Magnetic separation and recycle of catalyst components in a bio-mass to glycols process

#The presently disclosed subject matter relates to a process for preparing glycols, particularly ethylene glycol and propylene glycol, by converting a carbohydrate feed stock material in a reactor using a bi-functional catalyst system. More specifically, the presently disclosed subject matter relates to a process for magnetically separating and subsequently recycling catalyst components in a process for preparing glycols.

#Glycols such as ethylene glycol and propylene glycol are valuable materials with a multitude of commercial applications, e.g. as heat transfer media, antifreeze, and precursors to polymers, such as PET. The market for ethylene and propylene glycols (EG and PG) is expanding worldwide, with the EG market being vastly bigger than the market for PG (i.e., 1,2-propylene glycol). Ethylene and propylene glycols are typically made on an industrial scale by hydrolysis of the corresponding alkylene oxides, which are the oxidation products of ethylene and propylene, produced from fossil fuels/petrochemical feed stocks involving multiple processing steps. Use of bio-based feed stocks for the production of energy and chemicals has become increasingly desirable in the industry since this approach to use feeds from renewable sources provides a pathway for sustainable development.

#In recent years, increased efforts have focused on producing chemicals, including glycols, from renewable feedstocks, such as carbohydrate-containing feedstock. Carbohydrates are plentiful and renewable bio-mass feeds having the structural features resembling that of ethylene glycol; each carbon has one attached hydroxyl group or contains an oxygen function that can be readily converted into a hydroxyl. As such, EG and PG can be produced if the C—C bonds are selectively cleaved into C2 and C3 units.

#The accompanying drawings, which are included to provide a further understanding of the disclosed subject matter, are incorporated in and constitute a part of this specification. The drawings also illustrate embodiments of the disclosed subject matter and together with the detailed description serve to explain the principles of embodiments of the disclosed subject matter. No attempt is made to show structural details in more detail than may be necessary for a fundamental understanding of the disclosed subject matter and various ways in which it may be practiced.

#FIG. 1 shows an example process scheme according to an implementation of the disclosed subject matter.

#FIG. 2 shows an example process scheme according to an implementation of the disclosed subject matter.

#Carbohydrates are readily available and renewable bio-mass feeds, and they have the structural features resembling that of ethylene glycol; each carbon has one attached hydroxyl group or contains an oxygen function that can be readily converted into a hydroxyl. Ethylene glycol (EG) and propylene glycol (PG) can be produced by selectively cleaving the C—C bonds into C2 and C3 units. As such, the presently disclosed subject matter provides a process for the conversion of carbohydrate feed stock materials and hydrogen gas into glycols, particularly with ethylene glycol as the main product and propylene glycol as a smaller co-product.

#The process variables have major impacts on the conversion and selectivity of the reaction. For example, the particular catalyst(s) used and process conditions can provide for a successful reaction selectivity outcome under a set of practical reaction conditions. In addition, the ability to separate, regenerate, and recycle catalyst components are important to the overall success of the bio-mass to glycols process and the ability to operate the reactor in an uninterrupted continuous mode.

#The sugars to glycols hydrogenolysis reaction, which is carried out using a metal catalyst and in the presence of hydrogen, is a complex reaction known to produce hundreds of products. Since ethylene and propylene glycols are the desired products, the other products must be minimized by selecting the appropriate catalyst and conditions; additionally an EG/PG wt % ratio of at least 1:1 and preferably 7:1 or more is desirable. In general, sugars tend to cleave into C3 fragments more easily than the desired C2 fragment, resulting in the formation of propylene glycol as the single most predominant molecule. While the selection of the most appropriate catalyst, not only from the selectivity point of view but also from the point of view of catalyst longevity, is an important task, other aspects of the reaction must also be considered. The catalyst generally only controls the chemistry taking place on its surface; for example, the cleavage of the sugar molecules into smaller fragments taking place by discrete retro-Aldol reactions followed by hydrogenation of the intermediates into products is the desired pathway. However, quite a number of other reactions take place in solution and these side reactions must also be considered. A number of ions such as OH−, OAc−, etc. could be present in the solution under basic pH conditions or H+ ions could be present under acidic pH conditions. While these ions could also catalyze the retro-Aldol reaction, these ions are generally known to catalyze a variety of dehydration side-reactions causing the sugar molecules to degrade into wasteful products. These undesirable side reactions could become dominant particularly under high temperature conditions. A proper choice of catalysts and process conditions is therefore essential in order to realize the objectives of high glycol yields and long catalyst life. Multiple equations can be used to explain the various steps of the chemistry of the conversion of sugars to EG and PG, as shown below.