes to the strong absorption,Ï€-complexation can be easily broke up by increasing the temperature or reducing the pressure,which illustrates that the absorbent can be renewed.In practice, the absorbability of Ag(I) is largely depended on its surface area.In order to gain sufficient absorbing sites,Ag(I) is usually finely embedded on inert supporters,like zeolite,silica gel,γ-Al₂O₃ and other porous materials(As a reductant,activated carbon is not available).13X molecular sieve was used as a supporter to modify Ag(I) in this study.The absorbing capacity of the absorbents prepared in different situation has been tested with an plug flow reactor to optimise the preparation formula.The study shows that the modified Ag(I) with 16%Ag(I) loading(Ag(I)/13X molecular sieve, m/m),still soaking for 7 hours,dried at 120℃for 8 hours,activated at 250℃for 4 hours performs the relatively great aborbing capacity(7163μl/g).Heated at 120℃for 1 hour,the aborbents was renewed.And it shows that after the first regensis,the absorbility of the absorbent fell from 7163μl/g to 3141.38μl g^-1,after the second regensis,it decreased to 2147.568μl g^-1.the effect of Humidity on the absorbent has also been studied in this research,it shows that under the relative humidity of 98%, the absorbent totally lost its absorbability.Based on the absorbing characteristics of modified Ag(I),an effective and reasonably-priced ethylene absorbing system has been designed at the end of this study.