How should the synthesis process for ligands be selected?

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How should the process flow for hydrazine synthesis be chosen? For the methanol synthesis process used in ammonia production, most existing plants locate the methanol synthesis step before copper purification, that is, at the outlet of the fifth or sixth stage of the compressor. New plants use the dimethyl process; in some cases, the dihydroxymethane is operated at the same pressure level as ammonia synthesis, which is known as high-pressure dihydroxymethane synthesis. The methanol synthesis processes have evolved over time, and there are currently three such processes. It is common to have built-in heat exchangers within the synthesis tower, with no heat recovery; as shown in Figure 1: file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image1.png. The compressed gas mixes with the recycled gas and enters the oil separation unit. This mixture then splits into two streams: the main stream goes into the shell of the synthesis tower and its internal jacket, from where it proceeds to the lower heat exchanger, while the secondary stream goes directly to the bottom of the tower, enters the central tube, mixes there with the gas that has been heated, and then enters the catalyst baskets located inside the internal components. The gas containing methanol that comes out of the tower goes directly into the water cooler; after cooling, methanol is separated from the alcohol fraction, with one stream proceeding to copper washing while the other stream is sent to a compressor for pressurization before returning to the oil fraction. The crude alcohol obtained after alcohol separation is further refined by distillation before being sold as a product. As can be seen from the above, the heat exchanger installed inside the synthesis tower occupies high-pressure space, resulting in a reduced amount of catalyst that can be used. Additionally, the limited ability to adjust the gas flow rates in the main and auxiliary lines restricts the maximum level of CO entering the tower, thereby reducing the range of adjustments possible. For this reason, a second process was developed, one that involves installing a heat exchanger outside the tower. As shown in Figure 2, file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image2.png, the compressed gas mixes with the circulating gas and enters the oil fractionator. The main stream is heated in a heat exchanger before entering the shell and internals jacket of the synthesis tower, and then proceeds to the central tube of the internals to reach the catalyst basket. The secondary stream can directly enter the central tube of the internals and mix with the gas from the main stream inside the catalyst basket. The gas exiting the tower goes through a heat exchanger before reaching the water cooler and the alcohol fractionator. What differs from the previous process is that the heat exchanger inside the internal component is moved outside the tower, allowing full utilization of the high-pressure space in the synthesis tower and thereby enabling a larger range of adjustment compared to before. However, it should be noted in this process that the temperature at the tower outlet exceeds 200°C; in other words, from the outlet of the synthesis tower to the inlet of the heat exchanger, as well as at the bottom of the synthesis tower and the heat exchanger, gases with a temperature above 200°C are present, and the materials used there must be heat-resistant alloy steels. To this end, most of this process involves retaining some heat exchangers within the synthesis tower to keep the temperature exiting the tower below 200°C. This process is not very different from the previous one; no heat is utilized, only the control methods are changed and expanded, resulting in an increased methanol yield. The process that is now accepted by many manufacturers is one with heat recovery. As shown in Figure 3, file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image3.png, the main gas stream enters the jacket and then exits to the heat exchanger; after its temperature is increased, it serves as the second gas stream entering the tower and reaching the catalyst basket. The secondary gas stream can either enter the tower directly or be added to the second gas stream. The gas produced in the synthesis process enters the waste heat boiler (or water heater), where heat is recovered to generate steam (or to heat the boiler water used throughout the plant); thereafter, it goes to the heat exchanger, followed by the water cooler and the alcohol separation unit. In this process, when it is necessary to increase methanol production, the reaction heat can be recovered, which also reduces the load on the water cooler. It also enables more flexible adjustment, resulting in the highest methanol yield. However, the material of equipment and pipelines for applications with gas temperatures above 200°C must be taken into consideration. However, both its waste heat boiler and the outer shell of the heat exchanger can make full use of equipment discarded from ammonia synthesis.