LV14069B - Method for direct obtaining of smoke liquids - Google Patents

Abstract

A method for direct obtaining of benzo(a)pyrene-free liquid smoke by oxidative pyrolysis of wood or other lignocellulosic biomass in an externally heated flow reactor in superheated water vapour medium in the presence of a limited amount of air is proposed. The vapours and gases of wood thermal degradation formed as a result of restricted combustion and heating are oxidized, and the characteristic composition of curing smoke components (acids, phenols, carbonyl compounds) is formed, which imparts the typical aroma, flavour and resistance against the lipid oxidation during smoking or treatment with liquid smoke to the treated food-stuffs. To present the formation of carcinogenic polycyclic aromatic hydrocarbon substances, it is recommended to perform the oxidative pyrolysis in the superheated water vapour medium, which improves the heat transfer from the gaseous phase to the solid one and prevents the heating up of the wood carbonaceous residue above 350-450oc, the evaporation of polycyclic aromatic hydrocarbons and getting of carcinogenic substances, e.g. benzo(a)pyrene in the condensates. The presence of the surplus water vapour enhances the condensation of smoke components and produces liquid smoke directly without processing of the primary smoke condensate and dilution. The liquid smoke does not contain benzo(a)pyrene.

Description

The present invention relates to the production of smoke liquids from oxidative pyrolysis smoke condensate of wood or other lignocellulosic biomass prepared by bypassing the separation and treatment of primary products of condensation and not containing benzo (a) pyrene produced by water vapor injection into the oxidative pyrolysis zone.

Analysis of prior art

Although smoking foods has been a known process for hundreds of years, many changes have occurred in smoking technology and smoke extraction techniques in recent decades. The main reasons for the change are four: 1) a desire for more effective control of smoky taste and color, 2) a need to reduce the concentration of carcinogenic components in smoke, 3) requirements to reduce emissions from smokers, and 4) a continued desire to intensify smokefree production.

Significant improvements in smokehouse production, working with the old method and contacting fish or meat products with smoke, fail. For example, homogeneous product characteristics and quality are unsuccessful or difficult to achieve. Not only the flavoring and aromatic phenolic compounds (mainly siryric derivatives), antioxidants (carbonyl compounds and phenols), coloring agents in the smoke (carbonyl compounds, mainly 2-hydroxyacetaldehyde) are diffused directly into and onto the surface of the processed foodstuff through its smoke and mass. and organic acids, but also tar products containing high levels of polycyclic aromatic hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs) include carcinogens such as benzo (a) pyrene (BaP), benzoanthracene (BaA) and many others. The concentration of BaP in smoke condensate tar reaches up to 10,000 gg / kg and above. If BaP is only taken into account as a maximum of 10% of the PAH content of the potential carcinogens, the hazardous contamination of the tar is high. Studies have shown that it cannot be completely eliminated in the smoke generation process [B.H. Κγρκο, Χημηλ κοπηβΗΗΚ, h3A. ilmneBaa npoMbnnjieHHOCTt, MocKBa, 1969, 343c .; O.K). MeiKeHOBa, TexHOJiorna η Μετοπω κοπηεΗΗ »rmmeBbix nponyKTOB, η3Α · Προοπεκτ HayKH, MocKBa, 2006, 292 c.j.

Over the last 30-40 years, liquid smoke, κοπτιπΕΗΕίε> khakocth, has been increasingly introduced to the processing of meat products, fish and other food products (such as cheese). Already in 1892.g. Andrew J. Chase has filed a patent application for an apparatus for the production of liquid smoke products (U.S. Pat. No. 5,112,888). In 1949, U.S. Patent No. 2,670,295 proposed to inject smoked liquid directly into canned fish. During the 50s-90s of the last century, intensive development and patenting of a wide range of liquid smoke extraction techniques is underway, with the main aim of reducing the concentration of PAHs in liquid smoke and improving the composition of flavoring components.

The main advantages of using liquid smoke over traditional smoking are simple application, significantly reduced processing time, homogeneous properties of the finished product, which are easily replicated from batch to batch, and sanitary and ecological purity of the production process. In addition to these, the most important benefit is that before use, unlike smoke, it is possible to determine the concentration of toxic impurities and eliminate them during the preparation of liquids. In addition, smoking liquids have been shown to have antimicrobial activity [E. Sumeu, C. Aristimuno, B. Femandez-Galian, Food Research International 2003, 36, 111-116.]. It should be noted that smoke liquids are prepared from the aqueous fraction of smoke condensate from which the water-insoluble tar is mainly removed by sedimentation and filtration, but other techniques are also used.

PAO carcinogens can be disposed of by extraction. US 4,431,033 and US 4,494,251 recommend the use of dichloromethane for PAO liquid extraction from condensate in an extraction column or already in a condensation process in a scrubber. Unfortunately, most of the flavorings - phenols - disappear. Since the liquid retains carbonyl compounds, the liquids thus purified can be used mainly for coloring sausage skins and products. U.S. Pat. No. 5,637,339 recommends the separation of carcinogenic substances from smoke condensate using activated carbon. As the concentration of phenols in the liquid decreases, the liquid should be evaporated after purification, i. along with harmful impurities, methoxyphenols and dimethoxyphenols are sorbed and lost. An original method for avoiding PAH carcinogenic impurities is suggested by patent application WO 02 / 00040A1, which proposes the use of partially pyrolysed wood extraction with CO2, propane, ammonia and the like. in supercritical conditions. Produces water-soluble smoke liquid components.

U.S. Patent No. 4,359,481 recommends the removal of tar and harmful impurities into the water fraction of smoke condensate, which is a so-called primary product of smoking liquids, and is recommended to be achieved by a three-stage (1-70 ° C; 2nd-95 ° C; 3) - 20 ° C) condensation system because extraction and adsorption in the smoking liquids (primary products) leave too little phenol, which according to Fleischwirtschaft, 1974, 54, 183-187 gives 66% of the taste properties of the smoke. . US 3106473 recommends removing tar by condensing the smoke in a scrubber with warm (up to 49 ° C) recirculation to an acid concentration of 3%, and filtering the resulting condensate through a layer of cellulose fiber pulp to dispose of sapolymerized tar products.

US 4883676 recommends heating a thin (1-2 cm) sawdust layer from below at 250-350 ° C (continuous process) or 600 ° C (batch process) with airflow to reduce carcinogenic impurities in the smoke and increase condensed yield a chip layer and a supply close to the amount of air required for complete combustion (a «1). However, the achieved level of BaP in condensate is not shown.

It is recommended that US 3462282 and US 3634108 use as a heat carrier up to 250-390 ° C in a superheated water vapor mixture with air, mixed with additional oxygen to its air content of 25-30% by volume, to subject the sawdust, kappa or chips layer to oxidative thermolysis. or with 3.5% oxygen by volume. of the volume of superheated steam. During the process, oxidative wood pyrolysis, according to the author, occurs only at the bottom of the layer, but the top of the layer retains the formed tars and thus also the PAHs. Unfortunately, with the exception of the superheated steam temperatures shown, there are no other parameters (air supply, steam consumption, product yield). It is difficult to imagine that, at the indicated temperature, in the presence of oxygen-enriched air, the exothermic reaction of the whole layer to the process of roasting and tar formation does not begin in the wood particle layer. Whereas even deciduous hardwoods have a flash point of only 300-310 ° C in the presence of air oxygen [V. Babrauskas, Ignition of wood, Interflam, London, 2001, 71-88], does not exclude flame ignition of fine dispersion wood in the reported temperature range of 250-390 ° C.

In the aforementioned smoke and smoke condensed extraction techniques, the authors have sought to achieve a smoke composition that provides the desired taste, odor and lipid oxidation resistance of the smoke while minimizing the possible contact of the treated product with tar fraction and PAH. This is best achieved by using smoke liquids made from the smoke condensed water fraction (primary product).

Smoke generation is facilitated by incomplete combustion, which occurs during wood burning. The initial process of smoke generation is the lack of chemical bonding of wood macromolecules and polymers due to thermal exposure. The gases and vapors formed during these pyrolysis reactions in the wood come into contact with atmospheric oxygen in the oxidative zone surrounding the wood particles. Pyrolysis reactions that produce gaseous hydrocarbons from wood components are mainly endothermic reactions and as such do not release any heat energy to sustain the pyrolysis process. In the absence of an external source of heat, exothermic oxidation reactions are required to maintain the thermal degradation of the wood and the release of volatile products.

Oxidation of the excess carbon in the roasting process also contributes to the endothermic pyrolysis reaction. Fragmentation is best achieved when the wood particles have a large surface area (high surface to volume ratio) because it facilitates the oxidation reactions on the wood particles surface and dampens the oxidation reaction in the gas phase due to the easy dissipation of heat and gas diffusion. Sawdust and other small-dispersed lignocellulosic biomass are also suitable fuels for roasting.

In older smokers, but not infrequently nowadays, sawdust grits in a thick layer under natural draft. The temperature in the roasting zone reaches 860-940 ° C and the process maintains itself. However, under these conditions, along with the desired components of smoking smoke, many PAHs and tar products are formed. In addition, it is difficult to regulate the supply of air to the thermal decomposition zone under such conditions, which largely determines the properties of smoke, smoke condensates and smoke liquids, as well as the composition of their carcinogens. Most researchers report that this amount of air is 15-20% of the amount of air needed to completely burn wood or other lignocellulosic biomass.

Recently, research has shown that as a result of the heat treatment of cellulose, aromatic compounds are formed already in the solid phase, which, as the temperature increases, form PAO compounds in the solid carbonation residue, from where they are released at temperatures above 350-400 ° C [M. Hajaligol, B. Waymack, D. Kellog, Fuel, 2001, 80,1799-1807],

As noted above, modern equipment utilizes external heating equipment to maintain the roasting process and a thin layer of fine dispersion wood to prevent the effects of high temperature on charcoal biomass particles. However, high temperatures cannot be prevented unless sophisticated intensive mixing plants or a fluidized bed are used which are not easy to implement in smoke generating plants.

SUMMARY OF THE INVENTION The present invention is directed to a process for the direct production of a B (a) P smoke-free liquid by oxidative thermolysis of wood or other lignocellulosic biomass in a superheated water vapor medium by heating small dispersed wood or other lignocellulosic lignocellulosic air in a wall continuous machine.

Summary of the Invention

The present invention proposes to carry out the process of roasting wood or other suitable lignocellulosic biomass in a well-known external heating rotary hermetic thermoreactor, which provides intense thin-bed mixing of fine dispersion fuel, minimizing direct contact of each particle with the reactor steel wall. Such an apparatus makes it easy to accurately dispense the required amount of air. In addition, the original invention proposes a thermal decomposition and partial oxidation of volatile thermolysis products in a superheated water vapor environment in the presence of a limited amount of oxygen in the air. The superheated steam serves as an environment with improved heat transfer properties (vapor-gas phase and solid biomass particles) and promotes faster removal of the vapor-gas mixture from the high temperature zone in the thermoreactor, since the superheated steam at 350-400 ° C occupies a large volume. In addition, the presence of vapor contributes to the effective condensation of the water-soluble products of the wood or other biomass, which is water soluble, and the concentration of the resulting solutions corresponding to that required for the ready-to-use smoking liquid. Experiments and experience show that the smoke liquids produced by this technique do not contain benzo (a) pyrene, which is a PAO sample for assessing the carcinogenicity of products.

The recommended temperature for the reactor is 300-400 ° C, but the reactor wall temperature should not exceed 350-450 ° C. The air supply to the reactor depends on the feedstock, but should be maintained within the range of 10-25% (preferably 15-20%) of the amount of air needed for complete combustion of the wood or biomass. The vapor reaction medium is introduced into the thermoreactor in a slightly overheated form (105-125 ° C), but in no way plays the role of a heat carrier. It is preferably present in an amount of 0.5 to 2.0 kg / kg of absolute dry wood, preferably 0.7 to 1.4 kg / kg of a.s. wood.

The condensation system consists of 2 stages: 1) a tar trap in which the vapor-gas mixture cools down to 105-115 ° C and in which the trapped tar with the addition of water can be used as a fuel to maintain the process; (2) a condenser-cooler which traps water with the smoke components dissolved therein and which is a ready-to-use smoke liquid with a small amount of insoluble sediment that settles and, after separation, is used as fuel. The solid residue which, depending on the selected process temperature, yields 2535% of absolute dry lignocellulosic biomass, is a high quality fuel with an average combustion heat of 27 to 30 MJ / kg and is easy to use in modern furnaces, including heating of the smoke generator itself and steam. for generating.

Depending on the selected amount of steam fed into the reactor, the water fraction of the distillate yields 1-2 l / kg a.s. biomass. Depending on the fuel used, the selected process temperature and air supply as well as the concentration of the main components of the solutions can vary over a fairly wide range. Quality is controlled by measuring the concentration of acids (as acetic acid), phenol (as 2,6-dimethoxyphenol), carbonyl compounds (as 2-butanone) and benzopyrene.

Examples of realization of the invention

Example 1 A laboratory tubular external heating rotary reactor, 90 mm in diameter and 1000 mm in length, placed in a thermal chamber is heated to 350 ° C in a reactor and the chamber electrical heating is adjusted to maintain this temperature during the process. Turn on the electric motor and adjust the reactor rotation to 5 rpm. Turns on the retort auger, which is set at 0.4 revolutions per minute, which corresponds to a sawdust of alder wood with a particle size of 0.63-2.00 mm for a feed rate of 240-250 g / h. The reactor feed hopper is filled with 1000 g alder sawdust with a relative humidity of 7.5%, the hopper is sealed and the sawdust is fed to the heated retort using a auger. At the same time as the sawdust is fed into the reactor through an auger shaft, which is a pipe, it is supplied with a flow of air maintained at a constant flow rate of 5.6 rpm through the flow regulator. or 20% of the amount of air needed to completely burn the sawdust. At the same time, a saturated steam at a temperature of 100 ° C is supplied to the reactor from a steam generator set at a feed rate of 6.0 to 6.2 g / min.

The sawdust rotating retort, inclined (3 ° to the horizon), in contact with the retort stainless steel wall at 400-450 ° C, thermally decomposes into volatile products - smoke and solid charcoal - within 30 minutes of roasting. The smoke components retort in the superheated water vapor medium, partially oxidize with the oxygen in the inlet air and condense on leaving the retort.

The condensation system consists of a metallic tar trap, where most tar condenses, and a glass condenser-cooler to capture the water fraction of the condensate smoke. Non-condensable gases and part of the tar spray are removed from the system by means of a fan blower. The draft is controlled by a differential pressure gauge reading and the retort maintains a pressure close to ambient pressure (ΔΡ s -0.01 mbar) to prevent uncontrolled inflow of excess air into the retort and smoke loss in the surrounding area.

Recycling 1000g alder sawdust with a relative humidity of 7.5% yields: tar condensate - 212g; water condensate - 1435 g; charcoal (carbonation residue) - 400 g with a moisture content of 24% or 304 g, expressed as an absolute dry mass, but the water in the condensate after filtration through a filter paper filter found: benzo (a) pyrene - 0 pg / kg; acid (as acetic acid) 3.1%; phenols (as circulating-2,6-dimethoxyphenol) - 3 mg / g; carbonyl compounds (as 2-butanone) - 42.1 mg / g. The product obtained meets the requirements of the smoke liquid and contains no benzo (a) pyrene according to the composition and concentrations of the components. Tar condensate, solid carbonation residue and non-condensable gas with tar aerosol can be used as fuel to maintain the process in production conditions.

Example 2 A laboratory tubular external heating rotary reactor, 90 mm in diameter and 1000 mm in length, placed in a thermal chamber, is heated to a temperature of 370 ° C and the chamber electrical heating is adjusted to maintain this temperature during the process. Turn on the electric motor and adjust the reactor rotation to 5 rpm. Turns on the retort auger set at 0.6 rpm, which corresponds to an alpine sawdust with a particle size of 0.63-2.00 mm for a feed rate of 320-350 g / h. The reactor feed hopper is filled with 1024 g of alder sawdust with a relative humidity of 7.5%, the hopper is hermetically sealed and the sawdust is fed to the heated retort using a snail conveyor. At the same time as the sawdust is fed into the reactor through the auger conveyor axis, which is a tube, the air flow is maintained at a constant rate of 5.6 rpm with the help of the flow regulator. or 20% of the amount of air needed to completely burn the sawdust. At the same time, a saturated steam at a temperature of 100 ° C is supplied to the reactor from a steam generator set at a feed rate of 6.0 to 6.2 g / min.

The sawdust rotating retort, inclined (3 ° to the horizon), in contact with the retort stainless steel wall at 400-450 ° C, thermally decomposes into volatile products - smoke and solid charcoal - within 30 minutes of roasting. The smoke components retort in the superheated water vapor medium, partially oxidize with the oxygen in the inlet air and condense on leaving the retort.

The condensation system consists of a metallic tar trap, where most tar condenses, and a glass condenser-cooler to capture the water fraction of the condensate smoke. Non-condensable gases and part of the tar spray are removed from the system by means of a fan blower. The draft is controlled by differential manometer readings and the retort maintains a pressure close to ambient pressure (ΔΡ = -0.01 mb) to prevent uncontrolled excess air inflow into the retort and smoke loss in the surrounding area.

Recycling 1000 grams of alder wood with a relative humidity of 7.5% yields: tar condensate - 162 g; water condensate - 1092 g; Charcoal (carbonation residue) - 420 g, moisture content 28% or 303 g, expressed in absolute dry mass. The water condensate after filtration through a filter paper filter was found: benzopyrene - 0 pg / kg; Acids (as acetic acid) - 3.5%; phenols (as circulating-2,6-dimethoxyphenol) - 3.8 mg / g; carbonyl compounds (as 2-butanone) - 55.9 mg / g. The product obtained meets the requirements of the smoke liquid and contains no benzo (a) pyrene according to the composition and concentrations of the components. Tar condensate, carbonate solid residue and non-condensable gas with tar aerosol can be used as fuel for process maintenance (in production conditions).

Example 3 (for comparison) The laboratory tubular external heating rotary reactor of Examples 1 and 2 is prepared for operation as described in the following examples: Preheat the reactor to 370 ° C, Set alder wood chips to 380 g / h, Air supply to 5, 6 rpm or d = 0.2. The reactor feed hopper is filled with 2000 g alder sawdust with a relative humidity of 7.8% and a particle size of 0.63 to 2.00 mm, and undergoes oxidative pyrolysis as in Examples 1 and 2, except that no water vapor is released into the reactor, and the thermal decomposition of wood, the partial oxidation of volatile products and the solid residue does not occur in a superheated water vapor medium.

Recycling of 2000 g alder chips with a relative humidity of 7.8% yields: tar condensate - 167.2 g; water condensate - 472.1 g; Charcoal (carbonation residue) - 680 g with a moisture content of 13.2% or 591 g, expressed as an absolute dry mass. The following was found in the water condensate after filtration through a filter paper filter: benzopyrene 0.72 pg / kg; Acids (as acetic acid) 10.0%; phenols (as circulating-2,6-dimethoxyphenol) 8.7 mg / g; carbonyl compounds (as 2-butanone) - 119.7 mg / g. The product obtained meets the requirements for primary water condensate in terms of composition and concentration of the components. However, unlike the liquids obtained in Examples 1 and 2, it contains benzopyrene.

Claims (5)

1. A process for the direct extraction of benzo (a) pyrene-containing smoke from wood or other lignocellulosic biomass in an oxidative pyrolysis process in the presence of a limited amount of air oxygen by heating the moving bed of fine dispersion feedstock by external heat transfer through a partition and the process of oxidative pyrolysis is carried out in the steam atmosphere of superheated water. A process according to claim 1, characterized in that the oxidative pyrolysis process is carried out in a continuous operation in an external heating thermal reactor. Method according to claim 1 or 2, characterized in that the ratio of the injected vapor to the finely dispersed lignocellulosic biomass is 0.5 to 2.0, preferably 0.7 to 1.4. Process according to claim 1 or 2, characterized in that the temperature in the thermal reactor is maintained between 300 and 400 ° C, preferably between 350 and 400 ° C. Process according to claim 1 or 2, characterized in that the reactor wall temperature is in the range of 350 to 450 ° C, preferably 400 to 450 ° C.