Catalysis fermentation

Conventional biorefineries Starch (corn, wheat, cassava) and sugar crops (sugarcane, sugar beet), wood Pretreatment, chemical and enzymatic hydrolysis, catalysis, fermentation, fractionation, separation Commercial Sugar, starch, oil, dietary fibers, pulp and paper... 

Biochemical processes (enzymatic catalysis, fermentation, biological waste water treatment)... 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

A catalyst is a substance that iacreases the rate of approach to equiUbrium of a chemical reaction without being substantially consumed itself. A catalyst changes the rate but not the equiUbrium of the reaction. This definition is almost the same as that given by Ostwald ia 1895. The term catalysis was coiaed ia ca 1835 by Ber2eHus, who recognized that many seemingly disparate phenomena could be described by a single concept. For example, ferments added ia small amounts were known to make possible the conversion of plant materials iato alcohol and there were numerous examples of both decomposition and synthesis reactions that were apparendy caused by addition of various Hquids or by contact with various soHds. 

In 1878 the term enzyme, Greek for "in yeast," was proposed (8). It was reasoned that chemical compounds capable of catalysis, ie, ptyalin (amylase from sahva), pepsin, and others, should not be called ferments, as this term was already in use for yeast cells and other organisms. However, proof was not given for the actual existence of enzymes. EinaHy, in 1897, it was demonstrated that ceU-free yeast extract ("zymase") could convert glucose into ethanol and carbon dioxide in exactiy the same way as viable yeast cells. It took some time before these experiments and deductions were completely understood and accepted by the scientific community. 

The study of the reactions with the participation of glycosyl bonds is important not only for the theoiy of carbohydrates structure and reactional ability of carbohydrates. They represent a significant interest and solution for a number of important problems of organic, bioorganic chemistry, and molecular biology, fermentative catalysis, since the glycosyl bond is one of the most important structural elements of many biologically active compounds. 

The need for catalysis in this field is very clear. Molecular conversion technologies of non-food biomass have, so far, only been implemented for fermented cellulose. Even for those products, conversion into energy carriers is not yet very efficient. 

Apart from new catalytic methods, cascade conversions require new process technologies, such as in situ product recovery, reactor design, and compartmental-ization. In the long term, part of the present-day stoichiometric chemistry as well as bio- and chemocatalytic conversions in multi-step syntheses will gradually be replaced by cascade catalysis in concert, and full fermentations by cell factory design, or combinations thereof (Fig. 13.17). 

Using fermentation and other examples from plant and animal sources, Berzelius in 1837 introduced the concept of catalysis, stating ... 

The term catalysis was coined by Berzelius over 150 years ago when he had noticed changes in substances when they were brought in contact with small amounts of certain species called "ferments". Many years later in 1895 Ostwald came up with the definition that we use until today A catalyst is a substance that changes the rate of a chemical reaction without itself appearing into the products. This means that according to Ostwald a catalyst can also slow down a reaction The definition used today reads as follows A catalyst is a substance which increases the rate at which a chemical reaction approaches equilibrium without becoming itself permanently involved. 

The early history of enzymes is associated widi die process of brewing and die production of wine because of die economic importance of these processes in Europe in the nineteenth century. Following on from the work of Pasteur, it was Buchner and others who showed that an extract of yeast carried out fermentation (i.e. die conversion of glucose to alcohol) as well as die yeast cell itself. The agents diat did diis catalysis in the extract were simply described as in yeast which, from the Greek enQn) and zyme, is the name enzyme was derived. 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

Catalysis is not a new phenomenon, but its intentional utilization by humans has begun only in this century. One of the first catalytic processes was probably the fermentation of fruits to obtain alcoholic beverages. Enzymes found in yeast were used as catalysts for the conversion of sugar into alcohol. In fact, ancient Sumerians described beer preparation on... 

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