CN116462572B - Process for preparing ethylene glycol by hydrogenating dimethyl oxalate - Google Patents
Process for preparing ethylene glycol by hydrogenating dimethyl oxalate Download PDFInfo
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- C07C29/147—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH of carboxylic acids or derivatives thereof
- C07C29/149—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH of carboxylic acids or derivatives thereof with hydrogen or hydrogen-containing gases
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Abstract
The invention relates to the technical field of ethylene glycol preparation from synthesis gas, and in particular discloses a process for preparing ethylene glycol by hydrogenating dimethyl oxalate, which comprises the following steps: s1: uniformly mixing a hydrogenation catalyst and inert ceramic balls, and then filling the mixture into a fixed bed reactor to form a hydrogenation catalyst and inert ceramic ball mixed layer; s2: introducing a gas medium into the top of the fixed bed reactor, and heating the hydrogenation catalyst to realize the activation of the hydrogenation catalyst; s3: and (3) allowing gas-phase dimethyl oxalate and hydrogen to flow in parallel, introducing the gas-phase dimethyl oxalate and the hydrogen from the top of the fixed bed reactor, and carrying out gas-solid two-phase hydrogenation reaction on the dimethyl oxalate and the hydrogen in the fixed bed reactor. By adopting the technical scheme provided by the invention, the technical problems that in the prior art, in the process of preparing ethylene glycol by hydrogenating dimethyl oxalate, the hydrogenation catalyst at the position is easy to coke and pulverize due to severe reaction at the upper part of a reactor and large amount of reaction heat released can be solved, the service life of the hydrogenation catalyst is shorter, and byproducts are increased.
Description
Technical Field
The invention relates to the technical field of ethylene glycol preparation from synthesis gas, in particular to a process for preparing ethylene glycol by hydrogenating dimethyl oxalate.
Background
Ethylene Glycol (EG) is an important petrochemical base organic feedstock from which more than 100 chemicals can be derived. The process route for synthesizing glycol by converting coal or natural gas into synthetic gas is gradually perfected, and the method is called as the process for preparing glycol from the synthetic gas. Compared with the traditional ethylene glycol preparation method, the ethylene glycol preparation method by using the synthesis gas has the advantages of wide raw material sources, low price, short process flow, high technical economy and the like.
The method for preparing glycol from the synthesis gas mainly comprises a direct method and an indirect method. The direct method is to directly synthesize glycol from synthesis gas by a noble metal catalyst at high temperature and high pressure, and the method meets the requirement of atom economy, but is difficult to carry out in thermodynamics due to the limitation of chemical reaction balance, has the problems of overhigh synthesis pressure, contradiction between the activity and stability of the catalyst at high temperature and the like, and is temporarily not suitable for industrial application. The indirect method is to synthesize some intermediate products by using synthesis gas, and then prepare ethylene glycol by catalytic hydrogenation, and mainly comprises a formaldehyde method and an oxalate method. The formaldehyde route has a plurality of methods, but most of the methods are in a test stage at present, and industrialization is not realized; the oxalate route has low requirements on process conditions, the reaction conditions are relatively mild, and the method enters a large-scale industrialized production application stage.
The oxalate method (CO oxidative coupling method) is also called a synthetic gas oxidative coupling method, and commonly used oxalate comprises dimethyl oxalate. The dimethyl oxalate route is that dimethyl oxalate is synthesized by CO gas phase catalysis, and ethylene glycol is prepared by catalytic hydrogenation. The route reaction is divided into three steps: first, oxidation and esterification reaction: methanol reacts with NO to generate methyl nitrite; secondly, CO oxidative coupling reaction: the CO and methyl nitrite are subjected to carbonylation coupling reaction to prepare dimethyl oxalate; thirdly, oxalate hydrogenation reaction: further hydrogenating dimethyl oxalate to synthesize ethylene glycol. The reaction of synthesizing ethylene glycol by hydrogenating dimethyl oxalate in the third step is key to the technical route, and the reaction step has the following problems in practice:
The partial position reaction in the reactor is intense, a large amount of reaction heat is released to cause the hot spot temperature to be higher, the operation of the device is influenced, the device is safe, stable, long, full and excellent, the hydrogenation catalyst at the position is easy to coke and pulverize, on one hand, the service life of the hydrogenation catalyst is short, on the other hand, the resistance of the hydrogenation catalyst is increased, the impurities such as methyl glycolate, ethanol and butanediol are increased, the impurities are deposited on the surface of the hydrogenation catalyst, the pore canal of the hydrogenation catalyst is blocked, the active site of the hydrogenation catalyst is covered, the side reaction is further increased, and the utilization rate of materials is reduced.
Disclosure of Invention
The invention aims to provide a process for preparing ethylene glycol by hydrogenating dimethyl oxalate, which solves the technical problems of easy coking and pulverization of a hydrogenation catalyst at the position, short service life of the hydrogenation catalyst and increased byproducts caused by severe reaction and large heat release of reaction at the upper part of a reactor in the process of preparing ethylene glycol by hydrogenating dimethyl oxalate in the prior art.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a process for preparing ethylene glycol by hydrogenating dimethyl oxalate comprises the following steps:
S1: filling a hydrogenation catalyst, uniformly mixing the hydrogenation catalyst with inert ceramic balls, and filling the mixture into a fixed bed reactor to form a hydrogenation catalyst and inert ceramic ball mixed layer;
S2: activating a hydrogenation catalyst, introducing a gas medium into the top of the fixed bed reactor, and heating the hydrogenation catalyst to realize the activation of the hydrogenation catalyst;
S3: and (3) carrying out hydrogenation reaction on the dimethyl oxalate, wherein gaseous dimethyl oxalate and hydrogen are parallel-current, the gaseous dimethyl oxalate and the hydrogen are introduced from the top of the fixed bed reactor, and the gaseous-solid two-phase hydrogenation reaction is carried out on the dimethyl oxalate and the hydrogen in the fixed bed reactor.
The principle and the advantages of the scheme are as follows:
1. The reaction temperature is uniform: according to the scheme, the hydrogenation catalyst and the inert ceramic balls are uniformly mixed and then are filled once, so that the filling is convenient, and the inert ceramic balls do not participate in the chemical reaction of dimethyl oxalate hydrogenation and only play a role in heat conduction, so that the dimethyl oxalate hydrogenation is changed from concentrated reaction to disperse reaction, the reaction heat distribution of all parts in the fixed bed reactor is uniform, and the temperature difference of all parts in the fixed bed reactor is reduced.
2. Heat transfer capability enhancement: because the heat conduction performance of the inert porcelain ball is superior to that of the hydrogenation catalyst, the heat generated by the hydrogenation reaction of the dimethyl oxalate can be quickly transferred to the reaction circulation gas phase and the column wall of the fixed bed reactor through the inert porcelain ball, thereby greatly improving the heat transfer efficiency of the fixed bed reactor, enhancing the heat transfer capacity of the fixed bed reactor, avoiding the local accumulation of the reaction heat, reducing the hot spot temperature in the fixed bed reactor and being beneficial to ensuring the long-period safe operation of the fixed bed reactor.
3. Prolonging the service life of the catalyst: because the dimethyl oxalate hydrogenation reaction in the fixed bed reactor tends to be mild, the reaction heat distribution of each part in the reactor is more uniform, the temperature difference is reduced, and the temperature of a hot spot in the fixed bed reactor is reduced, the situation that the hydrogenation catalyst at the part is coked and pulverized due to the high temperature of the hot spot caused by local reaction heat accumulation is avoided, and therefore, the scheme is favorable for prolonging the service life of the catalyst.
4. The byproducts are reduced, and the material utilization rate is high: the problems of coking and pulverization of the hydrogenation catalyst caused by temperature reduction of the hot spots in the fixed bed reactor are solved, so that the catalytic resistance of the hydrogenation catalyst is reduced, and the generation of impurities such as methyl glycolate, ethanol and butanediol serving as byproducts can be effectively reduced, so that the impurities are prevented from depositing on the surface of the hydrogenation catalyst to block the pore channels of the hydrogenation catalyst and cover the active sites of the hydrogenation catalyst, the selectivity of the catalyst is further improved, the progress of side reaction is slowed down, the generation of byproducts is reduced, and the material utilization rate is improved.
5. The catalyst use efficiency is improved: the hydrogenation catalyst and the inert porcelain balls are uniformly mixed and filled, so that the dimethyl oxalate hydrogenation reaction is changed from concentrated reaction to dispersed reaction, the whole reaction is uniform along the height direction of the fixed bed reactor, and the problems of larger output of the hydrogenation catalyst positioned at the upper part, small output of the hydrogenation catalyst positioned at the lower part and uneven output of the hydrogenation catalyst caused by severe reaction at the upper part and mild reaction at the lower part of the fixed bed reactor are avoided, and the service efficiency of the catalyst is effectively improved.
6. Promote long period operation ability: because the dimethyl oxalate hydrogenation reaction in the fixed bed reactor tends to be mild, the service lives of the hydrogenation catalysts at the upper and lower parts in the fixed bed reactor are the same, the situation that the hydrogenation catalyst at the upper part is deactivated before the service life of the hydrogenation catalyst, so that the device is forced to stop to replace the hydrogenation agent at the upper part of the fixed bed reactor or replace all the hydrogenation catalyst is avoided, the stopping times of the device due to the replacement of the catalyst can be reduced, the long-period operation capability of the device is effectively improved, and the production efficiency of glycol is further improved.
7. The difficulty in discharging the catalyst is reduced: the hydrogenation catalyst and the inert porcelain balls are uniformly mixed and filled, so that the dimethyl oxalate hydrogenation reaction is changed from concentrated reaction to disperse reaction, the reaction heat in the fixed bed reactor is uniformly distributed, and the problem that the hydrogenation catalyst is difficult to discharge after the reaction is finished can be avoided by avoiding high local temperature in the fixed bed reactor caused by accumulation of the reaction heat, thereby avoiding the blockage of the pipeline due to coking of the hydrogenation catalyst.
8. In addition, the scheme adopts the gaseous dimethyl oxalate and hydrogen to carry out hydrogenation reaction, and compared with the liquid dimethyl oxalate and hydrogen to carry out hydrogenation reaction, the partial concentration of the dimethyl oxalate in the fixed bed reactor can be prevented from being too high, so that the partial reaction is severe, the reaction heat is released too much, the scheme is favorable for reducing the hot spot temperature, thereby avoiding coking and pulverization of the hydrogenation catalyst, prolonging the service life of the hydrogenation catalyst, reducing the occurrence of side reaction and further reducing byproducts.
Preferably, as an improvement, the pure hydrogenation catalyst and the pure inert ceramic balls are sequentially filled from top to bottom below the hydrogenation catalyst and inert ceramic ball mixed layer in the step S1, so as to form a pure hydrogenation catalyst layer and a pure inert ceramic ball layer respectively.
By adopting the scheme, the pure hydrogenation catalyst is filled below the hydrogenation catalyst and inert porcelain ball mixed layer to form a pure hydrogenation catalyst layer, and the upper part of the fixed bed reactor can convert concentrated reaction into disperse reaction due to the existence of the inert porcelain balls in the hydrogenation reaction process of dimethyl oxalate, so that the problem of high hot spot temperature caused by accumulation of reaction heat at the upper part of the fixed bed is avoided; the pure hydrogenation catalyst layer positioned at the middle lower part of the fixed bed reactor can ensure the mild reaction even if the centralized reaction is carried out at the middle lower part of the fixed bed reactor, and further avoid the problem of higher hot spot temperature caused by the accumulation of a large amount of reaction heat because the gas-phase dimethyl oxalate and hydrogen introduced from the top part are partially reacted under the catalysis of the hydrogenation catalyst at the upper part. By adopting the filling mode, the hydrogenation reaction of the dimethyl oxalate and the methyl glycolate can be prevented from being incomplete and penetrating through a pure hydrogenation catalyst bed layer, side reaction products are reduced, and the filling amount of the hydrogenation catalyst in the unit fixed bed reactor volume can be improved, so that the filling rate of the hydrogenation catalyst in the fixed bed reactor is high, the size of the fixed bed reactor can be reduced under the condition that the hydrogenation catalyst amount required by the reaction is fixed, and the equipment investment is saved and the production cost is reduced.
The pure inert porcelain ball is filled below the pure hydrogenation catalyst layer to form a pure inert porcelain ball layer, on one hand, the inert porcelain ball can support the hydrogenation catalyst above the pure inert porcelain ball layer so as to prevent the hydrogenation catalyst from falling off from the bottom of the fixed bed reactor in the filling and using processes; on the other hand, the inert porcelain ball is used as an inert substance to be filled in the position of the tube plate at the lower part of the fixed bed reactor, does not participate in the reaction in the dimethyl oxalate hydrogenation reaction process, can prevent the hydrogenation catalyst from participating in the reaction at the tube plate at the lower part of the fixed bed reactor to cause heat accumulation so as to cause safety problem, and ensures the safe proceeding of the reaction.
Preferably, as a modification, a supporting spring is filled below the pure inert porcelain ball layer to form a supporting spring layer.
By adopting the scheme, the supporting spring is filled below the pure inert ceramic ball layer to form the supporting spring layer, the pure inert ceramic ball layer above the supporting spring layer and the pure hydrogenation catalyst layer above the pure inert ceramic ball layer can be further supported, the inert ceramic ball and/or the hydrogenation catalyst are prevented from falling off from the bottom of the fixed bed reactor in the filling and using processes, the stability of the filled bed layer in the fixed bed reactor is ensured, and the dimethyl oxalate hydrogenation reaction can be stably carried out.
Preferably, as a modification, the hydrogenation catalyst and inert ceramic ball mixed layer in the S1 comprises 65-90wt% of the hydrogenation catalyst and 10-35wt% of the inert ceramic balls.
By adopting the scheme, 65-90wt% of hydrogenation catalyst and 10-35wt% of inert porcelain balls are mixed and then filled into a fixed bed reactor to form a hydrogenation catalyst and inert porcelain ball mixed layer, and the production cost can be reasonably controlled while the service life and the material utilization rate of the hydrogenation catalyst are ensured in the subsequent dimethyl oxalate hydrogenation reaction process. If the content of the hydrogenation catalyst is more than 90wt%, the content of the inert porcelain balls is less than 10wt%, at this time, the content of the inert porcelain balls in the unit volume of the mixed layer of the hydrogenation catalyst and the inert porcelain balls is too small, in the case of dimethyl oxalate hydrogenation, it is difficult to effectively convert the dimethyl oxalate hydrogenation from 'concentrated reaction' to 'dispersed reaction', namely, the upper part reaction in a tubular reactor is severe, a large amount of reaction heat is released in unit time, a small amount of inert porcelain balls cannot timely transfer the heat to the circulating gas phase and the tubular wall of the reactor, the problem that the upper hot spot temperature is high still exists, the hydrogenation catalyst is easy to coke and deactivate under the high-temperature environment, and the side reaction is aggravated to reduce the material utilization rate. If the content of the hydrogenation catalyst is less than 65wt%, the content of the inert ceramic balls is more than 35wt%, and at this time, the content of the hydrogenation catalyst in the unit volume of the mixed layer of the hydrogenation catalyst and the inert ceramic balls is too small, so that in the hydrogenation reaction of dimethyl oxalate, in order to achieve the same catalytic effect, the volume of the tubular reactor and the loading amount of the mixed catalyst need to be increased, which results in increased production cost.
Preferably, as a modification, the ratio of the height of the hydrogenation catalyst and inert porcelain ball mixed layer to the height of the pure hydrogenation catalyst layer is 1: (4-7).
By adopting the scheme, the ratio of the heights of the hydrogenation catalyst and inert porcelain ball mixed layer to the pure hydrogenation catalyst layer is controlled at 1: in the range of (4-7), in the hydrogenation reaction process of dimethyl oxalate, the hydrogenation catalyst and inert porcelain ball mixed layer positioned at the upper part of the fixed bed reactor can convert concentrated reaction into dispersed reaction, so that the problems of severe reaction in the fixed bed reactor, particularly in the upper part, high temperature of a bed hot spot, coking of the catalyst and the like caused by reaction heat accumulation are solved; the pure hydrogenation catalyst layer positioned at the lower part of the fixed bed reactor can ensure the complete reaction of the dimethyl oxalate, prevent the penetration of the dimethyl oxalate, reduce side reaction products, ensure the filling rate of the hydrogenation catalyst in the fixed bed reactor and reduce equipment investment. If the ratio of the heights of the hydrogenation catalyst and the inert ceramic ball mixed layer to the pure hydrogenation catalyst layer is greater than 1:4, namely the heights of the upper hydrogenation catalyst and the inert ceramic ball mixed layer are higher, the heights of the lower pure hydrogenation catalyst layer are lower, the lower pure hydrogenation catalyst layer cannot ensure complete reaction of dimethyl oxalate due to the limit of the total tube length of the fixed bed reactor, and the dimethyl oxalate or methyl glycolate can penetrate through the pure hydrogenation catalyst layer, so that the conversion rate of the oxalic ester, the yield of the ethylene glycol and the quality of the crude ethylene glycol are reduced, the separation difficulty and the separation energy consumption of the crude ethylene glycol are increased, and the quality of an ethylene glycol product is seriously influenced. If the height ratio of the mixed layer of the hydrogenation catalyst and the inert ceramic balls to the pure hydrogenation catalyst layer is less than 1:7, namely the heights of the mixed layer of the upper hydrogenation catalyst and the inert ceramic balls are lower, and the heights of the mixed layer of the lower pure hydrogenation catalyst layer are higher, the effect of converting the dimethyl oxalate hydrogenation reaction from concentrated reaction to disperse reaction by the mixed layer of the upper hydrogenation catalyst and the inert ceramic balls is reduced, the reaction intensity still exists in the fixed bed reactor, particularly in the upper reaction, the problems of higher temperature of a bed layer hot spot, coking of the hydrogenation catalyst and the like are caused by accumulation of reaction heat, and therefore, the effect of prolonging the service life of the hydrogenation catalyst at the upper part of the fixed bed is poor.
Preferably, as a modification, the gas medium in S2 is pure hydrogen or a mixed gas of hydrogen and nitrogen.
By adopting the scheme, pure hydrogen or the mixed gas of hydrogen and nitrogen is used as a gas medium to activate the hydrogenation catalyst, so that the introduction of impurities can be avoided; specifically, hydrogen is used as a reactant when the hydrogenation catalyst is activated, so that the reaction is not negatively influenced; nitrogen is used as inert gas, and the normal operation of the reaction is not affected. If other gas mediums are mixed in hydrogen to activate the hydrogenation catalyst, impurity gas is introduced, so that on one hand, the activation process of the hydrogenation catalyst is influenced, the service performance and the service life of the hydrogenation catalyst are influenced, the activity, the strength and the like of the hydrogenation catalyst are obviously reduced when serious, and even the problem of poisoning and deactivation of the hydrogenation catalyst is caused; on the other hand, introducing other impurity gases can lead the components of the system to deviate from the normal components, influence the performance and the circulation gas quantity of the circulation compressor, and simultaneously lead to the fact that a large amount of hydrogen is replaced when hydrogen replacement is carried out after the hydrogenation catalyst is reduced, so that the waste of materials is caused, the feeding and starting time can be prolonged, the starting cost is increased, and the production cost is increased.
Preferably, as a modification, the activation end point temperature of the hydrogenation catalyst in S2 is 220 ℃.
By adopting the scheme, the end temperature of the hydrogenation catalyst for heating and activating is 220 ℃, so that the hydrogenation catalyst is fully activated, and the reduction of the activity, strength and service life of the hydrogenation catalyst caused by excessive activation of the hydrogenation catalyst is avoided. Specifically, if the heating activation end point temperature of the hydrogenation catalyst is higher than 220 ℃, the hydrogenation catalyst is excessively activated, so that the activity, strength and service life of the hydrogenation catalyst are reduced, the hydrogenation catalyst is pulverized and deactivated when serious, and in addition, the over-high heating temperature can cause the over-temperature of a fixed bed reactor, so that the operation safety of equipment is affected; if the heating activation end point temperature of the hydrogenation catalyst is lower than 220 ℃, the activation of the hydrogenation catalyst is incomplete, and the performance of the hydrogenation catalyst cannot meet the index requirement, so that the subsequent dimethyl oxalate hydrogenation reaction is affected.
Preferably, as a modification, the purity of the dimethyl oxalate in the S3 is 99.8-100wt%.
By adopting the scheme, the purity of the dimethyl oxalate in the S3 is set to be 99.8-100wt%, so as to ensure that the feed materials meet the purity requirement, prevent impurity components such as dimethyl carbonate and the like from entering a hydrogenation catalyst bed, further prevent the hydrogenation catalyst from reacting with impurities such as dimethyl carbonate and the like, ensure the efficient implementation of the dimethyl oxalate hydrogenation reaction, and not only facilitate reducing byproducts, but also facilitate reducing unnecessary consumption of the hydrogenation catalyst so as to prolong the service life of the hydrogenation catalyst. If the purity of the dimethyl oxalate is reduced, the efficiency of the dimethyl oxalate hydrogenation reaction is reduced, and the reaction energy consumption is increased; in addition, the dimethyl carbonate in the impurities can generate gas-phase and liquid-phase impurities such as carbon monoxide, ethylene carbonate and the like, the generated gas-phase impurities can influence the activity of a hydrogenation catalyst, so that the hydrogenation reaction of dimethyl oxalate is influenced, and the liquid-phase impurities can increase the subsequent rectification difficulty and energy consumption of an ethylene glycol product and also seriously influence the quality of the ethylene glycol product; and part of impurities can be adsorbed on the surface and in micropores of the hydrogenation catalyst, so that the catalytic resistance of the hydrogenation catalyst is increased. In order to remove generated gas phase impurities and ensure the purity of hydrogen in the recycle gas, a purge gas purification device PSA hydrogen production device connected with a fixed bed reactor is forced to increase the load, thereby influencing the hydrogen yield of the hydrogenation system purge gas PSA hydrogen production device, reducing the hydrogen yield and increasing the unit consumption of hydrogen, and increasing the cost for preparing unit ethylene glycol products.
Preferably, as a modification, the molar ratio of hydrogen to dimethyl oxalate in S3 is (80-120): 1.
The molar ratio of the hydrogen to the dimethyl oxalate has an important influence on the hydrogenation reaction, and from the viewpoint of reaction balance, excessive hydrogen can lead the reaction balance to move towards the direction of the product, so that the conversion rate of the dimethyl oxalate can be improved; from the dynamics point of view, the excessive hydrogen can accelerate the reaction rate, and the flow of a large amount of hydrogen can improve the heat transfer of the bed layer of the fixed bed reactor, so that the removal of reaction heat is facilitated, the hot spot temperature is effectively prevented from being higher due to the accumulation of the reaction heat, and the hydrogenation catalyst at the position is prevented from being sintered due to the overhigh local temperature of the hydrogenation catalyst. The dimethyl oxalate hydrogenation is a strong exothermic reaction, and under the condition of keeping the space velocity of hydrogen unchanged, the flow of the dimethyl oxalate at the inlet of the fixed bed reactor is actually increased, so that the reaction heat in the fixed bed reactor is greatly increased, the hot spot temperature of the hydrogenation catalyst bed layer is obviously increased due to the reduction of the hydrogen ester ratio, and the excessive hydrogenation of glycol and the increase of the selectivity of ethanol can be caused.
By adopting the scheme, the molar ratio of the hydrogen to the dimethyl oxalate is limited to be (80-120): 1, is a more proper hydrogen-ester ratio, and can maintain the temperature of the hydrogenation catalyst bed layer in the fixed bed reactor within a reasonable range while guaranteeing the service life of the hydrogenation catalyst. When the ratio of hydrogen to ester is less than 80:1, partial pressure of dimethyl oxalate in a hydrogenation system is too high, so that the dimethyl oxalate is insufficient in gasification, partial liquid dimethyl oxalate locally reacts violently in micropores of a hydrogenation catalyst, thermal shock is formed on the hydrogenation catalyst, the selectivity of the hydrogenation catalyst is reduced, side reaction products are increased, partial side reaction products (such as coking of ethylene glycol methyl ether and polymerization of methyl glycolate) or dirt are gradually deposited in the micropores of the hydrogenation catalyst, the hydrogenation catalyst is broken, the catalytic resistance of the hydrogenation catalyst is increased, and the service life of the hydrogenation catalyst is shortened. When the hydrogen-ester ratio is greater than 120:1, the temperature of the hydrogenation catalyst bed in the fixed bed reactor is reduced, and when the temperature of the hydrogenation catalyst bed is seriously reduced, the pressure of a hydrogenation system loop is increased, so that the energy consumption of a circulating compressor is increased.
Preferably, as a modification, the temperature of the hydrogenation reaction of the dimethyl oxalate in the step S3 is 165-200 ℃ and the pressure is 2.4-3.0MPa.
By adopting the scheme, the temperature of the dimethyl oxalate hydrogenation reaction is limited to 165-200 ℃, so that 100% conversion rate of the dimethyl oxalate can be ensured, the temperature of a reaction bed layer is uniform, the hot spot temperature is prevented from being higher due to heat accumulation of the reaction bed layer, the service life of a hydrogenation catalyst and the selectivity of ethylene glycol can be ensured, ethanol, 1, 2-butanediol and 1, 2-propylene glycol generated by side reaction are reduced, the energy consumption of the rectification of ethylene glycol products is further reduced, and the quality of the ethylene glycol products is further improved. If the temperature of the hydrogenation reaction of the dimethyl oxalate is too high, namely, higher than 200 ℃, the hot spot temperature of the hydrogenation catalyst bed layer is increased, the reaction heat is greatly increased, the increase of the bed layer temperature in the fixed bed reactor is further aggravated, the strength of the hydrogenation catalyst is reduced, the catalytic resistance is increased, the service life is shortened, and the glycol selectivity of the hydrogenation catalyst is also reduced; when the reaction temperature is increased to above 200 ℃, the increase of the ethanol content in the product is measured, which indicates that the reaction is excessively hydrogenated at a higher temperature, side reactions begin to generate, the ethanol and the glycol generated by the reaction can further undergo carburetion reaction, the boiling points of the generated 1, 2-butanediol and 1, 2-propanediol are very close to those of the glycol, and the difficulty and the energy consumption of the subsequent glycol product rectification are increased. If the temperature of the dimethyl oxalate hydrogenation reaction is too low, namely lower than 165 ℃, the reaction rate of the dimethyl oxalate is reduced, and the dimethyl oxalate hydrogenation is incomplete, so that the dimethyl oxalate or methyl glycolate penetrates through a hydrogenation catalyst bed, and the dimethyl oxalate undergoes hydrogenation reaction and side reactions are increased, tar and other substances are generated, and even coking accidents can be caused; the cokes are filled in gaps among hydrogenation catalyst particles and in micropores of the hydrogenation catalyst, so that on one hand, the catalytic resistance of a hydrogenation catalyst bed layer is increased, the activity and the service life of the catalyst are influenced, and on the other hand, the contact area of reactants on the surface of the catalyst is reduced, thereby reducing the conversion rate of dimethyl oxalate, the yield of glycol and the quality of crude glycol, and meanwhile, the separation difficulty and the separation energy consumption of the crude glycol are increased, and the quality of glycol products is influenced in severe cases.
The pressure of the hydrogenation reaction of the dimethyl oxalate is limited to 2.4-3.0MPa, so that the reaction rate of the dimethyl oxalate is increased, the complete reaction of the dimethyl oxalate is ensured, the side reaction is reduced, and the product quality is improved; on the other hand, the investment cost of system equipment and pipelines can be reduced, the equipment leakage rate is reduced, the manufacturing difficulty and the manufacturing cost of the hydrogenation catalyst are reduced, and the 'safe, stable, long, full and excellent' operation of the device is ensured. If the pressure of the dimethyl oxalate hydrogenation reaction is too high, namely higher than 3.0MPa, on one hand, the investment cost of system equipment and pipelines can be increased, the leakage rate of the equipment can be increased, and the safe and stable long-period operation of the device can be influenced; on the other hand, the reaction pressure is too high, the strength requirement on the hydrogenation catalyst is higher, and the manufacturing difficulty and the manufacturing cost of the hydrogenation catalyst can be increased. If the temperature of the dimethyl oxalate hydrogenation reaction is too low, namely lower than 2.4MPa, the reaction rate of the dimethyl oxalate is reduced, the dimethyl oxalate hydrogenation is incomplete, not only is the material wasted, but also the dimethyl oxalate or methyl glycolate penetrates through the hydrogenation catalyst bed layer, the service life of the hydrogenation catalyst is seriously influenced, the conversion rate of the dimethyl oxalate, the absorption rate of glycol and the quality of crude glycol are reduced, the separation difficulty and the separation energy consumption of the crude glycol are increased, and the quality of glycol products is also influenced in serious cases.
Drawings
Fig. 1 is a schematic process flow diagram of embodiment 1 of the present invention.
FIG. 2 is a schematic diagram showing the structure of a fixed bed reactor in example 1 of the present invention.
Detailed Description
The following is a further detailed description of the embodiments:
Reference numerals in the drawings of the specification include: a fixed bed reactor 100, a hydrogenation catalyst and inert ceramic ball mixed layer 101, a pure hydrogenation catalyst layer 102, a pure inert ceramic ball layer 103, a supporting spring layer 104, a hydrogenation catalyst a, an inert ceramic ball b and a supporting spring c.
Example 1
A process for preparing ethylene glycol by hydrogenating dimethyl oxalate is shown in figure 1, and comprises the following steps:
S1: filling a hydrogenation catalyst a, uniformly mixing the hydrogenation catalyst a and the inert ceramic balls b, and filling the mixture into a fixed bed reactor 100 to form a hydrogenation catalyst and inert ceramic ball mixing layer 101; pure hydrogenation catalyst a and pure inert ceramic balls b are sequentially filled below the hydrogenation catalyst and inert ceramic ball mixed layer 101 from top to bottom to form a pure hydrogenation catalyst layer 102 and a pure inert ceramic ball layer 103 respectively; a supporting spring c is filled under the pure inert porcelain ball layer 103 to form a supporting spring layer 104.
Specifically, the mixed layer of hydrogenation catalyst and inert ceramic balls 101 comprises 65-90wt% of hydrogenation catalyst a and 10-35wt% of inert ceramic balls b, and the ratio of the height of the mixed layer of hydrogenation catalyst and inert ceramic balls 101 to the height of the pure hydrogenation catalyst layer 102 is 1: (4-7). In this embodiment, the mixed layer of hydrogenation catalyst and inert ceramic balls 101 includes 80wt% of hydrogenation catalyst a and 20wt% of inert ceramic balls b, and the ratio of the height of the mixed layer of hydrogenation catalyst and inert ceramic balls 101 to the height of the pure hydrogenation catalyst layer 102 is 1:5.5.
After the completion of the loading of the hydrogenation catalyst a, a fixed bed reactor 100 as shown in fig. 2 was obtained.
S2: the hydrogenation catalyst a is activated, and a gaseous medium is introduced into the top of the fixed bed reactor 100 shown in fig. 2, and the hydrogenation catalyst a is heated, so that the activation of the hydrogenation catalyst a is realized.
Specifically, the gas medium is pure hydrogen or mixed gas of hydrogen and nitrogen, and the activation end point temperature of the hydrogenation catalyst a is 220 ℃.
S3: dimethyl oxalate hydrogenation reaction, gas phase dimethyl oxalate and hydrogen are parallel-flow, and are introduced from the top of a fixed bed reactor 100 shown in fig. 2, and the dimethyl oxalate and the hydrogen are subjected to gas-solid two-phase hydrogenation reaction in the fixed bed reactor 100.
Specifically, the purity of the dimethyl oxalate is 99.8-100wt%, and the molar ratio of hydrogen to dimethyl oxalate is (80-120): 1, the temperature of the hydrogenation reaction of the dimethyl oxalate is 165-200 ℃ and the pressure is 2.4-3.0MPa. In this example, the molar ratio of hydrogen to dimethyl oxalate was 90:1, the temperature of the hydrogenation reaction of the dimethyl oxalate is 178 ℃.
Table 1: examples 1 to 5, comparative examples 1 to 4, hydrogen-ester ratio of dimethyl oxalate hydrogenation, reaction temperature, service life of hydrogenation catalyst a and content of each component in the product
Experimental data show that the molar ratio of the hydrogen to the dimethyl oxalate is 90:1, and the hydrogenation reaction temperature of the dimethyl oxalate is 178 ℃, so that the service life of the hydrogenation catalyst a is prolonged to 550 days; the best reaction effect can be obtained, so that the content of ethylene glycol in the product is up to 79.8%, and the content of dimethyl oxalate in the product is 0%, namely the conversion rate of the dimethyl oxalate is up to 100%; can effectively reduce side reaction, so that the content of methyl glycolate and ethanol which are side reaction products in the product is only 0.01 percent and 0.018 percent respectively.
The experimental data of examples 1-3 and comparative examples 2 and 3 in Table 1 show that the hydrogenation reaction temperature of dimethyl oxalate is constant, and specifically, the molar ratio of hydrogen to dimethyl oxalate is (80-120) at 178 ℃: compared with the molar ratio of hydrogen to dimethyl oxalate which is more than 80:1 and less than 120:1, the method is more beneficial to prolonging the service life of the hydrogenation catalyst a, and can achieve better reaction effect, namely the side reaction is reduced, and the material utilization rate is improved.
Wherein, in the product of the comparative example 1, although the content of dimethyl oxalate is 0%, namely the conversion rate of the dimethyl oxalate reaches 100%, the content of the required glycol is lower than that of the products of the comparative example 1 and the content of methyl glycolate and ethanol which are side reaction products are higher than that of the products of the examples 1 to 3 are shown that the side reaction of the comparative example 1 is more and the material utilization rate is lower than that of the products of the examples 1 to 3; and the service life of the hydrogenation catalyst a of the comparative example 1 is only 350 days, which is reduced by more than 100 days compared with the embodiments 1-3, and the hydrogenation catalyst a needs to be replaced frequently, so that the production cost of glycol is greatly increased.
Although the content of the ethanol in the product of the comparative example 2 is only 0.014% and is lower than that of the products of examples 1-3, the content of the methyl glycolate in the product of the comparative example 2 is 0.021% and is higher than that of the products of examples 1-3, which indicates that the side reaction of the comparative example 2 is still more severe and is unfavorable for improving the utilization rate of materials; in addition, the product of comparative example 2 contains less than examples 1-3 of ethylene glycol and 0.015% of dimethyl oxalate, which means that the dimethyl oxalate of comparative example 2 is not completely converted, which is not beneficial to improving the material utilization rate; in addition, the service life of the hydrogenation catalyst a in comparative example 2 is also shorter than that of examples 1 to 3, and the hydrogenation catalyst a needs to be replaced more frequently, which is disadvantageous in reducing the production cost of ethylene glycol.
The experimental data of examples 1, 4-5 and 3-4 in table 1 show that when the molar ratio of hydrogen to dimethyl oxalate is certain, specifically 90:1, the temperature of dimethyl oxalate hydrogenation reaction is 165-200 ℃ compared with the temperature of dimethyl oxalate hydrogenation reaction which is less than 165 ℃ and greater than 200 ℃, the service life of hydrogenation catalyst a can be effectively prolonged, better reaction effect can be achieved, namely side reaction is reduced, and the material utilization rate is improved.
Wherein, in the product of comparative example 3, the content of the byproduct ethanol is only 0.01% and is lower than that of examples 1,4 and 5, but in the product of comparative example 3, the content of the side reaction product methyl glycolate is 0.04% and is higher than that of examples 1,4 and 5, which indicates that the side reaction of comparative example 3 is still more severe and is unfavorable for improving the material utilization rate; in addition, the required ethylene glycol content in the product of the comparative example 3 is lower than that of examples 1,4 and 5, and 0.04% of dimethyl oxalate is also contained, which indicates that the dimethyl oxalate of the comparative example 3 is not completely converted, and is not beneficial to improving the material utilization rate; in addition, the service life of the hydrogenation catalyst a in comparative example 3 is also shorter than that of examples 1,4 and 5, and the hydrogenation catalyst a needs to be replaced more frequently, which is disadvantageous in reducing the production cost of ethylene glycol.
In the product of comparative example 4, although the content of dimethyl oxalate is 0%, that is, the conversion rate of dimethyl oxalate reaches 100%, and the content of methyl glycolate as a side reaction product is 0.01% which is less than or equal to that of methyl glycolate as a side reaction product in examples 1, 4 and 5, the content of ethanol as a side reaction product in the product of comparative example 4 is much higher than that in examples 1, 4 and 5, which means that the side reaction of comparative example 4 is still more severe and the material utilization rate is still lower; and in the product of comparative example 4, the required ethylene glycol content is at least 1% lower than that of examples 1, 4 and 5, the yield of ethylene glycol is not high, and the service life of the hydrogenation catalyst a in comparative example 4 is only 200 days, which is at least 80 days less than that of examples 1, 4 and 5, the replacement frequency of the hydrogenation catalyst a can be greatly increased, resulting in the increase of the production cost of ethylene glycol.
The foregoing is merely exemplary of the present application, and specific technical solutions and/or features that are well known in the art have not been described in detail herein. It should be noted that, for those skilled in the art, several variations and modifications can be made without departing from the technical solution of the present application, and these should also be regarded as the protection scope of the present application, which does not affect the effect of the implementation of the present application and the practical applicability of the patent. The protection scope of the present application is subject to the content of the claims, and the description of the specific embodiments and the like in the specification can be used for explaining the content of the claims.
Claims (6)
1. A process for preparing ethylene glycol by hydrogenating dimethyl oxalate is characterized by comprising the following steps of: the method comprises the following steps:
s1: filling a hydrogenation catalyst, uniformly mixing the hydrogenation catalyst with inert ceramic balls, and filling the mixture into a fixed bed reactor to form a hydrogenation catalyst and inert ceramic ball mixed layer; the pure hydrogenation catalyst and the pure inert ceramic balls are sequentially filled below the hydrogenation catalyst and inert ceramic ball mixing layer from top to bottom to form a pure hydrogenation catalyst layer and a pure inert ceramic ball layer respectively; a supporting spring is filled below the pure inert porcelain ball layer to form a supporting spring layer;
S2: activating a hydrogenation catalyst, introducing a gas medium into the top of the fixed bed reactor, and heating the hydrogenation catalyst to realize the activation of the hydrogenation catalyst;
S3: the dimethyl oxalate hydrogenation reaction, the gaseous dimethyl oxalate and hydrogen are parallel flow, the mole ratio of the hydrogen and the dimethyl oxalate is (80-120): 1, introducing the dimethyl oxalate and hydrogen from the top of a fixed bed reactor, and carrying out gas-solid two-phase hydrogenation reaction in the fixed bed reactor, wherein the temperature of the dimethyl oxalate hydrogenation reaction is 165-200 ℃, and the pressure is 2.4-3.0MPa.
2. The process for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 1, wherein the process comprises the following steps: the hydrogenation catalyst and inert ceramic ball mixed layer in the S1 comprises 65-90wt% of hydrogenation catalyst and 10-35wt% of inert ceramic balls.
3. The process for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 2, wherein the process comprises the following steps: the ratio of the heights of the hydrogenation catalyst and inert porcelain ball mixed layer to the pure hydrogenation catalyst layer is 1: (4-7).
4. The process for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 1, wherein the process comprises the following steps: the gas medium in the step S2 is pure hydrogen or mixed gas of hydrogen and nitrogen.
5. The process for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 4, wherein the process comprises the following steps: the activation end point temperature of the hydrogenation catalyst in the step S2 is 220 ℃.
6. The process for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 1, wherein the process comprises the following steps: the purity of the dimethyl oxalate in the S3 is 99.8-100wt%.
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