Method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions through programmed temperature control

Abstract

A method for preparing formic acid by hydrolyzing and oxidizing biomass with iron salt under acidic conditions through program temperature control. The method comprises placing biomass in an inorganic acid aqueous solution, adding an iron salt catalyst, wherein 450-1500 mL of an inorganic acid aqueous solution of 1 wt%-10 wt%, 4.257-31.536 g of an iron salt catalyst, and 0.5-5 Mpa of air or oxygen are added per 100 g of biomass, and program temperature control is performed at 80-170°C to allow the biomass to react continuously at a low temperature for 2-5 hours to fully hydrolyze, and then react continuously at a high temperature for 2-5 hours to achieve hydrolysis and oxidation to formic acid. The method adopts a program temperature control method, firstly promotes the hydrolysis reaction of native biomass under low temperature conditions, and then increases the temperature to accelerate the oxidation process, thereby achieving efficient preparation of formic acid from native biomass. The method has the advantages of high-yield conversion of native biomass, generation of high-concentration formic acid, low catalytic cycle cost, environmental friendliness, and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing formic acid from biomass, and specifically to a method for preparing formic acid from biomass by efficiently hydrolyzing and oxidizing iron salts under acidic conditions through programmed temperature control. Background Art

[0002] Biomass is the most abundant green renewable energy in nature. Among them, non-food biomass is a renewable biomass resource that does not conflict with food, such as crop straw. Non-food biomass is a biomass energy carrier formed by absorbing water and carbon dioxide directly or indirectly through photosynthesis. Its main components are cellulose (~35-50%), hemicellulose (~20-30%) and lignin (~15-30%), collectively known as lignocellulose, which has the potential to be converted into green energy and chemicals. Formic acid is a bulk chemical widely used in leather, rubber, printing and dyeing, pesticides and other fields. Recent studies have shown that: (1) formic acid can be catalytically decomposed to produce hydrogen under mild conditions, and is a potential effective hydrogen storage material; (2) formic acid can also be used to prepare fuel cells, which has the advantages of being non-toxic, non-flammable and easy to store and transport. The main methods for industrial preparation of formic acid are the formamide method and the methyl formate method. The raw materials used (high-pressure carbon monoxide and methanol) are all from non-renewable fossil resources, and carbon monoxide is highly toxic. Therefore, it is of great significance to develop a method for efficiently preparing formic acid using biomass as raw material.

[0003] Currently, there are three main methods for preparing formic acid using biomass. The first is the alkali-hydrogenation method; the second is the hydrothermal oxidation method using vanadium as a catalyst; and the third is the photocatalytic oxidation method. The alkali-hydrogen peroxide method uses H2O2 (hydrogen peroxide) as an oxidant, water as a solvent, and bases such as sodium hydroxide as stable formic acid reagents and catalysts to produce formic acid (Fangming Jin, Enomoto H. Rapid and highly selective conversion of biomass into value-added products in hydrothermal conditions: Chemistry of acid / base-catalysed and oxidation reactions. Energy Environ. Sci. 2011, 4, 382–397. Jun Yun, Guodong Yao, Fangming Jin, et al. Low-Temperature and Highly Efficient Conversion of Saccharides into Formic Acid under Hydrothermal Conditions. AIChE J. 2016, 62, 3657–3663. Can Wang, Xi Chen, Man Qi, et al. Room temperature, near-quantitative conversion of glucose into formic acid. Green Chem. 2019, 21, 6089–6096). The oxidant required for the alkali-hydrogen oxidation method is H2O2, which has strong oxidizing properties. The formic acid generated in the reaction is easily further oxidized, so a large amount of alkali is required to be added to the reaction to improve the selectivity and yield of formic acid. The final product is formate rather than formic acid, which limits the direct application of formic acid in subsequent reactions. This method has limited conversion of cellulose in native biomass, and a large amount of alkali and oxidant H2O2 need to be added in each cycle, which is costly and not conducive to industrial recycling applications.

[0004] The vanadium-catalyzed hydrothermal oxidation method uses vanadium-containing compounds as catalysts and oxygen as an oxidant to produce formic acid at below 200°C. The vanadium-containing compounds mainly include heteropoly acids (HPA-x, x=0-6), VOSO4, and NaVO3. Heteropoly acids are oxygen-containing acids formed by connecting multiple atoms (such as V, Mo, P, etc.) through oxygen bridges according to certain rules. Heteropoly acids have a good catalytic effect on small molecule sugar monomers, but the conversion and decomposition of cellulose in native biomass is very limited. Therefore, additives such as toluenesulfonic acid (TSA) and organic solvents such as hexanol and heptanol are added to these systems to further improve the reaction yield (Albert J, R,BosmannA,et al.Selective oxidation of complex,water-insoluble biomass to formic acid using additives as reactionaccelerators.Energy Environ.Sci.2012,5,7956–7962. R,Taccardi N, A,et al.Selective catalytic conversion of biobased carbohydrates to formicacid using molecular oxygen.Green Chem.2011,13,2759–2763.Albert J,Lüders D, A, et al. Spectroscopic and electrochemical characterization of heteropoly acids for their optimized application in selective biomass oxidation to formic acid. Green Chem. 2014, 16, 226–237. Jenny Reichert, Birgit Brunner, Andreas Jess, et al., Biomass oxidation to formic acid in aqueous media using polyoxometalate catalysts–boosting FA selectivity by in-situ extraction. Energy Environ. Sci. 2015, 8, 2985–2990.). The selectivity of heteropoly acid-catalyzed biomass to formic acid is not high, and a large amount of organic acid additives and organic solvents are added, which invisibly increases the cost of the reaction and is not conducive to the purification of formic acid.

[0005] The VOSO4 catalytic system uses VOSO4 as a catalyst to prepare formic acid from glucose and cellulose at 2.0 MPaO2 and 160°C. This method mainly uses monosaccharides and polysaccharides as raw materials, does not achieve the preparation of formic acid from native biomass, and the yield is generally low (Tang Z, Deng W, Wang Y, et al., Transformation of cellulose and itsderived carbohydrates into formic and lactic acids catalyzed by vanadylcations. ChemSusChem 2014, 7, 1557–1567). In addition, the concentration of the reaction raw materials in this method is very low, and the same raw materials require a larger volume of solvent. Therefore, this method is not conducive to the separation and large-scale circulation of formic acid.

[0006] The NaVO3 / H2SO4 catalytic system is to add NaVO3 to a dilute H2SO4 aqueous solution to produce formic acid and realize the conversion of cellulose in native biomass, such as wheat straw (Wang WH, Niu MG, Hou YC, et al., Catalytic conversion of biomass-derived carbohydrates to formic acid using molecular oxygen. Green Chem. 2014, 16, 2614–2618. Niu MG, Hou YC, Ren SH, Wu W Z, et al., Conversion of wheat straw into formic acid in NaVO3-H2SO4 aqueous solution with molecular oxygen. Green Chem. 2015, 17, 453–459.). This method uses ether extraction to separate formic acid, but the separation cost is increased, which is not conducive to widespread industrial application. In 2018, the inventor team added a trace amount of DMSO to the vanadium-catalyzed hydrothermal oxidation system, which significantly promoted the conversion of biomass to formic acid. The obtained formic acid aqueous solution can be directly used to produce hydrogen. The hydrogen produced by this catalytic system can be directly supplied to fuel cells and converted into stable electricity. This technology demonstrates an application example of biomass hydrogen production (Zhang P, Guo YJ, Beller M, LiY, et al., Streamlined Hydrogen Production from Biomass. Nat. Catal. 2018, 1, 332–338.). In order to avoid the consumption of DMSO, in subsequent work, the inventors realized the catalytic cycle of the additive DMSO, further reducing the production cost. Although this method can efficiently prepare formic acid, the vanadium catalyst used is highly toxic, environmentally unfriendly, and requires the introduction of expensive DMSO as an additive, which to a certain extent limits its large-scale production application (Yan-Jun Guo, YuLan, Yang Li, et al., Practical DMSO-promoted selective hydrolysis-oxidation of lignocellulosic biomass to formic acid attributed to hydrogen bonds. Green Chem. 2021, 23, 7041–7052).

[0007] In 2018, Wu Weize's team selected two iron salts, FeCl3 and Fe2(SO4)3, as catalysts, and used 2.0wt% H2SO4 solution as solvent. At 160°C, the yields of formic acid produced using cellulose as raw material were 48.3% and 47.8%, respectively. This method does not achieve the preparation of formic acid from native biomass, and the reaction concentration is very low. The mass ratio of the reaction raw material feed to the aqueous solution is 1:60, resulting in a formic acid mass fraction of only about 1%; in addition, the product formic acid in the cycle experiment of this method needs to be extracted with butanone to regenerate the catalytic system (FeCl3+H2SO4), resulting in a significant increase in the product separation cost (Hou YC, Lin ZQ, Niu M G, Ren S H, Wu W Z. Conversion of Cellulose into Formic Acid by Iron(III)-Catalyzed Oxidation with O2 in Acidic Aqueous Solutions. ACS Omega 2018, 3, 14910-14917). The practical application of this method is greatly limited.

[0008] In 2023, the inventor team used metal iron salts as catalysts to achieve the preparation of formic acid from biomass under visible light irradiation. Although this method can achieve the conversion under normal temperature and low pressure conditions, the formic acid yield is low in the reaction with native biomass as raw materials (Zhang, WM; Feng, KW; Hu, RG; Guo, YJ; Li Y. Visible-Light-Induced IronRedox-Catalyzed Selective Transformation of Biomass into Formic Acid. Chem 2023, 9, 430–442), and has no practical industrial application prospects; in addition, photocatalytic technology is greatly affected by the environment, and the reaction will be terminated when there is no light at night or insufficient light indoors.

[0009] In summary, the existing biomass formic acid preparation technologies all have problems such as being unable to simultaneously meet the requirements of high-yield conversion of native biomass, generation of high-concentration formic acid, low catalytic cycle cost, and environmental friendliness. Summary of the invention

[0010] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing formic acid by hydrolyzing and oxidizing biomass with iron salts under acidic conditions through programmed temperature control. The programmed temperature control method is firstly used to avoid the production of by-products in the hydrolysis process under relatively low temperature conditions, promote the efficient hydrolysis of native biomass into intermediate systems such as monosaccharides, and then increase the temperature to achieve efficient oxidation, thereby realizing the efficient preparation of formic acid from biomass. The method has the advantages of high-yield conversion of native biomass, generation of high-concentration formic acid of 10-20wt%, low catalytic cycle cost (10 cycles, stable formic acid yield), and environmental friendliness.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0013] The biomass is placed in an inorganic acid aqueous solution and an iron salt catalyst is added, wherein 450-1500 mL of an inorganic acid aqueous solution with a concentration of 1 wt%-10 wt%, 4.257-31.536 g of an iron salt catalyst, and 0.5-5 MPa of air or oxygen are added per 100 g of biomass. The temperature is programmed to be controlled at 80-170°C so that the biomass is reacted at a low temperature for 2-5 hours to be fully hydrolyzed, and then the reaction is continued at a high temperature for 2-5 hours to achieve hydrolysis and oxidation to formic acid.

[0014] After the reaction was completed, the formic acid yield was determined to be 25%–96% (calculated based on the C atoms in the feed amount).

[0015] The biomass is glucose, xylose, arabinose, fructose, cellulose and a series of original biomass such as wheat straw, corn straw, rice straw, reed stalk or domestic waste such as waste newspaper and waste cardboard.

[0016] The iron salt catalyst is FeCl3, Fe2(SO4)3, Fe(NO3)3·9H2O, Fe(acac)3 or Fe(OTf)3.

[0017] The inorganic acid is H2SO4, HCl, HNO3 or H3PO4.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention adopts programmed temperature control to fully hydrolyze the biomass at a relatively low temperature and achieve hydrolysis and oxidation to formic acid at a relatively high temperature; the programmed temperature control strategy adopted in this method makes the yield of formic acid preparation from biomass significantly higher than that of other methods.

[0020] 2. The present invention directly uses primary biomass as raw material for large-scale (100 g) conversion without using any additives, avoiding the introduction of equivalent alkali, p-toluenesulfonic acid (TSA), and additives such as n-hexanol and n-heptanol, making the method low-cost.

[0021] 3. Although the alkali-hydrogenation method achieves the conversion of glucose to formic acid with a yield of 91.3%, the method adds a large amount of strong base and uses hydrogen peroxide as an oxidant, which is expensive and has certain safety risks when used on a large scale. The present invention uses air or oxygen as the terminal oxidant, which is low in cost and has a small safety risk.

[0022] 4. The mass fraction of formic acid obtained by the present invention is 10%-20% higher, thereby reducing the cost of formic acid separation and improving the practical applicability of the catalytic method.

[0023] 5. Although the hydrothermal oxidation method can achieve the conversion of biomass to formic acid well, the vanadium oxides used are generally toxic and cause serious environmental pollution. The present invention uses cheap and readily available metal iron salts as catalysts. The iron catalyst is safe, non-toxic, mild in nature, and the entire catalytic reaction process does not produce harmful by-products. After the reaction is completed, there is no need to worry about complex and rigorous waste treatment processes. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the embodiments.

[0025] Example 1, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0026] Corn stalks were placed in a sulfuric acid aqueous solution, and an iron salt catalyst FeCl3 was added, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 4.2573 g of FeCl3, and 0.5 MPa of oxygen were added per 100 g of corn stalks. The temperature was controlled to react at 80°C for 2 hours, then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0027] After the reaction was completed, the formic acid yield was determined to be 28% (calculated based on the C atoms in the feed amount).

[0028] Example 2, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0029] Glucose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst FeCl3 was added, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 8.515 g of FeCl3, and 2 MPa of air were added for every 100 g of glucose. The temperature was programmed to react at 120°C for 3 hours, then the temperature was raised to 170°C and the reaction was continued for 3 hours.

[0030] After the reaction was completed, the formic acid yield was determined to be 96% (calculated based on the C atoms in the feed amount).

[0031] Example 3, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0032] Xylose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst FeCl3 was added, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 12.722 g of FeCl3, and 5 MPa of air were added per 100 g of xylose. The temperature was programmed to react at 140°C for 5 hours and then the temperature was raised to 170°C for further reaction for 5 hours.

[0033] After the reaction was completed, the formic acid yield was determined to be 44% (calculated based on the C atoms in the feed amount).

[0034] Example 4, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0035] Cellulose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 5.256 g of Fe2(SO4)3, and 0.5 MPa of air were added per 100 g of cellulose, and the temperature was programmed to react at 80°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0036] After the reaction was completed, the formic acid yield was determined to be 80% (calculated based on the C atoms in the feed amount).

[0037] Example 5, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0038] Arabinose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 450 mL of 1 wt% H2SO4 aqueous solution, 15.768 g Fe2(SO4)3, and 2 MPa of oxygen were added for every 100 g of arabinose. The temperature was programmed to react at 120°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0039] After the reaction was completed, the formic acid yield was determined to be 90% (calculated based on the C atoms in the feed amount).

[0040] Example 6, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0041] Xylose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 31.536 g of Fe2(SO4)3, and 5 MPa of air were added for every 100 g of xylose. The temperature was programmed to react at 80°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0042] After the reaction was completed, the formic acid yield was determined to be 88% (calculated based on the C atoms in the feed amount).

[0043] Example 7, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0044] Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe(NO3)3·9H2O, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 5.308 g of Fe(NO3)3·9H2O and 0.5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 80°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0045] After the reaction was completed, the formic acid yield was determined to be 30% (calculated based on the C atoms in the feed amount).

[0046] Example 8, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0047] Place rice straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe(NO3)3·9H2O, wherein 450 mL of a 5 wt% H2SO4 aqueous solution, 13.27 g of Fe(NO3)3·9H2O and 2 MPa of air are added per 100 g of rice straw. The temperature is programmed to react at 80°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0048] After the reaction was completed, the formic acid yield was determined to be 35% (calculated based on the C atoms in the feed amount).

[0049] Example 9, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0050] Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe(NO3)3·9H2O, wherein 450 mL of a 10 wt% H2SO4 aqueous solution, 30 g of Fe(NO3)3·9H2O and 5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 140°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0051] After the reaction was completed, the formic acid yield was determined to be 68% (calculated based on the C atoms in the feed amount).

[0052] Example 10, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0053] Place wheat straw in a hydrochloric acid aqueous solution and add an iron salt catalyst Fe(NO3)3·9H2O, wherein 450 mL of a 1 wt% HCl aqueous solution, 5.308 g of Fe(NO3)3·9H2O and 0.5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 80°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0054] After the reaction was completed, the formic acid yield was determined to be 58% (calculated based on the C atoms in the feed amount).

[0055] Example 11, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0056] Place wheat straw in a hydrochloric acid aqueous solution and add an iron salt catalyst Fe2(SO4)3, wherein 450 mL of a 5 wt% HCl aqueous solution, 10.512 g of Fe2(SO4)3 and 2 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0057] After the reaction was completed, the formic acid yield was determined to be 40% (calculated based on the C atoms in the feed amount).

[0058] Example 12, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by programmed temperature control, comprising the following steps:

[0059] Place wheat straw in a hydrochloric acid aqueous solution and add an iron salt catalyst FeCl3, wherein 450 mL of a 10 wt% HCl aqueous solution, 12.722 g of FeCl3, and 5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 140°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0060] After the reaction was completed, the formic acid yield was determined to be 40% (calculated based on the C atoms in the feed amount).

[0061] Example 13, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by programmed temperature control, comprising the following steps:

[0062] Place wheat straw in a hydrochloric acid aqueous solution and add an iron salt catalyst Fe2(SO4)3, wherein 800 mL of a 1 wt% HCl aqueous solution, 5.256 g of Fe2(SO4)3 and 0.5 MPa of air are added for every 100 g of wheat straw. The temperature is programmed to react at 80°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0063] After the reaction was completed, the formic acid yield was determined to be 30% (calculated based on the C atoms in the feed amount).

[0064] Example 14, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0065] Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe2(SO4)3, wherein 800 mL of a 5 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3 and 2 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C for a further 2 hours.

[0066] After the reaction was completed, the formic acid yield was determined to be 38% (calculated based on the C atoms in the feed amount).

[0067] Example 15, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by programmed temperature control, comprising the following steps:

[0068] Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe2(SO4), wherein 800 mL of a 10 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3 and 5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 140°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0069] After the reaction was completed, the formic acid yield was determined to be 40% (calculated based on the C atoms in the feed amount).

[0070] Example 16, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0071] Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst FeCl3, wherein 800 mL of a 1 wt% H2SO4 aqueous solution, 4.257 g FeCl3, and 0.5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 140°C for 2 hours and then raised to 170°C for a further 2 hours.

[0072] After the reaction was completed, the formic acid yield was determined to be 32% (calculated based on the C atoms in the feed amount).

[0073] Example 17, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0074] Place wheat straw in a sulfuric acid aqueous solution, add an iron salt catalyst FeCl3, wherein 800 mL of a 5 wt% H2SO4 aqueous solution, 6.386 g FeCl3, and 2.5 MPa of air are added per 100 g of wheat straw, program the temperature to 120°C for reaction for 2 hours and then raise the temperature to 170°C for further reaction for 2 hours.

[0075] After the reaction, the formic acid yield was determined to be 45% (calculated based on the C atoms in the feed amount).

[0076] Example 18, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by programmed temperature control, comprising the following steps:

[0077] Place wheat straw in a sulfuric acid aqueous solution and add an iron salt catalyst FeCl3, wherein 800 mL of a 10 wt% H2SO4 aqueous solution, 12.772 g of FeCl3, and 5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C for a further 2 hours.

[0078] After the reaction, the formic acid yield was determined to be 52% (calculated based on the C atoms in the feed amount).

[0079] Example 19, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0080] Cellulose stalks were placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe(NO3)3·9H2O was added, wherein 800 mL of a 1 wt% H2SO4 aqueous solution, 5.308 g of Fe(NO3)3·9H2O, and 0.5 MPa of air were added per 100 g of cellulose. The temperature was programmed to react at 80°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0081] After the reaction was completed, the formic acid yield was determined to be 28% (calculated based on the C atoms in the feed amount).

[0082] Example 20, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0083] Place reed stalks in an aqueous sulfuric acid solution, add an iron salt catalyst Fe(NO3)3·9H2O, wherein 800 mL of a 5 wt% H2SO4 aqueous solution, 15.925 g of Fe(NO3)3·9H2O, and 2.5 MPa of air are added per 100 g of reed stalks, program the temperature to 120°C for reaction for 2 hours and then increase the temperature to 170°C for continued reaction for 2 hours.

[0084] After the reaction was completed, the formic acid yield was determined to be 32% (calculated based on the C atoms in the feed amount).

[0085] Example 21, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0086] Place waste newspapers in a sulfuric acid aqueous solution and add an iron salt catalyst Fe(NO3)3·9H2O, wherein 800 mL of a 10 wt% H2SO4 aqueous solution, 30 g of Fe(NO3)3·9H2O and 5 MPa of air are added per 100 g of waste newspapers. The temperature is programmed to react at 140°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0087] After the reaction was completed, the formic acid yield was determined to be 45% (calculated based on the C atoms in the feed amount).

[0088] Example 22, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0089] Place waste cardboard in a sulfuric acid aqueous solution and add an iron salt catalyst Fe2(SO4)3, wherein 1500 mL of a 1wt% H2SO4 aqueous solution, 5.256 g of Fe2(SO4)3 and 0.5 MPa of air are added per 100 g of waste cardboard, and the temperature is programmed to react at 80°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0090] After the reaction was completed, the formic acid yield was determined to be 32% (calculated based on the C atoms in the feed amount).

[0091] Example 23, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0092] Fructose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 1500 mL of a 5 wt% H2SO4 aqueous solution, 5.256 g of Fe2(SO4)3, and 2.5 MPa of air were added for every 100 g of fructose. The temperature was programmed to react at 120°C for 2 hours and then the temperature was raised to 170°C for a further 2 hours.

[0093] After the reaction was completed, the formic acid yield was determined to be 40% (calculated based on the C atoms in the feed amount).

[0094] Example 24, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0095] Corn stalks were placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added. For every 100g of corn stalks, 1500mL of 10wt% H2SO4 aqueous solution, 5.256g of Fe2(SO4)3, and 5Mpa of air were added. The temperature was controlled at 140°C for 2 hours, and then the temperature was raised to 170°C for a further 2 hours.

[0096] After the reaction was completed, the formic acid yield was determined to be 42% (calculated based on the C atoms in the feed amount).

[0097] Example 25, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0098] Corn straw was placed in an aqueous sulfuric acid solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 1500 mL of a 1 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3, and 0.5 MPa of air were added for every 100 g of corn straw. The temperature was programmed to react at 80°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0099] After the reaction was completed, the formic acid yield was determined to be 34% (calculated based on the C atoms in the feed amount).

[0100] Example 26, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0101] Cellulose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 1500 mL of 8 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3, and 2.5 MPa of air were added per 100 g of cellulose, and the temperature was programmed to react at 120°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0102] After the reaction was completed, the formic acid yield was determined to be 78% (calculated based on the C atoms in the feed amount).

[0103] Example 27, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0104] Cellulose was placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 was added, wherein 1500 mL of a 10 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3, and 5 MPa of air were added per 100 g of cellulose, and the temperature was programmed to react at 120°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0105] After the reaction was completed, the formic acid yield was determined to be 82% (calculated based on the C atoms in the feed amount).

[0106] Example 28, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0107] Cellulose is placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe(acac)3 is added, wherein 1500 mL of a 1 wt% H2SO4 aqueous solution, 9.276 g of Fe(acac)3, and 2.5 MPa of oxygen are added per 100 g of cellulose, and the temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0108] After the reaction was completed, the formic acid yield was determined to be 77% (calculated based on the C atoms in the feed amount).

[0109] Example 29, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0110] Cellulose was placed in a phosphoric acid aqueous solution, and an iron salt catalyst Fe(acac)3 was added, wherein 1500 mL of a 1 wt% H3PO4 aqueous solution, 9.276 g of Fe(acac)3, and 2.5 MPa of oxygen were added per 100 g of cellulose, and the temperature was programmed to react at 120°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0111] After the reaction was completed, the formic acid yield was determined to be 78% (calculated based on the C atoms in the feed amount).

[0112] Example 30, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, comprising the following steps:

[0113] Cellulose is placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe(acac)3 is added, wherein 900 mL of a 2 wt% H2SO4 aqueous solution, 8.12 g of Fe(acac)3, and 2.5 MPa of oxygen are added per 100 g of cellulose, and the temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

[0114] After the reaction was completed, the formic acid yield was determined to be 65% (calculated based on the C atoms in the feed amount).

[0115] Example 31, a method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by programmed temperature control, comprising the following steps:

[0116] Wheat straw was placed in a phosphoric acid aqueous solution, and an iron salt catalyst Fe(acac)3 was added, wherein 900 mL of a 2 wt% H3PO4 aqueous solution, 8.12 g of Fe(acac)3, and 2.5 MPa of oxygen were added per 100 g of wheat straw. The temperature was programmed to react at 120°C for 2 hours and then the temperature was raised to 170°C and the reaction was continued for 2 hours.

[0117] After the reaction was completed, the formic acid yield was determined to be 60% (calculated based on the C atoms in the feed amount).

Claims

1. A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, characterized in that: The following steps are involved: The biomass is placed in an inorganic acid aqueous solution and an iron salt catalyst is added, wherein 450-1500 mL of an inorganic acid aqueous solution of 1 wt%-10 wt%, 4.257-31.536 g of an iron salt catalyst, and 0.5-5 MPa of air or oxygen are added per 100 g of biomass, and the temperature is programmed to be controlled at 80-170°C so that the biomass is reacted at a low temperature for 2-5 hours to be fully hydrolyzed, and then the reaction is continued at a high temperature for 2-5 hours to achieve hydrolysis and oxidation to formic acid.

2. The method according to claim 1, characterized in that: The biomass is primary biomass of wheat straw, corn straw, rice straw, reed stalk, or domestic waste such as waste newspaper and waste cardboard, and derivatives thereof such as glucose, xylose, arabinose, cellulose or fructose.

3. The method according to claim 1, characterized in that: The iron salt catalyst is FeCl3, Fe2(SO4)3, Fe(NO3)3·9H2O, Fe(acac)3 or Fe(OTf)3.

4. The method according to claim 1, characterized in that: The inorganic acid is H2SO4, HCl, HNO3 or H3PO4.

5. A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, characterized in that: The following steps are involved: Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe(NO3)3·9H2O, wherein 450 mL of a 1 wt% H2SO4 aqueous solution, 5.308 g of Fe(NO3)3·9H2O and 0.5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 80°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

6. A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, characterized in that: The following steps are involved: Place wheat straw in a hydrochloric acid aqueous solution and add an iron salt catalyst Fe2(SO4)3, wherein 450 mL of a 5 wt% HCl aqueous solution, 10.512 g of Fe2(SO4)3 and 2 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

7. A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, characterized in that: The following steps are involved: Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst Fe2(SO4), wherein 800 mL of a 10 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3 and 5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 140°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.

8. A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, characterized in that: The following steps are involved: Place wheat straw in an aqueous sulfuric acid solution and add an iron salt catalyst FeCl3, wherein 800 mL of a 10 wt% H2SO4 aqueous solution, 12.772 g of FeCl3, and 5 MPa of air are added per 100 g of wheat straw. The temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C for a further 2 hours.

9. A method for preparing formic acid by efficiently hydrolyzing and oxidizing biomass with iron salts under acidic conditions by temperature-programmed control, characterized in that: The following steps are involved: Cellulose is placed in a sulfuric acid aqueous solution, and an iron salt catalyst Fe2(SO4)3 is added, wherein 1500 mL of 8 wt% H2SO4 aqueous solution, 15.768 g of Fe2(SO4)3, and 2.5 MPa of air are added per 100 g of cellulose. The temperature is programmed to react at 120°C for 2 hours and then the temperature is raised to 170°C and the reaction is continued for 2 hours.