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− | + | The first step of two-step oxidation of acrylic acid is propylene reacts with oxygen, producing acrolein. And then, acrolein | |
− | + | reacts with oxygen, producing acrylic acid. The conversion rate is up to 90%. Chemical | |
− | + | Formula (1) and (2) are showed below. This method is widely used in industry production | |
− | + | of acrylic acid. | |
− | + | <br> | |
− | + | <br>H2C=CH-CH3+3/2O2→H2C=CH-CHO+H2O(1) | |
− | + | ||
+ | <br> H2C=CH-CHO+ 1/2O2→H2C=CH-COOH(2) | ||
+ | <br> | ||
+ | <br> The process of the oxidation method of the propylene is mentioned in the patent | ||
+ | of the Japanese Catalyst Company in the 1880s. The reaction temperature of the first | ||
+ | step is 320-330℃. If other additives such as W, Co, K, Si and O are added to the | ||
+ | catalyst MoBiFe, the yield of acrolein can reach more than 90% [4]. The reaction | ||
+ | temperature of the second step is 210-255 ℃. The compositions of the catalyst are | ||
+ | Mo, Bi, Fe, Co, K and O. The yield of acrylic acid can reach 97.5% [4]. The yield | ||
+ | of acrylic acid in the two-step oxidation process is much higher than that of the | ||
+ | direct oxidation of propylene to produce acrylic acid. This is because the reaction | ||
+ | temperature in the one-step process is 325-350 ° C, at which the conversion of propylene | ||
+ | to acrolein is high. But acrolein and acrylic acid are further oxidized at that temperature | ||
+ | [4]. Therefore, to obtain higher yields of acrylic acid, control the reaction at | ||
+ | different stages by controlling the temperature and changing the catalyst composition | ||
+ | in the two-step method is more reasonable and more valuable. As the most widely used | ||
+ | method in the industrial production of acrylic acid, oxidation of propylene has the | ||
+ | advantages: high conversion efficiency and simple production process. | ||
+ | |||
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− | + | So far, the researchers have found that certain microorganisms which contain nitrilase can catalyze the conversion of acrylonitrile | |
− | + | to acrylic acid. Nitrilase can catalyze the nitrile compound directly to produce | |
− | + | the corresponding products of carboxylic acid [5]. Nitrilases are present in Rhodococcus, | |
− | + | Pseudomonas, Nocardia and Bacillus [6]. | |
− | + | <br> | |
− | + | <br>There are many advantages of Hydrolysis of Acrylonitrile to produce acrylic acid, | |
− | + | for example, specificity of nitrilases, high conversion rate of acrylonitrile, the | |
+ | moderate reaction conditions, and less by-products. However, acrylonitrile is a chemical | ||
+ | product comes from fossils, and the price is higher than acrylic acid, so it is not | ||
+ | suitable for the needs of sustainable development and does not meet the long-term | ||
+ | development of society. | ||
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− | + | Acrylamide also relies on petrochemical resources to obtain the product. According to current report, Rhodococcus (Rhodococcus | |
− | + | AJ270), Pseudomonas aeruginosa, Bacillus thuringiensis BR449 and other microorganisms | |
− | + | can catalyze the conversion of acrylamide to acrylic acid[10]. Acrylamide is converted | |
− | + | to acrylic acid by amidase. Rhodococcus AJ270 can grow with acetamide as a carbon | |
− | + | source and show high amidase activity during metabolism. The conversion of acrylamide | |
− | + | has the advantages of moderate reaction conditions, high conversion rate, long reaction | |
− | + | time and large yield, but it has the same shortcomings as the conversion of acrylonitrile. | |
+ | Rhodococcus AJ270 needs amidase as raw material to express acetamide, and the price | ||
+ | of acetamide and acrylamide is high, thus limiting the industrial production using | ||
+ | this method. | ||
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− | + | Just as its name implies, lactic acid dehydration pathway refers to a metabolic pathway using the dehydration of lactic acid | |
− | + | to produce acrylic acid. Because the fermentation production process of lactic acid | |
− | + | is very mature, so using the dehydration of lactic acid to produce acrylic acid has | |
− | + | long been aroused the interest of the researchers. | |
− | + | <br> | |
− | + | <br>At present, the method mainly uses Clostridium propionicum as the starting strain. | |
− | + | Specific metabolic pathway is shown in Figure 1.2 [14]. Although the route is short, | |
+ | but there are still many problems when used in producing acrylic acid. | ||
+ | <br> | ||
+ | <br>As can be seen from Figure 1.2, metabolism of lactic acid is divided into the left | ||
+ | side, the oxidation pathway and the right side, the reduction pathway. When Clostridium | ||
+ | propionate uses lactic acid as a source of energy, one molecule of lactic acid produces | ||
+ | one third of the molecule of acetic acid and 2/3 of the propionic acid [15]. In the | ||
+ | production process of acetic acid, there will be four electrons and 4 protons generate, | ||
+ | as well as offering ATP for bacteria to grow. The acryloyl CoA in the reduction pathway | ||
+ | receives electrons to produce propionyl CoA and finally generates propionic acid. | ||
+ | <div align="center"> | ||
+ | <img src="https://static.igem.org/mediawiki/2017/7/7f/Lactate_dehydration_pathway.png" class="img-responsive" width="50%" height="50%" | ||
+ | style="padding-top:20px"> | ||
+ | </div> | ||
+ | |||
+ | |||
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− | + | 3-hydroxy propionic acid (3-HP) is an important chemical intermediate, there are a number of patents have reported the methods | |
− | + | of sugar conversion to 3-HP [20-22]. And 3-HP has two functional groups, carboxyl | |
− | + | and hydroxyl. It is possible to synthesize a variety of important chemical substances | |
− | + | such as 1,3-propanediol, succinic acid through oxidation, dehydration and esterification | |
− | + | reaction,. Using 3-HP to develop downstream products, such as acrylic acid is also | |
− | + | one of the hot spots. | |
− | + | <div align="center"> | |
+ | <img src="https://static.igem.org/mediawiki/2017/f/fb/3-hydroxypropionic_acid_pathway.png" class="img-responsive" width="50%" height="50%" | ||
+ | style="padding-top:20px"> | ||
+ | </div> | ||
+ | |||
+ | |||
+ | <br> Using 3-hydroxypropionic acid-related pathways to construct engineering bacteria | ||
+ | to produce acrylic acid is a hotspot in recent years [30-33], but the yield is generally | ||
+ | not high, partly because of the toxic side effects of acrylic acid on cells and, | ||
+ | on the other hand, the pathway is long, and the reaction requires vitamin B12 to | ||
+ | participate in, it is very difficult to achieve high yield of acrylic acid with this | ||
+ | approach. | ||
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− | + | Propionic acid oxidation pathway refers to Clostridium propionate use propionic acid as a substrate to produce acrylic acid | |
− | + | under the aerobic conditions. It is speculated that Propionic acid oxidation pathway | |
− | + | is the reverse pathways from lactic acid to propionic acid in Clostridium propionate, | |
− | + | namely propionic acid to propionyl CoA, and then to acryloyl CoA , finally converted | |
− | + | to acrylic acid. Propionic acid oxidation pathway has the same problem as lactate | |
− | + | dehydration pathways, that is, need to add exogenous electron acceptor to achieve | |
− | + | coenzyme regeneration, so that the entire cell system remained stable. | |
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− | + | Dimethylsulphoniopropionate (DMSP) is a sulfur metabolite synthesized in some higher plants in sea water, algae and marine | |
− | + | microalgae [36]. Some marine organisms such as bacteria, phytoplankton have DMSP | |
− | + | lyase, which cleaves the DMSP into acrylate and dimethyl sulfide (DMS) [37], which | |
− | + | is also commonly found in Alcaligines faecalis, The route is shown in Figure 1.3. | |
− | + | Extracellular DMSP is transported into the body by the carrier protein, be cleaved | |
− | + | into acrylic acid and DMS by DMSP lyase. Acrylic acid is further reacted to form | |
− | + | β-HP. | |
+ | <div align="center"> | ||
+ | <img src="https://static.igem.org/mediawiki/2017/b/b8/DMSP_pathway.png" class="img-responsive" width="50%" height="50%" style="padding-top:20px"> | ||
+ | </div> | ||
+ | |||
+ | <br>The DMSP pathway is the only biological pathway that can directly produce acrylic | ||
+ | acid. The DMSP lyase is the key enzymes, but it is not clear at present that there | ||
+ | is no definite sequence of its genes. Therefore, research report about making use | ||
+ | of or modifying DMSP pathway is rarely seen. | ||
+ | |||
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Revision as of 08:06, 28 October 2017