In contrast, for Reactions 1 and 2 effective purification of the methanol product may be achieved by a single column-separation followed by a stripping operation, without the need for a dedicated light ends column to further separate the desired product from impurities in the condensed overhead stream, or a heavies column to remove heavy oil impurities, or other special separations techniques.
The system for conversion and separation of gases includes a reactor producing a crude product stream and a fractionation column connected at an overhead section to a heat exchanger and a stripper unit Figure 2. A carrier gas stream 2 is bubbled through the stripper unit to selectively remove impurities such as CO 2 from the overhead stream of the fractionation column after the stream has been condensed in the heat exchanger.
Variations of the stripper unit may include a gas sparger unit integrated with a reflux drum, the reflux drum being configured to receive the condensed overhead stream from the heat exchanger. The gas sparger unit flows a stripping fluid, such as N 2 or H 2 gas, through the condensed overhead stream in the drum to selectively remove CO 2 from the methanol product without the use of a dedicated separation column. A variety of stripping fluids may be used.
The system may thus be adjusted to the specific configuration of products and reactants needed and available. Figure 2. A simplified diagram of a separations system showing the reactor and the gas sparger unit.
In a typical system, reactor effluent contained in the crude methanol stream is fed to separations section which comprises fractionation column and accompanying equipment. Owing to the composition of crude methanol, the stream contains virtually no CO or other light contaminants besides water and CO 2 , and therefore, only a single fractionation column is required for purifying the desired methanol product.
This is a singular advantage over most methanol purification processes which comprise dedicated light ends columns and associated equipment such as reboilers, condensers and drums in order to achieve adequate purification of the product. The condenser and reboiler provide the required duty for the fractionation column to separate the crude methanol stream into on-spec products. Furthermore, in the case where the reactor primarily consumes CO 2 as a feedstock for methanol synthesis, a viable alternative disposition for CO 2 emissions is available and recycling of the removed CO 2 to the reactor generates a continuous loop that may ultimately convert all the CO 2 into methanol.
The stripper unit may also be arranged either upstream or downstream of a reflux drum, as determined by the process requirements of a specific configuration or facility. Distillation is a highly energy-intensive process because of the inherent inefficiency of the separation process, which requires large duties in both the reboiler and condenser, as well as significant reflux rates to achieve desired separation.
In facilities or processes where substantial heat is left over from initial reaction units due to reaction or thermal inefficiencies, or high reaction exotherms , or from associated processes at the same facility or site as the separation process, the leftover heat, often being in the form of generated steam, may be used to provide duty to the reboiler of certain of the distillation operations.
However, such an arrangement may be undesirable in the first instance, as the generation of substantial waste heat in the reaction phase or in associated processes represents a thermodynamic inefficiency and consequently a negative effect on emissions from the facility.
It is therefore desirable to minimize the generation of waste heat as much as possible. It is also desirable to minimize heat requirements of processes located downstream of the reaction process which may otherwise utilize waste heat, such as in reboilers.
By so doing, requirements for added heat may be reduced. One approach to improving heat utilization efficiency is with a split column system wherein the bottom section of the column may operate at a higher pressure than the top section of the column. The reflux of the bottom section of the column may be integrated with the reboiler of the top section of the column, utilizing a single heat exchange device to reduce the total duties for the fractionation operation.
The energy savings realized through this arrangement further contributes to emissions reductions. Additionally, the heat exchange device may optimize temperature approach and as a result enhance thermodynamic efficiency between the integrated reboiler and condenser streams and thus between the two columns by utilizing a falling-film evaporator or thermosiphon design. The improved lower temperature approach of falling-film evaporator- and thermosiphon-type heat exchangers compared to, for example, the temperature approach of kettle reboilers, may enable a lower operating pressure in the higher-pressure column, as the pressure required for the overhead stream to provide sufficient reboiler duty for the lower pressure column is reduced.
This also minimizes capital and operating costs because the required reboiler duty is reduced and the column itself may be reduced in size , which puts further downward pressure on emissions. For the synthesis of methanol from CO 2 in geothermal steam, and utilizing the heat derived from the process, as is the case for Carbon Recycling International in Iceland, the efficiency of heat use and reuse becomes a crucial factor in the overall efficiency of the process.
Although a split tower arrangement is not unique to this process, there is certainly an economic advantage when used at this scale. For instance, a typical reformer-based methanol plant produces excess steam and there is little incentive to optimize heat reuse.
A CO 2 based process using renewable or geothermal energy, where heat generation is at a premium, must have tighter energy use requirements, and a split tower arrangement becomes essential, both because it lowers energy use and because it lowers the CO 2 footprint.
In a simplified system as shown in Figure 3 , the methanol stream is fed to separations section, which comprises a fractionation column. The fractionation column is arranged in a split tower arrangement comprising a top or low pressure LP section and a bottom or medium pressure MP section.
The LP section and MP section are connected by the stream which comprises primarily methanol and water, as well as by heat integration between the condenser of MP section and the reboiler of LP section. A Vapo-condenser unit integrates the functions of both condensing an overhead stream of the MP section and re-boiling a bottom stream of the LP section.
The operating pressure of the MP section is calibrated to be sufficiently high such that the condensation of the stream provides the required duty to re-boil the stream derived from the LP section.
The use of the split tower arrangement enhances thermodynamic efficiency by reducing total duty required in the fractionation column, as the duties that are integrated in the vapo-condenser between the two sections would otherwise be provided in a condenser at the overhead of MP section and a reboiler at the bottom of LP section, or in increased duties to the LP section condenser and the MP section reboiler. Figure 3. A simplified diagram of the split column separations systems.
Process and component labels are shown where they have not already been identified in Figure 2. Substantially no CO 2 is entrained in the stream entering the MP section because the CO 2 contained in the crude methanol stream entering the LP section is isolated in the overhead stream of the LP section.
A reboiler provides additional duty at a bottom portion of the MP section. Waste water product is obtained at the bottom of the MP section and disposed of. A reflux drum receives the condensed overhead stream of MP section, and splits the condensed overhead stream into a reflux return stream which is returned to the MP section, and a MP section methanol product stream which is combined with the LP section methanol product stream.
The combined methanol product stream can be sent to battery limits, storage, or to another disposition. In such applications, and in distillation generally, a separations section which minimizes heat requirements, such as in reboilers, is desirable to avoid the costs and emissions associated with steam generation to make up for heat recovered from hot sections of the process.
Additionally, it is desirable to minimize capital costs by reducing the size and number of units required to carry out a separation operation. In variations of the split column process, the split column may utilize mechanical vapor recompression MVR to further improve thermodynamic efficiency by taking a side cut from the top section of the column, recompressing the side cut, and then feeding the compressed side cut to the bottom section of the column.
This advantageously improves the efficiency of the separation by substituting the increased temperature and pressure resulting from compressing the side cut for the duty that would otherwise be required of a dedicated reboiler for the bottom section of the column. This arrangement thereby also reduces capital costs and operating costs. To illustrate its operation, the MVR unit is integrated in the separations section as shown in Figure 4.
The crude methanol stream containing methanol, water, and CO 2 is fed to the fractionation column, which is arranged in a split tower arrangement similar to the embodiment of Figure 3. The top or LP section is heat integrated with the bottom or MP section at a vapo-condenser which condenses an overhead stream of the MP section and re-boils a bottom stream of the LP section.
The crude methanol stream is received at an optimal location in the MP section. The LP section and MP section are further connected by streams originating from the lower and upper sections of the MP section, which function to provide material balance and reflux for the LP section if needed, thereby eliminating the need for a separate reflux stream from an overhead stream of LP section.
Waste water product is removed from the bottom of LP section. Figure 4. A simplified diagram showing the complete system featuring the reactor and the gas sparger unit, split column arrangement, and the mechanical vapor recompression unit. The labels and stream flows identified in Figures 2 , 3 apply to this diagram and are omitted for clarity. The additional process labels relating to the mechanical vapor recompression unit are included here and the additional stream flow numbering labels are as follows: 14 Lean methanol; 15 Rich methanol reflux to LP; 16 and 17 Recycle stream.
Because the direct streams from the MP to the LP sections provide reflux from the MP section, no reflux stream needs to be returned to the LP section from the LP section overhead stream. As a result, the required flowrate of the LP section overhead stream is reduced and the required size of condenser at the top of the LP section, as well as duty removed therethrough via cooling water, is consequently greatly reduced. This further reduces capital and operating costs, as well as emissions.
A sidecut from the LP section is fed to a MVR compressor which compresses the sidecut to an operating pressure suitable for the MP section, thereby also raising the temperature of the sidecut. The recompressed sidecut is fed to the MP section, preferably at a location near the bottom of the MP section. The recompressed sidecut replaces the reboiler of the MP section, as the added enthalpy of the compressed sidecut serves to provide the necessary duty to reboil the MP section and consequently the LP section.
The addition of this duty by the MVR compressor achieves enhanced thermodynamic efficiency and capital cost reductions compared to providing the duty through a reboiler unit. Recompression of a stream may thus advantageously utilize compressor work to raise the pressure and consequently temperature of a portion of a process stream such as a sidecut from the LP column section for the purposes of providing reboiler duty more efficiently than adding heat to the process through a conventional reboiler, especially a reboiler utilizing steam as a heat source.
Recompressing an existing vapor stream to a higher temperature and pressure using a compressor advantageously bypasses the phase change inefficiencies inherent in steam generation from boiler feed water due to the high enthalpy difference between boiler feed water and pressurized steam.
Mechanical vapor recompression therefore attains the desired increase in temperature and pressure with a much lower input of energy than traditional reboilers. The efficiency of the MVR is further enhanced by feeding the recompressed sidecut directly to a bottom portion of the MP section to replace the reboiler and the heat exchange inefficiencies associated therewith.
The recompressed sidecut can more efficiently transfer heat to the MP section by interacting directly with the contents of the column. The use of mechanical vapor recompression thus solves the problem of distillation and other process operations requiring added heat, and leads to lower emissions and decrease in capital and operating costs.
In this paper we put forward that there are both inherent advantages and disadvantages to producing methanol directly from separate sources of CO 2 and H 2 , and that overall, it is an advantageous, cleaner, less energy intensive and more environmentally friendly process than conventional processes using a fossil fuel based syngas.
We highlight several process advantages over the conventional methods, and offer ways to enhance the efficiency of industrial conversion of CO 2 and H 2 to methanol.
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A process layout for large scale methanol synthesis comprises one or more boiling water reactors and one or more radial flow reactors in series, the boiling water reactor s being fed with approximately fresh make-up syngas. The methanol synthesis loop comprises a make-up gas compressor K1, a recycle gas compressor K2, two or more boiling water converters for methanol synthesis A1, A2,..
Title: A methanol synthesis process layout for large production capacity. The present invention relates to a novel process layout for a methanol synthesis loop, which is suitable for large scale methanol production plants, i. The capacity of methanol plants is constantly increasing to reduce investments, taking advantage of the economy-of- scale. Even larger plants are considered to further improve economy and to provide the feedstock for the methanol-to-olefin MTO process.
A methanol plant can be divided into three main sections: In the first section of the plant, a feed gas such as natu- ral gas is converted into synthesis gas. The synthesis gas reacts to produce methanol in the second section, and then methanol is purified to the desired purity in the third section in the tail-end of the plant. Combustion of a hydrocarbon feed is carried out with sub-stoi- chiometric amounts of air, enriched air or oxygen by flame reactions in a burner combustion zone. Stand-alone ATR combines sub-stoichiometric combustion and catalytic steam reforming in one compact refractory-lined reactor to produce synthesis gas for large scale methanol production.
The stand-alone ATR produces a synthe- sis gas well suited for production of both fuel grade and high purity methanol; see for example applicant's WO. The design of the methanol synthesis section is essential. The optimal design and the choice of operating parameters depend on the desired product specification.
In many plants, boiling water reactors BWRs are used. The conversion from syngas is performed over a catalyst, which is most often a copper- zinc oxide-alumina catalyst. The conversion is, as already mentioned, performed over a copper-zinc oxide-alumina catalyst. Because of the widespread use of methanol, especially as the feedstock for the manufacture of other chemicals, the worldwide methanol production is huge, and methods and plants for large scale production are therefore in high de- mand.
However, large methanol plants are subject to the constraints imposed by size limitations on reactors and process equipment. These are largely based on a low pressure methanol synthesis re- actor with uniform temperature described in CN A. Then the obtained mixture is fed to a second, preferably gas-cooled reactor, in which a further part of the carbon oxides is converted to methanol.
In US 8. The synthesis gas is passed through a first, water-cooled reactor in which a part of the carbon oxides is catalytically converted to methanol. The resulting mixture containing synthesis gas and methanol vapor is fed to a second, gas-cooled reactor in which a further part of the carbon oxides is converted to methanol. Subsequently, methanol is separated from the synthesis gas, which is then recycled to the first reactor.
A large-scale methanol synthesis process is disclosed in CN A. In the process, raw material gas first enters a buffering tank, such that partial liquid is removed.
When this platinum electrocatalyst is in contact with one of the electrodes in a fuel cell, it increases the rate of oxygen reduction to water or hydroxide or hydrogen peroxide [3]. Despite the PtRu catalyst exhibiting good methanol oxidation activity, the state-of —the —art PtRu catalyst needs further improvement for higher catalytic activity and replacement of expensive nobel metals, Pt and Ru.
The most successful way to achieve both these goals is to add a third metal to the PtRu catalyst. Demirci used theoretical calculations and agreed that incorporation of a third metal might be the best way to improve the methanol oxidation activity [14].
The mixing of Pt with the third metal leads to weakly adsorbed CO on Pt sites and OH strongly adsorbed only on the third metal sites. Such tri-metallic catalysts favour the formation of OHads species which assist in the oxidation of COads [15].
In this paper we present a simple OMCVD method that can be used to synthesize highly dispersed tri-metallic electrocatalysts supported on carbon nanotubes. The procedure is a modified dry-mix method that produces particles with a very narrow size distribution, and results in stable nanoclusters with excellent electrochemical activities. Experimental Methods Commercial MCNTs were pre-treated and catalysts were prepared by a modified dry — mix method using organometallic chemical vapour deposition as reported previously [16].
The electrochemical EC activity and active surface area of the catalysts were evaluated by cyclic voltammetry CV , which was using 0. All CV cycles were done in a de-aerated solution bubbled nitrogen gas through the solution for 30 minutes , and under a blanket of nitrogen. Electrocatalyst inks were prepared by mixing 10 mg catalyst powder in The ink was allowed to sonicat for 30 minutes. Physico-Chemical Characteristics 3.
A good agreement between the theoretical and measured values is observed. These results demonstrate that the CVD method can be used to prepare the electrocatalysts with a well-defined atomic ratio.
Table 1. The broadening of the peaks on the in-house samples is due to the smaller particle size of the metal deposits [20]. It should be noted that as the crystallite size is related to the area of coherent diffraction, the particle size obtained from XRD can be smaller than the true particle size in general [21]. Figure 1. XRD patterns for electrocatalysts. Figure 3. The TEM images are given in Figure 2 a - c of catalysts. The catalysts showed well-separated nanoparticles with narrow-size distribution.
The average particle sizes are 2. These results are in agreement with particle sizes obtained from application of the Scherrer equation based upon the X-ray diffraction pattern of the catalysts.
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