243 results about "Phosgene" patented technology

The invention relates to a preparation method and a preparation device of isocyanate, and the preparation method comprises the following steps: carrying out cold reaction on a phosgene solution and an amine solution in a cold reactor to obtain an intermediate mixed solution; separating the intermediate mixed solution by adopting a cyclone, obtaining a carbamoyl chloride mixed solution from an underflow port of the cyclone, and obtaining an amine hydrochloride mixed solution from an overflow port of the cyclone; the carbamyl chloride mixed solution enters a first thermal reactor for thermal reaction to obtain a first reaction product, and the amine hydrochloride mixed solution enters a second thermal reactor for thermal reaction to obtain a second reaction product; mixing the first reaction product and the second reaction product in a staying reactor to obtain an isocyanate reaction solution; and carrying out post-treatment on the isocyanate reaction liquid to obtain the isocyanate. The method can reduce the generation amount of urea by-products, further inhibits the generation of other subsequent by-products, reduces the chromaticity of the product, and improves the quality of isocyanate.

The application discloses a continuous synthesis method of an amicarbazone intermediate 5-isopropyl-1,3,4-oxadiazole-2(3H)-ketone. The method comprises two continuous processes of hydrazinolysis and phosgenation: continuously feeding a mixture of isobutyric acid and a solvent, a mixture of hydrazine hydrate and a catalyst into a hydrazinolysis continuous reactor respectively, carrying out a warming reflux dehydration reaction, and obtaining an isobutyryl hydrazine solution shown in formula I; continuously feeding the isobutyryl hydrazine solution and phosgene into a phosgenation continuous reactor, carrying out a phosgenation reaction, and after distillation and desolventizing treatment of a reaction solution, obtaining 5-isopropyl-1,3,4-oxadiazole-2(3H)-ketone shown in formula II. The application has the advantages of simple reaction flow, high product yield, and significant production efficiency improvement, and is suitable for industrial large-scale production.

The present application relates to a kind of equipment and method for preparing hexamethylene diisocyanate by hexamethylene diaminoformate intermediate pyrolysis, the present application uses continuous pyrolysis reaction device, HDI can be prepared in high-boiling solvent, can completely replace the existing phosgene and phosgene derivative method for preparing HDI, solve the safety and pollution problem of phosgene method;Compared with low-boiling solvent process, the present application can greatly reduce energy consumption in product separation stage, and the energy consumption required for separating solvent in high-boiling solvent method is 1 / 10 of low-boiling solvent process, it is a green environmental protection energy-saving process;The present application uses non-toxic high-boiling solvent, compared with low-boiling solvent method, production safety is guaranteed;Compared with ordinary high-boiling solvent, the present application can avoid multiple contact between isocyanate and alcohol, and the yield of HDI can be further improved;The process flow of the present application is simple, and the operating condition is mild, it is a process that can be rapidly industrialized.

The application relates to the technical field of organic synthesis, and discloses a synthesis method of benzthiazuron, which comprises the following steps: step 1, addition reaction of alpha-methyl styrene and hydrogen chloride gas, and degassing to obtain a first reaction liquid; step 2, substitution reaction of the first reaction liquid and cyanate in the presence of a zinc chloride catalyst, and filtration to obtain a second reaction liquid containing isocyanate; and step 3, construction of an inorganic salt aqueous solution system with a density of 1.05-1.10 g / ml and a pH of 9-10, dropwise addition of the second reaction liquid into the system for condensation reaction with o-chlorobenzylamine, and post-treatment and refinement to obtain a target product. The non-phosgene route of chloro-isocyanate substitution is adopted, and the use of the toxic phosgene is completely avoided; the salting-out effect and interface control generated by the specific high-density salt solution effectively inhibit the isocyanate hydrolysis side reaction, and the reaction yield and product purity are obviously improved.

The invention discloses a synthetic carbamate compound based on 3-substituted dioxazolone as well as a preparation method and application of the synthetic carbamate compound, and belongs to the technical field of organic synthesis. The synthesis method comprises the following steps: (1) preparing 3-substituted dioxazolone from hydroximic acid with different substituent groups and phosgene under an ice bath condition; and (2) reacting the 3-substituted dioxazolone obtained in the step (1) with different phenols (alcohols) under an alkaline condition to obtain corresponding carbamate compounds. According to the method, the yield of carbamate is further improved by adjusting the conditions of alkali, equivalent weight, temperature and the like; the preparation method provided by the invention is novel and has the advantages of mild reaction conditions, few generated impurities, high yield, high safety, convenience in operation and the like; and the compound shows good cholinesterase activity in activity screening, and can be used in insecticides or pesticides.

The present invention relates to a method for using an optionally alkoxylated nitrogen-containing polymer in the capture of carbon dioxide, said optionally alkoxylated nitrogen-containing polymer comprising the following steps: a) a step of reacting (i) a di- or oligoamine (A) with (ii) a crosslinking compound (BC) to provide a nitrogen-containing polymer (NP), wherein the crosslinking compound (BC) is (I) phosgene; or (II) comprises at least two amine-reactive groups (ARG), the crosslinking compound (BC) being capable of binding to the amine groups of at least two di- or oligoamine (A) molecules, the nitrogen-containing polymer (NP) comprising the molecular components of the crosslinking compound (BC) that bind to at least two molecular components of the di- or oligoamine (A), the proportion of the crosslinking compound (BC) molecules bound to at least two di- or oligoamine (A) molecules being the crosslinking factor (BF) of the nitrogen-containing polymer (NP), the crosslinking factor (BF) exceeding 50%, the sum of the primary and secondary amine groups of the nitrogen-containing polymer (NP) being at least 600 mg KOH / g, the number average molecular weight (Mn) of the nitrogen-containing polymer (NP) exceeding 600 g / mol, and b) a step of reacting the nitrogen-containing polymer (NP) with an alkylene oxide (AO), wherein the molar ratio of the alkylene oxide (AO) to the NH functionality of the nitrogen-containing polymer (NP) is 0.25 or less, obtainable by a method comprising. The present invention further relates to a method for capturing carbon dioxide from a gas mixture using an optionally alkoxylated nitrogen-containing polymer.

The invention discloses a triphosgene continuous synthesis method and device, and belongs to the technical field of fine chemical production. The triphosgene continuous synthesis method comprises the following steps: S1, continuously conveying dimethyl carbonate to the lower part of a reactor, and continuously inputting chlorine from the bottom of the reactor; s2, after dimethyl carbonate and chlorine are mixed in a reactor, a reaction is initiated by irradiation of an ultraviolet light source with the wavelength of 295-395 nm, and molten triphosgene and hydrogen chloride gas are generated; wherein the temperature in the reactor is gradually increased from bottom to top to present a temperature gradient; and S3, continuously overflowing the molten-state triphosgene into a degassing tower to remove residual hydrogen chloride in vacuum, and enabling the degassed molten-state triphosgene product to enter a flaking section. According to the method, by optimizing reaction conditions and equipment design, the cost can be reduced, the utilization rate of raw materials can be increased, generation of byproducts can be reduced, meanwhile, the safety and efficiency of the reaction are guaranteed, and efficient, safe and continuous production of triphosgene is achieved.

The invention relates to the field of organic synthesis, in particular to a method for preparing aliphatic diisocyanate by a non-phosgene method. According to the method for preparing the aliphatic diisocyanate through the non-phosgene method, firstly, aliphatic diamine reacts with a carbonic acid diester compound to form an aliphatic dicarbamate compound, and then the aliphatic dicarbamate compound is subjected to a thermal cracking reaction to obtain the aliphatic diisocyanate. According to the method, aliphatic diamine can be converted into aliphatic diisocyanate under the condition that phosgene is not used, the preparation process is simple, a noble metal catalyst does not need to be used, the atom utilization rate is high, the product does not contain chlorine residues, the purity is high, and industrial large-scale application is facilitated.

The invention discloses a 2-hydroxy-benzonitril solution and a production method thereof, the production method comprises the step of preparing a wet 2-hydroxy-benzonitril product through reaction of salicylamide and phosgene, and is characterized in that the wet 2-hydroxy-benzonitril product is directly added into a sodium hydroxide aqueous solution to obtain the 2-hydroxy-benzonitril solution. The sodium salt solution can be directly produced without taking out the 2-hydroxy-benzonitril, so that exposure of the 2-hydroxy-benzonitril is avoided, personal injury is reduced, investment of drying equipment is reduced, and direct feeding of downstream products is facilitated.

The present invention relates to a method for preparing 2,4-disubstituted thiophene-3-sulfonyl isocyanate compounds having formula (I), wherein the method comprises reacting a compound having formula (II) with phosgene in the presence of a catalyst and a mixture of a nonpolar solvent and an organosulfur cosolvent, and optionally in the presence of a base.

The present application belongs to the technical field of phosgene reaction tail gas treatment, and particularly relates to a phosgene tail gas alkali destruction device and method, which comprises the following steps: an operator passes the tail gas into a falling film absorber, the falling film absorber absorbs hydrochloric acid in the tail gas to obtain treated gas one; the treated gas one is passed into a catalytic hydrolysis box, a catalytic hydrolysis method is used to destroy phosgene in the treated gas one to obtain treated gas two; the treated gas two is passed into a multi-stage alkali destruction tower, 1% to 10% of a dilute alkali solution is sent into the top of the alkali destruction tower through a delivery pump, inorganic salt solution and treated gas three are generated through an acid-base reaction; the inorganic salt solution is sent to a high-salt wastewater treatment device for treatment, the treated gas three is sent to a burning device for treatment to remove unreacted carbon monoxide, organic matter and other combustible gases to obtain final gas which is discharged to the outside. The scheme solves the problem of waste caused by a large amount of generated high-salt wastewater.

The invention relates to a polymer dispersant, a preparation method thereof and a synthesis method of isocyanate using the polymer dispersant. The polymer dispersant has a structure shown in a general formula (I), wherein [Core] is a residue of a polyfunctional group initiator, A is an aliphatic polyester chain segment, B is an aromatic compatible chain segment, L is a residue formed by diisocyanate, and D is an anchoring group. The polymer dispersant disclosed by the invention is specially used for stabilizing amine hydrochloride particles in a process of synthesizing isocyanate by a salifying phosgene method and preventing agglomeration among the particles. The reaction system can form stable and low-viscosity slurry consisting of fine and discrete particles, and amine can be completely converted into hydrochloride, so that the yield of isocyanate is increased.

The invention discloses a preparation method of Linzagolix, which comprises the following steps: taking 2, 3-difluoro-6-methoxybenzyl alcohol as a raw material, under the action of alkali and phosphine ligand, carrying out Mitsunobu reaction on 2, 3-difluoro-6-methoxybenzyl alcohol and 2-methoxy-4-fluorophenol to obtain a compound A, sequentially carrying out nitration reaction and reduction reaction on the compound A to obtain a compound C, and carrying out recrystallization on the compound C to obtain the Linzagolix. Under the alkaline condition and the action of triphosgene, the compound C and 4-aminothiophene-2, 3-dimethyl dicarboxylate hydrochloride are subjected to a one-pot condensation reaction to obtain a compound D, and the compound D reacts under the alkaline condition to generate Linzaolix. According to the invention, the synthesis process of Linazagolix is shortened to five steps, the reaction condition is mild, the operation is simpler and more convenient, and the method is suitable for industrial production.

The invention relates to a process for producing phosgene by gas-phase reaction of carbon monoxide and chlorine in the presence of a catalyst in a reactor which comprises a plurality of parallel catalyst tubes which are filled with the catalyst and around which at least one fluid heat transfer medium flows, where a feed stream of a mixture of a chlorine input stream and a carbon monoxide input stream is fed into the catalyst tubes and is allowed to react to give a phosgene-comprising product gas mixture, wherein the reaction is carried out at an area load of more than 2.75 kg of phosgene / m2s. The invention also provides a reactor for carrying out the process.

The application belongs to the technical field of bioreactors, and specifically discloses a microalgae bioreactor cooperating with phosgene, which comprises a barrel body, a gas collecting hopper fixedly connected to the bottom of the barrel body, a Venturi nano-bubble generator connected to the lower part of the gas collecting hopper, a liquid delivery pump connected to the Venturi nano-bubble generator, a bubble remover and a light guide structure and a thermometer detachably connected to the barrel body, wherein the light guide structure comprises optical fibers equally spaced and inserted into the barrel body, the optical fibers comprise outer sleeves inserted into the barrel body, and the inner part of the outer sleeves is fixedly connected with light guide cores. In actual use, the Venturi nano-bubble generator can deliver bubbles into the barrel body, the bubbles can drive the microalgae in the barrel body to float, and the light projected by the light guide cores can be refracted, so that the light can uniformly cover the inside of the barrel body, thereby realizing efficient cultivation of the microalgae.

The application provides a method for preparing low-chlorinated impurity isocyanate, and belongs to the technical field of isocyanate. The method is characterized in that two pretreatments are performed before isocyanate refining. On the one hand, naphthenes are used to extract the phosgenation reaction liquid, and insoluble substances such as urea and carbodiimide are removed before phosgene removal, thereby effectively reducing the generation of phosgene adducts. On the other hand, phosgene synthesis tail gas, phosgenation reaction tail gas and isocyanate refining tail gas are collected and mixed as stripping agents according to the target gas composition, and stripping treatment is performed in the phosgene removal stage. By controlling the source and gas composition of the stripping agent, phosgene can be quickly removed, the high-temperature polymerization of isocyanate and the generation of phosgene adducts can be inhibited, the generation of chlorinated isocyanate impurities can be reduced from the root, and the product quality is significantly improved.

The invention provides a method for synthesizing piperacillin with high selectivity. The method comprises the following steps: taking ampicillin as an initial raw material, under anhydrous and alkaline conditions, carrying out selective reaction on side chain amino of ampicillin and triphosgene to generate an isocyanate intermediate, and then coupling the intermediate with N-ethyl-2, 3-diketopiperazine to directly obtain piperacillin. The key point of the invention is that the generation of by-products such as self-coupling urea is effectively inhibited by utilizing the characteristics of moderate reaction activity and high selectivity of the isocyanate intermediate. The method has the advantages of simple route, high selectivity, few byproducts, high yield and the like, and provides a more economical and efficient way for industrial production of piperacillin.

The invention belongs to the technical field of fluorescent probes, and particularly relates to a single-molecule fluorescent probe based on a phenothiazine structure as well as a preparation method and application of the single-molecule fluorescent probe. The preparation method comprises the following steps: firstly introducing an alkyl chain to a nitrogen atom of a raw material to obtain the phenothiazine structure-based single-molecule fluorescent probe, then carrying out regioselective formylation on the raw material to obtain the phenothiazine structure-based single-molecule fluorescent probe, then treating the raw material by adopting aluminum trichloride to realize O-demethylation, and finally carrying out intramolecular cyclization reaction on the raw material and 1H-benzimidazole-2-acetonitrile to obtain the phenothiazine structure-based single-molecule fluorescent probe. The single-molecule fluorescent probe based on the phenothiazine structure prepared by the invention is compatible with orthogonal chemical reaction activity and maintains controllable electron transfer, so that different chemical events are converted into specific optical signals, and selective and mechanism specific fluorescent response to phosgene, copper ions and hypochlorite is realized.

The invention relates to a novel method of producing 4,4'-methylene diphenyl diisocyanate (MDI). A phosgene-free method of producing 4,4'-methylene diphenyl diisocyanate is characterized in that diphenylurea is produced from urea and aniline in an aromatic hydrocarbon medium, and the resulting diphenylurea is reacted with an excess of methanol to produce O-methyl-N-phenyl carbamate; molten O-methyl-N-phenyl carbamate is reacted with anhydrous derivatives of formaldehyde in the presence of acidic catalysts to produce 4,4'-methylene diphenyl dicarbamate; 4,4'-methylene diphenyl dicarbamate in the form of a melt, or of a suspension in an inert carrier liquid, or of a powder is subjected to continuous thermal decomposition in a stream of inert gas, and 4,4'-methylene diphenyl diisocyanate is isolated by fractionation. The invention provides a novel phosgene-free method of synthesizing 4,4'-MDI, which is suitable for industrial-scale implementation.

This utility model relates to the field of chemical equipment technology, specifically a phosgene recovery device. It includes a buffer tank equipped with a spray device and a gas dispersion plate. The top of the buffer tank has a chlorobenzene inlet and a gas outlet, and the bottom has a liquid outlet. A gas inlet is located at the connection point of the gas dispersion plate on the side wall of the buffer tank. The chlorobenzene inlet of the buffer tank is connected to a solvent replenishment tank. The gas outlet and liquid outlet of the buffer tank are respectively connected to the inlet of a falling film absorption tower. The liquid outlet of the falling film absorption tower is connected to the liquid inlet of a receiving vessel, and the gas outlet of the falling film absorption tower is connected to the gas inlet of the receiving vessel. The liquid inlet of the receiving vessel is also connected to a chlorobenzene storage tank. The liquid outlet of the receiving vessel is connected to the solvent replenishment tank, the falling film absorption tower, and the reaction vessel. This utility model can recover and reuse excess phosgene used in production, achieving energy conservation and emission reduction.

The invention belongs to the field of organic synthesis, and discloses a novel pymetrozine intermediate and a preparation method thereof. The structure of the novel pymetrozine intermediate is as shown in a formula I. The preparation method comprises the following steps: (1) reacting propionyl hydrazine, butyrylhydrazine or isobutyrylhydrazine with phosgene or solid phosgene in a solvent to obtain corresponding ethyl oxadiazolone, n-propyl oxadiazolone or isopropyl oxadiazolone, and then removing hydrogen chloride gas to obtain a uniform reaction solution; (2) adding an inorganic base, a phase transfer catalyst and chloroacetone into the reaction liquid obtained in the step (1) to react, and then sequentially desalting, distilling and concentrating to obtain a corresponding acetonyl intermediate; and (3) adding alcohol and hydrazine hydrate into the acetone-based intermediate obtained in the step (2), and sequentially cooling, crystallizing and separating after reaction. Compared with traditional acetamido triazinone, the acetamido triazinone is easier to synthesize, lower in cost, good in thermal stability and capable of remarkably reducing the cost of pymetrozine, and in the formula I, R is ethyl, propyl or isopropyl. Formula I.

The invention relates to a preparation method of 1-chloroethyl cyclohexyl carbonate, and belongs to the technical field of synthesis of drug intermediates. In order to solve the problems of long route and high toxicity in the prior art, the invention provides a preparation method of 1-chloroethyl cyclohexyl carbonate, which comprises the following steps: mixing cyclohexanol and 1-chloroethanol under the action of organic alkali with a nitrogen-containing cyclic structure, and introducing carbon dioxide for reaction to obtain the 1-chloroethyl cyclohexyl carbonate. According to the method, high-toxicity phosgene does not need to be adopted as a raw material, the characteristic of one-pot reaction is achieved, the method further has the advantage of being short in reaction route, conversion loss of intermediate steps and loss of intermediate operation are better reduced, the obtained product has the effect of being high in product yield and quality, the yield reaches 98% or above, and the purity reaches 99% or above.

The application belongs to the technical field of fine chemical synthesis, and particularly relates to a device and method for continuously preparing 1,5-pentamethylene diisocyanate through thermal cracking. 1,5-pentamethylene diurethane and bismuth neodecanoate are mixed, preheated, and then pumped into a reaction kettle containing tetraethylene glycol dimethyl ether to perform a thermal cracking reaction. The obtained reaction liquid is subjected to primary purification, and then secondary purification is continuously performed to obtain 1,5-pentamethylene diisocyanate. The application provides a device and method for continuously preparing 1,5-pentamethylene diisocyanate through thermal cracking. The preparation process adopts a non-phosgene method, is green and environmentally friendly, has small safety hazards, has mild reaction conditions, and is simple in process. The yield of 1,5-pentamethylene diisocyanate reaches more than 80%, and the purity reaches 99%.

The invention relates to a process for the production of isocyanates by the gas phase method, in which a corresponding amine is phosgenated with a trace amount of hydrogen chloride and a stoichiometric excess of phosgenum in the presence or absence of an inert medium, the reaction conditions being chosen such that at least the reaction components amine, hydrogen chloride, isocyanate and phosgenum are gaseous under these conditions, and at least one gas stream comprising amine and one gas stream comprising hydrogen chloride are fed into a pre-reaction zone, in which the pre-reaction takes place, and the pre-reaction stream and at least one gas stream comprising phosgenum are fed into a reaction zone, which makes it possible to extend the operating period of the apparatus more effectively and to increase the operating efficiency.

This invention relates to "an efficient and safe method for synthesizing perfluoropentanone," belonging to the field of organic chemical synthesis. The method for synthesizing perfluoropentanone is characterized by the following steps: under the action of hexafluoropropylene CF2=CF-CF3, fluorophosgene CF2O, and trifluorobromomethane CF3Br, perfluoropentanone (C5F) is generated in the gas phase. 10 O. The raw materials of this invention are inexpensive and readily available; the product separation and purification are simple; it is easy to industrialize; and it produces less industrial waste.

This invention belongs to the field of chloroformate synthesis technology, and particularly relates to a continuous preparation method of chloroformates, comprising the following steps: 1) feeding the reactant raw material alcohol and phosgene together into a synthesis tower via an absorption tower for reaction, generating crude chloroformate and byproduct hydrogen chloride; 2) sending the crude chloroformate formed in step 1) to a degassing tower, returning the phosgene removed from the degassing tower to the synthesis tower for further reaction, and then distilling the chloroformate after phosgene removal into a purification system to obtain the target product chloroformate; 3) sending the byproduct hydrogen chloride formed in step 1) into an absorption tower for washing with the raw material alcohol and then into the tail gas system. The beneficial effects of this invention are: it realizes continuous production of chloroformate products through synthesis and deacidification, improves the synthesis reaction rate, and shortens the deacidification time; simultaneously, through the recovery and recycling of phosgene, it reduces raw material consumption and forms a clean, inherently safe, automated production process.

The invention relates to a green synthesis method of carbendazim. The method comprises the following steps: (1) taking an o-phenylenediamine solution and a cyanamide solution as raw materials, and carrying out condensation cyclization reaction to generate an intermediate 2-aminobenzimidazole; and (2) mixing the 2-aminobenzimidazole obtained in the step (1) with dimethyl carbonate, and carrying out selective methoxycarbonylation reaction in the presence of a basic catalyst to obtain a reaction product containing carbendazim. According to the method, a biodegradable green reagent dimethyl carbonate is adopted to replace highly toxic methyl chloroformate and upstream phosgene which are required to be used in a traditional process, so that the green, safe and environment-friendly process is guaranteed from the source.

The present invention relates to a method for operating a plant for continuous production of an isocyanate by converting a primary amine A with phosgene P whilst maintaining, based on the amino groups of the primary amine, a stoichiometric excess of phosgene in the presence of a solvent L in the liquid phase, using a first, adiabatically operated reaction chamber and a second, isothermally operated reaction chamber. The method is characterised in that a combination of measures, in particular the maintenance of a sufficiently high starting pressure and a sufficiently high starting temperature, is applied in order to bring the plant back into the target state, standard operation, starting from a state of interruption to production.

The invention discloses an oolong tea indoor photosynthetic withering promoting production device in the technical field of tea leaf processing, the oolong tea indoor photosynthetic withering promoting production device comprises a withering tank body, one side of the withering tank body is fixedly connected with a driving motor, the withering tank body is provided with a phosgene dynamic assembly, and the phosgene dynamic assembly is used for dynamically dispersing gas and irradiating light on tea leaves. Through the collaborative design of the dynamic swing type phosgene integrated transverse pipe and the wave-shaped tea leaf bearing net plate, three-dimensional uniform distribution of illumination and carbon dioxide in a tea leaf layer is achieved. The device realizes efficient coordination and dynamic regulation and control of multiple factors by means of an environment sensor and a central controller. The uniformity and the stability of the withering process are remarkably improved, the high consistency of the quality of products in different batches is ensured, and the directional improvement of key flavor substances of oolong tea is realized by strengthening photosynthesis to accumulate a carbon source in the early stage of withering and directionally inducing synthesis of aroma substances in the later stage; and finally, the aroma quality and the overall flavor of the finished tea are stably and remarkably improved.

The present application relates to an isocyanate and its preparation method and application, the method comprising the following steps: (1) carrying out a phosgenation reaction of an amine compound with phosgene in a solvent to obtain a first mixed solution containing isocyanate; (2) removing hydrogen chloride and phosgene from the first mixed solution to obtain a second mixed solution; (3) carrying out a first solvent removal treatment on the second mixed solution to obtain an isocyanate crude product; (4) carrying out a separation treatment on the isocyanate crude product to obtain a polymeric isocyanate product and a third mixed solution; the third mixed solution comprises the solvent and pure isocyanate; and (5) carrying out a second solvent removal treatment on the third mixed solution to obtain a pure isocyanate product. The preparation method of the isocyanate of an embodiment of the present application can make the characteristic index be within a specific range by adjusting the process parameters in multiple steps, thereby improving the yield and color index of the prepared isocyanate product.